Ammonia Nitrogen Removal Efficiency Research Articles

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.

Harmless treatment of electrolytic manganese residue: Ammonia nitrogen recovery, preparation of struvite and nonsintered bricks

The ammonia nitrogen in electrolytic manganese residue (EMR) is easily transferred to water source, polluting the environment and endangering biological health. In this study, the ammonia nitrogen in EMR is removed by slaked lime, carbide slag (CS) and red mud (RM). The removal of ammonia nitrogen is influenced by the liquid–solid ratio, stirring time, and additives dosage. The removal efficiency of ammonia nitrogen of EMR pretreated with 7.4 % fresh CS for 15 min can reach 98.5 % when the liquid–solid ratio is 1.50. Under the synergistic effect of CS and RM, the ammonia nitrogen in EMR is quickly removed within 15 min, and the removal efficiency of ammonia nitrogen reaches 98.2 %. It is feasible to replace slaked lime with CS and RM to achieve the removal of ammonia nitrogen in EMR. Struvite has high quantity and good purity when the molar ratio of N, P and Mg is 1:1.6:1.6 and pH = 8.0. The remaining EMR after removal of ammonia nitrogen, blast furnace slag, Portland cement and aggregates was used as raw materials to prepare nonsintered bricks (NSB). The NSB according to the optimal formula after curing for 7 days had no free ammonia nitrogen detected. This study provided a new way to remove ammonium nitrogen in EMR by CS and RM, and demonstrated a solution to prepare struvite and nonsintered bricks.

Changes in the Composition of Digestate Liquid Fraction after Ozone and Ultrasonic Post-Treatment

There is a growing concern about environmental pollution with digestate, which is produced in significant amounts in the anaerobic digestion process. The inappropriate application of digestate in agriculture may lead to ammonia emission to the atmosphere, nutrients infiltration to groundwater and surface waters eutrophication. There is a great interest in the development of efficient downstream technologies that will help better handle digestate. This study assessed the effect of three different disintegration methods (ozonation, ultrasonication, combination of ozonation and ultrasound) on solids content, nutrient concentration and biodegradability of the liquid fraction of sugar beet pulp digestate. The influence of initial pH (7, 8, 9), ozone dose (0.05–0.45 g O3/g TS), specific ultrasound energy (10,381–51,903 kJ/kg TS) and vibration amplitude (50, 100%) on the performance of digestate liquid fraction treatment was investigated. The highest removal efficiencies of organic substances, total and ammonia nitrogen averaging at 13.81, 20.04 and 28.70%, respectively, in separate ozonation and ultrasonication processes, was obtained at ozone dose of 0.25 g O3/g TS, specific energy of 41,522 kJ/kg TS and amplitude of 100%. The application of combined processes, first ultrasonication and then ozonation, resulted in an increase in the above-mentioned removal efficiencies to 58.16, 36.60 and 48.71%, respectively.

A facile and efficient approach for the removal of high concentrations of ammonia nitrogen in wastewater: Liquid-phase plasma treatment

We report the facile and effective liquid-phase plasma treatment (LPPT) approach for removing high concentrations of ammonia nitrogen from wastewater. The effects of the operating parameters, including the pH and temperature, the pulse repetition frequency, the pulse duration, and the reaction time, were investigated to obtain the optimal removal conditions using a simulated wastewater sample. It was found that a higher pulse repetition, a longer pulse duration, and alkaline conditions were favorable for the removal of ammonia nitrogen. Thus, at pH 12, a pulse repetition frequency of 30 kHz, and a pulse duration of 3.0 μs, the removal efficiency of ammonia nitrogen reached 100% in 25 min during the LPPT. In addition, when isopropanol (IPA) and 1, 4-diazabicyclooctane triethylenediamine (DABCO) were used as scavengers for ∙OH and 1O2, respectively, the removal efficiency of ammonia nitrogen after 25 min decreased from 71.7% to 68.1% in the presence of DABCO and from 71.7% to 62.8% in the presence of IPA. Based on these results, the mechanism of ammonia nitrogen removal was proposed to constitute the collision of accelerated electrons and the oxidation reaction of ∙OH. Moreover, it was confirmed that the LPPT approach was feasible for the removal of ammonia nitrogen from wastewater.

Floating wetland treatment an ecological approach for the treatment of water and wastewater – A review

The demand for water increases day by day due to population growth; on the other hand, water quality is declining globally due to rapid industrialisation and climate change. The surface water sources such as ponds, lakes, rivers, and reservoirs are being polluted and have lost their ecological functions. Floating wetland treatment (FWT) is an emerging natural method for treating surface water bodies and restoring their ecological processes. This study attempted to collect and summarise literature to give an insight into the design, construction, applications, macrophytes, substrates, and pollutant removal efficiency of FWT. The pollutant removal mechanism of FWT mainly depends on the hydrophytes grown on a floating raft with substrates attached for the growth of microorganisms. This paper also reviews the performance of floating wetlands planted with different hydrophytes, growth mediums, and floating rafts in mesocosms, in-situ, and lab-scale environments. Several pollutants were also reviewed, including TN, TP, TSS, BOD, COD, and ammonium nitrogen removal efficiency between plant species and growth medium. This review found that combining native plant species with different substrates under varying climatic conditions has improved the performance of FWT. Many studies recommend further research on FWT by adopting other macrophytes and substrates to improve the removal efficiency of pollutants in water and wastewater.

Characteristics of denitrification and anammox in the sediment of an aquaculture pond

Denitrification and anaerobic ammonium oxidation (anammox) are the key processes of nitrogen removal in aquaculture pond sediment. However, the reaction characteristics remain unclear. In this study, considering the sediment of conventional freshwater fishponds as the object, we set the optimal conditions of organic carbon, temperature, and total nitrates for denitrification and anammox. We found that the abundance and diversity of denitrifying bacteria and anammox bacteria in the two groups were significantly different. Candidatus brocadia is the most important bacteria in aquaculture pond sediments. The removal efficiencies of nitrite (NO2−-N), nitrate (NO3−-N), ammonia nitrogen (NH4+-N), and total organic carbon (TOC) in the anammox optimal conditions group were 97.99%, 93.05%, 54.92%, and 58.82%, respectively; however, those in the denitrification optimal conditions group were 99.82%, 86.10%, 45.74%, and 70.76%, respectively. Comparing each optimal condition, the removal efficiency of NO2−-N and TOC in the denitrification optimal condition groups was higher, whereas those of NO3−-N and NH4+-N were higher in the anammox optimal condition groups. We provide a reference for resolving nitrogen pollution in aquaculture pond sediments.

Simultaneous methanogenesis and denitrification coupled with nitrifying biofilm for high-strength wastewater treatment: Performance and microbial mechanisms

A combined system consisting of an upflow blanket filter (UBF) and a moving-bed biofilm reactor (MBBR) was developed for the simultaneous removal of organic matters and ammonia from high-strength wastewater. With a constant COD of approximately 2000 mg/L and ammonium nitrogen in a series of concentrations (e.g., 50, 200 and 400 mg/L in stages I to III) of the influent wastewater, the removal efficiencies of COD, ammonium nitrogen and total nitrogen reached 96.10%-98.19%, 100%, and 79.12%-82.15%, respectively. With the increase of influent ammonia nitrogen concentration, the specific methanogenic activity of the UBF granules decreased significantly, while the specific denitrification rates of the UBF granules and specific nitrification rates of the MBBR biofilms increased significantly. Microbial community analysis showed that Methanobacterium and Methanosaeta were the dominant methanogens in the UBF granules, while Candidatus Competibacter, Thauera and Acinetobacter were identified as dominant denitrifiers. In addition, nitrifiers were enriched in MBBR biofilms at 11.33% and 13.87% of the average abundance of Nitrosomonas and Nitrospira, respectively, at stage III (influent ammonium at 400 mg/L, COD/NH4+-N = 5). The ecological network analysis, including full-networks and sub-networks, indicated that the interactions between methanogens and denitrifiers in the UBF granules were strong when the influent ammonium concentration reached 400 mg/L. No intensive interactions were observed among the functional bacteria in the MBBR biofilms over the entire operation. Overall, this study provides a new strategy for the application and construction of efficient biological processes to achieve simultaneous removal of organic matter and nitrogen for high-strength wastewater treatment.

Ecological restoration for the Liangtan river by Rotating biological contactors combined with hybrid constructed wetlands

Rotating biological contactors (RBCs) were first used as pretreatment units for hybrid constructed wetlands (HCWs) in practical engineering to treat polluted river water. The experimental results during 2019–2021, except the period of global COVID-19 pandemic (January to April, November and December in 2020), indicated the average removal efficiencies of ammonia nitrogen (NH4+–N), total phosphorous (TP), and chemical oxygen demand (COD) were 95.06%, 41.03%, and 45.46%, which met the Chinese Environmental Quality Standards Ⅰ, Ⅲ, Ⅳ (CEQS Ⅰ, Ⅲ, Ⅳ), respectively. RBCs and HCWs had synergistic and complementary effects on purification efficiency, especially on nitrogen removal. The remarkable nitrification efficiency of RBCs was not influenced by temperature and influent loads. The relative abundances of microorganisms at HCWs in cold seasons were comparable to that in warm seasons, which promoted the recovery of decontamination efficiency after overwintering. These results support RBCs combined with HCWs (R-HCWs) is an effective polluted river purification process, providing a new perspective on water ecological restoration.

Root exudates release from Myriophyllum aquaticum and effects on nitrogen removal by constructed wetlands

The root exudates released from macrophytes are critical for pollutant removal and associated microorganisms, but their role in nitrogen removal remains poorly understood in constructed wetlands (CWs). The release of root exudates by Myriophyllum aquaticum was quantified using a hydroponic experiment, and then four treatments with and without environmentally relevant concentrations of root exudates were conducted to investigate the effect of root exudates on nitrogen removal in CWs. The dissolved organic carbon (DOC) release rate of M. aquaticum was 1.1–2.2 mg g−1 h−1, significantly higher than that of Typha orientalis (0.58–0.78 mg g−1 h−1) and Iris pseudacorus (0.13–0.14 mg g−1 h−1). The DOC release rate of M. aquaticum was affected by the ammonium concentration and harvesting frequency. The removal efficiencies of ammonium and total nitrogen were higher in the CWs with plants than in those without plants, confirming the crucial role of plants in plant-microbe interactions and nitrogen removal in CWs. The CWs showed significantly higher ammonium removal efficiencies under the root exudate treatments (mean 90.4% and 69.3%) than the no-root exudate treatments (87.3% and 62.0%), while total nitrogen presented no significant difference. The phylum-level taxonomic classification of microbial sequences detected in the sediments was slightly different between the root exudate and no-root exudate treatments. The results suggested that the root exudate mass naturally released by plants may be insufficient to change the carbon to nitrogen ratios of wastewater. More gene copies were observed in the rhizosphere sediments than the bulk sediments (p < 0.05), indicating that root exudates had a positive effect on microbes distribution within the rhizosphere. Therefore, high levels of root exudates as external carbon sources should be added to enhance nitrogen removal in CWs for carbon-limited wastewater treatment. The present study provided new insights into the role of macrophytes in pollutant removal and management strategy of CWs for wastewater treatment.

A novel strategy for rapid formation of biofilm: Polylactic acid mixed with bioflocculant modified carriers

Aiming at the resolving long biofilm formation period problem of the moving bed biofilm reactor, a method for preparing modified carriers of bioflocculant doped in polylactic acid (PLA) to promote biofilm formation is proposed. The micron-scale porous structure is verified by optical microscopy and scanning electron microscope. The modified material also has nano-scale pores in BET test. FTIR shows that the bioflocculant modified carriers have amino carboxyl and polysaccharide functional groups. The biofilm formation time is shortened, and the removal efficiency of COD and ammonia nitrogen are 14.14–21.15% and 6.08–15.41% higher than that of polyethylene carrier. Extend DLVO theory shows that bioflocculant modified carriers have lower energy barrier (149.18 kT) than other modified carriers. By immersing modified carriers and ordinary carriers in the bioflocculant bacteria solution, the high-throughput sequencing reveals that the microorganisms attached on the carriers of bioflocculant doped in PLA have better biodiversity and abundance of functional gene expression than others.

Evidence for the occurrence of Feammox coupled with nitrate-dependent Fe(II) oxidation in natural enrichment cultures

Feammox is a newly discovered process of anaerobic ammonium oxidation driven by Fe(III) reduction. Nitrate-dependent Fe(II) oxidation (NDFO) is the coupling of Fe(II) oxidation and nitrate reduction to produce N2 under anaerobic conditions. It has not been reported whether the coupling of the two reactions exists in natural enrichment. In this study, enrichment culture experiments were carrired out to prove the occurrence of Feammox with NDFO. The results indicated that the nitrogen and iron cycle were formed during natural enrichment cultures, including Fe(III) reduction and NH4+-N was oxidation to NO3--N, NO2--N and N2, Fe(III) and Fe(II) were cyclically formed, and Fe(II) was oxidized with NO3--N reduced to N2. The removal efficiencies of ammonium nitrogen and total nitrogen in the incubation were about 92.9% and 20% respectively. Organic carbon experiments indicate that sodium acetate can promote the initial NO3--N removal and a low concentration of organic carbon limited the NDFO process because iron-oxidizing bacteria are mixotrophic microorganisms. The added 9,10-anthraquinone-2,6-disulfonate (AQDS) in the later stage can promote NDFO to remove nitrate, thereby increasing the TN removal efficiency to 50%. 15N-isotope tracer incubations provided direct evidence for the occurrence of Feammox coupled to NDFO, with rates producing 30N2 of Feammox (0.024-0.0288mgN·L-1·d-1) and NDFO (0.0465-0.0833mgN·L-1·d-1) in three groups (Wetland/Wheat soil/Sediment). 16S rRNA sequencing further demonstrated that Pseudomonas, Rhodanobacter, Acinetobacter and Thermomonas were the dominant generas among the enrichment cultures, and these bacteria belonged to FeOB and FeRB, which may further promote Feammox coupled to NDFO in the cultivation system.

Nitrogen removal performance and rapid start-up of anammox process in an electrolytic sequencing batch reactor (ESBR)

In this study, the electrolytic sequencing batch reactor (ESBR) with different current densities was constructed to investigate the nitrogen removal performance and rapid start-up of anaerobic ammonia oxidation (anammox) process. The changes of total nitrogen removal rate (TNRR), specific anammox activity (SAA) and nitrogen concentration under different current densities were analyzed, and then the effect of the optimal current density on the start-up of anammox in ESBR was explored. The results showed that ammonium nitrogen removal efficiency (92.7%), nitrite nitrogen removal efficiency (15.5%) and total nitrogen removal efficiency (28.1%) were obtained with the TNRR and SAA were 0.0118 g N L−1 d−1 and 0.0050 g N (g Vss d)−1, respectively under the optimal conditions (i.e., current density = 0.10 mA cm−2, temperature = 36 °C and pH = 7.6). In addition, the stoichiometric ratio indicated that anammox was initiated successfully for 91 days in ESBR with the current density of 0.10 mA cm−2, which was shortened by 10 days compared with the conventional SBR without current density. These results suggest that an array of rapid start-up processes of anammox can be developed through applying current density to stimulate the activity of anammox bacteria (AnAOB).

Phytomanagement of textile wastewater for dual biogas and biochar production: A techno-economic and sustainable approach

Phytoremediation has been widely employed for industrial effluent treatment due to its cost-effectiveness and eco-friendliness. However, this process generates large amounts of exhausted plant biomass, requiring appropriate management strategies to avoid further environmental pollution. To the best of the authors' knowledge, this study is the first to address the recyclability of water hyacinth after textile wastewater (TWW) phytoremediation for dual biogas and biochar production. A hydroponic culture system was occupied by 163 g (plant mass) per L (TWW) and operated under 16:8 h light:dark cycle (sunlight), 70–80% relative humidity, and 22–25 °C temperature. This water hyacinth-based system achieved chemical oxygen demand (COD), ammonia nitrogen (NH4+-N), and dye removal efficiencies of 58.60 ± 2.63%, 35.27 ± 1.65%, and 38.49 ± 2.24%, respectively, at a TWW fraction of 100 %v/v. The plant characterization study revealed that phytoabsorption and phytoextraction could be the main mechanisms involved in TWW pollution reduction. The lignin and hemicellulose of water hyacinth were slightly degraded during phytoremediation, making the cellulose fibers simply accessible to enzymes’ attack in the subsequent anaerobic digestion process. This hypothesis was validated by increasing the crystallinity index from 50.13% to 60.21% during TWW phytoremediation. The spent plant was cleaned and then co-digested (37 °C) with cow dung at 1:1 (w/w, dry basis) for bioenergy production. The generated biogas was 162.78 ± 8.34 mL CH4/g COD (i.e., 225.63 ± 11.36 mL CH4/g volatile solids), representing about 490% higher than the utilization of raw water hyacinth in a mono-digestion process. The pyrolysis of digestate-containing plant residues yielded biochar with concentrated cationic macroelements (K+, Mg2+, and Ca2+). The economic feasibility of the phytoremediation/co-digestion/pyrolysis combined system showed an initial investment of 2090 USD and a payback period of 9.08 yr. Because the project succeeded in recovering the cost of its initial investment, it could fulfill the targets of several sustainable development goals related to economic profitability, social acceptance, and environmental protection.

Nitrogen removal from low COD/N interflow using a hybrid activated sludge membrane-aerated biofilm reactor (H-MABR)

A hybrid activated sludge membrane-aerated biofilm reactor based on a two-stage simultaneous nitrification–denitrification (SND) process was built, and its utility for treating interflow with low chemical oxygen demand (COD)/total nitrogen (TN) (COD/N) was explored. The operating performance, functional microbial communities, and functional genes for nitrogen metabolism were evaluated at low COD/N (4–1.3). The reactor could achieve stable operation at COD/N = 4–1.5, and the removal efficiency of COD, TN, and ammonia nitrogen was stable at 90.30 ± 2.36 %, 85.69 ± 2.22 %, and 89.52 ± 6.06 %, respectively. The SND rates were 70.89 % and 50.75 % when influent COD/N was 2.0 and 1.7, respectively, indicating that SND makes an important contribution to nitrogen removal under these two COD/N conditions. Microbial analysis revealed that the sampling sites with a high abundance of denitrification genes in the outer ring experienced aerobic conditions, inferring that aerobic denitrification also plays an important role in denitrification.

Enhanced pre-treatment of sepiolite on coal gasification wastewater: Performance and adsorption mechanism

As a simple and feasible treatment method, adsorption can be applied in the pretreatment of coal gasification wastewater (CGW) to remove high-concentration contaminants. This study initially selected granular activated carbon (PAC) and different clay materials (sepiolite (SPI), bentonite (BTE), kaolin (KL), diatomite (DTI) and attapulgite (APG)) as adsorbents, and results showed that chemical oxygen demand (COD) removal efficiencies of by PAC, SPI, DTI, KL, BTE and APG were 54.28 %, 44.19 %, 27.15 %, 17.68 %, 16.08 % and 5.58 %, respectively. In contrast, SPI and PAC had high adsorption capacity for high concentrations of organics. Ammonia nitrogen (NH3-N) removal efficiency by SPI exceeded 27 %, while the effective capacity of PAC was only 9.3 %. Moreover, pseudo-second-order kinetics better fitted kinetic data for PAC and SPI, revealing that the adsorption of organic pollutants on SPI is multi-molecular layer adsorption. The Sips model well described the adsorption process of contaminants by SPI, and more remarkably, the maximum adsorption capacity of SPI for COD was 438.4 mg/g. Accordingly, SPI and PAC both had significant removal effects on phenol, 2-methylphenol, 4-methylphenol, catechol and other refractory organic pollutants through gas chromatograph-mass spectrometer (GC-MS). Simultaneously, acute biotoxicity of CGW was greatly reduced after PAC and SPI adsorption treatment. Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS) confirmed the presence of strong polar hydration bonds enabled SPI to adsorb organic pollutants through intermolecular forces. SPI still exhibited more than 30 % of COD removal for CGW after 5 cycles. And COD and total phenol (Tph) removal efficiencies in the stable period reached 37.34 % and 31.04 % during the anaerobic process, respectively. Specially, the cost of removing COD per kilogram of SPI is only 2.73 ¥ while the cost of PAC is as high as 26.61 ¥. On the whole, this study provided an important insight for the feasibility application of SPI in the CGW pretreatment process.

Enhancing the Stability of Aerobic Granular Sludge Process Treating Municipal Wastewater by Adjusting Organic Loading Rate and Dissolved Oxygen Concentration

Aerobic granular sludge (AGS) application in treating municipal wastewater has been greatly restricted due to its low stability. It has been found that operation parameters have a great impact on stability. The organic loading rate (OLR) and dissolved oxygen (DO) concentration are two very important parameters that impact stability. In this study, the organic loading rate (OLR) and aeration rate were studied to verify their influence on AGS system stability, which is indicated by determining pollutant removal performance, including chemical oxygen demand (COD), ammonia nitrogen, and total nitrogen (TN). The physical and chemical property changes of AGS and the effects of pollutant removal during the formation of AGS were systematically investigated. The AGS was formed after about 25 days and remained stable for about 45–50 days. The AGS was light-yellow globular sludge with an average particle size of 1.25 mm and a sludge volume index (SVI) of 33.9 mL/g. The optimal condition was obtained at an OLR of 4.2 kg COD/m3·d, aeration rate of 4 L/min, and a hydraulic retention time (HRT) of 4 h. The corresponding removal efficiencies of COD, ammonia nitrogen, and TN were 94.1%, 98.4% and 74.1%, respectively. The study shows that the AGS system has great potential for pollutant removal from wastewater.

Preparation of low-cost functionalized diatomite and its effective removal of ammonia nitrogen from wastewater.

A low-cost functionalization method was used to treat diatomite, and an efficient adsorbent for ammonia nitrogen was prepared by optimizing the functionalization conditions. The functionalized diatomite (DTCA-Na) was characterized by SEM, EDS, BET, XRD, FT-IR, and TG. The results demonstrate that DTCA-Na has excellent adsorption performance after being modified with H2SO4 (60.00 wt.%), NaCl (5.00 wt.%), and calcination at 400°C for 2h. While studying the effect of adsorption factors on the removal of ammonia nitrogen, the kinetic and thermodynamic behaviors in the adsorption process were discussed. The removal efficiency of the simulated wastewater with the initial ammonia nitrogen concentration of 10.00mg L-1 by the DTCA-Na was more than 80% when the contact time was 60min, pH was 6-10, the dosage of adsorbent was 1.00g, and the temperature was 25°C. The adsorption process of ammonia nitrogen was conformed to the pseudo-first-order and Langmuir isothermal model. The removal efficiency of ammonia nitrogen was still above 80% after 5 times adsorption-desorption experiments. The DTCA-Na has a brighter prospect of application in the field of ammonia nitrogen wastewater treatment due to its excellent adsorption performance and low-cost advantage.