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.     

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.     

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.     

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.     

Performance of upflow anaerobic sludge blanket (UASB) reactor treating wastewaters containing carbon tetrachloride

The anaerobic biodegradation of carbon tetrachloride (CT) was investigated during the granulation process by reducing the hydraulic retention time, increasing the chemical oxygen demand (COD) and CT loadings in a 2l laboratory-scale upflow anaerobic sludge blanket (UASB) reactor. Anaerobic unacclimated sludge and glucose were used as seed and primary substrate, respectively. Granules were developed 4 weeks after start-up, which grew at an accelerated rate for 8 months, and then became fully grown. The effect of operational parameters such as influent CT concentrations, COD, CT loading, food to biomass ratio and specific methanogenic activity (SMA) were also considered during granulation. The granular sludge cultivated had a maximum diameter of 2.1 mm and SMA of 1.6 g COD/g total suspended solid (TSS) day. COD and CT removal efficiencies of 92 and 88% were achieved when the reactor was firstly operating at CT and COD loading rates of 17.5 mg/l day and 12.5 g/l day, respectively. This corresponds to hydraulic retention time of 0.28 day and food to biomass ratio of 0.5 g COD/g TSS day. Kinetic coefficients of maximum specific substrate utilization rate, half velocity coefficient, growth yield coefficient and decay coefficient were determined to be 2.4 × 10^–3 mg CT/TSS day^–1, 1.37 mg CT/l, 0.69 mg TSS/mg CT and 0.046 day^–1, respectively for CT biotransformation during granulation.     

Anaerobic digestion of a petrochemical effluent using an anaerobic hybrid digester

Summary An anaerobic hybrid reactor was used in the anaerobic treatment of an acidic petrochemical effluent. An organic loading rate of 20.04 kg COD/(m³d) at a HRT of 17 hours was obtained with a volatile fatty acid removal of 91%, and COD removal of 84%. A final reactor effluent containing 44 mg/l ammonia nitrogen and 12.3 mg/l PO₄-P was produced.     

Fungal Treatment of an Edible-oil-containing Industrial Effluent

Summary A typical edible oil-processing plant discharges large volumes of effluent high in Chemical oxygen demand (COD). This leads to fines from the municipality and the consequent loss of profit. In this study the effluent composition of an oil-processing plant was monitored for 1 year. The COD ranged between 16,000 and 250,000 mg/l and the conductivity between 88.2 and 268 mS/m. It is known that edible oil is a good carbon source and Mucoralean fungi have the ability to accumulate large quantities of oil. Therefore, the reduction of the COD by 12 fungal strains (from culture collections) was determined. The most promising organisms were Rhizopus stolonifer (CBS 263.28), reducing the COD by 91.3%, a Penicillium species (TUTC 077) by 85.3%, Mucor circinelloides f. circinelloides (CBS 108.16) by 84.0% and Aspergillus niger (TUTC 120) by 83.8%. Although the reduction of the effluent COD was significant, the lowest COD of 1625.08 mg/l was still higher than the legal limits. This led to the isolation of fungi from soil, using selective media. Fifty-eight fungal strains were isolated, of which seven isolates could reduce the COD to below 760 mg/l (legal limit). The best isolate reduced the COD by 98.2% from 16,000 to 286.96 mg/l and was identified as Cunninghamella echinulata. The best COD reducers were tested for their ability to produce gammalinolenic acid (GLA) as a high value by-product. All these isolates were able to produce GLA and the best production was obtained from Emerisella nidulans, namely 408.70 mg GLA/l.     

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.     

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.     

Anaerobic digestion of food waste in a hybrid anaerobic solid–liquid system with leachate recirculation in an acidogenic reactor

Recirculation of the leachate in the acidogenic reactor was proposed to enhance anaerobic digestion of food waste in the hybrid anaerobic solid–liquid (HASL) system. Recirculation of the leachate in the acidogenic reactor provided better conditions for extraction of organic matter from the treated food waste and buffering capacity to prevent excessive acidification in the acidogenic reactor. It ensured faster supply of nutrients in the methanogenic reactor in experiment. The highest dissolved COD and VFA concentrations in the leachate from the acidogenic reactor were reached for shorter time and were 16,670 mg/l and 9450 mg/l in control and 18,614 mg/l and 11,094 mg/l in experiment, respectively. Recycling of the leachate in the acidogenic reactor intensified anaerobic digestion of food waste and diminished time needed to produce the same quantity of methane by 40% in comparison with anaerobic digestion of food waste without recirculation.     

Effect of toxic substances in anaerobic treatment of tannery wastewaters

Studies were carried out in the treatment of tannery wastewater using upflow anaerobic contact filter (reactor) and on the role of toxic substances viz tannin, sulphide, chromium (3+) in inhibiting the performance of the reactor. The influent COD concentration was varied in the range of 1500 to 16500?mg/l, at different hydraulic retention times viz 36,48,60 hr. The limiting concentrations of toxicity for the three substances viz tannin, sulphide, chromium (3+) were identified in terms of the performance of the reactor viz COD removal percent, biogas production etc. Toxic limits of the above mentioned substances were further estimated in batch process (in vials) to supplement the evidence. In anaerobic contact filter tannin beyond 914?mg/l inhibited the performance, whereas sulphide concentration even upto 180?mg/l and chromium (3+) concentration even upto 140?mg/l did not affect the reactor performance. In batch process tannin above 77 wt.% affected the anaerobic microbial growth. Hydrolysable tannin was present in these tannery wastewaters.     

Mesophilic anaerobic digestion in a fluidised-bed reactor of wastewater from the production of protein isolates from chickpea flour

A study of the anaerobic digestion of wastewater derived from the production of protein isolates from chickpea flour was carried out in a laboratory-scale, mesophilic (35 °C) fluidised-bed reactor with saponite as bacterial support. Soluble chemical oxygen demand (SCOD) removal efficiencies in the range of 96.8–85.2% were achieved in the reactor at organic loading rates (OLR) of between 0.58 and 2.10 g chemical oxygen demand (COD)/l per day, hydraulic retention times (HRT) of between 14.9 and 4.5 days and average feed COD concentration of 9.1 g/l. Eighty-five percent of feed COD could be removed up to OLR of 2.1 g COD/l per day. The yield coefficient of methane production was 0.34 l of methane (at STP) per gram COD removed and was virtually independent of the OLR applied. Because the buffering capacity of the experimental system was maintained at favourable levels with excess total alkalinity present at all loadings, the rate of methanogenesis was not affected by loading. Experimental data indicated that a total alkalinity in the range of 1090–2130 mg/l as CaCO₃ was sufficient to prevent the pH from decreasing to below 7.2 for OLR of up to 2.7 g COD/l per day. 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 2.7 g COD/l per day and 3.5 days, respectively. For a HRT of 2.8 days (OLR of 3.00 g COD/l per day) the start of acidification was observed in the reactor.     

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.     

Biological treatment of 2,4-dichlorophenol containing synthetic wastewater using a rotating brush biofilm reactor

A newly developed rotating brush biofilm reactor was used for DCP, COD and toxicity removal from 2,4-dichlorophenol (DCP) containing synthetic wastewater at different feed COD, TCP concentrations and A/Q (biofilm surface area/feed flow rate) ratios. A Box-Wilson statistical experiment design was used by considering the feed DCP (50-500 mg l(-1)), COD (2000-6000 mg l(-1)) and A/Q ratio (73-293 m2 d m(-3)) as the independent variables while percent DCP, COD, and toxicity removals were the objective functions. The experimental data were correlated by a quadratic response function and the coefficients were determined by regression analysis. Percent DCP, COD and toxicity removals calculated from the response functions were in good agreement with the experimental data. DCP, COD and toxicity removals increased with increasing A/Q ratio and decreasing feed DCP concentrations. The optimum A/Q ratio resulting in the highest COD (90%), DCP (100%) and toxicity (100%) removals with the highest feed COD (6000 mg l(-1)) and DCP (500 mg l(-1)) contents was nearly 210 m2 d m(-3).     

Continuous removal of aromatic hydrocarbons by an AF reactor under denitrifying conditions

Removal of three typical aromatic hydrocarbons, benzene, biphenyl and naphthalene by an anaerobic filter (AF) reactor under continuous mode and denitrifying conditions was studied. Results showed that the AF reactor could degrade these aromatic hydrocarbons effectively under above-mentioned conditions. When influent wastewater contained 900 mg COD/l and about 60 mg (total aromatic hydrocarbons)/l, 90% and 84% removal efficiency could be achieved for them respectively. When COD/NO₃ ⁻-N ratio (C/N) was in the range 5–30, the removal of benzene was slightly influenced by C/N and it remained stable at about 90%. However, degradation of naphthalene, biphenyl and total COD was greatly influenced by C/N, and highest removal was achieved at C/N = 15, it was 90%, 85% and 82% for COD, naphthalene and biphenyl, respectively. Degradation of these three aromatic hydrocarbons followed the order: benzene > naphthalene > biphenyl.     

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.     

Impact of leachate recirculation and recirculation volume on stabilization of municipal solid wastes in simulated anaerobic bioreactors

The effects of leachate recirculation and the recirculation rate on the anaerobic treatment of domestic solid waste was investigated in three simulated landfill anaerobic bioreactors. A single pass reactor was operated without leachate recirculation while the other two reactors were operated with leachate recirculation. The leachate recirculation rate was 9 l/day (13% of the reactor volume) in Reactor₉, while the recirculation rate was 21 l/day (30% of the reactor volume), in Reactor₂₁. pH, chemical oxygen demand (COD), volatile fatty acids (VFA), ammonium–nitrogen (NH₄–N) total and methane gas measurements in leachate samples were regularly monitored. After 220 days of anaerobic incubation, it was observed that the pH, COD, VFA concentrations, methane gas productions and methane percentages in Reactor₉ were better than the single pass reactor and Reactor₂₁. When the leachate recirculation rate was increased to three times a decrease in pH, and an increase in VFA and COD concentrations were observed in Reactor₂₁. The COD values were measured as 47 000, 39 000 and 52 000 mg/l while the VFA concentrations were 15 000, 13 000 and 21 000 mg/l, respectively, in single pass, Reactor₉ and Reactor₂₁ after 220 days of anaerobic incubation. The values of pH were 5.89, 6.44 and 6.16, respectively, after anaerobic incubation. The mean methane percentages of single pass reactor, Reactor₉ and Reactor₂₁ were 30, 50 and 40%, respectively, after 50 days of incubation. Leachate recirculation reduced the waste stabilization time and was effective in enhancing methane gas production and improving leachate. However, leachate recirculation was not effective in removing ammonia from the leachate. The amounts of COD recovered by methane were 62.9, 162.3 and 94.6 g for single pass, Reactor₉ and Reactor₂₁, respectively, at the end of 220 days of anaerobic incubation.     

Influence of media-packing ratio on performance of anaerobic hybrid reactors

In this study, the influence of media-packing ratio on the performances of anaerobic hybrid reactors (AHRs) at low, medium and high organic loading rates was evaluated by conducting COD profile, granulation and tracer studies. Four laboratory upflow anaerobic hybrid reactors, each with a total unpacked volume of 7.85 l, with varying packing depths, were operated at organic loading rates from 1 to 24 g COD/l d. The media-packing ratios were 75%, 60%, 40% and 20% of the total reactor height in the AHRs. Three types of soluble COD profiles along the reactor height were observed when the organic loading rate was gradually increased. When operated at 1 and 2 g COD/l d the COD profiles along the reactor height from bottom to top showed a plug-flow regime. From 4 to 12 g COD/l d the COD profiles were distorted in the reactors with 20%, 40% and 60% packing, while at 16 g COD/l d and above the COD profile indicated homogeneity in each reactor, suggesting a perfectly-mixed regime. The distorted COD profiles were considered to be caused by the non-ideal flow pattern prevalent in the reactors. The dead-space volume and the bypass flowrate due to short-circuiting were determined using the Cholette and Cloutier model. A `distortion index' (DI), which was calculated from the ratio of the average COD value of the sludge bed over the average COD value of the reactor, was used to describe distortion of the COD profile. The distortion index correlated well with the short-circuiting fraction.     

Degredation and interaction between organic concentrations and toxicity of 2,4,6-trichlorophenol in anaerobic system

When 2,4,6-TCP (trichlorophenol) as a toxicant was added to the reactors with 500, 1000, 2000 and 4000 mg COD/l, methane production ratios between the reactors with and without toxicant were 64, 75, 83 and 96 %. The 2,4,6-TCP was more toxic to methane production at COD concentrations lower than 1000 mg/l. In continuous operation, when the toxicant was fed to the reactor, methane production rate (CH4-l/g-COD) recovered in four days.     

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%.