Start-up alternatives and performance of an UASB pilot plant treating diluted municipal wastewater at low temperature

The most important technologies and highlights for biogas production worldwide

Bioenergy or green fuel has been considered the fuel of the future for being a type of renewable energy that contributes to the preservation of the environment as it helps to reduce greenhouse gas emissions. In this way, biogas offers a potential alternative to fossil fuels from anaerobic digestion (AD) bioprocess, which allows the action of several microorganisms in the transformation of substrates into biogas and secondary bioproducts. Over the years, researchers have discussed that low yields in AD are associated with different factors such as type of wastewater, reactor configuration, substrate concentration, temperature, organic loading rates, and biomass concentration inside of the reactor. In this way, to better conduct the AD, studies point to the reactor configuration as one of the factors in the determination of high biogas production for a long period. Understanding and knowing the type of reactor and how the parameters such as biomass accumulation and immobilization, pH, or temperature occur in the system would provide information and can help to improve the bioenergy production in different systems. Moreover, research opportunities about different technologies are essential for the anaerobic digestion of many substrates and the stability of interest production. Thus, this type of scientific study gives a broad overview of the principal systems used in the AD process and information about the circular economy in the production of biogas in the world. Important considerations are highlighted.Implication of Statement: The review paper provides information about the scenario of biogas in the world state-of-art and the biogas production from AD. Afterwards, an extensive analysis of different and principal types of reactors applied to the AD process, aimed at presenting an overview of the advantages and disadvantages of each configuration intending to gain new insights to improve traditional reactors or propose novel ones. This article enables us to have a perspective about the different technologies available and about new alternatives from an operational point of view for bioenergy from AD, not only in bench studies or pilot scale studies but also at an industrial level. Thus, this type of scientific study gives a broad overview of the principal systems used in the AD process and information about the circular economy in the production of biogas in the world.

Performance enhancement of up-flow anaerobic sludge blanket reactor for psychrophilic temperature during the dry season: Kality wastewater treatment plant

The main purpose of wastewater treatment plant (WWTP) is to reduce organic and inorganic pollutants to meet standards. But WWTPs employing up flow anaerobic sludge blanket (UASB) reactors under psychrophilic temperature are currently removing about 55% chemical oxygen demand (COD) and 70% total dissolved solids (TSS). The research was done to increase the treatment efficiencies of UASB reactor working under psychrophilic conditions through optimization of operational parameters like temperature, organic loading rate (OLR), pH and hydraulic retention time (HRT). Experimentation was carried out in a 0.0486 m3 square-shaped pilot-scale UASB reactor. Experimental design response surface method (RSM) for performance enhancement and optimization of UASB reactor operational parameters through five levels of central composite design (CCD) was used. The optimized operational parameters obtained from CCD-RSM were as follows: temperature of 21.58 °C, OLR of 2.99 kg COD/m3.d, HRT of 4.37hrs and pH of 6.3. Using optimized parameters, tests yielded efficiencies of 92.70%, 99.06%, and 94.50% for COD, TSS, and volatile suspended solid (VSS) respectively. The outlet concentrations of alkalinity, and volatile fatty acids (VFA), were found to be lower than the inlet concentrations. The alkalinity in the system accepts the hydrogen ion released by acids and the system is taken over by methanogensis to maintain the pH. The outlet concentration of sulfate ion was found to be increasing due to inhabitation of sulfur-reducing bacteria by an anaerobic condition of VFA and alkalinity at a pH less than 7.8.This process favors the production of CH4 than H2S gas. In general, there was a high likelihood of improving the performance of UASB reactor operating at psychrophilic temperature by optimizing operational parameters.

Effect of fruits and vegetables in the anaerobic digestion of food waste from university restaurant

The aim of this study was to evaluate the theoretical potential of methane production of the food waste generated by a university restaurant, as well as to verify the influence of the fruit and vegetable waste in the feeding composition of an anaerobic bioreactor treating this type of waste. Four feeding compositions combining three fractions of the food waste (fruit and vegetable fraction, soy protein and beans fraction, and rice fraction) at different concentrations were tested in anaerobic processes lasting 10 and 30 days. Additionally, a study of the theoretical potential of methane production from each fraction that composes the food waste was carried out, as well as the evaluation of the specific methanogenic activity of the anaerobic sludge. Despite its low theoretical potential of methane production (0.037 L_CH4/g), the presence of the fruit and vegetable mixture in three of the feeding compositions led to greater organic matter degradation (above 69%) and CH₄ yields (above 0.20 L_CH4/g_VS) in both periods tested, in comparison with the achieved by the feeding composition lacking this fraction. The results suggest that the presence of the fruit and vegetable mixture contributed with the supplementation of micro- and macroelements to the anaerobic sludge during the digestion of food waste.

Effects of operating conditions on microbial consortium of the heterotrophic ammonia oxidation process

This study aimed to investigate the ammonia removal by the consortium mainly comprising of ammonia-oxidizing bacteria under different initial pH, temperatures and stress of heavy metals. The results showed that the consortium exhibited a strong adaptation for broad pH ranging from 5 to 9. When the temperature dropped to 15℃, its ammonium removal and nitrate accumulation rates decreased by 72.23% and 95.12%, respectively. Meanwhile, the temperature correction coefficients of the ammonium removal and nitrate accumulation rates reached the maximum. In addition, the consortium could survive in the solutions containing 0-1.0 mg·L^-1 Cu²⁺ and 0-5.0 mg·L^-1 Fe³⁺. Moreover, the inhibition of free nitrous acid (FNA) against nitrite oxidation activity was found to be much more significant than that low-temperature treatment. Microbial diversity analysis showed that the bacterial community structure was shift significantly by the temperature drop, especially change the abundance of Nitrosomonas, Paracoccus, Pseudomonas and Nitrospirae.

Carbamazepine removal from low-strength municipal wastewater using a combined UASB-MBR treatment system

An Upflow Anaerobic Sludge Blanket reactor combined with a two-stage membrane bioreactor were operated for 193 days in order to evaluate the biological removal of carbamazepine (CBZ) from low-strength municipal wastewater. The system worked in three different organic load stages (0.7 ± 0.1 kg COD·m^-3·d^-1, 0.4 ± 0.1 kg COD·m^-3·d^-1 and 0.1 ± 0.0 kg COD·m^-3·d^-1) to assess the impact of the influent OLR on operational parameters such as anaerobic and aerobic sludge retention time (SRT), acidity, volatile fatty acids (VFAs), biomass activity or biogas production. The highest carbamazepine removals were achieved during the anaerobic stage (UASB reactor), reaching averages of 48.9%, 48.0% and 38.2% operating at high, medium and low OLR, respectively. The aerobic treatment (MBR) served as post-treatment, improving the removals, and the global UASB-MBR system reached averages of 70.0%, 59.6% and 49.8% when the influent was at medium and low OLR, respectively. The results demonstrate the potential of combined biological systems on the removal of recalcitrant pharmaceuticals.

Post treatment of anaerobically treated brewery effluent using pilot scale horizontal subsurface flow constructed wetland system

The anaerobic process is considered to be a sustainable technology for the treatment of wastewaters rich in organic matter mainly due to its lower energy consumption and production of value-added products such as biogas and organic fertilizer. However, it cannot be seen as providing 'complete' environmental solution as its treated effluents would typically not meet the desired discharge limits in terms of residual carbon, nutrients and other pollutants. This has given impetus to subsequent post treatment in order to meet the environmental standards and protect the receiving water bodies and environment. The aim of this study was to evaluate the post-treatment potential of a pilot scale two-stage horizontal subsurface flow constructed wetland (HSSFCW) system planted with Cyperus alternifolius and Typha latifolia, respectively, for enhanced removal of residual carbon and nutrient from an up-flow anaerobic sludge blanket (UASB) reactor treated brewery effluent. A pilot scale two-stage HSSFCW was integrated with the UASB reactor, and its performance efficiency was assessed for the removal of total suspended solids (TSS), chemical oxygen demand (COD), total nitrogen (TN), ammonium-nitrogen (NH4-N), total phosphorous (TP), and orthophosphate (PO43-). Macrophytes aboveground biomass and nutrient accumulation potential were also determined following standard methods. The results from this study showed that Cyperus alternifolius planted CW cell removed 68.5% TSS, 74.2% COD, 55.7% TN, 68.6% NH4-N, 41.1% TP and 48.1% PO43-. Moreover, further polishing with Typha latifolia planted CW cell enhanced the removal efficiencies to 89% TSS, 92% COD, 83.6% TN, 92.9% NH4-N, 74.4% TP, and 79.5% PO43-. Strong linearity and Pearson correlation was found between macrophyte biomass and nutrient accumulation in each CW cell (Cyperus alternifolius: R2 = 0.91, r = 0.97 for TN; R2 = 0.92, r = 0.96 for TP; and Typha latifolia: R2 = 0.96, r = 0.98 for TN and TP), and showed substantial nutrient reduction with cumulative nutrient accumulation of 1290 gTNm-2 and 708.7 gTPm-2 in the complete system. The performance of the pilot CW system as a tertiary treatment for brewery wastewater showed that the effluent meets the permissible discharge standards throughout the year excluding phosphorous.

Taking the water out of "wastewater": An ineluctable oxymoron for urban water cycle sustainability

Water, energy, and food are key resources that could easily limit sustainability of human society development. Water supply requires considerable amounts of energy, and "usedwater" carries considerable amounts of embedded energy and recoverable materials within. Usedwater is increasingly considered as a potential resource, rather than as a waste. Among process technology options that may allow efficient recovery of that energy, anaerobic digestion could be considered the most mature, already sporting countless applications worldwide. However, the present inefficient dilution-base collection systems paradigm produces rather dilute sewage, preventing to a large degree a more efficient application of this technology. A new collection system paradigm, based on liquid sources segregation and minimal organics dilution, could result in significant energy savings for conveyance and treatment. This could also enhance recovery of nutrients and reclamation of potentially reusable water, with the associated benefit of reduced production of process residuals requiring further disposal. Implications of this model are discussed. PRACTITIONER POINTS: The nexus between water, energy, and food is an impending challenge on water cycle sustainability Current paradigms of urban water management are based on disadvantageous paradigms: high dilution and gravity flow Taking the water out of wastewater may improve energy and recovery efficiency of urban water systems and water reuse options Technologies exist (high-rate anaerobic, vacuum sewers) and are mature for more widespread application of new urban sanitation paradigms.

A composite indicator approach to assess the sustainability and resilience of wastewater management alternatives

Evaluating the sustainability of wastewater management alternatives is a challenging task. This paper proposes an innovative methodology to assess and compare the sustainability of four wastewater management alternatives: a) centralised water resource recovery facility (WRRF) based on activated sludge (AS); b) centralised WRRF with membrane bioreactors (MBR); c) decentralised WRRFs with upflow anaerobic sludge blanket reactors and trickling filters; d) centralised-decentralised hybrid system. In doing so, a composite indicator embracing total annual equivalent costs, carbon emission intensity, eutrophication and resilience (based on robustness and rapidity metrics) was developed using the analytic hierarchy process (AHP) method. The results show that decentralised and hybrid systems contribute less to carbon emission and eutrophication because of energy and fertilizer harvest and with a trade-off of higher costs of 7-17% than the ones of AS and MBR. In addition, decentralised and hybrid systems are more resilient, contributing to lower environmental impacts facing natural disasters. Based on the weights obtained by AHP, the decentralised alternative appears to be the most sustainable option due to its best performance in terms of carbon emission intensity and resilience. By contrast, the MBR alternative appeared the least sustainable evaluated wastewater management alternative. However, this alternative is sustainable option when the eutrophication criterion is heavily prioritized. The proposed approach contributes to the selection of the most sustainable wastewater management alternative from a holistic perspective.

Anaerobic treatment of chocolate-processing industry wastewater at different organic loading rates and temperatures

The objective of the present study was to determine the optimum operating temperature of laboratory-scale upflow anaerobic sludge blanket (UASB) reactors during the treatment of a chocolate-processing industry wastewater at medium applied organic loading rates (OLR_appl). Four UASB reactors were operated at different temperature (15, 20, 25 and 30 °C) and three OLR_appl (2, 4 and 6 kg soluble chemical oxygen demand (COD_s)/(m³ d)). The flowrate and the hydraulic retention time were constant (11.5 L/d and 6 h, respectively). The monitored parameters were pH, temperature, COD_s, and total and volatile suspended solids. The COD_s removal efficiency (RE) and biogas production rate (BPR) were calculated. The 15 °C UASB reactor had the lowest RE (39 to 78%) due to the low operating temperature. Regardless of the OLR_appl, the RE of the 20, 25 and 30 °C reactors was high and similar to each other (between 88 and 94%). The BPR of the four UASB reactors had the same behaviour as the RE (BPR of 15 °C: 0.3 to 0.5 L_biogas/(L_reactor d) (L_b/(L_r d)) and BPR of 20, 25 and 30 °C: 0.5 to 1.9 L_b/(L_r d)).

Review of Upflow Anaerobic Sludge Blanket Reactor Technology: Effect of Different Parameters and Developments for Domestic Wastewater Treatment

The upflow anaerobic sludge blanket (UASB) reactor has been recognized as an important wastewater treatment technology among anaerobic treatment methods. The objective of this study was to perform literature review on the treatment of domestic sewage using the UASB reactor as the core component and identifying future areas of research. The merits of anaerobic and aerobic bioreactors are highlighted and other sewage treatment technologies are compared with UASB on the basis of performance, resource recovery potential, and cost. The comparison supports UASB as a suitable option on the basis of performance, green energy generation, minimal space requirement, and low capital, operation, and maintenance costs. The main process parameters such as temperature, hydraulic retention time (HRT), organic loading rate (OLR), pH, granulation, and mixing and their effects on the performance of UASB reactor and hydrogen production are presented for achieving optimal results. Feasible posttreatment steps are also identified for effective discharge and/or reuse of treated water.

Low temperature treatment of domestic wastewater by purple phototrophic bacteria: Performance, activity, and community

Low wastewater temperatures affect microbial growth rates and microbial populations, as well as physical chemical characteristics of the wastewater. Wastewater treatment plant design needs to accommodate changing temperatures, and somewhat limited capacity is a key criticism of low strength anaerobic treatment such as Anaerobic Membrane Bioreactors (AnMBR). This study evaluates the applicability of an alternative platform utilizing purple phototrophic bacteria for low temperature domestic wastewater treatment. Two photo-anaerobic membrane bioreactors (PAnMBR) at ambient (22 °C) and low temperatures (10 °C) were compared to fully evaluate temperature response of critical processes. The results show good functionality at 10 °C in comparison with ambient operation. This enabled operation at 10 °C to discharge limits (TCOD < 100 mg L(-1); TN < 10 mg L(-1) and TP < 1 mg L(-1)) at a HRT < 1 d. While capacity of the system was not limited, microbial community showed a strong shift to a far narrower diversity, almost complete dominance by PPB, and of a single Rhodobacter spp. compared to a more diverse community in the ambient reactor. The outcomes of the current work enable applicability of PPB for domestic wastewater treatment to a broad range of regions.

Pilot scale application of anaerobic baffled reactor for biologically enhanced primary treatment of raw municipal wastewater

A four-cell anaerobic baffled reactor (ABR) was operated for two years treating raw municipal wastewater at ambient water and air temperatures of 12-23 °C and -10 to 35 °C, respectively. The 1000-L pilot reactor operated at a 12-h hydraulic residence time and was located in the Headworks building of the Plum Creek Water Reclamation Authority. The average influent was TSS = 510 ± 400 mg/L, BOD5 = 320 ± 80 mg/L and the average removal of TSS and BOD5 was 83 ± 10% and 47 ± 15%, respectively. The TSS and BOD removal exceeded that of conventional primary clarification, with no wasting of the settled solids over the two-years and stoichiometric production of methane. The estimated energy content of the biogas produced per unit volume of wastewater treated averaged 0.45 kWh/m(3). The TSS and total COD removal in the first cell averaged 75 ± 15% and 43 ± 14%, respectively, but methane production was only 20% of the total observed for the full ABR. The performance of the ABR relative to the extent of solids hydrolysis and methane production can be varied by the number of cells and hydraulic residence time. The anaerobic baffled reactor is an energy-positive technology that can be used for biologically enhanced primary treatment of raw municipal wastewater in cold climates.

Effect of temperature, salinity, heavy metals, ammonium concentration, pH and dissolved oxygen on ammonium removal by an aerobic nitrifier

An aerobic nitrifier WY-01 was identified asAlcaligenes faecalisby its 16S rRNA gene sequence analysis. It could remove ammonium effectively in varying physico-chemical conditions, such as low temperature, high salinity and high ammonium loads.

Impact resistance of different factors on ammonia removal by heterotrophic nitrification-aerobic denitrification bacterium Aeromonas sp. HN-02

To give reference for the application of heterotrophic nitrification-aerobic denitrification bacteria in actual wastewater treatment, the impact resistance of extreme pH, low temperature, heavy metals and high salinity on ammonia removal by a typical heterotrophic nitrifying-aerobic denitrifying bacterium Aeromonas sp. HN-02 was investigated. The results showed that HN-02 demonstrated strong acid- and alkali-resistance. In addition, it remained active at 5°C, and the removal rates of ammonia and COD were 0.90 mg L(-1)h(-1) and 22.34 mg L(-1)h(-1), respectively. Under the same extent of immediate temperature drop, the temperature correction coefficients of ammonia, COD removal rates and cell growth rate were close. Moreover, HN-02 could survive in the solution containing 0.5 mg L(-1) Cu(2+) or 8 mg L(-1) Zn(2+), or 0.5 mg L(-1) of equivalent Cu(2+)-Zn(2+). Furthermore, efficient ammonia removal was retained at salinity below 20 g L(-1), thus it could be identified as a halotolerant bacterium. At last, stronger stress resulted in higher ΔCOD/ΔTN ratio.

Simultaneous energy recovery and autotrophic nitrogen removal from sewage at moderately low temperatures

This study assessed the technical feasibility of treating sewage with a combination of direct anaerobic treatment and autotrophic nitrogen removal, while simultaneously achieving energy recovery and nitrogen removal under moderately low temperatures. The concentrations of ammonia, nitrite, and COD in effluent were below 1, 0.1, and 30 mg/L, respectively. In the up-flow, anaerobic sludge fixed-bed, there was no obvious change observed in the total methane production at temperatures of 35 ± 1 °C, 28 ± 1 °C, 24 ± 3 °C, and 17 ± 3 °C, with the accumulation of volatile fatty acids occurring with decreasing temperatures. The control strategy employed in this study achieved a stable effluent with equimolar concentrations of nitrite and ammonium, coupled with high nitrite accumulation (>97 %) in the partial nitrification sequencing batch reactor system at moderately low temperatures. In the anaerobic ammonium oxidation (anammox) reactor, a short hydraulic retention time of 0.96 h, with a nitrogen removal rate of 0.83 kgN/(m(3)/day) was achieved at 12-15 °C. At low temperatures, the corresponding fluorescence in situ hybridization image revealed a high amount of anammox bacteria. This study demonstrates that efficient nitrogen removal and energy recovery from sewage at moderately low temperatures can be achieved by utilizing a combined system. Additionally, this system has the potential to become energy-neutral or even energy-producing.

Biological sulfate removal from acrylic fiber manufacturing wastewater using a two-stage UASB reactor

A two-stage UASB reactor was employed to remove sulfate from acrylic fiber manufacturing wastewater. Mesophilic operation (35 +/- 0.5 degree C) was performed with hydraulic retention time (HRT) varied between 28 and 40 hr. Mixed liquor suspended solids (MLSS) in the reactor was maintained about 8000 mg/L. The results indicated that sulfate removal was enhanced with increasing the ratio of COD/SO4(2-). At low COD/SO4(2-), the growth of the sulfate-reducing bacteria (SRB) was carbon-limited. The optimal sulfate removal efficiencies were 75% when the HRT was no less than 38 hr. Sulfidogenesis mainly happened in the sulfate-reducing stage, while methanogenesis in the methane-producing stage. Microbes in sulfate-reducing stage performed granulation better than that in methane-producing stage. Higher extracellular polymeric substances (EPS) content in sulfate-reducing stage helped to adhere and connect the flocculent sludge particles together. SRB accounted for about 31% both in sulfate-reducing stage and methane-producing stage at COD/SO4(2-) ratio of 0.5, while it dropped dramatically from 34% in sulfate-reducing stage to 10% in methane-producing stage corresponding to the COD/SO4(2-) ratio of 4.7. SRB and MPA were predominant in sulfate-reducing stage and methane-producing stage respectively.

Treatment of low-strength wastewater in an anaerobic down-flow hanging sponge (AnDHS) reactor at low temperature

The process performance of a novel anaerobic down-flow hanging sponge (AnDHS) reactor for the treatment of low strength wastewater was investigated. A lab-scale experiment was conducted in which 300-400 mgCOD L(-1) of artificial wastewater was fed in over 600 days. The reactor exhibited sufficient performance: 70-90% of total COD removal, and 60-90% of methane recovery were maintained at 20°C, with a hydraulic retention time (HRT) of 2 h. It was possible to maintain COD removal by extending the HRT to 4 h at 15°C and 10 h at 10°C. With regard to the wastewater feed, one-pass mode (without effluent recirculation) gave better performance in COD removal as compared with recirculation mode. The results of batch feeding experiments using single substrates (such as acetate, propionate or sucrose) indicated that acetate degradation was more strongly affected by decreasing operational temperature. In addition, the AnDHS reactor system had no significant problems related to sludge retention such as massive loss of sludge throughout the experiment. Microbial structure analysis of the retained sludge with respect to the domain Archaeal 16S rRNA gene showed the proliferation of relatives of both the acetate-utilizing genus Methanosaeta and the hydrogen-utilizing genus Methanolinea.

Bioreactor performance and methanogenic population dynamics in a low-temperature (5-18 °C) anaerobic fixed-bed reactor

The effect of temperature on the functionality of microbial community structure in a low temperature, anaerobic fixed-bed reactor was studied by decreasing the operating temperature from 18 °C to 5 °C. The reactor was productive within 20 days and produced stable methane content in biogas (above 77%) throughout the trial period. At 17 °C and 15 °C, chemical oxygen demand (COD) removal efficiency and biogas production of reactor were significantly reduced. These might be temperature thresholds when fixed-bed reactors are operated under low temperatures. The methanogen community composition was analyzed using 16S rRNA gene clone library screening and quantitative PCR. At low ambient temperatures, Methanomicrobiales were dominant methanogens, and they preferentially adhered to the carbon fiber carrier. The results indicated that 16S rRNA levels of Methanomicrobiales and Methanosaetaceae in adhering sludge were higher than in deposited sludge, and they all contributed to the efficient performance of the fixed-bed reactor at low operating temperatures.

Simultaneous removal and evaluation of organic substrates and NH3-N by a novel combined process in treating chemical synthesis-based pharmaceutical wastewater

A full-scale novel combined anaerobic/micro-aerobic and two-stage aerobic biological process is used for the treatment of an actual chemical synthesis-based pharmaceutical wastewater containing amoxicillin. The anaerobic system is an up-flow anaerobic sludge blanket (UASB), the micro-aerobic system is a novel micro-aerobic hydrolysis acidification reactor (NHAR) and the two-stage aerobic process comprised cyclic activated sludge system (CASS) and biological contact oxidation tank (BCOT). The influent wastewater was high in COD, NH(3)-N varying daily 4016-13,093 mg-COD L(-1) and 156.4-650.2 mg-NH(3)-N L(-1), amoxicillin varying weekly between 69.1 and 105.4 mg-amoxicillin L(-1), respectively; Almost all the COD, NH(3)-N, amoxicillin were removed by the biological combined system, with removal percentages 97%, 93.4% and 97.2%, respectively, leaving around 104 mg-COD L(-1), 9.4 mg-NH(3)-N L(-1) and 2.6±0.8 mg-amoxicillin L(-1) in the final clarifier effluent. The performance evaluation of the wastewater treatment plant (WWTP) by mathematical statistic methods shown that at most of time effluent can meet the higher treatment discharge standard. In addition, the fate of amoxicillin in the full-scale WWTP and the amoxicillin removal rate of each different removal routes in UASB, NHAR, CASS, BCOT and final clarifier processes are investigated in this paper. The results show that biodegradation, adsorption and hydrolysis are the major mechanisms for amoxicillin removal.

Evaluation of performance and microbial community in a two-stage UASB reactor pretreating acrylic fiber manufacturing wastewater

A two-stage UASB reactor was employed to pretreat acrylic fiber manufacturing wastewater. Mesophilic operation (35 ± 0.5°C) was performed with hydraulic retention time (HRT) varied between 28 and 40 h. Mixed liquor suspended solids (MLSS) in the reactor was maintained about 8000 mg/L. The results showed COD and sulfate removal could be kept at 51% and 75%, respectively, when the HRT was no less than 38 h. Sulfate reduction mainly occurred in the acidification-stage reactor while methane production mainly occurred in the methane-stage reactor. The size of granule formed in the acidification-stage reactor ranged between 1 and 5mm while the largest size of granule in the methane-stage reactor ranged from 0.5 to 2mm. Compared to microbial populations in the acidification-stage reactor, the microbial diversity in methane-stage reactor was more abundant. In the acidification-stage reactor, the Syntrophobacter sulfatireducens devoted to both sulfate reduction and acetate production.

Fate of organic carbon in UAFB treating raw sewage: impact of moderate to low temperature

The anaerobic biological treatment of raw sewage under low ambient temperatures was investigated in an up-flow anaerobic fixed bed (UAFB) reactor, over a 220-day trial period. The operating temperature was lowered stepwisely from 35 to 25, 20 and 15°C. Obvious accumulation of acetic acid was observed in the effluent as the temperature dropped, which almost tripled at 15°C compared to that at 35°C. An interesting psychrophilic-forward-shift trend of methane production rate following the decrease of temperature was discovered. The methane yield at each trial was 169, 201, 256 and 269 L(STP) CH(4)/kg COD(removed). For each temperature trial, about 32.6%, 28.3%, 34.4% and 34.9% were removed in form of methane. Based on PCR-DGGE results, the band corresponded to Methanosphaera spp. only showed up on 15°C profile. Analysis of both methane production and DGGE results indicated that psychro-tolerant microorganisms dominated the archaeal populations in the UAFB under low-temperature.

Performance and model of a full-scale up-flow anaerobic sludge blanket (UASB) to treat the pharmaceutical wastewater containing 6-APA and amoxicillin

A full-scale test was conducted with an up-flow anaerobic sludge blanket (UASB) pre-treating pharmaceutical wastewater containing 6-aminopenicillanic acid (6-APA) and amoxicillin. The aim of the study is to investigate the performance of UASB in the condition of a high chemical oxygen demand (COD) loading rate from 12.57 to 21.02 kgm(-3)d(-1) and a wide pH from 5.57 to 8.26, in order to provide a reference for treating the similar chemical synthetic pharmaceutical wastewater containing 6-APA and amoxicillin. The results demonstrated that the UASB average percentage reduction in COD, 6-APA and amoxicillin were 52.2%, 26.3% and 21.6%, respectively. In addition, three models, built on the back propagation neural network (BPNN) theory and linear regression techniques were developed for the simulation of the UASB system performance in the biodegradation of pharmaceutical wastewater containing 6-APA and amoxicillin. The average error of COD, 6-APA and amoxicillin were -0.63%, 2.19% and 5.40%, respectively. The results indicated that these models built on the BPNN theory were well-fitted to the detected data, and were able to simulate and predict the removal of COD, 6-APA and amoxicillin by UASB.

Improving solids retention in upflow anaerobic sludge blanket reactors at low temperatures using lamella settlers

Lamella settlers were used to increase sludge concentration in pilot scale UASB reactors treating concentrated sewage at low temperature. The aim was to increase sludge retention time (SRT) and achieve better digestion in UASB reactors without the need for increasing the hydraulic retention time (HRT). Two modified UASB reactors were used for this purpose. In the first reactor, lamella settlers were installed in the settling zone of the UASB reactor and the reactor was named UASB-ESR1. In the second reactor, lamella settlers were installed underneath the gas liquid separator (GLS) and the reactor was named UASB-ESR2. The sludge concentration, sludge profile, and system performance of each reactor were monitored. The obtained sludge concentrations were 50 and 53 g TS/l for UASB-ESR1 and UASB-ESR2, respectively. The measured concentrations were almost double the concentrations reported for conventional UASB reactors ranging 16-26 g TS/l. The calculated SRT in the modified UASB reactors was 103 days in both reactors. The average total COD (COD(tot)) and suspended COD (COD(ss)) removal efficiencies were 38% and 60%, respectively for the UASB-ESR1. The average COD(tot) and COD(ss) removal efficiencies for the UASB-ESR2 were 41% and 62%, respectively. The modified reactors were considered at the startup period and the performances of the modified systems are expected to significantly improve when arriving at steady state conditions.

Start-up procedures and analysis of heavy metals inhibition on methanogenic activity in EGSB reactor

The effectiveness of operating an industrial UASB reactor, treating wastewater from the beer industry, with flows containing heavy metals was evaluated. A pilot-scale UASB reactor, already used to simulate the industrial reactor, was unsuccessfully employed. An easy start-up was obtained arranging it as an EGSB reactor. Considerations about this modification are reported. The effects of Cu(II), Ni(II) and Cr(III) ions on the anaerobic activity were analyzed by measurements of methane production rate and COD removal. The employed biomass was the sludge of the industrial UASB reactor, while a solution of ethanol and sodium acetate with COD of 3000 mg/L and a heavy metal concentration of 50 mg/L were continuously fed. Experimental results proved higher biomass sensitivity for copper and much slighter for nickel and chromium. Moreover, copper inhibition has been demonstrated to be less significant if a metal-free feed was provided to the system before copper addition.

Methanogenic toxicity in anaerobic digesters treating municipal wastewater

In upflow anaerobic sludge blanket (UASB) digesters treating raw sewage at low temperatures, the sludge progressively lost methanogenic activity, indicating the possibility of methanogenic activity inhibition caused by wastewater constituents. To check this fact, batch and semi-continuous methanogenic toxicity assays were carried out with raw and centrifuged sewage. Permanent methanogenic toxicity on anaerobic sludge of approximately 50% was found when the sludge exposure to wastewater was renewed in a semi-continuous way. A stronger methanogenic inhibition of about 70-100% was observed when an active anaerobic sludge was exposed to mixed liquor from the UASB digester treating municipal wastewater. Suspended solids removal from sewage slightly reduced methanogenic toxicity. Effective concentration of municipal wastewater that caused a 50% reduction in methanogenic activity was estimated to be in the range of 150-200 mg CODl(-1). As methanogenic inhibition appeared to be related to remaining COD, higher methanogenic toxicity in digesters operating with low conversion efficiency will be expected.

Evaluation of UASB reactor performance during start-up operation using synthetic mixed-acid waste

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.

Anaerobic treatment of low-strength municipal wastewater by a two-stage pilot plant under psychrophilic conditions

A two-stage anaerobic treatment pilot plant was tested for the treatment of raw domestic wastewater under temperatures ranging from 21 to 14 degrees 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.