Ammonia Nitrogen Removal Efficiency Research Articles

Optimization of Simultaneous Nutrients and Chemical Oxygen Demand Removal from Anaerobically Digested Liquid Dairy Manure in a Two-Step Fed Sequencing Batch Reactor System Using Taguchi Method and Grey Relational Analysis.

The technological development for efficient nutrient removal from liquid dairy manure is critical to a sustainable dairy industry. A nutrient removal process using a two-step fed sequencing batch reactor (SBR) system was developed in this study to achieve the applicability of simultaneous removal of phosphorus, nitrogen, and chemical oxygen demand from anaerobically digested liquid dairy manure (ADLDM). Three operating parameters, namely anaerobic time:aerobic time (min), anaerobic DO:aerobic DO (mg L-1), and hydraulic retention time (days), were systematically investigated and optimized using the Taguchi method and grey relational analysis for maximum removal efficiencies of total phosphorus (TP), ortho-phosphate (OP), ammonia-nitrogen (NH3-N), total nitrogen (TN), and chemical oxygen demand (COD) simultaneously. The results demonstrated that the optimal mean removal efficiencies of 91.21%, 92.63%, 91.82%, 88.61%, and 90.21% were achieved for TP, OP, NH3-N, TN, and COD at operating conditions, i.e., anaerobic:aerobic time of 90:90 min, anaerobic DO:aerobic DO of 0.4:2.4 mg L-1, and HRT of 3 days. Based on analysis of variance, the percentage contributions of these operating parameters towards the mean removal efficiencies of TP and COD were ranked in the order of anaerobic DO:aerobic DO > HRT > anaerobic time:aerobic time, while HRT was the most influential parameter for the mean removal efficiencies of OP, NH3-N, and TN followed by anaerobic time:aerobic time and anaerobic DO:aerobic DO. The optimal conditions obtained in this study are beneficial to the development of pilot and full-scale systems for simultaneous biological removal of phosphorus, nitrogen, and COD from ADLDM.

Improved integrated anaerobic–anoxic–oxic system for landfill leachate treatment using domestic wastewater as carbon source: Performance study and optimization

Landfill leachate has been treated by using an anaerobic–anoxic–oxic (A2/O) system at Datansha Wastewater Treatment Plant in Guangzhou, South China for nearly five years. Through the pilot-scale testing and engineering experiments, the impulse loads of the wastewater treatment systems were successfully reduced. The results showed that the highest removal efficiencies of chemical oxygen demand (COD), ammonium-nitrogen (NH4+-N), and total nitrogen (TN) for the combined treatment of domestic wastewater and landfill leachate were achieved under the operating conditions of hydraulic retention time = 11 h, dissolved oxygen = 3 mg/L, mixed liquid return ratio = 200%, and sludge return ratio = 80%. Compared with the data obtained from the previous operating A2/O system, the removal efficiencies of COD, NH4+-N, and TN increased by 5.6%, 9.8%, and 5.3%, respectively, under the optimal operating conditions for one year. The average effluent concentrations of BOD5, COD, NH4+-N, TN, and total phosphorus were 12.4, 29.9, 2.5, 18.0, and 0.5 mg/L, respectively, and these values could be kept below standard discharge limits in China.

Changes of nitrogen and phosphorus removal pattern caused by alternating aerobic/anoxia from the perspective of microbial characteristics.

The purpose of this study was to compare the impact of different numbers of alternating aerobic/anoxic (A/O) cycles on pollutant removal. Three sequential batch reactors (SBRs) with varying numbers of alternating A/O cycles were established. Under the tertiary anoxic operating conditions, the removal efficiencies of chemical oxygen demand (COD), ammonia nitrogen (NH4+-N), total nitrogen (TN), and total phosphorus (TP) were 88.73%, 89.56%, 72.15%, and 77.61%, respectively. Besides, alternating A/O affected the dominant microbial community relative abundance (Proteobacteria and Bacteroidetes) and increased microbial richness and diversity. It also increased the relative abundance of aerobic denitrifying, heterotrophic nitrifying, and denitrifying phosphorus removal bacteria to change N and P removal patterns. Furthermore, the abundance of carbohydrate metabolism and amino acid metabolism was improved by alternating A/O to improve organic matter and TN removal.

Effective removal of nitrogen and phosphorus from a black-odorous water by novel oxygen-loaded adsorbents

Black-odorous water, caused by hypoxia and overloading of nitrogen and phosphorus, is ubiquitous in global urban rivers. In this study, we developed oxygen-loaded adsorbents by loading oxygen into activated carbon, Attapulgite, Phoslock, and Muscovite via vacuum-pressure swing method, and investigated their aeration and removal efficiency of phosphate, ammonia nitrogen, and total nitrogen in black-odorous water. Results showed that the addition of oxygen-loaded coal-based columnar activated carbon (OCC) or oxygen-loaded Muscovite (OM) alone could increase the dissolved oxygen (DO) concentration at the sediment–water interface to more than 6 mg·L-1 on the first day, and OCC could maintain the high level of oxidation–reduction potential (ORP) (up to + 327 mV) for 15 days. Most oxygen-loaded adsorbents remarkably reduced phosphate in water, essentially from 0.27 mg·L-1 to < 0.05 mg·L-1. Additionally, ammonia nitrogen and total nitrogen were reduced by more than 50 % by adding materials after oxygen loading treatment. The 16 s RNA results showed that Dechloromonas was dominant in abundance, and the reduction of nitrogen was mainly affected by microbial activity. Our results provided a series of oxygen-loaded adsorbent materials with potential engineering applications for rapid treatment of urban black-odorous water.

Effect of plant-self debris on nitrogen removal, transformation and microbial community in mesocosm constructed wetlands planted with Myriophyllum aquaticum

Aquatic macrophytes debris decomposition could release pollutants and nutrients into the water of constructed wetlands (CWs), but their role in nitrogen removal and transformation remains poorly understood. The present study investigated the effects of plant-self debris on nitrogen removal and microbial communities in mesocosm CWs planted with Myriophyllum aquaticum. During the 68-day operation, the plant debris addition did not change the mean removal efficiency of ammonium (NH4+-N) and total nitrogen (TN) of CWs but showed significant differences over the operation time. The NH4+-N and organic nitrogen released from the plant debris decomposition affected the nitrogen removal. The plant debris decreased the effluent nitrate concentration and N2O emission fluxes of the CWs with the increased abundance of denitrifying bacterial genera, indicating that plant debris decomposition increased the denitrification activities via dissolved organic carbon release. High-throughput sequencing indicated that the plant debris altered the distribution and composition of the microbial community in the sediments. Proteobacteria was the dominant phylum (28–52%), and the relative abundance of denitrifying bacteria genera was significantly higher in the sediments with debris addition (37–40%) than in the non-addition (6.6–7.7%). The present study provided new insights into the role of macrophytes in pollutant removal and the plant management strategy of CWs.

Identification of microbial consortia for sustainable disposal of constructed wetland reed litter wastes.

Reed is a typical emerged plant in constructed wetlands (CWs). Its litters were used as raw materials for preparing Fe-C ceramic-filler (Fe-C-CF). The physical and chemical properties of Fe-C-CF were studied under different conditions, including the mass ration of Fe to carbon (Fe/C ratio), sintering temperature, and time, to determine the optimum preparing conditions. Meanwhile, the denitrification performance and CO2 emission flux of the surface flow constructed wetland (SFCW) systems were investigated when using Fe-C-CF as the matrix. The optimum preparing conditions for Fe-C-CF were Fe/C ratio of 1:1, sintering temperature and time of 500°C and 20min, respectively. The SFCW system with Fe-C-CF obtained a higher total nitrogen (TN), nitrate nitrogen (NO3--N), and ammonia nitrogen (NH3-N) removal efficiencies than the control SFCW system without Fe-C-CF. Compared with the heterotrophic denitrification process, the SFCW system with Fe-C-CF decreased CO2 emission by 67.9gm-2 per year. The results of microbial community analysis indicated that addition of Fe-C-CF increased the diversity and abundance of microbial communities in the SFCW systems. The dominant genus of the SFCW system with Fe-C-CF was Bacillus, while Uliginosibacterium was the dominant genus in the system without the filler.

Ammonia-Nitrogen Removal by Hydroxyapatite Prepared from Waste Fish Scale

The pollution of ammonia-nitrogen in water became more serious with the development of the industry. In this paper, hydroxyapatite (HAP) was prepared from waste fish scales; the XRD, FTIR, SEM, TEM and Raman were used to characterize the prepared samples, and the prepared HAP samples were studied as degradation photocatalyst and adsorbing material for the removal of ammonia-nitrogen. The ammonia-nitrogen removal efficiency (ANRE, Removal Rate = (Initial Concentration–Current Concentration)/Initial Concentration × 100%) of the samples was also discussed. The results showed that the HAP sample, which was calcinated at 800 °C for 2 h, had the best ANRE, which was 41%. The UV-Vis, EIS, and PL were used to analyze the reason for the different ANRE. The reason for the high ANRE was attributed to the samples’ superior adsorption capability resulting from their large specific surface area, as well as their superior properties for photocatalytic degradation. This was a meaningful work to explore a treatment of ammonia-nitrogen by HAP.

Long-term exposure of polytetrafluoroethylene-nanoplastics on the nitrogen removal and extracellular polymeric substances in sequencing batch reactor

The impact of polytetrafluoroethylene-nanoplastics (PTFE-NPs) on biological sewage disposal was delved, containing nitrogen remotion, microbiological activity and composition of extracellular polymer (EPS). The addition of PTFE-NPs reduced the removal efficiencies of chemical oxygen demand (COD) and ammonia nitrogen (NH4+-N) by 3.43 % and 2.35 %, respectively. In comparison with no PTFE-NPs, the specific oxygen uptake rate (SOUR), specific ammonia oxidation rate (SAOR), specific nitrite oxidation rate (SNOR) and specific nitrate reduction rate (SNRR) decreased by 65.26 %, 65.24 %, 41.77 % and 54.56 %, respectively. The PTFE-NPs inhibited the activities of nitrobacteria and denitrobacteria. It was worth noting that, nitrite oxidized bacterium was more resistant to adverse environments than ammonia oxidizing bacterium. Compared with no PTFE-NPs, the reactive oxygen species (ROS) content and lactate dehydrogenase (LDH) grew by 130 % and 50 % under PTFE-NPs pressure. The appearance of PTFE-NPs affected the normal function of microorganisms by inducing endocellular oxidative stress and destroying the completeness of the cytomembrane. The protein (PN) and polysaccharide (PS) levels in loosely bound EPS (LB-EPS) and tightly bound EPS (TB -EPS) increased by 4.96, 0.70, 3.07 and 0.71 mg g−1 VSS, under PTFE-NPs. Meanwhile, the PN/PS ratios of LB-EPS and TB -EPS increased from 6.18 and 6.41–11.04 and 9.29, respectively. The LB-EPS might provide sufficient binding sites for PTFE-NPs adsorption due to its loose and porous structure. The defense mechanism of bacteria against PTFE-NPs was mainly the PN in loosely bound EPS. Moreover, the functional groups referred to the complexation of EPS with PTFE-NPs were mainly related to N-H, CO, and C-N in proteins and O-H in polysaccharides.

Treatment of High-Ammonia-Nitrogen Wastewater with Immobilized Ammonia-Oxidizing Bacteria Alcaligenes sp. TD-94 and Paracoccus sp. TD-10

In this study, modified granular activated carbon (GAC) and immobilized cells were used to improve the biological efficiency of high-ammonia-nitrogen wastewater treatment using microorganisms. The results showed that using sodium-hydroxide-modified activated carbon (NaOH-GAC) greatly increased the immobilized numbers of the ammonia-oxidizing bacteria Alcaligenes sp. TD-94 and Paracoccus sp. TD-10. Using NaOH-GAC increased the number of immobilized cells by 63.27% over GAC. Compared with free cells, those immobilized on modified activated carbon were more effective in the removal of high ammonia nitrogen levels from wastewater. In wastewater with an ammonia nitrogen concentration of 100 mg·L−1, the ammonia nitrogen removal efficiencies of NaOH-GAC-immobilized cells and free cells within 24 h were 100% and 4.17%, respectively. After 45 cycles, NaOH-GAC-immobilized cells maintained an ammonia nitrogen removal efficiency of 79.24%. After 70 days of storage at 4 °C, the ammonia nitrogen removal efficiency was still as high as 100%. The removal efficiencies of ammonia nitrogen (NH4+-N), total nitrogen (TN), and chemical oxygen demand (COD) in high-ammonia-nitrogen wastewater from petrochemical enterprises reached 99.27%, 88.39%, and 69.85%, with removal rates of 75.21, 69.43, and 1117.40 mg·L−1·d−1, respectively. The findings demonstrated that NaOH-GAC improved the capacity of the biological treatment to remove ammonia nitrogen from wastewater and provide a practical option for the remediation of environmental pollution.

Removal of mixed contaminants from landfill leachate-contaminated soil by flushing with bio-surfactant: laboratory column tests.

Landfill leachate-contaminated soil is widespread all over the world. In order to study the removal of mixed contaminants from landfill leachate-contaminated soil by flushing with bio-surfactant, soil column test was conducted to select an optimum concentration of bio-surfactant saponin (SAP) at first. Then, the removal efficiencies of organic contaminants, ammonia nitrogen, and heavy metals from landfill leachate-contaminated soil by flushing with SAP were studied. At last, the toxicity of contaminated soil before and after flushing was estimated by sequential extraction of heavy metals and plant growth test. The test results showed that the SAP solution with the concentration of 2.5 CMC could effectively remove the mixed contaminants from soil and would not introduce excessive pollutants of SAP in soil. Specifically, the removal efficiencies of organic contaminant and ammonia nitrogen were 47.01% and 90.42%, respectively. And the removal efficiencies of Cu, Zn, and Cd were 29.42%, 22.55%, and 17.68%, respectively. During flushing, hydrophobic organic compounds as well as physisorption and ion-exchange ammonia nitrogen in soil were removed by the solubilization effect of SAP, and heavy metals were removed by the chelation of SAP. After flushing with SAP, the reduced partition index (IR) value of Cu and Cd increased, and the mobility index (MF) value of Cu decreased. In addition, flushing with SAP reduced the plant toxicity of contaminated soil, and the residual SAP in soil promoted the plant growth. Therefore, flushing with SAP offered great potentials in remediating the landfill leachate-contaminated soil.

Influence of powdered activated carbon on gravity-driven ultrafiltration for decentralized drinking water treatment: Insights from microbial community and biofilm structure

Gravity-driven membrane (GDM) filtration, an appealing approach for decentralized drinking water treatment, tolerates the development of membrane biofilms for the benefit of low energy consumption and stable flux. In this study, the effect of introducing powdered activated carbon (PAC) on the biofilm generated during long-term GDM filtration was investigated. The results indicated that the addition of PAC significantly enhanced the removal of dissolved organic compounds (DOC) (31 %), whereas only 15.7 % removal was achieved in the control GDM system without PAC. The improved permeate quality was attributed to the combined effects of adsorption and biodegradation of organic compounds by PAC. However, the presence of PAC reduced the permeability of the GDM system by 39 % compared to the control one, which was related to the synergetic effect of the increased extracellular polymeric substances (EPS) content and the decreased metazoan amounts (especially Nematoda) in the biofilm. A large number of substrates adsorbed by PAC facilitated the growth of bacteria and hence intensified the secretion of EPS. Meanwhile, the deposition of PAC on the membrane surface limited the movement space of metazoans, leading to a denser and flatter biofilm basal structure. Furthermore, fewer metazoans meant less predation on bacteria, which also contributed to bacterial reproduction. In addition, an enhanced removal efficiency of ammonia nitrogen was observed in the PAC/GDM system, corresponding to a much higher abundance of Nitrospira in bacterial community. This study links microbial community to hydraulic resistance of biofilm and has practical implications for the application of GDM processes.

A Review of Bubble Aeration in Biofilter to Reduce Total Ammonia Nitrogen of Recirculating Aquaculture System

Aeration becomes an essential aspect of biofilter performance to reduce ammonia nitrogen in the Recirculating Aquaculture System (RAS). Efficient aeration introduces air into water media and offers an aerobic environment in the biofilter for microbial degradation of organic matter and ammonia nitrogen. The efficiency of the bubble aeration depends on the size of the bubbles; these include coarse bubble, microbubble, fine bubble, and ultrafine bubble or nanobubble. This review highlights an overview of bubble aeration features in a biofilter to reduce ammonia nitrogen. Moreover, key aspects responsible for the ammonia nitrogen removal efficiencies, such as oxygen transfer, microbial community, and biofilm thickness, are evaluated in this review. In conclusion, the bubble size of aeration affects the microbial community of nitrifying bacteria, consequently determining the growth and thickness of biofilm to improve ammonia removal efficiency. It is emphasized that fine bubble and nanobubble aeration have very positive prospects on improving biofilter performance, though they are currently not widely used in RAS.

Synergistic analysis of performance, functional genes, and microbial community assembly in SNDPR process under Zn(II) stress

One of the most prevalent heavy metals found in rural sewage is Zn(II), while its effect on simultaneous nitrification, denitrification and phosphorus removal (SNDPR) remains unclear. In this work, the responses of SNDPR performance to long-term Zn(II) stress were investigated in a cross-flow honeycomb bionic carrier biofilm system. The results indicated that Zn(II) stress at 1 and 5 mg L−1 could increase nitrogen removal. Maximum ammonia nitrogen, total nitrogen, and phosphorus removal efficiencies of up to 88.54%, 83.19%, and 83.65% were obtained at Zn(II) concentration of 5 mg L−1. The functional genes, such as archaeal amoA, bacterial amoA, NarG, NirS, NapA, and NirK, also reached the highest value at 5 mg L−1 Zn(II), with the absolute abundances of 7.73 × 105, 1.57 × 106, 6.68 × 108, 1.05 × 109, 1.79 × 108, and 2.09 × 108 copies·g−1 dry weight, respectively. The neutral community model demonstrated that deterministic selection was responsible for the system's microbial community assembly. Additionally, response regimes with extracellular polymeric substances and cooperation among microorganisms facilitated the stability of the reactor effluent. Overall, the findings of this paper contribute to improving the efficiency of wastewater treatment.

Performance evaluation of moving bed bioreactor for simultaneous nitrification denitrification and phosphorus removal from simulated fertilizer industry wastewater.

With increasing demand for agricultural production, chemical fertilizers are now being intensively manufactured and used to provide readily available nutrients in larger quantities, which often leach out and contaminate the groundwater source. At the same time, effluents from fertilizer plants also pollute water bodies, when disposed of without proper treatment. The present study evaluates nitrogen and phosphorus removal efficiencies in a single-stage aerobic moving bed bioreactor (MBBR) from diammonium phosphate(DAP)-spiked wastewater containing no organic carbon. To date, no similar study has been undertaken that treats fertilizer plant effluent or agricultural runoff without the aid of external carbon, where organic carbon ishypothesized to be supplied from endogenous degradation of biomass. Both denitrification and phosphorus removal occurs in the anoxic zones of deeper layers of the biofilm. The present investigation demonstrates the feasibility of the processes with the requirement of a two-stage MBBR for effective simultaneous nitrification, denitrification, and phosphorus removal (SNDPr) together with a polishing technology to bring down the phosphorus concentration within limits. A novel bio-carrier designed for efficient SND was used in the study, with a carrier filling ratio of 35% that supported the formation of deep biofilms creating anoxic zones in the inner surface. Identification of the bacterial species reflects the occurrence of simultaneous nitrification, denitrification, and phosphorous removal (SNDPr) in the reactor. A maximum ammonium nitrogen removal efficiency of 98% was recorded with 95% total nitrogen removal, 69% phosphorus removal, and 85% SND efficiency, indicating the applicability of the process with a tertiary phosphorus removal unit to lower the nutrient concentration of effluents prior to disposal.

Nitrogen transfer and transformation in bioretention cells under low temperature conditions

The nitrogen removal effect of traditional bioretention cells is generally poor under low temperature conditions, with significant levels of fluctuation and leaching often reported. Therefore, the migration characteristics of nitrogen were explored in bioretention cells under low temperature conditions, with the aim of improving the nitrogen removal effect. Four groups of modified collapsible loess bioretention cells were constructed and operated at 1, 5, 10 and 25 °C. The nitrogen removal effect of the cells was determined at different temperatures and the nitrogen migration and transformation characteristics under low temperature conditions were discussed. Experimental results showed that during the rainfall period, the ammonia nitrogen removal efficiency remained similar at different temperatures (above 97 %), while the nitrate nitrogen removal efficiency varied significantly at 1, 5, 10 and 25 °C, from 28.15 %–65.22 %, 96.68 %–98.8 %, 96.75 %–98.88 % and 80.14 %–96.72 %, respectively. In addition, nitrate nitrogen accumulation occurred in the filler during rainfall events, with lower temperature conditions increasing the final concentration of nitrate nitrogen accumulated. Following a rainfall event, the content of nitrate nitrogen in the filler decreased significantly over a 60 h dry period. However, the nitrate nitrogen reduction rate was significantly lower under low temperature conditions, than at 25 °C. Overall, low temperature conditions had a negative effect on the accumulation of nitrate nitrogen in the filler during rainfall events, as well as the transformation and migration of nitrate nitrogen within the filler during drought periods, with the adverse effects most significant at temperatures lower than 5 °C.

Onsite treatment of decentralized rural greywater by ecological seepage well (ESW)

Seepage well, as an ancient facility for sewage collection and treatment in China, still has reference significance for effective treatment of source-separated greywater in rural China under the background of rural revitalization. This study surveyed the discharge characteristic of rural greywater, and proposed onsite treatment of decentralized rural greywater using a novel ecological seepage well (ESW). In northwestern China, four rural households produced greywater with an average quantity of 128–146 L/d, with chemical oxygen demand (COD) of 213.6–235.9 mg/L as the main pollutant. For treating greywater, ESW with ceramsite and zeolite mixed in the packing layers and metallic corrugated plates (MCPs) set in the aeration zone achieved higher removal efficiencies of COD, total phosphorous (TP), total nitrogen (TN) and ammonia nitrogen (NH4+-N). When the influent C/N ratio was 16, the enhanced removal performance was realized by cutoff duration of 9 h, and the effluent met the Chinese standard for irrigation water quality with COD, TP, TN and NH4+-N removal efficiencies of 88.58%, 65.60%, 92.94% and 93.65%, respectively. Under the optimal condition, mechanism of pollutant removal by ESW was investigated. The variation of EPS and microbial morphology along the height illustrated that a micro-aerobic environment was formed in the lower layer of ESW. High throughput sequencing indicated plentiful denitrifying bacteria (DNB) and denitrifying phosphate accumulating organisms (DNPAOs), together with a higher relative abundance of ammonia oxidizing bacteria (AOB) than nitrite oxidizing bacteria (NOB) in the lower layer, which was relative to simultaneous nitrification, denitrification and phosphorous removal. This study provided theoretical and practical support for effective treatment mode of rural sewage.

Starting-up performances and microbial community shifts in the coupling process (SAPD-A) with sulfide autotrophic partial denitrification (SAPD) and anammox treating nitrate and ammonium contained wastewater

A novel coupling process (SAPD-A) with sulfide autotrophic partial denitrification (SAPD) (NO3−-N→NO2−-N) and anaerobic ammonium oxidation (Anammox) was developed using anaerobic sequencing batch reactor (ASBR) in this work. The integrated process comprised two stages. Firstly, the starting-up of SAPD process succeeded by gradually increasing the influent nitrate and sulfide in 95 days. The average nitrate removal efficiency (NRE) and NO2−-N accumulation rates were 71.24% ± 0.21% and 46.44% ± 0.53% at SAPD process (days 75–95). Then, successful coupling process (SAPD-A) was implemented in two stages (stage I and stage II of SAPD-A). In stage I, it is feasible to promote the successful construction of SAPD-A process by elevating influent ammonium only based on SAPD system, making the NRE increased from 44.45% ± 0.46% (day 95) to 64.62% ± 0.12% at the end of stage I in SAPD-A system (day 126). Meanwhile, the ammonium nitrogen removal efficiency (ARE) and total nitrogen removal efficiency (TN-RE) also rose up to 42.46% ± 2.02% and 63.28% ± 0.54% respectively. Furthermore, the average ARE, NRE and TN-RE during the stage II in the bioreactor could reach 65.17% ± 1.45%, 74.50% ± 0.81% and 77.81% ± 0.37% by loading some biofilters (with of approximate 10% of the volume of the bioreactor) attached anaerobic ammonium oxidation bacteria (AnAOB). High-throughput sequencing results showed that the dominant genera concerning nitrogen removal were norank_f_norank_o_Fimbriimonadates (with the abundance of 2.88–8.54%), norank_ o_ norank _ c_ OM190 (2.48–4.41%), norank_f_norank_o_norank_c_WWE3 (11.01–17.69%), subgroup_10 (1.97–3.81%), Limnobacter（2.17–3.49%）, norank_f_n orank_ o_norank_ c_OLB14 (2.03–5.23%), norank-f-PHOS-HE36 (2.18–5.5%), Ellin6067 (1.34–2.24%) and Candidatus_ Brocadia (1.95–2.42%) during the whole starting-up period of coupling SAPD-A process. Batch experiments revealed that the sulfide was fully oxidized within 2 h, with the maximum reaction rate of 38.30 ± 1.53 mg (L h)−1 in the first 1 h. Simultaneously, the concentration of nitrate sharply decreased from 53.08 ± 0.23 mg L−1 to 24.16 ± 0.42 mg L−1 with the reaction rate of 66.41 ± 2.12 mg (L h)−1 in 0.5 h. Also, the ammonium concentration significantly declined from 47.88 ± 0.34 mg L−1 to 10.98 ± 0.39 mg L−1 in 8 h. Anammox process was responsible for the dominant nitrogen removal in the coupling SAPD-A system.

Application Potential of Constructed Wetlands on Different Operation Mode for Biologically Pre-Treatment of Rural Domestic Wastewater

In order to satisfy the requirements of rural domestic sewage, a bio-ecological combination system was proposed, including a biological treatment section (anaerobic hydrolysis tank and aerobic tank) and an ecological post-treatment section. This study observed the application potential of constructed wetlands (CW) on different operation modes for biologically pre-treated rural domestic wastewater. The organics and nutrient removal efficiency of the tidal flow constructed wetland (TFCW) and the horizontal subsurface flow constructed wetland (HFCW) were compared at a temperature range of 20–40 °C. During the stable phase, the higher chemical oxygen demand (COD), ammonia nitrogen (NH4+-N), and total phosphorus (TP) removal efficiencies existed in TFCW than HFCW, corresponding to the efficiency of COD 69.46%, NH4+-N 96.47%, and TP 57.38%, but lower performance on COD (61.43%), NH4+-N (84.99%), and TP (46.75%) removal in HFCW, which should be attributed to the increasement of aerobic heterotrophic bacteria (Arthrobact and Sphingomonas), nitrifiers (Nitrospira), and phosphate accumulating organisms (PAOs) (Pseudomonas). The microbial biomass was also increased from 2.13 ± 0.14 mg/g (HFCW) to 4.64 ± 0.18 mg/g (TFCW), which proved to strengthen the formation and growth of biofilm under a better oxygen supplement. Based on the relative abundance of functional genera in the microbial community, it showed that TFCW was more favorable for promoting the growth of heterotrophic bacteria, nitrifiers, and phosphate-accumulating organisms (PAOs). When temperature changed from −4 °C to 15 °C, the two-stage constructed wetlands (TFCW-HFCW and HFCW-TFCW) were used for improving the performance of pollutants removal. The results demonstrated that the effluent concentrations of TFCW-HFCW and HFCW-TFCW met the Class 1A discharge standard of DB32/3462-2020 in JiangSu Province, China. Therefore, this study will provide a useful and easy-to-implement technology for the operation as an ecological post-treatment section.

Removal of low concentration ammonia nitrogen enhanced by hydraulic cavitation combined with ozonation

The combination of hydraulic cavitation and ozone oxidation improves the removal efficiency of low concentration ammonia nitrogen. Focusing on the treatment of low concentration ammonia nitrogen wastewater (about 25mg/L), the study discusses the treatment effect of cavitation combined with different gases (O2, O3) on low concentration ammonia nitrogen. The treatment effect of ozone 3L/min combined with cavitation on ammonia nitrogen is 33.07%. The treatment effect of oxygen (3mg/L) combined with cavitation on ammonia nitrogen was 16.91%. At the same time, the treatment efficiency of ammonia nitrogen at different PH values was compared. When the initial concentration was adjusted from 7 to 10, the treatment efficiency increased from 33.07% to 84.55%. When PH=10, the ammonia nitrogen concentration in water finally dropped to 3.5mg/L, reaching the Chinese first-level emission standard (15mg/L). In addition, the mechanism of treating ammonia nitrogen in water by hydraulic cavitation combined with ozonation was discussed. The results show that ozone combined cavitation is very effective for the treatment of low concentration ammonia nitrogen wastewater.

Synergistic removal of ammonia nitrogen by UV photo-electrocatalytic process: Heterogeneous reaction pathways and mechanism

UV photo-electrocatalytic process has emerged as a promising approach for the abatement of ammonia nitrogen in wastewater. However, the radical chemistry for ammonia nitrogen removal in this process requires further clarification. The heterogeneous reaction pathways and mechanism of ammonia nitrogen oxidation in the UV photo-electrocatalytic process were investigated in this study. Photocurrents of the Ti/RuO2-IrO2-TiO2 electrodes with good electrocatalytic behavior were enhanced by UV radiation. Compared with the electrocatalytic process, the removal rates of ammonia nitrogen were improved by 12.4%∼20% at the Cl− concentration of 50 mM in the photo-electrocatalytic process. The ammonia nitrogen was mainly transferred into N2, meanwhile, the formation of nitrogenous by-products, active chlorine, and chloramines was inhibited in the photo-electrocatalytic process. The contribution of UV radiation was to photo-decompose the active chlorine and chloramines, generating free radicals. The removal efficiency of ammonia nitrogen reached more than 64% after the elimination of free radicals. The electro-generated HOCl was the principal species for ammonia nitrogen removal, and the synergistic effect for the acceleration of ammonia nitrogen oxidation resulted from the photo-generated chlorine radicals. This investigation provides insight into the electrochemistry, photochemistry, and radical chemistry for the heterogeneous catalytic degradation of ammonia nitrogen by UV photo-electrocatalytic process.