Effect of chloride and condensable tannin in anaerobic degradation of tannery wastewaters

Toxic effect due to chloride and condensable tannin on anaerobic digestion of vegetable tanning wastewater was investigated at different hydraulic retention times viz 24, 48 and 60 hr respectively. The toxicity to anaerobic contact filter was observed at a chloride concentration of 4500 mg/l and tannin concentration of 790 mg/l respectively under synergistic condition. In the case of constant influent tannin concentration of 600 mg/l, the toxicity due to chloride on anaerobic contact filter was observed at 5500 mg/l. The COD removal percent ranged from 50% to 79% at 48 hr and 67% to 91% at 60 hr HRT respectively. In the case of constant influent chloride concentration of 4000 mg/l and at an increasing influent COD concentration, the toxicity due to tannin on anaerobic contact filter was observed at 1180 mg/l. The COD removal percent ranged from 64% to 89% at 48 hr and 78% to 96% at 60 hr HRT respectively. The results showed that at least 60 hr HRT would be desirable to have good COD removal percent.     

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.     

Improved treatment of tannery wastewater using Zoogloea ramigera and its extracellular polymer in an activated sludge process

Summary When Zoogloea ramigera and its extracellular polymer were daily added to the laboratory scale activated sludge reactor treating tannery wastewater, more than 15% of the COD concentration (COD; 151 mg/l) and 32% of the turbidity (NTU; 9.2) were removed compared with a controlled reactor (COD; 336 mg/l, NTU; 43.5) operated without any additions.     

The inhibitory effects and removal of dieldrin in continuous upflow anaerobic sludge blanket reactors

The inhibitory effects and removal efficiency of dieldrin (DLD) in anaerobic reactors were investigated. Anaerobic toxicity assay (ATA) experiments conducted in batch reactors revealed that 30 mg/l DLD had inhibitory effects on the unacclimated mixed anaerobic cultures. Continuous reactor experiments performed in a lab-scale two-stage upflow anaerobic sludge blanket (UASB) reactor system which was fed with ethanol as the sole carbon source, indicated that anaerobic granular cultures could be successfully acclimated to DLD. Chemical oxygen demand (COD) removal efficiencies were 88-92% for the two-stage system. The influent DLD concentration of 10 mg/l was removed by 44-86% and 86-94% in the second stage and overall UASB system, respectively. Biosorption of DLD on granular anaerobic biomass was found to be a significant mechanism for DLD removal in the UASB system. The maximum DLD loading rate and minimum HRT achievable for the first stage UASB reactor were 0.5 mg/lday (76 microg DLD/g VSS.day) and 10 h, respectively, which resulted in the overall COD removal efficiency of 85%.     

Thermophilic anaerobic treatment of sulphur rich forest industry wastewater

Thermophilic anaerobic treatment of sulphur-rich paper mill wastewater (0.8-3.1 gCOD/l, 340–850 mgSO₄/l; COD:SO₄ 3.4-5.3) was studied in three laboratory-scale, upflow anaerobic sludge blanket (UASB) reactors and in bioassays. The reactors were inoculated with non-adapted thermophilic granular sludge. In the bioassays, no inhibition of the inoculum was detected and about 62% COD removal (sulphide stripped) was obtained. About 70 to 80% of the removed COD was methanised. In the reactors, up to 60–74% COD removal (effluent sulphide stripped) was obtained at loading rates up to 10–30 kgCOD/m³d and hydraulic retention times down to 6 to 2 hours. The effluent total sulphide was up to 150–250 mg/l. Sulphide inhibition could not be confirmed from the reactor performances. The results from bioassays suggested that both the inoculum and sludge from the UASB reactor used acetate mainly for methane production, while sulphide was produced from hydrogen or its precursors.     

Effect of initial COD concentration, nutrient addition, temperature and microbial acclimation on anaerobic treatability of broiler and cattle manure

In this study, anaerobic treatability and biogas generation potential of broiler and cattle manure were investigated. For this purpose, seven sets of anaerobic batch reactor experiments were performed using broiler and cattle manure and their mixtures in five different ratios (100% broiler; 75% broiler, 25% cattle; 50% broiler, 50% cattle; 25% broiler, 75% cattle; 100% cattle). These manure mixtures had two different initial chemical oxygen demand (COD) (12,000 and 53,500 mg/l) concentrations. The effects of initial COD concentration, nutrient and trace metal supplementation, microbial acclimation and digestion temperature were investigated. Results revealed that the efficiency of total COD removal was 32.0-43.3% and 37.9-50% for initial COD concentrations of 12,000 and 53,500 mg/l, respectively. The biogas yields observed for initial COD concentrations of 12,000 and 53,500 mg/l were 180-270 and 223-368 ml gas/g COD added, respectively. A decrease in biogas yield was observed as the fraction of broiler manure increased in mixture of broiler and cattle manure at initial COD values of 53,500 mg/l.     

Continuous anaerobic treatment of wastewaters containing formaldehyde and urea

The toxicity of formaldehyde (FA) in batch assays, using volatile fatty acids (VFA) as co-substrate, and the continuous anaerobic treatment of wastewaters containing FA in upflow anaerobic sludge blanket (UASB) reactors was investigated. In batch studies, FA exerted a 50% methanogenic toxicity on VFA at concentrations of around 100 mg/l, 2.5 times lower than values reported with sucrose. Although at FA concentrations higher than 200 mg/l methanogenesis was completely inhibited, a partial recovery of the bacterial activity was observed after 250 h when the FA had been removed from the medium. The continuous anaerobic degradation of FA at concentrations up to 2 g/l, using 1.6 g/l of glucose as co-substrate, was studied in a UASB reactor. A stable and efficient operation was observed at organic loading rates (OLR) of 6.0 g COD/l·d and with a COD/FA ratio as low as 1.4. A synthetic substrate with the same characteristics as the effluents produced during fibreboard adhesives manufacturing (based on urea-FA), i.e. 0.95 g FA/l and 0.35 g urea/l, was treated in a UASB reactor. The applied OLR and nitrogen loading rate (NLR) were 3.45 g COD/l·d and 0.58 g N/l·d, respectively. COD removal efficiencies were maintained at 90–95%, FA and urea being completely degraded.     

Ambient temperature treatment of low strength wastewater using anaerobic sequencing batch reactor

Low strength wastewater having chemical oxygen demands (COD) concentrations of 1000, 800, 600 and 400mg/l were treated at 35, 25, 20 and 15¡C using four anaerobic sequencing batch reactors (ASBRs). Reactor 1 was operated at hydraulic retention time (HRT) of 48h, reactor 2 at 24h HRT, reactor 3 at 16h HRT and reactor 4 at 12h HRT. 80 to 99% soluble COD was removed at the various operational conditions, except during 15¡C treatment of 1000 and 800mg/l COD wastewater at 12h HRT and 1000mg/l COD wastewater at 16h HRT, where excessive loss of biological solids occurred. The ASBR process can be an effective process for the treatment of low concentrated wastewaters which are usually treated aerobically with large amount of sludge production and higher energy expenditures.     

Anaerobic treatment of winery wastewater using laboratory-scale multi- and single-fed filters at ambient temperatures

A lab-scale investigation was conducted to examine the effectiveness of a multi-fed upflow anaerobic filter process for the methane production from a rice winery effluent at ambient temperatures. The experiment was carried in two identical 3.0-l upflow filters, a single-fed reactor and a multi-fed reactor. The results showed that the multi-fed reactor, operated at the ambient temperatures of 19–27 °C and influent chemical oxygen demand (COD) of 8.34–25.76 g/l, could remove over 82% of COD even at an organic loading rate (OLR) of 37.68 g-COD/l d and a short hydraulic retention time (HRT) of 8 h. This reactor produced biogas with a methane yield of 0.30–0.35 l-CH₄/g-COD_removed. The multi-fed upflow anaerobic filter was proved to be more efficient than the single-fed reactor in terms of COD removal efficiency and stability against hydraulic loading shocks. A linear-regression model with influent COD concentration and HRT terms adequately described the multi-fed upflow anaerobic filter system for the treatment of rice winery wastewater at ambient temperatures.     

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.     

Granulation mechanism of a UASB reactor supplemented with iron

The aim of this paper was to propose a granulation mechanism in order to interpret all the experimental observations that arose during experiments on two UASB reactors, where one was supplemented with ferrous iron at a dose of 0.01 g Fe(2+) per g COD feed. This supplementation with ferrous iron allowed COD removal of more than 98% at a loading rate of 9 g COD/L per day, which was 24% higher than for the reactor not receiving the ferrous iron. Moreover, in the Fe(2+)-dosed reactor, a higher increase of the granule diameter was observed. Indeed, the granule diameter in the Fe(2+)-dosed reactor at the end of the experiments was 56% greater than that of the control reactor. This mechanism describes the course of anaerobic granule growth. The formation of the inorganic precipitate of ferrous sulphide constitutes the inert nuclei around which the biomass is attached. This initiates the formation of new granules.     

Biodegradation of tech-hexachlorocyclohexane in a upflow anaerobic sludge blanket (UASB) reactor

Biodegradability of technical grade hexachlorocyclohexane (tech-HCH) was studied in an upflow anaerobic sludge blanket reactor (UASB) under continuous mode of operation in concentration range of 100-200 mg/l and constant HRT of 48 h. At steady state operation more than 85% removal of tech-HCH (upto 175 mg/l concentration) and complete disappearance of beta-HCH was observed. Kinetic constants in terms of maximum specific tech-HCH utilization rate (k) and half saturation velocity constant (K(L)) were found to be 11.88 mg/g/day and 8.11 mg/g/day, respectively. The tech-HCH degrading seed preparation, UASB reactor startup and degradation in continuous mode of operation of the reactor is presented in this paper.     

Treatment of slaughterhouse wastewater in a UASB reactor and an anaerobic filter

A study was performed to assess the feasibility of anaerobic treatment of slaughterhouse wastewaters in a UASB (Upflow Anaerobic Sludge Blanket) reactor and in an AF (Anaerobic Filter). Among the different streams generated, the slaughter line showed the highest organic content with an average COD of 8000 mg/l, of which 70% was proteins. The suspended solids content represented between 15 and 30% of the COD. Both reactors had a working volume of 21. They were operated at 37°C. The UASB reactor was run at OLR (Organic Loading Rates) of 1–6.5 kg COD/m³/day. The COD removal was 90% for OLR up to 5 kg COD/m³/day and 60% for an OLR of 6.5 kg COD/m³/day. For similar organic loading rates, the AF showed lower removal efficiencies and lower percentages of methanization. At higher OLR sludge, flotation occurred and consequently the active biomass was washed out from the filter. The results indicated that anaerobic treatment systems are applicable to slaughterhouse wastewaters and that the UASB reactor shows a better performance, giving higher COD removal efficiencies than the AF.     

实验室模拟高负荷SPAC厌氧反应器运行

采用模拟废水, 对新型高负荷螺旋式自循环(Spiral automatic circulation, SPAC)厌氧反应器的运行性能进行了实验室模拟研究。结果表明: 在30oC, 水力停留时间(HRT)为12 h, 进水COD浓度从8000 mg/L升至20 000 mg/L的条件下, 反应器的COD去除率为91.1%~95.7%, 平均去除率为93.6％。在进水浓度为20 000 mg/L, HRT由5.95 h缩短至1.57 h的工况下, COD去除率从96.0%降低至78.7%, 反应器达到最高容积负荷率306 g COD/(L·d), 最大容积COD去除率240 g/(L·d), 最高容积产气率131 L/(L·d)。该反应器对基质浓度的连续提升具有良好的适应能力。进水COD浓度由8000 mg/L提升至20 000 mg/L时, 出水COD浓度一直处在较低水平(平均为852?mg/L), 容积COD去除率和容积产气率分别提高162%和119%。该反应器对HRT的连续缩短也有良好的适应能力。HRT由5.95 h缩短至1.57 h时,反应器容积COD去除率和容积产气率分别升高191%和195%。     

Advanced monitoring and supervision of biological treatment of complex dairy effluents in a full-scale plant

The operation of a wastewater treatment plant treating effluents from a dairy laboratory was monitored by an advanced system. This plant comprises a 12 m(3) anaerobic filter (AF) reactor and a 28 m(3) sequential batch reactor (SBR) coupled in series and is equipped with the following on-line measurement devices: biogas flow meter, feed and recycling flow meters, temperature sensor, dissolved oxygen analyzer, and redox meter. Other parameters such as chemical oxygen demand (COD), volatile fatty acids (VFA), etc. were determined off-line. The plant has been in operation for 634 days, the influent flow rate being 6-8 m(3)/d. COD concentration of the influent ranged between 8 and 12 kg COD/m(3), resulting in COD values in the effluent around 50-200 mg/L. The behavior of the system was studied using the set of measurements collected by the data acquisition program especially developed for this purpose. Monitoring of variables such as anaerobic reactor temperature permitted the detection and prevention of several failures such as temperature shocks in the AF reactor. Besides, off-line measurements such as the alkalinity or the VFA content, together with the on-line measurements, provided immediate information about the state of the plant and the detection of several anomalies, such as organic overloads in the SBR, allowing the implementation of several fast control actions.     

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.     

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.     

Characteristics of the bioreactor landfill system using an anaerobic-aerobic process for nitrogen removal

A sequential upflow anaerobic sludge blanket (UASB) and air-lift loop sludge blanket (ALSB) treatment was introduced into leachate recirculation to remove organic matter and ammonia from leachate in a lab-scale bioreactor landfill. The results showed that the sequential anaerobic-aerobic process might remove above 90% of COD and near to 100% of NH4+ -N from leachate under the optimum organic loading rate (OLR). The total COD removal efficiency was over 98% as the OLR increased to 6.8-7.7 g/l d, but the effluent COD concentration increased to 2.9-4.8 g/l in the UASB reactor, which inhibited the activity of nitrifying bacteria in the subsequent ALSB reactor. The NO3- -N concentration in recycled leachate reached 270 mg/l after treatment by the sequential anaerobic-aerobic process, but the landfill reactor could efficiently denitrify the nitrate. After 56 days operation, the leachate TN and NH4+ -N concentrations decreased to less than 200 mg/l in the bioreactor landfill system. The COD concentration was about 200 mg/l with less than 8 mg/l BOD in recycled leachate at the late stage. In addition, it was found that nitrate in recycled leachate had a negative effect on waste decomposition.     

Studies on SAGO wastewater treatment using anaerobic rotating biological contactor

Experimental studies were done in a laboratory scale Anaerobic Rotating Biological Contactor (RBC), for treatment of Synthetic sago wastewater. This paper describes the development and laboratory testing of an Anaerobic RBC process that couples the advantages of the fixed film horizontal flow RBC process with the high strength, starch degradation capabilities of anaerobic systems. The reactor was operated at ambient temperature and was subjected to organic and hydraulic loading rates. The reactor performance with respect to Chemical Oxygen Demand (COD) removal, alkalinity, volatile acids at each stage and biogas production were evaluated. The Anaerobic RBC reactor liquid volume is 70 litres and total disc surface area is 4.45 m². The reactor was operated with about 100% of the disc area submerged and with a rotational speed held constant at 9?rev/min. The synthetic sago wastewater was started with a COD value of 1087?mg/l at a hydraulic retention time(HRT) of 42?h and it was varied till maximum COD of 9522?mg/l. From the present study, the optimum COD load was found to be 6860?mg/l with a COD removal efficiency of 97.2%.With this optimum COD load, hydraulic loading rate(HLR) study was done at 24?h to 48?h HRT. COD removal efficiencies at hydraulic loading rates were compared with the work of Subrahmanyam &; Sastry (1988). From the present study, the proportionality coefficient was found to be 1.18 with process efficiencies at different hydraulic loading rates.     

Distribution and change of microbial activity in combined UASB and AFB reactors for wastewater treatment

A thermophilic upflow anaerobic sludge blanket (UASB) reactor was combined with a mesophilic aerobic fluidized bed (AFB) reactor for treatment of a medium strength wastewater with 2,700?mg COD?l^?1. The COD removal efficiency reached 75% with a removal rate of 0.2 g COD?l^?1 h^?1 at an overall hydraulic retention time 14 hours. The distribution of microbial activity and its change with hydraulic retention time in the two reactors were investigated by measuring ATP concentration in the reactors and specific ATP content of the biomass. In the UASB reactor, the difference in specific ATP was significant between the sludge bed and blanket solution (0.02?mg ATP g VS^?1 versus 0.85?mg ATP g VS^?1) even though the ATP concentrations in these two zones were similar. A great pH gradient up to 4 was developed along the UASB reactor. Since a high ATP or biological activity in the blanket solution could only be maintained in a narrow pH range from 6.5 to 7.5, the sludge granules showed a high pH tolerance and buffering capacity up to pH 11. The suspended biomass in AFB reactor had a higher specific ATP than the biomass fixed in polyurethane carriers (1.6?mg ATP g VS^?1 versus 1.1?mg ATP g VS^?1), which implies a starvation status of the immobilized cells due to mass transfer limitation. The aerobes had to work under starvation conditions in this polishing reactor. The anaerobic biomass brought into AFB reactor contributed to an increase in suspended solids, but not the COD removal because of its fast deactivation under aerobic conditions. A second order kinetic model was proposed for ATP decline of the anaerobes. The results on distribution of microbial activity in the two reactors as well as its change with hydraulic retention time lead to further performance improvement of the combined anaerobic/aerobic reactor system.