Reactor R1 Research Articles

Reductive transformation and dechlorination of chloronitrobenzenes in UASB reactor enhanced with zero-valent iron addition

BACKGROUND: Zero-valent iron (ZVI) is increasingly being applied in biological wastewater treatment to enhance the conversion of various contaminants. The objective of this present study was to investigate the effect of ZVI on the anaerobic biotransformation and dechlorination of chloronitrobenzenes (3,4-DClNB and 4-ClNB). Experiments were conducted in two upflow anaerobic sludge blanket (UASB) reactors, one (R2) with 30 g L−1 ZVI added, and the other (R1), serving as control reactor. RESULTS: ZVI-based anaerobic granular sludge (ZVI-AGS) composed of bacteria associated with precipitated FeCO3 and FeS was successfully developed within 5 months in reactor R2. ZVI addition obviously enhanced 3,4-DClNB transformation and dechlorination efficiencies under high 3,4-DClNB loads, and further promoted dechlorination of 4-chloroaniline (4-ClAn) to aniline. Compared with the AGS formed in R1 reactor, iron and its corrosion products were observed and colonized with anaerobes such as methanothrix in ZVI-AGS, and the specific transformation rates of 3,4-DClNB and 4-ClNB using ZVI-AGS were improved by 34.0% and 64.4%, respectively. Furthermore, ZVI-AGS provided higher 3,4-dichloronailine and 4-ClAn dechlorination efficiency than AGS. Abiotic transformation of ClNBs by ZVI, appropriate concentration of iron corrosion products, lower redox potential and greater hydrogen production were the main factors providing enhanced transformation and dechlorination of ClNBs in the UASB reactor. CONCLUSION: Addition of ZVI to a UASB reactor enhanced the reductive transformation and dechlorination of ClNBs. It provides a feasible proposal for the design and optimization of a high-rate anaerobic wastewater treatment technique for industrial wastewater. Copyright © 2010 Society of Chemical Industry

Applying an electric field in a built-in zero valent iron – Anaerobic reactor for enhancement of sludge granulation

A zero valent iron (ZVI) bed with a pair of electrodes was installed in an upflow anaerobic sludge blanket (UASB) reactor to create an enhanced condition to increase the rate of anaerobic granulation. The effects of an electric field and ZVI on granulation were investigated in three UASB reactors operated in parallel: an electric field enhanced ZVI-UASB reactor (reactor R1), a ZVI-UASB reactor (reactor R2) and a common UASB reactor (reactor R3). When a voltage of 1.4 V was supplied to reactor R1, COD removal dramatically increased from 60.3% to 90.7% over the following four days, while the mean granule size rapidly grew from 151.4 μm to 695.1 μm over the following 38 days. Comparatively, COD removal was lower and the increase in granule size was slower in the other two reactors (in the order: R1 > R2 > R3). The electric field caused the ZVI to more effectively buffer acidity and maintain a relatively low oxidation–reduction potential in the reactor. In addition, the electric field resulted in a significant increase in ferrous ion leaching and extracellular polymeric substances (EPS) production. These changes benefited methanogenesis and granulation. Scanning electron microscopy (SEM) images showed that different microorganisms were dominant in the external and internal layers of the reactor R1 granules. Additionally, fluorescence in situ hybridization (FISH) analysis indicated that the relative abundance of methanogens in reactor R1 was significantly greater than in the other two reactors. Taken together, these results suggested that the use of ZVI combined with an electric field in an UASB reactor could effectively enhance the sludge granulation.

Comparison of Ca 2+ and Mg 2+ enhancing aerobic granulation in SBR

Two sequencing batch reactors (SBRs) were operated to investigate the effect of Ca 2+ and Mg 2+ augmentation on aerobic granulation. Reactor R1 was augmented with Ca 2+ at 40 mg/L, while Mg 2+ was added to the reactor R2 with 40 mg/L. Results showed that the reactor R1 had a faster granulation process compared with R2, and the mature granules in R1 showed better physical characteristics. However, the mature granules in R2 had the higher production yield of polysaccharides and proteins, and aerobic granules in R2 experienced a faster substrate biodegradation. Microbial and genetic characteristics in mature granules were analyzed using polymerase chain reaction (PCR) and denaturing gradient gel electrophoresis (DGGE) techniques. The results revealed that Mg 2+ addition led to higher microbial diversity in mature granules. In addition, an uncultured bacterium (AB447697) was major specie in R1, and β-proteobacterium was dominant in R2. It can be concluded that Ca 2+ had an important effect on physical properties of aerobic granules, while Mg 2+ played a key role on biological properties during the sludge granulation.

Fate of aerobic bacterial granules with fungal contamination under different organic loading conditions

Aerobic sludge granulation is an attractive new technology for biological wastewater treatment. However, the instability of aerobic granules caused by fungal growth is still one of the main problems encountered in granular bioreactors. In this study, laboratory experiments were conducted to investigate the fate and transformation of aerobic granules under different organic loading conditions. Bacterial granules (2–3 mm) in a poor condition with fungi-like black filamentous growth were seeded into two 1 L batch reactors. After more than 100 d of cultivation, the small seed granules in the two reactors had grown into two different types of large granules (>20 mm) with different and unique morphological features. In reactor R1 with a high organic loading rate of 2.0 g COD L −1 d −1, the black filaments mostly disappeared from the granules, and the dominance of rod-shaped bacteria was recovered. In contrast, at a low loading of 0.5 g COD L −1 d −1 in reactor R2, the filaments eventually became dominant in the black fungal granules. The bacteria in R1 granules had a unique web-like structure with large pores of a few hundred μm in size, which would allow for effective substrate and oxygen transport into the interior of the granules. DNA-based molecular analysis indicated the evolution of the bacterial population in R1 and that of the eukaryal community in R2. The experimental results suggest that a high loading rate can be an effective means of helping to control fungal bloom, recover bacterial domination and restore the stability of aerobic granules that suffer from fungal contamination.

Biological sulphate reduction with primary sewage sludge in an upflow anaerobic sludge bed (UASB) reactor – Part 3: Performance at 20°C and 35°C

The performance of 2 biological sulphate reduction (BSR) upflow anaerobic sludge bed (UASB) reactors fed primary sewage sludge (PSS) and sulphate, one at 20oC (R2) and one at 35oC (R1) is described. To maintain the effluent sulphate concentration below 250 mgSO42-/., the hydraulic retention time (HRT) and bed solids retention time (SRT or sludge age) both needed to be longer and the feed primary sewage sludge (PSS) COD to SO4 2- ratio higher at 20oC than at 35oC, viz. 20.4 to 21.0 h, 24 d and 1.75 gCOD/gSO4 2- at 20oC and 16.4 to 17.0 h, 21 d and 1.75 gCOD/gSO4 2- at 35oC respectively. The longer HRT, SRT and higher feed PSS COD/ SO4 2- ratio is a consequence of a slower PSS hydrolysis/acidogenesis rate at 20oCresulting in a lower biodegradable particulate organics conversion to volatile fatty acids (VFA). Solid liquid separation in both systems was good yielding average particulate and soluble organic COD concentrations of (150 and 100 mgCOD/. for R1; 138 and 96 mgCOD/. for R2). The sulphate reduction was >90% in both systems. The UASB reactor R1 (at 35oC) was also operated at an increased influent sulphate concentration (1 800 mgSO4 2-/.) to investigate the inhibition effect by un-dissociated hydrogen sulphide generated from the reduction of this high sulphate concentration. It was found that a highsulphate reduction (~ 92%) was maintained even at the relatively low HRT of 18.5 h. The COD and S mass balances above 95% were achieved over both systems indicating that the performance data obtained from them is reliable for developing and calibrating mathematical models.

Extracellular polymeric substances (EPS) in upflow anaerobic sludge blanket (UASB) reactors operated under high salinity conditions

Considering the importance of stable and well-functioning granular sludge in anaerobic high-rate reactors, a series of experiments were conducted to determine the production and composition of EPS in high sodium concentration wastewaters pertaining to anaerobic granule properties. The UASB reactors were fed with either fully acidified substrate (FAS) consisting of an acetate medium (reactor R1) or partly acidified substrate (PAS) consisting of acetate, gelatine and starch medium (reactors R2, R3, and R4). For EPS extraction, the cation exchange resin (CER) method was used. Strength and particle size distribution were determined by assessing the formation of fines sludge under conditions of high shear rate and by laser diffraction, respectively. Batch tests were performed in 0.25 L bottles to study Ca 2+ leaching from anaerobic granular sludge when incubated in 20 g Na +/L in the absence of feeding for 30 days. Results show a steady increase in the bulk liquid Ca 2+ concentration during the incubation period. UASB reactor results show that the amounts of extracted proteins were higher from reactors R2 and R3, fed with PAS compared to the sludge samples from reactor R1, fed with FAS. Strikingly, the amount of extracted proteins also increased for all reactor sludges, irrespective of the Na + concentration applied in the feed, i.e. 10 or 20 gNa +/L. PAS grown granular sludges showed an important increase in particle size during the operation of the UASB reactors. Results also show that, addition of 1 gCa 2+/L to the high salinity wastewater increases the granules' strength.

Alternating anoxic feast/aerobic famine condition for improving granular sludge formation in sequencing batch airlift reactor at reduced aeration rate

In this study the influence of a pre-anoxic feast period on granular sludge formation in a sequencing batch airlift reactor is evaluated. Whereas a purely aerobic SBR was operated as a reference (reactor R2), another reactor (R1) was run with a reduced aeration rate and an alternating anoxic-aerobic cycle reinforced by nitrate feeding. The presence of pre-anoxic phase clearly improved the densification of aggregates and allowed granular sludge formation at reduced air flow rate (superficial air velocity (SAV) = 0.63 cm s −1). A low sludge volume index (SVI 30 = 45 mL g −1) and a high MLSS concentration (9–10 g L −1) were obtained in the anoxic/aerobic system compared to more conventional results for the aerobic reactor. A granular sludge was observed in the anoxic/aerobic system whilst only flocs were observed in the aerobic reference even when operated at a high aeration rate (SAV = 2.83 cm s −1). Nitrification was maintained efficiently in the anoxic/aerobic system even when organic loading rate (OLR) was increased up to 2.8 kg COD m −3 d −1. In the contrary nitrification was unstable in the aerobic system and dropped at high OLR due to competition between autotrophic and heterotrophic growth. The presence of a pre-anoxic period positively affected granulation process via different mechanisms: enhancing heterotrophic growth/storage deeper in the internal anoxic layer of granule, reducing the competition between autotrophic and heterotrophic growth. These processes help to develop dense granular sludge at a moderate aeration rate. This tends to confirm that oxygen transfer is the most limiting factor for granulation at reduced aeration. Hence the use of an alternative electron acceptor (nitrate or nitrite) should be encouraged during feast period for reducing energy demand of the granular sludge process.

Anthraquinone-2,6-disulfonate (AQDS) as a catalyst to enhance the reductive decolourisation of the azo dyes Reactive Red 2 and Congo Red under anaerobic conditions

In this study, we assessed the catalytic effect of anthraquinone-2,6-disulfonate (AQDS) to enhance the reductive decolourisation of the azo dyes Reactive Red 2 and Congo Red in batch and continuous-flow experiments. While testing the anaerobic sludge 1 in assays free of AQDS, the highest values for the first-order kinetic constant ( k1) were found with co-substrates formate and glucose. In the assays that contained 50 μM of AQDS, the k1 values increased with all co-substrates tested, increasing by 3.5-fold when ethanol was the electron donor. The upflow anaerobic sludge blanket (UASB) reactors R1 (AQDS-free) and R2 (AQDS-supplemented) reached excellent decolourisation efficiencies (higher than 90%) even for the high Congo Red concentration tested (1.2 mM). However, electron donor depletion in the influent drastically decreased the colour removal capacity in both bioreactors. Reactor R2 presented higher stability and decolourisation efficiency compared to R1, indicating that the addition of a redox mediator can be valuable for treating dye-coloured wastewaters.

Conversion of Nitrous Oxide by Positive Pulsed Corona Discharge

The conversion of nitrous oxide in a positive pulsed corona discharge (PPCD) was studied using two stainless-steel corona reactors with the inner high-voltage electrode made of metal wire (0.3 mm in diameter). The length of the active zone was 0.75 m (reactor R1) or 0.45 m (reactor R2). In the experiments with 5% of oxygen (reactor R1), the overall conversion of N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O (to oxygen, nitrogen, and NO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> ) considerably decreased, which was about 50% smaller than that in argon alone under the same conditions. The presence of a small amount of oxygen in the gas, containing N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O, allowed us to carry out the process using a considerably lower initial concentration of nitrous oxide. For the initial N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O concentration below 1%, it was observed that the corona discharge is not stable and changes into a spark discharge. When the N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O conversion was carried out in argon and oxygen (5% by volume), the conversion of N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O to NO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> was 11.7% for the initial N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O concentration of 2%. The influence of oxygen in Ar + N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O (10%) on the overall conversion and conversion of N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O to NO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> was also investigated. The increase of oxygen concentration from 5% to 45% resulted in a decrease of the overall N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O conversion and its conversion to NO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> . PPCD could have been unstable and changed into a spark discharge when the N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O concentration was low.

Possible role of denitrification on aerobic granular sludge formation in sequencing batch reactor

The aim of this work was to evaluate and quantify the influence of denitrification of nitrate on the aerobic granular sludge development. Two parallel sequencing batch reactors (SBRs) were fed with synthetic wastewater, the first reactor (R1) receiving nitrate at a fixed concentration whereas the second reactor (R2) did not receive any external source of nitrate. Both systems were working at the same operational conditions with a low specific air velocity (0.07 cm s −1), a relatively low and acceptable oxygen concentration (1.8 ± 0.8 mg L −1) and without significant biomass selection pressure (minimal velocity 0.4 m h −1). The results showed that the sludge settling properties of R1 were comparable to granular sludge (settling velocity ≈ 10.6 m h −1, SVI 5 ≈ 13–30 mL g −1, SVI 30 ≈ 11–28 mL g −1 and SVI 5/SVI 30 ratio ≈ 1.05–1.1). In the opposition, biomass of the reactor R2 reveals more traditional properties. Nitrogen measurements revealed that a significant denitrification (up to 80% of fed nitrate) occurred in R1 in the core of aggregates, as aerobic condition was maintained in the bulk. After the mean particle size was reduced from 250 to 125 μm by an increase of mechanical stirring rate, it was shown that denitrification decreased from 80% to 20%. These parallel experiments definitively proved that the presence of nitrate in SBRs can assist the densification of the biological aggregates in aerobic condition. The presence of nitrate (commonly provided by nitrification) should be considered as a possible factor which helps to maintain the granulation process.

Influence of ferrous iron on the granularity of a UASB reactor

The effect of ferrous ion addition on the granularity of an upflow anaerobic sludge blanket (UASB) reactor was investigated. Two UASB reactors (R1 and R2) (35 °C; pH 7) were operated for 3 months at a 20-h hydraulic retention time (HRT) at organic loads from 1.4 to 10.0 g COD L−1 d−1. Ferrous iron was fed only to reactor R1 in a range of load from 0.014 to 0.100 g Fe2+ L−1 d−1. The addition of ferrous iron induced a stable and excellent COD conversion rate. The enhancement of the performance of reactor R1 may be accredited to the mean granule diameter increase as well as to the sludge bed porosity decrease. The addition of iron to reactor R1 had a pronounced effect on the quality of the granular sludge, increasing the characteristic settling velocities. The formation of ferrous sulphide was mainly responsible for the promotion of sludge granulation.

Effect of nitrate on the reduction of Reactive Red 2 by mesophilic anaerobic sludge

This research aimed to evaluate the effect of nitrate on anaerobic azo dye reduction by using mesophilic bioreactors, in the absence (reactor R2) and in the presence (reactor R1) of redox mediators. The azo dye Reactive Red 2 (RR2) and the redox mediator anthraquinone-2,6-disulphonate (AQDS) were selected as model compounds. The results showed that the bioreactors were efficient on RR2 reduction, in which ethanol showed to be a good electron donor to sustain dye reduction under anaerobic conditions. The redox mediator AQDS increased the rates of reductive decolourisation, but its effect was not so remarkable compared to the previous experiments conducted. Contrary to the raised hypothesis that the nitrate addition could decrease decolourisation rates and catalytic properties of the redox mediators, no effect of nitrate was observed in the bioreactors, suggesting that the presence of nitrate in textile wastewaters will not decrease the capacity of anaerobic reactors supplemented or not with redox mediators to decolourize azo dyes.

Treatment of screened dairy manure by upflow anaerobic fixed bed reactors packed with waste tyre rubber and a combination of waste tyre rubber and zeolite: Effect of the hydraulic retention time

Two laboratory-scale anaerobic fixed bed reactors were evaluated while treating dairy manure at upflow mode and semicontinuous feeding. One reactor was packed with a combination of waste tyre rubber and zeolite (R1) while the other had only waste tyre rubber as a microorganism immobilization support (R2). Effluent quality improved when the hydraulic retention time (HRT) increased from 1.0 to 5.5 days. Higher COD, BOD5, total and volatile solids removal efficiencies were always achieved in the reactor R1. No clogging was observed during the operation period. Methane yield was also a function of the HRT and of the type of support used, and was 12.5% and 40% higher in reactor R1 than in R2 for HRTs of 5.5 and 1.0 days, respectively. The results obtained demonstrated that this type of reactor is capable of operating with dairy manure at a HRT 5 times lower than that used in a conventional reactor.

Thermogravimetric characteristics of aerobic granules developed at different salinities

AbstractBACKGROUND: Aerobic granular sludge is a self‐immobilization biotechnology for wastewater treatment. The thermogravimetric characteristics of aerobic granules were investigated in this study.RESULTS: The strongly physically bound water in granules that developed at a salinity of 1% (in reactor R1) and 5% (in reactor R2) were 5% and 3%, respectively. In addition, the extracellular polymer substances (EPS) affected the bound water more significantly at a low salinity than a higher one. Based on thermogravimetric analysis (TGA), granules that developed at low salinity (such as 1% in R1) exhibited a rich diversity of organic components, and higher total EPS concentrations, inferred from the ratios of volatile solids to total solids. Additionally, the maximum weight loss rates of the granules in all reactors occurred at a temperature of around 250 °C and the endothermic peaks shifted to a relatively low temperature with increasing salinity regardless of the existence of EPS.CONCLUSION: Increasing the salinity in the substrates slightly decreased the bound water fraction in granules and reduced the richness of the granule components as well as the biodiversity. This study provides detailed information on the components of aerobic granule. Copyright © 2007 Society of Chemical Industry

Characteristics and stability of aerobic granules cultivated with different starvation time

The characteristics of aerobic granules at steady state and the effects of starvation time on the stability of aerobic granules during the long-term operation were investigated in three sequencing batch reactors (SBRs R1-R3). The SBRs were operated with a cycle time of 1.5, 4.0, and 8.0 h, respectively, which resulted in a starvation time of 0.8, 3.3, and 7.3 h in three reactors, respectively. Results showed that aerobic granules were successfully cultivated in the three reactors, but the granules in R2 with a starvation time of 3.3 h showed the highest density and the best settleability at steady state. It is obvious that the starvation time has an optimum value in terms of settleability of granules. In addition, it was found that the coexistence of a minority of fluffy granules with smooth granules was the potential unstable factor in R1 with a starvation time of 0.8 h at the steady state. The sudden dominance of fluffy granules in R1 after the 160-day operation led to the operation failure of the reactor R1, whereas the granules in R2 with a starvation time of 3.3 h and R3 with a starvation time of 7.3 h showed good stability during the long-term operation. As short starvation time leads to the instability of granules, and long starvation time is not advisable for practical application due to low efficiency, starvation time should be controlled in a reasonable range.

Starvation is not a prerequisite for the formation of aerobic granules

Activated sludge with sludge volume index (SVI)(30) of 77 ml g(-1) and SVI(30) of 433 ml g(-1) was inoculated to start up reactors R1 and R2, respectively. In both R1 and R2, cycle time of 1 h and the influent chemical oxygen demand (COD) concentrations of 1,000 mg l(-1) were employed. Initial settling time of 2 min resulted in the loss of a substantial amount of biomass as wash-out and high effluent COD concentrations within the first week of operation. This implied that there was no starvation phase in each cycle of R1 and R2 during the first week of operation. However, aerobic granules with a size above 400 mum formed by day 7. Thus, it was concluded that starvation was not a prerequisite for the formation of aerobic granules. When cycle time was 1 h, the instability of aerobic granules was observed. When cycle time was prolonged to 1.5 h and granular sludge of 200 ml was used to start up reactor R3, the reactor R3 reached steady state within 1 week. SVI, size, and the morphology of granular sludge in R3 remained stable during the 47-day operation, which indicated that prolonged starvation time had positive effects on the stability of aerobic granules.

Influence of cycle time on kinetic behaviors of steady-state aerobic granules in sequencing batch reactors

To investigate kinetic behaviors of aerobic granules under different cycle times, we cultivated aerobic granules in sequencing batch reactors R1, R2, and R3 with cycle time of 1.5, 4, and 8 h, respectively. After the three reactors reached the steady state, we found that granules in R1 with a cycle time of 1.5 h were the biggest while the most compact granules with density of 74.6 g l −1 was produced in reactor R2 with a cycle time of 4 h. Both granule density and granule size greatly influenced the specific COD removal rate ( q s) and the specific oxygen uptake rate (SOUR) because of the mass transfer limitation in granules. However, the difference of COD removal rate by different granules could be neglected in aerobic granular reactor as 1000 mg l −1 of influent COD was depleted during 30 min by the biomass with high concentration in the reactor. Furthermore, we found that the observed specific biomass growth rate ( μ obs) of granular sludge decreased from 0.266 to 0.031 d −1 while the observed biomass growth yield ( Y obs) of granular sludge decreased from 0.316 to 0.063 g VSS g −1 COD when cycle time varied from 1.5 to 8 h. Both μ obs and Y obs had good linear relationships with organic loading rate (OLR). However, the high μ obs with cycle time of 1.5 h would be harmful to the long-term stability of aerobic granules although OLR and reactor treating capacity could be enhanced greatly by shortening cycle time. In addition, high effluent biomass concentration and high Y obs with short cycle time would burden the sedimentation tanks and the sludge disposal. The balance between advantages and disadvantages by using short cycle time thus should be considered. The results in this study can be applied for the process design and optimization of biological wastewater treatment with aerobic granules.

Low-temperature anaerobic biological treatment of toluene-containing wastewater

Two expanded granular sludge bed-anaerobic filter (EGSB-AF) bioreactors, R1 and R2, were operated at 15 °C for the treatment of toluene-contaminated volatile fatty acid-based wastewater. The seed inoculum and the R1 reactor were unexposed to toluene, prior to and during the trial, respectively. Both reactors were operated at a hydraulic retention time of 24 h at applied organic loading rates of 0.71–1.43 kg chemical oxygen demand (COD) m −3 d −1. Toluene was supplemented to the R2 influent at concentrations of 5–104 mg toluene l −1 (solubilised in ethanol). Bioreactor performance was evaluated by COD and toluene removal efficiency, and the methane content of biogas (%). Specific methanogenic activity and toxicity assays were employed to investigate the activity and toluene toxicity thresholds of key trophic groups, respectively, within the seed and reactor biomass samples. COD and toluene removal efficiencies of 70–90% and 55–99%, respectively, were achieved during the 630-d trial. Metabolic assays suggested that a psychrotolerant H 2/CO 2-utilizing methanogenic community developed in the toluene-degrading biomass. The results indicate the viability of low-temperature anaerobic digestion for the treatment of wastewater containing toluene.

Evaluation of sequencing batch reactor performance with aerated and unaerated FILL periods in treating phenol-containing wastewater

Performance of the sequencing batch reactor (SBR) treating synthetic phenolic wastewater at influent phenol concentrations from 100 to 1000 mg/L was evaluated. Two identical SBRs were built and operated with FILL, REACT, SETTLE and DRAW periods in the ratio of 4:6:1:1 for a cycle time of 12 h. One of the reactors was operated with aerated FILL (R1) and the other with unaerated FILL (R2). The treated effluent quality and the rate of degradation during REACT were the criteria for evaluating performance of the two reactors. The results showed that the FILL mode had no significant influence on the treatment efficiency of phenol and COD for the entire range of influent phenol concentrations investigated. However, reactor R1 required a relatively shorter REACT time for phenol removal as compared to R2. This meant that R1 had the advantage of providing treatment at a higher organic loading rate.

Performance of anaerobic reactors at low organic load subjected to sudden change in feed substrate types

Many researchers have studied the impact of stress/shock imposed due to change in environmental and operational conditions using the same feed substrate type on performances of anaerobic reactors. However, limited reports are available on performance of anaerobic reactors subjected to shock/stress conditions due to sudden change in feed substrate and hence the present work is directed towards this end. Three suspended growth batch reactors (R1, R2 and R3) were started up and operated at an organic loading rate of 1.40 kg COD m−3 d−1 with simple soluble feed substrate (i.e. jaggery) to obtain similar performance before application of shock. The shock was applied by suddenly changing feed substrate to reactors R2 (from jaggery to cerelac—a complex suspended type feed) and R3 (from jaggery to neutralized acetic acid) while keeping reactor R1 as the control. The immediate impact of sudden change in feed substrate was observed in reactor R3, which showed reduced gas production rate, while no visible impact on reactor R2 was observed for gas production rate. The performance of reactor R2 deteriorated marginally in respect of biogas production during the shock period. However, performance of reactor R3 deteriorated very much during the shock period: gas production ceased completely and indicated build-up of high levels of volatile fatty acid. Lastly, reactors R2 and R3 were restored to jaggery feed substrate. Reactor R3 responded by producing biogas along with the other two reactors. It was observed that all three reactors started giving steady performance within 2 weeks of operation, which was similar to pre-shock conditions. This study indicated that extreme caution is needed when there is a possibility of sudden stress/shock conditions due to complete change in feed substrate, even though all other operational and environmental parameters are planned to be maintained at pre-shock conditions. Copyright © 2006 Society of Chemical Industry