Performance of anaerobic contact filter in series for treating distillery spentwash

Investigations were carried out by using rigid polyurethane foam as a packing material in the anaerobic contact filter (series) to treat distillery spentwash. The effect of hydraulic retention time (HRT) in treatment efficiency of reactor (I) and (II) was evaluated at different initial substrate concentrations ranging from 1500 mg/l to 19,000 mg/l. The effect of toxic parameters such as sulphate present in the distillery spentwash and the corresponding parameters such as total sulphide and un-ionized hydrogen sulphide generated during digestion of wastewater were evaluated to assess the reactor performance. The results showed that at 4 d HRT the overall COD removal percent ranged from 98% to 73% for an influent COD of 1500 mg/l to 19,000 mg/l. The overall performance of COD removal percent in reactor (I) and (II) at 2, 3 and 4 d HRT's were investigated. At 3 d HRT the reactor (II) showed a higher COD removal percent when compared to reactor (I), which clearly shows the role of hydraulic retention time in degradation of the organic matter present in the wastewater above an influent COD concentration of 5000 mg/l.     

Carbon and nitrogen substrates consumption, ammonia release and proton transfer in relation with growth of Geotrichum candidum and Penicillium camemberti on a solid medium

The influence of hydraulic retention time (HRT) and gelatin concentration on the acidification of gelatinaceous wastewater in an upflow anaerobic reactor was investigated at pH 5.5 and 37 degrees C. The degree of gelatin degradation increased with the HRT, from 84.1% at 4 h to 89.6% at 24 h, but decreased with the increase of the gelatin concentration in the influent from 65.2% at 2 g-CODl(-1) to 51.9% at 30 g-CODl(-1). The degradation of gelatin followed the Monod kinetics with a maximum rate of 1.10 g (g-VSS x d)(-1) and a half-rate constant of 0.23 gl(-1). The overall production rate of VFA and alcohols decreased with HRT, from 0.33 g (g-VSS x d)(-1) at 4 h to 0.15 g (g-VSS x d)(-1) at 24 h, but increased with gelatin concentration in the influent, from 0.10 g (g-VSS x d)(-1) at 4 g-CODl(-1) to 0.58 g (g-VSS x d)(-1) at 30 g-CODl(-1). The key acidification products were acetate, propionate and butyrate, plus i-butyrate, valerate, i-valerate, caproate and ethanol in smaller quantities. Formate, methanol, propanol and butanol were found only in certain runs. Only 4.5-7.8% of COD in wastewater was converted to hydrogen and methane. The sludge yield was estimated as 0.320+/-0.014 g-VSS (g-COD)(-1).     

Degradation of 4-chlorophenol in UASB reactor under methanogenic conditions

Treatment of simulated wastewater containing 40 mg/l of 4-chlorophenol (4-CP) was carried out in an upflow anaerobic sludge blanket (UASB) reactor under methanogenic condition. The performance of this test UASB reactor was evaluated in terms of 4-CP removal. Hydraulic retention time (HRT) and substrate:co-substrate ratio for the 4-CP removal was optimized by varying the influent flow rate (13-34.7 ml/min) and sodium acetate concentration (2-5 g/l), respectively. A control UASB reactor, which was not exposed to 4-CP was also operated under similar conditions. Organic loading rate (OLR) was varied in the range of 2-5.3 kg/m(3)/d and 1.7-4.2 kg/m(3)/d, respectively, for HRT and substrate:co-substrate ratio studies, respectively. The optimum HRT and substrate:co-substrate ratio for the removal of 4-CP was 12h and 1:75, respectively. Removal of 4-CP achieved at optimum HRT and substrate:co-substrate ratio was 88.3+/-0.7%. Removal of 4-CP occurred through dehalogenation and caused increase in chloride ion concentration in the effluent by 0.23-0.27 mg/mg 4-CP removed. The ring cleavage test showed the ortho mode of ring cleavage of 4-CP. Change in the elemental composition of the anaerobic biomass of UASB reactors was observed during the study period. Concentration of Ca(2+) increased in the biomass and this could be attributed to the biosoftening. Specific methanogenic activity of the sludge of control and test UASB reactor was 0.832 g CH(4) COD/g VSS d and 0.694 g CH(4) COD/g VSS d, respectively.     

Performance evaluation of a mesophilic anaerobic fluidized-bed reactor treating wastewater derived from the production of proteins from extracted sunflower flour

A study of the anaerobic digestion of wastewater derived from the production of protein isolates from extracted sunflower flour was carried out in a laboratory-scale, mesophilic (35 degrees C) fluidized-bed reactor with saponite as bacterial support. Chemical oxygen demand (COD) removal efficiencies in the range of 98.3-80.0% were achieved in the reactor at organic loading rates (OLR) of between 0.6 and 9.3 g COD/I d, hydraulic retention times (HRT) of between 20.0 and 1.1 d and average feed COD concentration of 10.6 g/l. Eighty percent of feed COD could be removed up to OLR of 9.3 g COD/l d. The yield coefficient of methane production was 0.33 l of methane (at STP) per gram of COD removed and was virtually independent of the OLR applied. Because the buffering capacity of the experimental system was maintained at favorable levels with excess total alkalinity present at all loadings, the rate of methanogenesis was not affected by loading. The experimental data indicated that a total alkalinity in the range of 2,000-2,460 mg/l as CaCO3 was sufficient to prevent the pH from dropping to below 7.0 for OLR of up to 9.3 g COD/l d. The volatile fatty acid (VFA) levels and the VFA/alkalinity ratio were lower than the suggested limits for digester failure (0.3-0.4) for OLR and HRT up to 9.3 g COD/l d and 1.1 d, respectively. For a HRT of 0.87 d (OLR of 12.1 g COD/l d) the start of acidification was observed in the reactor.     

Aerobic treatment of dairy wastewater with sequencing batch reactor systems

Performances of single-stage and two-stage sequencing batch reactor (SBR) systems were investigated for treating dairy wastewater. A single-stage SBR system was tested with 10,000 mg/l chemical oxygen demand (COD) influent at three hydraulic retention times (HRTs) of 1, 2, and 3 days and 20,000 mg/l COD influent at four HRTs of 1, 2, 3, and 4 days. A 1-day HRT was found sufficient for treating 10,000-mg/l COD wastewater, with the removal efficiency of 80.2% COD, 63.4% total solids, 66.2% volatile solids, 75% total Kjeldahl nitrogen, and 38.3% total nitrogen from the liquid effluent. Two-day HRT was believed sufficient for treating 20,000-mg/l COD dairy wastewater if complete ammonia oxidation is not desired. However, 4-day HRT needs to be used for achieving complete ammonia oxidation. A two-stage system consisting of an SBR and a complete-mix biofilm reactor was capable of achieving complete ammonia oxidation and comparable carbon, solids, and nitrogen removal while using at least 1/3 less HRT as compared to the single SBR system.     

Anaerobic biodegradation of spent sulphite liquor in a UASB reactor

Anaerobic biodegradation of fermented spent sulphite liquor, SSL, which is produced during the manufacture of sulphite pulp, was investigated. SSL contains a high concentration of lignin products in addition to hemicellulose and has a very high COD load (173 g COD l(-1)). Batch experiments with diluted SSL and pretreated SSL indicated a potential of 12-22 l methane per litre SSL, which corresponds to 0.13-0.22 l methane (g VS)(-1) and COD removal of up to 37%. COD removal in a mesophilic upflow anaerobic sludge blanket, UASB. reactor ranged from 10% to 31% at an organic loading rate, OLR, of 10-51 g (1 d)(-1) and hydraulic retention time from 3.7 to 1.5 days. The biogas productivity was 3 1 (l(reactor d)(-1), with a yield of 0.05 l gas (g VS)(-1). These results suggest that anaerobic digestion in UASB reactors may provide a new alternative for the treatment of SSL to other treatment strategies such as incineration. Although the total COD reduction achieved is limited, bioenergy is produced and readily biodegradable matter is removed causing less load on post-treatment installations.     

A comparison of the performance of mesophilic and thermophilic anaerobic filters treating papermill wastewater

Two anaerobic filters, one mesophilic (35 degrees C) and one thermophilic (55 degrees C), were operated with a papermill wastewater at a series of organic loadings. The hydraulic retention time (HRT) ranged from 6 to 24 h with organic loading rates (OLR) 1.07-12.25 g/l per day. At loading rates up to 8.4 g COD/l d, there was no difference in terms of the removal of soluble COD (SCOD) and gas production. At the higher organic loading rate, the SCOD removal performance of thermophilic digester was slightly better compare to mesophilic digester. Similar trend was also observed in terms of the daily methane production. The stability of thermophilic digester was also better than mesophilic digester particularly for the higher organic loadings. Volatile fatty acid accumulation was observed in the effluent of the mesophilic filter at the higher organic loading rates. The Stover-Kincannon model was applied to both digesters and it was found that model was applicable to both digesters for papermill wastewater. K(B) and U(max) constants from the Stover-Kincannon model were also derived.     

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.     

人工湿地对猪场废水有机物处理效果的研究

分别以香根草 (Vetiveriazizanioides)和风车草 (Cyperusalternifolius)为植被 ,按 1.0m× 0 .5m×0 .8m建立人工湿地 ,通过 4季测试 ,研究其对猪场废水有机物的净化功能及其随季节、进水浓度及水力停留时间变化的规律 .结果表明 ,4个季节香根草或风车草人工湿地对COD和BOD有较稳定的去除效果 ,两湿地抗有机负荷冲击能力强 .在春季 ,停留时间 1～ 2d ,COD和BOD去除率分别为 70 %和 80 %;在夏季 ,进水COD高达 10 0 0～ 140 0mg·L-1情况下 ,COD去除率接近 90 %;在秋季 ,停留时间 1～ 2d ,COD和BOD去除率分别为 5 0 %～ 6 0 %和 5 0 %;在冬季 ,进水COD达 10 0 3mg·L-1情况下 ,COD去除率在 70 %以上 .COD、BOD和SS的去除率在两湿地间没有显著差异 .人工湿地污染物 (Y)随水力停留时间 (t)延长的降解遵从指数方程规律Yt=Y0 ·e( -kt) .在相同停留时间时 ,随进水污染物浓度 (x)提高的出水污染物浓度 (y)的回归关系遵从直线方程规律 y =a+bx .     

Effect of feeding strategy on the stability of anaerobic sequencing batch reactor responses to organic loading conditions

The goal of this study was to examine the effect of feeding strategy on the capability for treatment and the stability of an anaerobic sequencing batch reactor (ASBR) under increasing organic loading. The lab-scale ASBR systems were operated at 35 degrees C using synthetic organic wastewater under both batch and fed-batch operational modes with different feed to cycle time (F:C) ratios. Experimental studies were conducted over a wide range of volumetric organic loading rates (VOLRs) (1.524 g COD/l/d) by varying the hydraulic retention time (HRT) (1.25, 2.5, and 5d) and the feed wastewater's COD (3750-30,000 mg/l). With an F:C ratio greater than or equal to 0.42, the fed-batch mode operation showed higher system efficiency in COD removal, volumetric methane production rate (VMPR), and specific methane production rate (SMPR) as compared to those in the batch mode with identical VOLR and HRT. In the fed-batch mode, the COD removals reached 86-95% with VOLR up to 12 g COD/l/d. The maximums for VMPR of 3.17 l CH4/l/d and for SMPR of 1.63 g CH4-COD/g VSS/d were achieved with a VOLR of 12 g COD/l/d at HRTs of 2.5 and 1.25 d, respectively. The fed-batch operation presented a lower concentration of volatile fatty acids (VFAs) than those in the batch operation. A lower concentration of VFAs confirmed the stability and efficiency of the fed-batch mode operation. The specific methanogenic activity (SMA) analysis showed that the VFA-degrading activity of the biomass in the fed-batch mode was higher for acetate and butyrate, and lower for propionate. Determined biomass yield and bacterial decay coefficients in the fed-batch operational mode were 0.05 g VSS/g COD rem and 0.001 d(-1), respectively.     

Anaerobic co-digestion of olive mill wastewater with olive mill solid waste in a tubular digester at mesophilic temperature

Anaerobic co-digestion is a well established process for treating many types of organic wastes, both solid and liquid. In this study we have investigated, on a laboratory scale, the anaerobic co-digestion of olive mill wastewater (OMW) with olive mill solid waste (OMSW) using semi-continuous, feeding, tubular digesters operated at mesophilic temperatures. Each digester was fed with an influent, composed of OMW and OMSW, at an organic loading rate (OLR) varying between 0.67 and 6.67 g COD/l/d. The hydraulic retention times (HRT) were 12, 24 and 36 days. The TCOD concentrations of OMW used as the main substrate were 24, 56 and 80 g COD/l; the amount of the dry OMSW used as a co-substrate was fixed to approximately 56 g/l of OMW. The results indicated that the best methane production was about 0.95 l/l/day obtained at an OLR = 4.67 g COD/l/d, corresponding to influent TCOD = 56 g COD/l at an HRT = 12d. In contrast, the maximum TCOD removal efficiency (89%) was achieved at an OLR = 0.67 g COD/l/d, corresponding to influent TCOD = 24 g COD/l at an HRT = 36 d. Moreover, the inhibition of biogas production was observed at the highest OLR studied.     

Thermophilic (55 degrees C) conversion of methanol in methanogenic-UASB reactors: influence of sulphate on methanol degradation and competition

Two upflow sludge bed reactors (UASB) were operated for 80 days at 55 degrees C with methanol as the substrate with an organic loading rate (OLR) of about 20 g CODl(-1) per day and a hydraulic retention time (HRT) of 10 h. One UASB was operated without sulphate addition (control reactor-R1) whereas the second was fed with sulphate at a COD:SO4(2-) ratio of 10 (sulphate-fed reactor-R2), providing an influent sulphate concentration of 0.6 g l(-1). For both reactors, methanogenesis was the dominant process with no considerable accumulation of acetate. The methanol removal averaged 93% and 83% for R1 and R2, respectively, and total sulphate removal was achieved in the latter. The pathway of methanol conversion for both sludges was investigated by measuring the fate of carbon in the presence and absence of bicarbonate or specific inhibitors for a sludge sample collected at day 72. In both sludges, about 70% of the methanol was syntrophically converted to methane and/or sulphide, via the intermediate H2/CO2. A strong competition between methanogens and sulphidogens took place in the R2 sludge with half of the methanol-COD being used by methane-producing bacteria and the other half by sulphate-reducing bacteria. Acetate was not an important intermediate for both sludges, and played a slightly more important role for the sulphate-adapted sludge (R2), sustained by the higher amount of bicarbonate produced during sulphate-reduction. The pathway study indicates that, although acetate does not represent an important intermediate, the system is susceptible to its accumulation.     

Treatment of recycled wastewaters from fishmeal factory by an anaerobic filter

Fishmeal industries processes produce effluents with high load organic matter. These effluents, after recycling and physical-chemical pretreatment, have a high organic content (5-6 g COD/l), proteins (3-5 g/l), salinity close to sea water, sodium chloride (30 g/l) and sulphate (1-3.3 g/l). An anaerobic filter was used for the treatment of this wastewater, with marine sediment as anaerobic inoculum. Anaerobic filter removed up to 70% of the influent COD concentrations at organic loading rates (OLR) of 9.5 and 14.3 (g/l d) and sulphate up to 80% at OLR of 7.1 and 14.3 (g/l d) whereas the pH ranged between 7.0 and 7.5. These results show that anaerobic filter systems are applicable to recycled wastewaters from fishmeal.     

Competitive reaction kinetics of sulfate-reducing bacteria and methanogenic bacteria in anaerobic filters

A kinetic model for the anaerobic filter (AF) that takes into account the mass fractions of sulfate-reducing bacteria (SRB) (f(SRB)) and methanogenic bacteria (MB) (f(MB)) and an inhibiting effect of H(2)S on bacterial groups is proposed. When the acetate-fed AFs were maintained at the low organic loading rate of 2.5kg COD/m(3)d, variations of the influent COD/SO(4)(2-) ratio (0.5-3.0) does not materially affect the acetate removal efficiency (all varying between 98.1% and 99.7%). With an increase in influent COD/SO(4)(2-) ratio, both the biofilm thickness and the specific substrate utilization rate decreased slightly but f(SRB) decreased markedly. The estimated results of f(SRB) and f(MB) showed that SRB out-competed MB for bacterial growth if the influent COD/SO(4)(2-) ratio was maintained at less than 1.3, whereas MB out-competed SRB for bacterial growth if the influent COD/SO(4)(2-) ratio was maintained at greater than 2.0. The specific substrate utilization rate of SRB (0.19-0.24mg acetate/mg VSSd) was lower than that of MB (0.31-0.59mg acetate/mg VSSd). The estimated kinetic parameters disclosed that the affinity of acetate to MB was higher and unionized H(2)S imposed a greater inhibiting effect on MB. The model simulation results (acetate and sulfate removal) agreed well with the experimental results.     

Removal of Pb2+ and Ni2+ by bio-sludge in sequencing batch reactor (SBR) and granular activated carbon-SBR (GAC-SBR) systems

Living bio-sludge from domestic wastewater treatment plant was used as adsorbent of heavy metals (Pb(2+), Ni(2+)) and its adsorption capacity was about 10-30% reduced by autoclaving at 110 degrees C for 10 min. The living bio-sludge acclimatized in synthetic industrial estate wastewater (SIEWW) without heavy metals showed the highest Pb(2+) and Ni(2+) adsorption capacities at 840+/-20 and 720+/-10 mg/g bio-sludge, respectively. The adsorbed Pb(2+) and Ni(2+) were easily eluted (70-77%) from bio-sludge by washing with 0.1 mol/l HNO(3) solution. The heavy metals (Pb(2+), Ni(2+)) removal efficiency of both SBR and GAC-SBR systems were increased with the increase of hydraulic retention time (HRT), or the decrease of organic loading. The SBR system showed higher heavy metals removal efficiency than GAC-SBR system at the same organic loading or HRT. The Pb(2+), Ni(2+), BOD(5), COD and TKN removal efficiencies of GAC-SBR system were 88.6+/-0.9%, 94.6+/-0.1%, 91.3+/-1.0%, 81.9+/-1.0% and 62.9+/-0.5%, respectively with industrial estate wastewater (IEWW) with 410 mg/l glucose, 5 mg/l Pb(2+) and 5 mg/l Ni(2+) under organic loading of 1.25 kg BOD(5)/m(3) d (HRT of 3 days). The bio-sludge quality (sludge volume index: SVI) of the system was less than 80 ml/g. The excess sludge from both SBR and GAC-SBR systems with SIEWW under the organic loading of 1.25-2.50 kg BOD(5)/m(3) d contained Pb(2+) and Ni(2+) at concentrations of 240-250 mg Pb(2+)/g bio-sludge and 180-210 mg Ni(2+)/g bio-sludge, respectively.     

Performance of a down-flow fluidized bed reactor under sulfate reduction conditions using volatile fatty acids as electron donors

The use of a down-flow fluidized bed (DFFB) reactor for the treatment of a sulfate-rich synthetic wastewater was investigated to obtain insight into the outcome of sulfate reduction in a biofilm attached to a plastic support under a down-flow regime. Fine low-density polyethylene particles were used as support for developing a biofilm within the reactor. The reactor treated a volatile fatty acids mixture of acetate or lactate, propionate, and butyrate at different chemical oxygen demand (COD) to sulfate ratios ranging from 1.67 to 0.67 (g/g). Organic loading rate changed from 2.5 to 5 g COD/L x day and sulfate loading rate increased from 1.5 to 7.3 g SO(4) (2-)/L x day. At the beginning of continuous operation, methanogenesis was the predominant process; however, after 187 days, sulfate reduction became the main ongoing biological process. After 369 days, a COD removal of 93% and a sulfate removal of 75% were reached. Total sulfide concentrations in the reactor ranged from 105, when the reactor was mainly methanogenic, to around 1,215 mg/L at the end of the experiment. The high sulfide concentrations did not affect the performance of the reactor. Results demonstrated that the configuration of the DFFB reactor was suitable for the anaerobic treatment of sulfate-rich wastewater.     

Effect of temperature on low-strength wastewater treatment by UASB reactor using poly(vinyl alcohol)-gel carrier

The feasibility of treating low-strength wastewater with an up-flow anaerobic sludge blanket (UASB) reactor, using a poly(vinyl alcohol)-gel carrier, at various temperatures and hydraulic retention times (HRTs) was examined. The temperature was decreased from 35°C to 25°C and then to 15°C. The HRT was reduced from 2.0 h to 0.22 h. The COD removal rate reached 28 kg-COD m(-3)d(-1) at 35°C, 16 kg-COD m(-3)d(-1) at 25°C, and 6 kg-COD m(-3)d(-1) at 15°C. The COD removal rate was reduced by half for each temperature reduction of 10°C.     

Some properties of a sequencing batch reactor system for removal of vat dyes

Bio-sludge from a wastewater treatment plant could be used as an adsorbent of vat dye from textile wastewater. Resting bio-sludge gave a higher adsorption capacity than dead bio-sludge. The resting bio-sludge from a textile wastewater treatment plant gave relatively high COD, BOD5 and dye adsorption capacity of 364.4 +/- 4.3, 178.0 +/- 9.0 and 50.5 +/- 1.3 mg/g of bio-sludge, respectively, in synthetic textile wastewater containing 40 mg/l Vat Yellow 1. Another advantage of the bio-sludge was that, after washing with 0.1 N NaOH solution, it was reusable without any activity loss. Through treatment with a sequencing batch reactor (SBR) system, both organic and dye in STIWW could be removed. The maximum dye (Vat Yellow 1), COD, BOD5 and TKN removal efficiencies of the SBR system under an MLSS of 2000 mg/l and an HRT of three days were 98.5 +/- 1.0%, 96.9 +/- 0.7%, 98.6 +/- 0.1% and 93.4 +/- 1.3%, respectively. Although, the dye and organic removal efficiencies of the SBR system with real textile wastewater were quite low, they could be increased by adding organic matters, especially glucose. The dye, COD, BOD5 and TKN removal efficiencies of the SBR system with glucose (0.89 g/l) supplemented textile industrial wastewater were 75.12 +/- 1.2%, 70.61 +/- 3.4%, 96.7 +/- 0.0%, and 63.2 +/- 1.1%, respectively.     

Anaerobic treatment of a chemical synthesis-based pharmaceutical wastewater in a hybrid upflow anaerobic sludge blanket reactor

In this study, performance of a lab-scale hybrid up-flow anaerobic sludge blanket (UASB) reactor, treating a chemical synthesis-based pharmaceutical wastewater, was evaluated under different operating conditions. This study consisted of two experimental stages: first, acclimation to the pharmaceutical wastewater and second, determination of maximum loading capacity of the hybrid UASB reactor. Initially, the carbon source in the reactor feed came entirely from glucose, applied at an organic loading rate (OLR) 1 kg COD/m(3) d. The OLR was gradually step increased to 3 kg COD/m(3) d at which point the feed to the hybrid UASB reactor was progressively modified by introducing the pharmaceutical wastewater in blends with glucose, so that the wastewater contributed approximately 10%, 30%, 70%, and ultimately, 100% of the carbon (COD) to be treated. At the acclimation OLR of 3 kg COD/m(3) d the hydraulic retention time (HRT) was 2 days. During this period of feed modification, the COD removal efficiencies of the anaerobic reactor were 99%, 96%, 91% and 85%, and specific methanogenic activities (SMA) were measured as 240, 230, 205 and 231 ml CH(4)/g TVS d, respectively. Following the acclimation period, the hybrid UASB reactor was fed with 100% (w/v) pharmaceutical wastewater up to an OLR of 9 kg COD/m(3) d in order to determine the maximum loading capacity achievable before reactor failure. At this OLR, the COD removal efficiency was 28%, and the SMA was measured as 170 ml CH(4)/g TVS d. The hybrid UASB reactor was found to be far more effective at an OLR of 8 kg COD/m(3) d with a COD removal efficiency of 72%. At this point, SMA value was 200 ml CH(4)/g TVS d. It was concluded that the hybrid UASB reactor could be a suitable alternative for the treatment of chemical synthesis-based pharmaceutical wastewater.     

Effect of COD to sulphate ratio and temperature in expanded-granular-sludge-blanket reactors for sulphate reduction

In an ethanol-fed expanded-granular-sludge-blanket (EGSB) reactor at 33°C, 80–90% of the sulphate load was removed at a rate of 4 g S/l d, provided that at least 6 g chemical oxygen demand (COD) per g sulphate-sulphur was supplied. The reactor started up in a matter of days. Gradually decreasing the ethanol to sulphate ratio (R) to about stoichiometry, resulted in 60–70% sulphate removal at rates of 7 g S/l d. Similar tendencies were observed with ethylene glycol as sole carbon and energy source. Total COD removal never reached more than 70–75%. This was related to a rather high biomass washout. The sulphate removal efficiency decrease when R was set at levels below 6, apparently because sulphate reducing bacteria (SRB) could not compete with methane producing bacteria (MPB) for acetate produced from the substrate dosed. Thermophilic operation at 55°C, after a stepwise increase in the reactor temperature over a period of 23 days, did not favour acetotrophic sulphate reduction. Yet, operation at 48°C and subsequently returning the temperature to 33°C clearly enhanced acetate conversion by SRB. In the case of an electron donor price of 0.035–0.075 USD/kg COD, the cost for operation at R=6 was found to be competitive to that at stoichiometry, i.e. R=2, provided the biogas produced was effectively used.