Search Results (121)

Improving the effluent quality of municipal wastewater treatment plants (WWTPs) is essential for sustainable water management and water quality protection in the Yellow River Basin. Many existing WWTPs in northern China were constructed under earlier discharge requirements and now face dual challenges of stricter effluent standards and poor low-temperature performance in winter. In this study, a municipal WWTP with a design capacity of 5 × 10⁴ m³/d in northern China was upgraded to improve winter treatment performance and support stable compliance with the discharge requirements of the Yellow River Basin. The original anaerobic + oxidation ditch process suffered from unstable effluent quality, excessive sludge loading, and insufficient pollutant removal under low-temperature conditions. A land-saving retrofit strategy was therefore proposed, involving oxidation ditch wall-height raising to extend the hydraulic retention time (HRT) and membrane bioreactor (MBR) integration to increase the mixed liquor suspended solids (MLSS) concentration. After the retrofit, the total HRT increased to 19.82 h, and the average MLSS concentration reached 7050 mg/L. The relative abundances of key nitrogen-removing bacteria, including Nitrospiraceae, Nitrosomonadaceae, and Rhodocyclaceae, increased markedly. Meanwhile, denitrification sludge loading and BOD₅ sludge loading decreased to 0.030 and 0.033 kg/(kg·d), respectively. Under low-temperature conditions, the theoretical removal capacities of total nitrogen (TN) and BOD₅ reached 44.32 and 286.19 mg/L, respectively, enabling stable effluent compliance. The results show that this retrofit strategy can improve WWTP effluent quality while avoiding large-scale land expansion, providing a practical and sustainable solution for upgrading cold-region WWTPs along the Yellow River Basin. Full article

Acidogenic fermentation is a promising biotechnology for converting organic wastes into carboxylic acid (CA), which has significant commercial value and diverse applications in the food, chemical, pharmaceutical, and cosmetic industries. However, major challenges such as limited substrate hydrolysis and lower CA production hinder further development of this biotechnology towards full-scale implementation. This review provides a comprehensive overview of the current status of acidogenic fermentation, focusing on substrate composition, inoculum, and reactor design, along with potential strategies to overcome reactor-specific limitations and enhance CA production. It was found that the substrate composition, particularly its carbohydrate, protein, and lipid contents, strongly influences both CA production and yield. Specifically, carbohydrate-rich substrates yield higher CA production compared to protein- and lipid-rich substrates. These substrates have been investigated in different reactor configurations for CA production. Among them, the leachate bed reactor and anaerobic membrane bioreactor have demonstrated superior performance, achieving higher CA production with acetic and butyric acids as the dominant CA composition. These reactors are generally operated using three types of inocula: aerobic and anaerobic inoculum, enriched inoculum, and rumen microorganisms. Interestingly, rumen microorganisms are effective in degrading complex substrates, whereas enriched inoculum accelerates hydrolysis and acidogenesis processes within a shorter fermentation time. The findings presented herein will provide valuable information for addressing the challenges associated with acidogenic fermentation and lay the foundation for future research aimed at upscaling this biotechnology to a commercial scale. Full article

The juice industry generates substantial quantities of solid waste and wastewater. Consequently, efforts have focused on their treatment and valorization to obtain high-value-added products. Traditionally, these wastes are managed through landfill disposal and treatment in municipal wastewater facilities, respectively. In the present work, two alternative scenarios for the valorization of orange juice waste were developed and assessed in comparison to the conventional approach by performing a Life Cycle Assessment (LCA). Scenario 1 involved hydro-distillation of solid waste for essential oil recovery, followed by anaerobic digestion for biogas and fertilizer production, with wastewater treated via membrane filtration and chlorination. In Scenario 2, solvent-free microwave extraction (SFME) was employed for essential oil recovery, followed by anaerobic digestion. Wastewater was treated in a membrane bioreactor followed by ultraviolet treatment. According to the results, Scenario 1 achieved a 36% reduction in greenhouse gas emissions due to the beneficial effects of biogas and fertilizer production, despite its high energy demands. Scenario 2 exhibited the best environmental performance due to lower energy demands and higher extraction efficiency compared to Scenario 1, with reductions of 46% in greenhouse gas emissions and 48% in resource depletion. Overall, the findings highlight the potential of integrating innovative, energy-efficient technologies for the sustainable valorization of juice industry waste, offering measurable environmental advantages for industrial-scale implementation. Full article

Landfill leachate is highly concentrated wastewater containing non-biodegradable organic compounds and toxic substances. For this reason, advanced treatment methods are necessary for its treatment. The article discusses the possibility of treating leachate in a hybrid system combining ultrasonic pretreatment and anaerobic co-digestion with dairy wastewater in an anaerobic membrane bioreactor. Two laboratory-scale submerged anaerobic membrane reactors with a capillary module with membranes with a pore size of 0.1 μm and an effective filtration area of 0.35 m² were used in this study. An ultrasound disintegrator at 22 kHz (amplitude 14 µm) was used for leachate pretreatment. It was found that, as a result of leachate sonification (time > 10 min), the BOD₅/COD ratio in the wastewater increased from 0.1 to 0.4, and the content of dissolved organic compounds accounted for more than 40% of the total COD. Preliminary sonication of the leachate resulted in improved co-digestion efficiency in a reactor fed with conditioned leachate. A 92% reduction in organic pollutants was achieved, as well as a biogas production rate of 0.5 L biogas/g COD removed. Full article

Wastewater nitrogen pollution is a serious environmental problem, and traditional treatment techniques are frequently constrained by their high energy requirements and operational complexity. The anaerobic ammonium oxidation (anammox) process combined with membrane bioreactor (MBR) technology (anammox-MBR) offers a practical and energy-efficient solution for the sustainable removal of nitrogen, further enhanced by its potential to minimize emissions of nitrous oxide (N₂O), a potent greenhouse gas with a global warming potential nearly 300 times that of carbon dioxide. This review outlines the most recent advancements in anammox-MBR systems, highlighting their ability to achieve nitrogen removal efficiencies of more than 70–90% and, in integrated systems with reverse osmosis, to recover up to 75% of the inflow as high-quality reusable water. Significant advancements such as high-rate activated sludge coupling, reverse osmosis integration, microaeration methods, and membrane surface modifications have decreased membrane fouling, accelerated startup times, and enhanced system stability. Despite these achievements, there are still issues that hinder widespread use, such as membrane fouling exacerbated by hydrophobic anammox metabolites, sensitivity to low temperatures (≤10 °C), and the persistent challenge of suppressing nitrite-oxidizing bacteria (NOB), which compete for the essential nitrite substrate. To enable cost-effective, energy-efficient, and environmentally sustainable large-scale applications, future research directions will focus on creating cold-tolerant anammox strains, advanced anti-fouling membranes, and AI-driven process optimization. Full article

Following on from a circular economy in water, membrane technologies can play a role in resource recovery and high-quality water production but should also consider membrane industry circularity. Anaerobic membrane bioreactors (AnMBRs) are being used for advanced wastewater treatment, and their applications are growing due to advantages like lower sludge volume, better permeate quality, and the generation of biogas. High-Rejection (HR) AnMBRs retain a higher fraction of dissolved and particulate components to further promote resource recovery and obtain improved effluent quality. With the development of membrane technologies, end-of-life (EOL) membrane recycling is emerging for various applications. The feasibility of transforming EOL Reverse Osmosis (RO) membranes into ultrafiltration (UF)- and nanofiltration (NF)-like membranes and applying these membranes to submerged HR-AnMBR applications was evaluated. A small pilot AnMBR with granular biomass was operated with EOL RO membranes converted to submerged UF- and NF-like membranes and compared to commercial microfiltration (MF) membranes. UF- and NF-like plates were constructed, characterized, and introduced step-by-step into the AnMBR by the substitution of MF plates. A chemical oxygen demand (COD) removal study showed that while 77% removal of COD was possible with MF membranes, improved COD removal (i.e., 81.40% and 88.39%) was achieved using UF-like and NF-like membranes, respectively. Because of the higher retention of salts of the NF-like membrane, the salinity in the membrane bioreactor increased from 1300 to 1680 µS·cm⁻¹ but stabilized quickly and without a negative impact on system performance. Even without cleaning, minimal fouling and flux decline were observed for all tested configurations thanks to the use of granular biomass and low permeation flux. Permeate flux in the case of the NF-like membrane was slightly lower due to the required higher pressure. The present study demonstrated that the EOL-RO membranes may find applications in HR-AnMBRs to achieve superior permeate quality and move toward circular membrane processes. Full article

This study investigates membrane fouling control in a submerged anaerobic ceramic membrane bioreactor (AnCMBR) treating high-strength food wastewater (chemical oxygen demand (COD): 10–30 g/L). A hybrid strategy combining mechanical cleaning via a moving rubber blade (MRB) (termed anaerobic ceramic blade MBR (AnCBMBR)) with intermittent salt-assisted backwash (SAB) was tested to manage transmembrane pressure (TMP) and sustain treatment performance. During more than 300 days of field operation, MRB alone maintained stable TMP below 0.15 kg_f/cm² without backwashing, achieving more than 90% COD removal at a very short hydraulic retention time (HRT) of 1–2 days. Introducing intermittent SAB further stabilized operations and enhanced total phosphorus (T-P) removal by facilitating struvite formation through the interaction of MgCl₂ and phosphorus in the reactor. The AnCBMBR system demonstrated reliable, long-term fouling control and treatment efficiency, even under high organic loads, proving its viability for small-scale facilities managing concentrated food wastewater. This study advances practical strategies for sustainable anaerobic MBR operation under challenging industrial conditions. Full article

This study assesses the impact of hydraulic retention time (HRT) on the performance of an anaerobic dynamic membrane bioreactor (AnDMBR) system using a carbon fabric membrane for treating high-strength wastewater. The evaluation of AnDMBR performance encompasses the removal of soluble chemical oxygen demand (sCOD), biogas/methane production, and membrane fouling. The average influent sCOD concentration was 11,814 ± 1064 mg/L, with two HRT applications at 8 and 5 days and high biomass concentration (MLVSS 14,600 ± 500 mg/L). An impressive sCOD removal efficiency exceeding 98% was achieved throughout the operation period. The AnDMBR system exhibited the highest biogas production, reaching 4.33 ± 0.51 L/day, with a methane content of approximately 67.77 ± 2.9% during the 5-day HRT stage. Transmembrane pressure (TMP) increased gradually at the 8-day HRT stage, leading to membrane fouling, whereas fouling occurred more rapidly at the 5-day HRT stage. Biomass analysis showed minimal variations in MLVSS, extracellular polymeric substance (EPS), and soluble microbial product (SMP) concentrations (protein and carbohydrate) across both HRT application stages. This study suggests that the AnDMBR system can be adopted effectively for treating high-strength wastewater, maintaining high COD removal efficiency and biogas production with 5-day HRT. Full article

This study explores AnMBR technology as a promising method for treating wastewater from the meat-processing industry by analysing its characteristics and impact under continuous feeding. The solids were retained, utilising an ultrafiltration membrane with a pore size of 0.2 µm, and the efficacy of reducing the organic load was evaluated. Although the COD removal rate decreased from 100% at an OLR of 0.71 g/(L*d) to 73% at an OLR of 2.2 g/(L*d), maximum methane yields were achieved at the highest OLR, 292.9 Nm³/t (COD) and 397.8 Nm³/t (VS) per loaded organics and 353.1 Nm³/t (COD) and 518.7 Nm³/t (VS) per removed organics. An analysis of the microbial community was performed at the end of the experiment to assess the effects of the process and the substrate on its composition. The AnMBR system effectively converts meat-processing wastewater into biogas, maintaining high yields and reducing the loss of dissolved methane in the permeate, thanks to a temperature of 37 °C and high salt levels. AnMBR enables rapid start-up, efficient COD removal, and high biogas yields, making it suitable for treating industrial wastewater with high organic loads, enhancing biogas production, and reducing methane loss. Challenges such as high salt and phosphate levels present opportunities for a wider use in nutrient recovery and water reclamation. Full article

The presence of pharmaceutical compounds, including iodinated contrast media (ICM), in aquatic systems poses significant ecological and health risks due to their biological activity at low concentrations. This study investigated the removal efficiency of three selected ICM—diatrizoate, iohexol, and iodipamide—from synthetic hospital wastewater using anaerobic membrane bioreactors (MBRs) operated at varying sludge ages of 40, 70, and 100 days. The results indicated that the performance of the MBRs in removing organic compounds improved with increased sludge age. Diatrizoate exhibited the highest removal efficiency, achieving 72% at a sludge age of 40 days and nearly 90% at 70 and 100 days, with no substantial differences between the two higher sludge ages. In contrast, iohexol and iodipamide demonstrated relatively low and inconsistent removal efficiencies, reaching a maximum of 40%, with no observable dependency on sludge age. The findings underscore the importance of optimizing sludge age in biological treatment processes for effective ICM removal. Full article

This review provides a comprehensive overview of the advancements and challenges of anaerobic digestion technology in waste stream treatment plants under the framework of the circular economy, emphasizing its role in achieving “dual carbon” goals. As climate change intensifies, with waste stream treatment contributing significantly to global emissions, there is a pressing need to optimize energy efficiency and reduce carbon outputs in this sector. Anaerobic digestion is highlighted as a solution for converting organic waste into renewable biogas and digestate, enabling energy self-sufficiency and reducing greenhouse gasses. The study highlights that anaerobic digestion enables the conversion of organic waste into renewable biogas and nutrient-rich digestate, facilitating energy self-sufficiency and significant reductions in GHG emissions. Successful implementations, such as in Weifang, China, demonstrate the feasibility of upgrading biogas into biomethane for local energy use. Advanced technologies like bioelectrochemical methanation and membrane bioreactors enhance biogas production efficiency, while co-digestion proves effective even in challenging conditions. Despite these advancements, the review identifies critical challenges, including high investment costs, technical inefficiencies, and regulatory barriers, particularly in developing countries. This study provides insights into integrating anaerobic digestion with circular economy principles and offers a foundation for future policies and research aimed at achieving carbon neutrality and sustainable waste management. Full article

Bioplastics are designed to degrade at the end of their lifecycle, but effective management of their end-of-life phase and integration into existing organic waste management systems remain significant challenges. Some bioplastics decompose under anaerobic conditions, with the anaerobic digestion (AD) process being a potential solution for their disposal. AD is a promising technology for valorising organic wastes, enabling biomethane production, reducing carbon footprints, and promoting product circularity. This study focuses on evaluating the continuous co-digestion of bioplastics with mixed sludge from an urban wastewater treatment plant (WWTP). Polyhydroxybutyrate (PHB) was the selected bioplastic, as various studies have reported its high and rapid degradation under anaerobic mesophilic conditions. PHB’s biodegradability under typical WWTP anaerobic digestion conditions (35 °C, 20-day retention time) was assessed in batch tests and the results indicate that PHB degradation ranged from 68 to 75%, depending on particle size. To further explore the potential of AD for PHB valorisation, the feasibility of anaerobic co-digestion of PHB with WWTP sludge was tested on a continuous laboratory scale using two digesters: a conventional digester (CSTR) and an anaerobic membrane bioreactor (AnMBR). The results indicated complete degradation of PHB, which led to higher biomethanisation percentages in both digesters, rising from 58% to 70% in the AnMBR and from 44% to 72% in the CSTR. The notable increase observed in the CSTR was attributed to changes in microbial populations that improved sludge biodegradability. Full article

Ubiquitous microplastics (MPs) severely affect the efficiency of anaerobic membrane bioreactors (AMBR) for wastewater treatment and energy recovery by inhibiting the metabolic activity of anaerobic microorganisms. The electrochemical system can not only accelerate waste metabolism but also improve microbial resistance by promoting interspecies electron transfer within the system, which has broad application potential in the remediation of MPs wastewater. This paper attempts to evaluate the effect of electrical stimulation on the efficiency of biological wastewater treatment processes containing MPs employing an electrochemical system coupled to an anaerobic membrane bioreactor (ECAMBR). The results showed that although MP exposure inhibited methanogenic performance, electrical stimulation effectively alleviated this inhibitory effect. Further analysis showed that microplastics increased cell damage and affected enzyme activity, but electrical stimulation could affect the stress response of microorganisms, leading to changes in their cell viability and enzyme activities. The 16S-rRNA sequencing indicated that the highest abundance of hydrolytic–acidogenic bacteria Firmicutes and Bacteroidota was found at the phylum level, whereas at the genus level, it was Christensenellaceae_R-7_group, and methanogens were dominated by Methylomonas, Methyloversatilis, and Methylobacter. Functional prediction analysis indicated that carbohydrate metabolism, amino acid metabolism, and energy metabolism were the dominant metabolic pathways and that electrical stimulation could enhance their activities. This study demonstrated the important role of electrochemical stimulation in the remediation of wastewater containing high concentrations of MPs. Full article

The production of microbial proteins (MPs) has emerged as a critical focus in biotechnology, driven by the need for sustainable and scalable alternatives to traditional protein sources. This study investigates the efficacy of two experimental setups in producing MPs using the nitrogen-fixing bacterium Klebsiella oxytoca M5A1. K. oxytoca M5A1, known for its facultative anaerobic growth and capability to fix atmospheric nitrogen, offers a promising avenue for environmentally friendly protein production. This research compares the performance of a simple bubble column (BC) bioreactor, which promotes efficient mixing and cross-membrane gas transfer, with static fermentation, a traditional method lacking agitation and aeration. The study involved the parallel cultivation of K. oxytoca M5A1 in both systems, with key parameters such as microbial growth, glucose utilization, protein concentration, and metabolite profiles monitored over a 48 h period. The results indicate that the BC bioreactor consistently outperformed static fermentation regarding the growth rate, protein yield, and glucose utilization efficiency. The BC exhibited a significant increase in protein production, reaching 299.90 µg/mL at 48 h, compared to 219.44 µg/mL in static fermentation. The organic acid profile reveals both synthesis and utilization regimes of varying patterns. These findings highlight the advantages of the BC bioreactor for MP production, particularly its ability to maintain aerobic conditions that support higher growth and yield. Full article

In the framework of a circular economy, wastewater treatment should be oriented toward processes that allow the recovery of the resources present in the wastewater while ensuring good effluent quality. Nitrogen recovery is usually carried out in streams concentrated in this nutrient because these high concentrations facilitate nitrogen valorization. On the other hand, the mainstream of a wastewater treatment plant (WWTP) has a high potential for nitrogen recovery, but it is not usually considered because it is hard to manage due to its low nitrogen concentration. To solve this problem and facilitate the recovery of nitrogen in the mainstream, this work proposes ion exchange with zeolites as a stage of ammonium concentration, to provide a nitrogen-concentrated stream that could be valorized by another technology, while obtaining a nitrogen-free effluent. The working stream, the permeate of an AnMBR process in the mainstream, has suitable characteristics to be treated in an ion exchange column (free of suspended solids and with very low organic matter content). To this end, the effect of the working flow rate (17.5 to 4.4 BV/h) and the ammonium concentration (54 to 17 mg NH₄-N/L) on the adsorption capacity of the zeolite in the loading phase was evaluated. The adsorption curves were fitted to three mathematical models: Thomas, Bohart–Adams, and Yoon–Nelson. The effect of the regeneration flow rate (from 8.7 to 2.2 BV/h) and the regenerant concentration (NaOH at 0.2, 0.1, and 0.05 M) on regeneration capacity and efficiency were also studied. A novel control strategy based on effluent conductivity was used in both phases to control the duration of the adsorption and regeneration phases. Full article