Low-temperature anaerobic biological treatment of toluene-containing wastewater

Two expanded granular sludge bed-anaerobic filter (EGSB-AF) bioreactors, R1 and R2, were operated at 15 degrees C for the treatment of toluene-contaminated volatile fatty acid-based wastewater. The seed inoculum and the R1 reactor were unexposed to toluene, prior to and during the trial, respectively. Both reactors were operated at a hydraulic retention time of 24h at applied organic loading rates of 0.71-1.43kg chemical oxygen demand (COD)m(-3)d(-1). Toluene was supplemented to the R2 influent at concentrations of 5-104 mg toluenel(-1) (solubilised in ethanol). Bioreactor performance was evaluated by COD and toluene removal efficiency, and the methane content of biogas (%). Specific methanogenic activity and toxicity assays were employed to investigate the activity and toluene toxicity thresholds of key trophic groups, respectively, within the seed and reactor biomass samples. COD and toluene removal efficiencies of 70-90% and 55-99%, respectively, were achieved during the 630-d trial. Metabolic assays suggested that a psychrotolerant H(2)/CO(2)-utilizing methanogenic community developed in the toluene-degrading biomass. The results indicate the viability of low-temperature anaerobic digestion for the treatment of wastewater containing toluene.     

Performance of an up-flow anaerobic stage reactor (UASR) in the treatment of pharmaceutical wastewater containing macrolide antibiotics

The performance of an up-flow anaerobic stage reactor (UASR) treating pharmaceutical wastewater containing macrolide antibiotics was investigated. Specifically, it was determined whether a UASR could be used as pre-treatment system at an existing pharmaceutical production plant to reduce the antibiotics in the trade effluent. Accordingly, a UASR was developed with an active reactor volume of 11 L being divided into four 2.75 L stages. Each stage of the reactor was an up-flow sludge blanket reactor and had a 3-phase separator baffle to retain biomass. The reactor was fed with real pharmaceutical wastewater containing Tylosin and Avilamycin antibiotics and operated with step-wise increases in the reactor organic loading rate (OLR) from 0.43 to 3.73 kg chemical oxygen demand (COD) m(-3)d(-1), and then reduced to 1.86, over 279 days. The process performance of the reactor was characterised in terms of its COD removal, Tylosin reduction, pH, VFA production, methane yield and sludge washout. At a total hydraulic retention time (HRT) of 4 d and OLR of 1.86 kg COD m(-3)d(-1), COD reduction was 70-75%, suggesting the biomass had acclimated to the antibiotics. Furthermore, an average of 95% Tylosin reduction was achieved in the UASR, indicating that this antibiotic could be degraded efficiently in the anaerobic reactor system. In addition, the influence of elevated Tylosin concentrations on the UASR process performance was studied using additions of Tylosin phosphate concentrate. Results showed similar efficiency for COD removal when Tylosin was present at concentrations ranging from 0 to 400 mgL(-1) (mean removal over this range was 93%), however, at Tylosin concentrations of 600 and 800 mgL(-1) there was a slight decline in treatment efficiency at 85% and 75% removal, respectively.     

两相厌氧工艺处理高盐纤维素醚废水的研究

采用接种特定污泥的两相厌氧反应器处理高盐纤维素醚废水,重点考察了启动过程及其处理效果。试验结果表明,当产酸相的HRT为18 h时,其所能承受的最大容积负荷为8.18kg/(m3.d),此时其对COD的去除率为20%左右;当产甲烷相的HRT为24 h时,其所能承受的最大容积负荷为5.5 kg/(m3.d),此时其对COD的去除率为35%左右;产甲烷相对COD的去除率与产酸相出水的酸化度呈显著正相关。在产酸相进水COD为6 000 mg/L、产甲烷相进水pH值为7的条件下,当产酸相进水pH值为6、HRT为18 h及产甲烷相的HRT为48 h时,系统的处理效果较佳,出水COD为1 800 mg/L,对COD的总去除率可达70%左右。     

Low-temperature (7 °C) anaerobic treatment of a trichloroethylene-contaminated wastewater: microbial community development

The feasibility of low-temperature (7 °C) anaerobic digestion for the treatment of a trichloroethylene (TCE) contaminated wastewater was investigated. Two expanded granular sludge bed (EGSB) bioreactors (R1 and R2) were employed for the mineralisation of a synthetic volatile fatty acid based wastewater at an initial organic loading rate (OLR) of 3 kg COD m⁻³ d⁻¹, and an operating temperature of 15 °C. Successive reductions in OLR to 0.75 kg COD m⁻³ d⁻¹, and operational temperature to 7 °C, resulted in stable bioreactor operation by day 417, with COD removal efficiency and biogas CH₄ content ≥74%, for both bioreactors. Subsequently, the influent to R1 was supplemented with increasing concentrations (10, 20, 30 mg l⁻¹) of TCE, while R2 acted as a control. At an influent TCE concentration of 30 mg l⁻¹, although phase average TCE removal rates of 79% were recorded, a sustained decrease in R1 performance was observed, with COD removal of 6%, and % biogas CH₄ of 3% recorded on days 595 and 607, respectively. Specific methanogenic activity (SMA) assays identified a general shift from acetate- to hydrogen-mediated methanogenesis in both R1 and R2 biomass, while toxicity assays confirmed an increased sensitivity of the acetoclastic community in R1 to TCE and dichloroethylene (DCE), which contributed to acetate accumulation. Quantitative Polymerase Chain Reaction (qPCR) analysis of the methanogenic community confirmed the dominance of hydrogenotrophic methanogens in both R1 and R2, representing 71-89% of the total methanogenic population, however acetoclastic Methanosaeta were the dominant organisms, based on 16S rRNA gene clone library analysis of reactor biomass. The greatest change in the bacterial community, as demonstrated by UPGMA analysis of DGGE banding profiles, was observed in R1 biomass between days 417 and 609, although 88% similarity was retained between these sampling points.     

Anaerobic biodegradation of aircraft deicing fluid in UASB reactors

A central composite design was employed to methodically investigate anaerobic treatment of aircraft deicing fluid (ADF) in bench-scale Upflow Anaerobic Sludge Blanket (UASB) reactors. A total of 23 runs at 17 different operating conditions (0.8% 1.6% ADF (6000-12,000mg/L COD), 12-56h HRT, and 18-36gVSS/L) were conducted in continuous mode. The development of four empirical models describing process responses (i.e. COD removal efficiency, biomass-specific acetoclastic activity, methane production rate, and methane production potential) as functions of ADF concentration, hydraulic retention time, and biomass concentration is presented. Model verification indicated that predicted responses (COD removal efficiencies, biomass-specific acetoclastic activity, and methane production rates and potential) were in good agreement with experimental results. Biomass-specific acetoclastic activity was improved two-fold from 0.23gCOD/gVSS/d for inoculum to a maximum of 0.55gCOD/gVSS/d during ADF treatment in UASB reactors. For the design window, COD removal efficiencies were higher than 90%. The predicted methane production potentials were close to theoretical values, and methane production rates increased as the organic loading rate is increased. ADF toxicity effects were evident for 1.6% ADF at medium organic loadings (SOLR above 0.5gCOD/gVSS/d). In contrast, good reactor stability and excellent COD removal efficiencies were achieved at 1.2% ADF for reactor loadings approaching that of highly loaded systems (0.73gCOD/gVSS/d).     

Quantitative image analysis as a diagnostic tool for identifying structural changes during a revival process of anaerobic granular sludge

Due to unspecified operational problems, the specific acetoclastic activity (SAA) of the anaerobic granular sludge present in an industrial UASB reactor was considerably damaged (from 250 to less than 10mL CH(4)@STP/gVSS.d), significantly reducing the biogas production of that industrial unit. The hydrogenotrophic methanogenic activity exhibited a value of 600mL CH4@STP/gVSS.d, the settling velocity was 31.4+/-9.8m/h, the average equivalent diameter was 0.92+/-0.43mm, and about 70% of the VSS were structured in aggregates larger than 1mm. In order to study the recovery of the SAA, this sludge was collected and inoculated in a lab-scale expanded granular sludge blanket (EGSB) reactor. Ethanol was fed as the sole carbon source during a trial period of 106 days. Process monitoring included COD removal efficiency, methane production, and periodic determination of the specific methanogenic activity in the presence of acetate, propionate, butyrate, ethanol and H(2)/CO(2). Quantitative image analysis allowed for information to be obtained on granular fragmentation/erosion and filaments release. During the first operational period, biogas production was mainly due to the hydrogenotrophic activity. However, after 40 days, the SAA steadily increased achieving a maximum value of 183+/-13mL CH4@STP/gVSS.d. The onset of SAA recovery, granules breakdown and filaments release to the bulk occurred simultaneously. Further increase in SAA was accompanied by granular growth. In the last 25 days of operation, the size distribution was stable with more than 80% of projected area of aggregates corresponding to granules larger than 1mm (equivalent diameter). Confocal images from FISH hybridized sections of the granules showed that after SAA recovery, the granules developed an organized structure where an acidogenic/acetogenic external layer was apparent. Granular fragmentation and increase of filaments in the bulk, simultaneously with the increase in the acetoclastic activity are described for the first time and might represent a structural response of granular sludge to promote the optimal substrate uptake at minimal diffusion limitations.     

Simultaneous methanogenesis and denitrification of pretreated effluents from a fish canning industry

A lab-scale hybrid upflow sludge bed-filter (USBF) reactor was employed to carry out methanogenesis and denitrification of the effluent from an anaerobic industrial reactor (EAIR) in a fish canning industry. The reactor was initially inoculated with methanogenic sludge and there were two different operational steps. During the first step (Step I: days 1-61), the methanogenic process was carried out at organic loading rates (OLR) of 1.0-1.25 g COD l-1 d-1 reaching COD removal percentages of 80%. During the second step (Step II: days 62-109) nitrate was added as KNO3 to the industrial effluent and the OLR was varied between 1.0 and 1.25 g COD l-1 d-1. Two different nitrogen loads of 0.10 and 0.22 g NO3(-)-N l-1 d-1 were applied and these led to nitrogen removal percentages of around 100% in both cases and COD removal percentages of around 80%. Carbon to nitrogen ratio (C:N) in the influent was maintained at 2.0 and eventually it was increased to 3.0, by means of glucose addition, to control the denitrification process. From these results it is possible to establish that wastewater produced in a fish canning industry can be used as a carbon source for denitrification and that denitrifying microorganisms were present in the initially methanogenic sludge. Biomass productions of 0.23 and 0.61 g VSS:g TOC fed for Steps I and II, respectively, were calculated from carbon global balances, showing an increase in biomass growth due to denitrification.     

Anaerobic treatment of municipal wastewater at ambient temperature: Analysis of archaeal community structure and recovery of dissolved methane

Anaerobic treatment is an attractive option for the biological treatment of municipal wastewater. In this study, municipal wastewater was anaerobically treated with a bench-scale upflow anaerobic sludge blanket (UASB) reactor at temperatures from 6 to 31 °C for 18 months to investigate total chemical oxygen demand (COD) removal efficiency, archaeal community structure, and dissolved methane (D-CH₄) recovery efficiency. The COD removal efficiency was more than 50% in summer and below 40% in winter with no evolution of biogas. Analysis of the archaeal community structures of the granular sludge from the UASB using 16S rRNA gene-cloning indicated that after microorganisms had adapted to low temperatures, the archaeal community had a lower diversity and the relative abundance of acetoclastic methanogens decreased together with an increase in hydrogenotrophic methanogens. D-CH₄, which was detected in the UASB effluent throughout the operation, could be collected with a degassing membrane. The ratio of the collection to recovery rates was 60% in summer and 100% in winter. For anaerobic treatment of municipal wastewater at lower temperatures, hydrogenotrophic methanogens play an important role in COD removal and D-CH₄ can be collected to reduce greenhouse gas emissions and avoid wastage of energy resources.     

Anaerobic pre-treatment of herbal-based pharmaceutical wastewater using fixed-film reactor with recourse to energy recovery

The concept of immobilization technology has been incorporated in this research study for biomethanation of high strength herbal based pharmaceutical wastewater. Accordingly, an investigation has been made on laboratory scale to assess the feasibility of an anaerobic fixed film fixed bed reactor system to pre-treat herbal-based pharmaceutical wastewater with recourse to energy recovery, including influence of operating conditions. The work was carried out with laboratory-scale upflow reactor, equipped with nylon scrubber as random support. The reactor was operated at 35 degrees C. COD removal efficiencies ranging from 76 to 98% were achieved for organic loading rates upto 10 kgCOD/m3 d, while the highest organic loading rate (around 48 kg COD/m3 d) led to efficiencies of 46-50%. The influences of hydraulic retention time and substrate concentration were also studied. The reactors did now show destabilization under impulse hydraulic and organic overloadings. Reactor stability was easily achieved under intermittent operation, with breaks, after which the reactors rapidly returned to their optimal performance.     

Process modeling and analysis of palm oil mill effluent treatment in an up-flow anaerobic sludge fixed film bioreactor using response surface methodology (RSM)

In this study, the interactive effects of feed flow rate (QF) and up-flow velocity (V up) on the performance of an up-flow anaerobic sludge fixed film (UASFF) reactor treating palm oil mill effluent (POME) were investigated. Long-term performance of the UASFF reactor was first examined with raw POME at a hydraulic loading rate (HRT) of 3 d and an influent COD concentration of 44300 mg/l. Extreme reactor instability was observed after 25 d. Raw POME was then chemically pretreated and used as feed. Anaerobic digestion of pretreated POME was modeled and analyzed with two operating variables, i.e. feed flow rate and up-flow velocity. Experiments were conducted based on a central composite face-centered design (CCFD) and analyzed using response surface methodology (RSM). The region of exploration for digestion of the pretreated POME was taken as the area enclosed by the feed flow rate (1.01, 7.63 l/d) and up-flow velocity (0.2, 3 m/h) boundaries. Twelve dependent parameters were either directly measured or calculated as response. These parameters were total COD (TCOD) removal, soluble COD (SCOD) removal, effluent pH, effluent total volatile fatty acid (TVFA), effluent bicarbonate alkalinity (BA), effluent total suspended solids (TSS), CH4 percentage in biogas, methane yield (Y M), specific methanogenic activity (SMA), food-to-sludge ratio (F/M), sludge height in the UASB portion and solid retention time (SRT). The optimum conditions for POME treatment were found to be 2.45 l/d and 0.75 m/h for QF and V up, respectively (corresponding to HRT of 1.5 d and recycle ratio of 23.4:1). The present study provides valuable information about interrelations of quality and process parameters at different values of the operating variables.     

Effect of specific gas loading rate on thermophilic (55 degrees C) acidifying (pH 6) and sulfate reducing granular sludge reactors

The effect of the specific gas loading rate on the acidifying, sulfate reducing and sulfur removal capacity of thermophilic (55 degrees C; pH 6.0) granular sludge bed reactors treating partly acidified wastewater was investigated. A comparison was made between a regular UASB reactor and a UASB reactor continuously sparged with N(2) at a specific gas loading rate of 30 m(3)m(-2)d(-1). Both UASB reactors (upflow velocity 1.0 mh(-1), hydraulic retention time about 5h) were fed a synthetic wastewater containing starch, sucrose, lactate, propionate and acetate and a low sulfate concentration (COD/SO(4)(2-) ratio of 10) at volumetric organic loading rates (OLR) ranging from 4.0 to 49.8 gCODl(-1) reactord(-1). Immediately after imposing an OLR of 25 gCODl(-1) reactord(-1), the acidification and sulfate reduction efficiency dropped to 80% and 30%, respectively, in the UASB reactor. Both efficiencies recovered slowly to 100% during the course of the experiment. In the N(2) sparged reactor, both the acidification and sulfate reduction efficiency remained 100% following the OLR increase to 25 gCODl(-1) reactord(-1). However, the sulfate reduction efficiency gradually decreased to about 20% at the end of the experiment. The biogas (CO(2) and CH(4)) production rate in the UASB was very low, i.e. <3l biogasl(-1) reactorday(-1), resulting in negligible amounts (<20%) of H(2)S stripped from the reactor liquid. The total H(2)S concentration of the N(2) sparged UASB reactor effluent was always below 25 mgl(-1), but incomplete sulfate reduction kept the maximal H(2)S stripping efficiency below 70%.     

A novel application of TPAD-MBR system to the pilot treatment of chemical synthesis-based pharmaceutical wastewater

A pilot-scale test was conducted with a two-phase anaerobic digestion (TPAD) system and a subsequential membrane bioreactor (MBR) treating chemical synthesis-based pharmaceutical wastewater. The TPAD system comprised a continuous stirred tank reactor (CSTR) and an upflow anaerobic sludge blanket-anaerobic filter (UASBAF), working as the acidogenic and methanogenic phases, respectively. The wastewater was high in COD, varying daily between 5789 and 58,792 mg L(-1), with a wide range of pH from 4.3 to 7.2. The wastewater was pumped at a fixed flow rate of 1m(3)h(-1) through the CSTR, the UASBAF and the MBR in series, resulting in respective HRTs of 12, 55 and 5h. Almost all the COD was removed by the TPAD-MBR system, leaving a COD of around 40 mg L(-1) in the MBR effluent. The pH of the MBR effluent was found in a narrow range of 6.8-7.6, indicating that the MBR effluent can be directly discharged into natural waters. A model, built on the back propagation neural network (BPNN) theory and linear regression techniques, was developed for the simulation of TPAD-MBR system performance in the biodegradation of chemical synthesis-based pharmaceutical wastewater. The model well fitted the laboratory data, and was able to simulate the removal of COD.     

Anaerobic degradation of dimethyl phthalate in wastewater in a UASB reactor

Over 99% of dimethyl phthalate (DMP) and 93% of chemical oxygen demand (COD) were effectively removed in a continuous upflow anaerobic sludge blanket (UASB) reactor from a wastewater containing 600mg/L DMP at 8h of hydraulic retention time (HRT), corresponding to a loading rate of 3g-COD/(Ld). Each gram of sludge, expressed as volatile suspended solids (VSS), had a maximum specific methanogenic activity (SMA) of 24mg-CH(4)/(g-VSSd) using DMP as the sole carbon source. The sludge yield was estimated as 0.08g-VSS/g-COD. During anaerobic degradation, DMP was de-esterified, first to mono-methyl phthalate (MMP) and then to phthalate, before being de-aromatized and subsequently converted to CH(4) and CO(2). The maximum specific degradation rates of DMP, MMP and phthalate were 415, 88 and 36mg/(g-VSSd), respectively. Analysis based on polymerase chain reaction (PCR) and denaturing gradient gel electrophoresis (DGGE) showed a gradual shift of microbial population with the increase of DMP loading.     

Low-temperature anaerobic biological treatment of solvent-containing pharmaceutical wastewater

Low-temperature or psychrophilic (<20 degrees C) anaerobic digestion (PAD) has recently been demonstrated as a cost-effective option for the treatment of a range of wastewater categories. The aim of this work was 2-fold: (1) to screen three anaerobic sludges, obtained from full-scale reactors, with respect to suitability for PAD of pharmaceutical-like, solvent-contaminated wastewater; (2) to assess the feasibility of PAD of this wastewater category. Toxicity thresholds of key trophic groups within three candidate biomass samples were assessed against solvents prevalent in pharmaceutical wastewaters (propanol, methanol and acetone). Specific methanogenic activity (SMA) assays indicated that the metabolic optimum of each candidate biomass was within the mesophilic range. One biomass sample exhibited higher SMA assays than the other candidate samples and was also the sample least methanogenically inhibited by the addition of solvents to batch cultures. This sludge was selected as the biomass of choice for laboratory-scale trials. Two identical expanded granular sludge bed (EGSB)-based anaerobic reactors were used for the treatment of solvent-contaminated wastewater at 15 degrees C, and at applied organic loading rates (OLRs) of 5-20 kg chemical oxygen demand (COD) m(-3)d(-1). COD removal efficiencies of 60-70% were achieved during the 450 day trial. In addition, SMA assays carried out at the conclusion of the trial indicated the development of a putatively psychrophilic hydrogenotrophic methanogenic community.     

Performance of UASB reactor treating leachate from acidogenic fermenter in the two-phase anaerobic digestion of food waste

This study was conducted to investigate the performance of the upflow anaerobic sludge blanket (UASB) reactor treating leachate from acidogenic fermenter in the two-phase anaerobic digestion of food waste. The chemical oxygen demand (COD) removal efficiency was consistently over 96% up to the loading rates of 15.8 g COD/l d. The methane production rate increased to 5.51/l d. Of all the COD removed, 92% was converted to methane and the remaining presumably to biomass. At loading rates over 18.7 g COD/l d, the COD removal efficiency decreased due to sludge flotation and washout in the reactor, which resulted from short HRT of less than 10.6 h. The residual propionate concentration was the highest among the volatile fatty acids (VFA) in the effluent. The specific methanogenic activity (SMA) analysis showed that the VFA-degrading activity of granule was the highest for butyrate, and the lowest for propionate. Typical granules were found to be mainly composed of microcolonies of Methanosaeta. The size distribution of sludge particles indicated that partially granulated sludge could maintain the original structure of granular sludge and continue to gain size in the UASB reactor treating leachate from acidogenic fermenter.     

Psychrophilic and mesophilic anaerobic digestion of brewery effluent: a comparative study

Two expanded granular sludge bed-anaerobic filter (EGSB-AF) bioreactors (3.38 l active volume) were used to directly compare psychrophilic (15 degrees C), anaerobic digestion (PAD) to mesophilic (37 degrees C) anaerobic digestion (MAD) for the treatment of a brewery wastewater (chemical oxygen demand (COD) concentration of 3,136+/-891 mg l(-1)). Bioreactor performance was evaluated by COD removal efficiency and biogas yields at a range of hydraulic and organic loading rates. Specific methanogenic activity (SMA) assays were also employed to investigate the activity of the biomass in the bioreactors. No significant difference in the COD removal efficiencies (which ranged from 85-93%) were recorded between PAD and MAD during the 194-d trial at maximum organic and hydraulic loading rates of 4.47 kg m(-3) day(-1) and 1.33 m(3) m(-3) day(-1), respectively. In addition, the methane content (%) of the biogas was very similar. The volumetric biogas yield from the PAD bioreactor was approximately 50% of that from the MAD bioreactor at an organic loading rate of 4.47 kg COD m(-3) day(-3) and an applied liquid up-flow velocity (V(up)) of 2.5 m h(-1). Increasing the V(up) in the PAD bioreactor to 5 m h(-1) resulted in a volumetric biogas production rate of approximately 4.1 l d(-1) and a methane yield of 0.28 l CH(4) g(-1) COD d(-1), which were very similar to the MAD bioreactor. Significant and negligible biomass washout was observed in the mesophilic and psychrophilic systems, respectively, thus increasing the sludge loading rate applied to the former and underlining the robustness of the latter, which appeared underloaded. A psychrotolerant mesophilic, but not truly psychrophilic, biomass developed in the PAD bioreactor biomass, with comparable maximum SMA values to the MAD bioreactor biomass. PAD, therefore, was shown to be favourably comparable to MAD for brewery wastewater treatment and biogas generation.     

Pre-acidification in anaerobic sludge bed process treating brewery wastewater

The effect of pre-acidification on anaerobic granule bed processes treating brewery wastewater was the focus of a comparison study employing two configurations, (a) a single stage upflow anaerobic sludge bed (UASB) and (b) an upflow acidification reactor in series with a methanogenic UASB. The pre-acidification reactor achieved 20±4% SCOD removal and 0.08±0.003 L of methane produced per gram of SCOD removal at a hydraulic retention time (HRT) of 0.75–4 h. Butyric acid was not detected and short chain fatty acids (SCFAs) were mainly acetic and propionic acids. The acidification ratio was about 0.42±0.02 g SCFAs as COD/g of influent COD.

Both systems’ critical loading rate to achieve 80% COD removal was established at 34–39 kg COD/m³ of total sludge bed volume per day. SCOD removal efficiency of 90±3% was achieved by both systems at an organic loading rate of 25±1 kg COD/m³ of total sludge bed volume per day, indicating that the installation of an acidification reactor had no effect in terms of the maximum granular activity, biomass granulation and the settleability of granules. At an organic loading rate of 67 kg COD/m³ of total sludge bed volume per day at an HRT of 1 h, the series system outperformed the single UASB by a removal of 62 compared to 57%.     

Halophilic biological treatment of tannery soak liquor in a sequencing batch reactor

Hypersaline wastewater (i.e. wastewater containing more than 35 gl(-1) total dissolved solids (TDS)) is generated by various industrial activities. This wastewater, rich in both organic matter and TDS, is difficult to treat using conventional biological wastewater treatment processes. Among the industries generating hypersaline effluents, tanneries are prominent in India. In this study, tannery wastewater from soak pit was treated in a lab-scale SBR for the removal of organic matter. The characterisation of the soak liquor showed that this effluent is biodegradable, though not easily, and highly variable, depending on the origin and the nature of the hides. TDS was in the range of 21-57 gl(-1) and COD was in the range of 1.5-3.6 gl(-1). This soak liquor was biologically treated in an aerobic sequencing batch reactor seeded with halophilic bacteria, and the performance of the system was evaluated under different operating conditions with changes in hydraulic retention time, organic loading rate and salt concentration. The changes in salinity appeared to affect the removal of organic matter more than the changes in hydraulic retention time or organic loading rate. Despite the variations in the characteristics of the soak liquor, the reactor achieved proper removal of organic matter, once the acclimation of the microorganisms was achieved. Optimum removal efficiencies of 95%, 93%, 96% and 92% on COD, PO4 3-, TKN and SS, respectively, could be reached with 5 days hydraulic retention time (HRT), an organic loading rate (OLR) of 0.6 kg COD m(-3)d(-1) and 34 g NaCl l(-1). The organisms responsible for nitrogen removal appeared to be the most sensitive to the modifications of these parameters.     

Microbial community dynamics during start-up of acidogenic anaerobic reactors

Start-up of two acidogenic reactors under mesophilic (37 degrees C) and thermophilic (55 degrees C) conditions was carried out with methanogenic granular sludge as an inoculum and dairy wastewater as feed. During these 71 days of the start-up period, microbial community dynamics in these two acidogenic reactors, as monitored by denaturing gradient gel electrophoresis (DGGE) and dot-blot hybridization with group-specific oligonucleotide probes, was correlated to reactor performance. Due to pH drop to 5.5, DGGE community fingerprints for domains Bacteria and Archaea populations showed significant shifts after 13 days of operation, and this change was accompanied with an increase in volatile fatty acid production, a decrease in methane formation, and rapid sludge disintegration. Dot-blot hybridization results further indicated that the decrease in methane production was related to the decrease in Archaea population in particular with methanogens from 34.1% of total 16S-rRNA in the seed sludge to 8% within the first 13 days, and to 2-5% at day 71. Among the methanogens monitored, the class Methanomicrobiales was the most abundant followed up by Methanobacteriales and Methanococcales. Due to an elevated temperature, the microbial community change was more significant and rapid in the thermophilic reactor than in the mesophilic reactor. Significant microbial population changes took place at the first 13 days for both reactors, but a longer period up to 71 days was required to establish a microbial community with a stable metabolic activity.     

The effect of polymer addition on granulation in an anaerobic baffled reactor (ABR). Part I: process performance

The stability and performance of an anaerobic baffled reactor (ABR) treating an ice-cream wastewater at several organic loading rates have been investigated. Specifically, it was determined whether an ABR would promote phase separation and if a polymer additive was capable of enhancing granule formation in an ABR. In order to achieve these goals, two ABRs, having identical dimensions and configurations, were used to study the above objectives using a synthetic ice-cream wastewater. The ABR proved to be an efficient reactor configuration for the treatment of a high-strength synthetic ice-cream wastewater. An organic loading rate of around 15 kg CODm(-3) d(-1) was treated with a 99% COD removal efficiency. From the jar test and inhibition assay, it was concluded that Kymene SLX-2 was the most effective and least inhibitory polymer tested. The methane yield was higher in the polymer-amended reactor compared to the control reactor. In addition, polymer addition resulted in a considerably higher degree of biomass retention and lower solids washout from the ABR. Consequently, it demonstrated that there was a considerable potential for sludge conditioning in ABRs by facilitating better biomass retention within the reactor which in turn led to better process performance. Granulation was achieved in both ABRs within 3 months. However, the granules from the polymer-amended reactor appeared earlier and were generally larger and more compact, although this was not quantified in detail during the present study. The main advantage of using an ABR comes from its compartmentalised structure. The first compartment of an ABR may act as a buffer zone to all toxic and inhibitory material in the feed thus allowing the later compartments to be loaded with a relatively harmless, balanced and mostly acidified influent. In this respect, the latter compartments would be more likely to support active populations of the relatively sensitive methanogenic bacteria and partly explains why the best granules and the highest methane yield were obtained in Compartment 2. It is unlikely that a complete separation of phases (acidogenic and methanogenic) occurred within the ABRs since methane production was observed in all compartments, although this was low (approximately 40% of all gas composition) in Compartment 1, becoming higher (approximately 70%) in the following compartments.