Total Nitrogen Removal Efficiency Research Articles

Stress response mechanism of wastewater biological nitrogen removal systems to environmentally realistic concentrations of tire wear particles: Contribution of leachable additives

The study quantified the biological nitrogen removal performance, microbial metabolism, microbial community structure, and antioxidant system in a sequencing batch reactor under long-term exposure to 0.1 and 1 mg/L tire wear particles (TWPs), and determined the contribution of leachable additives to the biotoxicity of TWPs. The results showed that long-term exposure to 0.1 and 1 mg/L TWPs inhibited both the nitrification and denitrification processes, reducing ammonia nitrogen (NH4+-N) and total nitrogen (TN) removal efficiency. The TWP leachate (TWPL) primarily contributed to the denitrification inhibition by TWPs, potentially due to the high concentration of zinc ions in the leachable additive. Furthermore, both TWP and TWPL inhibit nitrogen conversion, with TWP inhibiting the generation and transfer of electrons, while TWPL only negatively affects the electron transfer process. This study presents novel insights into the impact of TWPs on biological nitrogen removal, underscoring its broader implications for the geochemical nitrogen cycle.

Electron transfer mechanism of intracellular carbon-dependent DNRA inside anammox bacteria

Generally, anaerobic ammonium oxidation (anammox) converts nitrite (NO2−) and ammonium (NH4+) to nitrogen gas (N2) but generates some nitrate (NO3−) (equivalent to 11% of inlet total nitrogen (TN)). Although it reported that anammox bacteria could degrade NO3− via dissimilatory nitrate reduction to ammonium (DNRA) pathway using the intracellular carbon as the electron donor, it is still unclear the specific electron transfer mechanism in this intracellular carbon-dependent DNRA inside anammox bacteria, and whether the sole anammox bacteria could achieve higher TN removal efficiency more than the theoretical maximum of 89%. In this study, transcriptome analysis and metabolic inhibitor experiments demonstrated that NADH generated from the decomposition of the intracellular carbon (glycogen) supplied electrons for the NO3−conversion; the electrons were transferred from NADH to nitrate reductase (Nar) and nitrite reductase forming ammonium (NrfA) from ubiquinone (UQ) and complex III, respectively. Combining the intracellular carbon-dependent DNRA with normal anammox process, an average TN removal efficiency of 95% was achieved by the sole anammox bacteria in a sequencing batch reactor. Fluorescent in situ hybridization (FISH) images and real-time fluorescence quantitative PCR (qPCR) results illustrated anammox bacteria could survive and proliferate in the SBR. Our work improved the understanding of the electron transfer mechanism inside anammox bacteria, and further exploit its potential in nitrogen pollutants removal.

Effect of zeolite–sponge iron combined substrate on microbial community in ecological floating bed

Substrate has been proven to be a useful way to enhance the purification effect of ecological floating bed (EFB), and it also affected the microbial community. While at cold temperature, there was a lack of research on the effect of substrates on plant growth and microbial communities. In this study, three EFBs, namely plant EFB (EFB-P), substrate EFB (EFB-S) and plant–substrate EFB (EFB-PS), were constructed. The effects of zeolite–sponge iron combined substrate on pollutant removal, plant growth and microbial community in the EFBs were investigated at low temperature (3.1 ∼ 11.7 °C). Results showed that the removal efficiencies of total nitrogen, total phosphorus and nitrate nitrogen by EFB-PS (60.35%, 95.09% and 64.43%) was significantly better than that of EFB-P (47.71%, 88.59% and 51.65%), but the relative growth of the aboveground biomass of plants (50.41%) was less than that of EFB-P (81.16%). In addition, the microbial biomass in EFB-PS (69.14 mg/(g DW·day)) and EFB-S (68.76 mg/(g DW·day)) was much larger than that in EFB-P (50.69 mg/(g DW·day)). High-throughput sequencing showed that the microbial diversity (Shannon (6.06 ∼ 8.33) and Simpson (0.88 ∼ 0.97)) and richness (Chao1 (1621.7 ∼ 2556.2) and Observed _ species (1437 ∼ 2423.3)) of EFB with adding zeolite–sponge iron combined substrate were also higher than those of EFB-P. In addition, the addition of combined substrates changed the microbial community structure, some genera with denitrification and nitrogen fixation functions, including Rhodobacter (36.03 ∼ 48.59%), Hydrogenopha (2.21 ∼ 5.89%), were abundantly enriched in the EFB with adding zeolite-sponge iron combined substrate. These results improved the effects of substrate low temperature operation on plant growth and microbial characteristics in EFB, and provide a theoretical basis for strengthening the operation of the low temperature conditions of the EFB.

Advanced synergetic nitrogen removal of municipal wastewater using oxidation products of refractory organic matters in secondary effluent by biogenic manganese oxides as carbon source.

Due to the high operational cost and secondary pollution of the conventional advanced nitrogen removal of municipal wastewater, a novel concept and technique of advanced synergetic nitrogen removal of partial-denitrification anammox and denitrification was proposed, which used the oxidation products of refractory organic matters in the secondary effluent of municipal wastewater treatment plant (MWWTP) by biogenic manganese oxides (BMOs) as carbon source. When the influent NH4+-N in the denitrifying filter was about 1.0, 2.0, 3.0, 4.0, 5.0 and 7.0mg/L, total nitrogen (TN) in the effluent decreased from about 22mg/L to 11.00, 7.85, 6.85, 5.20, 4.15 and 2.09mg/L, and the corresponding removal rate was 49.15, 64.82, 69.40, 76.70, 81.36 and 90.58%, respectively. The proportional contribution of the partial-denitrification anammox pathway to the TN removal was 12.00, 26.45, 39.70, 46.04, 54.97 and 64.01%, and the actual CODcr consumption of removing 1mg TN was 0.75, 1.43, 1.26, 1.17, 1.08 and 0.99mg, respectively, which was much lower than the theoretical CODcr consumption of denitrification. Furthermore, CODcr in the effluent decreased to 8.12mg/L with a removal rate of 72.40%, and the removed organic matters were mainly non-fluorescent organic matters. Kinds of denitrifying bacteria, anammox bacteria, hydrolytic bacteria and manganese oxidizing bacteria (MnOB) were identified in the denitrifying filter, which demonstrated that the advanced synergetic nitrogen removal was achieved. This novel technology presented the advantages of high efficiency of TN and CODcr removal, low operational cost and no secondary pollution.

Metagenomic analysis reveals the responses of microbial communities and nitrogen metabolic pathways to polystyrene micro(nano)plastics in activated sludge systems.

Microplastics (MPs) and nanoplastics (NPs) are prevalent in sewage and pose a potential threat to nitrogen biotransformation in wastewater treatment systems. However, investigations on how MPs and NPs affect the microbial nitrogen conversion and metabolism of the activated sludge are still scanty. Herein, the responses of microbiomes and functional genes to polystyrene MPs and NPs in activated sludge systems were investigated by metagenomic analysis. Results indicated that 1mg/L MPs and NPs had marginal impacts on the nitrogen removal performance of the activated sludge systems, whereas high concentrations of MPs and NPs (20 and 100mg/L) decreased the total nitrogen removal efficiency (13.4%-30.6%) by suppressing the nitrogen transformation processes. Excessive reactive oxygen species induced by MPs and NPs caused cytotoxicity, as evidenced by impaired cytomembranes and decreased bioactivity. Metagenomic analysis revealed that MPs and NPs diminished the abundance of denitrifiers (e.g. Mesorhizobium, Rhodobacter and Thauera), and concurrently reduced the abundance of functional genes (e.g. napA, napB and nirS) encoding for key enzymes involved in the nitrogen transformations, as well as the genes (e.g. mdh) related to the electron donor production, thereby declining the nitrogen removal efficiency. Network analysis further clarified the attenuate association between denitrifiers and denitrification-related genes in the plastic-exposed systems, elucidating that MPs and NPs restrained the nitrogen removal by inhibiting the contributions of microorganisms to nitrogen transformation processes. This study provides vital insights into the responses of the microbial community structure and nitrogen conversion processes to micro(nano)plastics disturbance in activated sludge systems.

Feasibility of bio-filter in treating low strength nitrogen wastewater under adverse temperatures

As a promising nitrogen removal technology, anammox still faces the bottlenecks of low temperatures, low substrates, and large wastewater flow in mainstream. This study investigated the feasibility of anammox bio-filter (A-BF) as advanced nitrogen removal unit for sewage treatment in low temperature climates. Results showed when treating 7 mg-NH4+-N·L−1 and 10 mg-NO2--N·L−1 wastewater, A-BF achieved 71.8 ± 5.6 % and 60.10 ± 10.31 % of total nitrogen removal efficiency (TNRE) under nitrogen loading rate (NLR) of 1.20 ± 0.30 kg-N m−3 d−1, within 0.3 h at 25 and 7.5 °C, respectively, based on ＜8 mg L−1 effluent. Further analysis showed that A-BF performance was recovered with TNRE of 71.8 ± 5.6 % when back to 25 °C after collapsing with TNRE of 24.30 ± 15.73 % at 5 °C. Dominant Candidatus Brocadia in anammox bacteria (AnAOB) (3.59–6.24 %) contributed to higher 0.22 and 0.46 g-N·g-VSS−1·d−1 biomass activity at 25 °C. This study provided possible and low-carbon strategy for advanced nitrogen removal.

Effects of zinc ion concentrations on the performance of SBR treating livestock wastewater and analysis of microbial community

Zinc ion (Zn2+) is a frequently occurring heavy metal in livestock wastewater. The effects of Zn2+ on the physicochemical properties and the microbial distribution of activated sludge are essential to controlling nitrogen removal performance. Nevertheless, there are raw studies on the effects of Zn2+ on nitrogen removal. This study investigated the effect of Zn2+ on the treatment performance of livestock wastewater in a sequencing batch reactor (SBR). The results indicated the low Zn2+ concentrations could improve nitrogen removal performance. However, as the Zn2+ concentration increased, the total nitrogen (TN) removal performance of the reactor gradually deteriorated. When the Zn2+ concentration was 90.00 mg/L, the TN removal efficiency was the lowest, only 2.40%. The contents of the Extracellular polymeric substance (EPS) presented a trend of first increasing and then decreasing with the increase of Zn2+ concentration, and the main reason was the decrease of protein-like and tryptophan-like. The 16SrRNA analysis indicated that Zn2+ within a specific concentration could increase the operational taxonomic units (OTUs) number, microbial richness, and diversity of microorganisms in the SBR. However, with Zn2+ concentration exceeding 10.00 mg/L, the relative abundance of denitrification functional bacteria (Dechloromonas, Nitrospira, and Thauera) decreased.

Effects of Al3+ on the microbial community, metabolic pathways, and morphological analysis of activated sludge

Al3+ generated during aluminum mining, electrolytic industry, and aluminum-based coagulant production enters sewage treatment plants and interacts with activated sludge, interfering with microbial growth and community succession. An anaerobic-anoxic-oxic (A2O) process was used to investigate the effect of Al3+ on biological denitrification, the metal form, and the microbial community structure. The results showed that a low concentration of Al3+ improved removal efficiencies of chemical oxygen demand (COD) and total nitrogen (TN) as well as biological activity. However, a high concentration of Al3+ reduced the COD and TN removal efficiencies. The removal efficiencies of COD, TN, and NH4+-N were the highest, and the INT-ETS values in the anaerobic, anoxic, and oxic zones were 93.21, 91.36, and 94.44 mg·INTF/(g·TSS·h) in the 10 mg/L Al3+ concentration treatment. Regardless of the change in Al3+ concentration, aluminum in the sludge mainly existed in the form of stable organic aluminum. Microbial richness and diversity decreased under the high concentration of Al3+. However, the relative abundance of Bacteroidetes and Chitinophagales increased, which was coincident with the change in microbial aluminum tolerance capacity. The dominant flora included Proteobacteria, Gammaproteobacteria, Betaproteobacteriales, Rhodocyclaceae, and Thauera. Amino acid and carbohydrate metabolism, as well as membrane transport and replication and repair, were the main metabolic pathways. K03088, K03406, and K02014 exhibited good adaptability under the high Al3+ concentration, which ensured effective removal of COD and TN.

Stability of aerobic granular sludge for treating inorganic wastewater with different nitrogen loading rates

ABSTRACT This paper investigated the effect of nitrogen loading rates (NLRs) on the stability of aerobic granular sludge (AGS) for treating simulated ionic rare earth mine wastewater with high ammonia nitrogen and extremely low organic content. Mature AGS from a sequencing batch reactor (SBR) was seeded into five identical SBRs (R1, R2, R3, R4 and R5). The five reactors were operated with different NLRs (0.2, 0.4, 0.8, 1.2 and 1.6 kg/m3·d). After 30 days of operation, R1, R2 and R5 were dominated by broken granules, while most of the granules in R3 and R4 still maintained a complete structure. The properties of granules from R1, R2, R3, R4 and R5 deteriorated to varying degrees, while the granules from R3 and R4 showed better stability than that from R1, R2 and R5. In R1, R2, R3 and R4, the steady-state ammonia nitrogen removal efficiencies were all greater than 90%, and the steady-state removal efficiencies of total inorganic nitrogen (TIN) were approximately 30%. In R5, the removal efficiencies of ammonia nitrogen and TIN were both approximately 70%. The dominant nitrifying and denitrifying bacterial genera of the granules from the five reactors were Nitrosomonas and Thauera, respectively, and their relative abundance was much higher in granules from R3 and R4. The results demonstrated that a relative equilibrium between the growth and metabolism of nitrifying/denitrifying bacteria was achieved when NLR was between 0.8 and 1.2 kg/m3·d, which could provide technical support for the stability maintenance of AGS in the treatment of ionic rare earth mine wastewater.

Start-up mechanism of simultaneous nitrification-endogenous denitrification process for treatment of low C/N wastewater: Insights into reactor performance and microbial community dynamics

The aim of this study is to propose a start-up strategy by reducing DO concentration, optimizing the duration of the operation mode and gradually decreasing influent C/N for simultaneous nitrification-endogenous denitrification (SNED) process to economically and effectively treat low carbon/nitrogen (C/N) wastewater, and to explore the start-up mechanism from the microbiome. After start-up, the efficiency of simultaneous nitrification-denitrification, nitrogen loading rate, and nitrogen removing rate increased from 8.3%, 60 mg N/L⋅d, and 55.2 mg N/L⋅d to 60.9%, 160 mg N/L⋅d, and 143.6 mg N/L⋅d, respectively. Meanwhile, the total nitrogen removal efficiency and the conversion of intracellular carbon were maintained at 90.2% and 89.1%. Correspondingly, microbial community diversity was significantly inhibited, however, the key functional microbes remarkably increased such as Defluviicoccus (denitrifying glycogen accumulating organisms), Paracoccus (heterotrophic nitrification and aerobic denitrification bacteria), etc. The reduction of heterotrophs led to the streamlining of network scale and complexity. But, the emergence of more positive interaction in functional subnetworks, stable module numbers, and the redundancy of keystone taxa contributes to the targeted regulation of functional microorganisms, as further confirmed by increased community function. Deterministic process dominated the community assembly during start-up period, where homogenizing selection is the main driving force for key functional microbes, e.g., Defluviicoccus and Paracoccus. This study provided key information for practical application of SNED process and laid the foundation for cost-effective treatment of low C/N wastewater.

Performance evaluation and optimization of simultaneous phosphorus and nitrogen removal from anaerobically digested liquid-dairy-manure using an intermittently-aerated-extended-idle sequencing batch reactor

Wastewater from confined dairy operations requires efficient treatment to reduce its potential to pollute the surrounding environments. In this study, a novel intermittently-aerated-extended-idle sequencing batch reactor (IA-EI SBR) process was developed, evaluated, and optimized for simultaneously removing phosphorus (P) and nitrogen (N) from anaerobically digested liquid-dairy-manure (ADLDM) with lower carbon-to-nutrient-ratios. Four influential operating parameters including cycle-time of 5–9 h, intermittent-aeration strategy of 10–50 min/h, two feed-phases of 6–30 min, and idle-phase of 40–120 min were statistically analyzed using central-composite design coupled with response-surface methodology for optimal removal efficiencies of ortho-phosphorus (%OPremoval), total-phosphorus (%TPremoval), ammonia-nitrogen (%NH3-Nremoval), total-nitrogen (%TNremoval), and chemical oxygen demand (%CODremoval). Results showed that the interactions of cycle time-idle phase, and aeration strategy-feed phases were significant in affecting %TPremoval (p-value ≤ 0.005). The synergistic effect of aeration strategy-idle phase was significant for %TNremoval and %CODremoval (p-value ≤ 0.006), while the cycle time-feed phases interaction had significant effect on %NH3-Nremoval. The maximum simultaneous nitrification-denitrification (SND) efficiency of 85.7% was recorded under influent COD and TN loading of 3,999.2 and 785.7 mg L−1 at 30 min/h aeration time in 7 h. The quadratic regression models based on statistical analysis of the experimental results adequately described the IA-EI SBR performance and showed that the applied levels of operating parameters were highly correlated with all five responses (p-value ≤ 0.030). Operating conditions for optimal IA-EI SBR process efficiency determined by desirability analysis were cycle-time of 8 h, intermittent-aeration strategy of 36 min/h, feed-phases of 24 min, and idle-phase of 100 min. Under these optimal conditions, the corresponding removal efficiencies for OP, TP, NH3-N, TN, and COD of 82.64, 95.82, 92.92, 73.84, and 90.94%, respectively, were achieved in validation experiments.

Microalgal-bacterial aerobic granular sludge for old leachate treatment: Development, performance, and lipid production

A lab-scale photo bio sequencing batch reactor (PSBR) was used to develop microalgal-bacterial aerobic granular sludge (MB-AGS) for old leachate treatment by seeding activated sludge, while indigenous microalgae were allowed to grow naturally. Upon 100 days of experiment, mature MB-AGS was successfully developed with an average diameter of 2.5 ± 1.5 mm and excellent settling properties, with a settling velocity of 39 ± 24 m/h. The biochemical oxygen demand (BOD), chemical oxygen demand (COD), ammonia (NH4+-N), total nitrogen (TN), and total phosphorus (TP) removal efficiencies were 80 ± 14%, 95 ± 2%, 88 ± 14%, 56 ± 16%, and 57 ± 14%, respectively. The shift in microbial populations were also examined, in which the abundant EPSs producing bacteria in the system could be one of the reasons behind the successful transformation of activated sludge flocs to mature MB-AGS. Furthermore, lipid was able to be extracted from the MB-AGS, in which the lipid production was 9.35 ± 1.1 mg/g-SS, accounting 0.56 ± 0.07 mg/L.d of lipid productivity.

The response of structure and nitrogen removal function of the biofilm on submerged macrophytes to high ammonium in constructed wetlands

The ammonium exceedance discharge from sewage treatment plants has a great risk to the stable operation of subsequent constructed wetlands (CWs). The effects of high ammonium shocks on submerged macrophytes and epiphytic biofilms on the leaves of submerged macrophytes in CWs were rarely mentioned in previous studies. In this paper, the 16S rRNA sequencing method was used to investigate the variation of the microbial communities in biofilms on the leaves of Vallisneria natans plants while the growth characteristics of V. natans plants were measured at different initial ammonium concentrations. The results demonstrated that the total chlorophyll and soluble sugar synthesis of V. natans plants decreased by 51.45% and 57.16%, respectively, and malondialdehyde content increased threefold after 8 days if the initial NH4+-N concentration was more than 5 mg/L. Algal density, bacterial quantity, dissolved oxygen, and pH increased with high ammonium shocks. The average removal efficiencies of total nitrogen and NH4+-N reached 73.26% and 83.94%, respectively. The heat map and relative abundance analysis represented that the relative abundances of phyla Proteobacteria, Cyanobacteria, and Bacteroidetes increased. The numbers of autotrophic nitrifiers and heterotrophic nitrification aerobic denitrification (HNAD) bacteria expanded in biofilms. In particular, HNAD bacteria of Flavobacterium, Hydrogenophaga, Acidovorax, Acinetobacter, Pseudomonas, Aeromonas, and Azospira had higher abundances than autotrophic nitrifiers because there were organic matters secreted from declining leaves of V. natans plants. The analysis of the nitrogen metabolic pathway showed aerobic denitrification was the main nitrogen removal pathway. Thus, the nitrification and denitrification bacterial communities increased in epiphytic biofilms on submerged macrophytes in constructed wetlands while submerged macrophytes declined under ammonium shock loading.

Insights into the response of Anammox sludge to the individual and combined stress of neodymium and salinity and the role of hydroxylamine regulation

Neodymium (Nd(III)) and sulfate (Na2SO4) are commonly present in neodymium mining wastewater. However, the effects of their coexistence on microorganisms responsible for removing nitrogen from wastewater have been poorly reported. In this study, the combined inhibition of Nd(III) and Na2SO4 on anaerobic ammonium oxidation (Anammox) and its recovery were investigated in terms of performance, kinetics, Nd(III) distribution characteristics and sludge morphology. The results shown that ≥ 150 mg·L−1 Nd(III) or ≥ 3 g·L−1 Na2SO4 decreased specific Anammox activity (SAA), and intracellular Nd(III) was identified as the primary factor for individual Nd(III) inhibition. Furthermore, the combined inhibition of Nd(III) and Na2SO4 on Anammox was stronger than individual inhibition, but low doses of hydroxylamine (NH2OH) could restore the Anammox. Notably, the combined effect of low doses of Na2SO4 (1 g·L−1) and Nd III (10 mg·L−1) on the long-term performance of Anammox reactor was not significant. However, when the dose of Nd(III) was kept constant and the dose of Na2SO4 was increased to 7 g·L−1, the total nitrogen removal efficiency (TNRE) decreased by 56.88%. Following the elimination of inhibitors and the addition of 5 mg·L−1 NH2OH, the TNRE of the Anammox reactor was increased from 20.83% to 29.78%. The Hill, modified Michaelis-Menten, and modified Boltzmann models were able to properly describe the inhibition effects of Nd(III) and Na2SO4 and recovery process of Anammox. In addition, scanning electron microscopy (SEM) and energy-dispersive X-ray (EDS) analysis revealed that the content of extracellular polymeric substances (EPS) and neodymium increased with increasing Na2SO4 concentration.

Enhanced reduction of nitrate by TDER packed with surface-modified plastic particles electrodes

Based on Iron cathodes, nitrate could be selectively decomposed into other lower-valence nitrogen compounds, including ammonia, nitrogen gas, nitrite and nitric oxide, but the removal efficiencies of nitrate and total nitrogen (TN), are affected significantly by the synergistic effects of anodes, chloride electrolyte and conductive plastic particles electrodes. In this work, the base material Titanium (Ti) metal plates and plastic particles which surfaces were mainly coated with Ru-Sn oxidizing compounds, were applied as plates anodes and conductive particles electrodes in Three Dimensional Electrode Reactors (TDER). The Ti/RuSn plate anodes showed excellent performance on degrading nitrate, more nitrogen gas (83.84%) and less ammonia (15.51%) was produced, less TN and Iron ion (0.02 mg/L) was left in the wastewater, and less amount of chemical sludge (0.20 g/L) was produced. Furthermore, the removal efficiencies of nitrate and TN were further increased by the surface-modified plastic particles, which were cheap, reusable, corrosion-resistance, easy to obtain as manufactured materials and light to be suspended in waters. The degradation of nitrate and its intermediates was enhanced possibly by the continuous synergistic reactions initiated by hydrogen radicals, which was generated on the countless surficial active Ru-Sn sites of Ti/RuSn metal plate anodes and plastic particles electrodes, among residual nitrogen intermediates, most of ammonia was selectively converted to gaseous nitrogen by hypochlorite from chloride ion reaction.

The Recovery of a Sequencing Biofilm Batch Reactor—Anammox System: Performance, Metabolic Characteristics, and Microbial Community Analysis

The mainstream application of the anammox process is often hindered by its long recovery phase and instability under disturbance. In this study, a lab-scale anammox sequencing biofilm batch reactor (SBBR) was rapidly recovered within 85 days by gradually increasing the influent nitrogen concentration, and the total inorganic nitrogen (TIN) removal efficiency achieved 83.44 ± 0.03%. During the recovery process, the nitrogen removal rate (NRR) increased from 0.05 to 0.34 kg/(m3·d), with the nitrogen loading rate (NLR) changing from 0.08 to 0.40 kg/(m3·d) in the anammox system. The activities of hydrazine oxidase (HZO) in the biofilm also increased from 0.17 to 10.80 μmol Cyt-c/(g VSS·s). Also, the dominant anammox genera in the biofilm were Candidatus Kuenenia and Candidatus Brocadia. The results of this study suggested that an SBBR–anammox system filled with a microbial carrier could facilitate the enrichment of anammox bacteria and contribute to performance recovery.

Oxidative and Photochemical Processes for Soft Drink–Industry Wastewater Treatment

Soft drinks–industry wastewater (SDIW) contains high concentrations of sugar (420–487 mg/L) and sodium (320–397 mg/L), has high pH (∼9), and contains biorefractory pollutants. Therefore, rapid and effective techniques are required for its treatment. In the present study, SDIW was subjected to microwave (MW) photocatalysis (PC) using electrodeless discharge lamps, and the outcomes were compared with other oxidative and photochemical advanced oxidation processes, including oxidation, MW oxidation (MWO), and ultraviolet–titanium dioxide PC, in terms of the removal efficiency of organics based on chemical oxygen demand (COD), total phosphate (TP), and total nitrogen (TN). The mineralization of organics was ∼3.5 times higher in the MWPC and MWO systems compared to the oxidation and PC systems. The COD removal efficiency after 60 min using the oxidation, PC, MWO, and MWPC systems was 22.7%, 25.41%, 79.36%, and 87.3%, respectively. Direct photolysis using UV (using 486 kJ/mole of energy) and photocatalytic degradation using increased hydroxyl radicals in the presence of MWs was the primary degradation mechanism in the MWPC system. The TP removal efficiency in the oxidation, PC, MWO, and MWPC systems was 15%, 40%, 50%, and 60%, respectively. The respective TN removal efficiencies for the four systems were 40%, 58%, 82%, and 85%. The main mechanism for organics, TP, and TN removal in the MWPC system involved the direct disruption of the chemical bonds of the organic molecules, photocatalytic phosphate reduction, and breaking of the primary amine bond in the organic nitrogen using the high-energy plasma and hotspots that formed in the MW-based systems. The electrical energy consumed by the systems [electrical energy per order (EEO)] occurred in the order PC > MWO > MWPC, with respective values of 14,614, 6,919, and 4,526 Rs/kg COD removal.

Enhancing algal growth and nutrient recovery from anaerobic digestion piggery effluent by an integrated pretreatment strategy of ammonia stripping and flocculation.

Anaerobic digestion piggery effluent (ADPE) with a quite high ammonium (NH4 +) concentration and turbidity (dark brown color) generally requires high dilution before microalgae cultivation, owing to its NH4 + toxicity and color inhibition to algal growth. An integrated pretreatment strategy of ammonia stripping and chemical flocculation may be a more practical pretreatment procedure for enhancing algae yield and nutrient recovery from anaerobic digestion piggery effluent. In this study, we determined the optimum pretreatment strategy of anaerobic digestion piggery effluent for subsequent microalgae cultivation and nutrient recovery. The results showed that the integrated anaerobic digestion piggery effluent pretreatment strategy of high-temperature ammonia stripping and chemical flocculation at a mixed dosage of 2gL-1 polyaluminum chloride (PAC) and 40mgL-1 cationic polyacrylamide (C-PAM), and 50mgL-1 ammonium nitrogen (NH4 +-N) enrichment provided maximum algal yield (optical density = 1.8) and nutrient removal (95.2%, 98.7%, 99.3%, and 78.5% for the removal efficiencies of total nitrogen, NH4 +-N, total phosphorus, and chemical oxygen demand, respectively) from anaerobic digestion piggery effluent. The integrated pretreatment strategy is expected to become a more practical pretreatment procedure for enhancing algae yield and nutrient recovery from anaerobic digestion piggery effluent.

Enhanced nitrogen removal in immersed rotating self-aerated biofilm reactor: Nitrogen removal pathway and microbial mechanism

To achieve energy-efficient treatment of the rural wastewater with satisfying performance, a novel immersed rotating self-aerated biofilm reactor (iRSABR) was proposed in this study. The iRSABR system showed better biofilm renewal performance and higher microbial activity. The effect of different regulation strategies on the iRSABR system was investigated in this study. The 70% immersion ratio and 4 r/min rotation speed (stage III) exhibited the best performance, with a total nitrogen removal efficiency of 86% and a simultaneous nitrification–denitrification (SND) rate of 76%, along with the highest electron transport system activity. The nitrogen removal pathway revealed that the SND was achieved through autotrophic/heterotrophic nitrification and aerobic/anoxic denitrification. The regulation strategy in the iRSABR system established a synergistic microbial community with main functional bacteria of nitrification (Nitrosomonas), anoxic denitrification (Flavobacterium, Pseudoxanthomonas), and aerobic denitrification (Thauera). This study highlighted the feasibility and adaptability of the iRSABR system toward energy-efficient rural wastewater treatment.

Microalgae Cultivation Using Municipal Wastewater and Anaerobic Membrane Effluent: Lipid Production and Nutrient Removal

Microalgae cultivation using wastewater is a combined process for pollutant removal and lipid production that has been widely studied in recent years. In this study, the effects of anaerobic membrane effluent (AME) and municipal wastewater (MW) ratios on microalgae growth and pollutant removal processes were investigated, and the lipid production properties were also explored. Results show that microalgae can grow in all AME/WW ratios, and a 40% AME content is the optimal condition for microalgal biomass accumulation (52.9 mg/L·d) and lipid production (0.378 g/L). Higher AME addition would inhibit microalgae growth. In addition, high ammonia (approximately 97%) and phosphate (around 90%) removal efficiencies can be achieved in all AME/WW ratio conditions, while the total nitrogen removal efficiencies decreased with the addition of AME. Total nitrogen and phosphate are the limiting factors in treating water to meet the requirements of the integrated wastewater discharge standard. This study provided a new method for anaerobic digestion and municipal wastewater treatment and also realized green energy production based on the sustainable development principles.