Characteristics of Food Industry Wastewaters and Their Potential Application in Biotechnological Production

Abstract

The food industry consumes large amounts of water across various processes, and generates wastewater characterized by parameters like biochemical oxygen demand, chemical oxygen demand, pH, suspended solids, and nutrients. To meet environmental standards and enable reuse or valorization, treatment methods such as physicochemical, biological, and membrane-based processes are applied. This review focuses on the valorization of food industry wastewater in the biotechnological production of high-value products, with an emphasis on starch-rich wastewater, wineries and confectionery industry wastewater, and with a focus on new technologies for reduces environmental burden but also supports circular economy principles. Starch-rich wastewaters, particularly those generated by the potato processing industry, offer considerable potential for biotechnological valorization due to their high content of soluble starch, proteins, organic acids, minerals, and lipids. These effluents can be efficiently converted by various fungi (e.g., Aspergillus, Trichoderma) and yeasts (e.g., Rhodotorula, Candida) into value-added products such as lipids for biodiesel, organic acids, microbial proteins, carotenoids, and biofungicides. Similarly, winery wastewaters, characterized by elevated concentrations of sugars and polyphenols, have been successfully utilized as medium for microbial cultivation and product synthesis. Microorganisms belonging to the genera Aspergillus, Trichoderma, Chlorella, Klebsiella, and Xanthomonas have demonstrated the ability to transform these effluents into biofuels, microbial biomass, biopolymers, and proteins, contributing to sustainable bioprocess development. Additionally, wastewater from the confectionery industry, rich in sugars, proteins, and lipids, serves as a favorable fermentation medium for the production of xanthan gum, bioethanol, biopesticides, and bioplastics (e.g., PHA and PHB). Microorganisms of the genera Xanthomonas, Bacillus, Zymomonas, and Cupriavidus are commonly employed in these processes. Although there are still certain regulatory issues, research gaps, and the need for more detailed economic analysis and kinetics of such production, we can conclude that this type of biotechnological production on waste streams has great potential, contributing to environmental sustainability and advancing the principles of the circular economy.

1. Introduction

Water containing dissolved and suspended substances that is discharged from various industrial processes, such as manufacturing, cleaning, and other commercial operation, is referred to as industrial wastewater [1]. Industrial wastewater includes sanitary waste, process effluents from manufacturing areas, wash water from equipment cleaning, and relatively clean water from heating and cooling operations. The nature of the contaminants in the industrial wastewater strongly depends on the type of industry [1,2,3,4]. The various contaminants in industrial can be chemicals, heavy metals, pesticides, pharmaceuticals, oils, silt and other industrial by-products [1,3,5,6].

The food processing industry is one of the largest consumers of water for different sections, such as production, cleaning, sanitizing, cooling, material transport and others, which significantly depend on type and process parameters, the sizes of industrial food units, rinsing and cleaning phases, and formation of both solid and liquid wastes [7,8,9]. Many of the constituents of food industry wastewaters may be biodegradable due to a high content of organic substance, and also may be nontoxic. But that may result in high concentrations of biochemical oxygen demand (BOD), chemical oxygen demand (COD), and suspended solids (SS) [2,10,11]. Other typical characteristic important for the evaluation of food industrial wastewater are pH, oil and grease content, total nitrogen and total phosphorus, chlorides, and minerals (salts) (Figure 1) [2,10,11,12].

COD refers to the total amount of oxygen needed by strong chemical oxidants to decompose both organic and inorganic substances in wastewater. It measures the amount of oxygen required to chemically oxidize the organic matter present in a water sample [13]. Along with COD, another commonly used indicator of oxygen demand is BOD. BOD quantifies the amount of dissolved oxygen needed by aerobic microorganisms to break down organic matter in wastewater. It is a traditional and widely used method for assessing the concentration of organic pollutants [13,14]. The test is based on the principle that, given sufficient oxygen, aerobic microorganisms will continue decomposing organic material until all biodegradable waste is consumed. However, COD analysis is an increasingly popular alternative to BOD, because it is faster method and can test wastewater that is too toxic for BOD. While the BOD test requires five days to complete, modern COD testing methods offer a faster alternative, allowing for real-time analysis. This enables wastewater operators to monitor conditions and make adjustments during processing. Unlike COD, BOD testing only measures the oxygen demand from biodegradable organic compounds, resulting in lower concentration values. COD analysis, on the other hand, serves as an indirect measure of organic pollutants in water and is a critical parameter in water quality assessment. It plays a key role in minimizing environmental and human health risks [13,14,15].

Suspended solids (SS) are visible particles present in sewage that remain dispersed in the water and do not readily settle over time. They are typically measured in milligrams per liter (mg/L) or parts per million (ppm) and represent the concentration of solid matter suspended in either influent or effluent wastewater [14]. Other significant properties of food wastewater are total solids (mg/L), volatile solids (mg/L), total dissolved solids (mg/L), total suspended solids (mg/L) and volatile suspended solids (mg/L), and certainly pH value, ranging from 3.5 to 6.5 [2,16].

The concentration and the type of contaminants present in food industry wastewater are depending on the origin of the wastewater.

Table 1. Characteristics of different food industry wastewaters.

Food Industry Wastewaters	Starch	Winery	Confectionery	Fruit and Vegetable	Diary	Meat
Parameters
Main organic load	Starch, glucose, dextrins	Sugars (glucose, fructose), ethanol, polyphenols	Sugars (sucrose, glucose), fats, proteins	Fibers, phenolic compounds, acids, minerals	Proteins, lactose, lipids, detergents	Proteins, fats, minerals
COD (g/L)	8.1–37	0.32–12.7	2.5–20.02	0.8–7.7	0.43–95	1.6–15
BOD5 (g/L)	0.005–5.4	0.125–130	3.132–8	0.5–6.1	0.35–48	0.6–8
Total solids (g/L)	0.26–42	1.602–79.635	11.1–44.6	0.2–0.4	0.2–5.8	0.25–6.4
Suspended solids (g/L)	0.007–6.4	0.06–30.300	0.47–1.31	-	0.8–4.4	0.22–9.3
Total nitrogen (g/L)	0.02–0.87	0–0.415	0.171–0.225	0.8–1.2	0.01–1.12	0.6–2.7
Total phosphorus (g/L)	0.014–0.160	0.003–0.188	0.01–0.028	0.045–0.5	0.05–0.55	0.15–0.32
Volatile solids (g/L)	0.45–6.685	0.13–54.952	0.0273–0.0301	-	-	-
Starch (g/L)	19.47–31.2	-	-	-	-	-
Total sugars (g/L)	-	8.1–13.2	7.4	-	-	-
pH (1)	4–10	3.93–12.9	3.9–9.5	4.6–7.9	6.8–9.4	6.5–9
References	[9,18,19,20,21,22,23]	[24,25,26,27,28,29,30]	[31,32,33,34]	[35,36,37,38,39]	[2,9,10,40,41]	[9,10,40,42]

presents the typical characteristics of untreated wastewater from various food processing and proximate concentration of usual contaminants. The characteristics of wastewater typically indicate the nature of the waste and its potential environmental impact [17]. Thus, the wide variability in wastewater parameters shown in Table 1 highlight the need for tailored wastewater treatment strategies.

The treatment of industrial wastewater has traditionally relied on physico-chemical processes such as coagulation–flocculation, adsorption, advanced oxidation, and membrane filtration. While effective in removing pollutants, these methods often demand high energy inputs, generate secondary waste, and are not sustainable in the long term [1]. Moreover, the treatment of wastewater from the food industry which is rich in organic matter, carbohydrates, proteins, and lipids, poses a unique challenge due to its variability and high BOD and COD [43].

In contrast to conventional treatments, biological wastewater treatment utilizing microorganisms offers an eco-friendly and cost-effective alternative. These systems harness the metabolic activity of bacteria, fungi, algae, and yeast to degrade organic contaminants while simultaneously allowing for the recovery or biosynthesis of value-added compounds. The implementation of such bioprocesses has gained increasing attention not only for their environmental benefits but also for their potential in circular bioeconomy frameworks [44,45].

Furthermore, advances in metabolic engineering and synthetic biology are enhancing the capability of microbial strains to tolerate harsh wastewater conditions and improve product yields [46]. The strategic use of microbial consortia and immobilized cell systems also improves stability and resistance to fluctuations in effluent composition, making these systems highly adaptable to real-world industrial scenarios.

So, the use of food industry wastewater as a feedstock in microbial biotechnology offers a promising path toward sustainable waste management and the production of economically significant bioproducts. Continued research into strain selection, process optimization, and system integration is essential to fully exploit this potential and move toward a bio-based circular economy.

Therefore, the relevance of the concept of sustainability and circular economy prompted us to investigate the possibility of valorization of wastewater in biotechnological production. Accordingly, the first goal of this review is a detailed analysis of the composition of selected wastewater from the food industry in order to determine the possibility of their application in biotechnological production. Confirmation that their composition largely matches the composition of the medium for growth, multiplication of microorganisms, but also the production of high-value products, led us to the second goal. The second goal of this paper was the analysis of the available scientific literature dealing with the possibilities of valorization of selected wastewater in the biotechnological production of high-value products, as well as the analysis of the possibilities of such biotechnological production as well as an analysis of potential limitations. These insights are crucial for selecting optimal media for microbial treatments and valorization strategies, supporting both environmental protection and circular bioeconomy development.

2. Food Industry Wastewaters

2.1. Starch Industry Wastewater

Starch is significant raw material, frequently used in different industrial sectors, such as food, chemistry, textile, papermaking, pharmaceutical, animal feed, personal and medicine care, and even petroleum industry [45,47,48]. However, the production of starch generates large volume of highly concentrated organic wastewater. Starch wastewater primarily contains dissolved starch, along with small amounts of protein, organic acids, dust, minerals, and small quantities of oil and fat. It is prone to spoilage and fermentation, which can turn the water black and smelly. It depletes dissolved oxygen, when discharged into rivers, encouraging the excessive growth of algae and aquatic plants. When discharged in large volumes, this wastewater can cause significant oxygen depletion, promote anaerobic decomposition, and produce strong odors in the water, leading to hypoxia and the subsequent death of aquatic organisms. Ultimately, this represents a significant environmental hazard with potential impacts on human health [45,47]. Therefore, it is essential to treat starch wastewater to meet regulatory demands for wastewater treatment before discharge. Moreover, the high organic content in the wastewater highlights its considerable potential as a resource for recovery and reuse. The production of starch in the EU implies main feedstocks such as corn, wheat and potatoes. However, a wide range of feedstocks is applied worldwide, like cassava, rice, rye, barley, oat, milo, sweet potatoes and sago palms. The type of applied feedstock during starch production determines different kind of wastewater at different steps of the process, such as washing of the feedstocks (e.g., potatoes), steeping of the feedstocks (corn), starch refinement (e.g., corn gluten water), starch saccharification (e.g., glucose wastewater), and modification of the starch [48,49].

During the washing phase of the feedstock, especially root feedstocks like potato or cassava, a large amount of water is generated. A substantial portion of the water used for starch extraction also became a wastewater. Another source of wastewater is the cleaning and rinsing of pipelines and equipment throughout the production process [50,51]. The desired purity of the final starch product significantly determines the volume of wastewater, as well as the type of used feedstock. Root crops such as potatoes and cassava contain more dirt and organic material compared to grains like wheat and corn; thus, more intensive washing and more water is used for root feedstocks. Moreover, their higher moisture content also contributes to greater wastewater output. Also, the design of production line has important effects on the quality and quantity of wastewater [49,52].

For every ton of produced starch, approximately 10 to 20 m³ of wastewater is generated. This wastewater typically contains high concentrations of pollutants and COD ranges from 5000 to 50,000 mg/L, BOD ranges from 3000 to 30,000 mg/L, and SS range from 1000 to 5000 mg/L [47,49].

Starch production from corn as a raw material is the most common starch production technology. During this production, generated starch wastewater can be divided into two parts, namely the pickling liquid and process water. The pickling liquid contains a high concentration of organic matter, primarily proteins, but has a low water content. In contrast, the process water is produced throughout the entire starch production process, which include corn breaking, germ removal, and starch drying and contains significantly more water, approximately 4 to 5 times more than the pickling liquid. The pickling liquid is a highly concentrated organic wastewater characterized by the high COD (8000–15,000 mg/L), high SS (1000–3000 mg/L), high total nitrogen (240–540 mg/L), high phosphate levels (15–130 mg/L in phosphorus terms), and low pH (ranging from 4.2 to 5) [53].

Process water, on the other hand, is considered a medium-strength organic wastewater. Its COD ranges from 2000 to 3500 mg/L, while concentrations of ammonia nitrogen and phosphate are relatively lower, around 20 mg/L and 14–32 mg/L, respectively [45]. Observing the corn starch as an example, which is the main product of corn deep processing, according to the current processing technology, about 1 t of starch output will produce 6 t of wastewater. Annually, this is too much wastewater produced during the whole starch manufacturing. Corn starch industry wastewater contains soluble starch, a small amount of protein, organic acids, dust, minerals and a small amount of oil, COD value is 8000~30,000 mg/L, BOD value is 5000~20,000 mg/L, and SS value is 3000~5000 mg/L [54].

According to the above data analysis, it can be concluded that the corn starch wastewater is rich in carbohydrates, nitrogen, and phosphorus, classifying it as a high-strength organic wastewater with good biodegradability. This makes it well-suited for treatment using biochemical processes designed for high-concentration organic waste. The wastewater contains relatively high levels of suspended solids and colloidal proteins, which can negatively affect the performance and development of anaerobic activated sludge systems. During the corn steeping (immersion) process, small amounts of sulfite ions (SO₃²⁻) are generated. In anaerobic treatment, these sulfur compounds can be reduced by microorganisms to hydrogen sulfide (H₂S), which may inhibit the activity of the anaerobic system [45,54].

Currently, in the corn starch processing, there are several wastewater treatment methods, like physical methods, chemical and physical–chemical methods, biochemical method, membrane biological reactor [45,50]. Physical starch wastewater treatments include sedimentation, flotation and filtration, adsorption methods, air flotation separation. Chemical and physical–chemical methods are based on mass transferring effects and physical chemistry to separate and remove the dissolved, colloidal pollutants from wastewater, or transform toxic substances into non-toxic substance, such as neutralization, coagulation, oxidation, reduction and extraction, stripping, adsorption, ion exchange, electric melting and reverse osmosis, etc. The most well-known are inorganic flocculation and precipitation treatment, organic flocculation and sedimentation, microbial flocculants treatment [45,49,55].

Biological treatment relies on microbial metabolism to break down and convert dissolved and colloidal organic pollutants into harmless substances. This approach to wastewater purification is generally categorized into two types: anaerobic and aerobic biological treatment. Given the high organic content and complexity of starch wastewater, a single biological treatment method is rarely sufficient. Instead, a combination of biological processes is typically employed. This integrated approach allows the strengths of each method to complement the weaknesses of the other, thereby enhancing overall treatment efficiency [45,47,49].

2.2. Winery Industry Wastewater

The production of wine requires a significant number of resources, such as water, organic supplements, energy, fertilizers and other, thus it produces a considerable volume of waste streams [56]. Winery wastewater, or the effluent generated during the winemaking process, consists of spilled wine or juice, wash water, cooling water, cleaning agents, leachate from solid byproducts, and brine from water softener regeneration [56,57]. The produced effluent contains various contaminants, such as ethanol, sugars, organic acids, phenolic compounds, etc. [56]. The quality of winery wastewater varies depending on the stage of winemaking (such as vintage, racking, or bottling), the vinification method (red, white, or specialty wine production), the facility’s operational practices, and the types of cleaning chemicals used [57]. On average, producing 1 L of wine generates approximately 0.2 to 4 L of winery wastewater [30]. The volumes of winery wastewater vary considerably between wineries and may reach 5000 L per 1000 tons of crushed grapes. The winery effluents for small wineries with up to 5000 kg of grapes crushed per tons of vintage (gc/v) are about 1000–9000 L of effluent per year, while medium wineries (5000–20,000 gc/v) produce about 5000–100,000 L of effluent per year. Large wineries (over 20,000 gc/v) produce 40,000–240,000 L of effluent per year [58].

Winery wastewater is typically acidic (pH = 4–5), which is due to the presence of organic acids, like lactic, tartaric, citric and malic acid and succinic acid [30,57]. It also contains significant levels of total solids (TS = 5–18 g/L) [56,57,59], volatile solids (VS = 6–20 g/L) [56,57], dissolved solids (DS = 6.6–8.6 g/L) [56], 5-day biochemical oxygen demand (BOD₅ = 1–13 g/L) [24,29], chemical oxygen demand (COD = 0.3–29 g/L) [24,30,60], even 49 g/L [59], total nitrogen (TN = 8–37 mg/L) [8,57], total phosphorus (TP = 2–28 mg/L) [8,56,57], polyphenols, and turbidity [57].

According to its composition, it is evident that proper winery wastewater treatment is necessary in the aim to reduce its environmental impact and enhance its overall sustainability [61]. That includes physicochemical (chemical precipitation, coagulation/flocculation, electrocoagulation, and sedimentation with flocculant aids), biological (both aerobic and anaerobic processes), membrane filtration and separation processes [30,61], advanced oxidation processes [28], adsorption and thermocatalytic oxidation processes [62]. Physicochemical methods have been efficiently used both as pretreatment and polishing step for the removal of suspended solids, turbidity, phosphorus, heavy metals (Cu, Zn), and color from winery wastewater, while reverse osmosis, used individually or combined to other treatment technologies, has shown high performance in terms of organic and inorganic content reduction, as well as ecotoxicity elimination [61]. Biological treatment is an adequate option for high biodegradability of the stream with high content of sugars and ethanol, facilitating degradation either on suspended or attached biomass [28,61].

The selection of the most appropriate treatment technology for a winery wastewater largely depends on the intended end use of the treated wastewater. To determine the most suitable option, wineries should carefully consider the factors such as the specific characteristics of the winery’s wastewater, the required effluent quality based on the end use (e.g., irrigation, municipal discharge), the available space, financial resources (both capital and operational), and the level of technical expertise needed to manage the treatment system [30].

2.3. Confectionery Industry Wastewater

The confectionery industry includes different confectionery products rich in sugar, sugar substitutes, cocoa, fats, emulsifiers and flavors [33]. Confectionery products can be broadly categorized into three main groups: sugar confectionery, chocolate products, and fine bakery goods [63]. The wastewater from the confectionery industry is daily and seasonal variable, dependent of its composition and quantity which significantly affects the process of its disposal. Confectionery wastewater is generally regarded as non-toxic, as it does not contain harmful substances like heavy metals, making it less hazardous than many other types of industrial effluents [64]. The wastewaters of confectionery industry are biologically degradable and confectionary plants discharge about 300–500 m³ per month of wastewater [31,33,64].

The main components of confectionary wastewater are organic compounds and suspensions; thus, the values of COD and BOD are high. The values of COD index are usually between 1000 and 12,000 mg O₂/L [31,33], while the values of BOD are up to 500–8000 mg O₂/L [31,33]. Considering the confectionery products composition, the organic substances present in confectionery wastewater are mainly sugars, fats, and dyes [33]. Confectionery plants consume significant amounts of fresh water for both production processes and the cleaning of machinery and equipment, resulting in the generation of large volumes of wastewater [65]. Also, the washing and disinfecting agents used after production process are also included in confectionary wastewater and significantly increase the content of nitrogen (30–120 mg N-NH₄/L) [31] and phosphorus (3.2–157 mg TP/L) [31] and change the pH value. The pH values of confectionery wastewater are mainly acidic [33,34,63].

Different treatment methods must be applied when the effluent contains a high sugar content, because a high load of organic compounds can create some technological and economic problems with the treatment [31]. Various treatment methods have been used for confectionery wastewater, including physicochemical, biological (aerobic/anaerobic) or multi-stage scheme processes [64]. Adsorption and coagulation/flocculation are not considered effective treatment methods for confectionery wastewater, because they only partially reduce the organic load and produce large volumes of sludge [33,64]. Although electrocoagulation and membrane technologies can significantly lower oxygen demand indicators within short retention times, they involve high operating and maintenance costs and generate leachates containing substantial pollutant levels [64,66]. Biological treatment systems are suitable processes for confectionery effluents, due to their high BOD and COD concentration [63]. However, for biodegradable high-strength industrial wastewater, anaerobic treatment provides greater suitability and environmental sustainability compared to aerobic processes [34,67].

2.4. Other Food Industry Wastewaters

The dairy industry is may consider as a major source of wastewater. It generates approximately 3.739 to 11.217 million m³ of wastewater annually, which is equivalent to 1 to 3 times the volume of milk processed [68]. Wastewater from the diary industry is primarily generated in milk processing units during operations such as pasteurization, homogenization, and the production of dairy products like butter, cheese, and milk powder. A significant volume of water is used to clean dairy processing plants, resulting in wastewater that may contain detergents, sanitizers, bases, salts, and organic matter, depending on the source [68]. Also, dairy wastewater and liquid waste are generated from various sections of the dairy industry, including cheese and butter production facilities, ice cream plants, condensed milk plants, as well as milk receiving and bottling units [69]. Thus, dairy effluents may contain soluble organics, suspended solids, trace organics. This wastewater contains high levels of organic substances such as carbohydrates, proteins, and fats or oils, along with fluctuations in temperature, pH, and elevated concentrations of phosphates and nitrates. Therefore, dairy industries require specialized treatment methods to effectively manage these contaminants [69].

Dairy waste is usually white and slightly alkaline. The pH varies in the range of 4.7–11 [70,71,72], but it can rapidly turn acidic as milk sugars ferment into lactic acid. This wastewater contains a high level of SS, in the range of 0.024–4.5 g/L, mainly fine curd particles from cheese production [73,74]. One of the primary environmental concerns with dairy effluent is its high and immediate oxygen demand. Moreover, the breakdown of casein can produce dense substances that may be harmful to the environment [74,75].

All these components significantly contribute to the high BOD and COD of dairy wastewater. Some of the main dairy wastewater quality parameters are BOD, COD, total suspended solids (TSS), settleable solids, pH, oils and greases, temperature and nutrients (N and P) [71,76]. The variation of COD is from 80–95,000 mg/L) and of BOD (40–48,000 mg/L). Significant amount of nitrogen originates mainly from milk proteins, 14–830 mg/L of total nitrogen, and is present either in organic nitrogen form such as proteins, urea and nucleic acids, or as ions such as NH⁺⁴, NO⁻², and NO⁻³. Total phosphorus in amount from 9–280 mg/L is mainly in inorganic forms such as orthophosphate (PO₄ ³⁻) and polyphosphate (P₂O₇ ⁴⁻), as well as in organic forms also of total phosphorus [73,77].

The complex nature of dairy wastewater, particularly its high fat content and elevated COD levels, makes it a challenging type of industrial effluent to treat [72]. Dairy wastewater treatment techniques typically involve three stages: a primary process for the removal of solids, oils, and fats; secondary treatment for eliminating organic matter and nutrients; and a final polishing stage using tertiary treatment methods [78]. Previous studies have explored various dairy wastewater treatments approaches, such as physical (filtration, sedimentation, flotation, adsorption) [72,73], chemical-based (coagulation, oxidation and advanced oxidation processes, adsorption) [72], and biological treatments that include microalgae or bacteria, and hybrid treatments like electrochemical, microbial electrochemical, membrane–microbial fuel cell, electrochemical and phytoremediation, UV radiation and phytoremediation, UV Irradiation and sodium hypochlorite and microalgae [72,79].

Biological treatment is considered one of the most effective methods for purifying dairy effluents, as it can process all components of the wastewater. However, it primarily targets soluble substances and fine colloidal particles [80].

Biological treatment generally includes both aerobic and anaerobic processes. Anaerobic and aerobic treatments are often combined, as each targets different components of dairy wastewater. This integrated approach offers an effective alternative to traditional single-phase biological treatment systems [81]. In certain cases, anaerobic treatment is followed by aerobic treatment to decrease soluble organic matter (BOD). To further reduce nitrogen and phosphorus content, biological nutrient removal (BNR) is applied. For disinfection prior to water reuse, chlorination of the treated effluent may also be carried out [73]. Also, membrane separation technology has become increasingly popular as an alternative method for treating dairy wastewater. Techniques like microfiltration, ultrafiltration, nanofiltration, and reverse osmosis enable efficient separation, concentration, and purification of the wastewater. These processes offer several benefits, including fewer processing steps, minimal impact on the final product quality, greater operational flexibility, and reduced energy consumption [82].

Significant amounts of water are also used in meat industry, primarily for cleaning and processing activities. Areas in which the effluents are generated are mainly lairage, slaughter and bleeding, dressing, paunch handling, rendering units, and various processing and cleaning sections [83]. Effluent from meat industry contains biodegradable organic matter measured in terms of BOD (700–8500 mg/L) [83,84,85,86]. High concentration of COD suggests a large amount of oxidizable organic substances in the meat wastewater (500–16,000 mg/L) [86,87]. It also contains high levels of grease, fat, and oil, which can accumulate and coat the treatment system. Nitrogen is present in effluent in three forms, organic N₂, ammonia salt, dissolved ammonia gas [84,87]. Both aerobic and anaerobic bacteria are present in the effluent which may be pathogenic or non-pathogenic (Escherichia coli, Echinococcus, Enterococcus, Klebsiella, Enterobacter cloacae, Campylobacter, Staphylococcus, Streptococcus, Listeria monocytogenes, Salmonella coliphages, Pseudomonas aeruginosa, Bovine enterovirus and many other strains) [88]. The temperature of effluent from meat industry is generally higher than that of natural water sources. This wastewater is typically turbid and often discolored. It commonly contains dissolved gases such as methane and sulfur dioxide (SO₂) [83].

The conventional treatment of meat industry wastewater follows a process similar to that of municipal wastewater, involving preliminary, primary, and secondary stages. After preliminary treatment, various combined methods are employed, with the most common use of physicochemical treatment as the primary stage and biological treatment as the secondary stage. Pressure-driven membrane processes such as membrane filtration, ultrafiltration, nanofiltration and reverse osmosis are widely studied for treatment of meat industry wastewater from as economic and effective alternative to conventional treatment [87]. Šereš et al. (2016) [89] investigated the treatment of wastewater from a vegetable oil refinery using a membrane filtration process, specifically microfiltration with a new generation of ceramic membranes. Their study aimed to reduce the chemical oxygen demand (COD) of edible oil refinery effluent. The results showed that microfiltration with an alumina ceramic membrane, featuring a pore size of 200 nm, was effective as a secondary treatment method—either for safe discharge into the environment or for potential reuse within the industrial process.

Figure 2 presents several commonly used treatment methods for various types of food industry wastewater. It is important to understand that a single treatment method is typically not sufficient for effective results. Therefore, a combination of treatment techniques is generally required, along with appropriate pretreatment of the wastewater. As can be seen at Figure 2, the hybrid biological and physicochemical methods are the mostly used treatments for majority of wastewaters generated by the food industry.

Also, different types of food industries have varying water requirements depending on the specific needs of their production processes. An approximate comparison of water usage across different sectors, ranked from highest to lowest demand, is as follows: meat processing industry, dairy industry, starch production, sugar manufacturing, confectionery and related sectors, fruit and vegetable processing, bakery, grain milling, edible oil production, and the fish industry [36].

Certainly, in addition to traditional methods of wastewater treatment, biological treatment, i.e., the use of microorganisms, has a dual benefit. In addition to the valorization of nutrients present in wastewater, which has a positive impact on environmental protection, this method of treatment enables the production of value-added products. Microorganisms are capable of converting organic-rich effluents into a range of high-value bioproducts, such as bioplastics, biofuels, organic acids, biosurfactants, enzymes, pigments, and polysaccharides. Below, we will present an overview of the potential for the application of starch-rich wastewater, wastewater from the winery and confectionery industry as media in the biotechnological production of high-value products.

2.5. Comparative Analysis of Physicochemical Characteristics of Food Industry Wastewaters

Wastewaters originating from different sectors of the food industry exhibit significant variations in their physicochemical properties, depending on the nature of the raw materials used and the specific industrial processes involved. A comparative overview of six major categories of food processing wastewaters, starch, winery, confectionery, fruit and vegetable, dairy, and meat, shows their distinct environmental profiles and biotechnological potentials. A detailed analysis of the characteristics of different food industry wastewaters is shown in Table 1.

Starch industry effluents are characterized by high concentrations of starch (19.47–31.2 g/L), glucose, and dextrins, resulting in a relatively high COD range (8.1–37 g/L). In the dairy sector, wastewater characteristics vary greatly depending on product type and composition [4]. Dairy wastewater is distinguished by its high content of proteins, lactose, lipids, and occasionally detergents from cleaning processes. These characteristics result in extremely variable COD (0.43–95 g/L) and BOD₅ (0.35–48 g/L) values, suggesting both high organic content and rapid biodegradability [2,9,10]. On the other hand, wastewater from fruit and vegetable processing contains fibers, phenolic compounds, organic acids, and minerals, but typically presents low COD (0.8–7.7 g/L) and BOD₅ (0.5–6.1 g/L) values, indicating a lower overall organic burden compared to other sectors [35,36,37,38]. In starch industry wastewater, BOD₅ values are moderate (0.005–5.4 g/L), the total solids content (0.26–42 g/L) and volatile solids (0.45–6.685 g/L) indicate a significant organic load and pH varies broadly from 4 to 10 [18,19,20,21]. In winery industry wastewater, volatile solids (0.13–54.952 g/L) and total solids (1.602–79.635 g/L) demonstrate high variability, and the acidic to alkaline pH range (3.93–12.9) reflects seasonal and operational fluctuations [24,25,26,27]. Confectionery effluents are notable for their content of sugars (up to 7.4 g/L), fats, and proteins, leading to moderately high COD (2.5–20.02 g/L) and BOD₅ (3.132–8 g/L) levels. The total solids range (11.1–44.6 g/L) reflects the high-density nature of these wastewaters. Though suspended solids are relatively low (0.47–1.31 g/L), nutrient-rich content supports microbial growth. The pH (3.9–9.5) is within a favorable range for biotechnological use [31,32,33]. Effluents from the meat industry contain proteins, fats, and minerals, contributing to COD values between 1.6 and 15 g/L and BOD₅ levels of 0.6–8 g/L. The total nitrogen (0.6–2.7 g/L) and phosphorus (0.15–0.32 g/L) contents are the highest among all surveyed sectors, indicating a high nutrient load. However, the presence of fats and high suspended solids (0.22–9.3 g/L) can inhibit oxygen transfer and microbial activity unless properly managed [9,10,40].

Each type of food industry wastewater exhibits a unique profile in terms of organic load, nutrient composition, and pH. While starch and confectionery effluents are rich in carbohydrates, dairy and meat wastewaters provide substantial protein and nutrient content. Winery and fruit/vegetable effluents, though more variable, present opportunities when treated or combined appropriately. Understanding these differences is essential for selecting tailored biotechnological strategies to valorize these waste streams, reduce pollution, and promote circular bioeconomy practices.

2.6. Other Potential Applications of Wastewaters from the Food Industry

In addition to their role as medium in biotechnological production, food industry wastewaters offer numerous other opportunities for valorization across sectors. There are different possibilities for valorization and further application of food industry wastewaters depending of their composition. Food-processing wastewater can be treated for reuse within industrial processes, enabling water reclamation, heat and energy recovery, and nutrient recycling. The industrial reuse of food industry wastewater includes applications in cooling systems, cleaning processes, and boiler feed water, in line with the principles of the circular economy [90]. Solids and sludge recovered from food wastewater, especially from fruit and vegetable or dairy processing can be composted and used as organic fertilizers or soil conditioners. This helps enhance soil structure and fertility by returning essential nutrients into the agricultural land [91,92]. Sludge contains valuable macronutrients (N, P, K) and organic matter, which can significantly enhance soil structure, organic carbon content, and water retention capacity. Composted biosolids, after proper pathogen reduction, can qualify as safe fertilizers for agriculture, landscaping, and land reclamation, improving soil enzyme activity and structural stability [93,94]. Food processing wastewater often contains compounds that can be recovered and reused: for example, pectin from fruit processing [37,95], proteins and enzymes from dairy or meat processing [96,97,98], and phenolic compounds from winery or olive mill wastewaters, which can be used in cosmetics or food additives due to their antioxidant properties [99,100,101,102].

Certain types of sludge, especially from starch or potato processing, can be incorporated into bio-bricks, cementitious materials after stabilization and drying [103,104,105]. This diverts waste from landfills and promotes sustainable construction.

In conclusion, the valorization of food industry wastewater offers diverse opportunities for resource recovery, including water reuse, nutrient recycling, and the extraction of valuable compounds. At the same time, we gave a number of examples for their biotechnological valorization. Through applications in agriculture, industry, and even construction, such practices not only reduce environmental impact but also align with the principles of the circular economy by transforming waste into useful products.

3. Valorization of Wastewater in Biotechnological Production

The term “sustainability”, which first appeared as a term in the 1960s, is a term that has been emphasized in recent years due to global industrialization, economic growth and the increase in the human population on earth [106,107]. The careless management of waste has led to climate change, loss of biodiversity and pollution, forcing society to make appropriate changes in terms of waste. This way of thinking has led to a growing recognition of the value of waste streams. As a result, a lot of waste is used nowadays to make chemicals, biofuels, and other high-value products.

The majority of industrial wastes are complex mixes that respond well to microbial fermentation as a valorizing technique. A more effective method of effluent management may be provided by microbes. Researchers in a variety of industries, including food production, textiles, and technology, are already using microorganisms and their compounds to create commercially viable products including metals, bioplastics, biofuel, and animal feed [108]. The ultimate objective is to change industry so that waste is recycled and used again instead of ending up in landfills. Most importantly, using wastes in microbial cultivation significantly reduces total production costs, and consequently affects the price of the final product. In the following, we will present the possibilities of applying three important wastewaters of the food industry in the biotechnological production of high-value products (Table 2).

3.1. Valorization of Starch-Rich Wastewater

Recently, there has been a growing interest in biotechnological strategies for utilizing industrial waste as cultivation media for microorganisms. Cultivation of microorganisms on media containing native or enriched wastewater, with the aim of producing high-value products, has become increasingly important in recent years [109]. One of the significant wastes that can be used as a medium for various microorganisms in the production of bioproducts is starch-rich wastewater [18]. Microorganisms capable of efficiently valorizing starch-rich wastewater represent a promising tool for sustainable biotechnological applications. A variety of fungi, including Aspergillus spp., and Rhizopus spp., Trichoderma spp., have demonstrated the ability to convert starch-containing effluents into high-value bioproducts such as organic acids, biopesticides, biofuels, microbial lipids, and industrially relevant enzymes. These microorganisms produce a range of hydrolytic enzymes, primarily amylases, which enable the breakdown of complex starch molecules into fermentable sugars that serve as substrates for further metabolic conversion [110].

In order to recycle potato processing wastewater for the production of biodiesel, the use of Aspergillus oryzae for microbial lipid synthesis was investigated by Muniraj et al. (2013) [20]. In their research, they used wastewater that they diluted with tap water to concentrations of 25%, 50% and 75% before fermentation. It was discovered that the ideal dilution ratio for lipid production was 25%, and the highest lipid concentration measured was 3.5 g/L. Also, diluting of the wastewater improved the removal of COD and nutrients in addition to lipid formation, starch utilization, and amylase secretion. Along with the generation of lipids, COD, total soluble phosphorus and nitrogen were removed to levels of 91%, 97%, and 98%, respectively. Major fatty acids including oleic acid (30.3%), stearic acid (19.3%), palmitolic acid (15.6%), palmitic acid (11.6%), linoleic acid (6.5%) and linolenic acid (5.5%), were found in the microbial lipids of A. oryzae, indicating that the lipids might be used to produce second-generation biodiesel.

On the other hand, Mishra et al. (2004) [111] used two Aspergillus isolates, A. niger and A. foetidus, for the purpose of producing biomass and reducing the organic load of potato chips industry wastewater. The result show that A. niger ITCC 2012 and A. foetidus MTCC 508 produced biomass of 2.85 and 2.4 g/L, respectively, and reduced COD by almost 60%. Also, compared to separate cultures at different pH levels, co-inoculation of both Aspergillus strains produced more fungal biomass and reduction in COD was higher. The biomass obtained by this treatment can be used as a feed supplement because it is a rich source of protein. A similar approach is presented in the paper by Souza Filho et al. (2019) [112], in which A. oryzae and Rhizopus oryzae remediate the wastewater of a wheat-starch plant to produce a protein-rich biomass that may be utilized as animal feed. After three days, A. oryzae removed almost 80% of the COD, outperforming R. oryzae. Furthermore, 12 g/L of dry biomass with a protein content of approximately 35% (w/w) was recovered, suggesting the potential of these fungi for wastewater valorization. Therefore, by analyzing the papers focused on biomass production, we can conclude that in terms of valorization of starch-rich wastewater, from the species of the genus Aspergillus, the fungus A. oryzae shows the best properties for multiplication and biomass production, as well as the highest COD reduction.

Gientka et al. (2019a) [113] investigated the effect of deproteinated potato wastewater (DPW) on biomass yield, specifically lipid production and fatty acid composition. When using DPW medium, Rhodotorula glutinis var. rubescens LOCKR13 strain was able to accumulate 18% cell dry weight of lipids, with stearic acids (5.8–7.5%), palmitic (15.3–17.8%) and oleic (41.0–51.5%) as dominating fatty acids. Theoretical simulations revealed that the methylation esters of lipids from R. glutinis var. rubescens yeast might be used to make biodiesel. Also, Xue et al. (2010) [114] obtained a lipid content of 35% in oleaginous yeast R. glutinis cultivated on corn starch wastewater supplemented with waste syrup. Kot et al. (2020b) [115] investigated the feasibility of R. gracilis ATCC 10788 cultivation in potato wastewater for lipid and carotenoid production. After 72 and 96 h of cultivation at 20 °C, the maximum intracellular lipid content (19 g/100 g _dw) was estimated in the yeast biomass. After 96 h of cultivation, the largest volumetric production of carotenoids (6.24 mg/L) and the highest amount of linoleic acid (28%) were discovered. From the above, we can conclude that the source of starch in the wastewater can affect the production of a particular production strain. Thus, the results showed that R. glutinis produces a greater amount of lipids on corn starch wastewater medium than on DPW medium. At the same time, enrichment of the medium can often increase the production of the desired product.

In a paper by Gientka et al. (2019b) [116], it was determined that the strain Trichosporon domesticum PCM 2960 was effective in the production of lipids on DPW medium enriched with glucose, and the biotechnological process implemented in the bioreactor enabled the production of lipids of 4.8 g/L. So, high levels of palmitic acid, oleic acid, linoleic acid and α-linolenic acid were found in the lipids of the T. domesticum PCM 2960 biomass. On the other side, Mitrović and Tančić Živanov [109] in their research attempted to produce biofungicides by cultivating Trichoderma harzianum K179 in water obtained from the potato processing industry. Cultivation was performed on wastewater of different dilutions, where it was found that cultivation of T. harzianum K179 on undiluted water provides the highest yield. Validation of the results on a larger scale showed that T. harzianum K179 culture broth had an antagonistic effect on corn phytopathogens, Aspergillus flavus and Fusarium graminearum, forming inhibition zone diameters of 31.33 and 54.33, respectively. These results demonstrate the potential of using wastewater from potato processing in the production of Trichoderma biofungicides.

Huang et al. (2003) [21] describe a feasibility assessment of a lactic acid generation system coupled with wastewater treatment at an industrial starch plant. Using potato wastewater, the ability of Rhizopus oligosporus, R. arrhizus and two strains of R. oryzae, to perform simultaneous saccharification and fermentation to lactic acid was evaluated. Kinetic analysis showed that the strain R. arrhizus DAR 36017 could produce a lactic acid output of 450 g/kg and nearly total starch saccharification after 20 h of cultivation.

Kurcz et al. (2018) [117] studied Candida utilis ATCC 9950 yeasts in medium containing potato wastewater and wastewater treated with various glycerol additions. After 72 h of cultivation in medium with 5% additional glycerol, the greatest biomass output (30 g/L) was achieved, and the biomass’s protein content was 36.7%. Additionally, Rhodotorula yeasts can use potato wastewater as a medium to synthesize carotenoids. Kot et al. (2017) [118] examined the effects of culture medium’s pH with potato wastewater and adding 5% glycerol on the effectiveness of R. glutinis yeast’s carotenoid production. Media with an initial pH between 4.0 and 7.0 had the highest carotenoid content (about 200 μg/g dw). Under these conditions, the yeast produced the least amount of torularhodin, and the most torulene and β-carotene. Also, the COD index was lowered by more than 45% after a 72 h of cultivation in medium containing potato wastewater with 5% glycerol addition.

Therefore, by analyzing the available scientific papers, it can be concluded that wastewater rich in starch has great potential for use in biotechnology (Figure 3). The activity of beneficial microorganisms on starch-rich wastewater enables the production of various high-value products, but also the purification of applied wastewater, making it less harmful to the environment. The application of such microbial systems contributes not only to effective wastewater treatment but also to the development of circular bioeconomy strategies by transforming waste streams into valuable biochemicals and biofuels [119].

3.2. Valorization of Winery Wastewater

Winery effluents are typically rich in organic matter, including sugars, polyphenols, and ethanol, making them suitable substrates for microbial fermentation and the production of high-value bioproducts such as biopolymers, biofuels, enzymes, and microbial biomass. The produced biomass can be further used for human and animal nutrition, thus obtaining a high-value product with minimal investment. Fungi and microalgae are mainly used for this purpose, but fungi are considered to be more suitable [25]. One of the reasons is their cheaper separation and purification of the cultivation medium. Also, almost any organic waste product that contains carbohydrates, such as confectionery and distillery waste, agricultural waste, and wood processing effluents, can be used to cultivate fungi. On the other hand, various bacterial strains, including Xanthomonas spp., Klebsiella pneumoniae, and some cyanobacteria have shown the capacity to grow on and metabolize components of winery wastewater. In addition to contributing to pollutant load reduction, the use of these microbial systems supports circular economy principles by enabling the transformation of agro-industrial waste streams into valuable products [120].

Zhang et al. (2008) [25] in their research examined Aspergillus oryzae WEBL0401, A. niger WEBL0901 and Trichoderma viride WEBL0702, with the aim of producing fungal biomass protein (FBP) and COD reduction on winery wastewater. Results show that in shake fermentation, T. viride without nitrogen addition and A. oryzae and A. niger with 0.5–1.0 g/L (NH₄)₂SO₄ addition produced more than 5 g/L of fungal biomass. Two strains of Aspergillus produced about 36% of the protein in fungal biomass, whereas T. viride produced 19.8% of the protein in biomass. Also, winery wastewater’s COD was reduced by 84–90% as a result of the FBP production process. The results of these investigations showed that by using these microorganisms, it is possible to develop a bioprocess for the treatment of winery wastewater integrated with the production of FBP. Similar conclusions were obtained by Hultberg and Bodin (2019) [121] after their experiment with T. harzianum on brewery waste streams, which indicates the great potential of Trichoderma isolates in the production of microbial biomass but also in the purification of wastewater from the alcoholic beverage industry. The studies conducted by Zhang et al. (2008) [25] and Hultberg and Bodin (2019) [121] demonstrate the significant potential of filamentous fungi, particularly Aspergillus and Trichoderma species, in simultaneously producing FBP and treating wastewater from the alcoholic beverage industry. The ability of these strains to generate fungal biomass with notable protein content, while achieving COD reduction of up to 90%, highlights their dual role in both valorization and environmental remediation.

Microalgae can grow in heterotrophic, autotrophic or mixotrophic environments based on the light and carbon supply they use for metabolism. Depending on the type and growth conditions, their composition varies in the proportion of carbohydrates, proteins and lipids, which are used for human and animal nutrition, but also for the production of biofuels. Today, various microalgae are used for these purposes, primarily the genera Arthrospira and Chlorella. However, applying the biorefinery concept is the only way to increase the competitiveness of microalgae biofuels on the global market from the perspective of biofuel production. Spennati et al. (2020) [122] in their research examined the co-cultures of A. platensis and C. vulgaris used in the treatment of winery wastewater in order to produce cheap biomass intended for the production of biodiesel. The results show that after four days of treatment on 20% winery wastewater, the highest biomass of 0.66 g _dw/l day and lipids of 7.10 ± 0.22 g _lipids/100 l day were produced. At the same time, the co-culture decreased the polyphenol and COD content of the three distinct wastewaters by over 50% and 92%, respectively. Similar results were obtained by Casazza et al. (2016) [123] and Spennati et al. (2019) [124] under slightly modified conditions, confirming the great potential of these microalgae in the purification of winery wastewater, as well as in the production of biomass for various applications. The REDWine project by Sousa et al. (2025) [125] investigates the potential of C. vulgaris biomass production on winery wastewater as an agricultural product. The study, which was conducted in 1700 mL photobioreactors and 250 mL Erlenmeyer flasks, focused on adding red wine wastewater to culture media to stimulate microalgae growth. Even at 30% (v/v) effluent concentrations, C. vulgaris showed notable growth, as long as the polyphenols concentration in the effluents was low. The best biomass production was recorded at 10% (v/v), where this study opens up new possibilities for creative approaches to sustainable agriculture by demonstrating the potential of using winery effluents to produce C. vulgaris A4F_Ma016 biomass. Optimizing growth conditions, such as effluent concentration and polyphenol content, is key to maximizing biomass yield and treatment efficiency. These findings reinforce the value of microalgae as multifunctional agents in circular economy approaches, combining environmental remediation with high-value biomass production.

The goal of the Policastro et al. (2022) [126] paper was to increase the amount of hydrogen produced from winery effluent through fermentative or co-fermentative processes. To find strains that produce hydrogen, a mixed microbial consortium was subjected to microbiological analysis. The separated pure cultures, the original mixed culture, and a co-culture of the two most effective photofermentative and dark fermentative strains, Klebsiella pneumoniae strain MF101 and Rhodopseudomonas sp. strain BR0Y6, were used in comparative fermentation studies. The obtained results showed that the highest yield of 290 NmlH₂/l was obtained using the initial mixed culture. Also, the cost of environmentally friendly technology can be significantly decreased by combining the generation of biodiesel with wastewater treatment. A study by Tsolcha et al. (2017) [127] used very significant wastewaters from the wine and raisin industries as medium for a mixed algal/cyanobacterial culture system that was dominated by the Leptolyngbya sp. Blends of the aforementioned wastewaters showed exceptional rates of removal of nutrients and COD (78.1%, 92.8%, and 99% for total nitrogen, COD, and phosphate, respectively), while the produced biomass included about 13% lipids (w/w) on a dry weight basis. Also, the results show that lipid’s saturated/monounsaturated fatty acid ratio of 85% indicates that the system is appropriate for producing biodiesel.

In addition to the aforementioned bacteria, Xanthomonas campestris has also been used to produce xanthan from winemaking wastewater. Many scientists have studied the production of this important biopolymer, but few have studied its production in wastewater media. Study by Bajić et al. (2015) [128] investigates the xanthan production on wastewater from the pressing, crushing, must clarifying, and fermentation stages of the white wine production. Depending on the wastewater used, both the xanthan yield and the percentage of sugar conversion varied, however, the results of the experiment in the bioreactor showed that the highest xanthan yield was achieved on must clarification water with a yield of 10.67 g/L of xanthan of satisfactory quality. A similar study with the isolate X. campestris ATCC 13951 was carried out by Rončević et al. (2019) [129] who optimized the process conditions for the production of xanthan in a laboratory bioreactor with the aim of obtaining the highest possible yield of this biopolymer. The optimal process conditions for production of xanthan on a medium based on winery wastewater with 30 g/L sugar were determined to be stirring speed of 475.50 rpm, aeration rate 1.95 vvm and the temperature of 29.34 °C. Under the indicated conditions, the xanthan yield of very good quality was 23.85 g/L, and at the same time, exceptional purification of the applied wastewater from the production of white wine was enabled, which is reflected in the conversion of nitrogen, sugar and phosphorus of 71.74%, 90.79% and 83.14%, respectively. On the other hand, Trivunović et al. (2021) [130] showed in their study that X. campestris can also produce xanthan on wastewater from red wine production. The results of these studies showed that the highest yield of xanthan is achieved using waste water after washing the fermentation tank (16.46 g/L), while X. campestris produces the least xanthan in the medium with waste water after washing the wine tank (9.24 g/L). In all mentioned papers, along with the production of xanthan gum, significant conversion of sugars, phosphates and nitrogen occurs, which implies that the microorganism X. campestris, in addition to its high productivity, also has the ability to purify applied wastewater. The summarized studies clearly illustrate the potential of biotechnological processes in the valorization of wine industry wastewater using different bacterial strains. The use of microbial consortia, including K. pneumoniae, Rhodopseudomonas sp. and cyanobacteria such as Leptolyngbya sp., shows promising results in the production of hydrogen and biodiesel, with simultaneous nutrient and COD removal efficiencies reaching up to 99%. In addition, X. campestris has shown an excellent ability to synthesize xanthan gum from various winery wastewaters, achieving high product yields while contributing to significant reductions in sugar, nitrogen and phosphorus levels. These findings highlight the feasibility of integrating wastewater treatment with the production of high-value bioproducts, offering an environmentally sustainable strategy that supports the principles of a circular bioeconomy.

Given the composition of the winery wastewater, they have also found their purpose in the production of kombucha beverage. In the publications of Vukmanović et al. (2024) [131] and Vitas et al. (2023) [132], kombucha beverage was produced using effluent derived from different stage in production of wine. The authors used various statistical tools in order to optimize the production process of this medical drink, but also to confirm its antioxidant effect and highlight the possibility of purification of winery wastewaters using kombucha culture. Thus, a kombucha culture consisting mainly of bacteria of the genus Acetobacter and five yeasts, Saccharomyces bisporus, S. cerevisiae, Saccharomycodes ludwigii, Zygosaccharomyces sp. and Torulopsis sp., demonstrated the ability to produce a fermented beverage with pronounced nutritional and medicinal properties on a sugar-rich medium, such as winery effluents.

By analyzing the above papers, it can be concluded that wastewater from wine production can be successfully utilized by various bacteria, yeasts, fungi, and microalgae for the production of value-added products, but also in their direct purification, which certainly has an economic and environmental impact. Both fungal and algal systems have demonstrated notable potential in producing protein-rich biomass, biofuels, and bioactive compounds (Figure 3), while simultaneously achieving substantial reductions in COD, polyphenols, and nutrient loads. Furthermore, bacteria such as X. campestris, K. pneumoniae, and cyanobacteria contribute not only to biopolymer synthesis and hydrogen production but also to effective effluent remediation. The integration of these microbial technologies with circular economy principles highlights the dual role of winery wastewater as both an environmental challenge and a renewable resource for sustainable bioprocessing. Continued optimization of cultivation parameters and bioreactor conditions, as well as strain selection, will be key to unlocking the full biotechnological potential of winery effluents.

Table 2. Recent studies of valorization of food industry wastewater in the biotechnological production of high-value products.

High-Value Product	Applied Wastewater	Main Carbon Source	Wastewater Availability	Usage	Microorganism Producer	References
Biodiesel	Potato processing wastewater	starch	All year	Fuel	Aspergillus oryzae	[20]
Biomass/protein	Potato chips industry wastewater	starch	All year	Feed supplement	A. niger ITCC 2012 A. foetidus MTCC 508	[120]
Biomass/protein	Wheat-starch plant wastewater	starch	Seasonal	Feed supplement	A.oryzae Rhizopus oryzae	[112]
Biodiesel/fatty acid	Deproteinated potato wastewater (DPW)	starch	All year	Fuel	Rhodotorula glutinis var. rubescens LOCKR13	[113]
Biodiese/lipids	Corn starch wastewater	starch	Seasonal	Fuel	R.glutinis	[114]
Lipid/carotenoid	Potato wastewater	starch	All year	Food, pharmaceuticals, and cosmetics industy	R. gracilis ATCC 10788	[115]
Palmitic, oleic, linoleic and α-linolenic acids	DPW medium enriched with glucose	starch, glucose	All year	Acids	Trichosporon domesticum PCM 2960	[116]
Biofungicides	Potato processing wastewater	starch	All year	Plant protection	Trichoderma harzianum K179	[109]
Lactic acid	Potato processing wastewater	starch	All year	Acids	Rhizopus oligosporus, R. arrhizus, R. oryzae	[19]
Biomass/protein	Potato processing wastewater/with glycerol	starch, glycerol	All year	Feed supplement	Candida utilis ATCC 9950	[117]
Carotenoid	Potato processing wastewater/with glycerol	starch, glycerol	All year	Food, pharmaceuticals, and cosmetics industy	R. glutinis	[118]
Biomass/protein	Winery wastewater	glucose, fructose	Seasonal	Feed supplement	A.s oryzae WEBL0401, A. niger WEBL0901 T. viride WEBL0702,	[25]
Biodiesel	Winery wastewater	glucose, fructose	Seasonal	Fuel	Co-cultures Arthrospira platensis and Chlorella vulgaris	[122]
Biomass/protein	Winery wastewater	glucose, fructose	Seasonal	Feed supplement	A. platensis, C. vulgaris	[123,124,125]
Hydrogen	Winery wastewater	glucose, fructose	Seasonal	Energy source	Klebsiella pneumoniae MF101, Rhodopseudomonas sp. BR0Y6	[126]
Biodiesel	Wine and raisin industries wastewater	glucose, fructose	Seasonal	Fuel	Leptolyngbya sp.	[127]
Xanthan	Winery wastewater	glucose, fructose	Seasonal	Biopolymer	Xanthomonas campestris	[128,129,130]
Kombucha beverage	Winery wastewater	glucose, fructose	Seasonal	Fermented beverage	Mixed microbial consortium	[131,132]
Xanthan	Confectionary industry wastewater	sucrose, glucose, fructose	All year/seasonal	Biopolymer	Xanthomonas campestris	[133,134]
Biofungicides	Confectionary industry wastewater	sucrose, glucose, fructose	All year/seasonal	Plant protection	Bacillus sp.	[135]
Bioethanol	Confectionary industry wastewater	sucrose, glucose, fructose	All year/seasonal	Fuel	Zymomonas mobilis ATCC 31821	[136]
Polyglutamic acid (PGA)	Chocolate, candy and marshmallow wastewater industry	sucrose, glucose, fructose	All year/seasonal	Cosmetics industy	B. licheniformis JCM 2505.	[136]
Polyhydroxyalkanoates (PHA, PHB)	Chocolate and candy-based industry wastewater	sucrose, glucose, fructose	All year/seasonal	Bioplastic	Alcaligenes latus DSM 1123, Cupriavidus necator DSM 428.	[136]

Table 2. Recent studies of valorization of food industry wastewater in the biotechnological production of high-value products.

High-Value Product	Applied Wastewater	Main Carbon Source	Wastewater Availability	Usage	Microorganism Producer	References
Biodiesel	Potato processing wastewater	starch	All year	Fuel	Aspergillus oryzae	[20]
Biomass/protein	Potato chips industry wastewater	starch	All year	Feed supplement	A. niger ITCC 2012 A. foetidus MTCC 508	[120]
Biomass/protein	Wheat-starch plant wastewater	starch	Seasonal	Feed supplement	A.oryzae Rhizopus oryzae	[112]
Biodiesel/fatty acid	Deproteinated potato wastewater (DPW)	starch	All year	Fuel	Rhodotorula glutinis var. rubescens LOCKR13	[113]
Biodiese/lipids	Corn starch wastewater	starch	Seasonal	Fuel	R.glutinis	[114]
Lipid/carotenoid	Potato wastewater	starch	All year	Food, pharmaceuticals, and cosmetics industy	R. gracilis ATCC 10788	[115]
Palmitic, oleic, linoleic and α-linolenic acids	DPW medium enriched with glucose	starch, glucose	All year	Acids	Trichosporon domesticum PCM 2960	[116]
Biofungicides	Potato processing wastewater	starch	All year	Plant protection	Trichoderma harzianum K179	[109]
Lactic acid	Potato processing wastewater	starch	All year	Acids	Rhizopus oligosporus, R. arrhizus, R. oryzae	[19]
Biomass/protein	Potato processing wastewater/with glycerol	starch, glycerol	All year	Feed supplement	Candida utilis ATCC 9950	[117]
Carotenoid	Potato processing wastewater/with glycerol	starch, glycerol	All year	Food, pharmaceuticals, and cosmetics industy	R. glutinis	[118]
Biomass/protein	Winery wastewater	glucose, fructose	Seasonal	Feed supplement	A.s oryzae WEBL0401, A. niger WEBL0901 T. viride WEBL0702,	[25]
Biodiesel	Winery wastewater	glucose, fructose	Seasonal	Fuel	Co-cultures Arthrospira platensis and Chlorella vulgaris	[122]
Biomass/protein	Winery wastewater	glucose, fructose	Seasonal	Feed supplement	A. platensis, C. vulgaris	[123,124,125]
Hydrogen	Winery wastewater	glucose, fructose	Seasonal	Energy source	Klebsiella pneumoniae MF101, Rhodopseudomonas sp. BR0Y6	[126]
Biodiesel	Wine and raisin industries wastewater	glucose, fructose	Seasonal	Fuel	Leptolyngbya sp.	[127]
Xanthan	Winery wastewater	glucose, fructose	Seasonal	Biopolymer	Xanthomonas campestris	[128,129,130]
Kombucha beverage	Winery wastewater	glucose, fructose	Seasonal	Fermented beverage	Mixed microbial consortium	[131,132]
Xanthan	Confectionary industry wastewater	sucrose, glucose, fructose	All year/seasonal	Biopolymer	Xanthomonas campestris	[133,134]
Biofungicides	Confectionary industry wastewater	sucrose, glucose, fructose	All year/seasonal	Plant protection	Bacillus sp.	[135]
Bioethanol	Confectionary industry wastewater	sucrose, glucose, fructose	All year/seasonal	Fuel	Zymomonas mobilis ATCC 31821	[136]
Polyglutamic acid (PGA)	Chocolate, candy and marshmallow wastewater industry	sucrose, glucose, fructose	All year/seasonal	Cosmetics industy	B. licheniformis JCM 2505.	[136]
Polyhydroxyalkanoates (PHA, PHB)	Chocolate and candy-based industry wastewater	sucrose, glucose, fructose	All year/seasonal	Bioplastic	Alcaligenes latus DSM 1123, Cupriavidus necator DSM 428.	[136]

3.3. Valorization of Confectionery Industry Wastewater

The confectionery sector contributes significantly to the formation of wastewater containing high levels of organic components such as proteins, lipids and sugars, resulting in a rise in the BOD and COD values. Because of this, these sectors are searching for the most cost-effective and environmentally friendly wastewater treatment technology [33]. One of the ways is certainly the application of beneficial microorganisms. Simple sugars, including glucose, fructose, and sucrose, are abundant in waste streams generated during chocolate and candy production. Such waters can be successfully used in single-strain bioprocesses. On the other hand, biscuits and cakes made with flour have higher amounts of complex carbohydrates, primarily in the form of starch, and lower amounts of simple sugars. Sometimes it is desirable to include two or more microbial cultures in bioprocesses to increase nutrient utilization from wastewater and improve yield [136].

Xanthan gum production is a challenging task from the aspect of the medium for the cultivation of bacteria of the Xanthomonas genus. However, we have already mentioned scientists who have successfully carried out this biosynthesis on a medium with winery wastewater. Bajić et al. (2014, 2017) [133,134] also investigated the production of xanthan gum from wastewater from a confectionary industry. These scientists conducted research on xanthan production in five different wastewaters from the confectionery industry using X. campestris during 2014. The results of xanthan yield depending on the applied wastewater ranged from 4.28 g/L to 10.03 g/L, which indicates the possibility of using wastewater from the confectionery industry in the production of this important biopolymer. On the other hand, their research conducted in 2017 is significantly more complex. Using process simulation software, they created a process and cost model for a xanthan production on confectionary wastewater. They compared the yield of this important biopolymer on a commercial medium and on a medium that is basically wastewater from the confectionery industry. The results showed very close yield values, which indicate great potential in economic and environmental terms for the production of xanthan on this effluent. While both wastewaters, from wineries and confectionery industries, supported xanthan biosynthesis, comparative analysis indicates that winery wastewater, particularly from the must clarification stage and fermentation tank washing, enabled higher xanthan yields. These results suggest that winery wastewaters, due to their sugar-rich composition and higher fermentability, are a better choice for xanthan production using X. campestris.

Another significant application of microorganisms as catalysts in obtaining high-value products in a wastewater medium is in the production of biopesticides. In their study, Dujković et al. (2024) [135] examined the possibility of producing a biocontrol agent using the microorganism Bacillus sp. in wastewater from the confectionery industry, as well as to evaluate the effects of the addition of essential oils on the antifungal activity against the phytopathogen Aspergillus flavus. The results of their research showed the potential of using wastewater from the confectionery industry for the production of Bacillus sp. biomass, as well as the fact that the addition of basil and oregano essential oils enabled an increase in biomass in the cultivation medium, and therefore enable a more pronounced antifungal activity against A. flavus.

The technical report by Harrison et al. (2019) [136] discusses the application of the biorefinery concept with wastewater from the confectionery industry through various examples. Depending on the origin of the wastewater from the confectionery industry, i.e., the carbohydrates present, the authors focused on the production of bioethanol using Zymomonas mobilis, production of polyglutamic acid (PGA) and polyhydroxyalkanoates (PHA). So, in addition to the yeast Saccharomyces cerevisiae, which is traditionally used in bioethanol production, but also its alternative Pichia stipitis, the authors wanted to try production with a microorganism, Z. mobilis ATCC 31821. What is significant about this bacterium compared to the aforementioned microorganisms is its resistance to high concentrations of ethanol. Successful bioethanol production experiments were carried out in small volumes in fermentation flasks, but also in a 5 L laboratory bioreactor. In addition, with regard to PGA production, the authors selected a bacterium of the genus Bacillus, B. licheniformis JCM 2505. The results showed that the applied microorganism can grow on confectionery waste obtained from the production of chocolate, candy and marshmallow and produce PGA. The same authors also examined PHA production on chocolate and candy-based media using the microorganisms Alcaligenes latus DSM 1123 and production of PHA homopolymer, PHB, by Cupriavidus necator DSM 428. The results of these investigations showed that the waste of the confectionery industry can be successfully used in the production of this important biopolymer with great potential in the production of bioplastics. Some authors have also successfully investigated biopolymer production from confectionery industry wastewater [137,138,139], while others have studied the production of methane and biohydrogen mainly using consortia of microorganisms [31,32].

The utilization of wastewater from the confectionery industry as a medium for microbial growth represents a sustainable and economically viable approach in modern biotechnology (Figure 3). Numerous studies have demonstrated the potential of this medium for microbial biosynthesis of xanthan gum, bioethanol, biopesticides, bioplastics (such as polyhydroxyalkanoates), and other valuable compounds. Furthermore, this practice contributes to the reduction in environmental pollution, lowers production costs, and supports the principles of circular economy. Overall, the biotechnological exploitation of confectionery wastewater not only adds value to industrial by-products but also aligns with global efforts toward greener and more sustainable industrial practices. Continued research and development of optimized microbial consortia and scalable processing technologies are essential for the commercial implementation of these promising biotechnological solutions.

4. Conclusions

The food industry is a major consumer of water across its various operational stages. These wastewaters are typically rich in biodegradable organic matter, making them non-toxic but often characterized by high levels of BOD, COD, and SS. Understanding these characteristics is essential for selecting appropriate treatment strategies and ensuring effective wastewater management. With proper treatment, food industry effluents can be managed sustainably, aligning with environmental protection goals and supporting resource recovery initiatives.

From an economic point of view, the use of food industry wastewater as a medium in microbial processes presents both cost-saving opportunities and operational challenges. As highlighted in the article, these wastewaters are rich in carbon and nutrients, often eliminating the need for expensive synthetic media in microbial cultivation. Such substitution can significantly reduce raw material costs, which are a major segment of total production expenses in industrial biotechnology. However, the economic feasibility is heavily dependent on several factors: the variability in wastewater composition; the need for pre-treatment or dilution; and the efficiency of microorganisms. At the same time, studies referenced in the paper indicate that product yields on waste medium can approach those obtained on commercial media, making the process economically viable. Still, the implementation of biotechnological production based on wastewater requires investment in infrastructure, process control systems, and waste logistics. Small-scale or decentralized food producers may lack the capital for such integration. Furthermore, the market value of the final product like bioplastics, bioethanol or enzymes, must justify the costs of downstream processing and regulatory compliance. Economic incentives such as subsidies for waste valorization, tax benefits, or inclusion in circular economy frameworks could enhance the financial attractiveness of these processes.

On the other hand, while significant progress has been made in the biotechnological valorization of food industry wastewater, several research gaps and development opportunities remain. As discussed throughout the paper, one major challenge is the inconsistency in wastewater composition, which can affect microbial performance and product yield. Also, more research is needed on co-culture systems and microbial consortia, which can enhance nutrient utilization and process stability.

Another underdeveloped area is the scaling-up of laboratory findings. Many experiments are still conducted in flasks or small bioreactors, with limited data on process kinetics, bioreactor design, and cost-effectiveness at pilot or industrial scales. Integrated biorefinery models that couple waste treatment with production of multiple value-added compounds are promising but require optimization and techno-economic validation. Additionally, life cycle assessment (LCA) and carbon footprint analysis are seldom included in current studies but are essential for proving the environmental sustainability of these systems.

At the same time, the valorization of food industry wastewater for biotechnological production must align with stringent environmental and safety regulations. Regulatory frameworks at national and international levels require compliance with discharge limits for parameters such as COD, BOD, total nitrogen and phosphorus, pH, and microbial load. These constraints aim to prevent water pollution and protect ecosystems and public health. As outlined in the reviewed paper, food industry wastewater is typically rich in biodegradable organic matter but varies in pollutant concentration depending on the source. Hence, pre-treatment is often necessary to meet legal thresholds prior to discharge or reuse.

Regulatory bodies such as the European Food Safety Authority (EFSA) and U.S. Environmental Protection Agency (EPA) enforce strict standards when waste-derived products are intended for use in food, feed, or agriculture. This includes restrictions on genetically modified microorganisms according to directives such as the EU Directive 2001/18/EC [140]. Also, EU Urban Waste Water Treatment Directive (91/271/EEC) [141] and U.S. EPA standards [142] impose specific limits for COD, BOD₅, total nitrogen, phosphorus, and microbial contaminants in effluents before discharge or reuse. Despite the high potential of valorization processes, regulatory compliance remains a key factor for commercial scale-up.

The biotechnological utilization of food industry wastewater, particularly from starch-rich, winery, and confectionery sources, presents a promising and sustainable approach to address both environmental and economic challenges. These waste streams, often considered pollutants, can be transformed into valuable resources through the action of diverse microbial systems, including bacteria, yeasts, fungi, and microalgae. The application of such systems not only enables the production of high-value biochemicals, biofuels, and bioplastics but also contributes significantly to wastewater purification by reducing organic load, nutrients, and toxic compounds. This dual benefit supports the development of circular bioeconomy models, where waste is reintegrated into the production cycle as a raw material. To fully realize this potential, further research focused on optimizing microbial cultures, bioprocess conditions, and large-scale process integration is essential. Ultimately, the integration of microbial biotechnology with sustainable waste management strategies offers a viable path toward greener, more resource-efficient industrial practices.