Factors affecting simultaneous nitrification and denitrification (SND) in a moving bed sequencing batch reactor (MBSBR) system as revealed by microbial community structures

Transition from sulfur autotrophic to mixotrophic denitrification: Performance with different carbon sources, microbial community and artificial neural network modeling

To address the limitations inherent in both sulfur autotrophic denitrification (SAD) and heterotrophic denitrification (HD) processes, this study introduces a novel approach. Three carbon sources (glucose, methanol, and sodium acetate) were fed into the SAD system to facilitate the transition towards mixotrophic denitrification. Batch experiments were conducted to explore the effects of influencing factors (pH, HRT) on the denitrification performance of the mixotrophic system. Carbon source dosages were varied at 12.5%, 25%, and 50% of the theoretical amounts required for HD (18, 36, and 72 mg/L, respectively). The results showed distinct optimal dosages for each of the three organic carbon sources. The mixotrophic system, initiated with sodium acetate at 25% of the theoretical value, demonstrated the highest denitrification performance, achieving NO3--N removal efficiency of 99.8% and the NRR of 6.25 mg/(L·h). In contrast, the corresponding systems utilizing glucose (at 25% of the theoretical value) and methanol (at 50% of the theoretical value) achieved lower removal efficiency of 77.0% and 88.4%, respectively. The corresponding NRRs were 4.85 mg/(L·h) and 5.65 mg/(L·h). Following the transition from SAD to a mixotrophic system, the abundance of Thiobacillus decreased from 78.5% to 34.4% at the genus level, and the mixotrophic system cultivated a variety of other denitrifying bacteria (Thauera, Aquimonas, Azoarcus, and Pseudomonas), indicating an enhanced microbial community structure diversity. The established artificial neural network (ANN) model accurately predicted the effluent quality of mixotrophic denitrification, which predicted values closely aligning with experimental results (R2 > 0.9). Furthermore, initial pH exerted greater relative importance for COD removal and sulfur conversion, while the relative importance of HRT was more pronounced for NO3--N removal.

Sequential bio-treatment of ammonia-rich wastewater from Chinese medicine residue utilization: Regulation of dissolved oxygen

To effectively treat actual ammonia-rich Chinese medicine residue (CMR) resource utilization wastewater, we optimized an anaerobic-microaerobic two-stage expanded granular sludge bed (EGSB) and moving bed sequencing batch reactor (MBSBR) combined process. By controlling dissolved oxygen (DO) levels, impressive removal efficiencies were achieved. Microaeration, contrasting with anaerobic conditions, bolstered dehydrogenase activity, enhanced electron transfer, and enriched the functional microorganism community. The increased relative abundance of Synergistetes and Proteobacteria facilitated hydrolytic acidification and fostered nitrogen and phosphorus removal. Furthermore, we examined the impact of DO concentration in MBSBR on pollutant removal and microbial metabolic activity, pinpointing 2.5 mg/L as the optimal DO concentration for superior removal performance and energy conservation.

Performance of a modified and intermittently operated slow sand filter with two different mediums in removing turbidity, ammonia, and phosphate with varying acclimatization periods

The present study investigated the utilization of blood clam shells as a potential substitute for conventional media, as well as the influence of the acclimation time on the efficacy of an intermittent slow sand filter (ISSF) in the treatment of real domestic wastewater. ISSF was operated with 16 h on and 8 h off, focusing on the parameters of turbidity, ammonia, and phosphate. Two media combinations (only blood clam shells [CC] and sand + blood clam shells [SC]) were operated under two different acclimatization periods (14 and 28 d). Results showed that SC medium exhibited significantly higher removal of turbidity (p < 0.05) as compared to CC medium (45.99 ± 26.84 % vs. 3.79 ± 9.35 %), while CC exhibited slightly higher (p > 0.05) removal of ammonia (23.12 ± 20.2 % vs. 16.77 ± 16.8 %) and phosphate (18.03 ± 11.96 % vs 13.48 ± 12 %). Comparing the acclimatization periods, the 28 d of acclimatization period showed higher overall performances than the 14 d. Further optimizations need to be conducted to obtain an effluent value below the national permissible limit, since the ammonia and phosphate parameters are still slightly higher. SEM analysis confirmed the formation of biofilm on both mediums after 28 d of acclimatization; with further analysis of schmutzdecke formation need to be carried out to enrich the results.

Effect of dissolved oxygen concentration on performance and mechanism of simultaneous nitrification and denitrification in integrated fixed-film activated sludge sequencing batch reactors

Integrated fixed-film activated sludge (IFAS) is a superior system for achieving simultaneous nitrification and denitrification (SND), however, the impact of dissolved oxygen (DO) has not been fully elucidated. Therefore, this study investigated the effect of DO concentration on performance and mechanism of SND in IFAS system. Results showed that IFAS outperformed control systems and achieved optimal SND performance at a DO concentration of 0.5 mg/L, with an SND efficiency of 88.51% and total nitrogen removal efficiency of 82.78%. Typical cycles analysis demonstrated limited-DO promoted SND performance. Further analysis implied biofilms exhibited high biomass and denitrification activity with decreasing DO. Microbial community analysis revealed low DO concentrations were responsible for abundant functional groups and genes associated with SND and promoted unconventional nitrogen removal pathways. Moreover, co-occurrence network analysis elucidated microbial interactions, responses to DO, and keystone genera. This study helps understanding the roles of DO for enhanced SND in IFAS.

Biological and physical selectors for mobile biofilms, aerobic granules, and densified-biological flocs in continuously flowing wastewater treatment processes: A state-of-the-art review

There have been significant advances in the use of biological and physical selectors for the intensification of continuously flowing biological wastewater treatment (WWT) processes. Biological selection allows for the development of large biological aggregates (e.g., mobile biofilm, aerobic granules, and densified biological flocs). Physical selection controls the solids residence times of large biological aggregates and ordinary biological flocs, and is usually accomplished using screens or hydrocyclones. Large biological aggregates can facilitate different biological transformations in a single reactor and enhance liquid and solids separation. Continuous-flow WWT processes incorporating biological and physical selectors offer benefits that can include reduced footprint, lower costs, and improved WWT process performance. Thus, it is expected that both interest in and application of these processes will increase significantly in the future. This review provides a comprehensive summary of biological and physical selectors and their design and operation.

Insight into the roles of microalgae on simultaneous nitrification and denitrification in microalgal-bacterial sequencing batch reactors: Nitrogen removal, extracellular polymeric substances, and microbial communities

This study explored the influence and mechanism of microalgae on simultaneous nitrification and denitrification (SND) in microalgal-bacterial sequencing batch reactors (MB-SBR). It particularly focused on nitrogen transformation in extracellular polymeric substances (EPS) and functional groups associated with nitrogen removal. The results showed that MB-SBR achieved more optimal performance than control, with an SND efficiency of 68.01% and total nitrogen removal efficiency of 66.74%. Further analyses revealed that microalgae changed compositions and properties of EPS by increasing EPS contents and improving transfer, conversion, and storage capacity of nitrogen in EPS. Microbial community analysis demonstrated that microalgae promoted the enrichment of functional groups and genes related to SND and introduced diverse nitrogen removal pathways. Moreover, co-occurrence network analysis elucidated the interactions between communities of bacteria and microalgae and the promotion of SND by microalgae as keystone connectors in the MB-SBR. This study provides insights into the roles of microalgae for enhanced SND.

Optimization of synthetic domestic wastewater treatment performance in anoxic/aerobic sequencing batch reactor with zeolite addition

In this study, treatment performance was investigated based on chemical oxygen demand (COD), ammonium nitrogen (NH4+-N), total inorganic nitrogen (TIN) and simultaneous nitrification and denitrification (SND) parameters in a zeolite-added anoxic/aerobic sequencing batch reactor. Response surface methodology (RSM) was used to model treatment performance, determine the impact of operating conditions, and optimize them. The effect of zeolite size, dosage and COD/NH4+-N (C/N) ratio as operating parameters were evaluated in the central composite design (CCD). Variance analysis (ANOVA) results of the quadratic model, high coefficients of determination and low values of the root mean square error (RMSE) for dependent variables indicated the validity of the model in predicting experimental results. The desirability function showed that optimum conditions were 0.80 mm for zeolite size, 3.05 g/L for zeolite dosage and 9.8 for C/N. Under these conditions, the maximum COD, NH4+-N, TIN removal efficiencies and SND efficiency were 92.85%, 93.3%, 77.33% and 82.96%, respectively. The results of the study showed that the most effective independent variable on dependent variables was the C/N ratio.

Recent advances in simultaneous nitrification and denitrification for nitrogen and micropollutant removal: a review

Simultaneous Nitrification and Denitrification (SND) is a promising process for biological nitrogen removal. Compared to conventional nitrogen removal processes, SND is cost-effective due to the decreased structural footprint and low oxygen and energy requirements. This critical review summarizes the current knowledge on SND related to fundamentals, mechanisms, and influence factors. The creation of stable aerobic and anoxic conditions within the flocs, as well as the optimization of dissolved oxygen (DO), are the most significant challenges in SND. Innovative reactor configurations coupled with diversified microbial communities have achieved significant carbon and nitrogen reduction from wastewater. In addition, the review also presents the recent advances in SND for removing micropollutants. The micropollutants are exposed to various enzymes due to the microaerobic and diverse redox conditions present in the SND system, which would eventually enhance biotransformation. This review presents SND as a potential biological treatment process for carbon, nitrogen, and micropollutant removal from wastewater.

Performance and microbial mechanism of eletrotrophic bio-cathode denitrification under low temperature

Insufficient amount of carbon in wastewater and low temperatures hinder the use of biological nitrogen removal for purification of wastewaters. Nitrogen removal using cold-tolerant electrotrophic cathodic microbes is a novel and unique autotrophic denitrification technique in which electrical current, not chemicals, is used as a source of electrons. In this study, integrated MFC (R_W) and open-circuit MFC (R_O) were cultured and acclimatized in stages at a low temperature (10 °C) to impart cold tolerance to electrotrophic cathodic microbes, investigate the effectiveness of simultaneous nitrification and denitrification (SND) process, and address the possible mechanism of microbial action. The results showed that (i) microbial communities in the R_W system were successfully enriched with the cold-tolerant electrotrophic cathodic microbes after five stages, and (ii) the degree of NH₄⁺-N removal and SND were 75.50% and 81.91%, respectively, but the respective values in the R_O system were only 40.47% and 54.01%. The desirable SND efficiency was obtained in R_W at a DO of ∼0.6 mg/L, a current of ∼20 mA, and pH ∼7.0. In R_W, Thauera, Pesudomonas, and Hydrogenophaga were the main electrotrophic cathodic denitrifying bacteria with cold tolerance capable of degrading ammonia, nitrate, and nitrite through autotrophic denitrification and cathodic-driven bio-electrochemical denitrification. Besides, for R_W, results from high throughput sequencing analysis revealed that the abundance of genes related to energy production and conversion, amino acid transport, and metabolism, signal transduction, environmental adaptation, and enzymatic activity (AMO, HAO, NAR, NIR, NOR, and NOS) were significantly higher than the corresponding parameters of the R_O system. This may explain the reason behind R_W having excellent ammonia and TN removal performance at low temperatures.

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

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

Performance evaluation and microbial community structure of a modified trickling filter and conventional activated sludge process in treating urban sewage

This study compares the performance and microbial composition of a conventional activated sludge process (ASP) with a modified trickling filter (MTF) for urban sewage treatment. MTF (2 h HRT with effluent recycling) and ASP (8 h HRT) showed >60 % removal efficiency for COD, NH₃-N and PO₄^3--P. MTF outperformed ASP in denitrification and 5 mg/L of NO₃^--N was detected in the effluent of MTF. The widespread distribution of nitrogen removal functional genes (amoA, nirK, nirS, napA, narG and nosZ) in MTF indicates simultaneous nitrification and denitrification (SND) as a key process controlling nitrogen removal. In addition, Miseq sequencing was used to examine the microbial community composition in MTF and ASP. The sequencing result revealed that Proteobacteria, Planctomycetes, Chloroflexi and Actinobacteriota were the dominant phyla in both MTF and ASP. Moreover, the co-occurrence of various nitrifiers, denitrifiers, aerobic denitrifiers, and ANAMMOX bacteria in MTF suggested their role in nitrogen removal.

Seasonal patterns of rhizosphere microorganisms suggest carbohydrate-degrading and nitrogen-fixing microbes contribute to the attribute of full-year shooting in woody bamboo Cephalostachyum pingbianense

Compared with the ordinary single-season shooting among woody bamboos in Poaceae, the attribute of full-year shooting in Cephalostachyum pingbianense represents a unique shooting type or mechanism. Nevertheless, except for the overall physiological mechanism, the effect of ecological factors, especially soil microorganisms, on this full-year shooting characteristic remains unclear. In this study, 16S rRNA and ITS rRNA genes were sequenced using the Illumina platform. Our aims were to detect the seasonal changes in rhizospheric microbial communities of C. pingbianense and to discover the correlations of soil microbes with soil properties and bamboo shoot productivity. The results showed that seasonal change had no significant effect on bacterial alpha diversity, but significantly affected bacterial and fungal community structures as well as fungal richness. Among all soil properties examined, soil temperature, soil moisture and organic matter were the predominant factors affecting bacterial community diversity and structure. Soil temperature and soil moisture also significantly influenced fungal community structure, while available phosphorus had the greatest effect on fungal diversity. In each season, bacterial genera Acidothermus, Roseiarcus, and Bradyrhizobium, along with fungal genera Saitozyma, Mortierella, Trichoderma, etc., were dominant in bacterial and fungal communities, respectively. Bacterial community functions in four seasons were dominated by chemoheterotrophy, cellulolysis, and nitrogen fixation. Saprotrophic fungi occupied a high proportion in soil samples of all seasons. In addition, correlation analysis revealed that the bamboo shoot productivity was positively correlated with multiple microbial taxa involved in carbon and nitrogen cycles. It is proposed that highly abundant microbes involved in carbohydrate degradation and nitrogen fixation in the rhizosphere soil may contribute to the attribute of producing bamboo shoots all year round in C. pingbianense. This study is among the few cases revealing the connection between bamboo shooting characteristics and soil microorganisms, and provides new physiological and ecological insights into the forest management of woody bamboos.

Simultaneous nitrification-denitrification in biofilm systems for wastewater treatment: Key factors, potential routes, and engineered applications

Simultaneous nitrification-denitrification (SND) is an advantageous bioprocess that allows the complete removal of ammonia nitrogen through sequential redox reactions leading to nitrogen gas production. SND can govern nitrogen removal in single-stage biofilm systems, such as the moving bed biofilm reactor and aerobic granular sludge system, as oxygen gradients allow the development of multilayered biofilms including nitrifying and denitrifying bacteria. Environmental and operational conditions can strongly influence SND performance, biofilm development and biochemical pathways. Recent advances have outlined the possibility to reduce the carbon and energy consumption of the process via the "shortcut pathway", and simultaneously remove both N and phosphorus under specific operational conditions, opening new possibilities for wastewater treatment. This work critically reviews the factors influencing SND and its application in biofilm systems from laboratory to full scale. Operational strategies to enhance SND efficiency and hints to reduce nitrous oxide emission and operational costs are provided.

Simultaneous Removal of Organic Matter and Nutrients from High Strength Organic Wastewater Using Sequencing Batch Reactor (SBR)

Industrial wastewater discharges often contain high levels of organic matter and nutrients, which can lead to eutrophication and constitute a serious hazard to receiving waters and aquatic life. The purpose of this study was to examine the efficacy of using a sequencing batch reactor (SBR) to treat high-strength organic wastewater for the removal of both chemical oxygen demand (COD) and nutrients (nitrogen and phosphorus). At a constant COD concentration of approximately 1000 mg/L, the effects of cycle time (3 and 9 h) and various C:N:P ratios (100:5:2, 100:5:1, 100:10:1, and 100:10:2) were investigated using four identical SBRs (R1, R2, R3, and R4). According to experimental data, a significant high removal, i.e., 90%, 98.5%, and 84.8%, was observed for COD, NH3-N, and PO43−-P, respectively, when C:N:P was 100:5:1, at a cycle time of 3 h. Additionally, when cycle time was increased to 9 h, the highest levels of COD removal (95.7%), NH3-N removal (99.6%), and PO43−-P removal (90.31%) were accomplished. Also, in order to comprehend the primary impacts and interactions among the various process variables, the data was statistically examined using analysis of variance (ANOVA) at a 95% confidence level, which revealed that the interaction of cycle time and C/N ratio, cycle time and C/P ratio is significant for COD and NH3-N removal. However, the same interaction was found to be insignificant for PO43−-P removal. Sludge volume index (SVI30 and SVI10) and sludge settleability were studied, and the best settling was found in R3 with SVI30 of 55 mL/g after 9 h. Further evidence that flocs were present in reactors came from an average ratio of SVI 30/SVI 10 = 0.70 after 9 h and 0.60 after 3 h.

A Comparison of Biosolids Production and System Efficiency between Activated Sludge, Moving Bed Biofilm Reactor, and Sequencing Batch Moving Bed Biofilm Reactor in the Dairy Wastewater Treatment

Dairy industry wastewater is rich in organic content, presenting a high biodegradability, and therefore biological treatments are widely employed. This study aimed to evaluate biosolids production in three systems: activated sludge (AS), movingbed biofilm reactor (MBBR), and sequencingbatch movingbed biofilm reactor (SBMBBR). Simulated dairy wastewater was used at different organic load rates (OLRs): 1.22, 2.87, and 5.44 gCOD L−1d−1. Besides biosolids production, COD, total carbon (TC), and total nitrogen (TN) removal efficiency was evaluated. Biosolids production was measured in the mixed liquor, carrier-adhered biomass, treated wastewater, and surplus sludge. The operational conditions were kept similar for the three systems, with a carrier filling ratio of 50% for MBBR and SBMBBR. The SBMBBR proved to have better performance in the removal efficiencies of COD, TC, and TN for all OLRs studied. The MBBR presented a similar COD and TC removal efficiency as the SBBR for the two highest OLRs (2.87 and 5.44 gCOD L−1d−1). Concerning biosolids production, the MBBR system produced less biomass and delivered the lowest amount of adhered biomass inside the carriers. The AS treatment generated the highest amount of sludge and offered the worst treatment capability for all OLRs evaluated.

Role of heterotrophic nitrifiers and aerobic denitrifiers in simultaneous nitrification and denitrification process: A non-conventional nitrogen removal pathway in wastewater treatment

Bacterial species capable of performing both nitrification and denitrification in a single vessel under similar conditions have gained significance in the wastewater treatment scenario considering their unique character of performing the above reactions under heterotrophic and aerobic conditions respectively. Such a novel strategy often referred to as simultaneous nitrification and denitrification (SND) has a tremendous potential in dealing with various wastewaters having low C:N content, considering that the process needs very little or no external carbon source and oxygen supply thus adding to its cost-effective and environmentally friendly nature. Though like other microorganisms, heterotrophic nitrifiers and aerobic denitrifiers convert inorganic or organic nitrogen-containing substances into harmless dinitrogen gas in the wastewater, their ecophysiological role in the global nitrogen cycle is still not yet fully understood. Attempts to highlight the role played by the heterotrophic nitrifiers and aerobic denitrifiers in dealing with nitrogen pollution under various environmental operating conditions will help in developing a mechanistic understanding of the SND process to address the issues faced by the traditional methods of aerobic autotrophic nitrification-anaerobic heterotrophic denitrification.

Temperature-induced difference in microbial characterizations accounts for the fluctuation of sequencing batch biofilm reactor performance

Generally, the purification performance of bioreactors could be influenced by temperature variation via shaping different microbial communities. However, the underlying mechanisms remain largely unknown. Here, the variation trends of microbial communities in three sequencing batch biofilm reactors (SBBRs) under four different temperatures (15, 20, 25, 30 °C) were compared. It was found that temperature increment led to an obvious enhancement in nutrient removal which was mainly occurred in the aerobic section. Meanwhile, distinct differences in dominant microbial communities or autotrophic nitrifiers were also observed. The performance of the SBBR reactors was closely associated with nitrifier communities since the treated wastewater was characterized by a severe lack of carbon sources (mean effluent COD ≤ 14.4 mg/L). Spearman correlation unraveled that: most of the differentiated microbes as well as the dominant potential functions were strongly associated with nutrient removal, indicating the temperature-induced difference in microbial community well explained the distinction in purification performance.

Simultaneous nitrification and denitrification in moving bed bioreactor and other biological systems

Moving bed bioreactor (MBBR), used for treatment of municipal and industrial wastewater, is a completely mixed attached growth type system that involves microorganisms which grow as biofilm on the surface of the suspended carriers within the reactor. If the biofilm is thick enough, dissolved oxygen in the reactor would not diffuse into deeper strata and thus anoxic/anaerobic condition develops in those regions facilitating growth of heterotrophic denitrifying bacteria. Autotrophic nitrifiers colonize the outer surface of biofilm in biocarriers as usual. Thus, development of aerobic nitrifying and anoxic denitrifying microorganisms facilitates nitrification and denitrification simultaneously within different zones of the same biofilm. The present paper summarizes the feasibility of nitrogen removal in MBBR systems via autotrophic nitrification followed by heterotrophic denitrification, including various aspects of simultaneous nitrification and denitrification (SND) process in other biofilm units as well. Apart from that, the areas for further investigation are briefly narrated from studies conducted earlier.