Soluble COD Removal Efficiency Research Articles

Effects of various pretreatments for enhanced anaerobic digestion with waste activated sludge

The purpose of this study was to enhance the efficiency of anaerobic digestion with waste activated sludge (WAS) by batch experiments. We studied the effects of various pretreatment methods (thermal, chemical, ultrasonic and thermochemical pretreatments) on the biogas production and pollutants reduction owing to solubilization enhancement, particle size reduction, increased soluble protein, and increased soluble COD. The thermochemical pretreatment gave the best results, i.e., the production of methane increased by more than 34.3% and soluble COD (SCOD) removal also increased by more than 67.8% over the control. In this case, the biogas production, methane production and the SCOD removal efficiency were about 5037 l biogas/m 3 WAS, 3367 l methane/m 3 WAS and 61.4%, respectively. Therefore, it is recognized that higher digestion efficiencies of the WAS were obtained through thermochemical pretreatment of the sludge.

Effects of Various Pretreatments for Enhanced Anaerobic Digestion with Waste Activated Sludge

The purpose of this study was to enhance the efficiency of anaerobic digestion with waste activated sludge (WAS) by batch experiments. We studied the effects of various pretreatment methods (thermal, chemical, ultrasonic and thermochemical pretreatments) on the biogas production and pollutants reduction owing to solubilization enhancement, particle size reduction, increased soluble protein, and increased soluble COD. The thermochemical pretreatment gave the best results, i.e. , the production of methane increased by more than 34.3% and soluble COD (SCOD) removal also increased by more than 67.8% over the control. In this case, the biogas production, methane production and the SCOD removal efficiency were about 5037 l biogas/m 3 WAS, 3367 l methane/m 3 WAS and 61.4%, respectively. Therefore, it is recognized that higher digestion efficiencies of the WAS were obtained through thermochemical pretreatment of the sludge.

Effect of an Organic Shock Load on the Stability of an Anaerobic Migrating Blanket Reactor

The goal of this study was to examine the effect of an organic shock load on the performance and stability of a laboratory-scale anaerobic migrating blanket reactor (AMBR). To accomplish an organic shock load, nonacidified sucrose solution was almost doubled in concentration, while maintaining a constant hydraulic retention time. The volumetric loading rate (VLR) was increased from 27 to 50 g chemical oxygen demand (COD) L\U-1\N day\U-1\N for a period of six hydraulic retention times (42 h). This resulted in an increase in the standard methane production rate (liters of methane at standard temperature and pressure per liter reactor volume per day) from 7 to 12 LL\U-1\N day \U-1\N. The pH levels stayed favorable and biomass washout was limited during the shock load due to the damping effects of a compartmentalized configuration. During the shock load, the propionate production in the initial compartments of the AMBR remained at the same level as before the shock load, while the acetate production rose sharply. Because propionate is the most difficult volatile fatty acid to be removed, unstable conditions due to excessive propionate accumulation during the shock load were prevented. Meanwhile, the acetate concentration in the liquid phase and hydrogen content in the headspace of the final compartments remained low, which ensured propionate degradation. Due to these intrinsic characteristics of the AMBR, the soluble COD removal efficiency stayed above 87% under these stressed conditions. Moreover, the performance of the AMBR reached pre-shock-load levels immediately after the VLR was restored to 25 g COD L\U-1\N day\U-1\N.

Effect of a chemical synthesis‐based pharmaceutical wastewater on performance, acetoclastic methanogenic activity and microbial population in an upflow anaerobic filter

AbstractThe performance of an upflow anaerobic filter (UAF) treating a chemical synthesis‐based pharmaceutical wastewater was evaluated under various operating conditions. During start‐up, the UAF was initially fed by glucose till an organic loading rate (OLR) of approximately 7.5 kg COD m−3 day−1 with a hydraulic retention time of 2.3 days. A soluble COD removal efficiency of 98% was achieved before the addition of the wastewater. Initially, the filter inertia was acclimatized to the wastewater by sequential feeding of 10% (w/v), 30% (w/v) and 70% (w/v) of the pre‐aerated wastewater mixed with glucose followed by a 100% (w/v) pre‐aerated wastewater. During the operation, the COD removal efficiency and methane yield decreased to 75% and 0.30 m3 CH4 kg−1 CODremoved respectively. As the UAF became accustomed to the pre‐aerated wastewater, raw wastewater was fed in increasing ratios of 20% (w/v), 60% (w/v) and 80% (w/v) with the pre‐aerated wastewater as the remaining part. During this stage of the operation, a COD removal efficiency in a range of 77–86% was achieved and the methane yield decreased to 0.24 m3 CH4 kg−1 CODremoved. Finally, 100% (w/v) raw wastewater was fed and a COD removal efficiency of 65% was achieved with a methane yield of 0.20 m3 CH4 kg−1 CODremoved. At the end of the operation, acetoclastic methanogenic activity was only measured in the bottom section of the UAF, this showed a 90% reduction in comparison with activity of inoculation sludge. Microscopic examinations revealed that rod‐shaped methanogens remained as the dominant species whereas Methanosarcina‐like species and filaments were present only in insignificant numbers along the UAF.© 2002 Society of Chemical Industry

Aerobic Biological Treatment of a Pharmaceutical Wastewater:: Effect of Temperature on COD Removal and Bacterial Community Development

The effect of temperature was studied on the efficiency of soluble COD removal and bacterial community development during the aerobic biological treatment of a pharmaceutical wastewater. Using wastewater and bacterial inoculum obtained from the full-scale facility treating this wastewater, batch laboratory cultures were operated at 5°C intervals from 30°C to 70°C. Following four culture transfers to allow for bacterial acclimation, residual soluble COD levels were measured and bacterial community fingerprints were obtained by denaturing gradient gel electrophoresis (DGGE) of polymerase chain reaction (PCR)-amplified 16S rRNA gene fragments. Soluble COD removal efficiency declined as temperature increased from 30°C (62%) to 60°C (38%). Biological treatment of this wastewater failed to occur at temperatures higher than 60°C. Gradual shifts in bacterial community structure were detected as temperature increased, including a concomitant reduction in the number of different bacterial populations. The impact of temperature on a two-stage biological treatment process was also compared. Better soluble COD removal was achieved when both reactors were operated at 30°C compared to a system where the two stages were consecutively operated at 55°C and 30°C. These results indicate that operation of aerobic biological wastewater treatment reactors at elevated temperatures can have adverse effects on process performance.

Anaerobic migrating blanket reactor treatment of low-strength wastewater at low temperatures.

The feasibility of the compartmentalized anaerobic migrating blanket reactor (AMBR) was studied for the treatment of low-strength soluble wastewater under low-temperature conditions. During an operating period of 186 days, a 20-L AMBR was fed nonfat dry milk substrate as a synthetic wastewater at low temperatures (15 and 20 degrees C). The concentration of the influent was constant at chemical oxygen demand (COD) and 5-day biological oxygen demand (BOD5) concentrations of 600 and 285 mg/L, respectively. The soluble COD (SCOD) removal efficiency was 73% at the end of the operating period (15 degrees C) at a 4-hour hydraulic retention time (HRT), while the total COD (TCOD) removal efficiency was 59%. At a 4-hour HRT, staged conditions promoted complete removal of propionic acid in the final compartments of the reactor. The specific methanogenic activity of granules increased slowly until the end of the operating time, improving the removal rate. Biomass was retained effectively, as evidenced by the solids retention time (SRT) that was always greater than 50 days even during step decreases of the reactor HRT from 12 hours to 4 hours. A long SRT also promoted system stability during changes in flow, which was observed by SCOD removal efficiencies staving greater than 70%. During a hydraulic stress test, the HRT was reduced from 4 hours to 1 hour for one day (24 HRTs) in which volatile suspended solids (VSS) in the effluent increased from an average background level of 8.7 g/d to 35 g/d and the SRT decreased from 50.5 days to 12.6 days. However, mixed liquor volatile suspended solids concentration decreased only by 1 g/L, and hence a similar COD removal efficiency and biogas production was found one day after the hydraulic stress (as compared to one day before the hydraulic stress).

Treatment of Septage Using an Upflow Anaerobic Sludge Blanket Reactor

This study examined the feasibility of applying an upflow anaerobic sludge blanket (UASB) reactor to treat septage. The UASB reactor was operated at 35 ± 1 °C, and the substrate septage had a total solids (TS) concentration of 13 200 mg/L. Reactor operation was initiated at a hydraulic residence time (HRT) of 10 days; thereafter, the HRT was shortened stepwise to 1.5 days. The TS, volatile solids (VS), and organic loading rates were 1.4 to 9.4 kg TS/m3·d, 5.6 to 8.5 kg VS/m3·d, and 1.1 to 6.7 kg chemical oxygen demand (COD)/m3·d, respectively. At the organic loading rate of 6.7 kg COD/m3·d (the HRT of 1.5 days), the total COD, soluble COD, and TS and VS removal efficiencies were 68, 74, and 66 and 73%, respectively. The average granule diameter and volatile suspended solids concentration were approximately 0.89 mm and 32 000 mg/L, respectively. Based on results obtained from 7 months of constant methane production and removal efficiencies, which are comparable to values previously reported in the literature for wastewater, it was concluded that a UASB reactor can successfully treat septage.

Characterization and treatment of the liquid effluents from the anaerobic digestion of biogenic solid waste

The process wastewater generated by the fermentation of biogenic fractions of solid waste (biowaste) is characterized by very specific composition features, which sets it apart from the well known categories of wastewater. Up to now, there is a definite lack of practical experience and know-how in the treatment of those effluents. In view of the increasingly wide acceptance awarded to the fermentation process, it appears necessary, however, to include the treatment of the generated wastewater in the overall process and to grant it the same priority as the fermentation step. In this study, pilot-scale experiments were conducted over 200 days in a sequencing batch reactor (SBR), with the wastewater from a full-scale Bavarian biowaste digestion plant. Characterization of the influent implementing molecular size distribution studies showed that 97% of the components were either in particular form or < 1 kD. The main classes of compounds present in these fractions have been identified. The treatment objectives of the SBR plant were carbon and nitrogen removal. Soluble COD removal efficiencies were comprised between 40 and 60%, yielding a residual, refractory COD concentration of about 2000 mg/L in the effluent. Ammonium removal efficiencies averaged 96% and denitrification occurred with the addition of acetic acid or pretreated biowaste as a carbon source. Pretreated biowaste also showed synergetic effects as a co-substrate for COD removal.

Treatment of landfill leachate using sequencing batch and continuous flow upflow anaerobic sludge blanket (UASB) reactors

Treatment of municipal landfill leachate was investigated/compared using sequencing batch and continuous flow upflow anaerobic sludge blanket (UASB) reactors. All reactors were operated at organic loading rates (OLRs) between 0.6–19.7 gCOD/l d. Performance of the continuous UASB and sequencing batch UASB reactors were very similar at low and intermediate OLRs. Continuous UASB reactors performed more favorably at the higher OLRs than the sequencing batch UASB (AnSBR) system. The sequencing batch UASB reactor had soluble chemical oxygen demand (COD) removal efficiencies ranging between 71% and 92% at hydraulic retention times (HRT) of 24, 18 and 12 h with dilute to concentrated leachate feed. For the continuous UASB reactor, soluble COD removal efficiency was consistently between 77% and 91% for all HRTs and feed concentrations. At high OLRs and fill to react ratios of 0.5, the AnSBR system showed signs of system failure. In order to ensure successful AnSBR treatment of municipal landfill leachate the specific organic loading rate during the fill cycle (SOLR fill) should not exceed 3 g COD/g VSS d. Both systems effectively resulted in a reduction in Microtox ® toxicity levels following treatment. Municipal leachate treated by either continuous or sequencing batch UASB reactor was not suitable for direct disposal into the sewerage according to Municipal Sewer Regulations. A post treatment option such as membrane filtration would be required.

Two-phase anaerobic treatment of cheese whey

Performance of two-phase anaerobic digestion of cheese whey was investigated in a system consisting of a continuous stirred tank reactor (CSTR) as the acidogenic reactor and an upflow anaerobic filter (UFAF) as the methanogenic reactor. The acidogenic reactor was operated at various hydraulic retention times (HRTs) between 18 hours and 4 days. The results showed that an optimum HRT for the acidogenic reactor with the same organic loading rate (OLR) between 0.5-2 g COD/MLSS day was 24 hours. At this retention time the acidification rate increased up to a maximum of 50%. Volatile fatty acids (VFAs) produced in the acidogenic reactor operating at an HRT of 24 hours were 52% acetic acid, with 14% propionic, 27% butyric and 7% isovaleric acids. Operating the acidogenic reactor at this HRT, the effluent was fed to the upflow anaerobic filter. Here HRT was varied between 3-6 days for the best COD removal efficiency and biogas production. At an HRT of 4 days a 90% soluble effluent COD removal efficiency was obtained with an outmost biogas yield of 0.55 m3/kg COD removed.

Two-phase anaerobic treatment of cheese whey

Performance of two-phase anaerobic digestion of cheese whey was investigated in a system consisting of a continuous stirred tank reactor (CSTR) as the acidogenic reactor and an upflow anaerobic filter (UFAF) as the methanogenic reactor. The acidogenic reactor was operated at various hydraulic retention times (HRTs) between 18 hours and 4 days. The results showed that an optimum HRT for the acidogenic reactor with the same organic loading rate (OLR) between 0.5-2 g COD/MLSS day was 24 hours. At this retention time the acidification rate increased up to a maximum of 50%. Volatile fatty acids (VFAs) produced in the acidogenic reactor operating at an HRT of 24 hours were 52% acetic acid, with 14% propionic, 27% butyric and 7% isovaleric acids. Operating the acidogenic reactor at this HRT, the effluent was fed to the upflow anaerobic filter. Here HRT was varied between 3-6 days for the best COD removal efficiency and biogas production. At an HRT of 4 days a 90% soluble effluent COD removal efficiency was obtained with an outmost biogas yield of 0.55 m 3 /kg COD removed.

Aerobic treatment of reverse osmosis permeate in the dairy industry for reuse

The aerobic treatment of reverse osmosis (R/O) permeate was investigated to determine its suitability for reuse in the dairy industry. The biodegradability was characterised by a series of batch tests and the biokinetic parameters μm, Ks and Y were found to be 2.4 d−1, 38 mg L−1 and 0.45 mg TSS/mg Chemical Oxygen Demand (COD) respectively. The permeate was treated aerobically in a 5 litre reactor resulting in an effluent soluble COD of 18 mg L−1. The feasibility of biotreatment was also tested at a pilot plant level. Soluble COD removal efficiencies of over 90% were achieved in trials at 10 and 20-hour hydraulic retention times. True steady state operation was never achieved due to highly variable influent substrate concentrations. The Sludge Volume Index was in the range of 40 to 50 at an HRT of 10 hours, and increased to 70 to 140 at a 20 hour HRT. The test showed that R/O permeate has biodegradability comparable to general dairy effluent, and can potentially be reused after secondary treatment.

Protein recovery during the overall treatment of wastewaters from fish-meal factories

The suspended solids contained in the wastewaters generated by fish-meal industries (5–40 g VSS/l) are composed mostly of protein, which could be recovered to optimise the manufacturing process. In this work, settling, centrifugation and coagulation-flocculation were studied as alternative treatment processes to attain this objective. Settling experiments showed that the flotation of a high fraction of suspended solids occurred (up to 45%), even with previous alkalinisation or the addition of a coagulant such as chitosan. Centrifugation at 10 000 rpm for 12·5 min gave optimum results, TSS and soluble COD removal efficiencies of 45–82% and 10%, respectively, being obtained. The amino acid profile of the solids was quite similar to fish meal, indicating the feasibility of solids reuse. Results obtained after coagulation-flocculation followed by centrifugation showed that among the different compounds assayed sodium polyacrylate and chitosan produced the best results, operating at pH 4 and 7·2–7·8, respectively, and giving TSS removal efficiencies up to 97 and 75%, respectively.

Aerobic treatment of reverse osmosis permeate in the dairy industry for reuse

The aerobic treatment of reverse osmosis (R/O) permeate was investigated to determine its suitability for reuse in the dairy industry. The biodegradability was characterised by a series of batch tests and the biokinetic parameters μm, Ks and Y were found to be 2.4 d−1, 38 mg L−1 and 0.45 mg TSS/mg Chemical Oxygen Demand (COD) respectively. The permeate was treated aerobically in a 5 litre reactor resulting in an effluent soluble COD of 18 mg L−1. The feasibility of biotreatment was also tested at a pilot plant level. Soluble COD removal efficiencies of over 90% were achieved in trials at 10 and 20-hour hydraulic retention times. True steady state operation was never achieved due to highly variable influent substrate concentrations. The Sludge Volume Index was in the range of 40 to 50 at an HRT of 10 hours, and increased to 70 to 140 at a 20 hour HRT. The test showed that R/O permeate has biodegradability comparable to general dairy effluent, and can potentially be reused after secondary treatment.

Effects of temperature and hydraulic retention time on anaerobic sequencing batch reactor treatment of low-strength wastewater

Four laboratory-scale anaerobic sequencing batch reactors (ASBRs) were used to treat synthetic wastewaters at COD concentrations of 1000, 800, 600 and 400 mg/liter (BOD 5 of 490, 392, 294 and 196 mg/liter respectively). The ASBRs were operated at temperatures of 35, 25, 20 and 15°C. Reactor 1 was operated at a 48-h HRT, reactor 2 at 24-h HRT, reactor 3 at 16-h HRT and reactor 4 at a 12-h HRT. The four substrate concentrations were treated in each reactor and each temperature. Results of the study show 80–90% soluble COD removal efficiency at the various substrate concentrations, temperatures and HRTs, except during 15°C treatment of the more concentrated wastewater at the shorter HRTs. These findings show that the ASBR process could be used for the treatment of low-strength wastewaters at low temperatures, usually treated aerobically with high energy expenditures and large amounts of sludge production.

Removal of contaminants from recirculated white water by ultrafiltration and/or biological treatment

AbstractThis study investigated the potential of ultrafiltration technology and/or biological treatment to remove contaminants such as total dissolved solids (TDS), chemical oxygen demand (COD), total organic carbon (TOC), and resin and fatty acids (RFAs) from recirculated white water. Batch ultrafiltration experiments indicated that TDS, soluble COD, and TOC removal efficiencies were affected by membrane molecular weight (molar mass) cut‐off, but were independent of the operating temperature, in the 20 to 60°C range. Except for fatty acids, where average removals exceeded 90%, the separation efficiency of the process for all other parameters (TDS, soluble COD, TOC, and resin acids) was moderate, ranging from 10 to 41%. Biological treatment using a sequencing batch reactor (SBR) unit was very effective in removing RFAs, TOC, total and soluble COD. Furthermore, ultrafiltration of the biologically treated process water resulted in significant additional TDS, soluble COD, and TOC removal.

Use of Anaerobic Hybrid Reactors for Treatment of Synthetic Pharmaceutical Wastewaters Containing Organic Solvents

The performance of anaerobic hybrid reactors treating an organic solvent-containing synthetic pharmaceutical wastewater was evaluated under various wastewater volumetric loading rates and influent compositional changes. The biodegradation, toxicity and treatability of the target C3 and C4 solvents, tert-butanol, isopropanol, isobutanol, sec-butanol and ethyl acetate, were examined. At a hydraulic retention time (HRT) of 2 days and volumetric loading rates ranging from 3·5 to 4·5 kg COD m−3 day−1, the reactors achieved total and soluble COD removal efficiencies of 97–99% in less than five times the HRT. These removal rates were achieved following the introduction of target solvents not previously supplied to the reactors. However, inadequate removal of tert-butanol resulted in a decrease in the soluble COD removal efficiency to 58%. Bacterial enrichments from the reactor biomass using tert-butanol as the sole substrate proved unsuccessful, confirming that tert-butanol is poorly degradable anaerobically. Inclusion of a trace metal cocktail in the feed did not affect steady-state reactor performance, but was beneficial during changes in the influent composition. After 405 days of operation, the matrix-associated biomass contributed only a minor fraction (2–4%) of the total biomass present in both reactors. On takedown, the retained biomass present in the matrix-free section of both reactors was found to be granular in nature, despite the omission of trace elements from the influent to one of the AHRs. The specific methanogenic activity profile of the granular sludge from the trace element limited AHR was, however, significantly lower (α = 0·05) than that of the reference AHR.

Brewery Wastewater Treatment in UASB Reactor at Ambient Temperature

Granulation was examined in the 12.3 L upflow anaerobic sludge blanket reactor at the average ambient temperature of 21.8°C. Brewery wastewater with an average chemical oxygen demand (COD) of 2,030 mg/L and biochemical oxygen demand of 1,150 mg/L was used as substrate, and anaerobic digested sludge as inoculum. During start-up, the sludge loading rate was gradually increased when 80% of soluble COD removal efficiency was achieved. The granules were initially developed after 4-month operation and fully grown after 6-month operation. At 21.8°C, the influent alkalinity seemed to have played a positive role in the granulation process by improving the biogas release from the sludge, with the appropriate value of 1,200 mgCaCO3/L. The granules cultivated ranged from 0.4 mm to 1.5 mm in diameter, with specific methanogenic activity of 0.92 gCH4-COD/gVSS⋅d and sludge volume index of 14 mL/g of suspended solids. After granulation, the upflow anaerobic sludge blanket reactor performed stably with soluble COD and biochemical oxygen demand removal efficiencies of 89.1% and 91.3%, respectively, under the volumetric loading rate of 12.2 gCOD/L⋅d and hydraulic retention time of 4 h.

Entrapped mixed microorganisms to treat organic wastewater from food industry

Limited land and insufficient technicians to operate a wastewater treatment system are main restrictions for many factories. Therefore, an ideal wastewater treatment method for a small or land-limited factory must possess merits such as high performance efficiency, high organic loading rate, little odor, simple operation, easy maintenance, and little land required (simultaneously). An entrapment technique to immobilize mixed microorganisms to treat organic wastewater, which was developed in the present work, possesses these characteristics. This project was done on a laboratory scale. The microorganisms were activated sludge (an undefined mixture of microorganisms obtained directly from a domestic wastewater treatment plan) and the mixed microorganisms were immobilized in cellulose triacetate by means of an entrapment technique to treat organic wastewater from food industry. After wastewater was treated by this system, the SCOD (soluble COD) removal efficiency of 81% evaluated samples exceeded 80% in 1.5 ± 0.9 g SCOD/L/d of the volumetric loading rate and 7–10 h for the hydraulic retention time. This wastewater treatment method can be applied to other organic industrial wastewater.

Modeling of the upflow anaerobic sludge bed-filter system: a case with hysteresis

A hybrid upflow sludge bed-filter (UBF) anaerobic reactor was successfully used for treatment of synthetic soluble 1% sugar waste. An hysteresis phenomenon was observed and discussed with respect to changes in acidogenic/acetoclastic specific activities ratio. The Haldane equation was adapted for predicting performance inhibition by undissociated acids as a function of substrate-COD and pH. The Monod and adapted Haldane models were solved simultaneously with substrate mass balance for a UBF reactor. The soluble COD removal efficiency and methane productivity were predicted as a function of the dilution rate. Critical values of solid and hydraulic residence times were also estimated and discussed in detail.