Activated Sludge Sequencing Batch Reactor Research Articles

Comparative evaluation of activated sludge and aerobic granular sludge for biological treatment of real domestic wastewater with oxytetracycline dosing

Aerobic granular sludge technology is an emerging choice for effective and sustainable wastewater treatment. The aim of this study was to determine the effect of antibiotics such as oxytetracycline on biological nutrient removal pathways in aerobic granular sludge and activated sludge sequencing batch reactors treating real domestic wastewater. The aerobic granular sludge and activated sludge reactors were operated in parallel for evaluating treatment of domestic wastewater and its response to 50–300 µg/L oxytetracycline dosing. The aerobic granular sludge and activated sludge sequencing batch reactors were dominated by compact granules (sludge volume index (SVI): 60 mL/g) and flocs (SVI: >100 mL/g), respectively, during treatment of real wastewater. Aerobic granular sludge has significantly outperformed activated sludge in achieving high phosphate removal of ∼99% against just 57%. This was corroborated with higher abundance of polyphosphate accumulating organisms and enhanced bio-P removal in the aerobic granular sludge system. In contrast, phosphate removal was achieved through normal bio-P removal in the activated sludge reactor. Oxytetracycline removals were distinct at 90% and 23%, respectively, in the aerobic granular sludge and activated sludge systems. High total nitrogen and phosphate removals of 97% and 96%, respectively, were maintained in the aerobic granular sludge system even during OTC dosing. In contrast, the total nitrogen and phosphate removals have dropped to 78% and 16%, respectively, in the activated sludge system due to oxytetracycline stress. Efficient biological nutrient removal and process stability along with environmental sustainability are critical for choosing aerobic granular sludge technology in wastewater treatment plants.

Combination of sequencing batch reactor activated sludge process with sludge lysis using thermophilic bacterial community for minimizing excess sludge

Sludge reduction is a major challenge in biological wastewater treatment. Hydrolytic enzymes secreted by thermophilic bacteria can lyse sludge and thus achieve sludge reduction, and the indigenous thermophilic community in sludge can lyse sludge more effectively. In this study, the feasibility of combining a sludge lysis reactor based on thermophilic bacteria community (LTBC reactor, 75 °C) with a conventional sequencing batch activated sludge reactor (SBR) for sludge reduction (i.e., LTBC-SBR process) was systematically investigated first time. The effect of lysed sludge returning to the biochemical tank on pollutant removal efficiency, sludge flocculation, sludge settling, and microbial community and function of the LTBC-SBR process was studied. In the LTBC1-SBR process, a sludge growth rate of 0.71 g TSS/day was observed when the lysed sludge reflux ratio (LRR) was 1, and the sludge generation was reduced by 81.5% compared to the conventional SBR reactor. In the LTBC1-SBR process, the removal efficiencies of chemical oxygen demand and total nitrogen were 94.0% and 80.5%, respectively. There was no significant difference in the sludge volume index from the SBR to the LTBC1-SBR stage, however, the effluent suspended solids concentration increased from 35.2 ± 2.1 mg/L to 80.1 ± 5.3 mg/L. This was attributed to the reflux of sludge lysate. In addition, the changes in extracellular polymers content and composition resulted in poor sludge flocculation performance. Heterotrophic bacteria associated with Actinobacteria and Patescibacteria enriched in LTBC1-SBR with relative abundance of 28.51 ± 1.25% and 20.01 ± 1.21%, respectively, which decomposed the macromolecules in the refluxed lysed sludge and contributed to the sludge reduction. Furthermore, due to the inhibition of nitrite-oxidizing bacteria, the nitrite concentration in the effluent of the LTBC1-SBR system reached 4.7 ± 1.1 mg/L, and part of the denitrification process was achieved by short-cut nitrification and simultaneous denitrification. These results indicate that in-situ sludge reduction technology based on lyse sludge lysing by thermophilic community has considerable potential to be widely used in wastewater treatment.

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.

Study on the Efficacy of Polyethylene Filled SBMBBR Process for Treating Low Temperature Municipal Wastewater

To tackle the hassle of low efficiency of low temperature denitrification in wintry weather in northern region,Sequencing Batch Moving Bed Biofilm Reactor (SBMBBR) used to be used for deep treatment of low temperature municipal wastewater and polyethylene fillers have been compared. The outcomes confirmed that the Sequencing Batch Activated Sludge Reactor (SBR) used to be started correctly at 64 d beneath the prerequisites of water temperature 9-12 °C,pH 7-8 and HRT of 48 h,and two polyethylene fillers had vast biofilm after 7 d operation,and the elimination rates of COD,Ammonia Nitrogen and TP in polyethylene K3 fillers have been stabilized at 83.6%,74.4% and 60.8% respectively as the quality fillers after 24 d operation. After optimizing the process parameters,the steady effluent evaluation effect used to be determined for 27 d operation beneath the most advantageous anoxic (3 h) and aerobic time (7 h) modes of the reactor,and the corresponding elimination quotes of COD and Ammonia Nitrogen were 87.7% and 93.5%,respectively,and the corresponding average effluent concentrations had been 44.4 mg/L and 1.9 mg/L,which reached the Pollutant Discharge Standard for Urban Sewage Treatment Plants (GB 18918-2002). Two vital factors,Dissolved Oxygen (DO) concentration and Hydraulic retention time (HRT) in the aerobic part were studied,and the great HRT of 82 h was once performed in the biointensive domestication SBR machine under the stipulations of the foremost vary of DO attention of 6.0-7.5 mg/L in the aerobic part at low water temperature.

Properties of alginate-like exopolymers recovered from flocculent and granular microbial sludges of different biological treatment systems treating real municipal wastewater

Treatment of excess microbial sludge and its safe disposal is a major challenge in wastewater treatment plants (WWTPs) due to pathogens, economic and regulatory issues. There is a considerable interest in developing newer technologies for the excess sludge treatment and recovering value-added products. This study investigated recovery of biopolymers from the microbial sludge generated in three different biological treatment systems such as conventional activated sludge process (ASP), activated sludge sequencing batch reactor (AS-SBR) and aerobic granular sludge SBR (AGS-SBR). Alginate-like exopolymer (ALE) was the dominant biopolymer in AS and AGS irrespective of the employed treatment system. ALE content was determined to be 32%, 39% and 44% in the microbial sludge of ASP, AS-SBR and AGS-SBR, respectively. ALE extraction markedly decreased the biosolids content by up to 54%. ALE recovered from AS harvested from ASP had poor gelation properties and did not form beads with calcium. Whereas, the ALE recovered from AS and AGS from the SBRs exhibited gelation properties and formed nice beads with calcium ions. The biopolymer recovered from the microbial sludge developed in the SBRs contained high guluronic (G) acid in the form of poly-guluronic acid (GG) blocks, responsible for excellent gelation property. Extraction of biopolymers mitigates sludge management challenges, pathogens-spread and improves resource recovery in WWTPs.

Effects of bioaugmentation on the performance of industrial-scale activated sludge sequencing batch reactor under load shock of heavy oil refinery wastewater

The stable and efficient operation of the cyclic activated sludge sequencing batch reactor (CASSBR) in heavy oil refineries has become an urgent necessity in wastewater biotreatment. Here, the present study focuses on the selection of inoculated strains, the optimization of process parameters, and the effects of bioaugmentation on the performance in CASSBR under the different rates of heavy oil refinery wastewater shock loading. Results showed that the shock resistance of the CASSBR gradually enhanced and the normal performance was restored in a short time by the addition of a 0.1% biofortifier, and the average removal efficiency of chemical oxygen demand and total nitrogen reached 86% and 55% within 15 days, respectively. The recovery time of the reactor was shortened to 6 days by bioaugmentation measures. This study not only presents a detailed case on the ecological trade-off of the bioreactor and pollutant removal of inoculated strains during bioaugmentation, but also provides a theoretical basis and technical support for evaluating the effects of heavy oil refinery wastewater shock loading on biological wastewater treatment systems.

Ammonia-Nitrogen Reduction in Low Strength Domestic Wastewater by Polyvinyl Alcohol (PVA) Gel Beads

This study aimed to evaluate the efficacy of polyvinyl alcohol (PVA) gel beads as an immobilized biofilm carrier to enhance the reduction rate of Ammonia-Nitrogen (NH3-N) and Chemical Oxygen Demand (COD) in domestic wastewater. Laboratory scale reactors were developed to assess the reduction levels of ammonia-nitrogen and COD with and without PVA gel beads using optimal and non-optimal treatment mode settings based on operation procedures from the sewage treatment plant in Taman Kajang Utama, Selangor. The treatment method used is an activated sludge sequencing batch reactor with a treatment cycle duration of 288 minutes. The findings showed the ammonia-nitrogen reduction by non-optimal treatment mode is more effective, with a reduced rate of 62.96% to 65.71% compared to optimal treatment mode with a reduced rate of 30.94% and treatment without PVA gel beads (optimal and non-optimal) with a reduced rate of 32.41% to 47.85%. The ammonia-nitrogen reduction rate using PVA gel beads for non-optimal treatment mode was significantly increased from 17.86% to 18.82% and complied with ammonia-nitrogen reduction parameter 10mg/L, Standard A of Environmental Quality (Sewage) Regulations 2009 (EQSR 2009). The rate of COD reduction using the non-optimal treatment mode was also more stable, with a reduced rate of 70.68%. It was also found that the COD reduction rate using PVA gel beads for the non-optimal mode was better than the optimal mode, which was 70.68% compared to 42.0%, and both treatment modes complied with COD reduction parameters 120mg/L, Standard A of EQSR 2009.

Structural effects of sulfonamides on the proliferation dynamics of sulfonamide resistance genes in the sequencing batch reactors and the mechanism

Antibiotic resistance genes (ARGs) can be easily promoted by antibiotics, however, the structural effects of antibiotics on the proliferation of ARGs dynamic and the associated mechanisms remain obscure in, especially, activated sludge sequencing batch reactors. In the present study, the effects of 9 sulfonamides (SAs) with different structures on the proliferation dynamic of sulfonamide resistance genes (Suls) in the activated sludge sequencing batch reactors and the corresponding mechanisms were determined (30 days), and the results showed that the largest proliferation value (∆AR) of Suls dynamic for SAs (sulfachloropyridazine) was approximately 2.9 times than that of the smallest one (sulfadiazine). The proliferation of Suls was significantly related to the structural features (minHBint6, SssNH, SHBd and SpMax2_Bhm) that represent the biological activity of SAs. To interpret the phenomenon, a mechanistic model was developed and the results indicated that the biodegradation of SAs (T1/2) rather than conjugative transfer frequency or mutation frequency tends to be the key process for affecting Suls proliferation. T1/2 was proved to be dependent on the interactions between SAs and receptors (Ebinding), the cleavage mode (bond dissociation energy), and the site of nucleophilic assault. Besides, the metagenomic analysis showed that SAs posed significant effect on antibiotic resistome and Tnp31 played a vital role in the proliferation of Suls. Overall, our findings provide important insight into a theoretical basis for understanding the structural effects of SAs on the proliferation of ARGs in SBR systems.

The Impact of Bioaugmentation on the Performance and Microbial Community Dynamics of an Industrial-Scale Activated Sludge Sequencing Batch Reactor under Various Loading Shocks of Heavy Oil Refinery Wastewater

The stable and efficient operation of the activated sludge sequencing batch reactor (ASSBR) in heavy oil refineries has become an urgent necessity in wastewater biotreatment. Hence, we constructed a green and efficient solid bioaugmentation agent (SBA) to enhance the resistance of the reactor to loading shock. The impact of bioaugmentation on the performance and microbial community dynamics under three patterns of heavy oil refinery wastewater (HORW) loading shock (higher COD, higher toxicity, and higher flow rate) was investigated on an industrial-scale ASSBR. Results showed that the optimal SBA formulation was a ratio and addition of mixed bacteria Bacillus subtillis and Brucella sp., of 3:1 and 3.0%, respectively, and a glucose concentration of 5.0 mg/L. The shock resistance of ASSBR was gradually enhanced and normal performance was restored within 6–7 days by the addition of 0.2% SBA. Additionally, the removal efficiency of chemical oxygen demand and total nitrogen reached 86% and 55%, respectively. Furthermore, we found that Burkholderiaceae (12.9%) was replaced by Pseudomonadaceae (17.1%) in wastewater, and Lachnospiraceae (25.4%) in activated sludge was replaced by Prevotellaceae (35.3%), indicating that the impact of different shocks effectively accelerated the evolution of microbial communities and formed their own unique dominant bacterial families.

The influence of aeration control and temperature reduction on nitrogen removal and microbial community in two anammox‐based hybrid sequencing batch biofilm reactors

AbstractBACKGROUNDTwo hybrid biofilm reactors, an integrated fixed‐film activated sludge–sequencing batch reactor (IFAS‐SBR) and a hybrid SBR with a mixture of activated sludge and granules, were used to reach enhanced nitrogen removal based on the anaerobic ammonium oxidation (anammox) process under intermittent aeration.RESULTSIFAS‐SBR reached a more stable performance after a rapid start‐up period of 25 days, and it showed a more reliable performance than the other reactor. The highest nitrogen removal efficiency (NRE) was up to 99% based on NH4+‐N concentration and 91% based on total nitrogen concentration (TIN). A nitrogen removal rate of 0.01 to 0.15 kgN m−3 d−1 was achieved throughout the operation based on the TIN. The set‐point of maximum dissolved oxygen (DO) at the peak of each aeration cycle was maintained at 1.2 ± 0.1 mg L−1. The optimum working range for daily average DO concentration was 0.2–0.7 mg L−1. Cold temperatures caused a decline of NRE, but NRE > 50% for temperatures above 13 °C was achieved.CONCLUSIONSResults implied a higher abundance of Candidatus brocadia species of anammox bacteria in the biofilm samples and Denitratisoma genus in the flocs. The most substantial contribution of shared taxa among all samples at class level was Betaproteobacteria and Gammaproteobacteria, and the least abundant class was Nitrospira. Overall, results implied that IFAS‐SBR is a robust configuration for anammox‐based nitrogen removal in sidestream, and controlled intermittent aeration could suppress nitrite oxidation and help to regain system efficiency.

Advanced nitrogen removal from low C/N municipal wastewater by combining partial nitrification-anammox and endogenous partial denitrification-anammox (PN/A-EPD/A) process in a single-stage reactor

In this study, an innovative partial nitrification-anammox (PN/A) and endogenous partial denitrification-anammox (EPD/A) process was developed in a single-stage integrated fixed film activated sludge sequencing batch reactor (IFAS-SBR) treating real municipal wastewater with C/N ratio below 3.2. Enhanced efficiency of total nitrogen (TN) removal reached 90.1% with low HRT of 12 h and DO of 0.4 ± 0.1 mg/L. Detailed nitrogen removal mechanism analysis of typical cycle revealed that 89.9% of TN was eliminated through anammox pathway. Anammox bacteria (Candidatus Brocadia) and endogenous denitrifying bacteria (Candidatus Competibacter) were abundant both in biofilms and suspended sludge, meanwhile ammonium-oxidizing bacteria has outcompeted nitrite-oxidizing bacteria, which all favored the synergistic effect of anammox with PN and EPD and contributed to the improvement of nitrogen removal. Overall, the above results confirmed that combined PN/A and EPD/A process is a reliable and efficient alternative for mainstream anammox process.

The effect of the COD: N ratio on mainstream deammonification in an integrated fixed-film activated sludge sequencing batch reactor

For eight months, a sequencing batch reactor (SBR) with integrated fixed-film activated sludge (IFAS) was operated in ambient temperature to study engineering and practical aspects of application of deammonification for mainstream conditions. For biofilm formation, K3 Kaldnes carriers were used, where the anaerobic ammonium oxidation (anammox) process can occur in deep layers of biofilm, while partial nitritation occurs in oxygen-rich outer layers. After the initial running phase of the reactor (Phase 1) to provide time for microorganisms to adapt, the COD: N ratio increased to around 2.6 in Phase 2 through reducing the ammonium concentration and increasing COD in synthetic wastewater to get closer to mainstream conditions. The total reaction time in each half-day batch cycle was kept 625 min throughout various phases, but the duration of intermittent aeration was regulated at 4 ± 1 min. While final nitrogen removal efficiency (NRE) for Phase 1 was 43%, at the end of Phase 2, it decreased to 37%. However, a maximum NRE at 90% was achieved during Phase 2. The identification of the responsible microorganisms was made through Fluorescence in situ hybridization (FISH), while Mixed Liquor Suspended Solid (MLSS) and Mixed Liquor Volatile Suspended Solid (MLVSS) was used to estimate the physical presence of bacteria. Ammonium oxidizing bacteria (AOB) and anaerobic ammonia-oxidizing bacteria (AnAOB) were dominant bacteria, respectively. The adverse effects of a gradual increase of COD: N ratio from 0.17 to more than 2.0 caused a decline in NRE to around 15%.

Effect of ozonation as pre-treatment and polishing step on removal of ecotoxicity and alkylphenol ethoxylates from tank truck cleaning wastewater

Wastewater originating from tank truck cleaning (TTC) industry is reputed for its large variability and may lead to emission of recalcitrant and ecotoxic substances in discharge waters. In this study, TTC wastewater was biologically treated in two lab-scale activated sludge sequencing batch reactors. Two strategies were used, (1) influent pre-treatment with ozone followed by activated sludge treatment and (2) activated sludge treatment followed by polishing with ozone. Effluent soluble chemical oxygen demand (sCOD), ecotoxicity and the 4-nonylphenol (NP) concentration were used to evaluate and compare both strategies. Experiments were conducted for two different TTC companies using the same set-up. For Company 1, a decrease in ecotoxicity of 80 % was observed for algal growth inhibition and 10 % for Daphnia immobilization when using effluent polishing compared to pre-treatment. Hereby the NP concentration decreased below discharge limits (0.3 ng.mL−1). For Company 2 the ecotoxic effect in the algal growth inhibition test increased to 100 % when conducting effluent polishing, while ecotoxicity for the original effluent and the effluent from the pre-treated system were similar. sCOD did not decrease significantly and the discharge limit of NP was only met for one sample. Extended (7 h) effluent ozone polishing tests were conducted at two pH setpoints to assess the impact of radical formation during ozone treatment. In general, it was observed that ozone as a pre-treatment step had no significant influence on ecotoxicity and COD removal. Effluent polishing can improve ecotoxicity and effluent characteristics, despite the dependence on wastewater composition, as toxic side products may be produced.

Advanced biological sequential treatment of mature landfill leachate using aerobic activated sludge SBR and fungal bioreactor.

This study utilized Penicillium spp. to treat mature landfill leachate (MLL) in a continuous bioreactor and batch experimental tests under non-sterile conditions. MLL characteristics such as chemical oxygen demand (COD), soluble COD (sCOD), total carbon (TC), total organic carbon (TOC), and color removal efficiency were determined. The lignocellulosic enzymatic activity of laccase (Lac), lignin-peroxidase (LiP), and manganese-peroxidase (MnP) was also determined. The batch experimental test was carried out with raw and pretreated MLL containing the initial NH4 +-N concentrations of 0, 105, 352, and 914mg/L. A maximum COD reduction of 41% and maximum enzymatic activity of 193, 37, and 25U/L for Lac, LiP and MnP was recorded for the MLL containing 352mg/L NH4 +-N. The continuous bioreactor exhibited maximum values of 52, 54, 60, 58, and 75 percentage of COD, sCOD, TC, TOC, and color removal efficiency with MLL containing 352mg/L NH4 +-N that was pretreated at HRT 120h, while the maximum detected lignocellulosic enzymatic activities were 149, 27, and 16U/L for Lac, LiP, and MnP, respectively. A total of 64% COD reduction was achieved from the raw MLL considering 12% COD and 100% NH4 +-N reduction in the aerobic activated sludge sequencing batch reactor pretreatment process. The steady and higher removal efficiency of the bioreactor over the entire study period is promising for further exploration to enhance removal of refractory contaminants from the MLL.

Parametric optimization of domestic wastewater treatment in an activated sludge sequencing batch reactor using response surface methodology

In this work, the parametric optimization of real domestic wastewater treated in an activated sludge sequencing batch reactor (SBR) was performed by means of the response surface methodology (RSM). The influences of influent organic matter concentration as chemical oxygen demand (CODinf), biomass concentration (Xs) and aeration time (t) on the COD, organic matter removal efficiency as COD (η) and sludge volume index (SVI) were determined to evaluate the performance of activated sludge SBR. The results showed that organic matter efficiency and maximum SVI were obtained at a t of 12 h, 300 mg L−1 of CODinf and 2000 mg L−1 of Xs. The SBR-activated sludge exhibited a η of 73% and an SVI of 119 mL g−1. Both values indicated a very good performance. Furthermore, the COD of the effluent under these conditions complied with Mexican regulations for wastewater discharged into water bodies.

Diversity evolution of functional bacteria and resistance genes (CzcA) in aerobic activated sludge under Cd(II) stress

An activated sludge sequencing batch reactor (SBR) was used to treat divalent cadmium (Cd(II)) wastewater for 60 d to investigate the overall treatment performance, evolution of the bacterial community, and abundance of the Cd(II) resistance gene CzcA and shifts in its potential host bacteria. During stable operation with a Cd(II) concentration of 20 mg/L, the average removal efficiencies of Cd(II) and chemical oxygen demand (COD) were more than 85% and that of total phosphorus was greater than 70%, while the total nitrogen (TN) was only about 45%. The protein (PN) content in the extracellular polymeric substances (EPS) increased significantly after Cd(II) addition, while polysaccharides displayed a decreasing trend (p < 0.05), indicating that EPS prefer to release PN to adsorb Cd(II) and protect bacteria from damage. Three-dimensional fluorescence spectral analysis showed that fulvic acid-like substances were the most abundant chemical components of EPS. The addition of Cd(II) adversely affected most denitrifying bacteria (p < 0.05), which is consistent with the low TN removal. In addition, quantitative polymerase chain reaction analysis revealed that CzcA gene abundance decreased as the Cd(II) concentration increased, possibly because expression of the CzcA gene was inhibited by Cd(II) stress. The majority of CzcA gene sequences were carried by Pseudomonas, making it the dominant genus among Cd(II)-resistant bacteria.

Improving nitrogen removal in an IFAS nitritation–anammox reactor treating lagoon supernatant by manipulating biocarrier filling ratio and hydraulic retention time

A lab-scale integrated fixed-film activated sludge sequencing batch reactor (IFAS-SBR) was established for a one-stage nitritation–anammox process treating lagoon supernatant and optimized by altering both the biocarrier filling ratio and HRT for 500 days. The reactor’s nitrogen removal rate increased slightly from 0.25 kg N m−3 d−1 to 0.29 kg N m−3 d−1 when biocarrier filling ratio was increased from 35% to 55% at a HRT of 2.5 d, and further increased to 0.46 kg N m−3 d−1 and 0.54 kg N m−3 d−1 when the HRT was reduced to 1.5 d and 1.2 d, respectively. Meanwhile, both NH4+N and TN removal efficiencies increased from 81.8% and 74.8% to 95.2% and 87.4%, respectively, with the increased biocarrier filling ratio; however, they decreased slightly to 91.8% and 82.1% at HRT of 1.5 d and to 89.6% and 78.8% at HRT of 1.2 d, respectively. A distinct segregation of anammox bacteria and ammonium oxidizing bacteria (AOB) was achieved in the IFAS system and was highlighted by the decreased HRTs, which also contributed to the excellent nitrogen removal. The specific anammox activity was higher in biofilm than in suspended flocs, and vice versafor the specific AOB activity. The abundance of major microbial communities involved in this process were analyzed, which supported the observation of reactor performance changes. The present study provides critical knowledge for optimizing the one-stage IFAS nitritation–anammox reactor treating supernatant of anaerobically digested sludge thicken lagoon.

Anammox reactor optimization for the treatment of ammonium rich digestate lagoon supernatant - Step feeding mitigates nitrite inhibition

A laboratory-scale anammox integrated fixed-biofilm activated sludge sequencing batch reactor (IFAS-SBR) was operated for 339 days as the post treatment of a nitritation reactor treating ammonium rich digestate lagoon supernatant. By shortening the hydraulic retention time (HRT) from 2.5 d to 1.7 d, the inorganic nitrogen (N) loading rate increased from 0.38 ± 0.00 kg m3 d−1 to 0.61 ± 0.02 kg m−3 d−1; this led to a slight enhancement in the anammox activity. While the activity of anammox bacteria was inhibited by the interim accumulation of NO2−-N (141.2 – 219.2 mg L−1) in the reactor when the HRT was further reduced to 1.2 d, changing the reactor feeding strategy mitigated the nitrite inhibition and restored anammox activity. The presence of organic carbon in lagoon supernatant facilitated the growth of heterotrophic denitrifiers in the reactor; however, this had little impact on N reduction (93.2 ± 3.8% by anammox). Additional batch experiments and sequencing batch reactor cycle tests compared anammox bacterial specific activities under different operating strategies. The dynamics of anammox bacteria and heterotrophic denitrifiers along with the operating strategy changes were documented by qPCR analyses. Our study underlines the importance of optimizing operating strategies within anammox reactor operation for treating ammonia rich digestate lagoon supernatant.

Chemical composition of extracellular polymeric substances and evolution of microbial community in activated sludge exposed to ibuprofen

Ibuprofen (IBU) containing wastewater with a concentration of 1-5 mg/L was treated in an activated sludge sequencing batch reactor (SBR), for 60 days, in order to investigate the overall performance of the SBR, the parameter variations during a typical cycle, the chemical composition and content of extracellular polymeric substances (EPS) and the evolution of microbial community. The average removal efficiencies of COD, NH4+-N and TN were >85%, while >40% of the IBU was removed and the removal efficiencies of TP fluctuated around ~ 75%. The EPS content increased significantly with IBU addition (p < 0.01). Fulvic acid-like substances in the chemical composition of EPS increased during the stable operation phase. Proteobacteria associated with nitrogen removal was the dominant phylum, which can also resist IBU stress. For the denitrifying bacteria, the OTUs of both Rhodobacter and Pseudomonas increased from day 1-30 and reduced on day 60 (p < 0.01), which was opposite to the results observed for Rhodocyclaceae (phosphorus-accumulating bacteria). The OTUs of Acidovorax showed an increasing trend (p < 0.01), whereas the OTUs for Nitrospira (nitrite oxidizers) and Nitrosomonas (ammonia oxidizers) decreased significantly (p < 0.05).

Effect of silver nanoparticles on an integrated fixed-film activated sludge–sequencing batch reactor: Performance and community structure

The effects of silver nanoparticles (AgNPs) on reactor performance, extracellular polymeric substances composition and microbial community structure and function in integrated fixed-film activated sludge–sequencing batch reactors (IFAS–SBRs) were investigated. Results showed that the addition of AgNPs from 0.1 to 10 mg/L exhibited no significant effects on nutrient removal. The average overall removal of COD, NH4+–N and PO43−–P was 96.6%, 99.9% and 98.8%, respectively. The introduction of AgNPs caused an increase in extracellular polymeric substances content for the sludge and biofilm of IFAS–SBRs. The release of Ag+ from AgNPs and lactate dehydrogenase test implied the low toxicity of AgNPs to IFAS–SBRs. High-throughput sequencing revealed that microbial community structure showed significant shifts at phylum and genus levels after long-term exposure to AgNPs, but core functional groups responsible for nutrient removal remained at high abundance. Bacterial function prediction indicated that the metabolic categories showed no significant shifts under AgNPs stress, therefore good process performance could still be achieved.