Effect of digestion temperature and pH on treatment efficiency and evolution of volatile fatty acids during thermophilic aerobic digestion of model high strength agricultural waste

Thermophilic aerobic digestion (TAD) of a model agricultural waste, potato peel slurry, at soluble chemical oxygen demand (COD) load equivalent to approximately 8.0 gl(-1), was carried out under batch conditions at 0.5 vvm aeration rate. Digestions were carried out at temperatures of 45, 50, 55, 60 and 65 degrees C (or left unregulated) without pH control to study the effect of digestion temperatures on TAD. The effects of digestion pH on the process were studied at pH 6.0, 7.0, 8.0, 9.0 and 9.5 (and in unregulated control) all at 55 degrees C. Except for digestion at 65 degrees C, which was inoculated extraneously using culture of Bacillus strearothermophilus all reactions were carried out using the populations indigenous to the waste. During digestion at different temperatures, the removal of soluble COD increased with temperature to reach a peak at 60 degrees C before declining slightly, removal of soluble solid (SS) followed similar pattern and reached peak at 65 degrees C being the highest temperature studied, while the degradation of TSS and TS (TSS + TS) decreased with an increase in temperature. Digestion at pH 7.0 was more efficient than at other pH values. Acetate was the predominant volatile fatty acid (VFA) in all the reactions and accounted for up to 90% of the total. Digestion at 60 degrees C led to the greatest accumulation of acetate, and this coincided with the period of highest oxygen uptake, and rapid consumption of soluble carbohydrate. Iso-valerate was also produced at all pH values. Digestion at 55 degrees C and also at pH 7.0 led to rapid and efficient processes with least accumulation of VFA and should be of interest in full-scale processes whenever it is practicable to regulate the digestion pH and temperature. The result of digestion at unregulated pH indicates that gradual adaptation may be used to achieve efficient treatment at elevated pH values. This would be of interest in full-scale processes where it is not practicable to tightly regulate digestion pH, and where the waste is produced at a pH value much higher than neutral.     

Long-term, high-rate anaerobic biological treatment of whey wastewaters at psychrophilic temperatures

Two laboratory-scale anaerobic hybrid reactors, R1 and R2, treated low- (1 kg COD m-3) and high-strength (10 kg COD m-3) whey-based wastewaters, respectively, in a 500-day trial. The chemical oxygen demand (COD) removal efficiencies of R1 averaged 70-80%, at organic loading rates of 0.5-1.3 kg COD m-3 day-1, between 20 and 12 degrees C. The COD removal efficiencies of R2 exceeded 90%, at organic loading rates up to 13.3 kg COD m-3 day-1, between 20 and 14 degrees C. Lowering the operating temperature of R2 to 12 degrees C resulted in a decrease in COD removal efficiency, to between 50% and 60%, and a disintegration of granular sludge. The decline in performance, and granule disintegration, was reversed by decreasing the organic loading rate of R2 to 6.6 kg m-3 day-1. Specific methanogenic activity profiles revealed mesophilic (37 degrees C) temperature optima for biomass in both reactors, even after 500 days of psychrophilic operation, although the development of psychrotolerance in the biomass was noted.     

Effects of temperatures and organic loading rates on biomethanation of acidic petrochemical wastewater using an anaerobic upflow fixed-film reactor

The effect of temperature and organic loading rate on the rate of methane production from acidic petrochemical wastewater without neutralization was investigated by continuously feeding an anaerobic upflow fixed-film reactor. The temperatures selected for the studies were 25, 37, 45 and 55 degrees C. Organic loading rate (OLR) for each temperature was varied from 3.6 to 21.7 kg COD m(-3) d(-1). Best performance with respect to COD and BOD reduction, total gas production and methane yield was obtained with the reactor operating at 37 degrees C. OLR could be increased to a maximum of 21.7 kg COD m(-3) d(-1) with 90-95% COD and BOD reduction and methane yield of 0.450 m3 kg(-1) COD d(-1) added. The reactor operating at 55 degrees C gave the highest methane yield of 0.666 m3 kg(-1) COD d(-1) at an OLR of 6 kg COD m(-3) d(-1). This decreased to 0.110 m3 kg(-1) COD d(-1) when the OLR was increased to 18.1 kg COD m(-3) d(-1). The reactor operating at 45 degrees C gave a maximum methane yield of 0.416 m3 kg(-1) COD d(-1) added at an OLR of 6 kg COD m(-3) d(-1). On further increasing the OLR to 9 kg COD m(-3) d(-1), COD reduction was 89%, however, methane yield decreased to 0.333 m3 kg(-1) COD d(-1) added. The highest methane yield of 0.333 m3 kg(-1) COD d(-1) added at an OLR of 6 kg COD m(-3) d(-1) was obtained with reactors operating at 25 degrees C. These studies indicate potential rates of methane production from acidic petrochemical wastewater under different temperatures. This provides a guideline for various kinetic analyses and economic evaluation of the potential feasibility of fermenting acidic wastewater to methane.     

Comparative performance and microbial diversity of hyperthermophilic and thermophilic co-digestion of kitchen garbage and excess sludge

The objective of this study was to evaluate the performance characteristics of a hyperthermophilic digester system that consists of an acidogenic reactor operated at hyperthermophilic (70 degrees C) conditions in series with a methane reactor operated at mesophilic (35 degrees C), thermophilic (55 degrees C), and hyperthermophilic (65 degrees C) conditions. Lab-scale reactors were operated continuously, and were fed with co-substrates composed of artificial kitchen garbage (TS 9.8%) and excess sludge (TS 0.5%) at the volumetric ratio of 20:80. In the acidification step, COD solubilization was in the range of 22-46% at 70 degrees C, while it was 21-29% at 55 degrees C. The average protein solubilization was 44% at 70 degrees C. The double bond fatty acid removal ratio at 70 degrees C was much higher than at 55 degrees C. These results suggested that the optimal operation conditions for the acidogenic fermenter were about 3.1 days of HRT and 4 days of SRT at 70 degrees C. Methane conversion efficiency and the VS removal percentage in the methanogenic step following acidification was around 65% and 64% on average at 55 degrees C, respectively. The optimal operational conditions for this system are acidogenesis performed at 70 degrees C and methanogenesis at 55 degrees C. The key microbes determined in the hyperthermophilic acidification step were Anaerobic thermophile IC-BH at 6.4 days of HRT and Thermoanaerobacter thermohydrosulfuricus DSM 567 at 2.4 days of HRT. These results indicated that the hyperthermophilic system provides considerable advantages in treating co-substrates containing high concentrations of proteins, lipids, and nonbiodegradable solid matter.     

Postharvest behaviour of five Sardinian prune varieties as affected by immersion in heated sodium bicarbonate solution

Storage behaviour of 'Core', 'Core Columbu', 'Fradis' and 'Meloni' white prunes, and a black one ('Sighera') of Sardinian germplasm were evaluated following immersion for 0 (control), 15, 30, 45 or 60 sec in water at 20, 50, 55 or 60 degrees C with or without 2% (w/v) NaHCO3 (SBC). As international varieties, fruit from one white plum ('Shiro') and one black prune ('Stanly') were subjected to the same treatments. Fruit was harvested at commercial maturity, treated and then stored for 1 month at 5 degrees C and 90% RH followed by a simulated marketing period at 20 degrees C and 80% RH for 6 days. Fruit appearance, external damage, firmness and decay percentage were monitored after storage and SMP. Treatments did not induce rind damage (browning or discoloration) to any variety. SBC at 20, 45, 50 or 55 degrees C for 15 or 30 sec was not effective in controlling decay and compared to controls no improvement was observed. Immersion for 45 or 60 sec with SBC at all temperatures improved decay control with respect to controls and best results were obtained at 50 or 55 degrees C. Immersions at 60 degrees C improved decay control, but differences were not significant compared to the control attained with solutions of SBC heated at 55 degrees C. The overall appearance of 'Core', 'Core Columbu', 'Fradis' and 'Shiro' decreased significantly after the SMP period, especially when treated at 55 or 60 degrees C for 60 sec. Fruit shrivel was the main cause of the low rating. SBC did not affect shrivel indicating that heat treatment may be the probable cause. In general, local varieties were less affected by decay than other varieties and they performed well during storage.     

Effect of high and low temperatures on the drugstore beetle (Coleoptera: Anobiidae)

The drugstore beetle, Stegobium paniceum (L.) (Coleoptera: Anobiidae), is a pest of stored medicinal and aromatic plants. Generally, mortality of each stage increased with an increase of temperature and exposure time. Heat tolerance for different stages from highest to lowest was young larvae, old larvae, eggs, adult, and pupae. The mortality after 7 h at 42 degrees C for young larvae, old larvae, eggs, adults, and pupae, respectively, was 16 +/- 5, 31 +/- 6, 48 +/- 3, 63 +/- 8, and 86 +/- 2% (mean +/- SEM). Similar trends for stage specific mortality were seen with the lethal time for 90% mortality (LT90) at 42 degrees C; 773, 144, 12, and 11 h for old larvae, eggs, adults, and pupa respectively. Mortality was too low with young larvae to estimate LT90. The LT90 for young larvae at 42, 45, 50, 55, and 60 degrees C was 25, 20, 3.9, 0.18, and 0.08 h, respectively. The cold tolerance of different stages at 0 degree C from highest to lowest was adults, old larvae, young larvae, pupae, and eggs. The LT90 at 0 degrees C was 298, 153, 151, 89, and 53 h, respectively. The LT90 for adults at 5, -5, -10, and -15 degrees C was 792, 58, 2, and 0.8 h, respectively. The supercooling point of adults was -15.2 +/- 2 degrees C; young larvae, -9.0 +/- 0.8 degrees C; old larvae, -6.5 +/- 0.5 degrees C; and pupae, -4.0 +/- 1.4 degrees C. Heat treatments that control young larvae should control all other stages of S. paniceum. Cold treatments that control adults should control all other stages of S. paniceum. Dried plants stored at 5 degrees C for 45 d or 42 degrees C for 30 h and then kept below 18 degrees C throughout the rest of the year, should remain pest-free without any chemical control.     

Production and characterization of cellulolytic enzymes from the thermoacidophilic fungal Aspergillus terreus M11 under solid-state cultivation of corn stover

The production of extracellular cellulases by a newly isolated thermoacidophilic fungus, Aspergillus terreus M11, on the lignocellulosic materials was studied in solid-state fermentation (SSF). The results showed that the high-level cellulase activity was produced at 45 degrees C pH 3 and moisture 80% with corn stover and 0.8% yeast extract as carbon and nitrogen sources. 581 U endoglucanase activity, 243 U filter paper activity and 128 U beta-glucosidase activity per gram of carbon source were obtained in the optimal condition. Endoglucanase and beta-glucosidase exhibited their maximum activity at pH 2 and pH 3, respectively, and both of them showed remarkable stability in the range of pH 2-5. The activities of endoglucanase and beta-glucosidase were up to the maximum at 70 degrees C and maintained about 65% and 53% of their original activities after incubation at 70 degrees C for 6h. The enzyme preparations from this strain were used to hydrolyze Avicel. Higher hydrolysis yields of Avicel were up to 63% on 5% Avicel (w/v) for 72 h with 20 U FPase/g substrate.     

Effect of temperature and active biogas process on passive separation of digested manure

The objective of the study was to identify the optimum time interval for effluent removal after temporarily stopping stirring in otherwise continuously stirred tank reactors. Influence of temperature (10 and 55 degrees C) and active biogas process on passive separation of digested manure, where no outside mechanical or chemical action was used, within the reactor was studied in three vertical settling columns (100 cm deep). Variations in solids and microbial distribution at top, middle and bottom layers of column were assessed over a 15 day settling period. Results showed that best solids separation was achieved when digested manure was allowed to settle at 55 degrees C with active biogas process (pre-incubated at 55 degrees C) compared to separation at 55 degrees C without active biogas process (autoclaved at 120 degrees C, for 20 min) or at 10 degrees C with active biogas process. Maximum solids separation was noticed 24h after settling in column incubated at 55 degrees C, with active biogas process. Microbiological analyses revealed that proportion of Archaea and Bacteria, absent in the autoclaved material, varied with incubation temperature, time and sampling depth. Short rod shaped bacteria dominated at 55 degrees C, while long rod shaped bacteria dominated at 10 degrees C. Methanosarcinaceae were seen more abundant in the surface layer at 55 degrees C while it was seen more common in the top and bottom layers at 10 degrees C. Thus, passive separation of digester contents within the reactor can be used effectively as an operating strategy to optimize biogas production by increasing the solids and biomass retention times. A minimum of 1-2h "non-stirring" period appears to be optimal time before effluent removal in plants where extraction is batch-wise 2-4 times a day.     

Protein enrichment of corn cob heteroxylan waste slurry by thermophilic aerobic digestion using Bacillus stearothermophilus

Thermophilic aerobic digestion (TAD) of heteroxylan waste was implemented at waste load of 30gL(-1) with mineral nitrogen supplementation to study effect of the process on waste degradation, protein accretion and quality. Digestions were carried out at 45 50, 55, 60 and 65 degrees C using Bacillusstearothermophilus in a CSTR under batch conditions at 1.0vvm aeration rate, pH 7.0 for a maximum of 120h. Amylase and xylanase activities appeared rapidly in the digest, while basal protease activity appeared early in the digestion and increased towards end of the processes. Highest degradation of volatile suspended solid, hemicellulose and fibre occurred at 55 degrees C while highest degradation of total suspended solid occurred at 60 degrees C. Highest protein accretion (258.8%) and assimilation of mineral nitrogen and soluble protein occurred at 55 degrees C. The % content of amino acids of digest crude protein increased relative to raw waste and with digestion temperature. Quality of digest protein was comparable to the FAO standard for feed use. TAD has potentials for use in the protein enrichment of waste.     

Aerobic biodegradation of potato slops under moderate thermophilic conditions: effect of pollution load

The effect of the pollutant load on the efficiency of aerobic biodegradation of potato slops with a mixed population of thermo- and mesophilic bacteria of the genus Bacillus was examined. Batch biodegradation processes were carried out at 45 degrees C, using slops with the initial chemical oxygen demand (COD) totalling 11.3, 18.0, 42.6, 58.0 and 74.0 g O2/l. The extent of COD removal ranged from 80.4% (with COD of 11.3 g O2/l) to 88.7% (with COD of 58.0 g O2/l). With potato slops of higher initial COD levels (58.0 and 74.0 g O2/l), the first 24h of growth were characterised by a deficiency of oxygen and a considerable rise in the content of acetic acid, which was then removed. In the first 48 h of the process, irrespective of the initial COD level, the biodegradation of the pollutants removed in the course of the entire process exceeded 91%. The rate of COD removal calculated for that period was a linearly increasing function of the initial pollution load.     

The effect of temperature fluctuations on psychrophilic anaerobic sequencing batch reactors treating swine manure

Under northern climatic conditions, a temporary decrease in the temperature of anaerobic reactors treating swine manure is likely to happen at the farm. The objective of this study was to evaluate the impact of temperature fluctuations, between 10 and 20 degrees C, on the stability and performance of psychrophilic anaerobic sequencing batch reactors (ASBRs) treating swine manure. Methane yield decreased from 0.266+/-0.014 l/g of total chemical oxygen demand (TCOD) fed to the ASBRs at 20 degrees C to 0.218+/-0.022 and 0.080+/-0.002 l/g TCOD (fed) at 15 and 10 degrees C, respectively. Soluble chemical oxygen demand (SCOD) reduction decreased from 94.2+/-1.1% at 20 degrees C to 78.8+/-3.0% at 15 degrees C and 60.4+/-6.4% at 10 degrees C. Total COD removal also tended to decrease as temperature was lowered, but difference between operating temperatures was not as pronounced. A lower methanogenic activity in the ASBRs operated at 10 degrees C probably favoured quiescent conditions during the settling period, thereby increasing physical removal of the TCOD through sedimentation of the solids with the biomass. When the operating temperature was increased back to 15 and 20 degrees C, methane yield and SCOD reduction improved, but reactor performance remained significantly (P<0.05) lower than that achieved before the cycles at 10 degrees C. Results from this experiment nevertheless suggested that fluctuation in the operating temperature of psychrophilic ASBRs should only have temporary effects on the performance and stability of the process.     

Ecological clarification of cheese whey prior to anaerobic digestion in upflow anaerobic filter

Anaerobic digestion of cheese whey wastewaters (CW) was investigated in a system consisting of an ecological pretreatment followed by upflow anaerobic filter (UAF). The pretreatment was conducted to solve the inhibition problems during anaerobic treatment of CW caused by the amounts of fats, proteins and carbohydrates and to avoid the major problems of clogging in the reactor. The optimized ecological pretreatment of diluted CW induce removal yields of 50% of chemical oxygen demand (COD) and 60% of total suspended solids (TSS) after acidification by Lactobacillus paracasei at 32 degrees C during 20 h and neutralization with lime. The pretreated CW was used to feed UAF (35 degrees C). The effects of organic loading rate (OLR) and hydraulic retention time (HRT) on the pretreated CW anaerobic degradation were examined. The average total COD removals achieved was 80-90%. The performance of the reactor was depressed by increasing the COD concentration to 20 g/l (OLR = 4 gCOD/ld) and the COD removal efficiency was reduced to 72%. Significant methane yield (280 l/kg COD removal) was obtained at an HRT of 2 days.     

Decolourisation of a synthetic textile effluent using a bacterial consortium

In the present study we examined the performance of a thermoalkalophilic bacterial consortium, where the predominant strain was Bacillus sp. SF, in the degradation of Reactive Black 5 (RB5). We used a reactor working in continuous mode and investigated the effects of pH, hydraulic retention time (HRT) and several added salts on colour and chemical oxygen demand (COD) reductions. For the chosen operational conditions (pH 9, 55 degrees C and HRT of 12 h) the efficiencies achieved were 91.2 +/- 0.8 % for colour removal and 81.2% for COD removal. The system tolerated, with no significant decrease in colour removal efficiency, 30 g/L Na(2)SO(4), Na(2)CO(3) or NaCl. The latter two salts, however, led to a reduction in COD removal of 30% and 50%, respectively. The system proved to be very effective in the decolourisation of C.I. RB5 under alkaline conditions and at a comparatively high temperature.     

Acetate Degradation at 70 degrees C in Upflow Anaerobic Sludge Blanket Reactors and Temperature Response of Granules Grown at 70 degrees C

Anaerobic acetate degradation at 70 degrees C and at 55 degrees C (as a reference) was studied by running laboratory upflow anaerobic sludge blanket (UASB) reactors inoculated with mesophilic granular sludge. In UASB reactors fed with acetate-containing media (3 g of chemical oxygen demand [COD] per liter, corresponding to 47 mM acetate) approximately 50 days was needed at 70 degrees C and less than 15 days was needed at 55 degrees C to achieve an effluent COD of 500 to 700 mg/liter. In the UASB reactors at both 70 and 55 degrees C up to 90% of the COD was removed. Batch assays showed that sludges from two 70 degrees C UASB reactors, one run at a low effluent acetate concentration and the other run at a high effluent acetate concentration, exhibited slightly different responses to temperatures in the range from 37 to 70 degrees C. Both 70 degrees C sludges, as well as the 55 degrees C sludge, produced methane at temperatures of 37 to 73 degrees C. The 55 degrees C sludge exhibited shorter lag phases than the 70 degrees C sludges and higher specific methane production rates between 37 and 65 degrees C.     

Renaturation of bacteriophage lambda DNA. Determination of the optimal renaturation conditions using a single-strand-specific DNase and alkaline-sucrose-gradient assay system.

Reannealed hybrid molecules of wild-type bacteriophage lambda DNA were prepared in aqueous solutions of formamide at a variety of NaCl concentrations at both room temperature ( 22 degrees C) and 37 degrees C. Treatment of the hybrid DNA molecules with the single-strand-specific nuclease S1 from Aspergillus oryzae followed by alkaline sucrose gradient sedimentation was used to monitor the extent and fidelity of hybridization. The optimal renaturation conditions at room temperature were found to be: 50% formamide, 35-55 mM NaCl and 10 mM Tris-HCl (pH 8.5) at 20-25 mug DNA/ml. Optimal conditions at 37 degrees C were: 32% formamide, 35-55 mM NaCl and 10 mM Tris-HCl (pH 8.5) at 20-25 mug DNA/ml. Under these conditions approximately 85-90% of the input single-stranded DNA (molecular weight 1.5 X 10(7)) was rendered S1-nuclease-resistant within 8 h at room temperature and 5 h at 37 degrees C. Neither Mg2+ nor spermidine appeared to have an effect on either the extent or fidelity of duplex formation. Experiments performed with excess enzyme and with lambda/lambda imm 434 heteroduplex hybrids suggested that the hybrid that the hybrid DNA molecules formed under optimal conditions contained no, or only short (less than 1%), mismatched regions.     

Production of alkaline xylanase by an alkaliphilic Bacillus sp. isolated from an alkalinesoda lake

An alkaline xylanase-producing alkaliphilic Bacillus sp. AR-009 was isolated from analkaline soda lake in Ethiopia. The enzyme was optimally active at pH 9 and was stable over abroad pH range. The optimum temperature for xylanase activity, assayed at pH 9, was60°–65°C. Measured at pH 8 and 9, the enzyme had good stability at 55° and60°C. At both pH values, over 80% of its original activity was retained after heating for2·5 h at 55°C. At 60°C, the enzyme maintained 63% of its original activity after2·5 h incubation while at pH 9 it retained 54% of its original activity after 1 h heating. Theseproperties qualify the enzyme to be novel and potentially important for application in someindustrial processes.     

Simultaneous single-cell protein production and COD removal with characterization of residual protein and intermediate metabolites during whey fermentation by K. marxianus

Cheese whey fermentation with Kluyveromyces marxianus was carried out at 40 °C and pH 3.5 to examine simultaneous single-cell protein production and chemical oxygen demand (COD) removal, determine the fate of soluble whey protein and characterize intermediate metabolites. After 36 h of batch fermentation, the biomass concentration increased from 2.0 to 6.0 g/L with 55 % COD reduction (including protein), whereas soluble whey protein concentration decreased from 5.6 to 4.1 g/L. It was confirmed through electrophoresis (SDS-PAGE) that the fermented whey protein was different from native whey protein. HPLC and GC–MS analysis revealed a change in composition of organic compounds post-fermentation. High inoculum concentration in batch fermentation resulted in an increase in biomass concentration from 10.3 to 15.9 g/L with 80 % COD reduction (including protein) within 36 h with residual protein concentration of 4.5 g/L. In third batch fermentation, the biomass concentration increased from 7.3 to 12.4 g/L with 71 % of COD removal and residual protein concentration of 4.3 g/L after 22 h. After 22 h, the batch process was shifted to a continuous process with cell recycle, and the steady state was achieved after another 60 h with biomass yield of 0.19 g biomass/g lactose and productivity of 0.26 g/L h. COD removal efficiency was 78–79 % with residual protein concentration of 3.8–4.2 g/L. The aerobic continuous fermentation process with cell recycle could be applied to single-cell protein production with substantial COD removal at low pH and high temperature from cheese whey.     

Performance of microbial fuel cell subjected to variation in pH, temperature, external load and substrate concentration

During field application, the microbial fuel cell (MFC) will be exposed to variations in operating parameters. Hence, the performance of MFC, exposed to variation in temperature, pH, external resistance and influent chemical oxygen demand (COD), was investigated in the terms of coulombic efficiency (CE) and COD removal efficiency, while treating a synthetic wastewater. The performance was analyzed under two temperature ranges such as 20-35 degrees C and 8-22 degrees C. Operation under higher temperature range favored higher COD removal efficiency of 90% and lower current (0.7 mA) and CE (1.5%). At lower temperature range, although the COD removal efficiency of MFC decreased (59%), it gave higher current (1.4 mA) and CE (5%). The highest current was generated at pH of 6.5 in the anodic chamber with CE of 4%. Higher pH difference between anodic and cathodic electrolyte favored higher current and voltage. Within the range of COD tested (100-600 mg/l), linear correlation was observed between the current and substrate removed.     

Phosphorus removal in pilot plant using biofilm filter process from farm wastewater

Various environmental conditions affecting total phosphorus removal from farm wastewater in a biofilm filter, process were investigated using loess balls andChromobacterium LEE-38 at a pilot plant. WhenChromobacterium LEE-38 was used, the removal efficiency of total phosphorous was approximately 10- or 5-fold higher than that ofAcinetobacter CHA-2-14 orAcinetobacter CHA-4-5, respectively. When a loess ball of 11–14 mm manufactured at a 960°C calcining temperature was used, the removal efficiency of total phosphorous was 90.0%. When 70% of the volume fraction was used, the maximum efficiency of total phosphorus removal was 93.1%. Notably, when the initial pH was in the range of 6.0 to 8.0, the maximum removal efficiency of total phosphorus was obtained after 30 days. When the operating temperature was in the range of 30 to 55°C, the maximum removal efficiencies of total phosphorus, 95.6 to 94.6%, were obtained. On the other hand, at operating temperatures below 20°C or above 40°C, the removal efficiency of total phosphorous decreased. Among the various processes, biofilm filter process A gave the highest removal efficiency of 96.4%. Pilot tests of total phosphorus removal using farm wastewater from the biofilm filter process A were carried out for 60 days under optimal condition. WhenAcinetobacters sp. Lee-11 was used, the average removal efficiency in thep-adsorption area was only 32.5%, and the removal efficiencies of chemical oxygen demand (COD) and biological oxygen demand (BOD) were 56.7 and 62.5%, respectively. On the other hand, whenChromobacterium LEE-38 was used, the average removal efficiency was 95.1%, and the removal efficiencies of COD and BOD were 91.3 and 93.2%, respectively. The first two authors contributed equally to this work.     

Effects of process stability on anaerobic biodegradation of LAS in UASB reactors

Anaerobic biodegradation of linear alkylbenzene sulfonates (LAS) was studied in upflow anaerobic sludge blanket (UASB) reactors operated under mesophilic (37 degrees C) and thermophilic (55 degrees C) conditions. LAS C12 concentration in the influents was 10 mg.L(-1), and the hydraulic retention time in the reactors was 2 days. Adsorption of LAS C12 was assessed in an autoclaved control reactor and ceased after 115 days. The reactors were operated for a minimum of 267 days; 40-80% removal of LAS C12 was observed. A temperature reduction from 55 degrees C to 32 degrees C for 30 h resulted in process imbalance as indicated by increase of volatile fatty acids (VFA). The imbalance was much more intense in the LAS amended reactor compared with an unamended reactor. At the same time, the process imbalance resulted in discontinued LAS removal. This finding indicates that process stability is a key factor in anaerobic biological removal of LAS. After a recovery period, the removal of LAS resumed, providing evidence of biological anaerobic LAS degradation. The removal remained constant until termination of experiments in the reactor. Biodegradation of LAS in the mesophilic reactor was at the same level as in the thermophilic reactor under stable conditions.