COD, para-chlorophenol and toxicity removal from para-chlorophenol containing synthetic wastewater in an activated sludge unit

Chlorinated phenolic compounds present in some chemical industry wastewaters cause severe toxic effects on the organisms and often are resistant to biological degradation. Synthetic wastewater containing different concentrations of para-chlorophenol (4-chlorophenol, 4-CP) was biologically treated in an activated sludge unit for COD, 4-CP and toxicity removal. Effects of feed 4-CP concentration on COD, 4-CP, toxicity removals and on sludge volume index were investigated at a constant sludge age of 20 days and hydraulic residence time (HRT) of 25 h. Resazurin method based on dehydrogenase activity was used for determination of the toxicity of the feed and effluent wastewater. COD and 4-CP removals were not affected by the presence of 4-CP in the wastewater up to feed 4-CP concentration of 925 mg l(-1) because of almost complete degradation of 4-CP yielding lower than 50 mg l(-1) 4-CP in the aeration tank. Percent COD, 4-CP and toxicity removals decreased and the effluent COD, 4-CP and toxicity levels increased with further increases in the feed 4-CP concentrations above 925 mg l(-1) because of inhibitory concentrations of 4-CP in the reactor. Biomass concentration in the aeration tank decreased and the sludge volume index (SVI) increased with feed 4-CP concentrations above 925 mg l(-1) resulting in lower COD and 4-CP removal rates. The rates of COD and 4-CP removals indicated substrate (4-CP) inhibition for the feed 4-CP concentrations above 925 mg l(-1) corresponding to the reactor 4-CP of above 200 mg l(-1). The system should be operated at the feed 4-CP concentrations of less than 900 mg l(-1) (4-CP(R) < 200 mg l(-1)) in order to obtain high rates and extents of COD, 4-CP and toxicity removals at a sludge age of 20 days and HRT of 25 h.     

Elimination of Cu(II) toxicity by powdered waste sludge (PWS) addition to an activated sludge unit treating Cu(II) containing synthetic wastewater

Copper(II) ion toxicity onto activated sludge organisms was eliminated by addition of powdered waste sludge (PWS) to the feed wastewater for removal of Cu(II) ions by biosorption before biological treatment. The synthetic feed wastewater containing 14 or 22 mgl(-1) Cu(II) was mixed with PWS in a mixing tank where Cu(II) ions were adsorbed onto PWS and the mixture was fed to a sedimentation tank to separate Cu(II) containing PWS from the feed wastewater. The activated sludge unit fed with the effluent of the sedimentation tank was operated at a hydraulic residence time (HRT) of 10h and sludge age (SRT) of 10 days. To investigate Cu(II), COD and toxicity removal performance of the activated sludge unit at different PWS loadings, the system was operated at different PWS loading rates (0.1-1 gPWSh(-1)) while the Cu(II) loading rate was constant throughout the operation. Percent copper, COD and toxicity removals increased with increasing PWS loading rate due to increased adsorption of Cu(II) onto PWS yielding low Cu(II) contents in the feed. Biomass concentration in the aeration tank increased and the sludge volume index (SVI) decreased with increasing PWS loading rate due to elimination of Cu(II) from the feed wastewater by PWS addition. PWS addition to the Cu(II) containing wastewater was proven to be effective for removal of Cu(II) by biosorption before biological treatment. Approximately, 1 gPWSh(-1) should be added for 28 mgCuh(-1) loading rate for complete removal of Cu(II) from the feed wastewater to obtain high COD removals in the activated sludge unit.     

COD, 2,4,6-trichlorophenol (TCP) and toxicity removal from synthetic wastewater in a rotating perforated-tubes biofilm reactor

Synthetic wastewater containing different concentrations of 2,4,6-trichlorophenol (TCP) was biologically treated using a novel rotating perforated-tubes biofilm reactor (RTBR) for chemical oxygen demand (COD), TCP and toxicity removal. Performance of the reactor was investigated as function of major operating variables such as the feed TCP and COD concentrations and A/Q (biofilm surface area/feed flow rate) ratio. A Box-Behnken statistical experiment design method was used by considering the feed TCP (0-400 mg L(-1)), COD (1,000-4,000 mg L(-1)) and A/Q ratio (23-163 m(2)dm(-3)) as the independent variables while percent TCP, COD, and toxicity removals were the objective functions. The results were correlated with the quadratic model since this was found to be the most suitable one. Response function coefficients were determined by correlating the experimental data with the response function. Percent TCP, COD and toxicity removals estimated from the response functions were in good agreement with the experimental results. TCP, COD and toxicity removals increased with increasing A/Q ratio and decreasing feed TCP concentrations. Percent toxicity removals were always lower than TCP removals indicating presence or formation of some toxic by products from TCP biodegradation. For the feed TCP of 400 mg L(-1), the optimum conditions resulting in maximum COD (99%), TCP (100%) and toxicity (93%) removals were A/Q ratio of nearly 165 m(2)dm(-3) and feed COD of 2,985 mg L(-1).     

Aerobic decolourization of the indigo dye-containing textile wastewater using continuous combined bioreactors

An aerobic bioprocess was applied to Indigo dye-containing textile wastewater treatment aiming at the colour elimination and biodegradation. A combined aerobic system using continuous stirred tank reactor (CSTR) and fixed film bioreactor (FFB) was continuously operated at constant temperature and fed with the textile wastewater (pH: 7.5 and total chemical oxygen demand (COD): 1185 mg l(-1)). The CSTR is a 1l continuous flow stirred tank reactor with a 700 ml working volume, and operated with a variable wastewater loading rate (WLR) from 0.92 to 3.7 g l(-1) d(-1). The FFB is a 1.5l continuous flow with three compartments packed with a rippled cylindrical polyethylene support, operated with a variable WLR between 0.09 and 0.73 g l(-1) d(-1). The combined two bioreactors were inoculated by an acclimated microbial consortium and continuously operated with four total WLR. This system presented high COD elimination and colour removal efficiencies of 97.5% and 97.3%, respectively, obtained with a total hydraulic retention time (HRT) of 4 days and total WLR of 0.29 g l(-1) d(-1). The effects of WLR on absorption phenomena on the yield of conversion of substrate on biomass (R(TSS/COD)) and on the yield of conversion of substrate on active biomass (R(VVS/COD)) are discussed. The increase of WLR and the decrease of HRT diminished the performances of this system in terms of decolourization and COD removal explained by the sloughing of biofilm, and the washout phenomena.     

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.     

Biological treatment of para-chlorophenol containing synthetic wastewater using rotating brush biofilm reactor

A novel rotating brush biofilm reactor (RBBR) was used for para-chlorophenol (4-chlorophenol, 4-CP), COD and toxicity removal from synthetic wastewater containing different concentrations of 4-CP. Effects of major operating variables such as the feed 4-CP and COD concentrations and A/Q (biofilm surface area/feed flow rate) ratio on the performance of the biofilm reactor were investigated. A Box-Wilson statistical experiment design method was used by considering the feed 4-CP (0-1000 mg l(-1)), COD (2000-6000 mg l(-1)) and A/Q ratio (73-293 m(2) day m(-3)) as the independent variables while the 4-CP, COD and toxicity removals were the objective functions. The results were correlated by a response function and the coefficients were determined by regression analysis. Percent 4-CP, COD and toxicity removals determined from the response functions were in good agreement with the experimental results. 4-CP, COD and toxicity removals increased with decreasing feed 4-CP and increasing A/Q ratio. Optimum conditions resulting in maximum COD, 4-CP and toxicity removals were found to be A/Q ratio of nearly 180 m(2) day m(-3), feed COD of nearly 4000 mg l(-1) and feed 4-CP of less than 205 mg l(-1).     

Application of Box-Wilson experimental design method for 2,4-dinitrotoluene treatment in a sequential anaerobic migrating blanket reactor (AMBR)/aerobic completely stirred tank reactor (CSTR) system

A sequential aerobic completely stirred tank reactor (CSTR) following the anaerobic migrating blanket reactor (AMBR) was used to treat a synthetic wastewater containing 2,4-dinitrotoluene (2,4-DNT). A Box-Wilson statistical experiment design was used to determine the effects of 2,4-DNT and the hydraulic retention times (HRTs) on 2,4-DNT and COD removal efficiencies in the AMBR reactor. The 2,4-DNT concentrations in the feed (0-280 mg/L) and the HRT (0.5-10 days) were considered as the independent variables while the 2,4-DNT and chemical oxygen demand (COD) removal efficiencies, total and methane gas productions, methane gas percentage, pH, total volatile fatty acid (TVFA) and total volatile fatty acid/bicarbonate alkalinity (TVFA/Bic.Alk.) ratio were considered as the objective functions in the Box-Wilson statistical experiment design in the AMBR. The predicted data for the parameters given above were determined from the response functions by regression analysis of the experimental data and exhibited excellent agreement with the experimental results. The optimum HRT which gave the maximum COD (97.00%) and 2,4-DNT removal (99.90%) efficiencies was between 5 and 10 days at influent 2,4-DNT concentrations 1-280 mg/L in the AMBR. The aerobic CSTR was used for removals of residual COD remaining from the AMBR, and for metabolites of 2,4-DNT. The maximum COD removal efficiency was 99% at an HRT of 1.89 days at a 2,4-DNT concentration of 239 mg/L in the aerobic CSTR. It was found that 280 mg/L 2,4-DNT transformed to 2,4-diaminotoluene (2,4-DAT) via 2-amino-4-nitrotoluene (2-A-4-NT) and 4-amino-2-nitrotoluene (4-A-2-NT) in the AMBR. The maximum 2,4-DAT removal was 82% at an HRT of 8.61 days in the aerobic CSTR. The maximum total COD and 2,4-DNT removal efficiencies were 99.00% and 99.99%, respectively, at an influent 2,4-DNT concentration of 239 mg/L and at 1.89 days of HRT in the sequential AMBR/CSTR.     

Degradation of Procion Red H-E7B reactive dye by coupling a photo-Fenton system with a sequencing batch reactor

A bench-scale study combining photo-Fenton reaction with an aerobic sequencing batch reactor (SBR) to degrade a commercial homo-bireactive dye (Procion Red H-E7B, 250mgl(-1)) was investigated. The photo-Fenton process was applied as a pre-treatment, avoiding complete mineralisation, just to obtain a bio-compatible water able to be treated by means of the SBR in a second step. In this sense, different Fenton reagent concentrations were assessed by following dye solution biodegradability enhancement (BOD(5)/COD), as well as the toxicity (EC(50)), DOC, colour (Abs(543.5)) and H(2)O(2) evolution with photo-Fenton irradiation time. Obtained pre-treated solutions were biologically oxidized in a SBR containing non-acclimated activated sludge. Different hydraulic retention time (HRT) in the bioreactor were tested to attain the maximum organic load removal efficiency. Best results were obtained with 60min of 10mgl(-1) Fe(II) and 125mgl(-1) H(2)O(2) photo-Fenton pre-treatment and 1 day HRT in SBR.     

Mathematical modelling of 4-chlorophenol inhibition on COD and 4-chlorophenol removals in an activated sludge unit

A mathematical model was developed for an activated sludge unit treating 4-chlorophenol (4-CP) containing synthetic wastewater composed of diluted molasses, urea, KH(2)PO(4) and MgSO(4) with COD and 4-CP contents of 2500 and 500 mg l(-1), respectively. The model included 4-CP inhibition on COD and 4-CP removals. Experimental data obtained at different hydraulic residence times (HRT=5-30h) and sludge ages (SRT, 3-30 days) were used to estimate the kinetic and inhibition constants for COD and 4-CP removal rates. 4-CP inhibition on COD removal was negligible while the inhibition on 4-CP removal was significant. The specific rate constant (k), saturation constant (K(s)) for COD oxidation were found to be 2.64 day(-1) and 559 mg l(-1), respectively. A similar model was used for 4-CP oxidation in the activated sludge unit and the constants were found to be k'=1.44 day(-1), K'(s)=25.7 mgl(-1), K"(CP)=559 mg l(-1),and K(I,CP)=17 mg l(-1). Increases in death rate constant because of 4-CP inhibition was also quantified and the inhibition constants were determined for both COD and 4-CP removals. Model predictions with the estimated kinetic constants were in good agreement with the experimental data. Developed model can be used to estimate the performance of an activated sludge unit treating 4-CP containing wastewater under the specified experimental conditions.     

Simultaneous removal of C, N, P from cheese whey by jet loop membrane bioreactor (JLMBR)

The membrane bioreactor (MBR) used in this study consisted of a jet loop bioreactor (aerobic high rate system) and a membrane separation unit (microfiltration). Jet loop membrane bioreactor (JLMBR) system is a high performance treatment system. High organic loading rates can be achieved with a very small footprint. The JLMBR is a compact biological treatment system which requires much smaller tank volumes than conventional activated sludge system. Solid-liquid separation is performed with a membrane. The JLMBR system, of 35 L capacity, was operated continuously for 3 months with a sludge age of 1.1-2.8 days and chemical oxygen demand (COD) loads of 3.5-33.5 kg COD m(-3) day(-1). The mean concentration values of COD, total nitrogen (TN) and PO(4)3- in cheese whey (CW) were found as 78,680 mg L(-1), 1125 mg L(-1) and 378 mg L(-1), respectively. Ninety-seven percent COD removal rate was obtained at the sludge age (Thetac) of 1.6 days and volumetric loads of 22.2 kg COD m(-3) day(-1). TN removal was obtained as 99% at the loading rates of 17-436 g TN m(-3) day(-1). PO4(3-) removals were between 65 and 88% for the loading of 30-134 gPO4(3-) m(-3) day(-1). The system could simultaneously remove the COD, TN and PO(4)3- at high efficiencies. The sludge flocks were highly motile, dispersed and had poor settling properties.     

Process control, energy recovery and cost savings in acetic acid wastewater treatment

An anaerobic fixed bed loop (AFBL) reactor was applied for treatment of acetic acid (HAc) wastewater. Two pH process control concepts were investigated; auxostatic and chemostatic control. In the auxostatic pH control, feed pump is interrupted when pH falls below a certain pH value in the bioreactor, which results in reactor operation at maximum load. Chemostatic control assures alkaline conditions by setting a certain pH value in the influent, preventing initial reactor acidification. The AFBL reactor treated HAc wastewater at low hydraulic residence time (HRT) (10-12 h), performed at high space time loads (40-45 kg COD/m(3) d) and high space time yield (30-35 kg COD/m(3) d) to achieve high COD (Chemical Oxygen Demand) removal (80%). Material and cost savings were accomplished by utilizing the microbial potential for wastewater neutralization during anaerobic treatment along with application of favourable pH-auxostatic control. NaOH requirement for neutralization was reduced by 75% and HRT was increased up to 20 h. Energy was recovered by applying costless CO(2) contained in the biogas for neutralization of alkaline wastewater. Biogas was enriched in methane by 4 times. This actually brings in more energy profits, since biogas extra heating for CO(2) content during biogas combustion is minimized and usage of other acidifying agents is omitted.     

Effect of increasing nitrobenzene loading rates on the performance of anaerobic migrating blanket reactor and sequential anaerobic migrating blanket reactor/completely stirred tank reactor system

A laboratory scale anaerobic migrating blanket reactor (AMBR) reactor was operated at nitrobenzene (NB) loading rates increasing from 3.33 to 66.67 g NB/m³ day and at a constant hydraulic retention time (HRT) of 6 days to observe the effects of increasing NB concentrations on chemical oxygen demand (COD), NB removal efficiencies, bicarbonate alkalinity, volatile fatty acid (VFA) accumulation and methane gas percentage. Moreover, the effect of an aerobic completely stirred tank reactor (CSTR) reactor, following the anaerobic reactor, on treatment efficiencies was also investigated. Approximately 91–94% COD removal efficiencies were observed up to a NB loading rate of 30.00 g/m³ day in the AMBR reactor. The COD removal efficiencies decreased from 91% to 85% at a NB loading rate of 66.67 g/m³ day. NB removal efficiencies were approximately 100% at all NB loading rates. The maximum total gas, methane gas productions and methane percentage were found to be 4.1, 2.6 l/day and 59%, respectively, at a NB loading rate of 30.00 g/m³ day. The optimum pH values were found to be between 7.2 and 8.4 for maximum methanogenesis. The total volatile fatty acid (TVFA) concentrations in the effluent were 110 and 70 mg/l in the first and second compartments at NB loading rates as high as 66.67 and 6.67 g/m³ day, respectively, while they were measured as zero in the effluent of the AMBR reactor. In this study, from 180 mg/l NB 66 mg/l aniline was produced in the anaerobic reactor while aniline was completely removed and transformed to 2 mg/l of cathechol in the aerobic CSTR reactor. Overall COD removal efficiencies were found to be 95% and 99% for NB loading rates of 3.33 and 66.67 g/m³ day in the sequential anaerobic AMBR/aerobic CSTR reactor system, respectively. The toxicity tests performed with Photobacterium phosphoreum (LCK 480, LUMIStox) and Daphnia magna showed that the toxicity decreased with anaerobic/aerobic sequential reactor system from the influent, anaerobic and to aerobic effluents.     

Comparative performance of anaerobic reactors for treatment of sago industry wastewater

For a country like India where energy continues to be precious, with oil prices continuing to rise unlike in the West, anaerobic digestion has far greater relevance than it has to many other regions of the world. The cassava starch production in our country is mainly concentrated in small to medium scale factories, which generates 30,000–40,000 l of effluent per ton of sago produced. The effluent is acidic and highly organic in nature having chemical oxygen demand (COD) of 5,000–7,000 mg l^?1 during the season and 1,000–5,000 during the off-season. These effluents pose a serious threat to the environment and quality of life in the rural area. Since the treatment of cassava starch factory effluents through the normal biogas plants with 30–55 days retention period is very costly, attempts have been made to treat them through high-rate hybrid reactor with several hours of retention period. In Random-Packed Anaerobic Filter, the maximum COD reduction was observed (84.4 %) at 10 h hydraulic retention time (HRT). At 4 h HRT only 46.3 % COD was removed. Even though higher COD removal was achieved at 20 h, the better HRT was at 10 h as the difference between the 20 and 10 h HRT in only 0.2 %. In Up-flow Anaerobic Sludge Blanket reactor, the maximum COD removal (90 %) and total solid (TS) removal (82 %) were observed in a HRT of 30 h, whereas low COD (67 %) and TSs (64 %) removal was observed at 5 h HRT. The treatment of sago industry effluent in a hybrid reactor was studied and the HRT employed was 10, 24, 32, and 40 h. The COD removal rates were 86, 93, 94, and 95 %, and the TSs removal was 79, 85, 86, and 89 %. When the results of all these three reactors were compared, the hybrid reactor seems to be better with an optimum HRT range of 10–20 h. Hence, the anaerobic digestion has proved to be an effective method of treating the sago industry wastewater with simultaneous production of energy in the form of methane.     

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.     

Digestion of thermally hydrolyzed sewage sludge by anaerobic sequencing batch reactor

Laboratory experiments were conducted to investigate the performance of an anaerobic sequencing batch reactor (ASBR) for the digestion of thermally hydrolyzed sewage sludge. Both mesophilic ASBR and continuous-flow stirred tank reactors (CSTR) were evaluated with an equivalent loading rate of 2.71 kg COD/m(3)day at 20-day hydraulic retention time (HRT) and 5.42 kg COD/m(3)day at 10-day HRT. The average total chemical oxygen demand (TCOD) removals of the ASBR at the 20-day and 10-day HRT were 67.71% and 61.66%, respectively. These were 12.38% and 27.92% higher than those obtained by CSTR. As a result, the average daily gas production of ASBR was 15% higher than that of the CSTR at 20-day HRT, and 31% higher than that of the CSTR at 10-day HRT. Solids in thermally hydrolyzed sludge accumulated within ASBR were able to reach a high steady state with solid content of 65-80 g/L. This resulted in a relatively high solid retention time (SRT) of 34-40 days in the ASBR at 10-day HRT. However, too much solid accumulation resulted in the unsteadiness of the ASBR, making regular discharge of digested sludge from the bottom of the ASBR necessary to keep the reactor stable. The evolution of the gas production, soluble chemical oxygen demand (SCOD) and volatile fatty acids (VFAs) in an operation cycle of ASBR also showed that the ASBR was steady and feasible for the treatment of thermally hydrolyzed sludge.     

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.     

Biodegradation of p-nitrophenol using Arthrobacter chlorophenolicus A6 in a novel upflow packed bed reactor

A novel packed bed reactor (PBR) was designed with cross flow aeration at multiple ports along the depth to improve the hydrodynamic conditions of the reactor, and the biodegradation efficiency of Arthrobacter chlorophenolicus A6 on p-nitrophenol (PNP) removal in PBR at different PNP loading rates were evaluated. The novel PBR was designed to improve the hydrodynamic features such as mixing time profile (t(m95)), oxygen mass transfer coefficient (k(L)a), and overall gas hold up capacity (?(G)) of the reactor. PNP concentration in the influent was varied between 600 and 1400 mg l(-1) whereas the hydraulic retention time (HRT) in the reactor was varied between 18 and 7.5h. Complete removal of PNP was achieved in the reactor up to a PNP loading rate of 2787 mg l(-1)d(-1). More than 99.9% removal of PNP was achieved in the reactor for an influent concentration of 1400 mg l(-1) and at 18 h HRT. In the present study, PNP was utilized as sole source of carbon and energy by A. chlorophenolicus A6. Furthermore, the bioreactor showed good compatibility in handling shock loading of PNP.     

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.     

Anoxic sulfide biooxidation using nitrite as electron acceptor

Biotechnology can be used to assess the well being of ecosystems, transform pollutants into benign substances, generate biodegradable materials from renewable sources, and develop environmentally safe manufacturing and disposal processes. Simultaneous elimination of sulfide and nitrite from synthetic wastewaters was investigated using a bioreactor. A laboratory scale anoxic sulfide-oxidizing (ASO) reactor was operated for 135 days to evaluate the potential for volumetric loading rates, effect of hydraulic retention time (HRT) and substrate concentration on the process performance. The maximal sulfide and nitrite removal rates were achieved to be 13.82 and 16.311 kg/(m3 day), respectively, at 0.10 day HRT. The process can endure high sulfide concentrations, as the sulfide removal percentage always remained higher than 88.97% with influent concentration up to 1920 mg/L. Incomplete sulfide oxidation took place due to lower consumed nitrite to sulfide ratios of 0.93. It also tolerated high nitrite concentration up to 2265.25mg/L. The potential achieved by decreasing HRT at fixed substrate concentration is higher than that by increasing substrate concentration at fixed HRT. The process can bear short HRT of 0.10 day but careful operation is needed. Nitrite conversion was more sensitive to HRT than sulfide conversion when HRT was decreased from 1.50 to 0.08 day. Stoichiometric analyses and results of batch experiments show that major part of sulfide (89-90%) was reduced by nitrite while some autooxidation (10-11%) was resulted from presence of small quantities of dissolved oxygen in the influent wastewater. There was ammonia amassing in considerably high amounts in the bioreactor when the influent nitrite concentration reached above 2265.25mg/L. High ammonia concentrations (200-550 mg/L) in the bioreactor contributed towards the overall inhibition of the process. Present biotechnology exhibits practical value with a high potential for simultaneous removal of nitrite and sulfide from concentrated wastewaters at shorter HRT.     

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.