Development of denitrifying phosphate accumulating and anammox micro-organisms in anaerobic hybrid reactor for removal of nutrients from low strength domestic sewage

Biochar coupled with multiple technologies for the removal of nitrogen and phosphorus from water: A review

Water eutrophication caused by nitrogen (N) and phosphorus (P) has become a global environmental issue. Biochar is a competent adsorbent for removing N and P from wastewater. However, compared with commercial activated carbon, biochar has relatively limited adsorption capacity. To broaden the field scale application of biochar, biochar coupled with multiple technologies (BC-MTs) (such as microorganisms, electrochemistry, biofilm, phytoremediation, etc.) have been extensively developed for environmental remediation. Nevertheless, due to the fluctuations and differences in biochar types, coupling methods, and wastewater types, various techniques show different removal mechanisms and performance, hindering the promotion and application of BC-MTs. A systematic review of the research progress of BC-MTs is highly necessary to gain a better understanding of the current research status and progress, as well as to promote the application of these techniques. In this paper, the application of pristine and modified biochar in adsorbing N and P in wastewater is critically reviewed. Then the removal performance, influencing factors, mechanisms, and the environmental applications of BC-MTs in wastewater are systematically summarized. In addition, the cost analysis and risk assessment of BC-MTs in environmental applications are conducted. Finally, suggestions and prospects for future research and practical application are put forward.

Enhancement the wastewater treatment performance of multistage living machine by underwater lamp

Source separation and decentralized domestic wastewater treatment represent effective strategies to enhance sewage treatment performance and facilitate water reuse economically. The Living Machine (LM) system has gained widespread adoption for decentralized sewage treatment. While underwater light source has been demonstrated to enhance the treatment performance of open aerobic reactors in LM systems, its influence on the treatment efficiency of a fully multistage LM system remains underreported. In this study, an underwater lamp-added LM system (ULLM) with eight reactors was constructed and investigated. The introduction of underwater light source obviously improved the removal capacity of chemical oxygen demand (COD) and NH4+-N, which was 96.1% and 61.6%, respectively. The diversity of algae, zooplankton, and aquatic animals was notably higher in the light-treated reactors than in the control group (CK) without underwater light source, and substantial alteration in the microbial community of the light-treated reactors was observed compared with CK reactors. At the phylum level, Proteobacteria and Nitrospirae enriched in the underwater light-treated reactors, while Bacteroidetes and Actinobacteria exhibited a decrease after light exposure. At the genus level, Nitrospira and Rhodanobacter were enriched in the ULLM system. Importantly, the prevalence of these two dominant genera was sustained until the final operational stage, indicating their potential key roles in enhancing wastewater treatment performance. The addition of underwater light source proves to be an effective strategy for augmenting the treatment efficiency of the multistage living machine systems, resulting in substantial improvements in pollutant removal. These findings contribute valuable insights into optimizing LM systems for decentralized wastewater treatment.

High efficiency of drinking water treatment residual-based sintered ceramsite in biofilter for domestic wastewater treatment

Aluminum (Al)-based drinking water treatment residue (DWTR) has often been attempted to be recycled as dominant ingredient to produce sintered ceramsite for water treatment. This study aimed to determine the long-term performance of DWTR-based ceramsite in treating domestic wastewater based on a 385-d biofilter test and by using physicochemical, metagenomic, and metatranscriptomic analyses. The results showed that the ceramsite-packed biofilter exhibited high and stable capability in removing phosphorus (P) and chemical oxygen demand (COD), with removal efficiencies of 92.6 ± 3.97% and 81.1 ± 14.0% for total P and COD, respectively; moreover, 88-100% of ammonium-nitrogen (N) was normally converted, and the total N removal efficiency reached 80-86% under proper aeration. Further analysis suggested that the forms of the removed P in the ceramsite were mainly NH4F- and NaOH-extractable. Microbial communities in the ceramsite biofilter exhibited relatively high activity. Typically, various organic matter degradation-related genes (e.g., hemicellulose and starch degradations) were enriched, and a complete N-cycling pathway was established, which is beneficial for enriching microbes involved in ammonium-N conversion, especially Candidatus Brocadia, Candidatus Jettenia, Nitrosomonas, and Nitrospira. In addition, the structures of the ceramsite had high stability (e.g., compressive strength and major compositions). The ceramsites showed limited metal and metalloid pollution risks and even accumulated copper from the wastewater. These results demonstrate the high feasibility of applying ceramsite prepared from Al-based DWTR for water treatment.

Identification of some microbial flora contained in slaughterhouse effluent and likely to be effective in its treatment by biological process

The specific contributions of the different bacterial flora during the biological treatment of slaughterhouse effluents remain unclear. The objective of this study is to identify the different microbial flora which mainly contribute to the efficiency of the biodegradation of the organic, nitrogenous and phosphate loads contained in the slaughterhouse effluent during its biological treatment. To achieve this, the effluent to be treated was sampled from three slaughterhouses in the city of Ngaoundéré (Cameroon). The various effluents underwent a physicochemical and microbiological characterization. The effluent was subjected to biological treatment. The biodegradation process (biological treatment) took place in two reactors, each operating in batch. One of the two reactors was supplied with oxygen (aeration). The effluent being treated underwent a physicochemical and microbiological characterization for 30 days. The results obtained show organic matter and ammonium contents >1,000 mgO2/L in each of the three effluents. Bacillus cereus (69 × 108 CFU/mL), Pseudomonas aeruginosa (201 × 107 colony forming unit (CFU)/mL) and Yeasts (101 × 106 CFU/mL) globally constitute the majority of microbial groups among the seven microorganisms identified in the effluents of the three slaughterhouses. There is no real oxygenation effect of the medium on the growth of the three microbial flora during the treatment.

Enhanced treatment of synthetic wastewater by bioaugmentation with a constructed consortium

Bioaugmentation by adding well-functioning mixed microorganism consortia represents a potentially useful approach to improve contaminant removal in wastewater treatment plants (WWTPs). However, unfavorable environmental conditions (i.e., low temperatures) can severely inhibit microbial activity, drawing our attention to constructing cold-tolerant microorganism preparations and investigating their availability in practical applications. Here we screened four in situ functional isolates from the activated sludge of secondary sedimentation tanks in WWTPs to construct a psychrophilic microbial consortium, which was used to perform bioaugmentation for enhanced removal of nitrogen and phosphorus under low temperatures. The consortium was established by cocultivation of four isolates, characterized by 16 S rRNA as the COD-degrading bacterium Aeromonas sp. Z3, aerobic denitrifying bacterium Acinetobacter sp. HF9, nitrifying bacterium Klebsiella sp. X8, and polyphosphate-accumulating bacterium Pseudomonas sp. PC5 respectively. The microorganism preparation was composed of Z3, HF9, X8, and PC5 under the ratio of 1: 1: 3: 1, which can exert optimal pollutant removal under the conditions of 12 °C, 6.0-9.0 pH, 120-200 r‧min-1, and a dosage of 5% (V/V). A 30-day continuous operation of the bioaugmented and control sequencing batch reactors (SBRs) was investigated, and the bioaugmented SBR showed a shorter start-up stage and a more stable operating situation. Compared to the control SBR, the COD, NH4+-N, TN, and TP removal efficiency of the bioaugmented SBR increased by an average of 7.95%, 9.05%, 9.54%, and 7.45% respectively. The analysis of the microbial community revealed that the introduced isolates were dominant in the activated sludge and that functional taxa such as Proteobacteria, Bacteroidota, and Actinobacteria were further enriched after a period of bioaugmentation. The study provides some basis and guidance for the practical application of how to strengthen the stable operation of WWTPs under low temperatures.

From hybrid process to pure biofilm anammox process: Suspended sludge biomass management contributing to high-level anammox enrichment in biofilms

The application of mainstream anammox is highly desirable for municipal wastewater treatment. However, enrichment of anammox bacteria (AnAOB) is challenging, particularly given the vicious competition from denitrifying bacteria (DB). Here, suspended sludge biomass management, a novel operational strategy for hybrid process (suspended sludge/biofilm), was investigated for 570 days based on a modified anaerobic-anoxic-oxic system treating municipal wastewater. By successively decreasing the suspended sludge concentration, the traditional hybrid process was successfully upgraded to a pure biofilm anammox process. During this process, both the nitrogen removal efficiency (NRE) and rate (NRR) were significantly improved (P < 0.001), from 62.1 ± 4.5% to 79.2 ± 3.9% and from 48.7 ± 9.7 to 62.3 ± 9.0 g N/(m³·d), respectively. Mainstream anammox was improved in the following: Candidatus Brocadia was enriched from 0.70% to 5.99% in anoxic biofilms [from (9.94 ± 0.99) × 10⁸ to (1.16 ± 0.01) × 10¹⁰ copies/g VSS, P < 0.001]; the in situ anammox reaction rate increased from 8.8 ± 1.9 to 45.5 ± 3.2 g N/(m³·d) (P < 0.001); the anammox contribution to nitrogen removal rose from 9.2 ± 2.8% to 67.1 ± 8.3% (P < 0.001). Core bacterial microbiome analysis, functional gene quantification, and a series of ex situ batch experiments demonstrated that the stepwise decreases in suspended sludge concentration effectively mitigated the vicious competition of DB against AnAOB, enabling high-level AnAOB enrichment. This study presents a straightforward and effective strategy for enriching AnAOB in municipal wastewater, shedding fresh light on the application and upgradation of mainstream anammox.

Aerobic electrotrophic denitrification coupled with biologically induced phosphate precipitation for nitrogen and phosphorus removal from high-salinity wastewater: Performance, mechanism, and microbial community

Electrotrophic denitrification (ED) is a promising nitrogen removal technique; however, the potential of ED coupled with biologically induced phosphate precipitation (BIPP) has not been fully explored. In this study, the performances, mechanisms, and microbial communities of the coupled system were investigated. The results showed that excellent nitrogen and phosphorus removal (both exceeding 92 %) was achieved in the salinity range of 20-60 g/L. ED contributed to approximately 83.4 % of nitrogen removal. BIPP removed approximately 63.5 % of the phosphorus. Batch activity tests confirmed that aerobic/anoxic bio-electrochemical and autotrophic/heterotrophic denitrification worked together for nitrate removal. Sulfate reduction had a negative impact on denitrification. Moreover, phosphorus removal was controlled by ED and calcium ions. The alkaline solution environment created by denitrification may greatly promote the formation of hydroxyapatite. Microbial community analyses indicated that the key bacteria involved in aerobic ED was Arcobacter. These findings will aid in the advanced treatment of high-salinity wastewater.

Nutrients removal by Olivibacter jilunii immobilized on activated carbon for aquaculture wastewater treatment: ppk1 gene and bacterial community structure

In this study, immobilized biological activated carbon (IBAC) mediated with Olivibacter jilunii (strain PAO-9) was utilized to treat aquaculture wastewater for nutrients removal. IBAC with strain PAO-9 could load the greatest ppk1 gene copy numbers (129524.6) per gram on activated carbon at 28 °C for 2 d in 120 rpm of stirring speed and 2 d in stationary condition. Moreover, the results about the nutrients removal and microbiology community structure showed that strain PAO-9 on IBAC could alter the structure and diversity of microbial communities and then promoted to remove the total phosphorus and total nitrogen of eel aquaculture wastewater. The highest total phosphorus, chemical oxygen demand, ammonia and total nitrogen of the wastewater treated by strain PAO-9 on IBAC were 96.1 %, 98.0 %, 100.0 % and 97.4 %, respectively. In all, O. jilunii PAO-9 immobilized activated carbon was a potential and effective approach to remove the nutrients of eel aquaculture wastewater.

Starting up anammox system with high efficiency nitrogen removal at low temperatures: Performance optimization, sludge characterization and microbial community analysis

Anaerobic ammonia oxidation (anammox) has potential advantages for nitrogen removal when operating at medium temperatures, but the increased operation costs of heating limit its application. It would be advantageous to start and operate anammox at low temperatures, the feasibility of which was studied here on a lab scale. Two identical expanded granular sludge bed (EGSB) reactors were inoculated at 35 ± 1 °C (A_med) and 15 ± 3 °C (A_low). Results showed that anammox was successful after 138 d for A_low, only 7 d longer than A_med. Stable operation to 194 d in A_low, the nitrogen loading rate (NLR) increased to 1.01 kg m^-3·d^-1, giving a high nitrogen removal efficiency (NRE) of 85%, which was only slightly lower than that of A_med (90%). More extracellular polymeric substance (EPS) was produced by the microbes of A_low compared to A_med, which prevented anaerobic ammonia oxidizing bacteria (AnAOB) against low temperature stress. Microbial community revealed presence of Candidatus Jettenia in A_med with relative abundance 7.4%, while the "cold-tolerant" Candidatus Kuenenia with 4% was the dominant anammox bacteria in A_low. The anammox granules adapted well to low temperatures and demonstrated high efficiency in anammox process without heating. Therefore, constructing an energy-saving and cost-effective anammox system in high latitudes or high altitudes can be considered.

Biogas production and nutrients removal from slaughterhouse wastewater using integrated anaerobic and aerobic granular intermittent SBRs - Bioreactors stability and microbial dynamics

Slaughterhouse wastewater (SWW) was effectively treated in sequential anaerobic and aerobic granular intermittent sequencing batch reactors (ASBR+ISBR) for 665 days at different HRTs (48 h, 32 h, 24 h, and 12 h). The ASBR was stable at each HRT but performed relatively well at 12 h (OLR - 7.8-9.8 kg COD/m³-d) in terms of pollutants removal and biogas production than previously conducted research. The average biogas production was about 17.3 L/day having 70-76 % of CH₄ which could subsidize around 52 % of electricity demand while saving 103 US dollars/day if installed at full scale. In the case of post aerobic granular ISBR, carbon and nutrients removal (N&P) was achieved by enriching granules (1.7-2.2 mm) at low DO (0.5-0.8 mg/L) via the nitrite pathway. The ISBR was also well stable at 12 h HRT (average OLR of 2.1 kg COD/m³-d) and met the effluent discharge guidelines recommended by the Central Pollution Control Board of India. During steady-state conditions (12 h HRT), the average removal efficiencies for COD, TSS, O&G, TN, and PO₄-P were 98.8 %, 96.4 %, 98.7 %, 93.4 %, and 86.6 % respectively from combined ASBR and ISBR. The microbial analysis confirmed Euryarchaeota, Proteobacteria, Firmicutes, Chloroflexi, Bacteroidetes, Planctomycetes, and Synergistetes as the dominant phyla in ASBR. Methanosaeta (21.56 %) and Methanosarcina (6.48 %) were the prevailing methanogens for CH₄ production. The leading phyla observed in ISBR were Bacteroidetes, Proteobacteria, Firmicutes, Armatimonadetes, Verrucomicrobia, Chloroflexi, and Planctomycetes. Heterotrophic AOB (Thauera, Xanthomonadaceae, Pseudomonas, Sphingomonadaceae, and Rhodococcus) were mainly detected in the system for ammonia oxidation besides common autotrophic AOB. Similarly, a known PAO (Accumulibacter) was not identified but other PAO (Rhodocyclaceae, Dechloromonas, Pseudomonas, Flavobacteriaceae, and Sphingobacteriaceae) were prevalent inside aerobic granular ISBR that contributed to both carbon and nutrients removal. The results obtained would help implement the investigated reactor configurations at the pilot and full scale for SWW treatment.

Role of emerging chitosan and zeolite-modified adsorbents in the removal of nitrate and phosphate from an aqueous medium: A comprehensive perspective

Due to industrialization and population growth, freshwater supplies are diminishing and becoming impure with high organic pollutant concentrations such as nitrate and phosphate, which shows a high adverse impact on aquatic and human lives. In drinking water sources, particularly groundwater, nitrate is considered as one of the major pollutants which causes methemoglobinemia (in newborn infants), carcinogenic activities and diabetes. Excess concentration of phosphate leads to eutrophication and death of aquatic species due to reduced dissolved oxygen content. Therefore, all countries must implement highly effective technologies for treating wastewater. Chitosan and zeolite are naturally occurring and cost-effective adsorbent materials with a higher surface area that exhibit greater nitrate and phosphate adsorption. Surface modification of chitosan and zeolite increases the adsorption capacity of adsorbents for the removal of both anions selectively. This paper reviews the current development of modified chitosan and zeolite adsorbents for anion adsorption, with an emphasis on modification by zero and multivalent metals and metal oxides, different surfactants, biomass-derived carbon, and natural and synthetic polymers. Multiple adsorption parameters, optimum adsorption condition, adsorption mechanism, regeneration study, research gap and future aspects have been explained for further research work.

A novel strategy for rapid development of a self-sustaining symbiotic algal-bacterial granular sludge: Applying algal-mycelial pellets as nuclei

Algal-bacterial granular sludge (ABGS) is a promising technology for wastewater treatment, benefiting from the synergetic interactions between algae and bacteria. However, the rapid start-up of the ABGS system is not trivial. Herein, a novel strategy was proposed by applying the algal-mycelial pellets (AMPs) as the primary nuclei for accelerating the development of a self-sustaining symbiotic ABGS system. The results indicated that by using this strategy complete granulation was shortened to 12 days, much shorter than the control system without AMPs dosage (28 days). The ABGS had a large particle diameter (3.3 mm), compact granular structure (1.0253 g/mL), and excellent settleability (SVI30 of 53.2 mL/g). Moreover, 98.6% of COD, 80.8% of TN and 80.0% of PO43--P were removed by the ABGS. The nuclei of targeted algae (Chlorella) and filamentous fungi (Aspergillus niger), the enhanced production of extracellular polymeric substances (especially proteins) and the enrichment of functional bacteria (such as Neomegalonema and Flavobacterium) facilitated the granules development. The low surface free energy (-69.56 mJ/m2) and energy barrier (89.93 KT) were the inherent mechanisms for the strong surface hydrophobicity, the easy bacterial adhesion, and the short granulation period. This study provides an economically feasible approach to accelerate ABGS granulation and sustain system stability.

Effects of temperature and HRT on biogas production in moving and fixed bed of a novel upflow anaerobic hybrid (UAHB) reactor

The upflow anaerobic hybrid (UAHB) reactor combines the advantages of a upflow anaerobic sludge blanket (UASB-type) reactor and an anaerobic filter in a single compartment. A novel configuration of the UAHB reactor, composed of two three-phase separators (3PHS), was proposed to evaluate the biogas production in the moving and fixed bed in the treatment of synthetic sewage at a temperature range of 14-21 °C and hydraulic retention time (HRT) of 12, 10 and 8 h. The bench-scale reactor was operated in three different phases with organic loading rate (VOLR) of 0.6 (0.3-0.7), 0.7 ± 0.2, and 1.1 ± 0.1 kg COD m^-3 d^-1, respectively, for 225 days. The average removal efficiency of chemical oxygen demand (COD_t) was 78 (42-89)%, and the total biogas yield was 3090 (1704-4782) mL d^-1, with 66% of the lower 3PHS (moving bed) and 34% of the upper 3PHS (fixed bed). However, no significant difference was observed between the biogas yield on the 3PHS (p-value = 0.5048), thus confirming the influence of temperature in the biogas production. The average percentage of methane was 76 (60-82)% for both beds, and the filter media increased the production by 21%. Thus, it can be concluded that the fixed bed suppressed the instability of the moving bed regarding the biogas production and contributed to the final quality of the effluent.

Enhancement of algae ponds for rural domestic sewage treatment by prolonging daylight using artificial lamps

Algal ponds (APs) are widely used as treatment facilities for domestic sewage in sparsely populated rural areas. However, few AP studies have focused on daylight length to enhance pollutants removal. In this study, four algae ponds were set up, daylight was prolonged by 0, 2, 4, and 6 h with an illuminating intensity of 3000 lx. The highest removal efficiencies of total nitrogen, ammonium, and total phosphorus were 37.36%, 41.20%, and 21.56% due to the highest microbial abundance under optimum conditions (2 h PD), respectively. Excessive PD (4 h and 6 h) could inhibit the removal abilities. PD also increased the maximum relative electron transport rate of algae, leading to an increase in the photosynthetic capacity of APs. Meanwhile, the high microbial abundance indicates that chemoheterotrophic bacteria are the main influencing factor for the removal of nitrogen and phosphorus by the APs. Moreover, the system with PD using artificial lamps was proven to be feasible for engineering applications and potentially utilized in rural domestic wastewater treatment.

Nutrients removal by interactions between functional microorganisms in a continuous-flow two-sludge system (AAO-BCO): Effect of influent COD/N ratio

Denitrifying phosphorus removal (DPR) technology is one of the most effective approach to simultaneously realize nitrogen (N) and phosphorus (P) removal from low COD/N ratio wastewater. Identifying the interaction of denitrifying phosphate-accumulating organisms (DPAOs), denitrifying glycogen organisms (DGAOs) and denitrifying ordinary heterotrophic organisms (DOHOs) is critical for optimizing denitrification and anoxic P uptake efficiency in DPR processes. In this study, a novel DPR system of anaerobic anoxic oxic - biological contact oxidation (AAO-BCO) was employed to dispose actual sewage with various influent COD/N ratios (3.5-6.7). High efficiency of TIN (76.5%) and PO₄^3--P (94.4%) removal was observed when COD/N ratio was between 4.4 and 5.9. At the COD/N ratio of 5.7 ± 0.2, prominent DPR performance was verified by the superior DPR efficiency (88.7%) and anoxic phosphorus uptake capacity (PUA_DPAOs/ΔTIN = 1.84 mg/mg), which was further proved by the preponderance of DPAOs in C, N and P removal pathways. GAOs have a competitive advantage over PAOs for COD utilization at low COD/N ratio of 3.7 ± 0.2, which further limited the N removal efficiency. High proportion of N removal via DOHOs (21.2%) at the COD/N ratio of 6.5 ± 0.2 restrained the DPR performance, which should be attributed to the outcompete of DOHOs for NO₃^-. The nutrient removal mechanisms were explicated by stoichiometric calculation methodology to quantify the contribution of diverse functional microorganisms, contributing to improving the robustness of AAO-BCO system when facing the fluctuation of influent carbon source concentration.

Comprehensive review on iodinated X-ray contrast media: Complete fate, occurrence, and formation of disinfection byproducts

Iodinated contrast media (ICM) are drugs which are used in medical examinations for organ imaging purposes. Wastewater treatment plants (WWTPs) have shown incapability to remove ICM, and as a consequence, ICM and their transformation products (TPs) have been detected in environmental waters. ICM show limited biotransformation and low sorption potential. ICM can act as iodine source and can react with commonly used disinfectants such as chlorine in presence of organic matter to yield iodinated disinfection byproducts (IDBPs) which are more cytotoxic and genotoxic than conventionally known disinfection byproducts (DBPs). Even highly efficient advanced treatment systems have failed to completely mineralize ICM, and TPs that are more toxic than parent ICM are produced. This raises issues regarding the efficacy of existing treatment technologies and serious concern over disinfection of ICM containing waters. Realizing this, the current review aims to capture the attention of scientific community on areas of less focus. The review features in depth knowledge regarding complete environmental fate of ICM along with their existing treatment options.

Development of a novel denitrifying phosphorus removal and partial denitrification anammox (DPR + PDA) process for advanced nitrogen and phosphorus removal from domestic and nitrate wastewaters

A novel energy-efficient DPR + PDA (denitrifying phosphorus removal and partial denitrification anammox) process for enhanced nitrogen and phosphorus removal was developed in the combined ABR-CSTR reactor. After 220 days operation, excellent total inorganic nitrogen (TIN) and phosphorus removal (97.57% and 95.66%, respectively) were obtained under external C/NO₃^--N of 0.7, with the effluent TIN and PO₄^3--P concentrations of 3.51 mg/L and 0.28 mg/L, respectively. At the steady period, DPR contributed major TN removal (58.65%), while PDA mediated an increasingly considerable impact and finally achieved 37.07%, in which anammox accounted for a significant percentage. Batch tests demonstrated that efficient PD with nitrate-to-nitrite transformation ratio of 97.67% supplying stable nitrite for anammox, and phosphorus was mainly removed using nitrate as electron acceptor via DPR with the ideal phosphorus release/uptake rate (7.73/22.17 mgP/gVSS/h). Accumulibacter (6.24%) dominated high phosphorus removal performance, while Thauera (8.26%) and Candidatus Brocadia (2.57%) represented the superior nitrogen removal performance.

A novel denitrifying phosphorus removal and partial nitrification, anammox (DPR-PNA) process for advanced nutrients removal from high-strength wastewater

This study developed a novel DPR-PNA (denitrifying phosphorus removal, partial nitrification and anammox) process for sustaining high-strength wastewater treatment in a modified continuous flow reactor without external carbon source. After 259-days operation, a synchronous highly-efficient total inorganic nitrogen, PO₄^3--P and COD_cr removal efficiencies of 88.5%, 89.5% and 90.1% were obtained, respectively even influent nitrogen loading rate up to 3.2 kg m^-3 d^-1. Batch tests revealed that denitrifying phosphorus accumulating organisms (DPAOs) using NO₃^--N as electron acceptors significantly enriched (74% in total PAOs), which emerged remarkable positive impacts on deep-level nutrient removal as the key limiting factor. Furthermore, the NO₂^--N inhibitory threshold value (∼20.0 mg L^-1) for DPAOs was identified, which demonstrated as an inhibitory component in excessive recycling NO_x^--N. From the molecular biology perspective, Dechloromonas-DPAOs group (18.59%) dominated the excellent dephosphatation performance, while Nitrosomonas-AOB (ammonia oxidizing bacteria) group (16.26%) and Candidatus_Brocadia-AnAOB (anammox bacteria) group (15.12%) were responsible for the desirable nitrogen loss process. Overall, the present work highlighted the novel DPR-PNA process for nutrients removal is a promising alternation for wastewater of high nitrogen but low carbon.

Simultaneous nitrogen and phosphorus removal by interactions between phosphate accumulating organisms (PAOs) and denitrifying phosphate accumulating organisms (DPAOs) in a sequencing batch reactor

The identification of phosphate-accumulating organisms (PAOs), denitrifying phosphate-accumulating organisms (DPAOs) and their relationship is a key pathway for optimizing nitrate and phosphate removal efficiency in activated sludge. In this study, the acclimatization of microorganisms in sequencing batch reactor were performed with anaerobic/aerobic (A/O) and anaerobic/anoxic (A/A) cycles, the biomass changes of PAOs and DPAOs and the correlations were then discussed. The results indicated that after acclimatization, the nutrient removal efficiencies reached to 85.34% (COD), 93.64% (PO₄^3--P) and 92.34% (NO₃^--N), respectively, with NO₃^--N:PO₄³-P of 1.5:1. The successful enrichment of PAOs and DPAOs (reached 97.9%) was verified by the change of relative metabolic activities, which was further proved by the change of bacterial diversity. The number of Candidatus Accumulibacter, Zoogloea, and Dechloromonas all increased at A/O and A/A stages while the number of Acinetobacter only increased at A/O stage. So Accumulibacter sp. was DPAO while Acinetobacter sp. was only PAO in this process, and genera Accumulibacter, Dechloromonas and Zoogloea greatly coordinated in denitrification and accumulating phosphorous though RDA and chord plot. This was worthy of attention and development to explore enhanced biological phosphorus removal (EBPR) in practical wastewater treatment via improving identification of bacterial species and symbiosis of bacteria community.

New insights on biological nutrient removal by coupling biofilm-based CANON and denitrifying phosphorus removal (CANDPR) process: Long-term stability assessment and microbial community evolution

It was difficult to obtain a stable and efficient biological nutrient removal for high-strength wastewater treatment, the possibility of exploiting innovative CANDPR process, integrating biofilm-based completely autotrophic nitrogen removal over nitrite (CANON) with denitrifying phosphorus removal (DPR) was evaluated to resolve the difficulty. Results revealed that the excellent NH₄⁺-N, PO₄^3--P and COD removal efficiencies of 96%, 96% and 91%, were achieved respectively under a high nitrogen loading rate (0.79 kg·m^-3·d^-1) without adding organic matters during 320 days operation. Promoting NO_x^--N recirculation demonstrated as an efficient strategy for further nutrient depletion, facilitating the enhanced NO₃^--N removal to 100% with the considerably high P-uptake performance. Batch tests confirmed that denitrifying phosphorus accumulating organisms (DPAOs) using NO₃^--N as electron acceptors accounting for 68% in total PAOs. Dechloromonas was identified as dominating genus in DPR, while Nitrosomonas (1.31%), Candidatus_Kuenenia (5.53%) and Candidatus_Brocadia (1.77%) contributed to the desirable nitrogen removal, indicating that cooperative consortia of DPAOs, AOB and AnAOB were harvested during long-term operation. The CANDPR process was verified to be energy-saving and treatment-reliable for renovating of existing plants.

Nutrient removal and microbial community in a two-stage process: Simultaneous enhanced biological phosphorus removal and semi-nitritation (EBPR-SN) followed by anammox

This study developed a two-stage process, including simultaneous enhanced biological phosphorus-removal and semi-nitritation (EBPR-SN) sequencing batch reactor (SBR), followed by Anammox SBR, to achieve advanced nitrogen (N) and phosphorus (P) removal from real sewage with low carbon/nitrogen (2.82). The long-term operation suggested that removal efficiencies for TIN (86.2 ± 3.5%) and P (95.0 ± 5.5%) were stably obtained, with nitrite accumulation ratio of 98.7% in EBPR-SN SBR. Mechanism analysis indicated contribution of anammox to N-removal being 57.3%-73.7% and superior P-removal due to the majority of removed organics (~74.5%) being stored by polyphosphate-accumulating organisms (PAOs). In EBPR-SN SBR, high-throughput sequencing showed ammonium-oxidizing bacteria was 0.03% while nitrite-oxidizing bacteria was not detected, and PAOs accounted for 30.07%. In Anammox SBR, Candidatus Brocadia (9.75%) was the only anammox bacteria. Remarkably, short aerobic hydraulic retention time (4.29 h) with low DO (0.3-1.2 mg/L) during the whole process provided desirable energy-saving.

The effect of supporting matrix on sludge granulation under low hydraulic shear force: Performance, microbial community dynamics and microorganisms migration

Granular sludge usually takes extracellular polymers (EPS) as matrices for colonizing microorganisms and maintaining structural stability. However, the low strength of EPS threatens the disintegration of granules, especially under low hydraulic shear force. To accelerate the formation and enhance the stability of granules, micro-sized melamine (ME) sponges (RA) and polyurethane (PU) sponges (RB) were screened out as matrix substitutes for developing aerobic granular biofilm (AGB) in this study. The superficial gas velocity was 0.8 cm s^-1. Both reactors achieved over 95% ammonium nitrogen removal efficiency within 10 days. During stabilization period, the chemical oxygen demand, total nitrogen and total phosphorus removal efficiencies were 90.5%, 70% and 95% in RA and 87.8%, 83% and 88% in RB, respectively. Confocal laser scanning microscopy (CLSM) detection revealed that β-polysaccharide was more concentrated in the outer layer in PU-AGB but uniformly dispersed in ME-AGB. The denitrifying phosphorus accumulating organisms (Flavobacterium) was dominant in RA, while the denitrifying glycogen accumulating organisms (Candidatus_Competibacter) was dominant in RB. Fluorescence in situ hybridization (FISH) analysis indicated that the microbial distribution in ME-AGB was relatively uniform, while there was a significant migration of functional microorganisms in PU-AGB. The super-hydrophilicity of ME and the high hydrophobicity of PU may be the main reasons for these differences. Overall, this study indicated that ME sponge is a more suitable material for supporting AGB than PU sponge.

Insight into the impacts of organics on anammox and their potential linking to system performance of sewage partial nitrification-anammox (PN/A): A critical review

Partial nitrification-anammox (PN/A) is an energy-efficient process for nitrogen removal from sewage. The influent organics of sewage is usually pre-removed, reducing the risk for enriching anammox bacteria (AnAOB). However, recent studies demonstrate that optimum influent organics could improve nitrogen removal and operational stability of PN/A. Thus, the impact of organics on PN/A-based process should not be overlooked. In this review, the complicated impacts of organics-containing influent on anammox and their linking to apply PN/A are discussed. Firstly, the effect of organics on AnAOB metabolism and the competition relationship between AnAOB and heterotrophic bacteria are summarized. Secondly, the combined effects of influent organics and operational strategies on PN/A-based process were reviewed. Thirdly, how to control influent organics in the real application of PN/A were discussed. Lastly, recent development of the PN/A-based process combined with denitrification were reviewed. Overall, influent organics could be an essential factor for successful application of sewage PN/A.

Exploring the linkage between bacterial community composition and nitrous oxide emission under varied DO levels through the alternation of aeration rates in a lab-scale anoxic-oxic reactor

Dissolved oxygen (DO) level is crucial in shaping bacterial community and impacts biological nitrogen removal and nitrous oxide (N₂O) emission. Online gaseous and off-line dissolved N₂O under varying DO levels through aeration rate alternations were measured in lab-scale anoxic-oxic reactors. It showed that sharp changes in DO levels caused immediate N₂O emission increase, while the total average gaseous N₂O emission stabilized at 0.011%, 0.046%, 0.308% and 0.229% of influent nitrogen as DO in oxic tanks averaged at 0.58, 1.67, 3.2 and 6.12 mg/L, respectively. Process with an average DO concentration of 1.67 mg/L had the highest microbial diversity and relative abundances of potential denitrifers and ammonia-oxidizing bacteria (NOB), while the least ammonia-oxidizing bacteria (AOB) were detected, which contributed to efficient nitrogen removal and minor N₂O emission. In conclusion, regulation and control of denitrifiers, AOB and NOB with the determination of a proper DO set point is feasible for N₂O mitigation.

Biological wastewater treatment (anaerobic-aerobic) technologies for safe discharge of treated slaughterhouse and meat processing wastewater

Slaughterhouse industry generates considerable amount of wastewater rich in proteins, lipids, fibres, and carbohydrates. Numerous technologies such as electrocoagulation, membrane separation, advanced oxidation, physico-chemical processes, and biological treatment have been implemented for reducing the concentrations of these compounds. Nevertheless, this review aims to provide extensive information solely on the biological treatment (anaerobic and aerobic) of slaughterhouse wastewater. The advantages of anaerobic treatment are excellent organic matter removal, less sludge production, low energy requirement, execution of higher loading rates, and considerable production of biogas. Aerobic treatment on the other hand is a less sensitive process, possess lower start-up period, and efficient nutrient removal process. Numerous case studies are described to bestow maximum understanding of the wastewater characteristics, kind of treatment employed, and complications involved in managing and treating of slaughterhouse effluent. Additionally, role of microbial community involved in the treatment of slaughterhouse waste is also discussed. Sequential anaerobic and aerobic reactors are also reviewed in order to present their advantages over single bioreactors. Intermittent sequencing batch reactor is a promising technology than other high rate digesters in the removal of carbon, nitrogen, and phosphorous.

Establishment and efficiency analysis of a single-stage denitrifying phosphorus removal system treating secondary effluent

For advanced phosphorus and nitrogen removal, denitrifying phosphorus removal (DPR) was used to treat secondary effluent of sewage plants based on alternating anoxic/anaerobic process within single-stage biofilter. Under the hydraulic load of 3 m³/(m²·h), average removal rates of TP and TN in the system were 61.05% and 90.54%. 82.7% of the NO₃^--N removal occurred in the upper of the packing layer. TP removal occurred in upper and lower of the packing layer, accounting for 42.02% and 57.98% of the total removal, respectively. Biomass and bioactivity decreased proportional to the height incensement of packing layer. Nitrogen and phosphorus removal rates increased with anaerobic time while decreased with hydraulic load. 16S rDNA sequencing results showed dominant DNPAOs in the system included Acinetobacter and Dechloromonas, while dominant denitrifying bacteria included Flavobacterium, Comamonadaceae, Hydrogenophaga, Thauera and Azospira. The study further provided an effective and feasible way for advanced wastewater treatment.