Upflow Anaerobic Sludge Blanket Research Articles

Integrated self-forming dynamic membrane (SFDM) and membrane-aerated biofilm reactor (MABR) system enhanced single-stage autotrophic nitrogen removal

The membrane aerated biofilm reactor (MABR) is a novel bioreactor technology, facilitating single-stage autotrophic nitrogen removal. Two laboratory-scale MABRs equipped with non-woven fabrics were operated simultaneously without and with a self-forming dynamic membrane (SFDM) filtration module. After 87 days of operation (system start-up), the reactor incorporated with SFDM filtration showed better performance in terms of total nitrogen removal (>80%) and effluent suspended solid (less than1 mg/L) than the MABR in the up flow anaerobic sludge blanket (UASB) configuration (i.e., without SFDM). The incorporation of SFDM has the ability to retain more slow growing biomass (anammox) inside the reactor. Microbial characterization by 16S rRNA-based amplicon sequencing shows that the abundance and composition of microbial communities in two MABR systems were different, i.e., the genusRhodanobacterwas abundant in UASB-MABR, while Calorithrixwas dominant in SFDM-MABR. PCA-based statistical analysis demonstrated a positive association between reactor performance, membrane characteristics and microbial communities.

Formation and characterization of conductive magnetite-embedded granules in upflow anaerobic sludge blanket reactor treating dairy wastewater

Promoting direct interspecies electron transfer (DIET) with conductive additives has proved effective in improving anaerobic digestion performance and stability. However, its application is limited by the need to replenish the washout loss of conductive materials. This study reports the formation of conductive magnetite-embedded granular sludge and its long-term influence on the performance of upflow anaerobic sludge blanket reactors treating dairy wastewater. The magnetite-supplemented reactor maintained better performance than the no-magnetite control, with greater sludge settling and electron transport activity, throughout the 192-d experiment at increasing organic loading rates (1.2–8.5 g chemical oxygen demand/L·d). The abundance of electroactive microbes also remained higher in the magnetite-supplemented reactor. The results suggest that DIET-based electric syntrophy was promoted in the magnetite-embedded granules. This study is the first to demonstrate the self-embedment of submicron conductive material into granular sludge and its benefits. These findings offer a new approach to enhancing anaerobic granular sludge systems.

Hydrogenotrophic methanogenic granular sludge formation for highly efficient transforming hydrogen to CH4

This paper presents a potential process that can enhance H2 transformation to CH4 and simultaneously upgrading biogas by using hydrogenotrophic methanogens. For the first time, anaerobic granules were developed in upflow anaerobic sludge blanket (UASB) reactor feeding H2/CO2 syngas as the sole substrate and the granule characterization was thoroughly investigated. The results from experiment revealed that the H2 consumption rates of UASB reactor increased from 32.2 mmol L−1·d−1 at H2 feeding rate 0.08 g L−1·d−1 to 132.0 mmol L−1·d−1 at 0.37 g L−1·d−1, indicating that the hydrogenotrophic methanogenesis pathway was stimulated by injection of H2. Abundant cavities and cracks were observed on the surface and cross-section of granules, which greatly facilitated internally transferring H2/CO2 synthesis gas and biogas escape. The abundance of hydrogenotrophic Methanobacterium increased, while Methanosaeta, Methanosarcina, and Methanomassiliicoccus decreased with increasing H2 feeding rate. In general, this paper offers a feasible solution in terms of energy transformation and connecting power to fuel.

Evaluating the resilience of a full-scale down-flow hanging sponge reactor to shock-loadings

Abstract The effect of shock-loading on the performance of a full-scale down-flow hanging sponge (DHS), used to treat effluent from an up-flow anaerobic sludge blanket treating municipal sewage, was evaluated. This full-scale DHS reactor comprises a polyurethane sponge that retains the sludge. It has a capacity of 500 m3/day and, at the time of this study, had been operating at a sewage treatment plant in India for more than 1,300 days. The DHS reactor was exposed to shock loadings of organics at double the normal rate for 400 min under summer and winter conditions. The results showed that the DHS reactor maintained stable operation under the organic shock loading and that it returned to a steady state soon after restart, confirming that the reactor was resilient to organic shock loadings.

Performance and Sustainability Assessment of Full-Scale Sewage Treatment Plants in Northern India Using Multiple-Criteria Decision-Making Methods

In this study, an intensive performance assessment of 36 sewage treatment plants (STPs) is carried out. The STPs were based on the process technologies: moving-bed bioreactor (MBBR), sequencing batch reactor (SBR), waste stabilization pond (WSP), and upflow anaerobic sludge blanket reactor (UASB) with posttreatment technologies of extended aeration (EA), surface aeration, and polishing ponds, with treatment capacities of 3 to 40 million L per day. The pollutant removal performance of the STPs was ranked using the gray relational analysis method, which revealed that the SBR systems ranked higher, followed by UASB with EA, whereas MBBRs, UASB with other posttreatment options, and WSP performed satisfactorily to poor. Further, the preference ranking organization method for enrichment evaluation (PROMETHEE) multiple-criteria decision-making (MCDM) approach using the fuzzy analytic hierarchy process followed by preference ranking organization method for enrichment evaluation method evaluated the major wastewater treatment technologies using three sustainability criteria: environmental, economic, and technical aspects. The MCDM method evaluation revealed that the UASB + EA method, with its lower greenhouse gas emissions, energy requirement, sludge generation, and energy and resource recovery characteristics, outranked other treatment technologies, followed by SBR. The MCDM results were later confirmed using geometrical analysis for the interactive aid method. Hence, this study summarizes that the anaerobic process followed by microaerobic technologies still possesses the capability to achieve stringent disposal standards almost equivalent to intensive aerobic technologies.

Prediction of effective substrate concentration and its impact on biogas production using Artificial Neural Networks in Hybrid Upflow anaerobic Sludge Blanket reactor for treating landfill leachate

In this study, a lab scale Hybrid Upflow Anaerobic Sludge Blanket reactor (HUASB) is used to treat landfill leachate at varying the Organic Loading Rates (OLRs) from 0.41 to 19.52 kg COD/ m3 d, over a period of 365 days. A three layer back propagation Artificial Neural Network (ANN) model was developed to assess the effective substrate concentration and maximum biogas yield. The proposed ANN model prediction accuracy was assessed based on the following factors, such as, Mean Square Error (MSE), Coefficient of Regression (R), Coefficient of determination (R2), Frictional Variances (FV) and Index of Agreement (IA). The results showed that OLR of 16.27 kg COD/ m3 d, is considered as an optimum. The highest biogas production of 30.07 L/d with methane content of 64% and COD removal of 89.6% is observed at this condition. In addition to this, the profile of alkalinity and Volatile Fatty Acid (VFA) supports the optimum OLR condition. The concentration of VFA shows fourfold increase from 710 to 2800 mg/L beyond optimum OLR. Further increasing the OLR beyond optimum conditions shows ineffective biogas yield and reactor operation. Similarly, the ratio between VFA/alkalinity reached critical limit, which indicates deterioration of reactor performance.

The contribution of tipping fees to the operation, maintenance, and management of fecal sludge treatment plants: The case of Ghana

Globally, collection of tipping fees is being promoted as a solution to sustain the operation of fecal sludge treatment plants (FSTPs). Currently, there are six large-scale FSTPs in Ghana, of which five were in operation in June 2017. In Kumasi, Sekondi-Takoradi and Tamale, fecal sludge (FS) is co-treated with landfill leachate using waste stabilization ponds (WSPs). In Tema and Accra, FS is treated using WSPs and a mechanical dewatering system coupled with an upflow anaerobic sludge blanket (UASB). The focus of this study is FSTPs and to assess how, and if, the tipping fees set by the municipalities could enable cost recovery to sustain their long-term operation. Using a questionnaire survey to interview plant managers from the public and private sectors, and directors of waste management departments, we found that the overall average operation, maintenance and management (OM&M) costs per 1000 m3 of treated waste (FS or FS + leachate) in 2017 were USD89 in Kumasi, USD150 in Tamale, USD179 in Tema, USD244 in Sekondi-Takoradi and USD1,743 in Accra. There were important disparities between FSTPs due to their scale, age, and level of treatment and monitoring. Currently, most FSTPs charge tipping fees that range between USD310 and USD530/1000 m3 of FS, averaging USD421 ± 98/1000 m3 of FS discharged at FSTPs. Our study also showed that the OM&M costs of large-scale intensive FSTPs cannot be sustained by relying solely on tipping fees. However, there could be potential to cover the routine expenditures associated with operating smaller FSTPs that relying on WSP technologies.

Potential mechanism of enhanced anaerobic degradation of high concentration phenol-containing wastewater by hazardous waste fly ash with high iron content: Direct interspecies electron transport pathway

Micron-grade high iron-containing fly ash (MHIFA)—a processed hazardous waste containing Fe3O4—was added to an up-flow anaerobic sludge blanket reactor to improve the removal performance of high concentration phenol-containing wastewater. The chemical oxygen demand and total phenol removal efficiency with MHIFA were 72.13% and 81.83%, respectively. Moreover, MHIFA addition increased the contents of coenzyme F420 and extracellular polymeric substances, as well as higher electron transport system activity in activated sludge. Additionally, microbial community analysis revealed that the total methanogens contents increased at genera level, producing an increase in methane production, while enriched Geobacter along with archaea Methanothrix might collaborate in direct interspecies electron transfer (DIET) by MHIFA stimulation, promoting the effect of phenolic compound fermentation. Finally, this technology allows for resource utilization of hazardous waste and enhances anaerobic degradation of toxic and refractory pollutants.

Impacts of granular activated carbon addition on anaerobic granulation in blackwater treatment

Upflow anaerobic sludge blanket (UASB) reactors, with or without granular activated carbon (GAC) amendment, were applied for blackwater treatment. The impact of GAC on the formation of granules and biomethane recovery was assessed. High organic loading rates (OLRs) up to 15.7 ± 2.1 kg COD/(m3d) were achieved with both reactors. Similar chemical oxygen demand (COD) removal and methane production rate were observed with OLRs ranging from 5.1 ± 1.0 to 9.3 ± 1.5 kg COD/(m3d). Under higher OLR conditions (13.6 ± 1.1 to 15.7 ± 2.1 kg COD/(m3d)), the GAC-amended UASB achieved a higher COD reduction than the UASB without GAC addition. Interestingly, volatile suspended solids (VSS) concentrations, granule size, and extracellular polymeric substance concentrations were lower in the GAC-amended UASB reactor as compared to the UASB without GAC. The methanogenesis activity of the granules in the GAC-amended UASB reactor was significantly higher than the methanogenesis activity of the UASB granules. The microbes o_Bacteroidales and Syntrophus were predominant in both reactors. The acetoclastic methanogens dominated in the UASB reactor without GAC addition; while hydrogenotrophic methanogens dominated in the GAC-UASB reactor. A phylogenetic investigation of communities by reconstruction of unobserved states (PICRUSt) indicated that syntrophic acetate oxidation improved with GAC addition. The co-occurrence network indicated that interactions between dominant bacteria and archaea were higher in the GAC-amended UASB reactor than in the UASB reactor without GAC addition. This study demonstrated the improved blackwater treatment performance as a result of granulation in UASB with the addition of GAC.

Two-phase anaerobic digestion of food waste: Effect of semi-continuous feeding on acidogenesis and methane production

In present investigation, effect of diverting acidogenic off-gas from leached bed reactor (LBR) to up-flow anaerobic sludge blanket (UASB) reactor during semi-continuous food waste (FW) anaerobic digestion was evaluated. In test LBR headspace pressure (3.3 psi) was maintained with intermittent headspace gas transfer into UASB. In control, same headspace pressure was maintained without gas transfer. The semi-continuous FW addition affected the characteristics and production of leachate in control and test LBR. The cumulative COD, total soluble products and methane yields were 1.26, 1.37 and 3 times higher in the test LBR than the control. The acetate and methane yields from test LBR were 697.8 g·kgVSadded−1 and 167.55 mL·gCOD−1feeding. Acidogenic gas transfer maintained low partial pressure of hydrogen and the hydrogen to carbon-di-oxide ratio in the headspace of LBR, which were thermodynamically favorable for microbial metabolism and concomitant high-rate production of acetate-rich volatile fatty acid and methane-rich biogas from FW.

Enhancement of Bioreactor Performance Using Acclimatised Seed Sludge in Anaerobic Treatment of Chicken Slaughterhouse Wastewater: Laboratory Achievement, Energy Recovery, and Its Commercial-Scale Potential.

Simple SummaryChicken slaughterhouses generate wastewater rich in organic contaminants and nutrients. Chicken slaughterhouse wastewater (CSWW) is considered high-strength wastewater, hence becoming a potential candidate for treatment processes that can recover energy. This study focused on the performance comparison of two sets of upflow anaerobic sludge blanket (UASB) reactors inoculated with different seed sludge treating CSWW. The reactor inoculated with seed sludge acclimatised on modified synthetic wastewater successfully produced a significant methane yield and removed chemical oxygen demand (COD) in the effluent, which complied with the discharge parameter set by the Department of Environment (DOE) Malaysia. At the optimum loading rate of bioreactor operation, energy recovery from laboratory scale (LS) and commercial scale (CS) systems were evaluated and proven to produce significant energy yield for wet market usage. Furthermore, a preliminary design of an on-site CS system was also proposed based on the actual daily volume of CSWW generated, output from process performance study, and existing design of the LS system.Lack of good management practice of chicken slaughterhouse wastewater (CSWW) has caused pollution into water bodies. In this study, the potential of seed sludge acclimatised modified synthetic wastewater (MSWW) on bioreactor performance and energy recovery of CSWW treatment was investigated. Two sets of upflow anaerobic sludge blanket (UASB) reactors were employed. The seed sludge in UASB 2 was acclimatised with MSWW for 30 days. In UASB 1, no acclimatisation process was undertaken on seed sludge for control purposes. After the acclimatisation process of UASB 2, both reactors were supplied with CSWW under the same condition of organic loading rate (OLR = 0.5 to 6 gCOD/L/d) and mesophilic condition (37 °C). COD removal efficiencies of UASB 2 were >80% all through the steady-state of the OLR applied. Meanwhile, a drastic decrease in overall performance was observed in UASB 1 when the OLR was increased to 3, 4, 5, and 6 gCOD/L/d. Energy recovery from laboratory scale and projected value from commercial-scale bioreactor were 0.056 kWh and 790.49 kWh per day, respectively. Preliminary design of an on-site commercial-scale anaerobic reactor was proposed at a capacity of 60 m3.

Quali-quantitative characterization of biogas with the temporal behavior of organic load on wastewater treatment plant with upflow anaerobic sludge blanket reactors through measurement in full‑scale systems

This study aims to present the time behavior of wastewater flow parameters, organic matter, biogas flow, biogas composition, and its relations, measured through online sensors, in a municipal wastewater treatment plant (WWTP) operating full-scale upflow anaerobic sludge blanket (UASB) reactors, installed in the south of Brazil. WWTP has online measurement devices to evaluate some physicochemical variables of the sewage and the biogas. The COD analyzer (UV– Vis probe), ultrasonic flow meter, biogas flow meter, and biogas composition analyzer were the equipment used. The monitoring occurred for two time periods each of 72 h and one time period for 48 h in the year 2018. Data were checked with descriptive statistics, data independence was checked through the autocorrelation Box– Ljung test, normality behavior was checked with several tests (Shapiro– Wilk, Kolmogorov–Smirnov, Lilliefors, Anderson–Darling, D’Agostino K2, and Chen–Shapiro), and Spearman’s correlation coefficient was used to evaluate the correlations among the parameters. The mean sewage flow was 345 ± 120 L.s-1; removed organic load was, in average, 48%; biogas quality values were 82.32% ± 3.62% v/v (CH4), 2.66% ± 1.19% v/v (CO2), and 3453 ± 1268 ppm (H2S); and the production per capita obtained was 4.51 ± 1.65 NL.hab-1.d-1. It was estimated an electric power generation of 3118.6 kWh.d-1, which is equivalent to an installed power of 130 KW. The behavior of removed organic load and biogas flow (Nm3.h-1), produced in the treatment plant, showed variable, periodic, and nonstationary time behavior.

Removal of denatured protein particles enhanced UASB treatment of oxytetracycline production wastewater

Enhanced hydrolysis, which can selectively destroy antibiotic potency, has been previously demonstrated to be an effective pretreatment technology for the biological treatment of antibiotic production wastewater. However, full-scale application of enhanced hydrolysis to the treatment of real oxytetracycline production wastewater showed that the up-flow anaerobic sludge blanket (UASB) reactors treating the pretreated wastewater could only be stable under a low organic loading rate (OLR) of 1.8 ± 0.4 g·COD/L/d. Deterioration of UASB was also confirmed in treating the same wastewater using a bench-scale reactor (R1) at an OLR of 4.4 ± 0.3 g·COD/L/d. Assuming that the particles formed due to the denaturation of soluble proteins under the hydrolysis temperature (110 °C), resulting in the significant increase of suspended solids (SS) in oxytetracycline production wastewater from less than 200 mg/L to 1200 ± 500 mg/L, were responsible for the deterioration of UASB, the pretreated wastewater was filtered using polypropylene cotton fiber and ultrafiltration membrane, and then fed into two parallel bench-scale UASB reactors (R2 and R3). Both reactors maintained a stable COD removal (53.2% ~ 61.1%) even at an OLR as high as 8.0 g·COD/L/d. When the feed of R3 was switched to unfiltered wastewater, however, deterioration of the reactor occurred again. Microscopic observation showed that the granules in R3 were fully covered by protein particles after the switch of the feed. It was possible that the tight layer of the denatured protein particles blocked the inner pores of the granules, resulting in the obstruction of substrate transfer and biogas emission, while removing the protein particles could abate such blockage problem. This study provides a scientific basis for the efficient treatment of antibiotic production wastewater.

Hydrodynamics of hybrid upflow anaerobic sludge blanket reactors using tracer studies

The hybrid upflow anaerobic sludge blanket reactor (HUASB) is a modified UASB wherein, inert media variants are used to prevent the biomass washout and its circular shape reduces biological and hydraulic dead zone. The flow pattern is crucial to facilitate hydraulic behavior as it has a direct effect on the microorganism-substrate utilization rate. So present study focuses on hydrodynamics of the HUASB reactors with different inert media viz. seashells (RA) and coconut husk fiber (RB). Tracer studies using a common dye (i.e. congo red) were performed in continuous mode for designed flow ranges from 600 to 1200 ml/hour to determine the hydrodynamic parameters and indices of mixing namely dispersion number (D/uL), peclet number (Pe), no. of reactors in series (N), morril dispersion index (MDI), index of short circuiting (Isc), index of mean retention time (Imean), index of modal retention time (Imodal) and index of average retention time (Iavg). The obtained results for both the reactors indicates the intermediate degree of dispersion seems to be best for max substrate conversion. According to the findings, both HUASB reactors is more closely to the arbitrary flow reactors.

Sequential Congo Red Elimination by UASB Reactor Coupled to Electrochemical Systems

Response surface methodology was investigated to determine the operational parameters on the degradation of Congo red dye (CR) and chemical oxygen demand (COD) in two electrochemical systems evaluated individually on effluent pretreated by an up-flow anaerobic sludge blanket (UASB) reactor. The UASB reactor was fed with 100 mg L−1 of CR and was operated for 12 weeks at different hydraulic residence times (HRTs) of 12 h, 10 h, and 8 h. Once stabilized at an HRT of 8 h, the effluent was collected, homogenized, and independently treated by electrooxidation (EO) and electrocoagulation (EC) cells. On both electrochemical systems, two electrode pairs were used; solid for EC (Fe and stainless-steel) and mesh electrodes for EO (Ti/PbO2 and Ti), and the effect of intensity (A), recirculation flow rate (mL min−1), and experimental time (min) was optimized on response variables. The maximum efficiencies of sequential systems for COD degradation and CR decolorization were 92.78% and 98.43% by EC and ≥99.84% and ≥99.71% by EO, respectively. Results indicate that the coupled systems can be used in textile industry wastewater treatment for the removal of dyes and the decolorized by-products.

Fates of intracellular and extracellular antibiotic resistance genes during the cattle farm wastewater treatment process

Cattle farm wastewater, as a significant reservoir for antibiotic resistance genes (ARGs), has received wide attention. Intracellular and extracellular ARGs (iARGs and eARGs) were detected during wastewater treatment, including solid–liquid separation, anaerobic regulation, upflow anaerobic sludge blanket (UASB) digestion, an anoxic–oxic-anoxic–oxic (A2O2) process, a membrane bioreactor (MBR), and ozone disinfection. Ten abundant ARGs were chosen as the target ARGs according to metagenomic sequencing. The concentrations of the total target iARGs and eARGs were 6.12 × 107 and 3.24 × 106 copy numbers/mL in raw wastewater, and then 3.79 × 103 and 3.95 × 105 copy numbers/mL in final effluent, because UASB, A2O2, MBR and ozone disinfection can gradually reduce the concentrations of most ARGs. The concentrations of ARGs were positively correlated with almost all wastewater quality indicators. Positive correlation was also observed between iARGs and Bacteroidetes, Firmicutes and Spirochaetes, indicating that the bacteria in these three phyla might be the main hosts of ARGs. Wastewater quality indicators and bacterial community composition affected the distribution and removal of ARGs during cattle wastewater treatment.

Assessing the effect of green tuff as a novel natural inorganic carrier on methane-producing activity of an anaerobic sludge microbiome

The upflow anaerobic sludge blanket (UASB) process is an anaerobic biological system that is widely used for the treatment of a variety of wastewater owing to its benefits such as low energy requirements and energy recovery as methane gas; however, unstable reactor performance is often observed. To solve this problem, several inert inorganic carriers and polymer materials have been studied for stabilization of the sludge microbial community and promotion of methane production. In this study, we demonstrate the effects of green tuff (GT) as a novel natural inorganic carrier on methane-producing activity (MPA) in combination with syntroph/methanogen-utilizable substrates and on the microbial community assembly of methanogenic batch cultures fed with granular sludge collected from UASB reactors treating milk- (MMW) or soy sauce- (SSW) manufacturing wastewater. The MPAs of MMW cultures with GT were 4.56- (propionate), 2.01- (n-butyrate), 1.37- (n-valerate), and 1.22- (benzoate) fold higher than those without GT. Likewise, SSW cultures with GT showed 1.34- (acetate) and 1.42- (propionate) fold higher MPA than those without GT. These results indicate that GT has potential to enhance MPAs during methanogenic degradation of these substrates. According to 16S rRNA transcripts-based community profiling, populations of syntrophic bacteria (Syntrophobacter and Smithella) and hydrogenotrophic methanogens (Methanobacterium and Methanolinea) in the cultures with GT were higher than in those without GT. Therefore, GT can be a potential solution for the activation of syntrophic partnerships and improvement/stabilization of reactor performance.

Mathematical modeling of methane production and sulfate reduction in upflow anaerobic sludge blanket reactors: Calibration, validation and prediction of reciprocal effects

Mathematical models are important tools for understanding and optimizing the performance of biotechnological processes. A user-friendly mathematical model is developed to simulate the sulfate reduction and methanogenesis of upflow anaerobic sludge blanket reactors. The good fit between the simulated and experimental concentrations reflects the model’s capability in simulating reactor performance when there are variations in operational conditions. The model with optimized parameters is used to quantitatively and systematically account for the interaction of influent organic loading rate and the ratio of organic to sulfate, influent chemical oxygen demand and sulfate concentrations, and influent organic composition and chemical oxygen demand concentration. The interaction between the OLR (3 ∼ 72 g-COD/L/d) and C/S ratio (0.5 ∼ 20) greatly influenced the ethanol concentration, yield ratio of methane and sulfate concentration. The removal of sulfate in the reactor was more influenced by the C/S ratio than the OLR. It provides a theoretical basis for reactor process optimization and control and greatly saves time required for experimental investigations. • The reaction of MPA and SRB in UASB were simulated by a user-friendly model. • Calibration and validation were thoroughly carried out using experimental studies. • The reciprocal effects of conditions were quantitatively predicted by the simulation. • The competition or cooperation relations between MPA and SRB were explained.

Fast start-up and reactivation of anammox process using polyurethane sponge

Anammox is a novel and efficient nitrogen removal technique, while the long start-up time limits its industrial application, thus carriers are always utilized to accelerate its start-ups. Meanwhile, the preservation of anammox bacteria is a key element in its application. Therefore, it is also quite significant to evaluate the effect of carriers in reactivation of the anammox process after preservation. Through addition of polyurethane sponge in the upflow anaerobic sludge blanket (UASB) reactor (R1), comparing with the one without polyurethane sponge addition (R2), the time for anammox start-up was shorten by 28%, and the reactivation time was reduced by 50%. The preservation in 4 ℃ did not significantly affect the survival of anammox bacteria, but significantly decreased their nitrogen removal rate (NRR). Moreover, during the preservation, the decomposed EPS in R1 (44%) was less compared to that in R2 (66%). It took 36 days for R1 to recover the NRR (0.084 kg·N·m-3·d-1), but took 60 days for R2. At the end of reactivation, the abundance of Candidatus (Ca.) Brocadia and Ca. Kuenenia (both are anammox bacteria) was 4.5% and 2.7%, respectively, in R1, whereas there was no identified Ca. Kuenenia and the Ca. Brocadia was only 0.2% in R2. Therefore, the addition of polyurethane sponge could short the start-up and reactivation time for anammox process by retaining more anammox bacteria in the reactor.

Calcium hypochlorite pretreatment improves thermophilic digestion of waste activated sludge in an upflow anaerobic sludge blanket reactor

Anaerobic wasted activated sludge (WAS) digestion has been widely applied to reduce sludge volume and generate bioenergy in the form of methane. However, anaerobic WAS digestion performance is often challenged with poor hydrolysis of biomass cellular structures. In the present study, the feasibility of using calcium hypochlorite (Ca(ClO)2) to improve the thermophilic digestion of WAS was studied. Two thermophilic upflow anaerobic sludge bed (UASB) reactors (one with and one without Ca(ClO)2 pretreatment) were operated for 120 days under low and high organic loading rate (OLR) conditions, corresponding hydraulic retention time (HRT) of 10 days and 6 days, respectively. Both reactors achieved satisfied performance during the studied period. Under the low OLR condition, Ca(ClO)2 pretreatment significantly improved WAS total volatile solids (VS) removal efficiency (from 48.06 ± 2.63% to 57.34 ± 3.54%) and methane yield (from 289.2 ± 27.6 to 362.2 ± 36.7 N mL/g VS). However, no significant improvement was observed under the high OLR condition. g_S1 and g_Fervidobacterium were predominant bacteria in the thermophilic UASB reactor fed with Ca(ClO)2 pretreated WAS. Methanosarcina was dominant archaea in both reactors. The treatment mechanism and application potential of using Ca(ClO)2 to enhance the WAS digestibility were further discussed.