Feasibility of expanded granular sludge bed reactors for the anaerobic treatment of low-strength soluble wastewaters

The application of the expanded granular sludge bed (EGSB) reactor for the anaerobic treatment of low-strength soluble wastewaters using ethanol as a model substrate was investigated in laboratory-scale reactors at 30oC. Chemical oxygen demand (COD) removal efficiency was above 80% at organic loading rates up to12 g COD/L . d with influent concentrations as low as 100 to 200 mg COD/L. These results demonstrate the suitability of the EGBS reactor for the anaerobic treatment of low-strength wastewaters. The high treatment performance can be attributed to the intense mixing regime obtained by high hydraulic and organic loads. Good mixing of the bulk liquid phase for the substrate-biomass contact and adequate expansion of the substrate-biomass contact and adequate expansion of the sludge bed for the degassing were obtained when the liquid upflow velocity (V(up)) was greater than 2.5 m/h. Under such conditions, an extremely low apparent K(s) value for acetoclastic methanogenesis of 9.8 mg COD/L was observed. The presence of dissolved oxygen in the wastewater had no detrimental effect on the treatment performance. Sludge piston flotation from pockets of biogas accumulating under the sludge bed occurred at V(up) lower than 2.5 m/h due to poor bed expansion. This problem is expected only in small diameter laboratory-scale reactors. A. more important restriction of the EGSB reactor was the sludge washout occurring at V(up) higher than 5.5 m/h and which was intensified at organic loads higher than 7 g COD/L. d due to buoyancy forces from the gas production. To achieve an equilibrium between the mixing intensity and the sludge hold-up, the operation should be limited to an organic loading rate of 7 g COD/L d. and to a liquid up-flow velocity between 2.5 and 5.5 m/h (c) 1994 John Wiley & Sons, Inc.     

Stability and reproducibility of low-temperature anaerobic biological wastewater treatment

The reproducibility of low-temperature anaerobic biological wastewater treatment trials was evaluated. Two identical anaerobic expanded granular sludge bed bioreactors were used to treat synthetic volatile fatty acid-based industrial wastewater under ambient conditions (18-20 degrees C) and to investigate the effect of various environmental perturbations on reactor performance and microbial community dynamics, which were assessed by chemical oxygen demand removal or effluent volatile fatty acid determination and terminal restriction fragment length polymorphism analysis, respectively. Methanogenic activity was monitored using specific methanogenic activity assays. Reactor performance and microbial community dynamics were each well replicated between Reactor 1 and Reactor 2. Archaeal dynamics, in particular, were associated with reactor operating parameters. Terminal restriction fragment length polymorphism data suggested dynamic acetoclastic and hydrogenophilic methanogenic populations and were in agreement with temporal specific methanogenic activity data. Putative psychrophilic populations were observed in anaerobic bioreactor sludge for the first time.     

Biosorption and biodegradation of pentachlorophenol (PCP) in an upflow anaerobic sludge blanket (UASB) reactor

In order to understand the fate of PCP in upflow anaerobic sludge blanket reactor (UASB) more completely, the sorption and biodegradation of pentachlorophenol (PCP) by anaerobic sludge granules were investigated. The anaerobic granular sludge degrading PCP was formed in UASB reactor, which was seeded with anaerobic sludge acclimated by chlorophenols. At the hydraulic retention time (HRT) of 20–22 h, and PCP loading rate of 200–220 mg l⁻¹ d⁻¹, UASB reactor exhibited good performance in treating wastewater which containing 170–180 mg l⁻¹ PCP and the PCP removal rate of 99.5% was achieved. Sequential appearance of tetra-, tri-, di-, and mono-chlorophenol was observed in the reactor effluent after 20 mg l⁻¹ PCP introduction. Sorption and desorption of PCP on the anaerobic sludge granules were all fitted to the Freundlich isotherm equation. Sorption of PCP was partly irreversible. The Freundlich equation could describe the behavior of PCP amount sorbed by granular sludge in anaerobic reactor reasonably well. The results demonstrated that the main mechanism leading to removal of PCP on anaerobic granular sludge was biodegradation, not sorption or volatization.     

厌氧颗粒污泥微生物群落结构与功能的研究进展

厌氧颗粒污泥(anaerobicgranularsludge,AnGS)是由多种功能微生物组成的自固定化聚集体,具有容积负荷高、工艺简单、剩余污泥产量低等优点,在废水处理领域中显示出巨大的技术和经济潜力,被认为是一种很有前景的低碳废水处理工艺。本文系统总结了近年来厌氧颗粒污泥微生物结构和功能的研究成果,从微生物学角度讨论了厌氧颗粒污泥形成及稳定的影响因素,并对今后厌氧颗粒污泥的研究进行了展望,以期为后续厌氧颗粒污泥技术的深入研究和实际工程应用提供参考。     

Formation of metabolites during biodegradation of linear alkylbenzene sulfonate in an upflow anaerobic sludge bed reactor under thermophilic conditions.

Biodegradation of linear alkylbenzene sulfonate (LAS) was shown in an upflow anaerobic sludge blanket reactor under thermophilic conditions. The reactor was inoculated with granular biomass and fed with a synthetic medium and 3 micromol/L of a mixture of LAS with alkylchain length of 10 to 13 carbon atoms. The reactor was operated with a hydraulic retention time of 12 h with effluent recirculation in an effluent to influent ratio of 5 to 1. A sterile reactor operated in parallel revealed that sorption to sludge particles initially accounted for a major LAS removal. After 8 days of reactor operation, the removal of LAS in the reactor inoculated with active granular biomass exceeded the removal in the sterile reactor inoculated with sterile granular biomass. The effect of sorption ceased after 185 to 555 h depending on the LAS homologs. 40% of the LAS was biodegraded, and the removal rate was 0.5 x 10(-6) mol/h/mL granular biomass. Acidified effluent from the reactor was subjected to dichloromethane extraction followed by gas chromatography/mass spectrometry. Benzenesulfonic acid and benzaldehyde were detected in the reactor effluent from the reactor with active granular biomass but not in the sterile and unamended reactor effluent. Benzenesulfonic acid and benzaldehyde are the first identified degradation products in the anaerobic degradation of LAS.     

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.     

Anammox bacteria enrichment in upflow anaerobic sludge blanket (UASB) reactor

We investigated the anaerobic ammonium oxidation (anammox) reaction in a labscale upflow anaerobic sludge blanket (UASB) reactor. Our aim was to detect and enrich the organisms responsible for the anammox reaction using a synthetic medium that contained low concentrations of substrates (ammonium and nitrite). The reactor was inoculated with granular sludge collected from a full-scale anaerobic digestor used for treating brewery wastewater. The experiment was performed during 260 days under conditions of constant ammonium concentration (50 mg NH₄/⁺-N/L) and different nitrite concentrations (50∼150 mg NO₂-N/L). After 200 days, anammox activity was observed in the system. The microorganisms involved in this anammox reaction were identified as CandidatusB. Anammoxidans andK. Stuttgartiensis using fluorescencein situ hybridization (FISH) method.     

A comparison study on the high-rate co-digestion of sewage sludge and food waste using a temperature-phased anaerobic sequencing batch reactor system

Assessing contemporary anaerobic biotechnologies requires proofs on reliable performance in terms of renewable bioenergy recovery such as methane (CH₄) production rate, CH₄ yield while removing volatile solid (VS) effectively. This study, therefore, aims to evaluate temperature-phased anaerobic sequencing batch reactor (TPASBR) system that is a promising approach for the sustainable treatment of organic fraction of municipal solid wastes (OFMSW). TPASBR system is compared with a conventional system, mesophilic two-stage anaerobic sequencing batch reactor system, which differs in operating temperature of 1st-stage. Results demonstrate that TPASBR system can obtain 44% VS removal from co-substrate of sewage sludge and food waste while producing 1.2 m³CH₄/m³_system/d (0.2 m³CH₄/kgVS_added) at organic loading rate of 6.1 gVS/L/d through the synergy of sequencing-batch operation, co-digestion, and temperature-phasing. Consequently, the rapid and balanced anaerobic metabolism at thermophilic stage makes TPASBR system to afford high organic loading rate showing superior performance on OFMSW stabilization.     

Design and analysis of a solar reactor for anaerobic wastewater treatment

The aim of this research was to design a solar heated reactor system to enhance the anaerobic treatment of wastewater or biological sludge at temperatures higher than the ambient air temperature. For the proposed reactor system, the solar energy absorbed by flat plate collectors was transferred to a heat storage tank, which continuously supplied an anaerobic-filter reactor with water at a maximum temperature of 35 degrees C. The packed reactor was a metallic cylindrical tank with a peripheral twin-wall enclosure. Inside this enclosure was circulated warm water from the heat storage tank. Furthermore, a mathematical model was developed for the prediction of the temperature distribution within the reactor under steady state conditions. Preliminary results based on model simulations performed with meteorological data from various geographical regions of the world suggested that the proposed solar reactor system could be a promising and environmentally friendly approach for anaerobic treatment of wastewater and biological sludge.     

Protein degradation during anaerobic wastewater treatment: derivation of stoichiometry

The stoichiometry of reactions that describe protein degradation in anaerobic treatment systems were investigated. A methodology was developed to describe protein degradation to organic acids using a single reaction step. The reactions for individual amino acid fermentation and their mediating organisms were reviewed. The dominant fermentation pathways were selected based on a number of assumptions. Using the amino acid content of a model protein, it was then possible to determine stoichiometric coefficients for each major organic acid product in the overall degradation of the protein. The theoretical coefficients were then compared to those determined from two experimental runs on a continuously-fed, well-mixed, laboratory-scale anaerobic wastewater treatment system. In general, the coefficients compared well thus validating the use of a single reaction step for the overall catabolic reaction of protein degradation to organic acids. Furthermore, even when the protein concentration in feed or the feed flow rate was doubled, the amino acid fermentation pathways were found to occur predominantly by only one pathway. Although the choice of Stickland reactions over uncoupled degradation provided good comparisons, an electron balance showed that only about 40% of the amino acids could have proceeded coupled to other amino acid reactions. Uncoupled degradation of the remaining amino acids must have relied on the uptake of hydrogen produced from these reactions by hydrogen-consuming methane bacteria.     

Determination of kinetic constants for a two-stage anaerobic upflow packed-bed reactor for dairy wastewater

A two-stage upflow packed-bed (reactors in series) system was used for the treatment of dairy wastewater. Nylon pads were used as supporting media for the biomass. This investigation aimed at the determination of various kinetic constants for substrate, biomass and biogas based on various models. The maximum loadings that could be applied to reactor I and reactor II were 14·29 and 5·0 kg of chemical oxygen demand (COD) per m³ per day, respectively. The maximum COD removal efficiencies at various loading rates were in the ranges of 93·8–98·5% and 72·5–84% for the two reactor systems, respectively. The combined biogas yield was between 0·196 and 0·386 m³ gas/kg COD_a.     

Anaerobic methanethiol degradation in upflow anaerobic sludge bed reactors at high salinity (> or =0.5 M Na(+))

The feasibility of anaerobic methanethiol (MT) degradation at elevated sodium concentrations was investigated in a mesophilic (30 degrees C) lab-scale upflow anaerobic sludge bed (UASB) reactor, inoculated with estuarine sediment originating from the Wadden Sea (The Netherlands). MT was almost completely degraded (>95%) to sulfide, methane and carbon dioxide at volumetric loading rates up to 37 mmol MT x L(-1) x day(-1), 0.5 M sodium (NaCl or NaHCO(3)) and between pH 7.3 and 8.4. Batch experiments revealed that inhibition of MT degradation started at sodium (both NaCl and NaHCO(3)) concentrations exceeding 0.8 M. Sulfide inhibited MT degradation already around 3 mM (pH 8.3).     

Cultivation of low-temperature (15°C), anaerobic, wastewater treatment granules

Aims: Anaerobic sludge granules underpin high‐rate waste‐to‐energy bioreactors. Granulation is a microbiological phenomenon involving the self‐immobilization of several trophic groups. Low‐temperature anaerobic digestion of wastes is of intense interest because of the economic advantages of unheated bioenergy production technologies. However, low‐temperature granulation of anaerobic sludge has not yet been demonstrated. The aims of this study were to (i) investigate the feasibility of anaerobic sludge granulation in cold (15°C) bioreactors and (ii) observe the development of methanogenic activity and microbial community structure in developing cold granules. Methods and Results: One mesophilic (R1; 37°C) and two low‐temperature (R2 and R3, 15°C) laboratory‐scale, expanded granular sludge bed bioreactors were seeded with crushed (diameter <0·4 mm) granules and were fed a glucose‐based wastewater for 194 days. Bioreactor performance was assessed by chemical oxygen demand removal, biogas production, granule growth and temporal methanogenic activity. Granulation was observed in R2 and R3 (up to 33% of the sludge). Elevated hydrogenotrophic methanogenesis was observed in psychrophilically cultivated biomass, but acetoclastic methanogenic activity was also retained. Denaturing gradient gel electrophoresis of archaeal 16S rRNA gene fragments indicated that a distinct community was associated with developing and mature granules in the low‐temperature (LT) bioreactors. Conclusions: Granulation was observed at 15°C in anaerobic bioreactors and was associated with H₂/CO₂‐mediated methanogenesis and distinct community structure development. Significance and Impact of the Study: Granulation underpins high‐rate anaerobic waste treatment bioreactors. Most LT bioreactor trials have employed mesophilic seed sludge, and granulation <20°C was not previously documented.     

Critical review of the influences of nanoparticles on biological wastewater treatment and sludge digestion

Nanoparticles (NPs), with at least one dimension less than 100?nm, are substantially employed in consumer and industrial products due to their specific physical and chemical properties. The wide uses of engineered NPs inevitably cause their release into the environment, especially wastewater treatment plants. Therefore, it is essential to systematically assess their potential impact on biological wastewater treatment and subsequent sewage sludge digestion. This review aims to provide such support. First, this paper reviews the recent advances on the analytical developments and nano–bio interface of NPs in wastewater and sewage sludge treatment. The effects of NPs on biological wastewater treatment and sewage sludge digestion and related mechanisms are discussed in detail. Finally, the key questions that need to be answered in the future are pointed out, which include on-line revelation of the changes of NPs in sewage and sludge environments, in situ assessment of the variations of microorganisms involved in these biological systems after they are exposed to NPs. Differentiation of the contribution of individual toxicity mechanisms to these systems, and the identification of under what conditions the nanoparticle-induced toxicity will be increased or decreased are also considered.     

Development of an efficient process for the treatment of residual sludge discharged from an anaerobic digester in a sewage treatment plant

In order to reduce the discharge of residual sludge from an anaerobic digester, pre-treatment methods including low-pressure wet-oxidation, Fenton oxidation, alkali treatment, ozone oxidation, mechanical destruction and enzymatic treatment were evaluated and compared. VSS removal efficiencies of greater than 50% were achieved in cases of low-pressure wet-oxidation, Fenton oxidation and alkali treatment. Residual sludge from an anaerobic digester was pre-treated and subjected to thermophilic anaerobic digestion. As a result, the process of low-pressure wet-oxidation followed by anaerobic digestion achieved the highest VSS removal efficiency of 83%. The total efficiency of VSS removal of sewage sludge consisting of primary and surplus sludge would be approximately 92%, assuming that the VSS removal efficiency of sewage sludge is 50% in the anaerobic digester of the sewage treatment plant.     

Full-scale and laboratory-scale anaerobic treatment of citric acid production wastewater

This paper reviews the operation of a full-scale, fixed-bed digester treating a citric acid production wastewater with a COD: sulphate ratio of 3–4 : 1. Support matrix pieces were removed from the digester at intervals during the first 5 years of operation in order to quantify the vertical distribution of biomass within the digester. Detailed analysis of the digester biomass after 5 years of operation indicated that H2 and propionate-utilising SRB had outcompeted hydrogenophilic methanogens and propionate syntrophs. Acetoclastic methanogens were shown to play the dominant role in acetate conversion. Butyrate and ethanol-degrading syntrophs also remained active in the digester after 5 years of operation.Laboratory-scale hybrid reactor treatment at 55 °C of a diluted molasses influent, with and without sulphate supplementation, showed that the reactors could be operated with high stability at volumetric loading rates of 24 kgCOD.m-3.d-1 (12 h HRT). In the presence of sulphate (2 g/l-1; COD/sulphate ratio of 6 : 1), acetate conversion was severely inhibited, resulting in effluent acetate concentrations of up to 4000 mg.l-1.     

Performance of down-flow hanging sponge (DHS) reactor coupled with up-flow anaerobic sludge blanket (UASB) reactor for treatment of onion dehydration wastewater

In this study, a promising system consisting of up-flow anaerobic sludge blanket (UASB) reactor followed by down-flow hanging sponge (DHS) reactor was investigated for onion dehydration wastewater treatment. Laboratory experiments were conducted at two different phases, i.e., phase (1) at overall hydraulic retention time (HRT) of 11 h (UASB reactor: 6 h and DHS reactor: 5 h) and phase (2) at overall HRT of 9.4 h (UASB reactor: 5.2 h and DHS reactor: 4.2 h). Long-term operation results of the proposed system showed that its overall TCOD, TBOD, TSS, TKN and NH₄N removal efficiencies were 92 ± 5, 95 ± 2, 95 ± 2, 72 ± 6 and 99 ± 1.3%, respectively (phase 1). Corresponding values for the 2nd phase were 85.4 ± 5, 86 ± 3, 87 ± 6, 65 ± 8 and 95 ± 2.8%. Based on the available results, the proposed system could be more viable option for treatment of wastewater generated from onion dehydration industry in regions with tropical or sub-tropical climates and with stringent discharge standards.     

Experiments and ANFIS modelling for the biodegradation of penicillin-G wastewater using anaerobic hybrid reactor

The performance of an anaerobic hybrid reactor (AHR) for treating penicillin-G wastewater was investigated at the ambient temperatures of 30-35 °C for 245 days in three phases. The experimental data were analysed by adopting an adaptive network-based fuzzy inference system (ANFIS) model, which combines the merits of both fuzzy systems and neural network technology. The statistical quality of the ANFIS model was significant due to its high correlation coefficient R² between experimental and simulated COD values. The R² was found to be 0.9718, 0.9268 and 0.9796 for the I, II and III phases, respectively. Furthermore, one to one correlation among the simulated and observed values was also observed. The results showed the proposed ANFIS model was well performed in predicting the performance of AHR.     

Biogas production from potato-juice, a by-product from potato-starch processing, in upflow anaerobic sludge blanket (UASB) and expanded granular sludge bed (EGSB) reactors

In this study, the utilization of potato-juice, the organic by-product from potato-starch processing, for biogas production was investigated in batch assay and in high rate anaerobic reactors. The maximum methane potential of the potato-juice determined by batch assay was 470 mL-CH₄/gVS-added. Anaerobic digestion of potato-juice in an EGSB reactor could obtain a methane yield of 380 mL-CH₄/gVS-added at the organic loading rate of 3.2 gCOD/(L-reactor.d). In a UASB reactor, higher organic loading rate of 5.1 gCOD/(L-reactor.d) could be tolerated, however, it resulted in a lower methane yield of 240 mL-CH₄/gVS-added. The treatment of reactor effluent was also investigated. By acidification with sulfuric acid to pH lower than 5, almost 100% of the ammonia content in the effluent could be retained during the successive up-concentration process step. The reactor effluent could be up-concentrated by evaporation to minimize its volume, and later be utilized as fertilizer.