Application of the Anammox in China-A Review

Anammox-based technologies: A review of recent advances, mechanism, and bottlenecks

The removal of nitrogen via the ANAMMOX process is a promising green wastewater treatment technology, with numerous benefits. The incessant studies on the ANAMMOX process over the years due to its long start-up and high operational cost has positively influenced its technological advancement, even though at a rather slow pace. At the moment, relatively new ANAMMOX technologies are being developed with the goal of treating low carbon wastewater at low temperatures, tackling nitrite and nitrate accumulation and methane utilization from digestates while also recovering resources (phosphorus) in a sustainable manner. This review compares and contrasts the handful of ANAMMOX -based processes developed thus far with plausible solutions for addressing their respective bottlenecks hindering full-scale implementation. Ultimately, future prospects for advancing understanding of mechanisms and engineering application of ANAMMOX process are posited. As a whole, technological advances in process design and patents have greatly contributed to better understanding of the ANAMMOX process, which has greatly aided in the optimization and industrialization of the ANAMMOX process. This review is intended to provide researchers with an overview of the present state of research and technological development of the ANAMMOX process, thus serving as a guide for realizing energy autarkic future practical applications.

Adjusted bacterial cooperation in anammox community to adapt to high ammonium in wastewater treatment plant

Bacterial cooperation is very important for anammox bacteria which perform low-carbon and energy-efficient nitrogen removal, yet its variation to adapt to high NH4 +-N concentration in actual wastewater treatment plants (WWTPs) remains unclear. Here, we found wide and varied cross-feedings of anammox bacteria and symbiotic bacteria in the two series connected full-scale reactors with different NH4 +-N concentrations (297.95 ± 54.84 and 76.03 ± 34.01 mg/L) treating sludge digester liquor. The uptake of vitamin B6 as highly effective antioxidants secreted by the symbiotic bacteria was beneficial for anammox bacteria to resist the high NH4 +-N concentration and varied dissolved oxygen (DO). When NH4 +-N concentration in influent (1785.46 ± 228.5 mg/L) increased, anammox bacteria tended to reduce the amino acids supply to symbiotic bacteria to save metabolic costs. A total of 26.1% bacterial generalists switched to specialists to increase the stability and functional heterogeneity of the microbial community at high NH4 +-N conditions. V/A-type ATPase for anammox bacteria to adapt to the change of NH4 +-N was highly important to strive against cellular alkalization caused by free ammonia. This study expands the understanding of the adjusted bacterial cooperation within anammox consortia at high NH4 +-N conditions, providing new insights into bacterial adaptation to adverse environments from a sociomicrobiology perspective.

Manganese(IV) reduction coupled with ammonium oxidation mediated by a single strain Aromatoleum evansii MAY27: Performance, metabolomics, and mechanism

Manganese(IV) (Mn(IV)) reduction coupled to anaerobic ammonium (NH4+-N) oxidation (Mnammox) is a recently identified metal oxide-mediated nitrogen (N) loss pathway, holding potential value for the efficient removal of NH4+-N from wastewater. However, little is known about the application of Mnammox in wastewater treatment. Here, a novel Mnammox bacterium Aromatoleum evansii (strain MAY27) was screened. Strain MAY27 can utilize MnO2 as an electron acceptor to achieve NH4+-N removal under a low C/N condition (C/N = 0.5). The influencing factors in the Mnammox process and the Mn(IV) reduction driving effect on NH4+-N oxidation were investigated. The physiological characteristics of strain MAY27 and differential metabolic pathways were identified through whole-genome sequencing and metabolomic analyses. A significant up-regulation of several key pathways upon the addition of MnO2, including glycolysis/gluconeogenesis, transmembrane transporter activity, and oxidoreductase activity. This study contributes to the advancement of biotechnological approaches for treating N-containing wastewater.

High-rate partial nitritation as a pretreatment of anammox process

In this study, a laboratory-scale partial nitrification reactor (PN reactor) was used to treat high-ammonia-nitrogen wastewater, by changing the influent NH4+-N conversion rate as the main operating strategy, to investigate the upper limit of its NH4+-N conversion rate (ACR) and explore its feasibility as an anammox pre-process. During the experiment, PN reactor was successfully activated in only 10 days. The PN reactor reached the highest ACR value of approximately 10.24 kg N/(m3 · day) when the influent ACR was 16.57 kg N/(m3 · day), and the ammonia conversion efficiency (ACE) was 61.78% at this time. The ratio of [NO2--N]Eff/[NH4+-N]Eff was approximately 1.37 which was close to the theoretical ratio of 1.32. And feasibility exploration experiment proved that it was feasible to use this PN reactor as a pre-process of anammox. The PCR-DGGE results showed that the dominant phylum and genus in the reactor during the ACR experiment were Proteobacteria and Nitrosomonas, respectively. With the increase in the ACR, the relative concentration of Nitrosomonas sp. G1 increased from 15 to 40%. This indicates that its abundance is directly correlated with the increase in the ACR. High-throughput sequencing showed that increasing the ACR of the PN reactor greatly reduced the diversity and abundance of the system microbial community structure and changed the dominant phylum and genus; however, the stability of the system was not disrupted. High-throughput sequencing experiments showed that the abundance value of nitrosation enzymes accounted for 91.62%, which was positively correlated with the expression of nitrification genes in the genus Nitrosomonas.

Integration of EBPR with mainstream anammox process to treat real municipal wastewater: Process performance and microbiology

The mainstream application of anaerobic ammonium oxidation (anammox) for sustainable N removal remains a challenge. Similarly, with recent additional stringent regulations for P discharges, it is imperative to integrate N with P removal. This research studied integrated fixed film activated sludge (IFAS) technology to simultaneously remove N and P in real municipal wastewater by combining biofilm anammox with flocculent activated sludge for enhanced biological P removal (EBPR). This technology was assessed in a sequencing batch reactor (SBR) operated as a conventional A2O (anaerobic-anoxic-oxic) process with a hydraulic retention time of 8.8 h. After a steady state operation was reached, robust reactor performance was obtained with average TIN and P removal efficiencies of 91.3 ± 4.1% and 98.4 ± 2.4%, respectively. The average TIN removal rate recorded over the last 100 d of reactor operation was 118 mg/L·d, which is a reasonable number for mainstream applications. The activity of denitrifying polyphosphate accumulating organisms (DPAOs) accounted for nearly 15.9% of P-uptake during the anoxic phase. DPAOs and canonical denitrifiers removed approximately 5.9 mg TIN/L in the anoxic phase. Batch activity assays, which showed that nearly 44.5% of TIN were removed by the biofilms during the aerobic phase. The functional gene expression data also confirmed anammox activities. The IFAS configuration of the SBR allowed operation at a low solid retention time (SRT) of 5-d without washing out biofilm ammonium-oxidizing and anammox bacteria. The low SRT, combined with low dissolved oxygen and intermittent aeration, provided a selective pressure to washout nitrite-oxidizing bacteria and glycogen-accumulating organisms, as relative abundances of.

Resilience of anammox application from sidestream to mainstream: A combined system coupling denitrification, partial nitritation and partial denitrification with anammox

Anaerobic ammonium oxidation (anammox) is a potential process to achieve the neutralization of energy and carbon. Due to the low temperature and variation of municipal sewage, the application of mainstream anammox is hard to be implemented. For spreading mainstream anammox in practice, several key issues and bottlenecks including the start-up, stable NO₂^--N supply, maintenance and dominance of AnAOB with high activity, prevention of NO₃^--N buildup, reduction of sludge loss, adaption to the seasonal temperature and alleviation of COD impacts on AnAOB are discussed and summarized in this review in order to improve its startup, stable operation and resilience of mainstream anammox. Hence a combined biological nitrogen removal (CBNR) system based on conventional denitrification, shortcut nitrification-denitrification, Partial Nitritation and partial Denitrification combined Anammox (PANDA) process through the management of organic matter and nitrate is proposed correspondingly aiming at adaptation to the variations of seasonal temperature and pollutants in influent.

An enriched ammonia-oxidizing microbiota enables high removal efficiency of ammonia in antibiotic production wastewater

High ammonia concentration hinders the efficient treatment of antibiotic production wastewater (APW). Developing effective ammonia oxidation wastewater treatment strategies is an ideal approach for facilitating APW treatment. Compared with traditional nitrification strategies, the partial nitrification process is more eco-friendly, less energy-intensive, and less excess sludge. The primary limiting factor of the partial nitrification process is increasing ammonia-oxidizing bacteria (AOB) while decreasing nitrite-oxidizing bacteria (NOB). In this study, an efficient AOB microbiota (named AF2) was obtained via enrichment of an aerobic activated sludge (AS0) collected from a pharmaceutical wastewater treatment plant. After a 52-day enrichment of AS0 in 250 mL flasks, the microbiota AE1 with 69.18% Nitrosomonas microorganisms was obtained. Subsequent scaled-up cultivation in a 10 L fermenter led to the AF2 microbiota with 59.22% Nitrosomonas. Low concentration of free ammonia (FA, < 42.01 mg L^-1) had a negligible effect on the activity of AF2, and the nitrite-nitrogen accumulation rate (NAR) of AF2 was 98% when FA concentration was 42.01 mg L^-1. The specific ammonia oxidation rates (SAORs) at 30 °C and 15 °C were 3.64 kg NH₄⁺-N·kg MLVSS^-1·d^-1 and 1.43 kg NH₄⁺-N·kg MLVSS^-1·d^-1 (MLVSS: mixed liquor volatile suspended solids). The SAOR was 0.52 kg NH₄⁺-N·kg MLVSS^-1·d^-1 when the NaCl concentration was increased from 0 to 20 g L^-1, showing that AF2 functioning was stable in a high-level salt environment. The ammonia oxidation performance of AF2 was verified by treating abamectin and lincomycin production wastewater. The NARs of AF2 used for abamectin and lincomycin production wastewater treatment were >90% and the SAORs were 2.39 kg NH₄⁺-N·kg MLVSS^-1·d^-1 and 0.54 kg NH₄⁺-N·kg MLVSS^-1·d^-1, respectively, which was higher than the traditional biological denitrification process. In summary, AF2 was effective for APW treatment via enhanced ammonia removal efficiency, demonstrating great potential for future industrial wastewater treatment.

Anammox process for aquaculture wastewater treatment: operational condition, mechanism, and future prospective

Treatment of ammonia- and nitrate-rich wastewater, such as that generated in the aquaculture industry, is important to prevent environmental pollution. The anaerobic ammonium oxidation (anammox) process has been reported as a great alternative in reducing ammoniacal nitrogen concentration in aquaculture wastewater treatment compared to conventional treatment systems. This paper will highlight the impact of the anammox process on aquaculture wastewater, particularly in the regulation of ammonia and nitrogen compounds. The state of the art for anammox treatment systems is discussed in comparison to other available treatment methods. While the anammox process is viable for the treatment of aquaculture wastewater, the efficiency of nitrogen removal could be further improved through the proper use of anammox bacteria, operating conditions, and microbial diversity. In conclusion, a new model of the anammox process is proposed in this review.

Integrating conventional nitrogen removal with anammox in wastewater treatment systems: Microbial metabolism, sustainability and challenges

The various forms of nitrogen (N), including ammonium (NH₄⁺), nitrite (NO₂^-), and nitrate (NO₃^-), present in wastewaters can create critical biotic stress and can lead to hazardous phenomena that cause imbalances in biological diversity. Thus, biological nitrogen removal (BNR) from wastewaters is considered to be imperatively urgent. Therefore, anammox-based systems, i.e. partial nitrification and anaerobic ammonium oxidation (PN/anammox) and partial denitrification and anammox (PD/anammox) have been universally acknowledged to consider as alternatives, promising and cost-effective technologies for sustainable N removal from wastewaters compared to nitrification-denitrification processes. This review comprehensively presents and discusses the latest advances in BNR technologies, including traditional nitrification-denitrification and anammox-based systems. To a deep understanding of a better-controlled combining anammox with traditional processes, the microbial community diversity and metabolism, as well as, biomass morphological characteristics were clearly reviewed in the anammox-based systems. Explaining simultaneous microbial competition and control of crucial operation parameters in single-stage anammox-based processes in terms of optimization and economic benefits makes this contribution a different vision from available review papers. The most important sustainability indicators, including global warming potential (GWP), carbon footprint (CF) and energy behaviours were explored to evaluate the sustainability of BNR processes in wastewater treatment. Additionally, the challenges and solutions for BNR processes are extensively discussed. In summary, this review helps facilitate a critical understanding of N removal technologies. It is confirmed that sustainability and saving energy would be achieved by anammox-based systems, thereby could be encouraged future outcomes for a sustainable N removal economy.

Response of mixed community anammox biomass against sulfide, nitrite and recalcitrant carbon in terms of inhibition coefficients and functional gene expressions

Anaerobic ammonium oxidation (anammox) has evolved as a carbon and energy-efficient nitrogen management bioprocess. However, factors such as inhibitory chemicals still challenge the easy operation of this powerful bioprocess. This research systematically evaluated the inhibition kinetics of sulfide, nitrite, and recalcitrant carbon under a genomic framework. The inhibition at the substrate and genetic levels of sulfide, nitrite and recalcitrant carbon on anammox activity was studied using batch tests. Nitrite inhibition of anammox followed substrate inhibition and was best described by the Aiba model with an inhibition coefficient [Formula: see text] of 324.04 mg N/L. Hydrazine synthase (hzsB) gene (anammox biomarker) expression was increased over time when incubated with nitrite up to 400 mg N/L. However, despite having the highest specific nitrite removal (SNR), the expression of hzsB at 100 and 200 mg N/L of nitrite was more muted than in most other samples with lower SNRs. Sulfide severely inhibited anammox activities. The inhibition was fitted with a Monod-based model with a [Formula: see text] of 4.39 mg S/L. At a sulfide concentration of 5 mg/L, the hzsB expression decreased throughout the experiment from its original value at he beginning. Recalcitrant carbon of filtrate from thermal hydrolysis process pretreated anaerobic digester had a minimal effect on maximum specific anammox activity (MSAA), and thus the value of the inhibition coefficient could not be calculated. At the same time, its hzsB expression profile was similar to that in the control. Resiliency and recovery tests indicated that the inhibition of nitrite (up to 400 mg N/L) and recalcitrant carbon (in 100% filtrate) were reversible. About 32% of MSAA was recovered after repeated exposures to sulfide at 2.5 mg/L, while at 5 mg/L, the inhibition was irreversible. Findings from this study will be helpful for the successful design and implementation of anammox in full-scale applications.

Advanced nitrogen removal from mature landfill leachate based on novel step-draining partial nitrification-denitrification and Anammox process: Significance of low volume exchange ratio

To save external carbon source dosage and simplify NH4+ to NO2- ratio control strategy, this study established a novel step-draining based partial nitrification-denitrification and Anammox (PND-AMX) system for advanced nitrogen removal from mature landfill leachate. Separation of partial nitrification and denitrification was realized based on step-draining, achieving 74.8 % nitrogen removal. 25 % was the optimal volume exchange ratio for synergistic removal of organics and nitrogen, allowing full use of carbon source. NH4+ to NO2- ratio was easily controlled by varying the volume ratio of the first and second effluent of PND reactor. Brocadia, Kuenenia and Jettenia collectively accounted for 13.61 % in AMX reactor, contributing 21.0 % of nitrogen removal. Nitrogen removal efficiency and nitrogen removal rate reached 98.3 ± 1.2 % and 3.07 ± 0.09 kgN/(m3∙d), respectively. Partial Anammox process based on step-draining was easier to realize and of practical significance for application in treatment of landfill leachate.

Full-Scale Application of One-Stage Simultaneous Nitrification and Denitrification Coupled with Anammox Process for Treating Collagen Casing Wastewater

The ammonia nitrogen (NH₄⁺-N) concentration in the effluent released from the secondary sedimentation tank of the original collagen enteric coating wastewater treatment process considerably exceeded the Chinese effluent discharge standard. Therefore, a one-stage simultaneous nitrification and denitrification coupled with the anaerobic ammonia oxidation (SNDA) process was designed to terminally treat collagen enteric coating wastewater containing low COD/NH₄⁺-N (C/N). The entire process start-up and NH₄⁺-N loading (NLR) domestication phase was completed within two months. During the NLR domestication, the NH₄⁺-N removal rate was more than 90% and its effluent concentration was less than 15 mg/L, guaranteeing that the NH₄⁺-N in the subsequent effluent was within the standard value. The results of microbial diversity show that Acinetobacter, Bacillus, and other heterotrophic nitrification–aerobic denitrification bacteria, and anammox ammonia oxidation bacteria were the main functional bacteria at the genus level, exhibiting high denitrification performance. The one-stage SNDA process effectively and stably removed nitrogen; the treated sewage satisfied the national comprehensive wastewater discharge standard (GB8978-1996), effectively saving 30–40% of the floor area and reducing 67.6% of the additionally added alkali, wherein the system’s denitrifying bacteria compensated for some alkali consumed during the nitrification reaction.

Modeling of novel processes for eliminating sidestreams impacts on full-scale sewage treatment plant using GPS-X7

The novel process consisted of two steps was established by combining all sidestreams lines (supernatant gravity thickener, underflow mechanical thickener, and centrate), treating them together away from the mainstream treatment plant, and returning treated sidestreams effluents to the plant outfall instead of plant head. The two steps novelty treatment combined degradation, nitrification, and dilution processes. To treat combined sidestreams, a novel pilot extended nutrient moving bed biofilm reactor was developed. The effects of sidestream elimination on a full-scale anaerobic/anoxic/oxic system were simulated using GPS-X7. The statistical results of R values greater than 0.8 and NMSE values near zero proved the calibrated model's validation. The novel system successfully removed 98, 93, 100, 85, 98, 100, and 98% of BOD, COD, NH₄, NO₃, TSS, H₂S, and PO₄-P from sidestreams, respectively. Furthermore, the simulation results showed that eliminating sidestreams has reduced volumes of full-scale A²/O facilities, controlled hydraulic and pollutants shocks, and minimized cost and energy. The novel process proved successful in treating combined sidestreams and eliminating their impacts on the A/O² system.

Advances in Studies on Microbiota Involved in Nitrogen Removal Processes and Their Applications in Wastewater Treatment

The discharge of excess nitrogenous pollutants in rivers or other water bodies often leads to serious ecological problems and results in the collapse of aquatic ecosystems. Nitrogenous pollutants are often derived from the inefficient treatment of industrial wastewater. The biological treatment of industrial wastewater for the removal of nitrogen pollution is a green and efficient strategy. In the initial stage of the nitrogen removal process, the nitrogenous pollutants are converted to ammonia. Traditionally, nitrification and denitrification processes have been used for nitrogen removal in industrial wastewater; while currently, more efficient processes, such as simultaneous nitrification-denitrification, partial nitrification-anammox, and partial denitrification-anammox processes, are used. The microorganisms participating in nitrogen pollutant removal processes are diverse, but information about them is limited. In this review, we summarize the microbiota participating in nitrogen removal processes, their pathways, and associated functional genes. We have also discussed the design of efficient industrial wastewater treatment processes for the removal of nitrogenous pollutants and the application of microbiome engineering technology and synthetic biology strategies in the modulation of the nitrogen removal process. This review thus provides insights that would help in improving the efficiency of nitrogen pollutant removal from industrial wastewater.

Recent advances in partial denitrification-anaerobic ammonium oxidation process for mainstream municipal wastewater treatment

To solve the bottleneck of the unstable accumulation of nitrite in the partial nitrification (PN)-anammox (AMX) in municipal wastewater treatment, a novel process called partial denitrification (PD)-AMX has been developed. PD-AMX, which is known for cost-efficiency and environmental friendliness, has currently exhibited a promising potential for the removal of biological nitrogen from municipal wastewater and has attracted much research interest regarding its process mechanisms, as well as its practical applications. Here, we review the recent advances in the PD process and its coupling to the anammox process, including the development, basic principles, main characteristics, and critical process parameters of the stable operation of the PD-AMX process. We also explore the microbial community and its characteristics in the system and summarize the knowledge of the dominant bacteria to clarify the key factors affecting PD-AMX. Then, we introduce the engineering feasibility and economic feasibility as well as the potential challenges of the process. The induction and implementation of partial denitrification and maintenance of mainstream anammox are critical issues to be urgently solved. Meanwhile, the implementation of a full mainstream anammox application remains burdensome, while the mechanism of partial denitrification coupled to anammox needs to be further studied. Additionally, stable operation performance and process control¹ methods need to be optimized or developed for the PD-AMX system for better engineering practice. This review can help to accelerate the research and application of the PD-AMX process for municipal wastewater treatment.

Recent advancements in the biological treatment of high strength ammonia wastewater

The estimated global population growth of 81 million people per year, combined with increased rates of urbanization and associated industrial processes, result in volumes of high strength ammonia wastewater that cannot be treated in a cost-effective or sustainable manner using the floc-based conventional activated sludge approach of nitrification and denitrification. Biofilm and aerobic granular sludge technologies have shown promise to significantly improve the performance of biological nitrogen removal systems treating high strength wastewater. This is partly due to enhanced biomass retention and their ability to sustain diverse microbial populations with juxtaposing growth requirements. Recent research has also demonstrated the value of hybrid systems with heterogeneous bioaggregates to mitigate biofilm and granule instability during long-term operation. In the context of high strength ammonia wastewater treatment, conventional nitrification-denitrification is hampered by high energy costs and greenhouse gas emissions. Anammox-based processes such as partial nitritation-anammox and partial denitrification-anammox represent more cost-effective and sustainable methods of removing reactive nitrogen from wastewater. There is also growing interest in the use of photosynthetic bacteria for ammonia recovery from high strength waste streams, such that nitrogen can be captured and concentrated in its reactive form and recycled into high value products. The purpose of this review is to explore recent advancements and emerging approaches related to high strength ammonia wastewater treatment.

Holistic insights into extracellular polymeric substance (EPS) in anammosx bacterial matrix and the potential sustainable biopolymer recovery: A review

Anaerobic ammonia oxidation (anammox) process has been proven to be a favorable and innovative process, for treatment of nitrogen-rich wastewater due to decreased oxygen and carbon requirements at very high nitrogen loading rates. Anammox process is mainly operated through biofilm or granular sludge structures, as for such slow-growing microorganisms, elevated settling velocity of granules allows for adequate biomass retention and lowered potential risk of washouts. Stability of granular sludge biomass is extremely critical, yet the formation mechanism is poorly understood. There are number of important functions linked to Extracellular Polymeric Substance (EPS) in anammox bacterial matrix, such as; structural stability, aggregation promotion, maintenance of physical structure in the granules, water preserving and protective cell barrier. There is an increasing demand to introduce accurate methods for proper EPS extraction and characterization, to expand the perception of anammox granule stability and potential resource recovery. Analyzing EPS with a focus on various (mechanical and physical) properties can lead to biopolymer production from granular sludge. Biopolymers such as EPS are attractive alternatives substituting the conventional chemical polymers furthermore their recovery from the waste sludge and the potential applications in industrial sectors, leads to a radical enhancement of both environmental and economical sustainability, accelerating the circular economy advancements. Here, this study aims to overview the newest understanding on the structure of anammox sludge EPS, obtained recently and to assess the potential challenges and prospects to identify the knowledge gaps towards constructing an inclusive anammox EPS recovery and characterization procedure.

Purification of the key enzyme complexes of the anammox pathway from DEMON sludge

Anaerobic Ammonium Oxidation ("anammox") is a bacterial process in which nitrite and ammonium are converted into nitrogen gas and water, yielding energy for the cell. Anammox is an important branch of the global biological nitrogen cycle, being responsible for up to 50% of the yearly nitrogen removal from the oceans. Strikingly, the anammox process uniquely relies on the extremely reactive and toxic compound hydrazine as a free intermediate. Given its global importance and biochemical novelty, there is considerable interest in the enzymes at the heart of the anammox pathway. Unfortunately, obtaining these enzymes in sufficiently large amounts for biochemical and structural studies is problematic, given the slow growth of pure cultures of anammox bacteria when high cell densities are required. However, the anammox process is being applied in wastewater treatment to remove nitrogenous waste in processes like DEamMONification (DEMON). In plants using such processes, which rely on a combination of aerobic ammonia-oxidizers and anammox organisms, kilogram amounts of anammox bacteria-containing sludge are readily available. Here, we report a protein isolation protocol starting from anammox cells present in DEMON sludge from a wastewater treatment plan that readily yields pure preparations of key anammox proteins in the tens of milligrams, including hydrazine synthase HZS and hydrazine dehydrogenase (HDH), as well as hydroxylamine oxidoreductase (HAO). HDH and HAO were active and of sufficient quality for biochemical studies and for HAO, the crystal structure could be determined. The method presented here provides a viable way to obtain materials for the study of proteins not only from the central anammox metabolism but also for the study of other exciting aspects of anammox bacteria, such as for example, their unusual ladderane lipids.

Toxic metals in soil due to the land application of sewage sludge in China: Spatiotemporal variations and influencing factors

Land application has become a promising method for recycling energy and resources from sewage sludge; however, the changes that occur to the toxic metal concentrations in soil following the application of sewage sludge have been poorly investigated in China. The present study attempted to investigate the spatiotemporal variations of toxic metal concentrations in soil due to the land application of sewage sludge and the critical influencing factors. Overall, the results indicated that an increasing ratio of sewage sludge for land application, the concentrated disposal measures, and a shallower soil may lead to elevated toxic metal concentrations in soil. The worst scenario simulation showed that the cumulative discharge of toxic metals through sludge disposal were ranked as: Zn > Cu > Cr > Pb > Ni > As > Cd > Hg. After sewage sludge was applied to previously unaffected soil, i.e., background soil, the toxic metal concentrations in the soil increased annually over the period from 2006 to 2017. However, with respect to the affected soil, the concentrations of Zn and Cu increased, whereas the concentrations of As, Cd, Cr, and Pb decreased annually over the period from 2006 to 2017. The results indicate that, in practice, the selection of soil for sewage sludge disposal depends on the background and actual concentrations of toxic metals in a soil as well as the stress caused by the amount of sewage sludge application to cultivated land. We propose to use sewage sludge containing relatively lower concentrations of metals than the disposal soil for land application. Furthermore, land application of sewage sludge should be suited to local conditions in the future sewage sludge management.

Domestic Sewage Treatment Using a One-Stage ANAMMOX Process

A one-stage anaerobic ammonium oxidation (ANAMMOX) reactor can be quickly started within 40 days by mixing partial nitrifying sludge with ANAMMOX granular sludge with an average temperature of 30 °C. After 70 days of nitrogen load acclimation, Acinetobacter, including Candidatus Kuenenia, became the dominant strain of the system within the reactor, which exhibited high efficiency and a stable nitrogen removal performance. At an influent chemical oxygen demand (COD), NH₄⁺-N content, total nitrogen (TN) content, hydraulic retention time (HRT), temperature, and reactor dissolved oxygen (DO) content of 100, 60, and 70 mg/L, 6 h, 30 ± 1 °C, and below 0.6 mg/L, respectively, the one-stage ANAMMOX reactor could effectively treat domestic sewage on campus. The removal rates of COD, NH₄⁺-N, and TN were approximately 89%, 96.7%, and 70%, respectively.