Role of heterotrophic aerobic denitrifying bacteria in nitrate removal from wastewater

Next-Generation High-Throughput Sequencing to Evaluate Bacterial Communities in Freshwater Ecosystem in Hydroelectric Reservoirs

The quality of aquatic ecosystems is a major public health concern. The assessment and management of a freshwater system and the ecological monitoring of microorganisms that are present in it can provide indicators of the environment and water quality to protect human and animal health. with bacteria is. It is a major challenge to monitor the microbiological bacterial contamination status of surface water associated with anthropogenic activities within rivers and freshwater reservoirs. Understanding the composition of aquatic microbial communities can be beneficial for the early detection of pathogens, improving our knowledge of their ecological niches, and characterizing the assemblages of microbiota responsible for the degradation of contaminants and microbial substrates. The present study aimed to characterize the bacterial microbiota of water samples collected alongside the Madeira River and its small tributaries in rural areas near the Santo Antonio Energia hydroelectric power plant (SAE) reservoir in the municipality of Porto Velho, Rondonia state, Western Brazil. An Illumina 16s rRNA metagenomic approach was employed and the physicochemical characteristics of the water sample were assessed. We hypothesized that both water metagenomics and physicochemical parameters would vary across sampling sites. The most abundant genera found in the study were Acinetobacter, Deinococcus, and Pseudomonas. PERMANOVA and ANCOM analysis revealed that collection points sampled at the G4 location presented a significantly different microbiome compared to any other group, with the Chlamidomonadaceae family and Enhydrobacter genus being significantly more abundant. Our findings support the use of metagenomics to assess water quality standards for the protection of human and animal health in this microgeographic region.

Nitrogen transformation in slightly polluted surface water by a novel biofilm reactor: Long-term performance and microbial population characteristics

This study proposes a modular floating biofilm reactor (MFBR) for in situ nitrogen removal from slightly polluted water in rivers using enriched indigenous microorganisms. Its main structure is a 60 cm × 60 cm × 90 cm rectangular reactor filled with hackettens. After a 96-day startup, the removal efficiencies of ammonia-N and total N (TN) reached 80% and 25%, respectively, with a hydraulic retention time (HRT) of 10 h, whereas those in a control reactor (without biofilm) were only 4.9% and 0.2%, respectively. The influences of HRT and dissolved oxygen (DO) were also investigated. As a key factor, HRT significantly affected the removal efficiencies of ammonia-N and TN. When HRT was close to the actual value for a river studied (2.4 min), the removal efficiencies of ammonia-N and TN were only 8.7% and 3.1%, respectively. Aeration increased the concentration of DO in water, which enhanced nitrification but inhibited denitrification. When HRT was 2.4 min, aeration intensity was 20 L/min; the ammonia-N and TN removal rates were 9.5 g/(m²·d) and 11.3 g/(m²·d), respectively. The results of microbial community analysis indicated that the microorganisms forming the biofilm were indigenous bacteria. The findings demonstrated a concept-proof of MFBR, which may be evaluated in scaling up investigation for developing a new methodology for nitrogen removal from slightly polluted surface water in plain river networks.

Characterization of Isolated Aerobic Denitrifying Bacteria and Their Potential Use in the Treatment of Nitrogen-Polluted Aquaculture Water

Ammonia and nitrite treatments are the critical steps that must be done to ensure the healthy growth of aquatic animals. The nitrification process is often used for nitrogen removal purposes due to its efficiency and environmentally friendly properties. However, the varied growth rate between ammonia and nitrite-oxidizing bacteria can cause nitrite accumulation, leading to the massive mortality of aquatic animals at high concentrations. Therefore, this study aimed to integrate the fast-growing heterotrophic nitrite-reducing bacteria with nitrifying bacteria to achieve a quicker nitrite removal activity. The two denitrifying Bacillus sp. ST20 and Bacillus sp. ST26 were screened from shrimp ponds in Bac Lieu province, Vietnam. Obtained results showed that under anoxic conditions, the nitrite removal efficiency of these two strains reached 68.5-82% at nitrite initial concentration of 20 mgN-NO₂/L after 72 h. Higher efficiency of over 95% was gained under oxic conditions. Hence, it enabled the use of denitrifying and nitrifying bacteria-co-immobilized carriers for ammonia oxidation and nitrite reduction simultaneously in a single-aerated bioreactor. A total of over 96% nitrogen content was removed during the bioreactor operation, despite the increase of inputting nitrogen concentration from 40 to 200 mgN/L. Moreover, the suitable conditions for bacterial growth and nitrite conversion activity of the ST20 and ST26 were detected as 15‰ salinity and 35 °C. The isolates also utilized various C-sources for growth, hence widening their applicability. The present study suggested that the isolated aerobic denitrifying bacteria are potentially used for the complete removal of nitrogen compounds from aquaculture wastewater.

Pseudomonas oligotrophica sp. nov., a Novel Denitrifying Bacterium Possessing Nitrogen Removal Capability Under Low Carbon–Nitrogen Ratio Condition

Pseudomonas is a large and diverse genus within the Gammaproteobacteria known for its important ecological role in the environment. These bacteria exhibit versatile features of which the ability of heterotrophic nitrification and aerobic denitrification can be applied for nitrogen removal from the wastewater. A novel denitrifying bacterium, designated JM10B5a^T, was isolated from the pond water for juvenile Litopenaeus vannamei. The phylogenetic, genomic, physiological, and biochemical analyses illustrated that strain JM10B5a^T represented a novel species of the genus Pseudomonas, for which the name Pseudomonas oligotrophica sp. nov. was proposed. The effects of carbon sources and C/N ratios on denitrification performance of strain JM10B5a^T were investigated. In addition, the results revealed that sodium acetate was selected as the optimum carbon source for denitrification of this strain. Besides, strain JM10B5a^T could exhibit complete nitrate removal at the low C/N ratio of 3. Genomic analyses revealed that JM10B5a^T possessed the functional genes including napA, narG, nirS, norB, and nosZ, which might participate in the complete denitrification process. Comparative genomic analyses indicated that many genes related to aggregation, utilization of alkylphosphonate and tricarballylate, biosynthesis of cofactors, and vitamins were contained in the genome of strain JM10B5a^T. These genomic features were indicative of its adaption to various niches. Moreover, strain JM10B5a^T harbored the complete operons required for the biosynthesis of vibrioferrin, a siderophore, which might be conducive to the high denitrification efficiency of denitrifying bacterium at low C/N ratio. Our findings demonstrated that the strain JM10B5a^T could be a promising candidate for treating wastewater with a low C/N ratio.

PET particles raise microbiological concerns for human health while tyre wear microplastic particles potentially affect ecosystem services in waters

Although abundant and chemically peculiar, tyre wear microplastic particles (TWP) and their impact on the microbial communities in water are largely understudied. We tested in laboratory based semi-continuous cultures the impact of TWP and of polyethylene terephthalate (PET) derived particles (following a gradient of relative abundance) on the pathobiome (the group of potential human pathogenic bacteria) of a freshwater microbial community exposed to contamination by the effluent of a urban wastewater treatment plant, for a period of 28 days. We could define the modulated impact of the two types of microplastic particles: while PET does not favour bacterial growth, it offers a refuge to several potential pathogens of allochthonous origin (from the treated sewage effluent), TWP act as an additional carbon source, promoting the development and the massive growth of a biofilm composed by fast-growing bacterial genera including species potentially harmful and competitive in abating biodiversity in surface waters. Our results demonstrate the different ecological role and impact on freshwater environments of TWP and PET particles, and the need to approach the study of this pollutant not as a whole, but considering the origin and the chemical composition of the different particles.

Nitrogen Removal Characteristics of a Cold-Tolerant Aerobic Denitrification Bacterium, Pseudomonas sp. 41

Nitrogen pollution of surface water is the main cause of water eutrophication, and is considered a worldwide challenge in surface water treatment. Currently, the total nitrogen (TN) content in the effluent of wastewater treatment plants (WWTPs) is still high at low winter temperatures, mainly as a result of the incomplete removal of nitrate (NO3−-N). In this research, a novel aerobic denitrifier identified as Pseudomonas sp. 41 was isolated from municipal activated sludge; this strain could rapidly degrade a high concentration of NO3−-N at low temperature. Strain 41 completely converted 100 mg/L NO3−-N in 48 h at 15 °C, and the maximum removal rate reached 4.0 mg/L/h. The functional genes napA, nirS, norB and nosZ were successfully amplified, which provided a theoretical support for the aerobic denitrification capacity of strain 41. In particular, the results of denitrification experiments showed that strain 41 could perform aerobic denitrification under the catalysis of NAP. Nitrogen balance analysis revealed that strain 41 degraded NO3−-N mainly through assimilation (52.35%) and aerobic denitrification (44.02%), and combined with the gene amplification results, the nitrate metabolism pathway of strain 41 was proposed. Single-factor experiments confirmed that strain 41 possessed the best nitrogen removal performance under the conditions of sodium citrate as carbon source, C/N ratio 10, pH 8, temperature 15–30 °C and rotation speed 120 rpm. Meanwhile, the bioaugmentation test manifested that the immobilized strain 41 remarkably improved the denitrification efficiency and shortened the reaction time in the treatment of synthetic wastewater.

Influence of cerium oxide nanoparticles on dairy effluent nitrate and phosphate bioremediation

This study investigated, for the first time, the role of cerium oxide nanoparticles (CeO2 NPs) on dairy effluent nitrate and phosphate bioremediation using different inoculum sources. Two inoculum sources (wastewater and sludge) were obtained from the dairy wastewater treatment plant unit. A culture was prepared to be tested in the treatment of nitrate and phosphate effluent, and the role of CeO2 NPs was checked to be completely efficient after 5 days of incubation. The reduction efficiency of nitrate using sludge as inoculum source was improved up to 89.01% and 68.12% for phosphate compared to control. In the case of using wastewater as an inoculum source, the nitrate reduction was improved up to 83.30% and 87.75% for phosphate compared to control. The bacterial richness showed a significant variance (higher richness) between control and other samples. The optimal concentration of CeO2 NPs for inoculum richness and nitrate and phosphate reduction was (sludge: 1 × 10-10 ppm) and (wastewater: 1 × 10-12 ppm). The results revealed that CeO2 NPs could enhance the microbial growth of different inoculum sources that have a key role in dairy effluent nitrate and phosphate bioremediation.

Wild Heterotrophic Nitrifying Strain Pseudomonas BT1 Isolated from Kitchen Waste Sludge Restores Ammonia Nitrogen Removal in a Sewage Treatment Plant Shocked by Thiourea

Thiourea is used in agriculture and industry as a metal scavenger, synthetic intermediate, and nitrification inhibitor. However, in wastewater, it can inhibit the nitrification process and induce the collapse of the nitrification system. In such a case, ammonia-oxidizing bacteria (AOB) lose their ability to remove ammonia. We investigated the nitrification system of a 60,000-t/d municipal sewage treatment plant in Nanjing, which collapsed after receiving 5–15 ppm (5–15 mg/L) thiourea. Ammonia nitrogen removal quickly recovered to more than 95% after inoculation with 10 t high-efficiency nitrification sludge, which was collected from a kitchen waste treatment plant. A heterotrophic nitrification strain was isolated from the inoculated sludge and identified as wild Pseudomonas by 16S rDNA sequencing and named “BT1.” Based on thiourea tolerance tests, BT1 can tolerate a thiourea content of more than 500 ppm. For comparison, the in situ process was imitated by the simulation system, and the wastewater shocked by 10 ppm thiourea could still meet the emission standard after adding 1% (V/V) BT1. High-throughput sequencing analysis was applied to study microbial succession during thiourea shock loading. The results showed that Hydrogenophaga and Thiobacillus grew with the growth of BT1. Pseudomonas BT1 was used for a 6,000-t/d printed circuit board (PCB) wastewater treatment system, the nitrification system returned to normal in 15 days, and the degradation rate stabilized at more than 95%.

Sugar Beet Processing Wastewater Treatment by Microalgae through Biosorption

The aim of this study was to investigate the potential of environmental pollution reduction of sugar beet processing factory wastewater by the biorefinery approach and integration of microalgae biomass production. In the present study, Chlorella vulgaris was cultivated in wastewater collected from a sugar beet processing factory at the beginning and at the end of a sugar plant campaign in an aerobic bioreactor on a laboratory scale under controlled conditions, with an air flow of 0.4 L/min, a temperature of 26 °C, and pH = 8. Microalgae showed effective nutrient remediation from wastewater. During wastewater treatment, chemical oxygen demand (COD) and biological oxygen demand (BOD) removal efficiency was 93.7% and 98.1%, respectively; total organic carbon (TOC) content decreased by 95.7%. Nitrites and nitrates decreased by 96%, while the biggest decrease in metal ions was achieved for Ca and Mn (82.7% and 97.6%, respectively). The findings of this study suggest that coupling microalgae cultivation and wastewater treatment has a lot of potential for reducing contamination through biosorption, while also providing environmental advantages.

Nitrate Water Contamination from Industrial Activities and Complete Denitrification as a Remediation Option

Freshwater is a scarce resource that continues to be at high risk of pollution from anthropogenic activities, requiring remediation in such cases for its continuous use. The agricultural and mining industries extensively use water and nitrogen (N)-dependent products, mainly in fertilizers and explosives, respectively, with their excess accumulating in different water bodies. Although removal of NO3 from water and soil through the application of chemical, physical, and biological methods has been studied globally, these methods seldom yield N2 gas as a desired byproduct for nitrogen cycling. These methods predominantly cause secondary contamination with deposits of chemical waste such as slurry brine, nitrite (NO2), ammonia (NH3), and nitrous oxide (N2O), which are also harmful and fastidious to remove. This review focuses on complete denitrification facilitated by bacteria as a remedial option aimed at producing nitrogen gas as a terminal byproduct. Synergistic interaction of different nitrogen metabolisms from different bacteria is highlighted, with detailed attention to the optimization of their enzymatic activities. A biotechnological approach to mitigating industrial NO3 contamination using indigenous bacteria from wastewater is proposed, holding the prospect of optimizing to the point of complete denitrification. The approach was reviewed and found to be durable, sustainable, cost effective, and environmentally friendly, as opposed to current chemical and physical water remediation technologies.

Effects of different carbon sources on the efficiency of sulfur-oxidizing denitrifying microorganisms

This study aims to compare the effects of different carbon sources on sulfur-oxidizing denitrifying microorganisms by using glucose, ethanol, and acetate as carbon sources. Under the same chemical oxygen demand Cr (COD_Cr), nitrate, and sulfide concentrations, the removal rate of nitrate and total organic carbon, and the yield of elemental sulfur in a static experiment and a continuous flow reactor with glucose as the carbon source were lower than those with ethanol and acetic acid as the carbon source. The core sulfur-oxidizing denitrifying bacteria that use glucose as the carbon source were Azoarcus, Geoalkalibacter, and Mangroviflexus; those that use ethanol as the carbon source were Arcobacter, Pseudomonas, and Thauera; those that use acetate as the carbon source were Pseudomonas and Azoarcus. The metabolic activity of microorganisms that use different carbon sources was explained by functional gene detection. The fluctuation of gltA, a functional gene indicating heterotrophic metabolism of microorganisms, was small in three reactors, but that of the sulfur oxidation gene, Sqr, in the reactor with acetic acid as the carbon source was larger. Our results suggest that acetate is a more suitable carbon source for denitrification-desulfurization systems.

Characterization of Acinetobacter indicus ZJB20129 for heterotrophic nitrification and aerobic denitrification isolated from an urban sewage treatment plant

The Acinetobacter indicus strain ZJB20129 isolated from an urban sewage treatment plant demonstrated the heterotrophic nitrification-aerobic denitrification (HN-AD) ability. Strain ZJB20129 could remove 98.73% of ammonium-N, 97.26% of nitrite-N and 96.55% of nitrate-N, and the maximum removal rate was 3.66, 4.62 and 5.21 mg/L/h, respectively. Ammonium was preferentially used during simultaneous nitrification and denitrification. Strain ZJB20129 exhibited highest ammonium removal capability when carbon source was sodium succinate, C/N ratio was 15, pH was 8.0, and temperature was 35 ℃. Key enzymes involved in HN-AD including hydroxylamine oxidase, periplasmic nitrate reductase and nitrite reductase as well as their encoding genes were detected, and the metabolic pathway of HN-AD was subsequently predicted. Our results suggested that Acinetobacter indicus ZJB20129 displayed superior nitrogen removal performance on actual wastewater and thus made it have a good application prospect in wastewater biological treatment.

Agricultural practices linked to shifts in groundwater microbial structure and denitrifying bacteria

Irrigation enhances the connectivity between the surface and groundwater by facilitating the transport of energy sources and oxygen. When combined with fertilisers, the impact on groundwater microbial communities and their interactions with nitrogen cycling in aquifers is poorly understood. This study examines the impact of different landuses (irrigated and non-irrigated) on groundwater microbial communities. A total of 38 wells accessing shallow aquifers in three sub-catchments of the Murray Darling Basin, Australia, were sampled for water chemistry and microbial community structure using environmental DNA (eDNA) techniques. All sub-catchments showed evidence of intense irrigation and groundwater contamination with total nitrogen, nitrates and phosphorus concentrations often well above background, with total nitrogen concentrations up to 70 mg/L and nitrate concentration up to 18 mg/L. Across sub-catchments there was high microbial diversity, with differences in community structure and function between catchments and landuses. Of the 1100 operational taxonomic units (OTUs) recorded, 47 OTUs were common across catchments with species from Woesearchaeota, Nitrospirales, Nitrosopumilales and Acidobacter taxonomic groups contributing greatly to groundwater microbial communities. Within non-irrigated sites, groundwaters contained similar proportions of nitrifying and denitrifying capable taxa, whereas irrigated sites had significantly higher abundances of microbes with nitrifying rather than denitrifying capabilities. Microbial diversity was lower in irrigated sites in the Macquarie catchment. These results indicate that irrigated landuses impact microbial community structure and diversity within groundwaters and suggest that the ratios of denitrifying to nitrifying capable microbes as well as specific orders (e.g., Nitrososphaerales) may be useful to indicate long-term nitrogen contamination of groundwaters. Such research is important for understanding the biogeochemical processes that are key predictors of redox state and contamination of groundwater by N species and other compounds. This will help to predict human impacts on groundwater microbial structure, diversity, and ecosystem functions, aiding the long-term management groundwater resources.

Biological Approaches Integrating Algae and Bacteria for the Degradation of Wastewater Contaminants-A Review

The traditional approach for biodegradation of organic matter in sewage treatment used a consortium of bacterial spp. that produce untreated or partially treated inorganic contaminants resulting in large amounts of poor-quality sludge. The aeration process of activated sludge treatment requires high energy. So, a sustainable technique for sewage treatment that could produce less amount of sludge and less energy demanding is required for various developed and developing countries. This led to research into using microalgae for wastewater treatment as they reduce concentrations of nutrients like inorganic nitrates and phosphates from the sewage water, hence reducing the associated chemical oxygen demand (COD). The presence of microalgae removes nutrient concentration in water resulting in reduction of chemical oxygen demand (COD) and toxic heavy metals like Al, Ni, and Cu. Their growth also offers opportunity to produce biofuels and bioproducts from algal biomass. To optimize use of microalgae, technologies like high-rate algal ponds (HRAPs) have been developed, that typically use 22% of the electricity used in Sequencing Batch Reactors for activated sludge treatment with added economic and environmental benefits like reduced comparative operation cost per cubic meter, mitigate global warming, and eutrophication potentials. The addition of suitable bacterial species may further enhance the treatment potential in the wastewater medium as the inorganic nutrients are assimilated into the algal biomass, while the organic nutrients are utilized by bacteria. Further, the mutual exchange of CO2 and O2 between the algae and the bacteria helps in enhancing the photosynthetic activity of algae and oxidation by bacteria leading to a higher overall nutrient removal efficiency. Even negative interactions between algae and bacteria mediated by various secondary metabolites (phycotoxins) have proven beneficial as it controls the algal bloom in the eutrophic water bodies. Herein, we attempt to review various opportunities and limitations of using a combination of microalgae and bacteria in wastewater treatment method toward cost effective, eco-friendly, and sustainable method of sewage treatment.

Changes in microbial community diversity, composition, and functions upon nitrate and Cr(VI) contaminated groundwater

With the increasing occurrences of nitrate and Cr(VI) pollution globally, microbially driven pollutant reduction and its interaction effects were of growing interest. Despite the increasing number of experimental reports on the simultaneous reduction of nitrate and Cr(VI), a broad picture of the keystone species and metabolic differences in this process remained elusive. This study explored the changing of microorganisms with the introduction of Cr(VI)/NO₃^- through analyzing 242 samples from the NCBI database. The correlation between microbial abundance and environmental factors showed that, the types of energy substances and pollutants species in the environment had an impact on the diversity of microorganisms and community structure. The genus of Zoogloea, Candidatus Accumulibacter, and Candidatus Kapabacteria sp. 59-99 had the ability of denitrification, while genus of Alcaligenes, Kerstersia, Petrimonas, and Leucobacter showed effectively Cr(VI) resistance and reducing ability. Azoarcus, Pseudomonas, and Thauera were recognized as important candidates in the simultaneous reduction of nitrate and Cr(VI). Metagenomic predictions of these microorganisms using PICRUSt2 further highlighted the enrichment of Cr(VI)and nitrate reduction-related genes (such as chrA and norC). Special attention should therefore be paid to these bacteria in subsequent studies to evaluate their performance and mechanisms involved in simultaneous denitrification and chromium removal. The microbial co-occurrence network analysis conducted on this basis emphasized a strong association between community collaboration and pollution removal. Collectively, either site surveys or laboratory experiments, subsequent studies should focus on these microbial populations and the interspecific collaborations as they strongly influence the occurrence of simultaneous nitrate and Cr(VI) reduction.

Microbial explanation to performance stratification along up-flow solid-phase denitrification column packed with polycaprolactone

In this study, the fluctuating profiles of physicochemical and microbial characterizations along different filling heights of continuously up-flow solid-phase denitrification (SPD) columns packed with polycaprolactone (PCL) were investigated. It was found both the PCL filling area and non-filling area made significant contributions to treatment performance and denitrification mainly occurred near the bottom of the filling column. Nitrate displayed a high proportional removal (≥98.7%) among all the cases except the one with the lowest filling ratio (FR30) and highest NLR (3.99 ± 0.12 gN/(L·d)), while nitrite and ammonium displayed a weak accumulation in final effluents (nitrite ≤ 0.40 mg/L; ammonium ≤ 0.98 mg/L). The intensity of PCL hydrolysis in the top substrate was stronger than those in the middle or bottom. Both dissimilatory nitrate reduction to ammonium (DNRA) and microbial lysis contributed to ammonium accumulation, and nitrate was mainly removed via traditional denitrification and DNRA. JGI_0000069-P22_unclassified and Gracilibacteria_unclassified might contribute to denitrification.

Nitrates in the environment: A critical review of their distribution, sensing techniques, ecological effects and remediation

Nitrate pollution is eminent in almost all the developing nations as a result of increased natural activities apart from anthropogenic pollution. The release of nitrates in more than critical quantities into the water bodies causes accretion impacts on living creatures, environmental receptors, and human vigour by accumulation through the food chain. Nitrates have recently acquired researchers' huge attention and extend their roots in environmental contamination of surface and groundwater systems. The presence of nitrate in high concentrations in surface and groundwater triggers several health problems, for instance, methemoglobinemia, diabetes, eruption of infectious disorders, harmfully influence aquatic organisms. Sensing nitrate is an alternate option for monitoring the distribution of nitrate in different water bodies. Here we review electrochemical, spectroscopic, and electrical modes of nitrate sensing. It is concluded that, among the various sensors discussed in this review, FET sensors are the most desirable choice. Their sensitivity, ease of use and scope for miniaturisation are exceptional. Advanced functional materials need to be designed to satiate the growing need for environmental monitoring. Different sources of nitrate contamination in ground and surface water can be estimated using different techniques such as nitrate isotopic composition, co contaminants, water tracers, and other specialized techniques. This review intends to explore the research work on remediation of nitrate from wastewater and soil using different processes such as reverse osmosis, chemical denitrification, biological denitrification, ion exchange, electrodialysis, and adsorption. Denitrification proves as a promising alternative over previously reported techniques in terms of their nitrate removal because of its high cost-effectiveness.

OUP accepted manuscript

Oxygen (O₂) is the ultimate oxidant on Earth and its respiration confers such an energetic advantage that microorganisms have evolved the capacity to scavenge O₂ down to nanomolar concentrations. The respiration of O₂ at extremely low levels is proving to be common to diverse microbial taxa, including organisms formerly considered strict anaerobes. Motivated by recent advances in O₂ sensing and DNA/RNA sequencing technologies, we performed a systematic review of environmental metatranscriptomes revealing that microbial respiration of O₂ at nanomolar concentrations is ubiquitous and drives microbial activity in seemingly anoxic aquatic habitats. These habitats were key to the early evolution of life and are projected to become more prevalent in the near future due to anthropogenic-driven environmental change. Here, we summarize our current understanding of aerobic microbial respiration under apparent anoxia, including novel processes, their underlying biochemical pathways, the involved microorganisms, and their environmental importance and evolutionary origin.

Immobilization of microorganisms in activated zeolite beads and alkaline pretreated straws for ammonium-nitrogen removal from urban river water

The non-treated wastewater from residential areas contains high concentrations of ammonium-nitrogen (NH₄⁺-N). When discharged into the drainage water system, it deteriorates the water quality in urban rivers. This study used two types of materials to form eco-bags, using activated zeolite bead (AZB) and alkaline pretreated straw (APS), in geotextile bags for easy recovery and reuse. The AZB and APS provided the breeding habitat for the microorganisms that promoted biofilm formation on their surface. The immobilization of engineered denitrification microorganisms facilitated the removal of NH₄⁺-N from the urban river water. The NH₄⁺-N removal in the AZB and APS bags were in the range of 64-73%, and 56-61%, respectively, while the chemical oxygen demand (COD) removal in the AZB and APS bags ranged from 33-36%, and 30-31%, respectively. In addition, as evident from DNA and microbial community analysis, the microorganisms demonstrated a greater proclivity to grow and proliferate on the surface of AZB and APS and improved the water quality of urban rivers.

Simultaneous removal of nitrogen and arsenite by heterotrophic nitrification and aerobic denitrification bacterium Hydrogenophaga sp. H7

Introduction

Nitrogen and arsenic contaminants often coexist in groundwater, and microbes show the potential for simultaneous removal of nitrogen and arsenic. Here, we reported that Hydrogenophaga sp. H7 was heterotrophic nitrification and aerobic denitrification (HNAD) and arsenite [As(III)] oxidation bacterium.

Methods

The appearance of nitrogen removal and As(III) oxidation of Hydrogenophaga sp. H7 in liquid culture medium was studied. The effect of carbon source, C/N ratio, temperature, pH values, and shaking speeds were analyzed. The impact of strains H7 treatment with FeCl3 on nitrogen and As(III) in wastewater was assessed. The key pathways that participate in simultaneous nitrogen removal and As(III) oxidation was analyzed by genome and proteomic analysis.

Results and discussion

Strain H7 presented efficient capacities for simultaneous NH₄ ⁺-N, NO₃ ^--N, or NO₂ ^--N removal with As(III) oxidation during aerobic cultivation. Strikingly, the bacterial ability to remove nitrogen and oxidize As(III) has remained high across a wide range of pH values, and shaking speeds, exceeding that of the most commonly reported HNAD bacteria. Additionally, the previous HNAD strains exhibited a high denitrification efficiency, but a suboptimal concentration of nitrogen remained in the wastewater. Here, strain H7 combined with FeCl3 efficiently removed 96.14% of NH₄ ⁺-N, 99.08% of NO₃ ^--N, and 94.68% of total nitrogen (TN), and it oxidized 100% of As(III), even at a low nitrogen concentration (35 mg/L). The residues in the wastewater still met the V of Surface Water Environmental Quality Standard of China after five continuous wastewater treatment cycles. Furthermore, genome and proteomic analyses led us to propose that the shortcut nitrification-denitrification pathway and As(III) oxidase AioBA are the key pathways that participate in simultaneous nitrogen removal and As(III) oxidation.

Variations of N concentrations and microbial community in the start-up of anammox using anaerobic heterotrophic sludge: Influence of a long reaction-phase time and comparison of the efficiencies of attached-versus suspended-growth cultures

Anaerobic sludge was capable of producing anaerobic ammonium oxidation (anammox) cultures. However, the low activity of anammox bacteria in the seed sludge often led to a long time for stable anammox to initiate. The objective of this study was to investigate the influence of an extended reaction-phase time in the sequencing batch reactor (SBR) on the rapid startup of anaerobic ammonium oxidation (anammox) using anaerobic heterotrophic bacteria as the seed sludge. After the startup, suspended and attached bacteria in anammox were separately analyzed for comparison. The variations of nitrogen concentrations and shifts of the microbial community structures were studied. The results showed that anammox occurred after a long reaction-phase time in the SBR with the efficient removals of NH₄⁺ (96.4%) and NO₂^- (99.8%). The effective NO₂^- treatment before anammox startup was attributable to inevitable denitrification or dissimilatory nitrate reduction (e.g., Denitratisoma). The occurrence of anammox was supported by the anammox stoichiometry, bacteria diversity variation, and principal component analysis. The overall nitrogen removal rate (NRR) and nitrogen removal efficiency (NRE) was 0.07 kg/m³-d and 92.8%, respectively. The relative molar quantities of NH₄⁺ and NO₂^- removed as well as N₂ and NO₃^- formed were 1(1):1.29(1.32):1.45(1.02):0.15(0.26), as the numbers in the parentheses represent the theoretical values. Denitratisoma and Desulfatiglans dominated in the seed sludge, whereas Candidatus_Jettenia abundances were significantly higher in anammox attached- (26.0%) and suspended-growth cultures (14.5%). Fifty-three genera were simultaneously identified in all samples, suggesting their importance in the startup of anammox from anaerobic sludge. Candidatus_Jettenia was observed to be more associated with the growth of anammox biofilm (the abundances were 26.0% and 14.5% in attached- and suspended-growth cultures, respectively) and supported the fine nitrogen removal performance in the attached-growth cultures.

Tin dioxide nanomaterial-based photocatalysts for nitrogen oxide oxidation: a review

Semiconducting SnO₂ photocatalyst nanomaterials are extensively used in energy and environmental research because of their outstanding physical and chemical properties. In recent years, nitrogen oxide (NO _x ) pollutants have received particular attention from the scientific community. The photocatalytic NO _x oxidation will be an important contribution to mitigate climate change in the future. Existing review papers mainly focus on applying SnO₂ materials for photocatalytic oxidation of pollutants in the water, while studies on the decomposition of gas pollutants are still being developed. In addition, previous studies have shown that the photocatalytic activity regarding NO _x decomposition of SnO₂ and other materials depends on many factors, such as physical structure and band energies, surface and defect states, and morphology. Recent studies have been focused on the modification of properties of SnO₂ to increase the photocatalytic efficiency of SnO₂, including bandgap engineering, defect regulation, surface engineering, heterojunction construction, and using co-catalysts, which will be thoroughly highlighted in this review.

Enhanced nitrogen removal from low-temperature wastewater by an iterative screening of cold-tolerant denitrifying bacteria

The biological process to remove nitrogen in winter effluent is often seriously compromised due to the effect of low temperatures (< 13 °C) on the metabolic activity of microorganisms. In this study, a novel heterotrophic nitrifying-aerobic denitrifying bacterium with cold tolerance was isolated by iterative domestication and named Moraxella sp. LT-01. The LT-01 maintained almost 60% of its maximal growth activity at 10 °C. Under initial concentrations of 100 mg/L, the removal efficiencies of ammonium, nitrate, nitrite by LT-01 were 70.3%, 65.4%, 61.7% respectively for 72 h incubation at 10 °C. Nitrogen balance analysis showed that about 46% of TN was released as gases and 16% of TN was assimilated for cell growth. The biomarker genes involved in nitrification and denitrification pathways were identified by gene-specific PCR and revealed that the LT-01 has nitrite reductase (NirS) but not hydroxylamine reductase (HAO), which implies the involvement of other genes in the process. The study indicates that LT-01 has the potential for use in low-temperature regions for efficient sewage treatment.

RNA stable isotope probing and high-throughput sequencing to identify active microbial community members in a methane-driven denitrifying biofilm

AIMS

Aerobic methane oxidation coupled to denitrification (AME-D) is a promising process for removing nitrate from groundwater and yet its microbial mechanism and ecological implications are not fully understood. This study used RNA stable isotope probing (RNA-SIP) and high-throughput sequencing to identify the micro-organisms that are actively involved in aerobic methane oxidation within a denitrifying biofilm.

METHODS AND RESULTS

Two RNA-SIP experiments were conducted to investigate labelling of RNA and methane monooxygenase (pmoA) transcripts when exposed to ¹³ C-labelled methane over a 96-hour time period and to determine active bacteria involved in methane oxidation in a denitrifying biofilm. A third experiment was performed to ascertain the extent of ¹³ C labelling of RNA using isotope ratio mass spectrometry (IRMS). All experiments used biofilm from an established packed bed reactor. IRMS confirmed ¹³ C enrichment of the RNA. The RNA-SIP experiments confirmed selective enrichment by the shift of pmoA transcripts into heavier fractions over time. Finally, high-throughput sequencing identified the active micro-organisms enriched with ¹³ C.

CONCLUSIONS

Methanotrophs (Methylovulum spp. and Methylocystis spp.), methylotrophs (Methylotenera spp.) and denitrifiers (Hyphomicrobium spp.) were actively involved in AME-D.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first study to use RNA-SIP and high-throughput sequencing to determine the bacteria active within an AME-D community.

Effect of intermittent induced aeration on nitrogen removal and denitrifying-bacterial community structure in Cork and gravel vertical flow pilot-scale treatment wetlands

In this work, we have evaluated the impact of intermittent induced aeration in total nitrogen (TN), ammonia (NH₄-N) and nitrate-nitrogen (NO₃-N) removal in four pilot-scale vertical flow constructed wetlands (VFCW) (two aerated two non-aerated) using cork by-product or gravel as the filter material and planted with Phragmites australis. Both aerated and non-aerated systems achieved high COD and BOD₅ elimination rates (≥ 90%) at the end of the 5-month test period. However, the aerated systems presented maximal COD and BOD₅ removal from the third month of operation onwards since air supply favored the oxidative bioprocesses occurring within the wetlands. Cork and gravel aerated VFCW also proved to be more efficient (p < 0.05) in NO₃-N removal than the non-aerated systems and this upgraded performance was correlated with a significant higher relative abundance of the nirS gene. The aerated systems also showed a slightly improved NH₄-N removal. Noticeably, cork VFCW showed higher TN removal mean values (∼35%) than gravel wetlands (27-28%) regardless aeration. Moreover, cork VFCW showed higher relative abundance of the nosZ gene. Our results demonstrated a better nitrogen elimination for the aerated cork pilot-scale VFCW, and this behavior was correlated with a higher abundance of both nirS and nosZ, two of the key functional genes involved in nitrogen metabolism.

Role of heterotrophic nitrifiers and aerobic denitrifiers in simultaneous nitrification and denitrification process: A non-conventional nitrogen removal pathway in wastewater treatment

Bacterial species capable of performing both nitrification and denitrification in a single vessel under similar conditions have gained significance in the wastewater treatment scenario considering their unique character of performing the above reactions under heterotrophic and aerobic conditions respectively. Such a novel strategy often referred to as simultaneous nitrification and denitrification (SND) has a tremendous potential in dealing with various wastewaters having low C:N content, considering that the process needs very little or no external carbon source and oxygen supply thus adding to its cost-effective and environmentally friendly nature. Though like other microorganisms, heterotrophic nitrifiers and aerobic denitrifiers convert inorganic or organic nitrogen-containing substances into harmless dinitrogen gas in the wastewater, their ecophysiological role in the global nitrogen cycle is still not yet fully understood. Attempts to highlight the role played by the heterotrophic nitrifiers and aerobic denitrifiers in dealing with nitrogen pollution under various environmental operating conditions will help in developing a mechanistic understanding of the SND process to address the issues faced by the traditional methods of aerobic autotrophic nitrification-anaerobic heterotrophic denitrification.

A Novel Regulator Participating in Nitrogen Removal Process of Bacillus subtilis JD-014

Aerobic denitrification is considered as a promising biological method to eliminate the nitrate contaminants in waterbodies. However, the molecular mechanism of this process varies in different functional bacteria. In this study, the nitrogen removal characteristics for a newly isolated aerobic denitrifier Bacillus subtilis JD-014 were investigated, and the potential functional genes involved in the aerobic denitrification process were further screened through transcriptome analysis. JD-014 exhibited efficient denitrification performance when having sodium succinate as the carbon source with the range of nitrate concentration between 50 and 300 mg/L. Following the transcriptome data, most of the up-regulated differentially expressed genes (DEGs) were associated with cell motility, carbohydrate metabolism, and energy metabolism. Moreover, gene nirsir annotated as sulfite reductase was screened out and further identified as a regulator participating in the nitrogen removal process within JD-014. The findings in present study provide meaningful information in terms of a comprehensive understanding of genetic regulation of nitrogen metabolism, especially for Bacillus strains.

Impacts of ammonia loading and biofilm age on the prevalence of nitrogen-cycling microorganisms in a full-scale submerged attached-growth reactor

This study reports the impacts of seasonal ammonia load changes and biofilm age on the quantity of biomass and on the prevalence of ammonia- and nitrite-metabolizing organisms within a submerged attached-growth reactor (SAGR™) following lagoon treatment. Ammonia (NH₃ ) loadings (0.12-3.17 kg/d) in the primary SAGR were measured over 223 days from May to December in 2017. Adjustment of the wastewater flow path on September 1 successfully increased NH₃ loading to the primary SAGR, which subsequently caused reactor biomass to increase. The NH₃ removal rate in October (0.5 kg/d) was greater than rates in June and July (0.3 and 0.2 kg/d) despite a water temperature decrease from >24 to 15.6°C. This elevated removal rate in October, and the sustained removal rate in December (0.4 kg/d, 5.3°C) were associated with a measured increase in microbial biomass. The relative abundance of the anammox organism C. Brocadia was 5 times greater in the mature biofilm after 686 days of growth, and the genus Pseudomonas increased sevenfold. The presence of Pseudomonas, which contains denitrifying species, and anammox suggests a high potential for removal of total nitrogen in SAGRs. PRACTITIONER POINTS: Pseudomonas prevalence and the presence of anammox suggest a high potential for total nitrogen removal in mature SAGR biofilms. The abundance of the anammox microorganism C. Brocadia was greater after 686 days of biofilm growth compared with 33 days. Simple operational changes can increase biomass in the SAGR to maintain, or even increase, NH₃ transformation rates during cold weather.

The investigation of bioremediation potential of Bacillus subtilis and B. thuringiensis isolates under controlled conditions in freshwater

Bioremediation is widely used to remove water pollution as environmentally friendly smart solutions. In this study, Bacillus isolates were investigated in terms of the effectiveness of single and multiple cultures in eliminating aquatic pollution related to aquaculture activities. In the established experimental setups, the environments where Bacillus isolates were inoculated with single and multiple cultures at 1 × 10⁷ CFU/mL were evaluated comparatively with control groups without these isolates, and total aerobic mesophilic bacterial counts were performed in the petri dish by inoculation method. At the end of the 6 days of the experiment, in the environment in which single and multiple cultures of Bacillus isolates were presented with 17-20 ± 0.05 °C temperature and 5.1-8.1 pH 2-4.6 mg/l dissolved oxygen values (O₂), 2% increase in total phosphorus (TP) value was observed. On the other hand, 4% removal of Ammonia-nitrogen (NH₃-N), 80% removal of Nitrite-nitrogen (NO₂-N), and 100% removal of Nitrate-nitrogen (NO₃-N) were observed. In the changes in heavy metal concentrations, the removal of Ni, Cr, Se, Al, Cd, Mn, Fe, and B was observed from highest to lowest as 57%, 50%, 50%, 43%, 40%, 23%, 5%, and 2%, respectively. It also has been seen that B. thuringiensis isolate was observed to be more effective than B. subtilis in metal removal.

Performance and microbial community dynamics in anaerobic continuously stirred tank reactor and sequencing batch reactor (CSTR-SBR) coupled with magnesium-ammonium-phosphate (MAP)-precipitation for treating swine wastewater

The impacts of magnesium-ammonium-phosphate (MAP) precipitation on the performance and microbial dynamics in an anaerobic continuously stirred tank reactor (CSTR) coupled with sequencing batch reactor (SBR) for swine wastewater treatment were investigated. In CSTR-SBR systems, an overall higher removal efficiency for COD, NH₄⁺ and PO₄^3-as 98.6%, 98.7% and 97.9% was achieved with MAP precipitation, compared to CSTR-SBR without MAP pretreatment (i.e., 97.5, 74.3% and 19.9% for COD, NH₄⁺ and PO₄^3-, respectively). With MAP precipitation, the high C/N ratio of 6.6 after anaerobic CSTR was observed. The increase in the richness and diversity of microbial communities in CSTR with MAP was conducive to nitrogen and phosphorus removal, as well as biogas production. The core community was affiliated with bacterial phyla Firmicutes, Bacteroidetes, Proteobacteria, Cloacimonetes, and Spirochaetae. The study provide a new insight into the potential application of MAP precipitation as pretreatment for dealing with nutrient recovery from high-strength swine wastewater.

Isolation and Characterization of an Aerobic Denitrifier Bacillus sp. SC16 from an Intensive Aquaculture Pond

Overloading of ammonia and nitrite nitrogen in aquaculture can result in toxicity to aquatic animals. In order to eliminate the hazardous substances, a highly efficient denitrifying bacterium, Bacillus sp. SC16, was identified in a fishery pond and isolated subsequently. The strain SC16 could remove nitrate up to 97%, ammonia up to 36.6%, and nitrite up to 99.99% when incubated with nitrate at an initial concentration of 306.9 mg·L−1 for 72 h, ammonia at 165.49 mg·L−1 for 48 h, and nitrite at 200 mg·L−1 for 24 h under aerobic conditions. The nitrite reductase gene was identified as the nirK gene. The transcriptional levels of the nirK gene in strain SC16 incubated with ammonia, nitrate, and nitrite showed similar expression patterns. When the strain SC16 was used to treat the aquaculture water, the concentration of ammonia decreased significantly, from 8.35 mg·L−1 to 4.56 mg·L−1, and there was almost no accumulation of nitrite by the end of experiment. Therefore, the results indicated that Bacillus sp. SC16 could be a promising candidate for aquaculture water treatment.

Corpse decomposition increases nitrogen pollution and alters the succession of nirK-type denitrifying communities in different water types

Cadaver decomposition as high-quality nutrient inputs may exert strong perturbation on the aquatic environments, such as high nitrogen or nitrate pollution. Denitrifying bacteria may reduce nitrate to nitrogen gas, thereby decreasing the nitrogen pollution and improving self-purification ability of aquatic ecosystem. However, how nirK denitrifying communities in water respond to cadaver decomposition remains unknown. Thus, we employed high-throughput sequencing and chemical analysis to investigate the succession of nirK-type denitrifying communities in tap water and Yellow river water (experimental groups) as well as their corresponding control groups during two important stages of fish corpse decomposition called advanced floating decay and sunken remains. Our data showed that the concentration of NH₄⁺-N in the experimental groups increased approximately 3-4 times compared with the control groups. Proteobacteria was the predominant phylum for nirK denitrifying communities. Several potential pathogenic genera, such as Brucella and Achromobacter, were enriched in the corpse groups. Notably, nirK-type community structures were significantly impacted by cadaver decomposition. Community structures in the corpse groups become more similar with succession, indicating community convergence at the final stage. Water pH, oxidation-reduction potential (ORP) and treatment were three important factors affecting the community structures. However, water type was not a main driving factor determining carcass-associated nirK-type bacterial communities. Four phylogenetic clusters were detected in the denitrifying communities, but showed significantly different distribution between the corpse and control groups. These results provide an in-depth understanding for nirK denitrifying functional bacteria and potential pathogenic bacteria during carrion decomposition process, which offer valuable reference to environmental evaluation and management.

Biologically mediated release of endogenous N2O and NO2 gases in a hydrothermal, hypoxic subterranean environment

The migration of geogenic gases in continental areas with geothermal activity and active faults is an important process releasing greenhouse gases (GHG) to the lower troposphere. In this respect, caves in hypogenic environments are natural laboratories to study the compositional evolution of deep-endogenous fluids through the Critical Zone. Vapour Cave (Alhama, Murcia, Spain) is a hypogenic cave formed by the upwelling of hydrothermal CO₂-rich fluids. Anomalous concentrations of N₂O and NO₂ were registered in the cave's subterranean atmosphere, averaging ten and five times the typical atmospheric backgrounds, respectively. We characterised the thermal conditions, gaseous compositions, sediments, and microbial communities at different depths in the cave. We did so to understand the relation between N-cycling microbial groups and the production and transformation of nitrogenous gases, as well as their coupled evolution with CO₂ and CH₄ during their migration through the Critical Zone to the lower troposphere. Our results showed an evident vertical stratification of selected microbial groups (Archaea and Bacteria) depending on the environmental parameters, including O₂, temperature, and GHG concentration. Both the N₂O isotope ratios and the predicted ecological functions of bacterial and archaeal communities suggest that N₂O and NO₂ emissions mainly depend on the nitrification by ammonia-oxidising microorganisms. Denitrification and abiotic reactions of the reactive intermediates NH₂OH, NO, and NO₂^- are also plausible according to the results of the phylogenetic analyses of the microbial communities. Nitrite-dependent anaerobic methane oxidation by denitrifying methanotrophs of the NC10 phylum was also identified as a post-genetic process during migration of this gas to the surface. To the best of our knowledge, our report provides, for the first time, evidence of a niche densely populated by Micrarchaeia, which represents more than 50% of the total archaeal abundance. This raises many questions on the metabolic behaviour of this and other archaeal phyla.

Evaluating the effect of seasonal temperature changes on the efficiency of a rhizofiltration system in nitrogen removal from urban runoff

The study presents an evaluation of nitrogen removal efficiency of a pilot-scale rhizofiltration system in Pretoria, South Africa. The rhizofiltration system was divided into two sections, one side planted with common reeds (Phragmites australis) and the other side was without plants kept as a control. The objective of the study was to evaluate the influence of seasonal temperature on the removal of nitrogen species from the simulated urban runoff using the rhizofiltration system. The final effluent from the filter was collected bimonthly at different sampling points for 10 months after an application time of 5 min and 25 min. Duplicate samples were taken to determine the concentrations of TKN (Total Kjeldahl nitrogen), ammonium, nitrate and chemical oxygen demand (COD) for the raw influent and final effluent from the rhizofiltration system. Temperature and pH were determined on-site. During the monitoring period, there was no significant difference in the inflow concentration of ammonium in colder and warmer months for both planted and control sides. Furthermore, the composition of the feed medium to the rhizofilter was kept the same in both cold and warm season and for both planted and control sides. The removal of ammonium in colder and warmer months was not significant in both systems. At an average temperature increase of 5.2 °C in the warmer months, the ammonium removal efficiency in the planted side increased by 7.5%, while for the control side the removal efficiency increased by 2.4%. The difference in removal was not significant between the averages of effluent ammonium after an application time of 25 min in colder versus warmer months for the planted and control sides of the system. Furthermore, an increased nitrification rate was more evident in the planted than in the control side, which was subsequently denitrified. It was observed that 60.4% of nitrate concentration was potentially removed in the planted side whereas 45.4% was potentially denitrified in the control side. These results suggest positive correlation between nitrate concentration and the potential for denitrification. The nitrate removal efficiency dropped to 32.2% for the planted site and to 26.1% for the control system in colder months. Temperature had an effect on nitrogen removal, since nitrogen removal efficiency decreased in colder months. Complete nitrogen removal could not be achieved under the operating conditions.

Aerobic denitrifying bacterial communities drive nitrate removal: Performance, metabolic activity, dynamics and interactions of core species

Three novel mix-cultured aerobic denitrifying bacteria (Mix-CADB) consortia named D14, X21, and CL exhibited excellent total organic carbon (TOC) removal and aerobic denitrification capacities. The TOC and nitrate removal efficiencies were higher than 93.00% and 98.00%. The results of Biolog demonstrated that three communities displayed high carbon metabolic activity. nirS gene sequencing and ecological network model revealed that Pseudomonas stutzeri, Paracoccus sp., and Paracoccus denitrificans dominated in the D14, X21, and CL communities. The dynamics and co-existence of core species in communities drove the nutrient removal. Response surface methodology showed the predicted total nitrogen removal efficiency reached 99.43% for D14 community. The three Mix-CADB consortia have great potential for nitrogen-polluted aquatic water treatment because of their strong adaptability and removal performance. These results will provide new understanding of co-existence, interaction and dynamics of Mix-CADB consortia for nitrogen removal in nitrogen-polluted aquatic ecosystems.

Simultaneous nitrification-denitrification by phosphate accumulating microorganisms

Nitrogen and phosphorous are important inorganic water pollutants that pose a major threat to the environment and health of both humans and animals. The physical and chemical ways to remove these pollutants from water and soil are expensive and harsh, so biological removal becomes the method of choice to alleviate the problem without any side effects. The identification of microorganisms capable of simultaneous heterotrophic nitrification and aerobic denitrification has greatly simplified the sequestration of nitrogen from ammonium (NH₄⁺) into dinitrogen (N₂). Further, the discovery of phosphorous accumulating organisms offers greater economic benefits because these organisms can favourably and simultaneously remove both nitrogen and phosphorous from wastewaters hence reducing the nutrient burden. The stability of the system and removal efficiency of inorganic pollutants can be enhanced by the use of immobilized organisms. However, limited work has been done so far in this direction and there is a need to further the efforts towards refining process efficiency by testing low-cost substrates and diverse microbial populations for the total eradication of these contaminants from wastewaters.