Next Article in Journal
Increased Arctic NO3 Availability as a Hydrogeomorphic Consequence of Permafrost Degradation and Landscape Drying
Previous Article in Journal
Effects of Nitrogen Fertilization on Weed Flora and Productivity of Soybean [Glycine max (L.) Merr.] Crop
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:

Technologies for Biological and Bioelectrochemical Removal of Inorganic Nitrogen from Wastewater: A Review

Department of Biological and Agricultural Engineering, North Carolina State University, Raleigh, NC 27606, USA
Department of Mechanical and Aerospace Engineering, North Carolina State University, Raleigh, NC 27606, USA
Author to whom correspondence should be addressed.
Nitrogen 2022, 3(2), 298-313;
Submission received: 1 April 2022 / Revised: 19 April 2022 / Accepted: 12 May 2022 / Published: 14 May 2022


Water contamination due to various nitrogenous pollutants generated from wastewater treatment plants is a crucial and ubiquitous environmental problem now-a-days. Nitrogen contaminated water has manifold detrimental effects on human health as well as aquatic life. Consequently, various biological treatment processes are employed to transform the undesirable forms of nitrogen in wastewater to safer ones for subsequent discharge. In this review, an overview of various conventional biological treatment processes (viz. nitrification, denitrification, and anammox) have been presented along with recent novel bioelectrochemical methods (viz. microbial fuel cells and microbial electrolysis cells). Additionally, nitrogen is an indispensable nutrient necessary to produce artificial fertilizers by fixing dinitrogen gas from the atmosphere. Thus, this study also explored the potential capability of various nitrogen recovery processes from wastewater (like microalgae, cyanobacteria, struvite precipitation, stripping, and zeolites) that are used in industries. Further, the trade-offs, challenges posed by these processes have been dwelt on along with other biological processes like CANON, SHARON, OLAND, and others.

1. Introduction

The drastic increase in world population has led to intense industrialization and subsequent generation of wastewater from various sources. The generated wastewater is highly nutrient-rich in terms of ammonia, nitrate, nitrite, and other pollutants which need treatment before being discharged. Unless adequately treated, the nitrogenous pollutants from the wastewater can lead to eutrophication, cause methemoglobinemia or blue-baby syndrome, lead to oxygen depletion, aquatic toxicity, and have many other detrimental impacts on the environment [1,2,3,4]. Also, the aquaculture industry with intensive aquaculture practices further adds to the generation of wastewater saturated with nitrogenous contaminants [5,6]. The removal of these nitrogenous entities from wastewater can be conducted by various biological and physicochemical methods. However, the biological processes are more efficient and relatively cost-effective and hence globally adopted and preferred [7,8]. The biological methods of pollutant removal are generally employed for wastewater with low nitrogen concentration, with nitrification and denitrification being the most conventionally used ones. However, other processes of partial or combined nitrification/denitrification can also be used for nitrogenous removal [9,10,11,12]. Such avenues have been discussed in detail in this study.
In addition to this, energy is the most critical challenge that humanity of this century is facing. The challenges in the domain of energy scarcity have been explored by many studies worldwide [13,14,15,16,17,18,19,20,21]. These two challenges of nitrogenous contaminant removal and energy paucity can be simultaneously addressed by bioelectrochemical methods of wastewater treatment [22,23]. These novel methods also consider that “misplaced resources” is the befitting epithet that can be attributed to waste. This is since they harness bioelectricity from wastewater while providing green solutions to urban problems like the removal and recovery of nitrogenous contaminants from water.
This review focuses on the various conventional processes of biological methods of removal along with their working mechanism, microorganisms involved, and process technologies utilized. Additionally, novel bioelectrochemical methods of removal have also been discussed along with processes of nitrogen recovery from wastewater. This study can aid wastewater engineers and water professionals in decision-making and adopting strategies depending on the prevailing scenario.

2. Conventional Biological Treatment Processes

2.1. Nitrification

Nitrification includes two successive biological oxidation steps: (1) oxidation of NH4+ to NO2 and (2) conversion of NO2 to NO3. The first step is carried out by ammonium oxidizing bacteria (AOB, e.g., Nitrosomonas) with catalyzation by ammonia monooxygenase (AMO) [24,25,26,27] and hydroxylamine oxidoreductase (HAO) [28,29], along with the formation of the intermediate product hydroxylamine (NH2OH). The second step of nitrification, which entails the formation of NO3, is carried out by nitrite-oxidizing bacteria (NOB, e.g., Nitrobacter) in the presence of molecular oxygen. Catalyzation of this step is performed by nitrite oxidoreductases (NXR) and nitrite-oxidizing systems. NXR is an oxidation enzyme that occurs in Nitrobacter [30]. The reaction pathway of this process can be represented by: Nitrosomonas:
Nitrosomonas: NH4+ + 1.5O2 → NO2 + H2O + H2+
Nitrobacter: NO2+ 0.5O2 → NO3
Overall: NH4+ + 2O2 → NO3 + H2O + 2H+
The carbon requirements of nearly all nitrifiers are met by CO2 fixation of the Calvin cycle, and their only source of energy is generated during the oxidation of ammonia [31]. As reported by researchers, 80% of this produced energy is consumed for CO2 fixation, and for each fixed carbon atom, nitrifiers need to oxidize approximately 35 molecules of NH3 or 100 molecules of NO2 [32,33]. Due to this sluggish growth rate of nitrifiers, their microbial colonization can take 4–8 weeks depending on external parameters such as water temperature, alkalinity, salinity, and other stresses [34,35].
Parallel as well as in contrast to the other wastewater treatment technologies used, nitrification comes with its own set of advantages and disadvantages. Cost-effectiveness of the process has trade-off in the form of the slow rate of reaction, the requirement of controlling oxygen concentration and the impact of other parameters on nitrification activity, and long hydraulic retention time (HRT) and long solids retention time (SRT). To diminish the energy input of this process, many studies [30,36,37] are being conducted in the domain of partial nitrification, which has an upper hand over conventional nitrification processes in the form of: (i) 40% reduction in chemical oxygen demand (COD); (ii) twice the rate of nitrite reduction in the following denitrification process; (iii) 300% reduction in biomass; and (iv) 20% CO2 emission in the subsequent denitrification process. These studies also report that the partial nitrification process favors the growth and activity of AOB at the cost of inhibiting NOB (with the help of inhibitors like sulfide, hydroxylamine, salt, chlorate, hydrazine, etc. [38]. This is accomplished with consequent positive impacts of parameters like: (i) concentration of dissolved oxygen of about 1.5 mg/L (DO) [39]; (ii) temperature higher than 25 °C [40]; (iii) optimum pH range of 7.5 to 8.5 [36]; and (iv) optimum sludge retention time of 5 days (SRT) [41].

2.1.1. Participation of Microorganisms in Nitrification

The two-step process of aerobic nitrification is carried out by two phylogenetically unrelated groups, AOB and NOB. These chemolithoautotrophic microorganisms work in tandem to convert ammonia to nitrite in the nitrification system Equations (1)–(3). Their syntrophic association aids each other in the context of energy: AOB produces the substrate (nitrite) that NOB can efficiently use and thus makes do with the poor energy generated during nitrite oxidation to nitrate. On the contrary, NOB can protect AOB from the toxicity of generated nitrite by inhibiting its buildup [42].
AOBs are characterized by multi-layered cell walls with flagella as their locomotory organ. Majorly, five genera of AOBs in two different subclasses of β and γ-Proteobacteria have been reported by researchers [43,44]. The β-subclass of AOB includes Nitrosomonas (e.g., Nitrosococcus mobilis), Nitrosospira, Nitrisovibrio, and Nitrosolobus [45]. On the other hand, literature reports the detection of Nitrosococcus clusters belonging to the γ-subclass [46,47]. Though more than 25 AOB species have been reported, nonetheless, Nitrosomonas and Nitrobacter remain the most widely studied [48,49]. The key enzymes of AOB involved in the conversion of ammonia to nitrite are AMO and HAO. AMO is a membrane-bound hetero-trimeric copper enzyme, whereas HAO is positioned in the periplasm [36].
NOBs are more diverse and prevalent than AOBs in Proteobacteria [47]. Literature reports eight species of NOB and four phylogenetically varied groups [50]. The genera Nitrococcus and Nitrobacter have been allotted to the α- and γ-subclasses of Proteobacteria, respectively. Until recently, Nitrobacter was considered to be the most important one. However, recent studies have reported Nitrospira to be the most prevalent NOB in wastewater treatment plants (WWTPs) as well as drinking water and soil systems [49,51]. The key enzyme that mediates the conversion of nitrite to nitrate via NOB is NXR in Nitrobacter and the nitrite-oxidizing system in Nitrococcus, Nitrospina, and Nitrospira.

2.1.2. Process Technologies Used in Nitrification

Literature suggests the use of single-stage process in a reactor for nitrification technologies with a 200,000 m3/day step-fed activated sludge process [36,52,53,54]. Altering aeration patterns (varying of cycle frequency vs. continuous and low vs. high) to influence the N2O emission/production during nitrification has been observed to be a key parameter in reactor setups [55,56,57]. Additionally, membrane-biofilm reactor (MBFR)/membrane-aerated biofilm reactor (MABR) is an effective technology for nitrogen removal from wastewater. This process diffuses gases (viz. O2, H2, and CH4) that mediate as electron donors/acceptors through a hydrophobic and permeable membrane onto a biofilm that is colonizing on the surface of the membrane [58]. MABR can also be altered to lead to the formation of layered biofilm structures with oxygen-controlled systems.

2.2. Denitrification

Denitrification is the process whereby nitrate is converted to nitrogen gas as the end product. It is generally the subsequent step of nitrification and is mostly performed by heterotrophic denitrifiers but can also be carried out by a limited number of autotrophic nitrifiers [5,59]. Various parameters play a major role in this process viz. maintenance of anoxic conditions, supply of carbon source, and subsequent treatment of the treated wastewater. The use of an external organic source of carbon is needed as external carbon can act as an electron donor needed for the growth of denitrifiers. The external sources of carbon include glucose, methanol, ethanol, succinate, and acetate [60,61]. The denitrification process of converting nitrate to nitrogen gas follows the following reaction [62]:
5CH2O + 4NO3 → 2N2 + 5CO2 + 3H2O + 4OH
where CH2O represents an organic compound (carbon and energy source) and the denitrifiers use up nitrate instead of oxygen as electron acceptors. Denitrification often needs a posttreatment process, as the various external carbon sources often lead to turbidity (due to the presence of excessive biomass) in the treated water. Additionally, there is always a chance of the generation of the greenhouse gas nitrous oxide, which needs to be monitored [63].

2.2.1. Participation of Microorganisms in Denitrification

Microorganisms involved in this process include both autotrophic and heterotrophic bacteria, though the former is limited in number regarding its applicability than the latter. Additionally, the autotrophic bacteria display stunted growth and biomass generation with inefficient assimilation [64]. The working mechanism of autotrophic denitrifiers involves the oxidation of inorganic matter with the transport of discharged electrons to nitrate as a terminal acceptor. Rezvani et al. reported two types of autotrophic denitrifiers: hydrogen-based (Micrococcus denitrificans and Paracoccus denitrificans) and sulfur-based (Thiobacillus denitrificans and T. thioparus) [64]. In wastewater treatment processes, Thiobacillus sp. is the most widely observed autotrophic denitrifier [61].
Among the heterotrophic denitrifiers, the most widely observed are Pseudomonas and Bacillus [64]. These denitrifiers need strict anoxic conditions (with near-zero dissolved oxygen concentration of the wastewater), consume nitrate as the terminal electron acceptor, and harness the carbon from complex organic molecules. It has also been reported that these denitrifiers need smaller reactor volumes for effective bioconversion, thereby diminishing the cost factor associated with it. As reported in the literature, the most encountered denitrifiers in wastewater treatment units are members of the genera Thauera, Paracoccus, Comamonas, Denitratisoma, and the family Comamonadaceae [65,66,67].

2.2.2. Process Technologies Used in Denitrification

The various process technologies in denitrification include simultaneous nitrification and denitrification (SND) and shortcut nitrification and denitrification (SCND). The former is usually applied for wastewaters with a low C:N ratio (<5) where both nitrification and denitrification occur concomitantly in an anoxic environment [68]. SND function via both physical as well as biological methods. The former functions on the principle of the gradient of dissolved oxygen in the chamber, with limited diffusion of oxygen through the developed biofilm. Here, the nitrifiers confine themselves to areas having dissolved oxygen in the range of 1–2 mg/L, whereas the denitrifiers aggregate in the strata of low dissolved oxygen (<0.5 mg/L) [69,70]. In SCND, nitrification produces nitrite as the intermediate product, which is subsequently converted to nitrogen gas by nitrite denitrification [69]. The primary benefit of this process over conventionally used processes is that oxygen and electron donors are required less in the aerobic (25% less) and anoxic (40% less) stages, respectively [71].

2.3. Anammox

Anammox or anaerobic ammonium oxidation is a recently studied energy-efficient nitrogen removal process that is gaining popularity. In this process, nitrite and ammonium are used up, resulting in the formation of nitrogen gas along with NO and N2H4 intermediates (Equation (5)). In other words, it is the denitrification of nitrite, with ammonia acting as an electron donor. The nitrite can be gained from the oxidation of ammonium (nitrification) as well as partial denitrification of nitrate. Additionally, the anammox bacteria metabolize by using CO2 as their only source of carbon and nitrite as an electron donor (Equation (6)) [7]. The nitrification/denitrification can consume up to 100% of the organic content of the wastewater. Nitrification/anammox can produce methane gas which can aid in bioenergy recovery from wastewater treatment [72]. The first full-fledged anammox reactor was established for the treatment of reject water in Rotterdam, Netherlands, and has ever since gained wide popularity and application [30].
NH4+ + NO2 → N2 + 2H2O
CO2 + 2NO2 + H2O → CH2O + 2NO3

2.3.1. Participation of Microorganisms in Anammox

Anammox bacteria possess a distinct modus operandi for survival: they consume ammonia when oxygen is unavailable. The most prolific group of bacteria that plays a key role in this process is Planctomycete. It thrives in freshwater, seawater as well as in terrestrial environments where anammox occurs. Apart from this, other characteristic anammox bacteria include Brocadia anammoxidans and Kuenenia stuttgartiensis [73]. According to Rahimi et al., around nineteen species and largely six genera of anammox bacteria have been widely studied and identified [30]. Additionally, van Niftrik and Jetten reported the enrichment of four genera viz. Candidatus brocardia, Ca. kuenenia, Ca. anammoxoglobus, and Ca. jettenia from natural marine ecosystems [74]. Though researchers have not been able to detect the presence of pure culture among the anammox bacteria, nonetheless, studies have successfully endeavored to enrich anammox culture as monospecies (like Ca. scalindua) under controlled conditions [75].

2.3.2. Process Technologies Used in Anammox

Anammox processes were first reported by Mulder et al. when employing a denitrifying fluidized bed reactor to treat the wastewater generated from a methanogenic reactor [76]. Broda had also outlined two thermodynamically probable molar ratios of ammonium and nitrite (1:1 and 1:1.67) for the oxidation of ammonia under a limited supply of oxygen [77]. However, as various studies from the literature have reported, this stoichiometry can also range from 0.5 to 4 in accordance with varying functioning conditions and reactor technologies employed [78,79].
Recently studied anammox process technologies include SNAD (simultaneous partial nitrification, anammox, and denitrification) and DEAMOX (denitrifying ammonium oxidation). SNAD process works for the concomitant removal of organic carbon along with inorganic nitrogen. Chen et al. had reported that SNAD operates by employing three bacterial communities viz. aerobic AOB, anammox, and denitrifying bacteria inside a single-reactor unit under scarce oxygen availability [80]. On the other hand, DEAMOX operates as a combination of anammox with partial denitrification by treating ammonia and nitrate-containing effluents. These two processes working in tandem result in high nitrogen removal rates (93.6%), irrespective of variation of ambient temperatures [81]. This process has many economic and technological advantages over other processes as well, such as low production of sludge and its subsequent management, decreased aeration and organic carbon requirement, and a substantial decrease in the emission of greenhouse gases (CO2 and N2O) [82].

3. Bioelectrochemical Systems

Apart from the conventional biological methods of nitrogen removal from wastewater, there is an increased interest currently in the various innovative bioelectrochemical alternatives. Such systems directly convert chemical energy present in the chemical bonds of the organic matter into electricity via electrochemically active bacteria (EAB), e.g., electricigens, and have potential applications for simultaneous nitrogen and other contaminants removal from wastewater with bioenergy recovery [22,23]. Here, the electrons are shifted to the anode after the oxidation of the pollutants, thereby removing them due to organic matter decomposition. Bioelectrochemical systems can be of two major types, conditional on the cathodic reaction: microbial fuel cells (MFCs; Figure 1A) and microbial electrolysis cells (MECs; Figure 1B). The former generates electrical power as the anodic oxidation works in tandem with cathodic reduction where electron acceptors with high reduction potential get reduced. The latter needs an externally supplied voltage (>0.2 V) under a biologically conducive environment, where EAB oxidizes the organic matter to produce CO2, electrons, and protons. Subsequently, the EAB transfer the electrons to the anode and release the protons to the wastewater getting treated. When acetate is used as a substrate, the electrode reactions occurring are as follows [83,84]:
For MFC-
Anodic reaction: CH3COO + H2 → 2CO2 + 2H+ + 8e
Cathodic reaction: O2 + 4e + 4H+ → 2H2O
For MEC-
Anodic reaction: CH3COOH + 2H2O → 2CO2 + 8e + 8H+
Cathodic reaction: 8H+ + 8e → 4H2
Denitrification by bioelectrochemical systems can be performed in the cathodic chamber of the cells. Here, EAB in the anode oxidizes the substrate (like acetate) and supplies electrons which are utilized by the EAB at the cathode to perform denitrification. A tubular reactor MFC designed by Clauwaert et al. used acetate as an electron donor to perform denitrification with simultaneous bioelectricity production. The stepwise nitrate reduction reactions in this denitrification process are as follows [85]:
NO3 + 2e + 2H+ → NO2 + H2O
NO2 + e + 2H+ → NO + H2O
NO + e + H+ → 0.5N2O + 0.5H2
0.5N2O + e + H+ → 0.5N2 + 0.5H2O
2NO3 + 12H+ + 10e → N2 + 6H2O
Zhao et al. had studied the performance of denitrifying MFCs with nitrite as an electron acceptor in the cathode with successful nitrite and total nitrogen removal [86]. They had also observed the predominance of the phylum Proteobacteria (35.72%) along with Thiobacillus, Afipia, and Devosia. Additionally, Zhu et al. and Zekker et al. had reported the occurrence of simultaneous nitrification-denitrification and anammox-denitrification, respectively, in MFCs to enhance the removal of nitrogenous contaminants from wastewater with concomitant and enhanced bioelectricity recovery [87,88]. Nitrogen removal by bioelectrochemical systems offers various benefits like diminished environmental impact, ability to remove specific pollutants, relatively inexpensive operating factors etc. Nonetheless, this being a novel process, we are still understanding the microbial kinetics and extracellular activities of the EAB, and further research in the context of engineering design and biotechnology will lead to more effectiveness.

4. Other Treatment Processes for Nitrogen Removal

Apart from the conventional biological and the novel bioelectrochemical processes discussed above, researchers are now studying other innovative microbial potentials as well. This has become possible due to the ushering of new findings that the conversion of ammonium from wastewater to dinitrogen gas does not demand the absolute oxidation to nitrate that is consequently succeeded by heterotrophic denitrification. The following are a few such processes that explore the microbial abilities of the bacterial communities that can occur even during incomplete/partial oxidation of ammonium to nitrogen gas.

4.1. NOx Process

During the NOx process, the denitrification activity of bacteria similar to Nitrosomonas is controlled and stimulated by the addition of trace amounts of nitrogen oxides. The ratios of ammonium to nitrogen oxide that are added range from 1000:1 to 5000:1 [89,90]. With NOx supply under completely oxic conditions, the Nitrosomonas-like bacteria can nitrify as well as denitrify concomitantly, with N2 being the primary product. This process brings about 40% conversion of the ammonia present to nitrite and decreases the oxygen demand during the nitrification process by 50% with succeeding denitrification consuming less COD [7]. This is because here nitrite acts as the terminal electron acceptor to complete the process. The integrated nitrification-denitrification steps without NOx supply are represented below by Equations (16)–(18) and that with NOx supply by Equations (19)–(21). Here, the [H] denotes the reducing equivalents as provided by the external C-source. However, the stoichiometry and results might be influenced by the composition of the wastewater studied [91].
Conventional reactions:
Nitrification: 3NH4+ + 6O2 → 3NO3 + 6H+ + 3H2O
Denitrification: 3NO3 + 3H+ + 15[H] → 1.5N2 + 9H2O
Total: 3NH4+ + 6O2 + 15[H] → 1.5N2 + 3H+ + 12H2O
Reactions with NOx supply:
Nitrification: 3NH4+ + 3O2 → N2 + NO2 + 4H+ + 4H2O
Denitrification: NO2 + H+ + 3[H] → 0.5N2 + 2H2O
Total: 3NH4+ + 3O2 + 3[H] → 1.5N2 + 3H+ + 6H2O

4.2. Completely Autotrophic Nitrogen Removal over Nitrite (CANON)

The CANON process is an integration of partial nitrification and anammox processes [92,93,94]. The name of this process derives from the sequential working mechanism of the two sets of bacterial communities in a single and aerated reactor: Nitrosomonas-like aerobic and Planctomycete-like anaerobic bacteria (Equations (22) to (24)). These bacteria work in tandem to oxidize ammonia to nitrite (by nitrifiers), thereby consuming oxygen and subsequently creating an anoxic environment for anammox to proceed. This process is relatively sensitive to operational parameters viz. dissolved oxygen, the thickness of the biofilm developed, temperature, and loading rates of nitrogen [95]. This process has the economic advantage of requiring only a single reactor for operation.
NH4+ + 0.75O2 +HCO3 → 0.5NH4+ + 0.5NO2 + CO2 + 1.5H2O
NH4+ + 1.32NO2 + 0.066HCO3 + 0.13H+ → 0.066CH2O0.5N0.15 +1.02N2 + 0.26NO3 + 2.03H2O
NH4+ + 0.85O2 → 0.44N2 + 0.11NO3 + 1.43H2O + 0.14H+

4.3. Single-Reactor High-Activity Ammonium Removal over Nitrite (SHARON)

The SHARON process is a type of partial nitrification process that was initially conceptualized for ammonia removal by the nitrite path [96,97]. Here, both autotrophic nitrification and heterotrophic denitrification occur simultaneously in one SHARON reactor with sporadic aeration. This process is however not conducive for all types of wastewaters as it requires high temperature and works well for the elimination of high ammonium concentration (>0.5 g/L). Additionally, methanol needs to be added during the denitrification step of this process to better regulate pH and alkalinity production, required to balance the acidifying consequence of nitrification step. Equations (25)–(27) represent the stoichiometry of this process [7]:
2NH4+ + 3O2 → 2NO2 + 2H2O + 4H+
2NO2 + 4.8 g COD + 2H+ → N2 + 1.8 g sludge
2NH4+ + 3O2 + 4.8 g COD → N2 + 2H+ + 1.8 g sludge

4.4. Oxygen-Limited Autotrophic Nitrification and Denitrification (OLAND)

The OLAND process has been upheld by researchers as a one-step removal of ammonium without any supply of COD [98]. Though it is widely accepted that Nitrifiers are the responsible microorganisms in this process, nonetheless, studies are still being conducted to completely comprehend the mechanisms involved. Nevertheless, it appears to be based on either the CANON concept or the NOx process, i.e., the functioning of aerobic and anaerobic ammonia oxidizers or that of nitrifying denitrifiers with NOx being available [91]. Here, both the conversion efficiency and nitrogen loading rates are quite stunted [31,99]. The OLAND process has been represented by the following reactions [7]:
0.5NH4+ + 0.75O2 → 0.5NO2 +0.5H2O + H+
0.5NH4+ + 0.5NO2 → 0.5N2 + 2H2O
NH4+ + 0.75O2 → 0.5N2 + 1.5H2O + H+

4.5. Aerobic Deammonification

Aerobic deammonification is yet another single-step process of ammonium removal that is independent of COD supply. In this process, a part of the ammonium is converted to dinitrogen gas and another part to nitrate [91,100]. This process majorly works on the concept of CANON mechanism, where nitrifiers and anaerobic ammonia oxidizers collaborate under limited oxygen supply. However, the nitrogen loading, as well as removal rates, are stunted here. The following reactions illustrate the aerobic deammonification process:
NH3 + O2 → NH2OH + H2O → HNO2
HNO2 → 0.33N2 + 1.33H2O + 0.33NO2
NH3 + O2 → 0.33N2 + 1.33H2O + 0.33NO2

5. Processes of Nitrogen Recovery

Nitrogen is one of the most important building blocks of the formation of proteins and DNA. Though we have an abundance of gaseous nitrogen in the atmosphere, yet except for some bacteria, it cannot be utilized by most living organisms. To be utilized and to cater to the growing global human population in the form of fertilizers, it is imperative for nitrogen to be converted into its reactive forms such as ammonia, nitrate, nitrite, and ammonium. This is where recovery of nitrogen from wastewater can play an effective role to support agriculture as well as render wastewater fit for surface discharge at the end of the line to be reused as reclaimed water. In the following sections, nitrogen recovery by biological as well as chemical methods has been discussed.

5.1. Nitrogen Recovery by Microalgae and Cyanobacteria

Microalgae and cyanobacteria are potent alternatives for the biological treatment of wastewater with subsequent nitrogen recovery. As illustrated in Figure 2, microalgae and cyanobacteria photosynthetically produce O2 during the treatment of nutrient-rich wastewater. This generated O2 is subsequently used up by bacteria to disintegrate the organic matter present in wastewater into simpler inorganic molecules [101,102]. These inorganic contaminants are subsequently eliminated during the tertiary treatment stage of wastewater treatment by the microalgae and bacteria so that the treated water can be safely discharged. These microalgae and bacteria assimilate nitrate and ammonia, which further get converted to biomass rather than being released to the environment in the form of gaseous nitrogen by the process of dissimilatory nitrate reduction. Cyanobacteria and microalgae do not possess structural carbon (such as cellulose; with C:N = 5 to 20), which renders them more competent in wastewater treatment and higher biomass production compared to complex plants (C:N = 18 to 120) [11]. For optimum performance of microalgae and cyanobacteria in this process, various parameters such as pH, temperature, light, etc., require control and monitoring [11,12,103]. The microalgal biomass generated from this process can be utilized to produce fertilizer, bioenergy, animal feed, pharmaceutical products, etc.

5.2. Nitrogen Recovery by Chemical Processes

5.2.1. Struvite Precipitation

Struvite precipitation is a widely applied chemical method of ammonia and phosphorous removal from wastewater along with the associated environmental problems. This is a relatively simple yet effective and eco-friendly method of nitrogen recovery. The white crystalline mineral struvite (MgNH4PO4·6H2O) consists of equimolar ratios of Mg, NH4, and PO4. It is a potent slow-release fertilizer with a low level of contaminants that is poorly soluble in water and can substitute fertilizers [104]. This (Figure 3) process mainly occurs through the following reaction:
Mg2+ + NH4+ + PO43− + 6H2O → MgNH4PO4·6H2O
This reaction is mainly impacted by two parameters viz. pH (basic pH of 9–10 is conducive) and the molar ratio of Mg:NH4:P [82]. Escudero et al. reported that a molar ratio of 1:1:1 for Mg:NH4:P can effectively remove 95% of NH4+ from anaerobically treated wastewater in a timeframe of 30 sec [105]. Many researchers have studied the formation of struvite with subsequent ammonium recapture from treated wastewater (anaerobic), manure, urine, and industrial wastewater [106,107]. However, the disadvantage associated with this process is that, since the effluents are highly saturated with ammonia, they end up using large quantity of magnesium salts for effective precipitation. This ends up increasing the cost factor, thus stunting its large-scale application in many cases. Nonetheless, many studies have also suggested a multistage chemical method of integrating struvite precipitation with ammonia stripping (which is discussed below in Section 5.2.2) for successful ammonia removal along with other contaminants like COD and phosphorous [82].

5.2.2. Stripping Process

Stripping is a chemical method of removing ammonia by creating an environment thereby NH4+ gets converted to NH3. Here, air or any other gas is forced through the wastewater so that NH3 is rendered into the gas phase based on the process of desorption. The majority of the wastewaters contain ammonia or nitrogen-containing compounds in abundance. Further, as widely accepted, nitrogen removal from wastewater in the form of ammonia has lesser economic hindrances than that of other forms of nitrogenous species [108]. The concept behind this process is that NH3 being a weak base, reacts with water (a weak acid) to generate NH4OH (in the form of ions), which get converted to ammonia gas with the addition of lime or caustic (which shoots up the pH to 10.8 or 11.5). The NH4+ from the effluents can also be eliminated from the aqueous solution by steam or in the form of biogas [109]. Thus, the four key steps of its working are: (a) conversion of NH4+ to NH3 (g); (b) diffusion of NH3 to the borderline of air-water; (c) release of the formed NH3 to the air–water interface; and (d) subsequent diffusion of NH3 to the environment. Two types of ammonia stripping towers viz. cross-flow and countercurrent (as illustrated in Figure 4). The working mechanism of the cross-flow tower involves the flow of gas (air) along with the total depth of fill, as the alkaline wastewater streams downwards. Whereas, in the countercurrent tower, the air is introduced through the bottom while the wastewater is propelled to the top of the tower. Consequently, the stripping of free ammonia from the falling water droplets into the air stream occurs, which is then released into the atmosphere [110].
To minimize the greenhouse effect the released NH3 can cause, it can also be absorbed into phosphorous acid or sulfuric acid (as ammonium sulfate) [111]. However, this process finds the widest range of applications for nitrogen recovery in the form of fertilizer (40–60% ammonium sulfate solution with diminished organic contamination) [112]. This process has the potential to aid agriculture in many areas by providing the necessary fertilizer input. Additionally, this process is not highly sensitive to pH and air temperature variation with no necessity for backwash or regeneration. Nonetheless, only NH4+ can be stripped by this technology with little effect on nitrite, COD, or phosphorous elimination from the wastewater [82].

5.2.3. Nitrogen Recovery Using Zeolite

Zeolites are compounds of hydrated aluminosilicates with SiO4 and AlO4 forming a 3-D tetrahedral network that is bridged by joint oxygen atoms. The partial substitution of Al3+ and Si4+ leads to the surplus negative surface charge offset by alkali and alkaline earth cations. These resulting cations located inside the tetrahedral network permit zeolite to exchange ions efficiently and function as an adsorbent resin in the ion exchange process. This principle is efficiently exploited during the removal of ammonium (and to some extent nitrate) [113]. Various researchers have studied the internal porosity, surface charge, cation exchange capacity (CEC), surface area and other such physicochemical features of zeolite that enable it to effectively carry out water remediation as well as act as agricultural fertilizers with eventual release of the nutrients (specifically NH4+, K+, etc.) [114,115]. Specifically, after the release of ammonium ions, NH3 can be thermally recovered from zeolite. Recently, increased focus is on integrated zeolite-anammox process for the removal of ammonium and nitrate without the need of substrate regeneration from the primary effluent of WWTPs [116,117]. However, this study has been mostly limited to university or research institute labs, and further study is needed to fully exploit this integrated system at full-scale domestic level.

6. Conclusions

The conventional processes of biological removal of nitrogenous entities from wastewater embraced mainly nitrification and denitrification. However, the discovery and applicability of the anammox process enhanced our comprehension of the nitrogen cycle and aided in utilizing the anammox microorganisms for the removal of nitrogen from wastewater highly saturated with ammonium. Further, the research and subsequent use of other nitrogen removal processes like NOx, CANON, SHARON, OLAND, and aerobic deammonification with their combinations opened new vistas with enhanced removal efficiencies in wastewater treatment. Currently, the bioelectrochemical processes are very promising alternatives in the wake of climate change and environmental sustainability. However, these too face challenges in the context of scaling up with power generation that still needs to be enhanced. Additionally, further research is needed in the domain of reaction control, ease of electron shuttle via EAB, and materials used as electrodes. In a nutshell, considering the many attributes of the various processes discussed in this study, it often appears that their applicability cannot be generalized and is case-specific depending on the end use.

Author Contributions

Conceptualization; writing—original draft preparation; writing—review and editing, and supervision, equally contributed by D.P. and A.B. All authors have read and agreed to the published version of the manuscript.


This research received no external funding.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Conflicts of Interest

The authors declare no conflict of interest.


  1. Xu, W.; Xu, Y.; Su, H.; Hu, X.; Yang, K.; Wen, G.; Cao, Y. Characteristics of Ammonia Removal and Nitrifying Microbial Communities in a Hybrid Biofloc-RAS for Intensive Litopenaeus vannamei Culture: A Pilot-Scale Study. Water 2020, 12, 3000. [Google Scholar] [CrossRef]
  2. Cheng, X.; Zhu, D.; Wang, X.; Yu, D.; Xie, J. Effects of Nonaerated Circulation Water Velocity on Nutrient Release from Aquaculture Pond Sediments. Water 2016, 9, 6. [Google Scholar] [CrossRef] [Green Version]
  3. Humphrey, C.; O’Driscoll, M.; Iverson, G. Comparison of Nitrogen Treatment by Four Onsite Wastewater Systems in Nutrient-Sensitive Watersheds of the North Carolina Coastal Plain. Nitrogen 2021, 2, 268–286. [Google Scholar] [CrossRef]
  4. Yousaf, A.; Khalid, N.; Aqeel, M.; Noman, A.; Naeem, N.; Sarfraz, W.; Ejaz, U.; Qaiser, Z.; Khalid, A. Nitrogen Dynamics in Wetland Systems and Its Impact on Biodiversity. Nitrogen 2021, 2, 196–217. [Google Scholar] [CrossRef]
  5. Paul, D. Biological and Adsorptive Removal of Nitrogenous Species from Aquaculture Wastewater. Ph.D. Thesie, North Carolina State University, Raleigh, NC, USA, May 2021. Available online: (accessed on 12 May 2022).
  6. Hall, S.G.; Campbell, M.; Geddie, A.; Thomas, M.; Paul, D.; Wilcox, D.; Smith, R.; Eddy, N.; Frinsko, M.; Wilder, S.; et al. Engineering challenges in marine aquaculture. In Proceedings of the 2018 ASABE Annual International Meeting, Detroit, MI, USA, 29 July–1 August 2018; American Society of Agricultural and Biological Engineers: St. Joseph, MI, USA, 2018. [Google Scholar] [CrossRef]
  7. Ahn, Y.-H. Sustainable nitrogen elimination biotechnologies: A review. Process Biochem. 2006, 41, 1709–1721. [Google Scholar] [CrossRef]
  8. EPA US. Process Design Manual of Nitrogen Control 1993. Available online: (accessed on 31 March 2022).
  9. Ali, M.; Okabe, S. Anammox-based technologies for nitrogen removal: Advances in process start-up and remaining issues. Chemosphere 2015, 141, 144–153. [Google Scholar] [CrossRef]
  10. Arredondo, M.R.; Kuntke, P.; Jeremiasse, A.W.; Sleutels, T.H.J.A.; Buisman, C.J.N.; Ter Heijne, A. Bioelectrochemical systems for nitrogen removal and recovery from wastewater. Environ. Sci. Water Res. Technol. 2015, 1, 22–33. [Google Scholar] [CrossRef]
  11. Taziki, M.; Ahmadzadeh, H.; Murry, M.A.; Lyon, S.R. Nitrate and Nitrite Removal from Wastewater using Algae. Curr. Biotechnol. 2016, 4, 426–440. [Google Scholar] [CrossRef]
  12. Gonçalves, A.L.; Pires, J.C.M.; Simões, M. A review on the use of microalgal consortia for wastewater treatment. Algal Res. 2017, 24, 403–415. [Google Scholar] [CrossRef]
  13. Banerjee, A.; Paul, D. Developments and applications of porous medium combustion: A recent review. Energy 2021, 221, 119868. [Google Scholar] [CrossRef]
  14. Banerjee, A.; Roy, S.; Mukherjee, P.; Saha, U.K. Unsteady flow analysis around an elliptic-bladed Savonius-style wind turbine. In Proceedings of the Gas Turbine India Conference, New Delhi, India, 15–17 December 2014; American Society of Mechanical Engineers: New York, NY, USA, 2014; Volume 49644, p. V001T05A001. [Google Scholar] [CrossRef]
  15. Banerjee, A.; Saveliev, A.V. High temperature heat extraction from counterflow porous burner. Int. J. Heat Mass Transf. 2018, 127, 436–443. [Google Scholar] [CrossRef]
  16. Banerjee, A. Performance and flow analysis of an elliptic bladed Savonius-style wind turbine. J. Renew. Sustain. Energy 2019, 11, 033307. [Google Scholar] [CrossRef]
  17. Banerjee, A.; Kundu, P.; Gnatenko, V.; Zelepouga, S.; Wagner, J.; Chudnovsky, Y.; Saveliev, A. NOx Minimization in Staged Combustion Using Rich Premixed Flame in Porous Media. Combust. Sci. Technol. 2020, 192, 1633–1649. [Google Scholar] [CrossRef]
  18. Banerjee, A.; Saveliev, A. Emission characteristics of heat recirculating porous burners with high temperature energy extraction. Front. Chem. 2020, 8, 67. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  19. Paul, D.; Banerjee, A. Genetic algorithm based optimization technique for Savonius-style wind turbine. In Proceedings of the Gas Turbine India Conference, Virtual, Online, 2–3 December 2021; American Society of Mechanical Engineers: New York, NY, USA, 2021; Volume 76041, p. V001T09A009. [Google Scholar] [CrossRef]
  20. Paul, D.; Banerjee, A. Efficiency analysis of Savonius-style wind turbine in hydrodynamic flow field. In Proceedings of the Gas Turbine India Conference, Virtual, Online, 2–3 December 2021; American Society of Mechanical Engineers: New York, NY, USA, 2021; Volume 76209, p. V001T09A010. [Google Scholar] [CrossRef]
  21. Paul, D.; Banerjee, A. Experimental investigation of performance characteristics for Savonius-style VAWTs: A comparative study. In Proceedings of the Gas Turbine India Conference, Virtual, Online, 2–3 December 2021; American Society of Mechanical Engineers: New York, NY, USA, 2021; Volume 76040, p. V001T09A008. [Google Scholar] [CrossRef]
  22. Paul, D.; Noori, T.; Rajesh, P.; Ghangrekar, M.; Mitra, A. Modification of carbon felt anode with graphene oxide-zeolite composite for enhancing the performance of microbial fuel cell. Sustain. Energy Technol. Assess. 2018, 26, 77–82. [Google Scholar] [CrossRef]
  23. Noori, T.; Paul, D.; Ghangrekar, M.M.; Mukherjee, C.K. Enhancing the Performance of Sediment Microbial Fuel Cell using Graphene Oxide–Zeolite Modified Anode and V2O5 Catalyzed Cathode. J. Clean Energy Technol. 2018, 6(2), 150–154. [Google Scholar] [CrossRef]
  24. Caranto, J.D.; Lancaster, K.M. Nitric oxide is an obligate bacterial nitrification intermediate produced by hydroxylamine oxidoreductase. Proc. Natl. Acad. Sci. USA 2017, 114, 8217–8222. [Google Scholar] [CrossRef] [Green Version]
  25. Daims, H.; Lücker, S.; Wagner, M. A New Perspective on Microbes Formerly Known as Nitrite-Oxidizing Bacteria. Trends Microbiol. 2016, 24, 699–712. [Google Scholar] [CrossRef]
  26. Sedlacek, C.J.; Nielsen, S.; Greis, K.D.; Haffey, W.D.; Revsbech, N.P.; Ticak, T.; Laanbroek, H.J.; Bollmann, A. Effects of Bacterial Community Members on the Proteome of the Ammonia-Oxidizing Bacterium Nitrosomonas sp. Strain Is79. Appl. Environ. Microbiol. 2016, 82, 4776–4788. [Google Scholar] [CrossRef] [Green Version]
  27. Wang, M.; Wu, Y.; Zhu, J.; Wang, C.; Zhu, Y.; Tian, Q. The New Developments Made in the Autotrophic and Heterotrophic Ammonia Oxidation. IOP Conf. Ser. Earth Environ. Sci. 2018, 178, 012016. [Google Scholar] [CrossRef]
  28. Beman, J.M.; Sachdeva, R.; Fuhrman, J. Population ecology of nitrifying Archaea and Bacteria in the Southern California Bight. Environ. Microbiol. 2010, 12, 1282–1292. [Google Scholar] [CrossRef] [PubMed]
  29. Dionisi, H.M.; Layton, A.C.; Harms, G.; Gregory, I.R.; Robinson, K.G.; Sayler, G.S. Quantification of Nitrosomonas oligotropha-like Ammonia-Oxidizing Bacteria and Nitrospira spp. from Full-Scale Wastewater Treatment Plants by Competitive PCR. Appl. Environ. Microbiol. 2002, 68, 245–253. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  30. Rahimi, S.; Modin, O.; Mijakovic, I. Technologies for biological removal and recovery of nitrogen from wastewater. Biotechnol. Adv. 2020, 43, 107570. [Google Scholar] [CrossRef] [PubMed]
  31. Philips, S.; Laanbroek, H.J.; Verstraete, W. Origin, causes and effects of increased nitrite concentrations in aquatic environments. Rev. Environ. Sci. Biotechnol. 2002, 1, 115–141. [Google Scholar] [CrossRef]
  32. Kelly, D.P. Bioenergetics of chemolithotrophic bacteria. Companion Microbiol. 1978, 363–386. [Google Scholar]
  33. Wood, P.M. Nitrification as a bacterial energy source. Spec. Publ. Soc. Gen. Microbiol. 1986, 20, 39–67. [Google Scholar]
  34. Emparanza, E.J. Problems affecting nitrification in commercial RAS with fixed-bed biofilters for salmonids in Chile. Aquac. Eng. 2009, 41, 91–96. [Google Scholar] [CrossRef]
  35. Malone, R.F.; Pfeiffer, T.J. Rating fixed film nitrifying biofilters used in recirculating aquaculture systems. Aquac. Eng. 2006, 34, 389–402. [Google Scholar] [CrossRef]
  36. Ge, S.; Wang, S.; Yang, X.; Qiu, S.; Li, B.; Peng, Y. Detection of nitrifiers and evaluation of partial nitrification for wastewater treatment: A review. Chemosphere 2015, 140, 85–98. [Google Scholar] [CrossRef]
  37. Cao, Y.; Van Loosdrecht, M.C.M.; Daigger, G.T. Mainstream partial nitritation–anammox in municipal wastewater treatment: Status, bottlenecks, and further studies. Appl. Microbiol. Biotechnol. 2017, 101, 1365–1383. [Google Scholar] [CrossRef]
  38. Sinha, B.; Annachhatre, A.P. Partial nitrification—Operational parameters and microorganisms involved. Rev. Environ. Sci. Biotechnol. 2007, 6, 285–313. [Google Scholar] [CrossRef]
  39. Liu, C.; Shi, W.; Li, H.; Lei, Z.; He, L.; Zhang, Z. Improvement of methane production from waste activated sludge by on-site photocatalytic pretreatment in a photocatalytic anaerobic fermenter. Bioresour. Technol. 2014, 155, 198–203. [Google Scholar] [CrossRef] [PubMed]
  40. Paredes, D.; Kuschk, P.; Mbwette, T.S.A.; Stange, C.F.; Müller, R.A.; Köser, H. New Aspects of Microbial Nitrogen Transformations in the Context of Wastewater Treatment—A Review. Eng. Life Sci. 2007, 7, 13–25. [Google Scholar] [CrossRef]
  41. Galí, A.; Dosta, J.; van Loosdrecht, M.; Mata-Alvarez, J. Two ways to achieve an anammox influent from real reject water treatment at lab-scale: Partial SBR nitrification and SHARON process. Process Biochem. 2007, 42, 715–720. [Google Scholar] [CrossRef]
  42. Stein, L.Y.; Arp, D.J. Loss of Ammonia Monooxygenase Activity in Nitrosomonas europaea upon Exposure to Nitrite. Appl. Environ. Microbiol. 1998, 64, 4098–4102. [Google Scholar] [CrossRef] [Green Version]
  43. Purkhold, U.; Pommerening-Röser, A.; Juretschko, S.; Schmid, M.C.; Koops, H.-P.; Wagner, M. Phylogeny of All Recognized Species of Ammonia Oxidizers Based on Comparative 16S rRNA and amoA Sequence Analysis: Implications for Molecular Diversity Surveys. Appl. Environ. Microbiol. 2000, 66, 5368–5382. [Google Scholar] [CrossRef] [Green Version]
  44. Koops, H.P.; Pommerening-Röser, A. Distribution and ecophysiology of the nitrifying bacteria emphasizing cultured species. FEMS Microbiol. Ecol. 2001, 37, 1–9. [Google Scholar] [CrossRef]
  45. Woese, C.; Weisburg, W.; Paster, B.; Hahn, C.; Tanner, R.; Krieg, N.; Koops, H.-P.; Harms, H.; Stackebrandt, E. The phylogeny of purple bacteria: The beta subdivision. Syst. Appl. Microbiol. 1984, 5, 327–336. [Google Scholar] [CrossRef]
  46. Junier, P.; Molina, V.; Dorador, C.; Hadas, O.; Kim, O.-S.; Junier, T.; Witzel, K.-P.; Imhoff, J.F. Phylogenetic and functional marker genes to study ammonia-oxidizing microorganisms (AOM) in the environment. Appl. Microbiol. Biotechnol. 2010, 85, 425–440. [Google Scholar] [CrossRef] [Green Version]
  47. Fiencke, C.; Spieck, E.; Bock, E. Nitrogen Fixation in Agriculture, Forestry, Ecology, and the Environment, 1st ed.; Springer: Dordrecht, The Netherlands, 2005; p. 255. [Google Scholar] [CrossRef]
  48. Mobarry, B.K.; Wagner, M.; Urbain, V.; Rittmann, B.E.; Stahl, D.A. Phylogenetic probes for analyzing abundance and spatial organization of nitrifying bacteria. Appl. Environ. Microbiol. 1996, 62, 2156–2162. [Google Scholar] [CrossRef] [Green Version]
  49. Stopforth, J.D.; O’Connor, R.; Lopes, M.; Kottapalli, B.; Hill, W.E.; Samadpour, M. Validation of Individual and Multiple-Sequential Interventions for Reduction of Microbial Populations during Processing of Poultry Carcasses and Parts. J. Food Prot. 2007, 70, 1393–1401. [Google Scholar] [CrossRef] [PubMed]
  50. Lücker, S.; Wagner, M.; Maixner, F.; Pelletier, E.; Koch, H.; Vacherie, B.; Rattei, T.; Damsté, J.S.S.; Spieck, E.; Le Paslier, D.; et al. A Nitrospira metagenome illuminates the physiology and evolution of globally important nitrite-oxidizing bacteria. Proc. Natl. Acad. Sci. USA 2010, 107, 13479–13484. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  51. Wagner, M.; Loy, A. Bacterial community composition and function in sewage treatment systems. Curr. Opin. Biotechnol. 2002, 13, 218–227. [Google Scholar] [CrossRef]
  52. Kampschreur, M.J.; Temmink, H.; Kleerebezem, R.; Jetten, M.S.; van Loosdrecht, M. Nitrous oxide emission during wastewater treatment. Water Res. 2009, 43, 4093–4103. [Google Scholar] [CrossRef]
  53. Wett, B.; Omari, A.; Podmirseg, S.M.; Han, M.; Akintayo, O.; Gómez-Brandón, M.; Murthy, S.; Bott, C.; Hell, M.; Takács, I.; et al. Going for mainstream deammonification from bench to full scale for maximized resource efficiency. Water Sci. Technol. 2013, 68, 283–289. [Google Scholar] [CrossRef]
  54. Cao, S.; Wang, S.; Peng, Y.; Wu, C.; Du, R.; Gong, L.; Ma, B. Achieving partial denitrification with sludge fermentation liquid as carbon source: The effect of seeding sludge. Bioresour. Technol. 2013, 149, 570–574. [Google Scholar] [CrossRef]
  55. Pérez, J.; Lotti, T.; Kleerebezem, R.; Picioreanu, C.; van Loosdrecht, M. Outcompeting nitrite-oxidizing bacteria in single-stage nitrogen removal in sewage treatment plants: A model-based study. Water Res. 2014, 66, 208–218. [Google Scholar] [CrossRef]
  56. Castro-Barros, C.; Daelman, M.; Mampaey, K.; van Loosdrecht, M.; Volcke, E. Effect of aeration regime on N2O emission from partial nitritation-anammox in a full-scale granular sludge reactor. Water Res. 2015, 68, 793–803. [Google Scholar] [CrossRef]
  57. Ni, B.-J.; Smets, B.F.; Yuan, Z.; Pellicer-Nàcher, C. Model-based evaluation of the role of Anammox on nitric oxide and nitrous oxide productions in membrane aerated biofilm reactor. J. Membr. Sci. 2013, 446, 332–340. [Google Scholar] [CrossRef]
  58. Nerenberg, R. The membrane-biofilm reactor (MBfR) as a counter-diffusional biofilm process. Curr. Opin. Biotechnol. 2016, 38, 131–136. [Google Scholar] [CrossRef] [Green Version]
  59. Paul, D.; Hall, S.G. Biochar and Zeolite as Alternative Biofilter Media for Denitrification of Aquaculture Effluents. Water 2021, 13, 2703. [Google Scholar] [CrossRef]
  60. Razak, M.N.A.; Ibrahim, M.F.; Yee, P.L.; Hassan, M.A.; Abd-Aziz, S. Utilization of oil palm decanter cake for cellulase and polyoses production. Biotechnol. Bioprocess Eng. 2012, 17, 547–555. [Google Scholar] [CrossRef]
  61. Miao, L.; Liu, Z. Microbiome analysis and -omics studies of microbial denitrification processes in wastewater treatment: Recent advances. Sci. China Life Sci. 2018, 61, 753–761. [Google Scholar] [CrossRef] [PubMed]
  62. Delwiche, C.C. Denitrification, nitrification and atmospheric nitrous oxide. In The Nitrogen Cycle and Nitrous Oxide; Wiley & Sons: Hoboken, NJ, USA, 1981. [Google Scholar]
  63. Wang, X.M.; Wang, J.L. Nitrate removal from groundwater using solid-phase denitrification process without inoculating with external microorganisms. Int. J. Environ. Sci. Technol. 2013, 10, 955–960. [Google Scholar] [CrossRef] [Green Version]
  64. Zakhama-Sraieb, R.; Sghaier, Y.R.; Ben Hmida, A.; Cappai, G.; Carucci, A.; Charfi-Cheikhrouha, F. Variation along the year of trace metal levels in the compartments of the seagrass Posidonia oceanica in Port El Kantaoui, Tunisia. Environ. Sci. Pollut. Res. 2016, 23, 1681–1690. [Google Scholar] [CrossRef]
  65. Jiang, K.; Sanseverino, J.; Chauhan, A.; Lucas, S.; Copeland, A.; Lapidus, A.; Del Rio, T.G.; Dalin, E.; Tice, H.; Bruce, D.; et al. Complete genome sequence of Thauera aminoaromatica strain MZ1T. Stand. Genom. Sci. 2012, 6, 325–335. [Google Scholar] [CrossRef] [Green Version]
  66. Cowan, D.; Meyer, Q.; Stafford, W.; Muyanga, S.; Cameron, R.; Wittwer, P. Metagenomic gene discovery: Past, present and future. Trends Biotechnol. 2005, 23, 321–329. [Google Scholar] [CrossRef]
  67. Khan, S.T.; Horiba, Y.; Yamamoto, M.; Hiraishi, A. Members of the Family Comamonadaceae as Primary Poly(3-Hydroxybutyrate-co-3-Hydroxyvalerate)-Degrading Denitrifiers in Activated Sludge as Revealed by a Polyphasic Approach. Appl. Environ. Microbiol. 2002, 68, 3206–3214. [Google Scholar] [CrossRef] [Green Version]
  68. Guo, H.; Zhou, J.; Su, J.; Zhang, Z. Integration of nitrification and denitrification in airlift bioreactor. Biochem. Eng. J. 2005, 23, 57–62. [Google Scholar] [CrossRef]
  69. Zhu, G.; Peng, Y.; Li, B.; Guo, J.; Yang, Q.; Wang, S. Biological removal of nitrogen from wastewater. In Reviews of Environmental Contamination and Toxicology; Whitacre, D.M., Ed.; Springer: New York, NY, USA, 2008; pp. 159–195. [Google Scholar] [CrossRef]
  70. Chen, Q.; Ni, J.; Ma, T.; Liu, T.; Zheng, M. Bioaugmentation treatment of municipal wastewater with heterotrophic-aerobic nitrogen removal bacteria in a pilot-scale SBR. Bioresour. Technol. 2015, 183, 25–32. [Google Scholar] [CrossRef]
  71. Peng, Y.; Zhu, G. Biological nitrogen removal with nitrification and denitrification via nitrite pathway. Appl. Microbiol. Biotechnol. 2006, 73, 15–26. [Google Scholar] [CrossRef] [PubMed]
  72. Kartal, B.; Kuenen, J.G.; van Loosdrecht, M.C.M. Sewage Treatment with Anammox. Science 2010, 328, 702–703. [Google Scholar] [CrossRef] [PubMed]
  73. Shoda, M. Heterotrophic Nitrification and Aerobic Denitrification by Alcaligenes faecalis No. 4. Nitrification and Denitrification; IntechOpen Limited: London, UK, 2017; p. 31. [Google Scholar] [CrossRef] [Green Version]
  74. Van Niftrik, L.; Jetten, M.S.M. Anaerobic Ammonium-Oxidizing Bacteria: Unique Microorganisms with Exceptional Properties. Microbiol. Mol. Biol. Rev. 2012, 76, 585–596. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  75. Oshiki, M.; Shimokawa, M.; Fujii, N.; Satoh, H.; Okabe, S. Physiological characteristics of the anaerobic ammonium-oxidizing bacterium ‘Candidatus Brocadia sinica’. Microbiology 2011, 157, 1706–1713. [Google Scholar] [CrossRef] [Green Version]
  76. Mulder, A.; Van De Graaf, A.; Robertson, L.; Kuenen, J. Anaerobic ammonium oxidation discovered in a denitrifying fluidized bed reactor. FEMS Microbiol. Ecol. 1995, 16, 177–184. [Google Scholar] [CrossRef]
  77. Broda, E. Two kinds of lithotrophs missing in nature. Z. Allg. Mikrobiol. 1977, 17, 491–493. [Google Scholar] [CrossRef]
  78. Ahn, Y.-H.; Hwang, I.-S.; Min, K.-S. ANAMMOX and partial denitritation in anaerobic nitrogen removal from piggery waste. Water Sci. Technol. 2004, 49, 145–153. [Google Scholar] [CrossRef]
  79. Strous, M.; Fuerst, J.; Kramer, E.H.M.; Logemann, S.; Muyzer, G.; Van De Pas-Schoonen, K.T.; Webb, R.M.T.; Kuenen, J.G.; Jetten, M.S.M. Missing lithotroph identified as new planctomycete. Nature 1999, 400, 446–449. [Google Scholar] [CrossRef]
  80. Chen, H.; Liu, S.; Yang, F.; Xue, Y.; Wang, T. The development of simultaneous partial nitrification, ANAMMOX and denitrification (SNAD) process in a single reactor for nitrogen removal. Bioresour. Technol. 2009, 100, 1548–1554. [Google Scholar] [CrossRef]
  81. Du, R.; Cao, S.; Li, B.; Niu, M.; Wang, S.; Peng, Y. Performance and microbial community analysis of a novel DEAMOX based on partial-denitrification and anammox treating ammonia and nitrate wastewaters. Water Res. 2017, 108, 46–56. [Google Scholar] [CrossRef]
  82. Cao, L.; Wang, J.; Xiang, S.; Huang, Z.; Ruan, R.; Liu, Y. Nutrient removal from digested swine wastewater by combining ammonia stripping with struvite precipitation. Environ. Sci. Pollut. Res. 2019, 26, 6725–6734. [Google Scholar] [CrossRef] [PubMed]
  83. Kadier, A.; Simayi, Y.; Abdeshahian, P.; Azman, N.F.; Chandrasekhar, K.; Kalil, M.S. A comprehensive review of microbial electrolysis cells (MEC) reactor designs and configurations for sustainable hydrogen gas production. Alex. Eng. J. 2016, 55, 427–443. [Google Scholar] [CrossRef] [Green Version]
  84. Ucar, D.; Zhang, Y.; Angelidaki, I. An Overview of Electron Acceptors in Microbial Fuel Cells. Front. Microbiol. 2017, 8, 643. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  85. Clauwaert, P.; Rabaey, K.; Aelterman, P.; De Schamphelaire, L.; Pham, T.H.; Boeckx, P.; Boon, N.; Verstraete, W. Biological Denitrification in Microbial Fuel Cells. Environ. Sci. Technol. 2007, 41, 3354–3360. [Google Scholar] [CrossRef] [PubMed]
  86. Zhao, H.; Zhao, J.; Li, F.; Li, X. Performance of Denitrifying Microbial Fuel Cell with Biocathode over Nitrite. Front. Microbiol. 2016, 7, 344. [Google Scholar] [CrossRef] [PubMed]
  87. Zekker, I.; Bhowmick, G.D.; Priks, H.; Nath, D.; Rikmann, E.; Jaagura, M.; Tenno, T.; Tämm, K.; Ghangrekar, M.M. ANAMMOX-denitrification biomass in microbial fuel cell to enhance the electricity generation and nitrogen removal efficiency. Biodegradation 2020, 31, 249–264. [Google Scholar] [CrossRef] [PubMed]
  88. Zhu, G.; Huang, S.; Lu, Y.; Gu, X. Simultaneous nitrification and denitrification in the bio-cathode of a multi-anode microbial fuel cell. Environ. Technol. 2021, 42, 1260–1270. [Google Scholar] [CrossRef]
  89. Schmidt, I.; Zart, D.; Bock, E. Gaseous NO2 as a regulator for ammonia oxidation of Nitrosomonas eutropha. Antonie van Leeuwenhoek 2001, 79, 311–318. [Google Scholar] [CrossRef]
  90. Schmidt, I.; Hermelink, C.; van de Pas-Schoonen, K.; Strous, M.; Camp, H.J.O.D.; Kuenen, J.G.; Jetten, M.S.M. Anaerobic Ammonia Oxidation in the Presence of Nitrogen Oxides (NOx) by Two Different Lithotrophs. Appl. Environ. Microbiol. 2002, 68, 5351–5357. [Google Scholar] [CrossRef] [Green Version]
  91. Schmidt, I.; Sliekers, O.; Schmid, M.; Bock, E.; Fuerst, J.; Kuenen, J.G.; Jetten, M.S.; Strous, M. New concepts of microbial treatment processes for the nitrogen removal in wastewater. FEMS Microbiol. Rev. 2003, 27, 481–492. [Google Scholar] [CrossRef] [Green Version]
  92. Strous, M.; Van Gerven, E.; Kuenen, J.G.; Jetten, M. Effects of aerobic and microaerobic conditions on anaerobic ammonium-oxidizing (anammox) sludge. Appl. Environ. Microbiol. 1997, 63, 2446–2448. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  93. Koch, G.; Egli, K.; van der Meer, J.R.; Siegrist, H. Mathematical modeling of autotrophic denitrification in a nitrifying biofilm of a rotating biological contactor. Water Sci. Technol. 2000, 41, 191–198. [Google Scholar] [CrossRef]
  94. Third, K.; Sliekers, A.O.; Kuenen, J.; Jetten, M. The CANON System (Completely Autotrophic Nitrogen-removal over Nitrite) under Ammonium Limitation: Interaction and Competition between Three Groups of Bacteria. Syst. Appl. Microbiol. 2001, 24, 588–596. [Google Scholar] [CrossRef] [PubMed]
  95. Van Loosdrecht, M.C.M. Recent development on biological wastewater nitrogen removal technologies. In Proceedings of the International Conference on Wastewater Treatment for Nutrient Removal and Reuse (ICWNR’04), Pathumthani, Thailand, 26–29 January 2004. [Google Scholar] [CrossRef] [Green Version]
  96. Jetten, M.S.; Schmid, M.; Schmidt, I.; Wubben, M.; Van Dongen, U.; Abma, W.; Sliekers, O.; Revsbech, N.P.; Beaumont, H.J.; Ottosen, L.; et al. Improved nitrogen removal by application of new nitrogen-cycle bacteria. Rev. Environ. Sci. Biotechnol. 2002, 1, 51–63. [Google Scholar] [CrossRef]
  97. Hellinga, C.; Schellen, A.; Mulder, J.; van Loosdrecht, M.; Heijnen, J. The sharon process: An innovative method for nitrogen removal from ammonium-rich waste water. Water Sci. Technol. 1998, 37, 135–142. [Google Scholar] [CrossRef]
  98. Kuai, L.; Verstraete, W. Ammonium Removal by the Oxygen-Limited Autotrophic Nitrification-Denitrification System. Appl. Environ. Microbiol. 1998, 64, 4500–4506. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  99. Pynaert, K.; Smets, B.F.; Wyffels, S.; Beheydt, D.; Siciliano, S.; Verstraete, W. Characterization of an Autotrophic Nitrogen-Removing Biofilm from a Highly Loaded Lab-Scale Rotating Biological Contactor. Appl. Environ. Microbiol. 2003, 69, 3626–3635. [Google Scholar] [CrossRef] [Green Version]
  100. Hippen, A.; Helmer, C.; Kunst, S.; Rosenwinkel, K.-H.; Seyfried, C.F. Six years’ practical experience with aerobic/anoxic deammonification in biofilm systems. Water Sci. Technol. 2001, 44, 39–48. [Google Scholar] [CrossRef]
  101. Sood, A.; Renuka, N.; Prasanna, R.; Ahluwalia, A.S. Cyanobacteria as potential options for wastewater treatment. In Phytoremediation; Springer: Cham, Switzerland, 2015; pp. 83–93. [Google Scholar] [CrossRef]
  102. Delgadillo-Mirquez, L.; Lopes, F.; Taidi, B.; Pareau, D. Nitrogen and phosphate removal from wastewater with a mixed microalgae and bacteria culture. Biotechnol. Rep. 2016, 11, 18–26. [Google Scholar] [CrossRef]
  103. Xin, L.; Hong-Ying, H.; Yu-Ping, Z. Growth and lipid accumulation properties of a freshwater microalga Scenedesmus sp. under different cultivation temperature. Bioresour. Technol. 2011, 102, 3098–3102. [Google Scholar] [CrossRef]
  104. Lorick, D.; Macura, B.; Ahlström, M.; Grimvall, A.; Harder, R. Effectiveness of struvite precipitation and ammonia stripping for recovery of phosphorus and nitrogen from anaerobic digestate: A systematic review. Environ. Evid. 2020, 9, 27. [Google Scholar] [CrossRef]
  105. Escudero, A.; Blanco, F.; Lacalle, A.; Pinto, M. Struvite precipitation for ammonium removal from anaerobically treated effluents. J. Environ. Chem. Eng. 2015, 3, 413–419. [Google Scholar] [CrossRef]
  106. Huang, H.; Xu, C.; Zhang, W. Removal of nutrients from piggery wastewater using struvite precipitation and pyrogenation technology. Bioresour. Technol. 2011, 102, 2523–2528. [Google Scholar] [CrossRef] [PubMed]
  107. Etter, B.; Tilley, E.; Khadka, R.; Udert, K. Low-cost struvite production using source-separated urine in Nepal. Water Res. 2011, 45, 852–862. [Google Scholar] [CrossRef] [Green Version]
  108. Culp, R.L.; Wesner, G.M.; Culp, G.L. Handbook of Advanced Wastewater Treatment, 2nd ed.; Van Nostrand Reinhold: Florence, KY, USA, 1977. [Google Scholar]
  109. Limoli, A.; Langone, M.; Andreottola, G. Ammonia removal from raw manure digestate by means of a turbulent mixing stripping process. J. Environ. Manag. 2016, 176, 1–10. [Google Scholar] [CrossRef]
  110. EPA. Wastewater Technology Fact Sheet—Ammonia Stripping. 2000. Available online: (accessed on 17 April 2022).
  111. Shen, Y.; Tan, M.T.T.; Chong, C.; Xiao, W.; Wang, C.-H. An environmental friendly animal waste disposal process with ammonia recovery and energy production: Experimental study and economic analysis. Waste Manag. 2017, 68, 636–645. [Google Scholar] [CrossRef]
  112. Laureni, M.; Palatsi, J.; Llovera, M.; Bonmatí, A. Influence of pig slurry characteristics on ammonia stripping efficiencies and quality of the recovered ammonium-sulfate solution. J. Chem. Technol. Biotechnol. 2013, 88, 1654–1662. [Google Scholar] [CrossRef]
  113. Grismer, M.E.; Collison, R.S. The Zeolite-Anammox Treatment Process for Nitrogen Removal from Wastewater—A Review. Water 2017, 9, 901. [Google Scholar] [CrossRef] [Green Version]
  114. Paul, D.; Kasera, N.; Kolar, P.; Hall, S.G. Physicochemical characterization data of pine-derived biochar and natural zeolite as precursors to catalysts. Chem. Data Collect. 2020, 30, 100573. [Google Scholar] [CrossRef]
  115. Montalvo, S.; Huiliñir, C.; Borja, R.; Sánchez, E.; Herrmann, C. Application of zeolites for biological treatment processes of solid wastes and wastewaters—A review. Bioresour. Technol. 2020, 301, 122808. [Google Scholar] [CrossRef]
  116. Chester, A.L.H.; Eum, K.; Tsapatsis, M.; Hillmyer, M.A.; Novak, P.J. Enhanced Nitrogen Removal and Anammox Bacteria Retention with Zeolite-Coated Membrane in Simulated Mainstream Wastewater. Environ. Sci. Technol. Lett. 2021, 8, 468–473. [Google Scholar] [CrossRef]
  117. Collison, R.S.; Grismer, M.E. Upscaling the Zeolite-Anammox Process: Treatment of Anaerobic Digester Filtrate. Water 2018, 10, 1553. [Google Scholar] [CrossRef] [Green Version]
Figure 1. A two-chambered (A) microbial fuel cell and (B) microbial electrolysis cell.
Figure 1. A two-chambered (A) microbial fuel cell and (B) microbial electrolysis cell.
Nitrogen 03 00020 g001
Figure 2. Nitrogen recovery from wastewater using microalgae and cyanobacteria.
Figure 2. Nitrogen recovery from wastewater using microalgae and cyanobacteria.
Nitrogen 03 00020 g002
Figure 3. Nitrogen recovery by struvite precipitation.
Figure 3. Nitrogen recovery by struvite precipitation.
Nitrogen 03 00020 g003
Figure 4. (A) Cross-flow and (B) countercurrent ammonia stripping towers.
Figure 4. (A) Cross-flow and (B) countercurrent ammonia stripping towers.
Nitrogen 03 00020 g004
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Share and Cite

MDPI and ACS Style

Paul, D.; Banerjee, A. Technologies for Biological and Bioelectrochemical Removal of Inorganic Nitrogen from Wastewater: A Review. Nitrogen 2022, 3, 298-313.

AMA Style

Paul D, Banerjee A. Technologies for Biological and Bioelectrochemical Removal of Inorganic Nitrogen from Wastewater: A Review. Nitrogen. 2022; 3(2):298-313.

Chicago/Turabian Style

Paul, Diplina, and Abhisek Banerjee. 2022. "Technologies for Biological and Bioelectrochemical Removal of Inorganic Nitrogen from Wastewater: A Review" Nitrogen 3, no. 2: 298-313.

Article Metrics

Back to TopTop