Treatment Of Low-strength Wastewater Research Articles

Nitrogen removal performance and microbial community of an enhanced multistage A/O biofilm reactor treating low-strength domestic wastewater.

The low-strength domestic wastewater (LSDW) treatment with low chemical oxygen demand (COD) has drawn extensive attention for the poor total nitrogen (TN) removal performance. In the present study, an enhanced multistage anoxic/oxic (A/O) biofilm reactor was designed to improve the TN removal performance of the LSDW treatment. Efficient nitrifying and denitrifying biofilm carriers were cultivated and then filled into the enhanced biofilm reactor as the sole microbial source. Step-feed strategy and internal recycle were adopted to optimize the substrate distribution and the organics utilization. Key operational parameters were optimized to obtain the best nitrogen and organics removal efficiencies. A hydraulic retention time of 8h, an influent distribution ratio of 2:1 and an internal recycle ratio of 200% were tested as the optimum parameters. The ammonium, TN and COD removal efficiencies under the optimal operational parameters separately achieved 99.75 ± 0.21, 59.51 ± 1.95 and 85.06 ± 0.79% with an organic loading rate at around 0.36kg COD/m3d. The high-throughput sequencing technology confirmed that nitrifying and denitrifying biofilm could maintain functional bacteria in the system during long-period operation. Proteobacteria and Bacteroidetes were the dominant phyla in all the nitrifying and denitrifying biofilm samples. Nitrosomonadaceae_uncultured and Nitrospira sp. stably existed in nitrifying biofilm as the main nitrifiers, while several heterotrophic genera, such as Thauera sp. and Flavobacterium sp., acted as potential genera responsible for TN removal in denitrifying biofilm. These findings suggested that the enhanced biofilm reactor could be a promising route for the treatment of LSDW with a low COD level.

Influence of conductive material on the bioelectrochemical removal of organic matter and nitrogen from low strength wastewater

The treatment of low strength wastewater that has the level of discharge standard for wastewater treatment plant was studied using an upflow bioelectrochemical reactor with an applied voltage of 0.6 V. The direct interspecies electron transfer (DIET) between electroactive bacteria was activated in the upflow bioelectrochemical reactor, which improved the substrate affinity of bacteria. The effluent qualities in COD and ammonia nitrogen was stable at less than 3.5 mg/L and 7.46 mg/L at 1 h of hydraulic retention time, respectively. The conductive materials, including conductive sheets and conductive particles, further increased the biomass retention and the DIET by altering the abundance of dominant bacterial groups. The effluent qualities in COD and ammonia nitrogen was improved up to 1.98 mg/L and 2.65 mg/L, respectively, by the conductive sheets. The upflow bioelectrochemical reactor with conductive materials is a good tertiary treatment process for improving the quality of the final effluent discharged from wastewater treatment plant.

Metagenomics-based interpretation of AHLs-mediated quorum sensing in Anammox biofilm reactors for low-strength wastewater treatment

Anammox-based nitrogen removal can advance sustainable wastewater treatment, especially for the main-stream wastewater treatment. Two lab-scale Anammox biofilm reactors fed with influent ammonium concentrations of 110 mg/L (Anammox-H) and 50 mg/L (Anammox-L) were operated, and nitrogen removal and mechanisms of quorum sensing (QS)/quorum quenching (QQ) were examined. The achieved nitrogen removal rates were 0.65 g N/L·d in Anammox-H and 0.25 g N/L·d in Anammox-L. Candidatus Kuenenia was dominant in both reactors. Higher contents of tight extracellular polymeric substance and hydrophobic amino acid confirmed that dense Anammox biofilm developed in Anammox-H. N-hexanoyl-l-homoserine lactone and N-octanoyl-l-homoserine lactone were detected in Anammox-H and Anammox-L. High concentrations of acyl-homoserine lactones (AHLs) in water and biomass phases of Anammox-H were consistent with that more active QS processes existed in Anammox-H. Functional genes including hao, pmoA-amoC, nirK and narGZHY were detected and harbored by Candidatus Kuenenia stuttgartiensis, Nitrosomonas europaea and Lautropia sp. SCN 69-89. These organisms not only involved in nitrogen metabolism, but also in pyruvate, fatty acid and S-Adenosy-l-methionine synthesis (important for AHLs). Influent ammonium concentrations affected the balance between QQ and QS activities, resulting in different Anammox activity and biofilm morphology. This study advanced the Anammox application for low-strength wastewater, especially from the aspect of QQ and QS balance.

Novel staged anaerobic fluidized bed ceramic membrane bioreactor: Energy reduction, fouling control and microbial characterization

Aluminum dioxide (Al2O3) flat-tubular ceramic membrane was applied in a novel staged anaerobic fluidized bed ceramic membrane bioreactor (SAF-CMBR) for low-strength wastewater treatment. Granular activated carbon (GAC) particles were fluidized by bulk recirculation through the membrane reactor to control membrane fouling without any biogas sparging. The SAF-CMBR was operated for 350 days at 25 °C with total hydraulic retention time (HRT) between 1.3 and 2.1 h. A net permeate flux of 22 L/m2 h was achieved during the reactor operation combined with periodic maintenance cleaning using 25 mg/L of sodium hypochlorite solution under GAC fluidization. The overall chemical oxygen demand (COD) removal efficiency was 93%; with average SCOD was less than 30 mg/L in membrane permeate. Energy requirement to operate the SAF-CMBR was 0.024 kWh/m3 and it was only 10% of the electrical energy converted from methane produced by the reactor. Biosolids production averaged 0.01 g volatile suspended solids per g COD removed. With SAF-CMBR, microbial classification revealed that anaerobic treatment was achieved mainly by microbial communities grown on the GAC particles fluidized in which propionate-degrading syntrophs, aceticlastic/DIET-dependent CO2 reduction methanogens Methanothrix and exoelectrogenic Geobacter were dominated.

Performance of a UASB reactor for low-strength wastewater treatment under different hydraulic loading rates

Performance of a UASB reactor for low-strength wastewater treatment under different hydraulic loading rates

Modification of UASB reactor by using CFD simulations for enhanced treatment of municipal sewage.

Up-flow anaerobic sludge blanket (UASB) has been in use since last few decades for the treatment of organic wastewaters. However, the performance of UASB reactor is quite low for treatment of low strength wastewaters (LSWs) due to less biogas production leading to poor mixing. In the present research work, a modification was done in the design of UASB to improve mixing of reactor liquid which is important to enhance the reactor performance. The modified UASB (MUASB) reactor was designed by providing a slanted baffle along the height of the reactor having an angle of 5.7° with the vertical wall. A two-dimensional computational fluid dynamics (CFD) simulation of three phase gas-liquid-solid flow in MUASB reactor was performed and compared with conventional UASB reactor. The CFD study indicated better mixing in terms of vorticity magnitude in MUASB reactor as compared to conventional UASB, which was reflected in the reactor performance. The performance of MUASB was compared with conventional UASB reactor for the onsite treatment of domestic sewage as LSW. Around 16% higher total chemical oxygen demand removal efficiency was observed in MUASB reactor as compared to conventional UASB during this study. Therefore, this MUASB model demonstrates a qualitative relationship between mixing and performance during the treatment of LSW. From the study, it seems that MUASB holds promise for field applications.

Mechanism of high contaminant removal performance in the expanded granular sludge blanket (EGSB) reactor involved with granular activated carbon for low-strength wastewater treatment

The sludge granulation in an anaerobic bioreactor is rather difficult for treating low-strength wastewater. In this study, an expanded granular sludge blanket (EGSB) reactor involved with granular activated carbon (GAC) was employed to treat wastewater at different operational conditions. In general, a stable COD removal performance was operated at the HRT condition of 8, 6, 5, and 4 h, and Vup ranges from 1.09 to 2.44 m h−1. However, the NH3-N removal efficiency was at a relatively low level resulted from the nitrification efficiency was limited to the low dissolved oxygen concentration in anaerobic bioreactor. Adding GAC to the raw sludge, the average size of granular sludge and enzymatic [dehydrogenase activity (DHA) and specific methanogenic activity (SMA)] activities presented an increase trend with the experiment grows. In addition, the promotion of organic load rate (OLR) and Vup might stimulate the external mass transfer effect in EGSB reactor, which resulted in the increase of extracellular polymeric substances (EPS) content. DNA sequencing analysis demonstrated that the growth of Aeromonas genus was the main reason for the unstable distribution of acetoclastic and hydrogenotrophic methanogens in HRT condition of 4 h.

Deep purification of low-strength ammonium-containing wastewater with ANRE process

Ammonium-nitrogen pollution is the main cause of waterbody eutrophication and has been a severe problem for the treatment of river and groundwater. In this paper, a novel Advanced Nitrogen REmoval (ANRE) process was successfully developed based on anaerobic ammonium oxidation (ANAMMOX), aiming at the treatment of low-strength ammonium-containing wastewaters (5–15mg/L NH4+-N). The ANRE process was demonstrated to be high-efficient with the substrate (ammonium and nitrite) removal efficiency up to 97% and the effluent ammonium concentration less than 1mgN/L. Kinetic analysis indicated that the maximum specific ammonium utilization rate was 46.40mgN/(g VSS·d) and the half-saturation constants ks was 0.25mgN/L. The ANAMMOX granular sludge was observed to disaggregate gradually due to the consumption of extracellular polymeric substances (EPS). The Anaerobic Ammonium Oxidation Bacteria (AnAOB) were proved in the state of starvation, causing the stoichiometric change for cellular synthesis and energy production and leading to more nitrate accumulation.

Impact of food to microorganism ratio and alcohol ethoxylate dosage on methane production in treatment of low-strength wastewater by a submerged anaerobic membrane bioreactor

The effects of food to microorganism (F/M) ratio and alcohol ethoxylate (AE) dosage on the methane production potential were investigated in treatment of low-strength wastewater by a submerged anaerobic membrane bioreactor (SAnMBR). The fate of AE and its acute and/or chronic impact on the anaerobic microbes were also analyzed. The results indicated that AE had an inhibitory effect to methane production potential (lag-time depends on the AE dosage) and the negative effect attenuated subsequently and methane production could recover at F/M ratio of 0.088–0.357. VFA measurement proved that AE was degraded into small molecular organic acids and then converted into methane at lower F/M ratio (F/M<0.158). After long-term acclimation, anaerobic microbe could cope with the stress of AE by producing more EPS (extracellular polymeric substances) and SMP (soluble microbial products) due to its self-protection behavior and then enhance its tolerance ability. However, the methane production potential was considerably decreased when AE was present in wastewater at a higher F/M ratio of 1.054. Higher AE amount and F/M ratio may destroy the cell structure of microbe, which lead to the decrease of methane production activity of sludge and methane production potential.

Long-term stability and nutrient removal efficiency of aerobic granules at low organic loads

The feasibility of application of aerobic granular sludge cultivated with high organic loads for biological nutrient removal (BNR) from low-strength wastewater was studied. Granules obtained with high-strength (COD=1400mg/L) wastewater were fed with medium (COD=700mg/L) and then low-strength (COD=400mg/L) wastewater. The granules rapidly acclimated to the medium-strength wastewater. However, feeding with low-strength wastewater reduced the F/M ratio from 0.4 to 0.2gCOD/gVSSd and granules disintegration occurred. Re-granulation was obtained after poor settling biomass was washed out and the F/M ratio reached 0.4gCOD/gVSSd. Disintegration of granules coincided with the decrease in extracellular polymeric substances (EPS) content and protein-to-carbohydrate ratio and re-granulation was assisted with the increase in EPS and protein-to-carbohydrate ratio. The results indicated that cultivation of aerobic granules with high organic loads and its implication for BNR treatment of low-strength wastewater while balancing the F/M ratio can be an alternative to reduce start-up period.

Low energy single-staged anaerobic fluidized bed ceramic membrane bioreactor (AFCMBR) for wastewater treatment

An aluminum dioxide (Al2O3) ceramic membrane was used in a single-stage anaerobic fluidized bed ceramic membrane bioreactor (AFCMBR) for low-strength wastewater treatment. The AFCMBR was operated continuously for 395days at 25°C using a synthetic wastewater having a chemical oxygen demand (COD) averaging 260mg/L. A membrane net flux as high as 14.5–17L/m2h was achieved with only periodic maintenance cleaning, obtained by adding 25mg/L of sodium hypochlorite solution. No adverse effect of the maintenance cleaning on organic removal was observed. An average SCOD in the membrane permeate of 23mg/L was achieved with a 1h hydraulic retention time (HRT). Biosolids production averaged 0.014±0.007gVSS/gCOD removed. The estimated electrical energy required to operate the AFCMBR system was 0.039kWh/m3, which is only about 17% of the electrical energy that could be generated with the methane produced.

Development of a novel anaerobic membrane bioreactor simultaneously integrating microfiltration and forward osmosis membranes for low-strength wastewater treatment

Anaerobic osmotic membrane bioreactor (AnOMBR) has aroused growing interests for its low energy demand, ability to efficiently process low ionic strength wastewater and high effluent quality. However, salt accumulation remains a main obstacle for causing severe water flux decline, fouling aggravation and inhibitory on the microbial activity. Here, we report a novel microfiltration (MF) assisted AnOMBR (AnMF-OMBR) for mitigating salt accumulation. The results indicated that the MF membrane effectively prevented salt accumulation in the bioreactor. The stable salinity level (within the range of 2.5–4.0mS/cm) enabled the AnMF-OMBR to achieve a long-term continuous operation together with a higher methane production in comparison with a conventional AnOMBR. The forward osmosis (FO) permeate from the AnMF-OMBR had excellent water quality, while the MF permeate required further treatment (e.g., phosphorus precipitation and activated carbon adsorption) before its beneficial reuse. A thick fouling layer combining biofouling and inorganic scaling was existed on the FO membrane. Further confocal laser scanning microscopy (CLSM) revealed the dominance of polysaccharides and microorganisms over proteins. The current study demonstrated that the AnMF-OMBR can be a promising and sustainable wastewater treatment technology for its simultaneous energy recovery (in the form of biogas) and water reuse (from both FO and MF membranes).

Low-strength wastewater treatment in an anammox UASB reactor: Effect of the liquid upflow velocity

Two-stage systems have been proposed to overcome the drawbacks associated to the implementation of the autotrophic biological nitrogen removal process in the mainstream of urban wastewater treatment plants. In this study, an upflow anammox sludge blanket (UAnSB) reactor was successfully operated for 325days treating a low-strength synthetic influent mimicking mainstream conditions. A nitrogen loading rate of up to 1.8±0.2gNL−1d−1 was achieved at 26°C and the nitrogen removal rate obtained (1.7±0.1gNL−1d−1) resulted considerably higher than most of the previously reported values for systems treating low-strength wastewater at similar temperatures. Fluorescence in situ hybridization analysis showed a high enrichment in the anammox specie Candidatus Brocadia anammoxidans during the whole operation. The evolution of the granule diameter was followed throughout the operation of the UAnSB reactor and a direct correlation of the average granule diameter with the liquid upflow velocity (Vup) was established, being the higher the Vup, the bigger the granules. A stable granule diameter of 790±40μm was achieved by maintaining a Vup of 1.0±0.1mh−1. The low VupS applied avoid the use of effluent recirculation which would present a huge inconvenient to implement UAnSB reactors at real scale, however these low VupS led to external mass transfer problems in the reactor. In spite of the mass transfer limitations, not only a high specific anammox activity (0.26±0.02gNg−1VSd−1) was achieved in the UASB reactor but also a high nitrogen removal (80±3%).

Treatment of low-strength wastewater at mesophilic and psychrophilic conditions using immobilized anaerobic biomass

An anaerobic immobilized bio-plates reactor (AnIBPR) of effective volume of 14.5L and bio-plate packing ratio of 27.5% was used to treat low-strength synthetic wastewater (COD of 400mg/L) at a hydraulic retention time (HRT) of 16h. Treatment performance was investigated at different temperatures. The results showed that the reactor AnIBPR achieved COD removal of 86–92% at mesophilic (35°C and 25°C) and psychrophilic (15°C) conditions. Dissolved methane (CH4) was found to be oversaturated in the reactor (saturation factor of 1.03–1.21), increasing with decreasing temperature. Increased dissolved CH4 content at 15°C, albeit at decreased production, was attributed to significant mass transfer limitation due to lower KLa at low temperature, resulting in oversaturation of dissolved CH4. Increasing treatment temperature to mesophilic conditions led to increased reaction rates and yields. At steady state, gas-phase CH4 content was 75–83% and the overall yield was 0.22–0.26L/gCOD removed. Steady-state volatile fatty acids (VFAs) were measured at 3.3–12mgCOD/L, small amounts that were unlikely to hamper treatment performance.

A critical review of future trends and perspectives for the implementation of partial nitritation/anammox in the main line of municipal WWTPs

The use of technologies based on partial nitritation (PN) and anaerobic ammonium oxidation (Anammox) is a cost-efficient and sustainable alternative for nitrogen removal from wastewaters with low COD/N ratios. These technologies allow savings in biodegradable organic matter consumption; oxygen requirements (about 40% lower compared to the conventional process of nitrification/denitrification); and sludge treatment costs. Despite the advantages of the PN/Anammox process, it also has some limitations which led to a full-scale application relatively restricted to some wastewaters, especially the reject water line of wastewater treatment plants (WWTPs). However, the PN/Anammox process also opens the interesting possibility of transforming most of the biodegradable organic matter arriving at the WWTP into biogas, because that biodegradable COD is not necessary anymore to denitrify. This can lead to an energetically self-sufficient WWTP, which means important cost savings. The main aspects arising from this application would be: the treatment of low-strength wastewater with high variability in concentrations and loads; the possible effects of biodegradable COD reaching the PN/Anammox system; the operation at low temperatures; the effective retention of microbial populations of interest; the use of one-step or two-step systems; and the effective control of the process during the start-up and the stable operation. Some of the proposed solutions which will be detailed along this paper are: the use of biofilm biomass (with or without carrier); novel aeration strategies and control systems; and different reactor configurations.

Formation of aerobic granules for the treatment of real and low-strength municipal wastewater using a sequencing batch reactor operated at constant volume

This study aimed at evaluating the formation of aerobic granular sludge (AGS) for the treatment of real and low-strength municipal wastewater using a column sequencing batch reactor (SBR) operated in fill-draw mode (constant volume). The focus was on understanding how the wastewater upflow velocity (VWW) applied during the anaerobic feeding influenced the sludge properties and in turn the substrate conversion. Two different strategies were tested: (1) washing-out the flocs by imposing high wastewater upflow velocities (between 5.9 and 16 m h−1) during the anaerobic feeding (Approach #1) and (2) selective utilization of organic carbon during the anaerobic feeding (1 m h−1) combined with a selective sludge withdrawal (Approach #2). A column SBR of 190 L was operated in constant volume during 1500 days and fed with real and low-strength municipal wastewater. The formation of AGS with SVI30 of around 80 mL gTSS−1 was observed either at very low (1 m h−1) or at high VWW (16 m h−1). At 16 m h−1 the AGS was mainly composed of large and round granules (d > 0.63 mm) with a fluffy surface, while at 1 m h−1 the sludge was dominated by small granules (0.25 < d < 0.63 mm). The AGS contained a significant fraction of flocs during the whole operational period. A considerable and continuous washout of biomass occurred at VWW higher than 5.9 m h−1 (Approach #1) due to the lower settling velocity of the AGS fed with municipal wastewater. The low sludge retention observed at VWW higher than 5.9 m h−1 deteriorated the substrate conversion and in turn the effluent quality. High solid concentrations (and thus solid retention time) were maintained during Approach #2 (VWW of 1 m h−1), which resulted in an excellent effluent quality. The study demonstrated that the formation of AGS is possible during the treatment of real and low-strength municipal wastewater in a SBR operated at constant volume. Low wastewater upflow velocities should be applied during the anaerobic feeding phase in order to ensure enough biomass retention and efficient substrate removal.

Continuous treatment of high strength wastewaters using air-cathode microbial fuel cells

Treatment of low strength wastewaters using microbial fuel cells (MFCs) has been effective at hydraulic retention times (HRTs) similar to aerobic processes, but treatment of high strength wastewaters can require longer HRTs. The use of two air-cathode MFCs hydraulically connected in series was examined to continuously treat high strength swine wastewater (7–8g/L of chemical oxygen demand) at an HRT of 16.7h. The maximum power density of 750±70mW/m2 was produced after 12daysof operation. However, power decreased by 85% after 185d of operation due to serious cathode fouling. COD removal was improved by using a lower external resistance, and COD removal rates were substantially higher than those previously reported for a low strength wastewater. However, removal rates were inconsistent with first order kinetics as the calculated rate constant was an order of magnitude lower than rate constant for the low strength wastewater.

TRATAMIENTO DE AGUA RESIDUAL DOMÉSTICA MEDIANTE UN REACTOR RAFA Y UNA CELDA MICROBIANA DE COMBUSTIBLE

The performance of a system consisting of an up-flow anaerobic sludge blanket (UASB) reactor and a microbial fuel cell (MFC) for the treatment of low-strength wastewater and the recovery of energy was evaluated. The UASB reactor (1 L) was continuously fed with raw domestic wastewater under hydraulic retention times (HRT) of 12 and 6 h.The MFC (250 mL) was operated in batch mode and fed with either raw wastewater (HRT = 12 h) or the effluent from the UASB reactor (HRT = 6 h). It was found that the removal of organic matter by the coupled UASB–MFC system (88 % chemical oxygen demand (COD), 75 % total organic carbon (TOC) and 79 % total suspended solids (TSS)) was higher than the levels obtained by the UASB reactor (76 % COD, 66 % TOC and 73 % TSS) and the MFC (60 % COD, 53 % TOC and 40 % TSS) when these were operated individually. The highest power density obtained in the MFC was 176 mW/m2 with 1000 Ω resistance, whereas the coulombic efficiency was 8 %. The UASB-MFC system proved to be a good alternative for the treatment of wastewater and the simultaneous generation of electricity even under substrate limiting conditions, such as low concentration of organic matter in the influent.

Domestic wastewater treatment in parallel with methane production in a microbial electrolysis cell

Microbial electrolysis cells (MECs) have great potential as a technology for wastewater treatment in parallel to energy production. In this study we explore the feasibility of using a low-cost, membraneless MEC for domestic wastewater treatment and methane production in both batch and continuous modes. Low-strength wastewater can be successfully treated by means of an MEC, obtaining significant amounts of methane. The results also suggest that hydrogenotrophic methanogenesis reduce the incidence of homoacetogenic activity, thus improving the overall MEC performance. However, gas production rates are low and important aspects such as methane solubility in water still remain a challenge. Overall, MECs can offer competitive advantages not only for low-strength wastewater treatment but also as an aid to anaerobic methane production by improving the chemical oxygen demand (COD) removal and methane production rates.

Advances in Granular Growth Anaerobic Membrane Bioreactor (G-AnMBR) for Low Strength Wastewater Treatment

Advances in Granular Growth Anaerobic Membrane Bioreactor (G-AnMBR) for Low Strength Wastewater Treatment