Effect of hydraulic retention time on the biodegradation of complex phenolic mixture from simulated coal wastewater in hybrid UASB reactors

This study describes the feasibility of anaerobic treatment of complex phenolics mixture from a simulated synthetic coal wastewater using four identical 13.5L (effective volume) bench scale hybrid up-flow anaerobic sludge blanket (HUASB) (combining UASB+anaerobic filter) reactors at four different hydraulic retention times (HRT) under mesophilic (27+/-5 degrees C) conditions. Synthetic coal wastewater with an average chemical oxygen demand (COD) of 2240 mg/L and phenolics concentration of 752 mg/L was used as substrate. The phenolics contained phenol (490 mg/L); m-, o-, p-cresols (123.0, 58.6, 42 mg/L); 2,4-, 2,5-, 3,4- and 3,5-dimethyl phenols (6.3, 6.3, 4.4 and 21.3 mg/L) as major phenolic compounds. The study demonstrated that at optimum HRT, 24h, and phenolic loading rate of 0.75 g COD/(m(3)-d), the phenolics and COD removal efficiency of the reactors were 96% and 86%, respectively. Bio-kinetic models were applied to data obtained from experimental studies in hybrid UASB reactor. Grau second-order multi-component substrate removal model was best fitted to the hybrid UASB reactor. The second-order substrate removal rate constant (k(2(s))) was found as 1.72 h(-1) for the hybrid reactor treating complex phenolic mixture. Morphological examination of the sludge revealed rod-type Methanothrix-like, cells to be dominant on the surface.     

Effect of pentachlorophenol and chemical oxygen demand mass concentrations in influent on operational behaviors of upflow anaerobic sludge blanket (UASB) reactor

Upflow anaerobic sludge blanket (UASB) reactor that was seeded with anaerobic sludge acclimated to chlorophenols was used to investigate the feasibility of anaerobic biotreatment of synthetic wastewater containing pentachlorophenol (PCP) with additional sucrose as carbon source. Two sets of UASB reactors were operated at one time. But the seeded sludge for the two reactors was different and Reactor I was seeded with the sludge that was acclimated to PCP completely for half a year, and Reactor II was seeded with the mixed sludge that was acclimated for half a year to PCP, 4-CP, 3-CP or 2-CP, respectively. The degradation of PCP and the operation fee treating the wastewater are affected by the concentration of MEDS (microorganism easily degradable substrate). So the confirmation of the suitable ratio of [COD] and [PCP] was the key factor of treating the wastewater containing PCP economically and efficiently. During the experiment, the synthetic wastewater with 180.0 mg L(-1) PCP and 1250-10000 mg L(-1) COD could be treated steadily in the experimental Reactor I. The removal efficiency of PCP was more than 99.5% and the removal efficiency of COD was up to 90%. [PCP] (concentration of PCP) in effluent was less than 0.5 mg L(-1). [PCP] in influent could affect proper [COD] (concentration of COD) range in influent that was required for maintenance of steady running of the experimental reactor with a hydraulic retention time (HRT) from 20 to 22 h. [PCP] in influent would directly affect the necessary [COD] in influent when the UASB reactor ran normally and treated the wastewater containing PCP. When [PCP] was 100.4, 151.6 and 180.8 mg L(-1) in influent, respectively, [COD] in influent had to be controlled about 1250-7500, 2500-5000 and 5000 mg L(-1) to maintain the UASB reactor steady running normally and contemporarily ensure that [COD] and [PCP] in effluent were less than 300 and 0.5 mg L(-1), respectively. With the increase of [PCP] in influent, the range of variation of [COD] in influent endured by the UASB reactor was decreasing. The ratios of [COD] and [PCP] in influent could affect removal efficiency of PCP and COD, the concentration of total volatile fatty acids (VFA) in effluent, biogas quantity and methane content in biogas. [PCP] in influent was linearly or semi-logarithmically correlated to [COD] in effluent when [COD] in influent was 5750+/-250 mg L(-1), and so was the relationship between [COD] in influent and [PCP] in effluent when [PCP] in influent was 100.4 or 151.6 mg L(-1), less than the maximum permissible [PCP]. The sources of seeded sludge, the way of sludge acclimation and the characteristics of anaerobic sludge could all affect the UASB reactor capacity treating PCP. When [PCP] were less than 180.8 mg L(-1) for Reactor I and 151.6 mg L(-1) for Reactor II, the variation of [PCP] in influent had little effect on the UASB reactor volume gas production rate and substrate gas production rate. And [VFA] and pH value in effluent were affected a little. Volume biogas production rate and substrate biogas production rate of the UASB reactor were only affected by [COD] and loading rate in influent. But when [PCP] was more than 151.6 mg L(-1) for Reactor II, the biogas production fell quickly and was over 3 days later. [VFA] in effluent from Reactor II increased up to 2198.1 mg L(-1) quickly and the pH value fell to less than 7. Reactor II could not run normally. The component of VFA accumulated quickly was mainly acetate (above 50%). With [PCP] increased from 7.9 to 180.8 mg L(-1) gradually in influent, the methane content in biogas from Reactor II decreased from 70% to 60%, but the reactor could still run normally. Then as for Reactor II, the content of methane have fallen from 75% to 45% or so quickly. And Reactor II could not run steadily. So the conclusion could be drown that too high [PCP] in influent for UASB reactor mainly inhibited the activity of methane-producing bacteria cultures utilizing the acetate.     

Study of the aerobic biodegradation of coke wastewater in a two and three-step activated sludge process

A laboratory-scale biological plant composed of two aerobic reactors operating at 35 degrees C was used to study the biodegradation of coke wastewater. The main pollutants to be removed are organic matter, especially phenols, thiocyanate and ammonium nitrogen. The concentrations of the main pollutants in the wastewater during the study ranged between 922 and 1,980 mg COD/L, 133 and 293 mg phenol/L, 176 and 362 mg SCN/L and 123 and 296 mg NH(4)(+)-N/L. The biodegradation of these pollutants was studied employing different hydraulic residence times (HRT) and final effluent recycling ratios in order to minimize inhibition phenomena attributable to the high concentrations of pollutants. During the optimisation of the operating conditions, the removal of COD, phenols and thiocyanate was carried out in the first reactor and the nitrification of ammonium took place in the second. The best results were obtained when operating at an HRT of 98 h in the first reactor and 86 h in the second reactor, employing a recycling ratio of 2. The maximum removal efficiencies obtained were 90.7, 98.9, 98.6 and 99.9% for COD, phenols, thiocyanate and NH(4)(+)-N, respectively. In order to remove nitrate, an additional reactor was also implemented to carry out the denitrification process, adding methanol as an external carbon source. Very high removal efficiencies (up to 99.2%) were achieved.     

Wastewater treatment in a hybrid activated sludge baffled reactor

A novel hybrid activated sludge baffled reactor (HASBR), which contained both suspended and attached-growth biomass perfect mixing cells in series, was developed by installing standing and hanging baffles and introducing plastic brushes into a conventional activated sludge (CAS) reactor. It was used for the treatment of domestic wastewater. The effects on the operational performance of developing the suspended and attached-growth biomass and reactor configuration were investigated. The change of the flow regime from complete-mix to plug-flow, and the addition of plastic brushes as a support for biofilm, resulted in considerable improvements in the COD, nitrogen removal efficiency of domestic wastewater and sludge settling properties. In steady state, approximately 98+/-2% of the total COD and 98+/-2% of the ammonia of the influent were removed in the HASBR, when the influent wastewater concentration was 593+/-11 mg COD/L and 43+/-5 mg N/L, respectively, at a HRT of 10 h. These results were 93+/-3 and 6+/-3% for the CAS reactor, respectively. Approximately 90+/-7% of the total COD was removed in the HASBR, when the influent wastewater concentration was 654+/-16 mg COD/L at a 3h HRT, and in the organic loading rate (OLR) of 5.36kgCOD m(-3) day(-1). The result for the CAS reactor was 60+/-3%. Existing CAS plants can be upgraded by changing the reactor configuration and introducing biofilm support media into the aeration tank.     

Hydrolytic pretreatment of oily wastewater by immobilized lipase

The purpose of this study was to evaluate the hydrolysis of wastewater with high oil and grease (O&G) concentration from a pet food industry using immobilized lipase (IL) as a pretreatment step for anaerobic treatment through batch and continuous-flow experiments. The intrinsic Michaelis constant (K(m)) and maximum reaction rate (V(max)) were estimated experimentally and the K(m) value of IL (22.5g O&G/L) was six-folds higher than that of the free lipase (FL) (3.6gO&G/L), whereas V(max) of both FL (31.3mM/gmin) and IL (33.1mM/gmin) were similar. Preliminary batch anaerobic respirometric experiments showed that chemical oxygen demand (COD) and O&G reduction were 49 and 45% without pretreatment and 65 and 64% with IL pretreatment respectively, while the maximum growth rate (micromax) for pretreated wastewater (0.17d(-1)) was 3.4-folds higher than that of raw wastewater (0.05d(-1)) with similar Monod half-saturation constants (K(s) approximately 2.7gCOD/L). The continuous-flow experimental study showed the feasibility of employing the hybrid packed bed reactor (PBR)-upflow anaerobic sludge blanket (UASB) system for the treatment of high-strength oily wastewater, as reflected by its ability to operate at an oil loading rate (LR) of 4.9kgO&G/m(3)d (to the PBR) without any problems for a period of 100days. During pseudo-steady-state conditions, the hybrid UASB produced relatively higher biogas compared to the control UASB, The effluent COD and O&G concentrations of hybrid system were 100mg/L lower than that of the control UASB reactor and no foam production was observed in the hybrid UASB compared to the control UASB reactor.     

Simultaneous removal of phenol, ammonium and thiocyanate from coke wastewater by aerobic biodegradation

A laboratory-scale activated sludge plant composed of a 20 L volume aerobic reactor followed by a 12 L volume settling tank and operating at 35 degrees C was used to study the biodegradation of coke wastewater. The concentrations of ammonium nitrogen (NH(4)(+) -N), phenols, chemical oxygen demand (COD) and thiocyanate (SCN(-)) in the wastewater ranged between 504 and 2,340, 110 and 350, 807 and 3,275 and 185 and 370 mg/L, respectively. The study was undertaken with and without the addition of bicarbonate. The addition of this inorganic carbon source was necessary to favour nitrification, as the alkalinity of the wastewater was very low. Maximum removal efficiencies of 75%, 98% and 90% were obtained for COD, phenols and thyocianates, respectively, without the addition of bicarbonate. The concentration of ammonia increased in the effluent due to both the formation of NH(4)(+) as a result of SCN(-) biodegradation and to organic nitrogen oxidation. A maximum nitrification efficiency of 71% was achieved when bicarbonate was added, the removals of COD and phenols being almost similar to those obtained in the absence of nitrification. Batch experiments were performed to study the influence of pH and alkalinity on the biodegradation of phenols and thiocyanate.     

Anaerobic treatment of olive mill wastewater and piggery effluents fermented with Candida tropicalis

Olive mill wastewater (OMW) contains high concentrations of phenolic compounds that are inhibitory to many microorganisms making it difficult to treat biologically prior to discharge in waterways. The total mono-cyclic phenol reduction in OMW in this study was carried out by aerobic pre-treatment using the yeast Candida tropicalis in a 18 L batch reactor at 30 degrees C for 12 days followed by anaerobic co-digestion. A COD removal of 62% and a reduction in the total mono-cyclic phenol content by 51% of the mixture was achieved in the aerobic pre-treatment. Pig slurry was added as co-substrate to supplement the low nitrogen levels in the olive mill wastewater. Subsequent anaerobic treatment was carried out in a 20L fixed-bed reactor at 37 degrees C and HRT between 11 and 45 days. After a long start-up period, the OLR was increased from 1.25 to 5 kg COD m(-3)day(-1) during the last 30 days, resulting in subsequent increase in overall COD removal and biogas production, up to maximum values of 85% and 29 L(biogas)L(reactor)(-1)day(-1), respectively. Methane content of the biogas produced from the anaerobic digestion ranged between 65% and 74%.     

Treatability and kinetics studies of mesophilic aerobic biodegradation of high oil and grease pet food wastewater

In this work, batch activated sludge studies were investigated for the treatment of raw pet food wastewater characterized by oil and grease concentrations of 50,000-66,000 mg/L, COD and BOD concentrations of 100,000 and 80,000 mg/L, respectively, as well as effluent from an existing anaerobic digester treating the aforementioned wastewater. A pre-treatment process, dissolved air flotation (DAF) achieved 97-99% reduction in O&G to about 400-800 mg/L, which is still atypically high for AS. The batch studies were conducted using a 4-L bioreactor at room temperature (21 degrees C) under different conditions. The experimental results showed for the DAF pretreated effluent, 92% COD removal efficiency can be achieved by using conventional activated sludge system at a 5 days contact time and applied initial soluble COD to biomass ratio of 1.17 mg COD/mg VSS. Similarly for the digester effluent at average oil and grease concentrations of 13,500 mg/L, activated sludge affected 63.7-76.2% soluble COD removal at 5 days. The results also showed that all kinetic data best conformed to the zero order biodegradation model with a low biomass specific maximum substrate utilization rate of 0.168 mg COD/mg VSS day reflecting the slow biodegradability of the wastewater even after 99% removal of oil and grease.     

Kinetic analysis of phenol, thiocyanate and ammonia-nitrogen removals in an anaerobic-anoxic-aerobic moving bed bioreactor system

A simulated wastewater containing phenol (2500 mg/L), thiocyanate and ammonia-nitrogen (500 mg/L) was treated in an anaerobic (R1)-anoxic (R2)-aerobic (R3) moving bed biofilm reactor system at different hydraulic retention time (HRT) intervals (total HRT 3-8 days, R1: 1.5-4 days; R2: 0.75-2 days and R3: 0.75-2 days) and feed thiocyanate (SCN(-)) concentrations (110-600 mg/L) to determine substrate removal kinetics. In R1, phenol and COD reduction and specific methanogenic activity were inhibited due to the increase of SCN(-) in feed. Bhatia et al. model having inbuilt provision of process inhibition described the kinetics of COD and phenol utilization with maximum utilization rates of 0.398 day(-1) and 0.486 day(-1), respectively. In R2 and R3 modified Stover-Kincannon model was suitable to describe substrate utilization. In R2 respective maximum SCN(-), phenol, COD and NO(3)(-)-N utilization rates were 0.23, 5.28, 37.7 and 11.82 g/L day, respectively. In aerobic reactor R3, COD, SCN(-) and NH(4)(+)-N removal rates were, respectively, 10.53, 1.89, and 2.17 g/L day. The minimum total HRT of three-stage system was recommended as 4 days.     

Effect of easily degradable substrate on anaerobic degradation of pentachlorophenol in an upflow anaerobic sludge blanket (UASB) reactor

The effect of microbial easily degradable substrate (MEDS) on the anaerobic degradation of pentachlorophenol (PCP) in two upflow anaerobic sludge blanket (UASB) reactors was investigated. The results indicated that glucose-utilizing activity decreased with the increase of PCP concentration in the mixed culture, and MEDS promoted PCP-dechlorination and degrading activities. The concentration of MEDS increased from 917 to 4580 mg L(-1) with the increase of PCP concentration from 100 to 181 mg L(-1)in influent, which was necessary for maintenance of steady operation of the experimental reactors, the removal rate of PCP and COD ranged up to 99.5 and 90.0% and the concentration of PCP in the effluent was less than 0.5 mg L(-1). The concentration of PCP in effluent was linearly or logarithmically related to sucrose concentration in the influent while PCP was less than the maximum permissible PCP concentration. The activity of anaerobic sludge in the reactor decreased as the concentration of PCP increased, but it could be recovered step by step as time progressed. In the lowest layer of the reactor, the activity of sludge was the highest. So it is feasible to accelerate the degradation of the organic toxic compounds like PCP, by adding suitable quantities of microbial easily degradable substrate to the system.     

Improvement of COD and color removal from UASB treated poultry manure wastewater using Fenton's oxidation

The applicability of Fenton's oxidation as an advanced treatment for chemical oxygen demand (COD) and color removal from anaerobically treated poultry manure wastewater was investigated. The raw poultry manure wastewater, having a pH of 7.30 (+/-0.2) and a total COD of 12,100 (+/-910) mg/L was first treated in a 15.7 L of pilot-scale up-flow anaerobic sludge blanket (UASB) reactor. The UASB reactor was operated for 72 days at mesophilic conditions (32+/-2 degrees C) in a temperature-controlled environment with three different hydraulic retention times (HRT) of 15.7, 12 and 8.0 days, and with organic loading rates (OLR) between 0.650 and 1.783 kg COD/(m3day). Under 8.0 days of HRT, the UASB process showed a remarkable performance on total COD removal with a treatment efficiency of 90.7% at the day of 63. The anaerobically treated poultry manure wastewater was further treated by Fenton's oxidation process using Fe2+ and H2O2 solutions. Batch tests were conducted on the UASB effluent samples to determine the optimum operating conditions including initial pH, effects of H2O2 and Fe2+ dosages, and the ratio of H2O2/Fe2+. Preliminary tests conducted with the dosages of 100 mg Fe2+/L and 200 mg H2O2/L showed that optimal initial pH was 3.0 for both COD and color removal from the UASB effluent. On the basis of preliminary test results, effects of increasing dosages of Fe2+ and H2O2 were investigated. Under the condition of 400 mg Fe2+/L and 200 mg H2O2/L, removal efficiencies of residual COD and color were 88.7% and 80.9%, respectively. Under the subsequent condition of 100 mg Fe2+/L and 1200 mg H2O2/L, 95% of residual COD and 95.7% of residual color were removed from the UASB effluent. Results of this experimental study obviously indicated that nearly 99.3% of COD of raw poultry manure wastewater could be effectively removed by a UASB process followed by Fenton's oxidation technology used as a post-treatment unit.     

Evaluation of feed COD/sulfate ratio as a control criterion for the biological hydrogen sulfide production and lead precipitation

The ability of sulfate-reducing bacteria to produce hydrogen sulfide and the high affinity of sulfide to react with divalent metallic cations represent an excellent option to remove heavy metals from wastewater. Different parameters have been proposed to control the hydrogen sulfide production by anaerobic bacteria, such as the organic and sulfate loading rates and the feed COD/SO4(2-) ratio. This work relates the feed COD/SO4(2-) ratio with the hydrogen sulfide production and dissolved lead precipitation, using ethanol as carbon and energy source in an up-flow anaerobic sludge blanket reactor. A maximum dissolved sulfide concentration of 470+/-7 mg S/L was obtained at a feed COD/SO4(2-) ratio of 2.5, with sulfate and ethanol conversions of approximately 94 and 87%, respectively. The lowest dissolved sulfide concentration (145+/-10 mg S/L) was observed with a feed COD/SO4(2-) ratio of 0.67. Substantial amounts of acetate (510-1730 mg/L) were produced and accumulated in the bioreactor from ethanol oxidation. Although only incomplete oxidation of ethanol to acetate was observed, the consortium was able to remove 99% of the dissolved lead (200 mg/L) with a feed COD/SO4(2-) ratio of 1.5. It was found that the feed COD/SO4(2-) ratio could be an adequate parameter to control the hydrogen sulfide production and the consequent precipitation of dissolved lead.     

Anaerobic stabilisation of sludge produced during municipal wastewater treatment by electrocoagulation

Anaerobic digestion of sludge from small electrocoagulation wastewater treatment plant (SEWWTP) is described. The sludge for digestion (SEWWTP sludge) was taken from pilot-scale SEWWTP with the capacity of about 200-population equivalent (25 m3 of municipal wastewater per day). Due to the technology of wastewater treatment, the characteristics of SEWWTP sludge was different from sludge produced in conventional mechanical-biological wastewater treatment plant. Therefore, experiments were focused on possibilities of anaerobic sludge digestion and determination of conditions and parameters (amount and quality of the sludge, biogas production, etc.). Average COD removal efficiency in the pilot-scale SEWWTP exceeded 80%. Organic content of excess sludge (volatile suspended solids (VSS)) was in the range of 52.1-59.2% (these values are much lower compared to VSS content in raw sludge from conventional municipal wastewater treatment plant, where VSS is about 75%). Biogas production from anaerobic digestion of SEWWTP sludge was approximately three times lower compared to standard production in conventional municipal wastewater treatment plant. Low pH (6.5-6.7), high concentration of iron (up to 1400 mg/L) and aluminium (up to 1300 mg/L) and very low (almost zero) concentration of dissolved phosphorus in sludge water were the main factors limiting the rate of anaerobic processes. Based on these results, anaerobic digestion of SEWWTP sludge was not recommended as an appropriate stabilisation method.     

Performance of anaerobic–anoxic–aerobic batch fed moving-bed reactor at varying phenol feed concentrations and hydraulic retention time

A simulated wastewater containing phenol (1,000–2,500 mg/L), thiocyanate (SCN^?) of 800 mg/L, COD (4,200–8,150 mg/L), and ammonia–nitrogen (NH₄ ⁺–N) of 500 mg/L was treated in a sequential anaerobic (B1)–anoxic (B2)–aerobic (B3) batch fed moving-bed reactor (MBR) system. Total hydraulic retention time (HRT) was varied from 5 to 10 days with B1 2.5 to 5 days; B2 and B3: 1.25–2.5 days each. In B1, 25–63 % of phenol and 23–53 % of COD removals were achieved and feed phenol above 1,500 mg/L, inhibited COD and phenol removals in B1. In B2, more than 90 % phenol removal was achieved along with COD removal and denitrification. In B2, with increase in phenol loading, though phenol and COD removal rates increased, SCN^? removal rate decreased above phenol loading of 0.28 g/L day. In B3, NH₄ ⁺–N removal efficiency decreased above loading of 0.24 g NH₄ ⁺–N/L day. The overall efficiency of the fed batch MBR system was independent of feed phenol concentration up to 2,500 mg/L at constant total HRT of 6 days. NH₄ ⁺–N removal efficiency deteriorated significantly, when total HRT of fed batch MBR was less than 6 days. Modified Stover–Kincannon model showed the best fit for removal of substrates in three reactors and Haldane’s inhibition model predicted NH₄ ⁺–N removal in B3.     

Electrochemical oxidation of phenol in a parallel plate reactor using ruthenium mixed metal oxide electrode

In this study, electrochemical oxidation of phenol was carried out in a parallel plate reactor using ruthenium mixed metal oxide electrode. The effects of initial pH, temperature, supporting electrolyte concentration, current density, flow rate and initial phenol concentration on the removal efficiency were investigated. Model wastewater prepared with distilled water and phenol, was recirculated to the electrochemical reactor by a peristaltic pump. Sodium sulfate was used as supporting electrolyte. The Microtox bioassay was also used to measure the toxicity of the model wastewater during the study. As a result of the study, removal efficiency of 99.7% and 88.9% were achieved for the initial phenol concentration of 200 mg/L and chemical oxygen demand (COD) of 480 mg/L, respectively. In the same study, specific energy consumption of 1.88 k Wh/g phenol removed and, mass transfer coefficient of 8.62 x 10(-6)m/s were reached at the current density of 15 mA/cm(2). Electrochemical oxygen demand (EOD), which can be defined as the amount of electrochemically formed oxygen used for the oxidation of organic pollutants, was 2.13 g O(2)/g phenol. Electrochemical oxidation of petroleum refinery wastewater was also studied at the optimum experimental conditions obtained. Phenol removal of 94.5% and COD removal of 70.1% were reached at the current density of 20 mA/cm(2) for the petroleum refinery wastewater.     

Pilot-scale treatment of a trichloethylene rich synthetic wastewater in anaerobic hybrid reactor,with morphological study of the sludge granules

A pilot-scale research was conducted to study the biodegradation of trichloroethylene (TCE) in anaerobic hybrid reactor (AHR). At an influent TCE and COD concentrations of 50 and 2,000 mg/l, respectively, the AHR showed a maximum 99.93 ± 0.13 and 97.81 ± 0.42 % of TCE and COD removals, respectively, at 24 h of hydraulic retention time. The flocculent sludge (<0.5 mm diameter in size) was gradually converted to compact granular sludge (>2 mm diameter in size) after the completion of the acclimatization study. The biomass growth yield, the maximum substrate (COD), and the maximum co-substrate (TCE) utilization rates were found to be 0.05 mg VSS/mg COD/day, 0.526 mg COD/mg VSS/day, and 0.0125 mg TCE/mg VSS/day, respectively. The AHR has the high potentiality for the treatment of high concentration of TCE present in some industrial wastewater.     

Integrated treatment of olive mill wastewater (OMW) by the combination of Fenton's reaction and anaerobic treatment

The use of an integrated treatment scheme consisting of wet hydrogen peroxide catalytic oxidation (WHPCO) followed by two-stage upflow anaerobic sludge blanket (UASB) reactor (10l each) for the treatment of olive mill wastewater was the subject of this study. The diluted wastewater (1:1) was pre-treated using Fenton's reaction. Optimum operating conditions namely, pH, H(2)O(2) dose, Fe(+2), COD:H(2)O(2) ratio and Fe(+2):H(2)O(2) ratio were determined. The UASB reactor was fed continuously with the pre-treated wastewater. The hydraulic retention time was kept constant at 48h (24h for each stage). The conventional parameters such as COD, BOD, TOC, TKN, TP, TSS, oil and grease, and total phenols were determined. The concentrations of polyphenolic compounds in raw wastewater and effluents of each treatment step were measured using HPLC. The results indicated a good quality final effluent. Residual concentrations of individual organic compounds ranged from 0.432 mg l(-1) for rho-hydroxy-benzaldhyde to 3.273 mg l(-1) for cinnamic acid.     

Development of enhanced sulphidogenesis process for the treatment of wastewater having low COD/SO(4)(2-) ratio

An upflow hybrid sulphidogenesis reactor of 1.75 L volume was developed (at oxidation-reduction potential (ORP)=-225+/-25 mV) using flocculent extended aeration process sludge (selected based on screening study at COD/SO(4)(2-) ratio=1) for enhanced sulphidogenesis and COD removal. The reactor was subjected to various loading rate studies at a hydraulic retention time (HRT) of 1 day with COD/SO(4)(2-) ratio of 1.3. At loading rate of 2.5 kg COD/(m(3)day), excellent performance with more than 97% removal of sulphate was achieved within bottom 40% volume of the reactor. At a higher loading rate of 3.75 kg COD/(m(3)day), there was a decrease in both sulphate (70-75%) and COD (50%) removal efficiencies. A controlled and continuous air injection (0.19 L/(L min)) given at 40% volume of the reactor affected sulphide oxidation inside the reactor and enhanced the sulphate reduction in the reactor. The specific sulphate reduction capacity of mixed culture drawn from the bottom part of the reactor was 0.35 kg SO(4)(2-)/(kg VSS day). The results of this study showed that enhanced sulphidogenesis with sulphide inhibition control can maintain sulphate-reducing bacteria (SRB) in anaerobic reactor at low COD/SO(4)(2-) ratios between 1 and 2, with efficient simultaneous removal of COD and SO(4)(2-). The sulphide generated in the system can be recovered as elemental sulphur and/or oxidized back to sulphate.     

Biodegradation of diesel fuel-contaminated wastewater using a three-phase fluidized bed reactor

Aerobic biodegradation of diesel fuel (DF)-contaminated wastewater is carried out in a three-phase fluidized bed reactor under unsteady and steady state conditions. The solid phase lava rock particles, which act as the support for the biomass, are fluidized by the upward flows of influent wastewater, and air. The results show that the reactor under unsteady state operation achieved 100% DF removal from synthetic wastewater loaded with 0.43-1.03 kg/m3 day of DF. An average of over 97% of the influent chemical oxygen demand (COD) was also removed from the wastewater with COD concentrations in the range, 547-4025 mg/L. For influent COD concentrations up to 1345 mg/L, the removal is greater than 90%. Under steady state operation, the reactor was able to remove 100% of the DF, and an average of 96% of the COD from the wastewater. It had approximately 200 mg/L of DF, and 1237 mg/L of COD at a low hydraulic residence time of 4 h. In general, the results demonstrate that the reactor is very efficient, and requires short residence times to remove both DF and COD from heavily contaminated wastewater.     

An OUR-based approach to determine the toxic effects of 2,4-dichlorophenoxyacetic acid in activated sludge

This study uses the oxygen uptake rate (OUR) measurement to measure toxicity effects of 2,4-dichlorophenoxyacetic acid (2,4-D) on activated sludges fed with the wastewater from a small domestic wastewater treatment plant and peptone-based synthetic wastewater. Two 2l lab-scale batch reactors were run in parallel with the same F/M ratios (0.4 mg COD per mg VSS per day) to assess the inhibition effects of 2,4-D concentrations between 25 and 75 mg l(-1) considering at least a 100% dilution rate, as compared with a pesticide industry effluent containing 20,000-40,000 mg l(-1) COD, reaches a central treatment plant. It was noted that the OUR was decreased to 15 and 30%, respectively, when adding 75 mg l(-1) of 2,4-D to the domestic and synthetic reactors. Meanwhile, the addition of 25 plus 50 mg l(-1) of 2,4-D in sequence to the domestic wastewater reactor did not significantly affect the OUR profile. The OUR-based inhibition definition has been used in this research since the OUR methods have been frequently used and cited in the literature to study toxicity effects. However, the origin of the sludge used in the testing is also important. Synthetic wastewater may simulate the toxicity studies but with a higher response than actual systems, since the microorganisms are considerably becoming substrate-selective.