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A parametric model of the second-layer influent distributor is proposed to increase the reaction efficiency of the up-flow anaerobic sludge blanket. The impacts on the flow efficiency of the main parameters, including the length of distribution pipe, that is, the cylinder radius r1, the eccentricity of the nozzle e, and the number of nozzles n1, are investigated. The optimal parameter combination of the second-layer influent distributoris obtained by single factor analysis and orthogonal analysis. Then the two-layer distributor combination model, including the bottom influent distributor and the second-layer influent distributor, is established and the simulations are conducted to study the effect of the two-layer distributor on flow inside the reactor. The simulation results show that the proposed two-layer distributor can achieve a higher mixture efficiency than the single distributor. [ABSTRACT FROM AUTHOR]

A lab-scale Upflow Anaerobic Sludge Blanket (UASB) reactor was used as a model for evaluating synthetic and complex industrial wastewater treatment, using a solar heater to control temperature. Also, hydrodynamics was assessed using the Computational Fluid Dynamics (CFD) method. Initially, the UASB reactor was operated with synthetic wastewater at Hydraulic Retention Time (HRT) of 24 h in 20 ± 2 °C and 30 ± 2 °C to measure the biogas bubbles production for CFD study. COD removal efficiencies of 85 ± 3% and 95 ± 3%, respectively, with production of 27 and 39 ml CH4/h, correspondingly, were observed. After that, the reactor was fed with complex industrial wastewater. It was evaluated at 24 h in both temperatures. At 30 °C, low COD removal efficiency was observed, being 48 ± 13%, with methane production of 20 ± 3 ml CH4/h. The plug flow pattern was observed in the CFD modelling at HRT of 24 h and 20 °C without considering biogas bubbles interaction. Similar hydrodynamic behaviour was observed at HRT of 24 h and 30 °C. Nonetheless, when biogas bubbles were considered in the CFD modelling, hydrodynamics significantly changed, passing from a plug flow to a complete mix flow pattern. [ABSTRACT FROM AUTHOR]

The treatment of garlic processing wastewater was investigated in a UASB-SBR system. The experimental results showed that UASB was successfully started up after 64 days of continuous operation with COD removal rate of 45%. SBR start-up phase went through 60 days and the COD removal rate achieved 96%. UASB ran under optimal conditions (HRT of 45 h, pH of 7.5, and temperature of 35 ± 2°C) for 14d and performed well in organic matter treatment. SBR played a major part in nitrogen and phosphorus removal when running under optimal conditions (cycle time of 12 h, temperature of 25°C, organic loading of 0.72 kgCOD/(m3·d), and COD of 6000 mg/L) for 18d. Secondly, the microbial community structure indicated that the abundance of β-Proteobacteria and α-Proteobacteria in the sludge reached 30.05% and 47.57%, respectively, and played a crucial part for the organic matter, nitrogen and phosphorus removal in the SBR. After UASB-SBR system had been stabilised with influent COD of 9800 mg/L, the average COD, TP, NH3-N and TN removal rates were 99%, 94.82%, 87.07% and 94.87%, respectively, which were 3%, −2%, 1% and 3.5% higher than SBR running alone under optimal conditions. UASB coupled with SBR process had an excellent performance for high-concentration garlic processing wastewater. [ABSTRACT FROM AUTHOR]

The discharge of raw wastewater into the environment can be a contamination source of Giardia spp. cysts and Cryptosporidium spp. oocysts. The UASB (Upflow Anaerobic Sludge Blanket) reactor is the most popular technology applied for wastewater treatment in Brazil, nevertheless there is little information concerning its capacity for (oo)cyst removal. In this context, this study investigated the occurrence and removal of Giardia spp. cysts and Cryptosporidium spp. oocysts by three different UASB reactors (i.e. Reactor A, B, and C) treating different wastewater types. In the wastewater influent, the concentration varied from 493.3 to 14,000 cysts·L-1 for Giardia spp. and from 'not detected' to 53.3 oocysts·L-1 for Cryptosporidium spp.. The (oo)cyst concentration increased after the anaerobic treatment in Reactors A and B, while Giardia spp. log-removal of 0.5 ± 0.2 was found in Reactor C. The increment in (oo)cyst concentration may happened due to the inefficacy for (oo)cyst removal by the specific UASB reactor and/or due to the reduction of matrix interference for reactor effluent samples in the detection method. The results suggest that hydraulic retention time (HRT) may be the key parameter for Giardia spp. removal by the UASB reactor. Furthermore, no parameter analysed (physical-chemical and indicator microorganisms) showed a common correlation with the (oo)cyst concentration in the three UASB reactors. Considering that official data of cryptosporidiosis and giardiasis cases are rarely reported in Brazil, monitoring Giardia spp. cysts and Cryptosporidium spp. oocysts in wastewater could be an alternative to estimate the occurrence of diseases in the served population. [ABSTRACT FROM AUTHOR]

The utilization of foul condensate (FC) collected from a Kraft pulp mill for the anaerobic production of volatile fatty acids (VFA) was tested in upflow anaerobic sludge blanket (UASB) reactors operated at 22, 37 and 55°C at a hydraulic retention time (HRT) of ∼75 h. The FC consisted mainly of 11370, 500 and 592 mg/L methanol, ethanol and acetone, respectively. 42–46% of the organic carbon (methanol, ethanol and acetone) was utilized in the UASB reactors operated at an organic loading of ∼8.6 gCOD/L.d and 52–70% of the utilized organic carbon was converted into VFA. Along with acetate, also propionate, isobutyrate, butyrate, isovalerate and valerate were produced from the FC. Prior to acetogenesis of FC, enrichment of the acetogenic biomass was carried out in the UASB reactors for 113 d by applying operational parameters that inhibit methanogenesis and induce acetogenesis. Activity tests after 158 d of reactor operation showed that the biomass from the 55°C UASB reactor exhibited the highest activity after the FC feed compared to the biomass from the reactors at 22 and 37°C. Activity tests at 37°C to compare FC utilization for CH4 versus VFA production showed that an organic carbon utilization >98% for CH4 production occurred in batch bottles, whereas the VFA production batch bottles showed 51% organic carbon utilization. Furthermore, higher concentrations of C3–C5 VFA were produced when FC was the substrate compared to synthetic methanol rich wastewater. [ABSTRACT FROM AUTHOR]

Volatile fatty acids (VFA) production and degree of acidification (DA) were investigated in the anaerobic treatment of cheese whey by comparison of two processes: a continuous process using a laboratory upflow anaerobic sludge blanket (UASB) reactor and a discontinuous process using a sequencing batch reactor (SBR). The main purpose of this work was to study the organic loading rate (OLR) effect on the yield of VFA in two kinds of reactors. The predominant products in the acidogenic process in both reactors were: acetate, propionate, butyrate and valerate. The maximum DA obtained was 98% in an SBR at OLR of 2.7 g COD L−1 d−1, and 97% in the UASB at OLR at 15.1 g COD L−1 d−1. The results revealed that the UASB reactor was more efficient at a medium OLR with a higher VFA yield, while with the SBR reactor, the maximum acidification was obtained at a lower OLR with changes in the VFA profile at different OLRs applied. [ABSTRACT FROM AUTHOR]

The effect of salinity on the anaerobic ammonium oxidation (ANAMMOX) process in a UASB reactor was investigated by analysing ammonium, nitrite, nitrate and TN concentrations, and TN removal efficiency. Extracellular polymeric substances (EPSs) and specific ANAMMOX activity (SAA) were evaluated. Results showed the effluent deteriorated after salinity was increased from 8 to 13 g/L and from 13 to 18 g/L, and TN removal efficiency decreased from 80% to 30% and 80% to 50%, respectively. However, ANAMMOX performance recovered and TN removal efficiency increased to 80% after 40 days when the influent concentrations ofandwere 200 mg/L and salinity levels were at 13 and 18 g/L, respectively. The amount of EPSs decreased from 58.9 to 37.1 mg/g volatile suspended solids (VSS) when the reactor was shocked by salinity of 13 g/L, and then increased to 57.2 mg/g VSS when the reactor recovered and ran stably at 13 g/L. The amount of EPSs decreased from 57.2 to 49.1 mg/g VSS when the reactor was shocked by salinity of 18 g/L, and then increased to 60.7 mg/g VSS when the reactor recovered and ran stably at 18 g/L. The amount of EPS and the amounts of polysaccharide, protein and humus showed no evident difference when the reactor recovered from different levels of salinity shocks. Batch tests showed salinity shock load from 8 to 38 g/L inhibited the SAA. However, when the reactor recovered from salinity shocks, SAA was higher compared to that when the reactor was subjected to the same level of salinity shock. [ABSTRACT FROM PUBLISHER]

The efficiency of the up-flow anaerobic sludge blanket (UASB) reactor is quite low for the treatment of low strength wastewaters (LSWs) due to less biogas production leading to poor mixing. LSW may be treated efficiently by providing adequate mixing in the UASB reactor when gas production is low, and sufficient mixing can be achieved by modifying reactor geometry. Hence, modifying UASB reactor geometry for enhanced mixing and evaluating its performance for the treatment of LSWs would be a worthwhile effort. In the present study, UASB reactor configuration was modified by providing a vertical baffle along the height to promote mixing of reactor contents, and is termed as modified UASB (MUASB). The performance of an on-site pilot-scale MUASB reactor was evaluated for 375 days under ambient condition for the treatment of municipal sewage as LSW and compared with that of the conventional UASB and hybrid UASB (HUASB) reactors. The MUASB reactor showed better performance in terms of chemical oxygen demand (COD) removal efficiency as compared with UASB and HUASB reactors during this study. At 4 h hydraulic retention time, the total COD removal efficiency of UASB and HUASB reactors was 53.7% and 61%, respectively, which were much lower than the total COD removal efficiency of the MUASB reactor (72.7%). The better performance observed in the MUASB reactor is possibly due to improved mixing. Depth-wise analysis of reactor liquid showed that better mixing in the MUASB reactor enhances the contact of wastewater with biomass, which contributes to the improved treatment efficiency. It seems that MUASB holds promise for LSW treatment. [ABSTRACT FROM PUBLISHER]

Anaerobic digestion of alkaline kraft elemental chlorine-free bleaching wastewater in two mesophilic, lab-scale upflow anaerobic sludge bed reactors resulted in significantly higher biogas production (250 ± 50 vs. 120 ± 30 NmL g) and reduction of filtered total organic carbon (fTOC) (60 ± 5 vs. 43 ± 6%) for wastewater from processing of hardwood (HW) compared with softwood (SW). In all cases, the gas production was likely underestimated due to poor gas separation in the reactors. Despite changes in wastewater characteristics, a stable anaerobic process was maintained with hydraulic retention times (HRTs) between 7 and 14 h. Lowering the HRT (from 13.5 to 8.5 h) did not significantly affect the process, and the stable performance at 8.5 h leaves room for further decreases in HRT. The results show that this type of wastewater is suitable for a full-scale implementation, but the difference in methane potential between SW and HW is important to consider both regarding process dimensioning and biogas yield optimization. [ABSTRACT FROM AUTHOR]

This work focuses on combined scanning electron microscopy and energy dispersive X-ray analysis (SEM-EDX) applied to granular sludge used for biological treatment of high-strength wastewater effluents. Mineral precipitation is shown to occur in the core of microbial granules under different operating conditions. Three dairy wastewater effluents, from three different upflow anaerobic sludge blanket (UASB) reactors and two aerobic granular sequenced batch reactors (GSBR) were evaluated. The relationship between the solid phase precipitation and the chemical composition of the wastewater was investigated with PHREEQC software (calculation of saturation indexes). Results showed that pH, Ca:P ratios and biological reactions played a major role in controlling the biomineralization phenomena. Thermodynamics calculations can be used to foresee the nature of bio-precipitates, but the location of the mineral concretions will need further investigation as it is certainly due to local microbial activity. [ABSTRACT FROM AUTHOR]

The effects of zero-valent iron (Fe0) on the performance of a mesophilic upflow anaerobic sludge blanket (UASB) reactor treating high-strength wastewater from the vitamin C biosynthesis industry (VCW) was investigated during a 200-day period. The results showed that the chemical oxygen demand (COD) removal efficiency, CH4 content in biogas, specific methanogenic activity of sludge, and phosphate removal efficiency were significantly improved up to 81.8–96.1%, 76.5–79.6%, 1.71–2.87 g CH4-COD g−1 VSS d−1 and 68.5–85.2%, respectively, at elevated organic loading rates (OLRs) in the Fe0-amended reactor (RFe). In contrast, the corresponding values of 65.3–83.4%, 69.1–70.8%, 1.12–1.95 g CH4-COD g−1 VSS d−1 and 1.4–1.6%, respectively, were recorded in the control (R0). Elevated ferrous concentration of nearly 400 mg L−1 in sludge was detected in RFe, whereas in the effluent of both reactors it was low (<1.0 mg L−1). Batch tests further showed that Fe0 significantly enhanced the biodegradability of the VCW as shown by an increase in BOD/COD ratio from 0.41 to 0.65, and could serve as the electron donor for methanogenesis by anaerobic sludge, which were responsible for the differences between RFe and R0. The results suggest this integrated Fe0-microbial system is promising in facilitating the anaerobic digestion of VCW in UASB reactors. [ABSTRACT FROM PUBLISHER]

Pig slurry was treated in an upflow anaerobic sludge blanket (UASB) reactor. To maintain a stable operation, the organic loading rate (OLR) applied to the system was increased stepwise by decreasing the dilution ratio of the pig slurry. Finally, during the last operational stage, no dilution was applied to the influent. The reactor maintained a soluble chemical oxygen demand (CODs) removal efficiency of 82% when OLRs lower than 1.73 g CODs l-1 d-1 were applied, although its efficiency fell to 55% when operated at 2.48 g CODs l-1 d-1. System performance was not affected by the presence of free ammonia (concentrations up to 375 mg NH3 l-1). The distribution of the different molecular weight fractions changed significantly during anaerobic digestion. Proteins contained in the fractions higher than 10,000 Daltons are less degraded than those belonging to the lower fractions. An important percentage of both COD and BOD5 in the effluent were observed in the lowest fraction, probably caused by the presence of volatile fatty acids (VFA). [ABSTRACT FROM AUTHOR]

The hydrodynamic behaviour of UASB (Up Flow Anaerobic Sludge Blanket) reactors based on residence time distribution curves allows the implementation of global models, including the kinetic aspects of biological reactions. The most relevant hydrodynamic models proposed in the literature are discussed and compared with the extended tanks in series (ETIS) model. Although derived from the tanks in series model, the ETIS model's parameter is not an integer. The ETIS model can be easily solved in the Laplace domain and applied to a two-stage anaerobic digestion linear model. Experimental data from a 250 m3 UASB reactor treating malting wastewater are used to calibrate and validate the proposed model. [ABSTRACT FROM AUTHOR]

It is proposed that anaerobic treatment of municipal wastewater in temperate climates is attainable through the fortification of wastewater with primary sewage sludge to enhance the chemical oxygen demand (COD). Three bench-scale up-flow anaerobic sludge blanket (UASB) bioreactors (0.5 L) were operated to provide a preliminary verification of this approach. Mass and energy balances were modelled using the GPS-X (COST model, population equivalent of 118,500) to determine the energy balance of the primary sludge wastewater fortification process flowsheet in comparison with conventional aerobic secondary treatment with activated sludge. The addition of 5% primary sludge by volume to crude wastewater pretreated with ultrasound resulted in an increase in total COD from 536 mg L-1 to 2300 mg L-1. A COD removal of 86% ± 8% and methane production of 400 mL L-1 d-1 were achieved in the reactor that was supplied with this primary sludge fortified wastewater. In comparison a COD reduction of 77% ± 8% and 40 mL L-1 d-1 of methane were observed in the reactor which was supplied with crude wastewater only, and a 79% ± 8% COD removal and 156 mL L-1 d-1 of methane were observed in UASB2, which was supplied with crude wastewater pretreated with ultrasound. The modelled energy balance for the fortified wastewater treatment process flowsheet was -305 kWh d-1 compared with -937 kWh d-1 in the aerobic flowsheet, corresponding to an energy saving of 67%. [ABSTRACT FROM AUTHOR]

The present research was an investigation of the influence of an innovative design of reactor filled with polyethylene (PE) granulate on model dairy wastewater treatment efficiency under anaerobic conditions compared to that obtained in a typical UASB reactor. The experiment was conducted at laboratory scale. An innovative reactor was designed with the reaction chamber inclined 30° in relation to the ground with upward waste flow and was filled with PE granular material. Raw model dairy wastewater was fed to two anaerobic reactors of different design at the organic loading rate of 4 kg COD m-3 d-1. Throughout the experiment, a higher removal efficiency of organic compounds was observed in the reactor with an innovative design and it was higher by 7.1% on average than in the UASB reactor. The total suspended solids was lower in the wastewater treated in the anaerobic reactor with the innovative design. Applying a PE granulated filling in the chamber of the innovative reactor contributed to an even distribution of sludge biomass in the reactor, reducing washout of anaerobic sludge biomass from the reaction chamber and giving a higher organic compounds removal efficiency. [ABSTRACT FROM AUTHOR]

Treatment of artificial wastewater containing a large amount of suspended solids comprised of soybean processing waste and pig fodder was studied using a novel multi-staged upflow anaerobic sludge blanket reactor. The reactor consisted of three compartments, each containing a gas solid separator. The wastewater had chemical oxygen demand of approximately 21600 mg l-1, suspended solids of 12800 mg l-1, and an ammonia concentration of 945 mg l-1. A continuous experiment without effluent circulation showed that the multi-staged reactor was not that effective for the treatment of wastewater containing a large amount of suspended solids. However, operation of the reactor with circulation of effluent enabled the reactor to achieve organic removal of 85% and approximately 70% methane conversion at loading rates of between 4.0 to 5.4 kg-chemical oxygen demand per cubic meter per day, meaning that the reactor was more effective when effluent was circulated. Morphological investigation revealed that the crude fiber in the sludge was partially degraded and that it had many small depressions on its surface. Evolved biogas may have become caught in these depressions of the fibers and caused washout of the sludge. [ABSTRACT FROM AUTHOR]

The focus of this study was on sulfate-rich wastewater treatment in a novel anaerobic / micro-aerobic bioreactor system. The system was composed of an upward-flow anaerobic sludge blanket (UASB) reactor and a floated bed micro-aerobic reactor, which was packed with elastic porous carriers and was controlled in a situation of dissolved oxygen below 0.5 mg l-1. The floated bed micro-aerobic reactor was developed for accumulating a higher amount of biomass in carriers with a short hydraulic retention time (HRT) for biological oxidation of hydrogen sulfide to elemental sulfur. During long-term steady state operation, experimental results showed that an average of 70±6% of sulfate was transformed to hydrogen sulfide in UASB reactor. Moreover, the overwhelming majority of sulfide was oxidized to elemental sulfur and sulfate in micro-aerobic reactor; and the recirculation of effluent to UASB reactor reduced effectively the degree of inhibition caused by sulfate-rich wastewater. In UASB reactor, chemical oxygen demand (COD) removal efficiency increased with COD loading, in contrast, the performance of sulfate removal decreased with the increase in sulfate loading in a range of 1.0-1.75 kg SO42- m-3 d-1. In micro-aerobic reactor, sulfide was removed almost completely under the operation of HRT 2.8 h. Furthermore, experimental results of continuous operations revealed that oxidation-reduction potential (ORP) was an adequate parameter for controlling biological oxidation of sulfide. When ORP was regulated in a lower range of -250 to -300 mV, the amount of regenerated sulfate was reduced significantly in micro-aerobic reactor. [ABSTRACT FROM AUTHOR]

Two different types of microbial aggregates (granular sludge and biofilm onto a plastic matrix) were evaluated for their susceptibility to sulphide and dissolved oxygen. Their specific methanogenic and sulphate reducing activities were evaluated separately and simultaneously. Total sulphide concentrations that caused 50% loss of methanogenic activity were 800 and 1250 mg l-1 and for sulphate reduction 750 and 860 mg l-1 for the granular sludge and the attached biomass, respectively. Simultaneous methanogenesis and sulphate reduction resulted in an increased tolerance of the sulphate reducing process towards sulphide. Results suggest that methanogenesis in granular sludge is less resistant to sulphide than in the attached biomass structure, whereas in sulphate reduction the attached biomass exhibited a better tolerance to high concentrations of total sulphide than the granular sludge. The better sulphate reducing capacity in the attached biomass may suggest that biomass was selectively attached. The dissolved oxygen concentration that inhibited 50% the methanogenic activity was 4.9 and 6.4 mg l-1 for the granular sludge and attached biomass, respectively. When methanogenesis and sulphate reduction were carried out simultaneously, the whole process was not affected by the supplied oxygen, as produced sulphide was used by sulphide oxidizing microorganisms thus scavenging oxygen. Results showed that the integration of anaerobic/aerobic conditions in a single bioreactor is quite possible and can be used as a good strategy for the complete transformation of sulphate to elemental sulphur. [ABSTRACT FROM AUTHOR]

A study of the anaerobic biodegradability of the three categories of water separated from extracted crude oil (Venezuelan oilfields) - light, medium or heavy crude - was carried out at laboratory scale using UASB reactors working at mesophilic conditions. Chemical oxygen demand (COD) removal in a low loaded UASB reactor fed with water separated from extracted light crude was high, with an average 87 % purification efficiency. The remaining COD was made up of the non-biodegradable and the very slowly biodegradable fractions of the organic matter in the water. Owing a second period, the hydraulic retention time was reduced in stages, thus increasing the loading rate. In the experimental conditions used, COD concentration at the outlet remained below the Venezuelan standard limit for discharge into the environment (350mg COD 1-1) when the hydraulic retention lime (HRT) was above 10 hours and the OLR under 3 g COD 1-1 d-1. For URT less than 10 hours, or organic loading rate (OLR) greater than 3 g COD 1-1 d-1, COD at the outlet of the reactor rose as a consequence both of increased volatile fatty acids (VFA) concentrations (indicating an overloading of the methanogenic population) and, also, of the increase in the non-VFA COD (indicating a decease in the acidification efficiency). On the other hand, results with UASB reactors operated at a low loading rate and fed with water separated from extracted medium and heavy crude oil showed that purification efficiency was low with only 20 % and 37% COD removal respectively. Continuing the operation of the UASB reactor fed with water separated from medium oil over a prolonged period did not bring any improvement, indicating that no adaptation of the sludge occurred. [ABSTRACT FROM AUTHOR]

This paper reports the results of experimental investigations carried out on a full-scale ABR and on a pilot UASB to determine biomass washout for various intermittent feed conditions. Particularly, the tests aimed to determine the extent to which sludge washout is affected by such factors as: daily flow distribution; upflow velocity; concentration and sedimentation properties of the biomass. Moreover, in order to obtain a tool to estimate sludge washout in different influent flow conditions, a simulation model of the sludge transport phenomena in the upflow anaerobic reactors is proposed. The results showed that when the influent flow is interrupted for long periods (above 1 hour), once it is resumed considerable losses of biomass into the effluent were found, independent of the upflow velocity. In contrast, with shorter periods, regular sludge expansion took place even with very high upflow velocities (up to 4 m h-1), giving rise to limited sludge washout and high removal efficiencies. [ABSTRACT FROM AUTHOR]