ANAMMOX-denitrification biomass in microbial fuel cell to enhance the electricity generation and nitrogen removal efficiency

Anammox with alternative electron acceptors: perspectives for nitrogen removal from wastewaters

In the context of the anaerobic ammonium oxidation process (anammox), great scientific advances have been made over the past two decades, making anammox a consolidated technology widely used worldwide for nitrogen removal from wastewaters. This review provides a detailed and comprehensive description of the anammox process, the microorganisms involved and their metabolism. In addition, recent research on the application of the anammox process with alternative electron acceptors is described, highlighting the biochemical reactions involved, its advantages and potential applications for specific wastewaters. An updated description is also given of studies reporting the ability of microorganisms to couple the anammox process to extracellular electron transfer to insoluble electron acceptors; particularly iron, carbon-based materials and electrodes in bioelectrochemical systems (BES). The latter, also referred to as anodic anammox, is a promising strategy to combine the ammonium removal from wastewater with bioelectricity production, which is discussed here in terms of its efficiency, economic feasibility, and energetic aspects. Therefore, the information provided in this review is relevant for future applications.

Study of bacterial population dynamics in seed culture developed for ammonia reduction from synthetic wastewater

The waterbodies have been polluted by various natural and anthropogenic activities. The aquatic waste includes ammonia as one of the most toxic pollutants. Several biological treatment systems involving anoxic and semi anoxic bacteria have been proposed for reducing nitrogen loads from wastewater and increasing the efficiency and cost effectiveness. These bacteria play a vital role in the processes involved in the nitrogen cycle in nature. However, the enrichment, sustainability and identification of bacterial communities for wastewater treatment is an important aspect. Most of the chemolithotrophs are unculturable hence their identification and measurement of abundance remains a challenging task. In this study the different bacteria involved in total nitrogen removal from the wastewater are enriched for 700 days under anoxic condition. The synthetic wastewater containing 0.382 g/L of ammonium chloride was used. Molecular identification of the bacteria involved in various steps of the nitrogen cycle was carried out based on amplification of functional genes and 16S rRNA gene Polymerase chain reaction followed by DNA sequencing. Change in the abundance of chemolithotrophs was studied using qPCR. The mutual growth of various nitrifiers along with anaerobic bacteria were identified by molecular characterisation of DNA at various time intervals with the different genes involved in the nitrogen cycle. Nitrosomonas species like Nitrosomonas europaea were identified throughout the batch scale studies possessing the genes associated with ammonia oxidizing bacteria and nitrite oxidizing bacteria which act as a complete ammonia oxidizer. The uncultured species of Nitrospira and anammox bacteria were also observed which predicts the coexistence of the anammox and comammox bacteria in a batch scale study. The coexistence of the semi anoxic and anoxic bacteria helped in the growth of these bacteria for a longer duration of time. The nitrite produced by the comammox during nitrification can be utilized by anammox as an electron carrier. The other species of denitrifiers like Pseudomonas denitrificans and Aminobacter aminovorans were also observed. It is concluded that the enrichment of semi anoxic and anoxic bacteria was faster with the increase in growth of the bacteria involved in nitrification, comammox, anammox and partial denitrification process. The bacterial growth is enhanced and the efficiency is increased which can be further used in the development of small pilot scale bioreactor for total nitrogen removal.

Improving CH4/O2 energy ratio of meat processing wastewater treatment systems through micro-sieving

Micro-sieving is an effective way to prevent organic pollutants enter the main biological process and reduce aeration intensity and sludge production. However, few researchers quantified the effect of micro-sieving on meat processing wastewater treatment. The current study developed Excel-based models to compare the energy consumption and production of historical, conventional and innovative systems. Historical and conventional systems employ activated sludge (AS), nitrification, and denitrification as the main biological processes. Innovative systems are designed by using up-flow anaerobic sludge blanket (UASB) and partial nitrification/Anammox (PN/A) as the main treatment processes. Results show that the CH4/O2 energy ratios of the innovative treatment system are as high as 10 times of the historical and conventional systems. Therefore, innovative system can achieve electrical self-sufficiency. Micro-sieving reduces 5% of aeration demand. Furthermore, the impact of micro-sieving on the innovative treatment systemis assessed by cost-benefit analysis. System with micro-sieving has the shortest payback time of 2.1 years and reduces cost of the innovative treatment system. An excel-based model was developed to quantify the impact of micro-sieving on energy and cost of innovative treatment system, thereby providing a valuable reference for future sustainable engineering design of meat processing wastewater treatment.

Greywater treatment in SBR-SND reactor - optimization of hydraulic retention time, volumetric exchange ratio and sludge retention time

In this study, simultaneous nitrification and denitrification-sequencing batch reactor (SND-SBR) process was investigated to treat greywater. The effect of three process parameters, including hydraulic retention time (HRT), volumetric exchange ratio (VER) and sludge retention time (SRT), was optimised using a 23 full factorial design. The statistic model was developed for two response variables, i.e. chemical oxygen demand (COD) and ammonia (NH3-N) removal. The optimum conditions were 6.8 h HRT (anaerobic/aerobic/anoxic: 1.77 h/2.77 h/2.27 h), 0.7 VER and 7.94 d SRT, which resulted in 93.9% COD and 84.6% NH3-N removal efficiency. SRT was the most significant factor, followed by HRT and VER for COD and NH3-N removal. The interaction effect of VER and SRT was significant in COD removal. On the other hand, the interaction effects of HRT-VER and HRT-SRT were significant in NH3-N removal. The removal efficiencies of 89.6 ± 1.1% and 83.7 ± 2.3% were observed for TKN and TN, respectively, in the optimised SND-SBR system. NH3-N removal was obtained via nitrate pathway in the SND-SBR system. The PO43--P removal of 74.2 ± 3.4% was obtained via aerobic phosphorus uptake and post anoxic denitrification at the optimal condition. To enhance PO43--P removal, adsorption (using corn cob adsorbent) was integrated with SBR by adding the optimum adsorbent dose (0.5 g/L). The PO43--P removal efficiency in the SBR-adsorption system was found to be 80 ± 1.5%. The biodegradation of emerging contaminants (ECs) was also carried out in the SND-SBR system, and the results showed removal rate of 58.9 ± 2.3% benzophenone-3 (BP) and 80.1 ± 2.2% anionic surfactant (AS).

Enhanced biological phosphorus removal in low-temperature sewage with iron-carbon SBR system

This study proposed an AO-SBR (Anaerobic Aerobic Sequencing Batch Reactor) combined with iron-carbon micro-electrolysis (ICME) particles system for sewage treatment at low temperature and explored the dephosphorisation mechanism and microbial community structure. The experimental results illustrated that ICME particles contributed to phosphorus removal, metabolic mechanism of poly-phosphorus accumulating organism (PAO) and microbial community structure in the AO-SBR system. The optimal treatment effect was achieved under the conditions of pH 7, DO 3.0 mg/L and particle dosage of 2.6 g Fe-C/g MLSS, and the removal rates of COD, TP, NH4+-N and TN reached 80.56%, 91.46%, 69.42% and 57.57%. The proportion of phosphorus accumulating organisms (PAOs) increased from 4.54% in the SBR system to 10.89% in the ICME-SBR system at 10°C. Additionally, the metabolic rate of PAOs was promoted, and the activities of DHA and ETS both reached the maximum value of 13.34 and 102.88 μg·mg-1VSS·h-1. These results suggest that the ICME particles could improve the performance of activated sludge under low-temperature conditions. This technology provides a new way for upgrading the performance of sewage treatment in the cold area.

Examining current trends and future outlook of bio-electrochemical systems (BES) for nutrient conversion and recovery: an overview

Nutrient-rich waste streams from domestic and industrial sources and the increasing application of synthetic fertilizers have resulted in a huge-scale influx of reactive nitrogen and phosphorus in the environment. The higher concentrations of these pollutants induce eutrophication and foster degradation of aquatic biodiversity. Besides, phosphorus being non-renewable resource is under the risk of rapid depletion. Hence, recovery and reuse of the phosphorus and nitrogen are necessary. Over the years, nutrient recovery, low-carbon energy, and sustainable bioremediation of wastewater have received significant interest. The conventional wastewater treatment technologies have higher energy demand and nutrient removal entails a major cost in the treatment process. For these issues, bio-electrochemical system (BES) has been considered as sustainable and environment friendly wastewater treatment technologies that utilize the energy contained in the wastewater so as to recovery nutrients and purify wastewater. Therefore, this article comprehensively focuses and critically analyzes the potential sources of nutrients, working mechanism of BES, and different nutrient recovery strategies to unlock the upscaling opportunities. Also, economic analysis was done to understand the technical feasibility and potential market value of recovered nutrients. Hence, this review article will be useful in establishing waste management policies and framework along with development of advanced configurations with major emphasis on nutrient recovery rather than removal from the waste stream.

Pulsed electric field promotes the growth metabolism of aerobic denitrifying bacteria Pseudomonas putida W207-14 by improving cell membrane permeability

The purpose of this study was to explore the stimulation mechanism of low pulsed electric field (PEF) strength treatment to promote the growth metabolism of aerobic denitrifying bacteria Pseudomonas putida W207-14. The results indicated that compared with the control group, the strain W207-14 treated with PEF entered the logarithmic growth phase 5 h earlier, the growth time to reached the maximum cell optical density at 600 nm (OD600) of 1.935 ± 0.04 was only 24 h, which shortened by half. With the reduction of growth time, the metabolic rate of the strain increased significantly, in which the removal efficiency of COD, NO₃^--N and TN was 97.67 ± 1.12%, 90.34 ± 0.73% and 90.13 ± 0.10% in 24 h, respectively. The maximum nitrate removal rate increased from 3.49 mg/L/h to 7.53 mg/L/h. A large number of cells with simultaneous cell membrane damage and high physiological activity were observed by flow cytometry (FCM) in combination with fluorescence staining analysis, which confirmed the reversible electroporation on the cell membrane of strain W207-14 treated with PEF. Transcriptomic analysis indicated that PEF activated the highly significant differential expression of membrane porin (opdB, opdC, and oprB) and cytochrome oxidoreductase related genes (ccoP, ccoN, cioA and cioB) on the cell membrane, which promoted the transport of nutrients through the cell membrane and electron transfer during aerobic respiration and provided an explanation for the possible mechanism of PEF promoting the growth metabolism of strain W207-14 at the micro level. These results lay a foundation for the practical application of PEF enhanced aerobic denitrification technology.

Treatment capacity of a novel flexible fibre biofilm bioreactor treating high-strength milk processing wastewater

This study was focused on the capacity investigation of a novel multistage flexible fibre biofilm reactor (MS-FFBR) to treat milk processing wastewater (MPW) with high organic loading (OLR). The MS-FFBR performance was evaluated at four intermediate stages separately, and also the final effluent quality of the overall system with an influent chemical oxygen demand (COD_in) ranged from 1500 ± 20 to 6000 ± 50 mg/L and hydraulic retention times (HRTs) of 8, 12, and 16 h. By comparting the bioreactors into the four stages effectively enhanced the bioreactor's performance. The maximum TCOD removal efficiency was achieved at the first stage, which was about 89 ± 20, 82 ± 20, and 78 ± 20% at HRTs of 16, 12, 8 h, and low COD_in of 1600 ± 20, 1590 ± 20, and 1673 ± 20 mg/L, respectively. However, the first stage had less contribution to TCOD removal at high COD_in concentrations, reported to be about 42 ± 4%, 46 ± 4%, and 25 ± 4% at COD_in of 5960 ± 40, 5830 ± 40, and 5870 ± 40 mg/L, respectively. Furthermore, the MS-FFBR was effective in removing total suspended solids (TSS) and turbidity. The bioreactor has reduced the effluent turbidity to 9.0 ± 0.2, 20.0 ± 0.6, and 16.1 ± 0.5 NTU at low COD_in concentrations of 1600 ± 20, 1590 ± 20, and 1670 ± 20 mg/L and HRTs of 16, 12, and 8 h, respectively. The bioreactor revealed a high COD removal rate increased from 2.3 ± 0.1 to 12.2 ± 0.4 kg TCOD/m³d by increasing the OLR from 2.4 ± 0.1 to 17.6 ± 0.4 kg TCOD/m³d, confirming high reactor capacity for treatment of high-strength wastewater. Kinetic studies confirmed that the biomass yield was low at various HRTs ranging from 0.1 to 0.2 gVSS/gCOD.

Effects of multiple key factors on the performance of petroleum coke-based constructed wetland-microbial fuel cell

In this study, two constructed wetland-microbial fuel cells (CW-MFC), including a closed-circuit system (CCW-MFC) and an open-circuit system (OCW-MFC) with petroleum coke as electrode and substrate, were constructed to explore the effect of multiple key factors on their operation performances. Compared to a traditional CW, the CCW-MFC system showed better performance, achieving an average removal efficiency of COD, NH₄⁺-N, and TN of 94.49 ± 1.81%, 94.99 ± 4.81%, and 84.67 ± 5.6%, respectively, when the aeration rate, COD concentration, and hydraulic retention time were 0.4 L/min, 300 mg/L, and 3 days. The maximum output voltage (425.2 mV) of the CCW-MFC system was achieved when the aeration rate was 0.2 L/min. In addition, the CCW-MFC system showed a greater denitrification ability due to the higher abundance of Thiothrix that might attract other denitrifying bacteria, such as Methylotenera and Hyphomicrobium, to participate in the denitrifying process, indicating the quorum sensing could be stimulated within the denitrifying microbial community.

Transformation trend of nitrogen and phosphorus in the sediment of the sewage pipeline and their distribution along the pipeline

Microorganisms transform nitrogen and phosphorus in the sediment of sewage pipelines. When the sediment was scoured by water flow, these elements migrate. This work studied the changes in biofilm morphology and microbial community structure, and focused on the differences in the transformation of nitrogen and phosphorus along the pipeline. The results showed that the nitrogen and phosphorus concentrations varied systematically with time and space (the front, middle, and posterior segments of the pipe). With time, amino acid nitrogen (AAN) concentration in the sediment gradually decreased, NH₄⁺-N concentration slowly increased, NO₃^--N concentration began to increase after 25 days, and TP concentration continued to increase after 9 days. The AAN, NH₄⁺-N, and TP concentrations were highest in the posterior segment of the pipe and lowest in the front segment. However, NO₃^--N showed two stages: its concentration was highest in the front segment and lowest in the posterior segment during the first 17 days, after which the opposite was observed. Changes in the nitrogen and phosphorus concentrations were related to the microbial communities in the sediments. The abundances of Rhodobacter (0.001 <p ≤ 0.01), Trichococcus (p ≤ 0.001), Nakamurella (0.01 <p ≤ 0.05), and norank_f__norank_o__PeM15 (0.001 <p ≤ 0.01) in the terminal sediments were significantly higher than those in the initial sediments. Meanwhile, the abundances of Clostridium_sensu_stricto_1, Rhodobacter, norank_f__norank_o__PeM15, and Brevundimonas were different in the front, middle, and posterior segments. Furthermore, nitrogen and phosphorus were easily adsorbed on the small particles and were scoured and re-deposited on the posterior segment of the pipe, resulting in enrichment. The temporal variation in nitrogen and phosphorus and its spatial distribution along the pipeline were due to the combination of biotransformation and migration.

Characterization of a novel micro-pressure double-cycle reactor for low temperature municipal wastewater treatment

To solve the deterioration of effluent caused by low temperature in urban sewage treatment plant in cold areas, a new type of reactor was proposed, the biochemical environmental and low-temperature operating characteristics of the reactor were studied. Through analysis of flow simulation and dissolved oxygen (DO) distribution when the aeration rate was 0.6 m³/h, it showed that there were many different DO environments in the reactor at the same time, which provided favourable conditions for various biochemical reactions. The operation test showed that the average effluent removal rate of COD, TN, NH₄⁺-N and TP was 92.53%, 74.57%, 89.61% and 96.04%, respectively. And there were a variety of functional bacteria related to nitrogen and phosphorus removal in the system, most of them with strong adaptability at low temperatures. Among the dominant microorganisms, Flavobacterium and Rhodobacter were related to denitrification, Aeromonas and Thiothrix were related to phosphorous removal. Denitrifying phosphorus removal was the main way of phosphorus removal. Picrust2 results showed that the reactor operated well at low temperature, and the regional difference distribution of nitrification genes further confirmed the existence of functional zones in the reactor. The results showed that the Micro-pressure Double-cycle reactor worked well at low temperature, which provided a new idea and way for the upgrading of urban sewage treatment plants in cold areas.

Advanced simultaneous nitrogen and phosphorus removal for non-sterile wastewater through a novel coupled yeast-sludge system: Performance, microbial interaction, and mechanism

A novel coupled yeast-sludge system (CYSS) was constructed by the yeast Candida sp. PNY integrated with activated sludge to treat non-sterile mainstream wastewater. After 240-day cultivation, compared with single activated sludge, simultaneous removal efficiency of total organic carbon (TOC), nitrogen and phosphorus increased by 19.5% (176.34 mg TOC g^-1 d^-1), 21.3% (11.25 mg TN g^-1 d^-1) and 15.0% (6.95 mg TP g^-1 d^-1), respectively, while the amount of sludge reduced by 50%. Amplicon sequencing analysis showed that the abundance of Nitrosomonas, Nitrospira, Zoogloea, Dechloromonas, and Candidatus Accumulibacter significantly decreased to 0% on Day 200. Abundance of nirS and nirK for denitrification significantly decreased in CYSS by quantitative PCR (qPCR), and the copies of nirS and nirK were 3.37-fold and 1.71-fold decrease from Day 0 to Day 240, respectively. The results of Fluorescence in situ hybridization and co-occurrence network showed that Candida sp. PNY predominated its distribution in CYSS, and strongly connected with environmental variables based on network analysis. Furthermore, this study reconstructed the carbon, nitrogen and phosphorus metabolic pathways of the CYSS based on metagenomics.

Effects of electroconductive materials on treatment performance and microbial community structure in biofilter systems with silicone tubings

Biofilter systems coupling with microbial electrochemical technology can enhance the removal performance of pollutants. In this study, two types of coke (PK-A and PK-LSN) were used as electroconductive substrates in biofilter systems with silicone tubings. The results showed that the silicone tubings were beneficial for removing NH₄⁺-N. The PK-A systems reached removal efficiencies up to 83.5-85.3% for NH₄⁺-N without aeration. Compared to gravel systems, significantly higher removal efficiencies of NO₃^--N (84.8-95.4%) were obtained in coke systems, and better removal of PO₄^3--P (91.9-95.7%) was also simultaneously achieved in PK-A systems. Redundancy analysis (RDA) indicated that the better performances of coke systems rely on the functions of both electroactive (Trichococcus and Sulfurovum) and non-electroactive bacteria (Clostridium_sensu_stricto_1, Propionicicella, and Acinetobacter). These findings highlight the important contribution of silicone tubings to oxygen supply and provide useful guidance for the application of coke in composite matrix systems.

Insights into deterioration and reactivation of a mainstream anammox biofilm reactor response to C/N ratio

In-depth knowledge of the deterioration and reactivation of the anaerobic ammonium oxidation (anammox) induced by carbon-to-nitrogen (C/N) is still lacking. Herein, the anammox performance was investigated in an anaerobic sequence biofilm batch reactor fed with low-strength partial nitration effluent in the range of C/N ratio from 0.5 to 3. The anammox was hardly deteriorated at C/N lower than 1.5, while became worsen if C/N was above 2.0. The specific anammox activity (SAA) experiments showed an 85% decrease of SAA at C/N of 3.0 compared with the maximum value (C/N:0). However, anammox capacity was rapidly recovered once influent C/N was adjusted back to zero. Moreover, C/N also highly affected the composition, structure and function of extracellular polymeric substance of the anammox biofilm. High-throughput sequencing revealed a close correlation between C/N change and microbial structure shift. Finally, the potential inhibition and restoration mechanism of the C/N-dependent anammox were proposed based on metagenomic analysis. This research provides some insights into the reinstatement of a mainstream anammox biofilm process after it is interrupted by high C/N influent.

Insights into the response of anammox sludge to the combined stress of nickel and salinity

Anaerobic ammonium oxidation (anammox) is a promising technology applied to treat industrial wastewater, while the commonly coexistent heavy metals and salinity usually become a challenging issue to be addressed. In this study, the responses of anammox sludge in terms of performance, activity, functional enzyme and extracellular polymeric substance (EPS) to the combined stress of Ni(II) and salinity (20 ‰) were investigated holistically. It turned out that low Ni(II) concentration (0.2 mg·L^-1) together with salinity (20 ‰) showed an insignificant effect on the anammox performance, while a decreased nitrogen removal by 46.96 % was observed with the increased Ni(II) concentration to 1 mg·L^-1. It should be pointed out that the anammox system exhibited good robustness evidenced by rapid recovery to achieve 89.13 % of nitrogen removal efficiency and 1.21 kg·m^-3·d^-1 of nitrogen removal rate after the elimination of stress factors within 40 days. Ni(II) concentration was revealed to play a more important role in the specific activity of anammox sludge. The functional enzymes related to nitrogen removal, e.g. nitrite reductase (NIR), hydrazine oxidase (HZO) and heme c were found to be inhibited by the combined stress of Ni(II) and salinity, with decreased activity by 49.54 %, 39.39 % and 45.88 %, respectively. However, the enzyme related to assimilation, e.g. alkaline phosphatase (AKP) and nitrate reductase (NAR) appeared to be enhanced. The EPS content was found to decrease by 55.19 % under the combined stress. Detailed analysis of 3D-EEM and FTIR spectra further revealed that the combined stress of Ni(II) and salinity could change both the quantity and composition of EPS in anammox sludge. These results are expected to offer insights into the combined effect of nickel and salinity on the anammox system, and benefit the application of anammox technology for industrial metal-rich saline wastewater treatment.

Performance enhancement and population structure of denitrifying phosphorus removal system over redox mediator at low temperature

The development of denitrifying polyphosphate accumulating organisms (DPAOs) presents a strategy to carbon competition between denitrifying bacteria and phosphorus removing bacteria. However, low temperature inhibits the rate of enzyme-catalyzed and substrate diffusion during denitrifying phosphorus removal (DPR). Therefore, the present study assessed the addition of NQS (100 μmol/L) for enhancing the removal of TP and TN in DPR reactors operated at alternating anaerobic and anoxic phases and different influent phosphate concentrations. The results showed that the removal efficiency of TP and TN in NQS-DPR system at 10 °C were 99.9% and 42.0%, respectively, which were 2.1 and 2.0 times higher than that of DPR system. Adding NQS significantly alleviated the increase of pH under anoxic condition and decreased the ORP value of the reactor, which in turn enhanced the PHAs accumulation process. The determination of functional genes (nirK, narG and phoD) showed that Dechloromonas, Lentimicrobium, and Terrimonas were the dominant functional bacteria in NQS-DPR system at 10 °C with the relative abundance of 3.09%, 2.99% and 2.28%, respectively. This study can provide valuable information for the effects of the addition of the redox mediator on denitrifying phosphorus removal technology.

Future trends and patterns in leachate biological treatment research from a bibliometric perspective

Leachate has become a great deal of concern due to its complex properties which are primarily caused by the high concentrations of organics and ammonia. Thus, proper leachate treatment is required prior to its discharge. Leachate can be treated in various ways, and biological treatment is one of the approaches. This treatment has been shown to be both effective and cost-efficient while offering the possibility of resource recovery in the form of bioenergy. In this study, the underlying patterns in publications related to leachate biological treatment were uncovered through bibliometric analysis. This study also lays the groundwork for a deeper understanding of the past, current, and future trends of the leachate biological treatment. Research publications from 1974 to 2021 were retrieved from the Scopus database, and it was identified that 2013 articles were published in the span of 47 years. From the analyzed publications, China played a leading role in publishing leachate biological treatment research articles as well as having the most productive institutions and authors. Meanwhile, the USA was found to be the most active country in initiating international collaborations with 33 countries. The research hotspots were also successfully identified using keyword co-occurrences analysis. Anaerobic digestion and constructed wetland were revealed to be the research hotspots. The critical role of biological treatment in removing nitrogen from leachate was also highlighted. Besides, numerous research gaps were identified in the application of aerobic granular sludge (AGS) for leachate treatment. This can be a potential area for research in the future. Finally, future research should be encouraged to focus on the use of sustainable treatment systems in which energy recovery in the form of biogases is promoted.

Enhancement of denitrifying anaerobic methane oxidation via applied electric potential

In this study, single-chamber three-electrode electrochemical sequencing batch reactor (ESBR) was set up to investigate the impact of applying potential on denitrifying anaerobic methane oxidation (DAMO) process. When the applied potential was +0.8 V, the conversion rate of nitrite to nitrogen was superior to those of other potentials. With the optimal potential of +0.8 V for 60 days, the nitrite removal rate of ESBR could reach 3.34 ± 0.28 mg N/L/d, which was 4.5 times more than that of the non-current control (0.74 ± 0.16 mg N/L/d). The DAMO functional bacteria Candidatus Methylomirabilis exhibited noticeable enrichment under applying potential, and its functional gene of pmoA was significantly expressed. Through untargeted LC-MS metabolomics analysis, applied potential was shown to affect the regulation of prior metabolites including spermidine, spermine and glycerophosphocholine that were related to the metabolic pathways of glycerophospholipid metabolism and arginine and proline metabolism, which had positive effects on DAMO process. These results show that applying electric potential could be a useful strategy in DAMO process used for methane and nitrogen removal.

Hydrolyzed polyacrylamide biotransformation during the formation of anode biofilm in microbial fuel cell biosystem: Bioelectricity, metabolites and functional microorganisms

The anode biofilm serves as the core dominating the performance of microbial fuel cell (MFC) biosystem. This research provides new insights into hydrolyzed polyacrylamide (HPAM) biotransformation during the formation of anode biofilm. The current density, coulombic efficiency, voltage, power density, volatile fatty acid (VFA) production and total nitrogen (TN) removal enhanced with the thickening of biofilm (1-6 cm), and the maximums achieved 146 mA·m^-2, 47.3%, 8.76 V, 1.28 W·m^-2, 184 mg·L^-1 and 84.6%, respectively. HPAM concentration descended from 508 mg·L^-1 to 83.3 mg·L^-1 after 60 days. HPAM was metabolized into VFAs, N₂, NO₂^--N and NO₃^--N, thereby releasing electrons. Laccase and tyrosine/tryptophan protein induced HPAM metabolism and bioelectricity production. The microbial functions involving HPAM biotransformation and bioelectricity generation were clarified. The alternative resource recovery, techno-economic comparison and development direction of MFC biosystem were discussed to achieve the synchronization of HPAM-containing wastewater treatment and bioelectricity generation based on MFC biosystem.

Rapid cultivation and enrichment of anammox bacteria solely using traditional activated sludge as inoculum and biocarrier in low-strength real sewage treatment

In low-ammonia sewage anammox process, cultivation and enrichment of anammox bacteria (AnAOB) is a challenge especially from traditional activated sludge. To this end, a novel strategy solely using activated sludge as inoculum and biocarrier in a dynamic fixed-bed reactor was proposed in this study. During 115-day operation, excellent performance was achieved with influent total inorganic nitrogen (TIN) and effluent TIN of 55.3 mg·L-1 and 4.1 mg·L-1, respectively. Rapid enrichment of AnAOB (doubling time: 8.5 days) was demonstrated by augmented specific anammox activity (trace value to 1.85 mg N·g VSS-1·h-1) and increased hzsB gene number (106 to 109 copies·g-1 dry sludge), with predominance of Candidatus_Brocadia. Large-flocs aggregate was the primary habitat for AnAOB with highest abundance and capacity. The distinctive sludge properties, symbiotic microbial interactions and dynamic operation scheme facilitated AnAOB growth and retention. This study provides a simple, economic and workable approach for the start-up of mainstream anammox process.

Lactate as an effective electron donor in the sulfate reduction: impacts on the microbial diversity

The competition between sulfate-reducing bacteria and methane-producing archaea has a major influence on organic matter removal, as well as the success of sulfidogenic systems. This study investigated the performance of six batch sulfidogenic reactors in response to different COD/sulfate ratios (1.0 and 2.0) and electron donors (cheese whey, ethanol, and sodium lactate) by evaluating the biochemical mechanisms of sulfate reduction, organic matter oxidation, and microbial structure modification. A COD/sulfate ratio of 1.0 resulted in high sulfidogenic activity for all electron donors, thereby achieving a nearly 80% sulfate removal. Lactate provided high sulfate removal rates at COD/sulfate ratios of 1.0 (80%) and 2.0 (90%). A COD/sulfate ratio of 2.0 decreased the sulfate removal rates by 25 and 28% when ethanol and cheese whey were used as substrates. The sulfate-reducing bacteria populations increased using ethanol and lactate at a COD/sulfate ratio of 1.0. Particularly, Desulfovibrio, Clostridium, and Syntrophobacter were predominant. Influent composition and COD/sulfate ratio influenced the relative abundance of the microbial communities. Therefore, controlling these parameters may facilitate the wastewater treatment with high sulfate levels through bacterial activity.

Isolation, Identification and Characteristic Analysis of Plant Endophyte Electrogenic Bacteria Shinella zoogloeoides SHE10

Electroactive microorganisms play a significant role in microbial fuel cells (MFCs). These devices are environmentally friendly and can turn large quantities of organic material into renewable energy based on microbial diversity. Based on broad microbial diversity, it is necessary to obtain a comprehensive understanding of their resource distribution and to discover potential resources. In this study, sweet potato tissues were selected to isolate endophytic bacteria, and the electrochemical activity potential of those bacteria was evaluated by high-throughput screening with a WO₃ nanoprobe. This study was screened and obtained a strain SHE10 with electrochemical performance from the rhizome of sweet potato by a WO₃ nanoprobe, which was identified as Shinella zoogloeoides. After nearly 600 h of voltage monitoring and cyclic voltammetry analysis, the results showed that the average voltage of S. zoogloeoides SHE10 reached 122.5 mV in stationary period. The maximum power density is 78.3 ± 1.8 mW/m², and the corresponding current density is 223.0 mA/m². The good redox reaction also indicated that the strain had good electrical activity. Its electron transfer mode was diverse, but its power generation mechanism still needs to be further discussed. The study of S. zoogloeoides SHE10 provides scientific theoretical reference for expanding the resource pool of electroproducing bacteria and the types of electroproducing microorganisms.

Promotion of anammox process by different graphene-based materials: Roles of particle size and oxidation degree

Graphene oxide (GO) and reduced graphene oxide (RGO) have been applied in the anaerobic ammonium oxidation (anammox) process for nitrogen removal as electron shuttles. However, there is still controversy about their efficacy. In this study, nine graphene-based materials with a gradient of three particle sizes (large (l), medium (m) and small (s) sizes) and oxidation degrees, were used to compare their effects on the anammox process efficiency. The graphene-based materials include GO and its reduced products (RGO250 and RGO800) obtained at temperatures of 250 °C and 800 °C respectively. It was observed that their enhancements on the anammox process were in the order of GO > RGO800 > RGO250. In detail, at the dose of 100 mg/L, specific anammox activities (SAA) were promoted by 6.7% (l-GO), 4.9% (l-RGO800), 11.5% (m-GO), 7.3% (m-RGO800), 13.2% (s-GO) and 8.3% (s-RGO800) compared to the control respectively; while RGO250 with the same dose inhibited the process. In addition, the enhancement of the anammox process was increasing with the decreasing size of GO and RGO800. The nitrite reductase (NIR) activity was greatly increased by up to 24.9% with the presence of GO, which might be attributed to organized and specific electron transport with oxygen functional groups. The finding of hydroxyl on RGO and increasing content of oxygen determined after reaction detected by Fourier transform infrared spectroscopy and energy dispersive spectrometer respectively, indicated the essential condition for RGO's function on transferring electrons for key enzymes in annamox bacteria. Most importantly, O/C (Oxygen/Carbon) ratios of graphene-based materials had greater effects on the promotion of the anammox process than the particle size and electrical conductivity.

Mechanism of stable power generation and nitrogen removal in the ANAMMOX-MFC treating low C/N wastewater

This study investigated the mechanism of enhanced power generation and nitrogen removal in an ANAMMOX-MFC reactor through subsequent acetate addition. Data showed that nearly 99% total nitrogen removal (≤1 mg L^-1) and 1.41 W m^-3 power generation were achieved synchronously under low COD/N (∼1.5) after the subsequent addition of acetate (100 mgCOD·L^-1). The columbic efficiency of the system has increased by 15 times (from 0.64% to 9.48%) after adding acetate. Batch tests showed that the denitrification and ANAMMOX progress occurred synchronously before acetate addition the nitrogen removal rate was accelerated. A distinct shift of bacterial community driven by acetate addition was discovered. The high throughput sequencing analysis indicated acetate addition stimulated the enrichment of denitrifiers, such as Aquimonas, Bradyrhizobium, Thauera, and the potential exoelectrogens changing from Comamonas to Pseudomonas. Functional genes forecasts based on KEGG database and COG database showed that the expressions of TCA functional genes were highly promoted in ANAMMOX-MFC, which demonstrated the enhanced electron transfer pathway driven by acetate addition under low COD/N ratio.

Simultaneous removal of organic matter and nitrogen compounds by partitioned aeration in a 226 L-scale microbial fuel cell

Although microbial fuel cells (MFCs) have been widely studied as wastewater treatment technologies that convert organic matter to electricity, there are few reports of large-scale MFCs that treat both organic matter and nitrogen compounds. In this study, a 226 L reactor equipped with 27 MFC units was partially aerated at 10% of its total volume. The MFC unit consists of a cylindrical air core covered with a carbon-based air cathode, an anion exchange membrane, and a graphite non-woven fabric anode. The air-cathode MFC with 13 L min^-1 aeration rate produced a current density of 0.0012-0.15 A m^-2 with 40 to >93% biological oxygen demand (BOD) removal to have an effluent BOD of <5-36 mg L^-1 at a hydraulic retention time (HRT) of 12-47 h. Meanwhile, 55 ± 17% of the total nitrogen (TN) was removed, resulting in 9.7 ± 3.8 mg L^-1 TN in the effluent, although the TN removal was limited at ≥20 °C. The mono-exponential regression for BOD and TN (≥20 °C) estimated that an HRT of 21 h could meet the Japanese effluent quality standards of BOD and TN. Calculation of the total energy recovered via current generation and energy consumed by aeration suggested an energy consumption of 0.22 kW h m^-3. Decreasing the aeration rate and HRT in the reactor would further reduce energy consumption and increase energy production.

Exerting applied voltage promotes microbial activity of marine anammox bacteria for nitrogen removal in saline wastewater treatment

To date, the application of marine anammox bacteria (MAB) is still a challenge in saline wastewater treatment due to the low growth rate and high sensitivity. Herein, bioelectrochemical system with applied voltage was exerted for the first time to promote the activity of MAB for removing nitrogen from saline wastewater. At the optimal voltage of 1.5 V, the mean total nitrogen removal rate (TNRR) reached the maximum of 0.65 kg/m³•d, which was 27.45% higher than that without applied voltage. Besides, applied voltage reduced the microbial diversity of MAB-based consortia, but the relative abundance of Candidatus Scalindua increased by 4.63% at 1.5 V compared with that without applied voltage. Also, proper applied voltage promoted the secretion of EPS and heme c, which resulted in the enhancement of MAB activity. Based on the remodified Logistic model analysis, the lag time of the nitrogen removal process was shortened by 0.72 h at the voltage of 1.5 V. Furthermore, it was found that higher voltage (> 2.0 V) had a negative effect on the MAB activity for low TNRR of 0.33 kg/m³•d (2.5 V). However, TNRR increased back to 0.61 kg/m³•d after removing the high applied voltage, which implied that the bioactivity was recoverable after being inhibited. These findings demonstrated that external electrical stimulation is an effective strategy to promote nitrogen removal and MAB activity for treating saline wastewater.

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

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.

Effects of multiple antibiotics residues in broiler manure on composting process

At present, the effect of multiple antibiotics on aerobic composting process and its mechanism are not clear. So in this study, broiler manure containing different doses of Doxycycline (DOX) and Gatifloxacin (GAT) were used as raw materials and mixed with rice hull for aerobic composting, and the effects of the combination of multiple antibiotics on the process parameters of broiler manure composting and the succession of bacterial and fungal community structures were systematically analyzed. Our results showed that at the initial period of composting, the combination of multiple antibiotics led to a delayed temperature and pH increase (T1: 57.0 °C, T2: 48.3 °C, T3: 45.5 °C on Day 3 for temperature and T1: 7.44, T2: 7.1, T3: 6.88 on Day 5 for pH), and a slow total nitrogen decrease (T1: 1.56%, T2: 1.82%, T3: 1.74% on Day 5). Although these effects decreased gradually with the degradation of antibiotics, the relative abundance of Actinobacteriota (T1: 13.29%, T2: 10.57%, T3: 8.99%) and Bacteroidota (T1:27.52%, T2:40.03%, T3:39.81%)) were still influenced by multiple antibiotic residuals until the end of composting period. Higher levels of antibiotics had more lasting effects on the bacterial community (T3 > T2). However, the combination of these two antibiotics did not significantly promote or inhibit the succession of the fungal community structure. The heatmaps showed that composting stage had a greater effect on the microbial community structures than antibiotics. The results provided a theoretical reference for composting broiler manure containing DOX and GAT.

Long-term evaluation of an air-cathode microbial fuel cell with an anion exchange membrane in a 226L wastewater treatment reactor

Although the treatment of municipal wastewater using microbial fuel cells (MFCs) has been extensively studied, scaling the systems up for practical use remains challenging. In this study, a 226 L sewage treatment reactor was equipped with 27 MFC units, and its chemical oxygen demand (COD) removal and electricity production were evaluated. The MFC units were tubular air cores with a diameter of 5 cm and length of 100 cm, which were wrapped with a carbon-based cathode, anion exchange membrane (AEM), and nonwoven graphite fabric. The air-cathode-AEM MFC generated 0.12-0.30 A/m², 0.072-0.51 W/m³, and 1.7-4.6 Wh/m³ in a chemostat reactor with a COD of 140-36 mg/L and hydraulic retention time (HRT) of 9-42 h throughout a year. The decrease in the COD was represented as the first-order rate constant of 0.038. The rate constant was comparable to that of other air-cathode MFCs with cation exchange membranes, indicating the necessity of a posttreatment to meet the discharge standard. It has been estimated that the MFC operation for 24 h before post-aeration can reduce the energy required to meet the discharge standard by 70%, suggesting the potential applicability of MFC in long HRT-treatments such as oxidation ditch. The resistances of the anode, cathode, and AEM were 15, 7.0, and 0.51 mΩ m², respectively, and surface dirt rather than deterioration primarily increased the AEM resistance. A current exceeding 0.2 A/m² significantly increases the anode potential, indicating that the current was limited by low COD. Increasing the anode-specific surface area can improve air-AEM MFCs used for practical applications.

Advanced bioelectrochemical system for nitrogen removal in wastewater

Nitrogen (N) pollution in water has become a serious issue that cannot be ignored due to the harm posed by excessive nitrogen to environmental safety and human health; as such, N concentrations in water are strictly limited. The bioelectrochemical system (BES) is a new method to remove excessive N from water, and has attracted considerable attention. Compared with other methods, it is highly efficient and has low energy consumption. However, the BES has not been applied for N removal in practice due to lack of in-depth research on the mechanism and construction of high-performance electrodes, separators, and reactor configurations; this highlights a need to review and examine the efforts in this field. This paper provides a comprehensive review on the current BES research for N removal focusing on the reaction principles, reactor configurations, electrodes and separators, and treatment of actual wastewater; the corresponding performances in these realms are also discussed. Finally, the prospects for N removal in water using the BES are presented.

Editorial to Efficient Catalytic and Microbial Treatment of Water Pollutants

Several industries produce products and release waste compounds that can be very carcinogenic, and furthermore, can cause trouble for water organisms, such as algae and plants which rely on photosynthesis [...]

Varied interspecies interactions between anammox and denitrifying bacteria enhanced nitrogen removal in a single-stage simultaneous anammox and denitrification system

The simultaneous anammox and denitrification (SAD) system has received growing interest for the enhanced nitrogen removal, while the ecological traits of microbial community including spatial distribution characteristics, assembly processes and interspecies interactions have not been fully unraveled. The present study applied metagenomics and ecological analysis methods to gain the ecological traits of microbial communities in the SAD system across different organic substrate loadings. Results showed that organic matter significantly affected the bioreactor performance, and the optimal total nitrogen removal efficiency reached 93.4 ± 0.7% under the COD concentrations of 180 ± 18.2 mg/L. Functional organisms including Candidatus Brocadia (3.9%), Denitratisoma (1.6%), Dokdonella (4.4%) and Thauera (4.6%) obviously enriched under the optimal organic loading conditions. Moreover, microbial communities were significantly governed by deterministic process under high organic concentrations, and the denitrifying organisms displayed important ecological roles in the communities. Although anammox bacteria obviously enriched at the middle of bioreactor, it possessed the highest expression activities at both bottom and middle sites. Denitrifying bacteria that enriched at the bottom sites strongly achieved nitrate reduction and provided nitrite for anammox bacteria, while these organisms trended to compete nitrite with anammox bacteria at the middle site. These findings highlight the importance of microbial ecology in the SAD systems, which may expand our understanding of the synergistic patterns between anammox and denitrifying bacteria.

Nitrate removal under low carbon to nitrogen ratio by modified corn straw bioreactor: Optimization and possible mechanism

ABSTRACTThe removal of nitrate (NO₃^--N) from water bodies under the conditions of poor nutrition and low carbon to nitrogen (C/N) ratio is a widespread problem. In this study, modified corn stalk (CS) was used to immobilize Burkholderia sp. CF6 with cellulose-degrading and denitrifying abilities. The optimal operating parameters of the bioreactor were explored. The results showed that under the hydraulic retention time (HRT) of 3 h and the C/N ratio of 2.0, the maximum nitrate removal efficiency was 96.75%. In addition, the organic substances in the bioreactor under different C/N ratios and HRT were analyzed by three-dimensional fluorescence excitation-emission mass spectrometry (3D-EEM), and it was found that the microorganisms have high metabolic activity. Scanning electron microscope (SEM) showed that the new material has excellent immobilization effects. Fourier transform infrared spectrometer (FTIR) showed that it has potential as a solid carbon source. Through high-throughput sequencing analysis, Burkholderia sp. CF6 was observed as the main bacteria present in the bioreactor. These research results showed that the use of waste corn stalks waste provides a theoretical basis for the advanced treatment of low C/N ratio wastewater.

Symbiotic treatment of ammonia-nitrogen wastewater by algae and activated sludge: effects of algae and sludge inoculation rates

A symbiotic microalgal-bacterial system may be an optional technology for wastewater treatment. It was composed of microalgae and activated sludge and established in the SBR to explore the effect of different dosing ratios of algae and sludge on the removal of nitrogen and phosphorus from simulated wastewater containing ammonium. It can be seen from the result that varied algae-sludge dosing ratios had a higher removal effect on COD removal, but the difference was not significant. The algal-bacterial symbiosis system had a 100% removal rate for ammonium removal on the 8th day. Relatively speaking, the removal of nutrients and related mechanisms vary with environmental conditions (inoculation rate). In general, when the additive ratio was 5:1 (algae: AS), the removal rate of TN and TP was the highest, reaching 53.85% and 85.13% in the shortest time (14 days), among them, the removal rate of ammonium and COD was 100%, and the reduction rates of Nitrite nitrogen and Nitrate nitrogen were 362.99% and 73.42%, respectively. In addition, 16S rDNA gene analysis results demonstrated that the microbial community in the reactor with algal sludge inoculation ratio of 5:1 had differences in three stages of the initial reaction, the middle reaction and the end of the reaction. Comamonadaceae, Flavobacterium, Paenarthrobacter, Mesorhizobium, Nitrobacter were enriched during the reaction operation.

Biological Nitrogen Removal Database: A Manually Curated Data Resource

Biological nitrogen removal (BNR) technologies are the most effective approaches for the remediation of environmental nitrogen pollutants from wastewater treatment plants (WWTPs). Presently, research is going on to elucidate the structure and function of BNR microbial communities and optimizing BNR treatment systems to enhance nitrogen removal efficiency. The literature on BNR microbial communities and experimental datasets is not unified across various repositories, while a uniform resource for the collection, annotation, and structuring of these BNR datasets is still unavailable. Herein, we present the Biological Nitrogen Removal Database (BNRdb), an integrated resource containing various manually curated BNR-related data. At present, BNRdb contains 23,308 microbial strains, 46 gene families, 24 enzymes, 18 reactions, 301 BNR treatment datasets, 860 BNR-associated next-generation sequencing datasets, and 6 common BNR bioreactor systems. BNRdb provides a user-friendly interface enabling interactive data browsing. To our knowledge, BNRdb is the first BNR data resource that systematically integrates BNR data from archaeal, bacterial, and fungal communities. We believe that BNRdb will contribute to a better understanding of BNR process and nitrogen bioremediation research.

Novel biotechnologies for nitrogen removal and their coupling with gas emissions abatement in wastewater treatment facilities

Wastewaters contaminated with nitrogenous pollutants, derived from anthropogenic activities, have exacerbated our ecosystems sparking environmental problems, such as eutrophication and acidification of water reservoirs, emission of greenhouse gases, death of aquatic organisms, among others. Wastewater treatment facilities (WWTF) combining nitrification and denitrification, and lately partial nitrification coupled to anaerobic ammonium oxidation (anammox), have traditionally been applied for the removal of nitrogen from wastewaters. The present work provides a comprehensive review of the recent biotechnologies developed in which nitrogen-removing processes are relevant for the treatment of both wastewaters and gas emissions. These novel processes include the anammox process with alternative electron acceptors, such as sulfate (sulfammox), ferric iron (feammox), and anodes in microbial electrolysis cells (anodic anammox). New technologies that couple nitrate/nitrite reduction with the oxidation of methane, H₂S, volatile methyl siloxanes, and other volatile organic compounds are also described. The potential of these processes for (i) minimizing greenhouse gas emissions from WWTF, (ii) biogas purification, and (iii) air pollution control is critically discussed considering the factors that might trigger N₂O release during nitrate/nitrite reduction. Moreover, this review provides a discussion on the main challenges to tackle towards the consolidation of these novel biotechnologies.

An effective strategy for in situ start-up of mainstream anammox process treating domestic sewage

The feasibility of in situ start-up of mainstream anammox process was investigated in three parallel sequencing batch biofilm reactors (SBBRs) inoculated with nitrification sludge, partial nitrification sludge, and denitrifying phosphorus removal sludge, respectively. The SBBRs were operated under alternate anaerobic/aerobic/anoxic pattern at ambient temperature (16.5-26.8 °C). The influent organic and nitrogen loading rates were increased stepwise. Anammox bacteria grew exponentially with relative abundance and overall bacterial activity increasing from 0 to 0.004% to 0.29-0.40% and 'not detected' to 6-7 mg N/L/h, respectively. Desirable nitrogen removal efficiency of about 86% was obtained in 3-4 months for the influent nitrogen of 40.5-73.6 mg N/L. Anammox was the primary nitrogen transformation pathway. For the anammox bacterial enrichment, biofilm, alternate anaerobic/aerobic/anoxic pattern, and limited aeration played important roles. Seed sludge with high ammonium oxidizing bacterial activity further promoted the start-up of anammox process. The in situ start-up strategy could promote the full-scale application of mainstream anammox.

Fe(II) enhances simultaneous phosphorus removal and denitrification in heterotrophic denitrification by chemical precipitation and stimulating denitrifiers activity

Using Fe(II) salt as the precipitant in heterotrophic denitrification achieves improved TP removal, and enhancement in denitrification was often observed. This study aimed to obtain a better understanding of Fe(II)-enhanced denitrification with sufficient carbon source supply. Laboratory-scale experiments were conducted in SBRs with or without Fe(II) addition. Remarkably improved TP removal was experienced. TP removal efficiency in Fe(II) adding reactor was 85.8 ± 3.4%; whereas, that in the reactor without Fe(II) addition was 31.1 ± 2.8%. Besides improved TP removal, better TN removal efficiency (94.1 ± 1.1%) were recorded when Fe(II) was added, and that in the reactor without Fe(II) addition was 89 ± 0.8%. The specific denitrification rate were observed increase by 12.6% when Fe(II) was added. Further microbial analyses revealed increases in the abundances of typical denitrifiers (i.e. Niastella, Opitutus, Dechloromonas, Ignavibacterium, Anaeromyxobacter, Pedosphaera, and Myxococcus). Their associated denitrifying genes, narG, nirS, norB, and nosZ, were observed had 14.2%, 19.4%, 21.6%, and 9.9% elevation, respectively. Such enhancement in denitrification shall not be due to nitrate-dependent ferrous oxidation, which prevails in organic-deficient environments. In an environment with a continuous supply of Fe(II) and plenty of carbon sources, a cycle of denitrifying enzyme activity enhancement in the presence of Fe(II) facilitating nitrogen substrate utilization, stimulating denitrifier metabolism and growth, elevating denitrifying genes abundance, and increasing denitrifying enzymes expression were thought to be responsible for the Fe(II)-enhanced heterotrophic denitrification. Fe(II) salt is often a less expensive precipitant and has recently become attractive for TP removal in wastewater. The findings of this study solidify previous observation of enhancement of both TP and TN removal by adding Fe(II) in denitrification, and would be helpful for developing cost-effective pollutant removal processes.

Insight into enrichment of anaerobic ammonium oxidation bacteria in anammox granulation under decreasing temperature and no strict anaerobic condition: Comparison between continuous and sequencing batch feeding strategies

A continuous flow reactor (CFR) and a sequencing batch reactor (SBR) were operated in parallel to investigate the difference between anammox granulation in CFR and SBR under decreasing temperature and no strict anaerobic condition. The results showed that the biomass achieved initial granulation successfully (D [4, 3] = 280.44 and 346.28 μm) in both CFR and SBR on day 70. Compared with SBR, a better performance (0.33 kg N m^-3 d^-1) was gotten in CFR due to a better retention capacity of biomass (1397 mg L^-1), when seasonal drop of water temperature occurred (18-14 °C). Thus, different operations led to different granulation styles of anammox. Granules in CFR had better rheological properties than that in SBR. Based on a stable and suitable environment provided by CFR, anaerobic ammonium oxidation bacteria (AnAOB) are able to self-aggregate easily and secret extracellular polymeric substances (EPS), which can capture other bacteria as home guardians. In SBR, AnAOB live inside the tan granules under the protection of other bacteria and thick EPS; other aggregations stick to solid carrier surface to form biofilm.

Calcium modified basalt fiber bio-carrier for wastewater treatment: Investigation on bacterial community and nitrogen removal enhancement of bio-nest

Modified basalt fiber (MBF) is a sustainable material studied as novel wastewater treatment bio-carrier recently. This work studied the effects of calcium modification on the bacterial affinity of modified fiber (Ca-MBF), bacterial community, and nitrogen removal performance. Results showed that Ca-MBF with hydrophilic (62.66°) and positively-charged (7.80 mV) surface accelerated bacterial attachment. Volatile suspended solids on Ca-MBF (5.46 g VSS/g fiber) were increased by 2.61 times after modification, with high bacterial activity when bio-carriers were cultured in activated sludge. Extracellular polymeric substances on Ca-MBF was 4.35 times higher and consisted of more protein. Bio-nests with unique aerobic/anaerobic structure formed on the ultrafine carriers in bioreactor. Ca-MBF bioreactor exhibited total nitrogen removal efficiency above 72.2% and COD removal efficiency above 94.2% with more stable performance than unmodified carrier in long-term treatment using synthetic domestic wastewater.16S rRNA gene sequencing revealed enhanced abundance of nitrifying and denitrifying bacteria in Ca-MBF bio-nest.

Cascade Membrane System for Separation of Water and Organics from Liquid By-Products of HTC of the Agricultural Digestate—Evaluation of Performance

New regulations aimed at curbing the problem of eutrophication introduce limitations for traditional ways to use the by-product of anaerobic digestion—the digestate. Hydrothermal carbonisation (HTC) can be a viable way to valorise the digestate in an energy-efficient manner and at the same time maximise the synergy in terms of recovery of water, nutrients, followed by more efficient use of the remaining carbon. Additionally, hydrothermal treatment is a feasible way to recirculate recalcitrant process residues. Recirculation to anaerobic digestion enables recovery of a significant part of chemical energy lost in HTC by organics dissolved in the liquid effluent. Recirculating back to the HTC process can enhance nutrient recovery by making process water more acidic. However, such an effect of synergy can be exploited to its full extent only when viable separation techniques are applied to separate organic by-products of HTC and water. The results presented in this study show that using cascade membrane systems (microfiltration (MF) → ultrafiltration (UF) → nanofiltration (NF)), using polymeric membranes, can facilitate such separation. The best results were obtained by conducting sequential treatment of the liquid by-product of HTC in the following membrane sequence: MF 0.2 µm → UF PES 10 → NF NPO30P, which allowed reaching COD removal efficiency of almost 60%.

Coupling anammox with denitrification in a full-scale combined biological nitrogen removal process for swine wastewater treatment

In order to enhance nitrogen removal through anammox process in the full-scale swine wastewater treatment plant, an innovative regulation strategy of nitrate-based carbon dosage and intermittent aeration was developed to apply the combined biological nitrogen removal process in a full scale anaerobic-anoxic-oxic (A²/O) system. TN removal efficiency reached at 65.5 ± 6.0% in Phase 1 with decreasing external carbon dosage in influent due to the reduction of return nitrate concentration, and it increased to 83.5 ± 6.7% when intermittent aeration was adopted in oxic zone and external carbon source was stopped adding into influent in Phase 2. As a result, the energy consumption for the swine wastewater treatment decreased from 1.93 to 0.9 kW h/m³ and 4.18 to 2.57 kW h/kg N, respectively. Microbial community analysis revealed that the average abundances of Candidatus Brocadia increased from 0.76% to 2.43% and removal of TN through anammox increased from 39% to 77%.

Start-Up of Anammox SBR from Non-Specific Inoculum and Process Acceleration Methods by Hydrazine

Biological nutrient removal from wastewater to reach acceptable levels is needed to protect water resources and avoid eutrophication. The start-up of an anaerobic ammonium oxidation (anammox) process from scratch was investigated in a 20 L sequence batch reactor (SBR) inoculated with a mixture of aerobic and anaerobic sludge at 30 ± 0.5 °C with a hydraulic retention time (HRT) of 2–3 days. The use of NH4Cl, NaNO2, and reject water as nitrogen sources created different salinity periods, in which the anammox process performance was assessed: low (<0.2 g of Cl−/L), high (18.2 g of Cl−/L), or optimum salinity (0.5–2 g of Cl−/L). Reject water feeding gave the optimum salinity, with an average nitrogen removal efficiency of 80%, and a TNRR of 0.08 kg N/m3/d being achieved after 193 days. The main aim was to show the effect of a hydrazine addition on the specific anammox activity (SAA) and denitrification activity in the start-up process to boost the autotrophic nitrogen removal from scratch. The effect of the anammox intermediate hydrazine addition was tested to assess its concentration effect (range of 2–12.5 mg of N2H4/L) on diminishing denitrifier activity and accelerating anammox activity at the same time. Heterotrophic denitrifiers’ activity was diminished by all hydrazine additions compared to the control; 5 mg of N2H4/L added enhanced SAA compared to the control, achieving an SAA of 0.72 (±0.01) mg N/g MLSS/h, while the test with 7.5 mg of N2H4/L reached the highest overall SAA of 0.98 (±0.09) mg N g/MLSS/h. The addition of trace amounts of hydrazine for 6 h was also able to enhance SAA after inhibition by organic carbon source sodium acetate addition at a high C/N ratio of 10/1. The start-up of anammox bacteria from the aerobic–anaerobic suspended biomass was successful, with hydrazine significantly accelerating anammox activity and decreasing denitrifier activity, making the method applicable for side-stream as well as mainstream treatment.