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Direct anaerobic treatment in the main line of a wastewater treatment plant is a promising way of recovering chemical energy, even in moderate climates. Full-scale applications of upflow anaerobic sludge blanket (UASB) reactors are common in warm climates and have recently begun to appear in areas with colder climate. Several new types of reactors optimized for low temperature treatment were proposed such as UASB-Digester or anaerobic membrane bioreactor (AnMBR). However, long-term operation of such systems treating real wastewater at winter temperatures is needed to assess their suitability. The aim of this article is to evaluate the operation of a laboratory-scale UASB reactor (1.9 L) before and after the installation of ultrafiltration membrane for solids separation from the effluent. The laboratory model treated wastewater at 15°C for over 850 days. The organic loading rate of the UASB reactor and AnMBR was 1.4 and 1.6 g COD/[L·d], respectively, while the hydraulic retention time was around 9 and 10 h. Energy recovery from the wastewater in gaseous methane was 4% and 6% in the UASB reactor and AnMBR, respectively. The methane content was 63%±17% and 64%±2%, respectively. In the UASB reactor, 64% of the influent chemical oxygen demand (COD) was removed in long term. The AnMBR ran at average 85% COD removal. Results show that AnMBR can deliver more stable effluent quality for wastewater treatment even at low (15°C) temperature. However, even the AnMBR effluent requires further posttreatment. Thus, simpler and less energy demanding UASB appears more relevant for wastewater pretreatment under European conditions. [ABSTRACT FROM AUTHOR]

A wastewater treatment system composed of an upflow anaerobic sludge blanket (UASB) reactor followed by a packed-bed reactor (PBR) filled with Sorbulite® and Polonite® filter material was tested in a laboratory bench-scale experiment. The system was operated for 50 weeks and achieved very efficient total phosphorus (P) removal (99%), 7-day biochemical oxygen demand removal (99%) and pathogenic bacteria reduction (99%). However, total nitrogen was only moderately reduced in the system (40%). A model focusing on simulation of organic material, solids and size of granules was then implemented and validated for the UASB reactor. Good agreement between the simulated and measured results demonstrated the capacity of the model to predict the behaviour of solids and chemical oxygen demand, which is critical for successful P removal and recovery in the PBR. [ABSTRACT FROM AUTHOR]

The effect of temperature on selenium (Se) removal by upflow anaerobic sludge blanket (UASB) reactors treating selenate and nitrate containing wastewater was investigated by comparing the performance of a thermophilic (55 °C) versus a mesophilic (30 °C) UASB reactor. When only selenate (50 μM) was fed to the UASB reactors (pH 7.3; hydraulic retention time 8 h) with excess electron donor (lactate at 1.38 mM corresponding to an organic loading rate of 0.5 g COD L −1 d −1 ), the thermophilic UASB reactor achieved a higher total Se removal efficiency (94.4 ± 2.4%) than the mesophilic UASB reactor (82.0 ± 3.8%). When 5000 μM nitrate was further added to the influent, total Se removal was again better under thermophilic (70.1 ± 6.6%) when compared to mesophilic (43.6 ± 8.8%) conditions. The higher total effluent Se concentration in the mesophilic UASB reactor was due to the higher concentrations of biogenic elemental Se nanoparticles (BioSeNPs). The shape of the BioSeNPs observed in both UASB reactors was different: nanospheres and nanorods, respectively, in the mesophilic and thermophilic UASB reactors. Microbial community analysis showed the presence of selenate respirers as well as denitrifying microorganisms. [ABSTRACT FROM AUTHOR]

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]

A new technology for in-situ biogas upgrading and recovery of CH 4 from the effluent of biogas reactors was proposed and demonstrated in this study. A vacuum degassing membrane module was used to desorb CO 2 from the liquid phase of a biogas reactor. The degassing membrane was submerged into a degassing unit (DU). The results from batch experiments showed that mixing intensity, transmembrane pressure, pH and inorganic carbon concentration affected the CO 2 desorption rate in the DU. Then, the DU was directly connected to an upflow anaerobic sludge blanket (UASB) reactor. The results showed the CH 4 content was only 51.7% without desorption of CO 2 , while it increased when the liquid of UASB was recycled through the DU. The CH 4 content increased to 71.6%, 90%, and 94% with liquid recirculation rate through the DU of 0.21, 0.42 and 0.63 L/h, respectively. The loss of methane due to dissolution in the effluent was reduced by directly pumping the reactor effluent through the DU. In this way, the dissolved CH 4 concentration in the effluent decreased from higher than 0.94 mM to around 0.13 mM, and thus efficient recovery of CH 4 from the anaerobic effluent was achieved. In the whole operational period, the COD removal efficiency and CH 4 yield were not obviously affected by the gas desorption. [ABSTRACT FROM AUTHOR]

This paper examines the impact of increasing organic loading in a two phase anaerobic digestion system treating commercial food waste. The first phase is a series of sequentially fed leach bed reactors (LBRs). The second phase is an upflow anaerobic sludge bed (UASB). Leachate from the leach beds, form the influent to the UASB. Effluent from the UASB is re-circulated over the leach beds. Flow rates corresponded to 1 volume of leachate per effective LBR volume per day. The theoretical organic loading rate (OLR) of the UASB is based on the conversion of volatile solids (VS) in the LBR to chemical oxygen demand (COD). The experiment was set up such that the theoretical OLR would rise from 7.1 to 8.8 to 11.8 kg COD m −3 day −1 . The system operated effectively at the lowest organic loading rate producing 384 L CH 4 kg VS −1 which corresponded to 72% of the value obtained in a BMP test. COD conversion efficiency was recorded at 75%. The accumulation of COD over the life of the experiment led to a situation whereby the volumetric OLR (product of COD concentration in the leachate by the flow rate) was over twice the theoretical OLR at the end of the experiment (24.3 kg VS m −3 day −1 versus 11.8 kg VS m −3 day −1 ). At the highest loading rate total ammonia nitrogen (TAN) reached levels of 4500 mg L −1 with pH levels of 8.15. This resulted in significant reduction of methane production. [ABSTRACT FROM AUTHOR]

Zn was added to one of the two identical bench-scale upflow anaerobic sludge blanket (UASB) reactors in steady-state period treating swine wastewater to evaluate the effects of Zn on performance and methanogenic population. Real-time quantitative PCR (QPCR) was used to quantify the 16S rRNA gene concentrations of the four methanogenic orders. In both reactors, the hydraulic retention time (HRT) was sustained at 48 h and the inner temperature was kept at 35 °C. Both promotion and inhibition of Zn on chemical oxygen demand (COD) removal, methane production and methanogens community were observed in accordance with different Zn dosages. COD removal rate and methane production reacted in the same way as methanogens, suggesting that the impact of Zn on the methanogenic community was the critical reason that caused the changes of UASB performance in treating swine wastewater with unstable Zn concentration. Among the methanogenic community, Methanomicrobiales (MMB) was the dominant group which got visibly impacted by the dosed Zn. Overall, lower concentration of Zn, e.g., less than 17.8 mg/L, was supposed to be advisable for a stable and high efficient treatment of swine wastewater by UASB reactor in practice. [ABSTRACT FROM AUTHOR]

The aim of this study was to evaluate the long-term effect of ZnO nanoparticles (NPs) on the performance of high-rate anaerobic bioreactors. Laboratory-scale upflow anaerobic sludge blanket (UASB) reactors were fed with a mixture of volatile fatty acids and exposed to either low (0.32 mg Zn L−1) or high (34.5 mg Zn L−1) concentrations of ZnO NPs. Exposure to high NP concentrations caused a rapid and permanent decline in the methane production and the removal of acetate and propionate. In contrast, a gradual and partial inhibitory response was observed in the reactor exposed to low NP concentrations. The long-term effect of the NP exposure was also evident from a decline in the specific methanogenic activity, which was more severe for the acetoclastic compared to the hydrogenotrophic methanogens. ZnO NPs were removed by 62–82% during passage through the UASB reactors. The results taken as a whole indicate that ZnO NPs cause severe inhibition of acetoclastic methanogens. Even sub-ppm levels of the nano-ZnO in the influent had a negative impact on the performance of the UASB reactor due to long-term exposure of methanogens to NPs that accumulated in the sludge bed. [Copyright &y& Elsevier]

Construction and demolition debris (CDD) contains high levels of sulfate that can cause detrimental environmental impacts when disposed without adequate treatment. In landfills, sulfate can be converted to hydrogen sulfide under anaerobic conditions. CDD can thus cause health impacts or odor problems to landfill employees and surrounding residents. Reduction of the sulfate content of CDD is an option to overcome these problems. This study aimed at developing a biological sulfate removal system to reduce the sulfate content of gypsum contaminated CDD in order to decrease the amount of solid waste, to improve the quality of CDD waste for recycling purposes and to recover sulfur from CDD. The treatment leached out the gypsum contained in CDD by water in a leaching column. The sulfate loaded leachate was then treated in a biological sulfate reducing Upflow Anaerobic Sludge Blanket (UASB) reactor to convert the sulfate to sulfide. The UASB reactor was operated at 23 ± 3 °C with a hydraulic retention time and upflow velocity of 15.5 h and 0.1 m h−1, respectively while ethanol was added as electron donor at a final organic loading rate of 3.46 g COD L−1 reactor d−1. The CDD leachate had a pH of 8–9 and sulfate dissolution rates of 526.4 and 609.8 mg L−1 d−1 were achieved in CDD gypsum and CDD sand, respectively. Besides, it was observed that the gypsum dissolution was the rate limiting step for the biological treatment of CDD. The sulfate removal efficiency of the system stabilized at around 85%, enabling the reuse of the UASB effluent for the leaching step, proving the versatility of the bioreactor for practical applications. [Copyright &y& Elsevier]

Highlights: [•] Combined UASB–MBR is feasible for dairy wastewater treatment at ambient temperatures. [•] The system presented a high tolerance to loading changes and temperature fluctuations. [•] High biogas production with more than 70% methane content was obtained. [•] Overall biomass yield similar to anaerobic systems was obtained. [•] Permeability values similar to those reported for aerobic MBR systems were obtained. [ABSTRACT FROM AUTHOR]

Introduction. For this research work, the acid whey produced by Oaxaca cheese industry in a UASB reactor was used. The reactor was subjected to three constant charges and three punctual charges of the whey. The reactor had a nominal capacity of 2.9 L with 1.9 days of hydraulic retention with an upward flow and a sludge blanket of 40% of the reactor's volume. Objective. Evaluate the behavior of the UASB reactor with three different charges of whey. Materials and methods. Three different constant charges of whey were used (5200, 7800 and 10500 mg CDO/L each one) during 22 days, and punctual charges of 32000, 47000 and 65000 mg DQO/L per day of whey, for each one, during 24 hours. Both the influent and the effluent were determined: total of sugars, volatile fatty acids (VFA's) protein, pH, methane and CDO. Results. The findings demonstrated that in the constant charges used the removal efficiency of CDO was 26 %, and for the punctual charges was 57 %. The sugar degradation efficiency was 95% for the constant and the punctual charges. For the protein, the removal efficiencies in the constant charges were above 27 % and for the punctual charges the efficiency was 46 %. Conclusion. The values of volatile fatty acids and methane were all within the limits for a good functioning of the reactor. Nevertheless, the pH had acid values below the ones recommended. [ABSTRACT FROM AUTHOR]

Leachate treatment is a challenging issue due to its high pollutant loads. There are several studies on feasible treatment methods of leachate. In the scope of this study, high organic content of young leachate was eliminated using an upflow anaerobic sludge blanket (UASB) and a membrane bioreactor (MBR) in sequence and effluent of the system was given to single reactor for high activity ammonia removal over nitrite (SHARON) and anaerobic ammonia oxidation (Anammox) reactors to remove nitrogen content. All reactors were set up at lab scale in order to evaluate the usage of these processes in sequencing order for leachate treatment. COD and TKN removal efficiencies were over 90 % in the combined processes which were operated during the study. The biodegradable portion of organic matter was removed with an efficiency of 99 %. BOD concentration decreased to 50 mg/L by UASB and MBR in sequence even the influent BOD concentration was over 8,000 mg/L. Although high nitrogen concentrations were observed in raw leachate, successful removal of nitrogen was accomplished by consecutive operations of SHARON and Anammox reactors. The results of this study demonstrated that with an efficient pretreatment of leachate, the combination of SHARON-Anammox processes is an effective method for the treatment of high nitrogen content in leachate. [ABSTRACT FROM AUTHOR]

Static granular bed reactor (SGBR) and upflow anaerobic sludge blanket (UASB) reactor were demonstrated at mesophilic condition for the treatment of pulp and paper mill wastewater. The hydraulic retention times (HRTs) were varied from 4 to 24 h following 29-day start-up period. The overall chemical oxygen demand (COD) removal efficiency of the SGBR was higher than the UASB during this study. At 4 h HRT, the COD removal was greater than 70 % for the SGBR and 60 % for the UASB. Biomass yield and volatile fatty acids concentration of SGBR were slightly less than UASB at organic loading rates ranging from 1.2 to 5.1 kg/m/day. The results indicated that the SGBR system can be considered a viable alternative system for anaerobic treatment for pulp and paper wastewater. [ABSTRACT FROM AUTHOR]

The aim of this work was to evaluate the performance of a 244-L pilot-scale upflow anaerobic sludge blanket (UASB) reactor during the treatment of chocolate-processing industry wastewater under low-temperature conditions (18 ±0.6 WC) for approximately 250 d. The applied organic loading rate (OLR) was varied between 4 and 7 kg/m3/d by varying the influent soluble chemical oxygen demand (CODsol), while keeping the hydraulic retention time constant (6.4± 0.3 h). The CODsol removal efficiency was low (59-78%). The measured biogas production increased from 240±54 to 431±61 L/d during the experiments. A significant linear correlation between the measured biogas production and removed OLR indicated that 81.69 L of biogas were produced per kg/m3 of CODsol removed. Low average reactor volatile suspended solids (VSS) (2,700-4,800 mg/L) and high effluent VSS (177-313 mg/L) were derived in a short sludge retention time (SRT) (4.9 d). The calculated SRT was shorter than those reported in the literature, but did not affect the reactor's performance. Average sludge yield was 0.20 kg-VSS/kg-CODsol. The low-temperature anaerobic treatment was a good option for the pre-treatment of chocolate-processing industry wastewater. [ABSTRACT FROM AUTHOR]

Market dynamics offer positive (incentive) or negative (disincentive) feedback loops that shape the research needs for, or certain aspects of, a particular technology. Our case study results illustrate how market dynamics have influenced the evolution of research needs in the wastewater treatment sector, with specific emphasis on research on the seeding granules used to start up-flow anaerobic sludge blanket (UASB) reactors. Because of insufficient data on the actual market demand for seeding granules for UASB plants, surrogate data, on the number of UASB plants installed internationally from 1970 to 2007, were used to predict the potential future demand for seeding granules. Secondly, we also determined whether or not such a demand would provide sufficient economic justification for the installation of one or more plants for manufacturing seeding granules in South Africa. The direct relationship between the demand for seeding granules and increased numbers of UASB plants was based on the premise that the start-up of each plant required a seeding inoculum before effluent could be treated. Three methods were used to obtain the data used in this study, namely: a literature survey, a questionnaire survey, and interviews with people having expert knowledge of wastewater treatment technologies. Our findings suggest that the UASB technology has largely been marginalised in the wastewater treatment market because of the introduction of competing technologies, and due to high initial capital costs. As a result, South African market demand for the seeding granules is likely to be very small or non-existent, because the number of new UASB plants installed per year is likely to decrease in future. Secondly, our research suggests that market dynamics, political contexts and technologies will continue to change, exerting an increasing downward influence on the UASB technology over time. [ABSTRACT FROM AUTHOR]

In this study, an integrated system of an up-flow anaerobic sludge blanket (UASB) reactor and a microbial fuel cell (MFC) was used to treat oilfield wastewater at laboratory scale. Results showed that the integrated system performed efficiently in treating the wastewater. The removal efficiencies were higher than 90 and 83% for chemical oxygen demand and NH3-N, respectively, at 26 h hydraulic retention time. The instrumental analysis indicated that most of the hydrocarbons were satisfactorily biodegraded in the integrated system. This work demonstrated that the UASB and sequential MFC reactor coupled system could be applied to achieve electricity production with simultaneous oily wastewater treatment. [ABSTRACT FROM AUTHOR]

The treatment of palm oil mill effluent (POME) by an upflow anaerobic sludge bed (UASB) at organic loading rates (OLR) between 2.2 and 9.5 g COD l−1 day−1 was achieved by acclimatizing the mesophilic (37 °C) microbial seed to the thermophilic temperature (57 °C) by a series of stepwise temperature shifts. The UASB produced up to 13.2 l biogas d−1 with methane content on an average of 76%. The COD removal efficiency ranged between 76 and 86%. Microbial diversity of granules from the UASB reactor was also investigated. The PCR-based DGGE analysis showed that the bacterial population profiles significantly changed with the temperature transition from mesophilic to thermophilic conditions. In addition, the results suggested that even though the thermophilic temperature of 57 °C was suitable for a number of hydrolytic, acidogenic and acetogenic bacteria, it may not be suitable for some Methanosaeta species acclimatized from 37 °C. Specifically, the bands associated with Methanosaeta thermophila PT and Methanosaeta harundinacea can be detected during the four consecutive operation phases of 37 °C, 42 °C, 47 °C and 52 °C, but their corresponding bands were found to fade out at 57 °C. The DGGE analysis predicted that the temperature transition can result in significant methanogenic biomass washout at 57 °C. [Copyright &y& Elsevier]

Abstract: Nowadays, carbon emission and therefore carbon footprint of water utilities is an important issue. In this respect, we should consider the opportunities to reduce carbon footprint for small and large wastewater treatment plants. The use of anaerobic rather than aerobic treatment processes would achieve this aim because no aeration is required and the generation of methane can be used within the plant. High-rate anaerobic digesters receive great interests due to their high loading capacity and low sludge production. Among them, the upflow anaerobic sludge blanket (UASB) reactors have been most widely used. However, there are still unresolved issues inhibiting the widespread of this technology in developing countries or countries with climate temperature fluctuations (such as subtropical regions). A large number of studies have been carried out in order to enhance the performance of UASB reactors but there is a lack of updated documentation. In face of the existing limitations and the increasing importance of this technology, the authors present an up-to-date review on the performance enhancements of UASB reactors over the last decade. The important aspects of this article are: (i) enhancing the start-up and granulation in UASB reactors, (ii) coupling with post-treatment unit to overcome the temperature constraint, and (iii) improving the removal efficiencies of the organic matter, nutrients and pathogens in the final effluent. Finally the authors have highlighted future research direction based on their critical analysis. [Copyright &y& Elsevier]

Comparison of the performance of an up-flow anaerobic sponge reactor (UASR) versus a classical up-flow anaerobic sludge blanket (UASB) reactor for sewage treatment was investigated. Both reactors were operated at a hydraulic retention time (HRT) of 6.0 h and organic loading rate (OLR) of 2.3 kg COD m-3/d. The results obtained revealed that the UASR produced better effluent quality as compared to the UASB reactor. Residual values of CODtotal, CODsoluble and CODparticulate in the treated effluent of UASR were 170 ± 54, 88 ± 36 and 82 ± 41 mg/l, respectively. Corresponding values in the UASB reactor effluent were 247 ± 69, 120 ± 40 and 127 ± 74 mg/l respectively. Furthermore, residual values of VFA-COD, oil and grease were quite less in the effluent of UASR. The removal effi iencies of faecal coliform (FC) and faecal streptococci (FS), in both reactors did not exceed one log10. However, the geometric mean of residual bacterial count was less in case of UASR. Moreover; excess sludge production from UASR reactor was almost half that produced from the UASB reactor. Although, the UASR showed a better performance for COD fractions removal than the UASB reactor, the effluent quality still exceeds the limits for discharge and /or reuse in irrigation purposes. Therefore, moving bed biofilm reactor (MBBR) based on polyurethane carrier material was investigated as a post-treatment unit. The MBBR was operated at an OLR of 7.0 g COD m-2/d and a HRT of 3.6 h. The reactor achieved a substantial reduction of CODtotal, CODparticulate and CODsoluble resulting in an average effluent concentration of 63 ± 27, 19 ± 15 and 44 ± 27 mg/l respectively. Nitrate and nitrite data reveal that 68% of the ammonia removed occurred through nitrification. Moreover, the system achieved 70 ± 13% for TKj-N removal resulting an average value of 9.3 ± 3.9 mg/l in the treated effluent. The MBBR system provided an effluent quality of 2.9 x 104 MPN100 ml-1 for FC and 1.8 x 10³ MPN 100 ml-1 for FS corresponding to the removal efficiencies of 99.87 and 99.85% respectively. [ABSTRACT FROM AUTHOR]

Abstract: An upflow anaerobic sludge blanket (UASB) bioreactor was successfully used for the treatment of petroleum refinery effluent. Before optimization, chemical oxygen demand (COD) removal was 81% at a constant organic loading rate (OLR) of 0.4kg/m3 d and a hydraulic retention time (HRT) of 48h. The rate of biogas production was 559mL/h at an HRT of 40h and an influent COD of 1000mg/L. Response surface methodology (RSM) was applied to predict the behaviors of influent COD, upflow velocity (V up) and HRT in the bioreactor. RSM showed that the best models for COD removal and biogas production rate were the reduced quadratic and cubic models, respectively. The optimum region, identified based on two critical responses, was an influent COD of 630mg/L, a V up of 0.27m/h, and an HRT of 21.4h. This resulted in a 76.3% COD removal efficiency and a 0.25Lbiogas/Lfeedd biogas production rate. [Copyright &y& Elsevier]

The possibility of enhancing the process performance of the UASB-septic tank for treating strong sewage in Palestine by means of inoculating the reactor with well adapted anaerobic sludge and/or adding a packing media to the upper part of the reactor, creating an anaerobic hybrid (AH)-septic tank, was investigated. To achieve these objectives, two community onsite UASB-septic tank and AH-septic tank were operated in parallel at 2 days HRT for around 8 months overlapping the cold and hot periods of the year in Palestine. The achieved removal efficiencies of CODtot in the UASB-septic tank and AH-septic tank during the first months of operation, coinciding with the cold period and the subsequent hot period, were respectively 50(±15)% and 48(±15)% and 66(±8)% and 55(±8)%. This shows that the UASB-septic tank performed significantly better (p<0.05) than the AH-septic tank after rather long periods of operation. The difference in the CODtot removal efficiency was mainly due to the better CODss removal efficiencies in the UASB-septic tank. The removal efficiencies over the last 50 days of operation for CODtot, CODsus, CODcol and CODdis were 70, 72, 77 and 55% and 53, 54, 78 and 45% for the UASB-septic tank and AH-septic tank, respectively. Comparing the here achieved COD removal efficiencies with previously reported efficiencies of UASB-septic tanks operated in Palestine shows that the reactor performance in terms of COD removal and conversion, during the first 8 months of operation, has improved substantially by being started with well adapted anaerobic sludge, simulating and predicting long-term performance. Adding packing media did not lead to an improvement. [ABSTRACT FROM AUTHOR]

A combined upflow anaerobic sludge blanket (UASB) and CO-stripping system was evaluated for its capacity to simultaneously remove organic compounds and calcium from linerboard mill wastewater. A continuous-flow UASB has significant potential to remove organic compounds, and its removal efficiency is closely related to volumetric organic loading. After the UASB process, a gradual decrease of pH was observed and CO-stripping indicated the formation of acid/methane and carbonate. The high concentration of carbonate that was generated from the elevated pH of the CO stripper easily reacted with calcium in the wastewater to form a solid-phase calcium carbonate. The significant amount of methane that was produced during the UASB process implies that methane-producing bacteria dominate the microbial composition of the reactor. In the CO stripper system, calcium removal and alkalinity consumption rose simultaneously with increasing solution pHs. This result suggests that the combined activity of the UASB reactor and the CO stripper system is a powerful tool for removing organic compounds and calcium from linerboard wastewater. Such a system would allow water from the linerboard production process to be reused and be discharged with fewer toxic compounds. © 2010 American Institute of Chemical Engineers Environ Prog, 2011 [ABSTRACT FROM AUTHOR]

The construction of an up-flow anaerobic sludge blanket (UASB) reactor, as an advanced primary wastewater treatment step followed by a trickling filter as a post treatment has been investigated. The performance of the UASB reactor has been monitored for a period of 20 months by implementing an intensive monitoring program. After reaching the steady state (20 weeks), average percentage removal values were 70.05% ± 11.22 for total COD, 70.35 ± 12.97 for the total BOD and 85.56% ± 7.26 for the TSS. Analyzing COD mass balance has shown that 28.6% from influent COD is converted to methane production, 31.1% of the influent COD was accumulated in the sludge, 10.4% from influent COD was consumed for sulphate reduction while 29.88% from influent COD remained in the UASB effluent. The overall efficiency of the treatment plant was satisfactory. Average total BOD removal up to 90.26% was achieved. Corresponding values for total COD and TSS were 83.14% and 87.36%, respectively. The operation and maintenance costs of the UASB plant was compared to other operating wastewater treatment plants utilizing different technologies. The results indicated that O&M costs are 30-60% lower than those of other systems, mainly due to the low energy requirements. [ABSTRACT FROM AUTHOR]

Abstract: An aerobic granular sludge (AGS) reactor was run for 280 days to study the competition between Phosphate and Glycogen Accumulating Organisms (PAOs and GAOs) at high temperatures. Numerous researches have proven that in suspended sludge systems PAOs are outcompeted by GAOs at higher temperatures. In the following study a reactor was operated at 30 °C in which the P-removal efficiency declined from 79% to 32% after 69 days of operation when biomass removal for sludge retention time (SRT) control was established by effluent withdrawal. In a second attempt at 24 °C, efficiency of P-removal remained on average at 71 ± 5% for 76 days. Samples taken from different depths of the sludge bed analysed using Fluorescent in situ hybridization (FISH) microscopy techniques revealed a distinctive microbial community structure: bottom granules contained considerably more Accumulibacter (PAOs) compared to top granules that were dominated by Competibacter (GAOs). In a third phase the SRT was controlled by discharging biomass exclusively from the top of the sludge bed. The application of this method increased the P-removal efficiency up to 100% for 88 days at 30 °C. Granules selected near the bottom of the sludge bed increased in volume, density and overall ash content; resulting in significantly higher settling velocities. With the removal of exclusively bottom biomass in phase four, P-removal efficiency decreased to 36% within 3 weeks. This study shows that biomass segregation in aerobic granular sludge systems offers an extra possibility to influence microbial competition in order to obtain a desired population. [Copyright &y& Elsevier]

Abstract: Anaerobic digestion of palm oil mill effluent (POME) and deoiled POME was investigated both in batch assays and continuous reactor experiments using up-flow anaerobic sludge blanket (UASB) and expanded granular sludge bed (EGSB) reactors. The methane potential determined from batch assays of POME and deoiled POME was 503 and 610mL-CH4/gVS-added, respectively. For the treatment of POME in continuously fed reactors, both in UASB and EGSB reactors more than 90% COD removal could be obtained, at HRT of 5 days, corresponding to OLR of 5.8gVS/(L-reactor.d). Similar methane yields of 436–438mL-CH4/gVS-added were obtained for UASB and EGSB respectively. However, for treatment of deoiled POME, both UASB and EGSB reactors could operate at lower OLR of 2.6gVS/(L-reactor.d), with the methane yield of 600 and 555mL-CH4/gVS-added for UASB and EGSB, respectively. The higher methane yield achieved from the deoiled POME was attributed to lower portion of biofibers which are more recalcitrant compared the rest of organic matter in POME. The UASB reactor was found to be more stable than EGSB reactor under the same OLR, as could be seen from lower VFA concentration, especially propionic acid, compared to the EGSB reactor. [Copyright &y& Elsevier]

Abstract: To improve the performance of an upflow anaerobic sludge blanket (UASB) reactor treating raw domestic wastewater under temperate climates conditions, the addition of a sludge digester to the process was investigated. With the decrease in temperature, the COD removal decreased from 78% at 28°C to 42% at 10°C for the UASB reactor operating alone at a hydraulic retention time of 6h. The decrease was attributed to low hydrolytic activity at lower temperatures that reduced suspended matter degradation and resulted in solids accumulation in the top of the sludge blanket. Solids removed from the upper part of the UASB sludge were treated in an anaerobic digester. Based on sludge degradation kinetics at 30°C, a digester of 0.66l per liter of UASB reactor was design operating at a 3.20days retention time. Methane produced by the sludge digester is sufficient to maintain the temperature at 30°C. [Copyright &y& Elsevier]

This article evaluates the performance of 10 large scale upflow anaerobic sludge blanket (UASB) sewage treatment plants (STP) located in semi-tropical areas, 7 plants were located in Brazil, 2 in India and 1 in the Middle East. In addition to the UASB, essential functional units of the STP which potentially impact on the UASB are also evaluated. Most grit removal systems were performing adequately, however in one plant very little grit was being removed. This could have serious implications for the performance of the plant as in a relatively short period of time the reactors could become full of grit. The performance results obtained in this study (COD, BOD and TSS removal efficiencies) are compared to the results of recent literature publications and also to the results of some early pilot and full scale studies. The results found here are broadly similar to those result reported in the recent literature but show a lower performance in comparison with the early pilot scale plants. Factors such as improper design, poor operating procedures, insufficient maintenance and the presence of high sulphate concentrations have been identified as the main reasons for the lower performance. [ABSTRACT FROM AUTHOR]

The anaerobic biodegradability and inhibitory effects on the methane production of three different surfactants, two anionic: sodium lauryl sulfate (SLS) and sodium dodecylbenzene sulfonate (SDBS), and a cationic surfactant: trialkyl-methylammonium chloride (TMAC), were evaluated with two different anaerobic sludges, granular and flocculent. Five different concentrations of the surfactants, 5, 50, 100, 250 and 500 mg/L, were tested. SLS was biodegraded at concentrations of 5, 50 and 100 mg/L with flocculent sludge and at 100 and 250 mg/L with granular sludge. However an inhibitory effect on methane production was observed in both sludges at 500 mg/L. The results indicate that SDBS was not biodegradable under anoxic conditions. TMAC was slightly degraded 50 and 100 mg/L with the flocculent sludge, and from 100 to 500 mg/L with the granular sludge. [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]

Abstract: The effect of reactor process configuration on anaerobic production of useful energy (hydrogen and methane) from a complex substrate was investigated for the following reactor systems: suspended growth, two-phase mixed, two-stage mixed, upflow anaerobic sludge blanket (UASB) reactor, and two-phase UASB. The mixed two-phase and two-stage configurations yielded the highest specific energy productions of 13.3 and 13.4 kJ/g COD fed, respectively. Reactor process configuration influenced microbial pathways in acidogenic reactors in that butyrate was the predominant volatile acid in phased configurations, whereas acetate was predominant in the staged configuration. The UASB reactor achieved the highest average daily energy production per reactor volume of 101 kJ/L reactor-d. All reactor configurations achieved high COD removals on the order of 99%. However, hydrogen represented only 3% of the total energy produced by the two-phase mixed and two-phase UASB configurations. Theoretical analysis revealed that the maximum specific energy production by the two-phase suspended-growth configuration is only 9% higher than that for a single-stage mixed reactor. Consequently, the production of hydrogen from complex substrates in these process configurations does not seem to be justifiable solely from an energy point of view. Instead, it is suggested that phased anaerobic systems should be considered primarily for improved process stability whereas resultant hydrogen production is of secondary benefit. [Copyright &y& Elsevier]

Municipal wastewater separation into black and greywater proved to be an efficient system to prevent the contamination of greywater, reduce the volume of fecal contaminated wastewater as well as reducing the cost of treatment. Meanwhile, up-flow anaerobic sludge blanket (UASB) proved to be a cost effective pretreatment system for wastewater. On the other hand, constructed wetlands (CWs) offer a low-cost alternative for wastewater treatment in developing countries, particularly in the arid and semi-arid areas. In the present study, two separate UASB reactors were used as a primary treatment step followed by CW for the treatment of blackwater and greywater separately. The hydraulic residence time (HRT) of UASB was kept constant at 6 and 24 h for the two reactors, while the organic loading rates (OLRs) were 1.88 and 1.16 kg/m³/day for the treatment of blackwater and greywater, respectively. The removal efficiency of chemical oxygen demand (COD) in the UASB reactor was about 60% for greywater and 68% for blackwater. Further improvement of the quality of the treated wastewater was obtained after the application of the horizontal subsurface flow CW. The overall results indicated that the integration between the UASB and the CW proved to be very efficient for the treatment of blackwater. The overall removal of the key constituents represented by COD, biological oxygen demand (BOD) and total suspended solids (TSS) in the final effluent was 87.7%, 89.5% and 94% for greywater and 94.2%, 95.6% and 94.9% for blackwater. It therefore, recommended that the combination of UASB and CW is an effective system for the treatment of blackwater and greywater. [ABSTRACT FROM AUTHOR]

Simultaneous methanogenesis and nitrogen removal using a combined system consisting of an up-flow anaerobic sludge blanket (UASB) and aerobic membrane bioreactor (MBR) was investigated for treating synthetic municipal wastewater. A more reliable effluent quality of above 98.0% total organic carbon (TOC) and 98.0% NH4+-N removal was achieved consistently throughout the experiments. Total nitrogen (TN) removal of up to 82.8% could also be achieved when the recycling ratio was increased from 0 to 800%. Analysis of the biogas composition showed that the degradation of NOX−-N through denitrification did not have any obvious effect on the total methane production up to a recycling ratio of 400%. A higher recycling ratio of 800% resulted in an increase of CO2 and a decrease of CH4, due to more sludge being washed out from the UASB into the MBR and recycled back into the UASB, which resulted in a higher dissolved oxygen (DO) concentration in the UASB. Hence, an optimal recycling ratio of 400% was suggested to achieve higher carbon and nitrogen removal efficiencies with over 56.3% methane in the biogas using the new combined system. [ABSTRACT FROM AUTHOR]

Abstract: Wastewater treatment performance of the combined process of upflow anaerobic sludge blanket (UASB) reactorand sequencing batch reactor (SBR) was studied. An experimental study has been conducted investigating theperformance of the system under different operating conditions. Three experimental runs were considered. Theretention time in the UASB was changed from 4 h to 3 h and the aeration time in the SBR cycle varied from 2 to 5,and then to 9 h. The results indicated that the average percentage removal for the three runs for COD, BOD andTSS was 94%, 97% and 98% respectively. Complete nitrification of ammonia was achieved after 5 h aeration in theSBR. The water quality of the treated wastewater resulted from the integrated system at different operating conditionscomplied with the local standards regulating wastewater discharge into agriculture drains. The main advantage ofthe proposed treatment system is the minimization of investment and operational costs as compared to the use ofthe SBR systems alone. The implementation of the anaerobic pretreatment leads to reduction of the plant area,sludge production and oxygen requirement 40%, 58%and 62% respectively. [Copyright &y& Elsevier]

Upflow anaerobic sludge bed (UASB) bioreactors are commonly used for anaerobic wastewater treatment. Trace metals need to be dosed to these bioreactors to maintain microbial metabolism and growth. The dosing needs to balance the supply of a minimum amount of micronutrients to support a desired microbial activity or growth rate with a maximum level of micronutrient supply above which the trace metals become inhibitory or toxic. In studies on granular sludge reactors, the required micronutrients are undefined and different metal formulations with differences in composition, concentration and species are used. Moreover, an appropriate quantification of the required nutrient dosing and suitable ranges during the entire operational period has been given little attention. This review summarizes the state-of-the-art knowledge of the interactions between trace metals and cells growing in anaerobic granules, which is the main type of biomass retention in anaerobic wastewater treatment reactors. The impact of trace metal limitation as well as overdosing (toxicity) on the biomass is overviewed and the consequences for reactor performance are detailed. Special attention is given to the influence of metal speciation in the liquid and solid phase on bioavailability. The currently used methods for trace metal dosing into wastewater treatment reactors are overviewed and ways of optimization are suggested. [Copyright &y& Elsevier]

This Study describes the feasibility of anaerobic degradation of United States Environmental Protection Agency (USEPA) listed 4-chloro-2-nitrophenol (4C-2-NP), 2-chloro-4-nitrophenol (2C-4-NP), 2-chloro-5-methylphenol (2C-5-MP) from a simulated wastewater using four identical 7L bench scale hybrid up flow anaerobic sludge blankets (HUASBs) at five different hydraulic retention times (HRTs) under thermophilic condition (55±3°C). The substrate to co-substrate ratios were maintained between 1:33.3 and 1:166.6. Continuous monitoring of parameters like pH, volatile fatty acids (VFAs) accumulation, oxidation reduction potential, chemical oxygen demand (COD), alkalinity, gas productions, methane percentages were carried out along with compound reduction to asses the efficiency of biodegradation. The compound reduction was estimated by using spectrophotometric methods and further validated with high-performance liquid chromatography (HPLC). Optimum HRT values were observed at 24h. Optimum ratio of substrate (phenolic compounds) to co-substrate (glucose) was 1:100. Scanning electron micrographs show that the granules were composed of thermophilic Methanobrevibacter and thermophilic Methanothrix like bacteria. [Copyright &y& Elsevier]

The market for coconut water causes environmental problems as it is one of the major agroindustrial solid wastes in some developing countries. With the aim of reusing the coconut husk, Embrapa developed a system for processing this raw material. During the dewatering stage Coconut Husk Liquor (CHL) is generated with chemical oxygen demand (COD) varying from 60 to 70 g/L due to high concentrations of sugars and tannins. The present study evaluated the feasibility of anaerobic treatment of CHL through Anaerobic Toxicity Assay and the operation of a lab-scale Upflow Anaerobic Sludge Blanket (UASB) reactor. Results showed that CHL can be treated through a UASB reactor operating with an OLR that reaches up to 10 kg/m³·d and that is maintained stable during the whole operation. With this operational condition, the removal efficiency was higher than 80% for COD and approximately 78% for total tannins, and biogas production was 20 m³ of biogas or 130 KWh per m³ of CHL. Seventy-five percent of the biogas composition was methane and toxicity tests demonstrated that CHL was not toxic to the methanogenic consortia. Conversely, increasing the concentration of CHL leads to increased methanogenic activity. [ABSTRACT FROM AUTHOR]

Abstract: The hybrid up flow anaerobic sludge blanket reactor was evaluated for efficacy in reduction of chemical oxygen demand (COD) and biochemical oxygen demand (BOD) of bulk drug pharmaceutical wastewater under different operational conditions. The start-up of the reactor feed came entirely with glucose, applied at an organic loading rate (OLR) 1kgCOD/m3 d. Then the reactor was studied at different OLRs ranging from 2 to 11kgCOD/m3 d with pharmaceutical wastewater. The optimum OLR was found to be 9kgCOD/m3 d, where we found 65–75% COD and 80–94% of BOD reduction with biogas production containing 60–70% of methane and specific methanogenic activity was 320ml CH4/g-VSSd. By the characterization studies of effluent using GC–MS, the hazardous compounds like phenol, l,2-methoxy phenol, 2,4,6-trichloro phenol, dibutyl phthalate, 1-bromo naphthalene, carbamazepine and antipyrine were present. After the treatment, these compounds degraded almost completely except carbamazepine. Thermophilic methanothrix and methanosaetae like bacteria are present in the granular sludge. [Copyright &y& Elsevier]

The ADM1 is applied to simulate the behaviour of an Upflow Anaerobic Sludge Blanket Reactor (UASB) treating blood powder (spray dried blood meal) wastewater. Considering a completely mixed liquid phase, the model is defined by a set of differential equations which can be numerically solved. Experimental data allows validating the output of the model which is then used for performing numerous simulations. A single reactor is compared to a series of two identical reactors of half the volume each. For the same total hydraulic retention time, the series reaches an outlet concentration 74% inferior to that of the single reactor. Furthermore, for the same total conversion the volume required by the series is 43% of that of the single reactor. [ABSTRACT FROM AUTHOR]

Abstract: The wastewater treatment systems from the three local breweries consist of upflow anaerobic sludge blanket (UASB) and activated sludge (AS) connected in series for which the influent and effluent from each treatment step were collected and determined for their dissolved organic matter (DOM) surrogate parameters including dissolved organic carbon (DOC), UV254 and SUVA254. The analyses suggested that the influent wastewater contained a high level of aromatic organic content classified as humic substances with high average molecular weight. Organic removal mostly occurred in the UASBs where DOC and UV254 were reduced by 24–58% and 38–50%, respectively. Spectrofluorometry analysis (fluorescent excitation–emission matrix: FEEM) was reasonably accurate in evaluating DOM reduction during the treatment course. A total of eight fluorescent peaks were detected by the FEEM technique comprising (A) 230nmEx/315nmEm, (B) 275nmEx/315nmEm, (C) 230nmEx/365nmEm, (D) 285nmEx/365nmEm, (E) 290nmEx/400nmEm, (F) 335–355nmEx/405–465nmEm, (G) 255nmEx/455nmEm, and (H) 500nmEx/525nmEm. Peaks ‘A and B’ and ‘C and D’ were associated with tyrosine-like, tryptophan-like substances, respectively, whilst each individual peak E, F and G was associated with humic and fulvic acid-like substances. Peaks C, D, F and H were always found in the influent wastewater from all the breweries, whereas the effluents only exhibited Peak F. The origin of Peak H had not been recognized elsewhere and was not identified in this work. This suggested that FEEM could not only be used to monitor the reduction in DOM, but it could also provide details on the organic composition of the wastewater. [Copyright &y& Elsevier]

Abstract: The effect of ferrous ion addition on the granularity of an upflow anaerobic sludge blanket (UASB) reactor was investigated. Two UASB reactors (R1 and R2) (35°C; pH 7) were operated for 3 months at a 20-h hydraulic retention time (HRT) at organic loads from 1.4 to 10.0gCODL−1 d−1. Ferrous iron was fed only to reactor R1 in a range of load from 0.014 to 0.100g Fe2+ L−1 d−1. The addition of ferrous iron induced a stable and excellent COD conversion rate. The enhancement of the performance of reactor R1 may be accredited to the mean granule diameter increase as well as to the sludge bed porosity decrease. The addition of iron to reactor R1 had a pronounced effect on the quality of the granular sludge, increasing the characteristic settling velocities. The formation of ferrous sulphide was mainly responsible for the promotion of sludge granulation. [Copyright &y& Elsevier]

Abstract: The effects of lowering the operational pH from 6 to 5 on mesophilic (30°C) sulfate reduction during the acidification of sucrose at an organic loading rate of 5gCOD(lreactor d)−1 and at a COD/SO4 2− ratio of 4 were evaluated in a CSTR and in a UASB reactor. The HRT was 24h and 10h, respectively. Acidification was complete in both reactors at pH 6 and the lowering of the operational pH to 5 did not affect the acidification efficiency in the CSTR but decreased the acidification efficiency of the UASB to 72%. The decrease to pH 5 caused an increase in the effluent butyrate and ethanol concentrations in both reactors. Lowering the pH from 6 to 5 caused a decrease in sulfate reduction efficiencies in both reactors, from 43% to 25% in the CSTR and from 95% to 34% in the UASB reactor. The acidification and sulfate reduction efficiencies at pH 5 could be increased to 94% and 67%, respectively, by increasing the HRT of the UASB reactor to 24h. [Copyright &y& Elsevier]

Abstract: Biohydrogen production from Thermoanaerobacterium thermosaccharolyticum strain PSU-2 was examined in upflow anaerobic sludge blanket (UASB) reactor and carrier-free upflow anaerobic reactor (UA), both fed with sucrose and operating at 60°C. Heat-pretreated methanogenic granules were used as carrier to immobilize T. thermosaccharolyticum strain PSU-2 in UASB reactor operated at a hydraulic retention time (HRT) ranging from 0.75 to 24h and corresponding sucrose loading rate from 58.5 to 2.4mmol sucrosel−1 h−1. In comparison with hydrogen production rate of 12.1mmol H2 l−1 h−1 obtained by carrier-free reactor upflow anaerobic (UA) system, a greatly improved hydrogen production rate up to 152mmol H2 l−1 h−1 was demonstrated by the granular cells in UASB system. The biofilm of T. thermosaccharolyticum strain PSU-2 developed on treated methanogenic granules in UASB reactor substantially enhanced biomass retention (3 times), and production of hydrogen (12 times) compared to carrier-free reactor. It appears to be the most preferred process for highly efficient dark fermentative hydrogen production from sugar containing wastewater under thermophilic conditions. [Copyright &y& Elsevier]

PVA-gel beads were used as a biocarrier in a lab-scale UASB reactor treating synthetic wastewater composed of corn steep liquor (CSL) with the aim of evaluating its use as a growth nucleus to enhance granule formation. Over 117 days of operation, the organic loading rate was increased to 22.5kgCOD/m3/day with an influent COD of about 10.8g/L at an HRT of 12h with COD removal efficiencies greater than 87%. By the end of the study period, the PVA-gel turned black and granule formation was achieved as compared with the formation of much fewer natural granules without the PVA-gel nucleus. No filamentous bacteria were found on the surface or interior of the PVA-gel beads. The PVA-gel granules had an average settling velocity 200m/h (5cm/s), and a biomass attachment of 0.93g VSS/g PVA-gel. The required time for formation of PVA-gel granules was thus demonstrated to be shorter than that of ordinary sludge granules under the experimental conditions used in this study. [Copyright &y& Elsevier]

A start-up experiment was performed in a laboratory-scale, upflow anaerobic sludge blanket (UASB) reactor using seed sludge from a domestic waste treatment plant at 3.8–33.3gCODl−1 day−1 loading rates. Analysis over the height of the reactor with time showed that the VSS in the reactor was initially differentiated into active and non-active biomass at increasing gas production and upflow velocities, and specific update rates of the volatile fatty acids (VFA) components were pronounced at the bottom 10% of the reactor. During start-up, specific methanogenic activity and chemical oxygen demand (COD) uptake rate increased from 0.075 to 0.75gCOD–CH4 (gVSS)−1 day−1 and from 0.08 to 0.875gCOD removed (gVSS)−1 day−1, respectively. When seed sludge from a distillery waste treatment plant was used, improved performance due to a predominance of active biomass was evident when the loading rate was increased from 9.4 to 28.7gCODl−1 day−1. The proposed start-up evaluation is an effective tool to successfully monitor performance of UASB reactors. [Copyright &y& Elsevier]

Abstract: The treatment of high strength sewage was investigated in a one-stage upflow anaerobic sludge blanket (UASB) reactor and a UASB-digester system. The one-stage UASB reactor was operated in Palestine at a hydraulic retention time (HRT) of 10h and at ambient air temperature for a period of more than a year in order to asses the system response to the Mediterranean climatic seasonal temperature fluctuation. Afterwards, the one-stage UASB reactor was modified to a UASB-digester system by incorporating a digester operated at 35°C. The achieved removal efficiencies in the one-stage UASB reactor for total, suspended, colloidal, dissolved and VFA COD were 54, 71, 34, 23%, and −7%, respectively during the first warm six months of the year, and achieved only 32% removal efficiency for COD total over the following cold six months of the year. The modification of the one-stage UASB reactor to a UASB-digester system had remarkably improved the UASB reactor performance as the UASB-digester achieved removal efficiencies for total, suspended, colloidal, dissolved and VFA COD of 72, 74, 74, 62 and 70%. Therefore, the anaerobic treatment of high strength sewage during the hot period in Palestine in a UASB-digester system is very promising. [Copyright &y& Elsevier]

Abstract: The aim of this paper was to propose a granulation mechanism in order to interpret all the experimental observations that arose during experiments on two UASB reactors, where one was supplemented with ferrous iron at a dose of 0.01g Fe2+ per g COD feed. This supplementation with ferrous iron allowed COD removal of more than 98% at a loading rate of 9g COD/L per day, which was 24% higher than for the reactor not receiving the ferrous iron. Moreover, in the Fe2+-dosed reactor, a higher increase of the granule diameter was observed. Indeed, the granule diameter in the Fe2+-dosed reactor at the end of the experiments was 56% greater than that of the control reactor. This mechanism describes the course of anaerobic granule growth. The formation of the inorganic precipitate of ferrous sulphide constitutes the inert nuclei around which the biomass is attached. This initiates the formation of new granules. [Copyright &y& Elsevier]

Abstract: The effect of a low pH (6, 5 and 4) on macro- and micronutrient dynamics in anaerobic sludge granules was investigated in batch leaching experiments and thermophilic (55°C) Upflow Anaerobic Sludge Bed (UASB) reactors. The UASB reactors were fed with sucrose and sulfate at an organic loading rate of 3.5g COD (lreactor d)−1 and a COD/SO4 2− ratio of 9 or 3.5 over a period of 520 days at pH 6 and 270 days at pH 5 and 4. Decreasing the pH led to increased solubilisation of metals from the sludge in the leaching experiments within 48h. For many metals (Co, Ni, Fe, Zn and Al), the difference between pH 6 and 5 was very small. For the three pH values investigated, the degree of leaching was the highest for the macronutrients K, Ca and Mg while for the other micronutrients leaching decreased in the following order: Mn>Ni≈Co≈Fe>Al≈Zn≈Cu. In the continuously operating UASB reactors, most metals leached from the sludge granules except for Co at pH 6, Al at pH 6 and 5 and Cu and Zn at all three pH values investigated. At the end of the UASB reactor runs, the sludge granules were almost deprived of Fe and Mn both at pH 5 and 4. Despite the significant changes in the inorganic composition of the sludge granules, the granular form of the sludge was kept at the different pH values and sulfate loading rates applied, and no significant washout occurred, though the granules’ strength decreased at pH 5 and 4. The colour of the granules changed gradually from black to grey during the operation at pH 6 and to a pale yellow during the operation at pH 5 and 4. [Copyright &y& Elsevier]

A two-stage anaerobic treatment pilot plant was tested for the treatment of raw domestic wastewater under temperatures ranging from 21 to 14°C. The plant consisted of a hydrolytic upflow sludge bed (HUSB) digester (25.5m3) followed by an upflow anaerobic sludge blanket (UASB) digester (20.36m3). The hydraulic retention time (HRT) varied from 5.7 to 2.8h for the first stage (HUSB digester) and from 13.9 to 6.5h for the second stage (UASB digester). Total suspended solids (TSS), total chemical oxygen demand (TCOD), and biochemical oxygen demand (BOD) removals ranged from 76% to 89%, from 49% to 65%, and from 50% to 77%, respectively, for the overall system. The percentage of influent COD converted to methane was 36.1%, the hydrolysis of influent volatile suspended solids (VSS) reached 59.7% and excess biomass was 21.6% of the incoming VSS. Plant performance was influenced by the wastewater concentration and temperature, yet better results were obtained for influent COD higher than 250mg/l. [Copyright &y& Elsevier]

Abstract: Studies have been carried out to correlate biogas-induced mixing and granulation in upflow anaerobic sludge blanket (UASB) reactors, treating low-strength as well as high-strength biodegradable wastewaters. A dimensionless granulation index (GI) has been framed taking into account the mixing in sludge bed due to produced biogas. Analysis of full-scale, pilot-scale and lab-scale UASB reactors treating actual wastewaters reveals the significance of biogas-induced mixing, represented by GI, on granulation of biomass in the reactors. For obtaining proper granulation in UASB reactors (percentage granules greater than 50%, w/w), resulting in higher chemical oxygen demand (COD) removal efficiency, it is recommended to maintain GI values in the range of 15,000–57,000. [Copyright &y& Elsevier]

Abstract: The feasibility of using an up-flow anaerobic sludge blanket (UASB) reactor followed by activated sludge (AS system) for the treatment of wastewater discharged from dairy factory was explored. The UASB reactor was operated at a hydraulic retention time (HRT) of 24 h and organic loading rates (OLRs) ranging from 1.9 to 4.4 kgCOD/m3.d. The average total chemical oxygen demand (CODtotal) and total biological oxygen demand (BOD5total) concentrations of the UASB reactor effluent were 1385 and 576 mg/l, corresponding to percentage removal of 69% and 79%, respectively. Total suspended solids (TSS) and volatile suspended solids (VSS) removal averaged above 72% and 75%, respectively. Residual phosphorous and oil and grease concentrations of the UASB reactor effluent were 8.2 and 44 mg/l, corresponding to percentage removal values of 63% and 83%, respectively. This good performance could be attributed to the relatively long sludge residence time (SRT=76 d) imposed to the reactor. Total and faecal coliform counts were reduced in the treated effluent by a value of 1.07 and 0.9 log10, respectively. The net sludge yield coefficient was found to be 0.2 g VSS per g CODtotal removed per day, corresponding to 20% of the total influent COD imposed to the UASB reactor. The volatile solids/total solids (VS/TS) ratio of 0.66 of excess sludge revealed its good quality. Preliminary batch experiments of the AS system treating UASB reactor effluent indicated first-order removal kinetics between total organic carbon (TOC) and contact time. The TOC removal reached 80%, resulting in only 47 mg/l in the final effluent at a HRT of 2.0 h. Accordingly, the AS system was operated at a HRT of 2.0 h. The system achieved a substantial reduction of CODtotal, BOD5 total, TSS and oil and grease resulting effluent quality with residual values of only 35.0, 7.0, 14.0 and 2.8 mg/l, respectively. The geometric mean of total and faecal coliform counts was reduced by a value of 1.28 and 1.64 log10, respectively. Based on these results, it is recommended to use of an integrated system consisting of a UASB reactor followed by the AS system for the treatment of a combined dairy and domestic wastewater to produce a good effluent quality complying with the standards for discharge into agricultural drains. [Copyright &y& Elsevier]