Continuous anaerobic treatment of autoxidized bark extracts in laboratory-scale columns

Debarking wastewaters of the forest industry contain high concentrations of tannins that are inhibitory to methane bacteria. The tannins can be polymerized to nontoxic colored compounds by the applications of an autoxidation pretreatment, enabling the anaerobic treatment of easily biodegradable components in the wastewater. The continuous anaerobic treatment of untreated and autoxidized pine bark extract was studied in laboratory-scale columns packed with a granular sludge bed. The autoxidation doubled the conversion efficiency of bark extract COD to methane (from 19 to 40%). After 5 months of operation, anaerobic treatment of the autoxidized extracts was feasible at high influent concentrations (14 g COD/L) and loading rates (26 g biodegradable COD/L . d) with 98% elimination of the biodegradable fraction. The detoxification pretreatment polymerized the toxic tannins to poorly biodegradable high molecular weight tannins and humic compounds which were not eliminated during anaerobic treatment. Although the original tannins of the untreated extract were eliminated by 60%, they were not biodegraded to volatile fatty acids and methane but instead were transformed to phenolic degradation intermediates (phenol, p-cresol, 3-phenyl-propionate, and carboxycyclohexane). Therefore, the autoxidation pretreatment did not decrease the content of readily biodegradable substrates which accounted for 53% of the extract COD. The recalcitrant COD expected in the effluents of reactors treating autoxidized debarking waste-water can be effectively separated by calcium precipitation prior to anaerobic treatment.     

Performance of a horizontal-flow anaerobic immobilized biomass (HAIB) reactor and dynamics of the microbial community during degradation of pentachlorophenol (PCP)

The anaerobic biological treatment of pentachlorophenol (PCP) and methanol as the main carbon source was investigated in a horizontal-flow anaerobic immobilized biomass (HAIB) reactor at 30+/-1 degrees C, during a 220-day trial period. The reactor biomass was developed as an attached biofilm on polyurethane foam particles, with 24h of hydraulic retention time. The PCP concentrations, which ranged from 2.0 to 13.0 mg/L, were controlled by adding synthetic substrate. The HAIB reactor reduced 97% of COD and removed 99% of PCP. The microbial biofilm communities of the HAIB reactor amended with PCP, without previous acclimatization, were characterized by polymerase chain reaction (PCR) and amplified ribosomal DNA restriction analysis (ARDRA) with specific Archaea oligonucleotide primers. The ARDRA technique provided an adequate analysis of the community, revealing the profile of the selected population along the reactor. The biomass activities in the HAIB reactor at the end of the experiments indicated the development of PCP degraders and the maintenance of the population of methanogenic Archaea, ensuring the high efficiency of the system treating PCP with added methanol as the cosubstrate. The use of the simplified ARDRA method enabled us to monitor the microbial population with the addition of high concentrations of toxic compounds and highlighting a selection of microorganisms in the biofilm.     

Immobilized microbes and a high-rate, continuous waste processor for the production of high Btu gas and the reduction of pollutants

Microbes capable of degrading organic wastes (sewage) are densely packed (immobilized) within the pores of controlled-pore ceramics. When the ceramic displays the optimum pore range for the reproduction of these microbes, the minimum volume for a very efficient reactor is required. A two-stage, anaerobic, immobilized microbe reactor has been designed, and laboratoryscale units have been constructed. A few of these units have been operated continuously for two years. These reactors were designed for the efficent conversion of carbon to methane in biodegradable molecules and for the effective transfer of that gas. The reactors were operated at 20, 30, and 40 degrees C at residence times of 2-5.5 h. The total chemical oxygen demand (COD) of the sewage varied from 800-2600 mg/L. The resulting gas contained greater than 90% methane and less than 5% CO(2). Approximately 32-54% of the influent total carbon was recovered as methane. The reduction in COD varied from 63 to 89%.     

Biomass retention and performance of anaerobic fixed-film reactors treating acetic acid wastewater

An acetic-acid-based synthetic wastewater of different organic concentrations was successfully treated at 35 degrees C in anaerobic downflow fixed-film reactors operated at high organic loading rates and short hydraulic retention times (HRTs). Substrate removal and methane production rates close to theoretical values of complete volumetric chemical oxygen demand (COD) removal and maximum methane conversion were obtained. A high concentration of biofilm biomass was retained in the reactor. Steady-state biofilm concentration increased with increased organic loading rate and decreased HRTs, reaching a maximum of 8.3 kg VFS/m(3) at a loading rate of 17 kg COD/m(3) day. Biofilm substrate utilization rates of up to 1.6 kg COD/kg VFS day were achieved. Soluble COD utilization rates at various COD concentrations can be described by half-order reaction kinetics.     

Anaerobic treatment of highly concentrated aniline wastewater using packed-bed biofilm reactor

The performance of packed-bed biofilm reactor (PBBR) with self-floating bio-carriers was investigated to treat highly concentrated organic nitrogenous aniline wastewater with a COD value as high as 24,000 mg/L. With 45 vol% of carrier charge inside the reactor, the aniline wastewater can be effectively treated with 94% of COD removal efficiency at a low organic loading rate (OLR) of 0.9 kg COD/(m³ d). The removal efficiency decreased gradually down to 75% when OLR increased to 12.27 kg COD/(m³ d) that corresponded to 1 day of HRT. Separate tests with biofilm alone showed that the conversion contribution of the biofilm was about half of the overall COD conversion by the biofilm plus sludge system at the same OLRs of 3–4 kg COD/(m³ d), and that the biofilm had higher activity than suspended sludge. Ammonium released from decomposed aniline was increased gradually from 500 to 1700 mg/L with the OLR increase from 0.9 to 12.27 kg COD/(m³ d), which resulted in inhibitory effect to the microorganism due to the toxicity of free ammonia. Batch anaerobic toxicity tests showed that the biofilm was less sensitive to toxic compounds than suspended sludge and could tolerate higher concentration of free ammonia.     

Testing the Efficiency of Biofilms Formed on Natural Substratum,Coyonoxtle (Opuntia Imbricata), for the Anaerobic Degradation of Aromatic Compounds

In this study, previously developed anaerobic microbial consortia capable of degrading aromatic compounds were used to develop biofilms on a natural material, coyonoxtle (Opuntia imbricata), which is abundantly available in North Mexico. The developed biofilms were evaluated for their efficiency in the biodegradation of different aromatic compounds, viz., phenol, catechol, 4‐aminobenzoic acid and p‐phenylenediamine in batch reactors. It was observed that in reactors with biofilms a more than 90 % COD removal and a concomitant production of methane could be obtained. But the rate of COD removal and methane production varied depending upon the type of biofilm used. Rumen‐derived biofilms demonstrated a lag phase of 7 to 14 days, whereas sludge‐derived biofilms exhibited a lag phase of more than three weeks. Between the biofilms from two sources, rumen‐derived biofilms showed a higher COD removal and methane production than sludge‐derived biofilms. When biofilm reactors were compared with reactors containing freely suspended consortia, it was evident that both rumen– and sludge‐derived biofilm reactors exhibited a two‐fold higher COD removal and methane production. Based on the results obtained, it can be concluded that coyonoxtle has the potential for use as a substratum.     

Effects of influent DO/COD ratio on the performance of an anaerobic fluidized bed reactor fed low-strength synthetic wastewater

The effect of influent DO/COD (dissolved oxygen/chemical oxygen demand) ratio on the performance of an anaerobic fluidized bed reactor (AFBR) containing GAC was studied. A high influent DO concentration was found to have adverse impacts on organic removal efficiency, methane production, and effluent suspended solids (SS) concentration. These problems resulted with a DO/COD ratio of 0.12, but not at a lower ratio of 0.05. At first organic removal appeared satisfactory at the higher DO/COD ratio at a hydraulic retention time of 0.30 h, but soon a rapid growth of oxygen-consuming zoogloeal-like organisms resulted, eventually causing high effluent SS concentrations. The influent DO also had an inhibitory effect, resulting in a long recovery time for adequate methanogenic activity to return after influent DO removal began. With the growing interest in anaerobic treatment of low COD wastewaters, the increased possibility of similar adverse DO effects occurring needs consideration.     

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.     

Toxic effects of thiol-reactive compounds on anaerobic biomass

The objective of this study was to characterize the toxic effects of three well known thiol-reactive electrophilic compounds, N-ethylmaleimide (NEM), pentachlorophenol (PCP) and 1-chloro-2,4-dinitrobenzene (CDNB) on anaerobic biotransformation process. The work was part of a larger investigation on potassium efflux as a possible response mechanism of anaerobic microorganisms to the presence of thiol-reactive organic compounds and the interference of such compounds on the reductive dehalogenation process. Using anaerobic toxicity assay (ATA) and granular anaerobic biomass from a full-scale upflow anaerobic sludge blanket (UASB) reactor, inhibitory concentrations of these compounds that reduced the microbial activity of granular biomass to 50% of a control (IC50) were determined to be 592, 0.97, and 450 mg/l for NEM, PCP, and CDNB, respectively. Toxicity of NEM was also tested on anaerobic biomass from a municipal wastewater treatment plant digester and slightly lower IC50 of 532 mg/l was obtained. The results presented here indicate that anaerobic biomass can acclimate to the three thiol-reactive compounds studied and recover from inhibition as long as the toxicant concentration is below a threshold level. That threshold concentration was found to be 500 mg/l for NEM on biomass from the municipal digester, 1 mg/l for PCP, and 500 mg/l for CDNB, both on granular biomass. Granular anaerobic biomass showed recovery even at NEM concentrations of 1000 mg/l.     

Detoxification and partial mineralization of the azo dye mordant orange 1 in a continuous upflow anaerobic sludge-blanket reactor

In batch toxicity assays, azo dye compounds were found to be many times more toxic than their cleavage products (aromatic amines) towards methanogenic activity in anaerobic granular sludge. Considering the ability of anaerobic microorganisms to reduce azo groups, detoxification of azo compounds towards methanogens can be expected to occur during anaerobic wastewater treatment. In order to test this hypothesis, the anaerobic degradation of one azo dye compound, Mordant orange 1 (MO1), by granular sludge was investigated in three separate continuous upflow anaerobic sludge-blanket reactors. One reactor, receiving no cosubstrate, failed after 50 days presumably because of a lack of reducing equivalents. However, the two reactors receiving either glucose or a volatile fatty acids (acetate, propionate, butyrate) mixture, could eliminate the dye during operation for 217 days. The azo dye was reductively cleaved to less toxic aromatic amines (1,4-phenylenediamine and 5-aminosalicylic acid) making the treatment of MO1 feasible at influent concentrations that were over 25 times higher than their 50% inhibitory concentrations. In the reactor receiving glucose as cosubstrate, 5-aminosalicylic acid could only be detected at trace levels in the effluent after day 189 of operation. Batch biodegradability assays with the sludge sampled from this reactor confirmed the mineralization of 5-aminosalicylic acid to methane. Received: 11 July 1996 / Received revision: 18 September 1996 / Accepted: 18 September 1996     

Performances and microbial features of an aerobic packed-bed biofilm reactor developed to post-treat an olive mill effluent from an anaerobic GAC reactor

Background  

Olive mill wastewater (OMW) is the aqueous effluent of olive oil producing processes. Given its high COD and content of phenols, it has to be decontaminated before being discharged. Anaerobic digestion is one of the most promising treatment process for such an effluent, as it combines high decontamination efficiency with methane production. The large scale anaerobic digestion of OMWs is normally conducted in dispersed-growth reactors, where however are generally achieved unsatisfactory COD removal and methane production yields. The possibility of intensifying the performance of the process using a packed bed biofilm reactor, as anaerobic treatment alternative, was demonstrated. Even in this case, however, a post-treatment step is required to further reduce the COD. In this work, a biological post-treatment, consisting of an aerobic biological "Manville" silica bead-packed bed aerobic reactor, was developed, tested for its ability to complete COD removal from the anaerobic digestion effluents, and characterized biologically through molecular tools.     

Microbial community structure and operational performance of a fluidized bed biofilm reactor treating oil sands process-affected water

This study evaluated the treatment of oil sands process-affected water (OSPW) using a fluidized bed biofilm reactor (FBBR) with granular activated carbon (GAC) as support media. The bioreactor was operated for 120 days at different organic and hydraulic loading rates. The combined GAC adsorption and biodegradation process removed 51% of chemical oxygen demand (COD), 56% of acid-extractable fraction (AEF) and 96% of classical naphthenic acids (NAs) under optimized operational conditions. Bioreactor treatment efficiencies were dependent on the organic loading rate (OLR), and to a lower degree, on the hydraulic loading rate (HLR). Further ultra performance liquid chromatography/high resolution mass spectroscopy (UPLC/HRMS) analysis showed that the removal of classical NAs increased as the carbon number increased. Compared with planktonic bacterial community in OSPW, more diverse microbial structures were found in biofilms colonized on the surface of GAC after 120-day treatment, with various carbon degraders namely Polaromonas jejuensis, Algoriphagus sp., Chelatococcus sp. and Methylobacterium fujisawaense in the GAC-biofilm reactor. The results of this study, therefore, showed that the GAC-biofilm seems to be a promising biological treatment method for OSPW remediation.     

木质纤维素燃料乙醇蒸馏废水的高温厌氧处理及菌群结构分析

【目的】为开发高效的高浓度木质纤维素燃料乙醇蒸馏废水厌氧处理及资源化利用工艺,以活性炭为载体,在实验室规模上对高温厌氧流化床反应器处理木质纤维素燃料乙醇蒸馏废水进行研究。【方法】反应器经65 d梯度驯化后启动,对工艺参数进行一系列优化,并通过基于16S rRNA基因的分子生态学技术分析厌氧污泥中的优势菌群。【结果】实验获得了最优的反应条件和处理效果:厌氧流化床反应器(Anaerobic fluidized bed reactor,AFBR)在温度55±1°C、有机负荷率(OLR)13.8 g COD/(L·d)及水力停留时间(HRT)48 h操作时,COD去除率达到90%以上,同时甲烷产率达到290 mL/g COD;菌群鉴定分析结果显示高温厌氧活性污泥中Clostridia所占比例最大,产甲烷菌属以Methanoculleus和Methanosarcina为主,其它功能菌群主要为Alphaproteobacteria等。【结论】AFBR反应器可高效降解木质纤维素燃料乙醇蒸馏废水并产生生物能源甲烷,其反应体系内微生物种类丰富。     

Performance of the anaerobic baffled reactor under steady-state and shock loading conditions

The anaerobic baffled reactor (ABR) contains a granulated, mixed anaerobic culture segregated into compartments. Operation of four reactors under a range of hydraulic retention times showed that this novel reactor design offers highly efficient performance in the conversion of carbon in the feed stream to methane and carbon dioxide. The design parameter varied was the number of compartments. COD removal at 20 h retention time was routinely over 95% in all reactors, with low washout of biomass. Very high specific reaction rates were achievable (although with a loss of efficiency) at low biomass concentrations and high loading rates. In order to optimize volumetric reaction rates, a tradeoff has to be made between high biomass concentration, granule size, and the resulting mass transfer limitations. Formate is shown to be an important intermediate in the process under conditions of high loading.     

Granule development and performance in sucrose fed anaerobic baffled reactors

Two 90 L anaerobic baffled reactors were used to study the granulation of sludge and the effect of the organic loading rate and NaHCO3/COD ratios on reactor performance. Furthermore, it was determined whether an anaerobic baffled reactor would promote phase separation and if additive of bentonite or granular active carbon was capable of enhancing granule formation. In order to minimize feed variations, and have a totally biodegradable substrate, a synthetic sucrose substrate was used. Granulation was achieved in both reactors within 75 days. However, the granules from the granular active carbon amended reactor appeared earlier and were larger and more compact. The reactors were maintained at a hydraulic retention time of 20 h during performance study stage. The results showed that when organic loading rate were changed from 2.15 to 6.29 kg COD m(-3)day(-1), chemical oxygen demand (COD) removal was not decreased (91-93%), but a slight increase in effluent COD was observed. It was found that the COD removals were generally good (87-92%) and had not obviously change with the decreasing NaHCO3/COD ratios. From the bacterial distribution and the concentration of volatile fatty acids in four compartments, it was concluded that a separation of phases occurred within the anaerobic baffled reactors.     

Evaluation of straw as a biofilm carrier in the methanogenic stage of two-stage anaerobic digestion of crop residues

Straw was evaluated as a biofilm carrier in the methanogenic stage of the two-stage anaerobic digestion of crop residues. Three reactor configurations were studied, a straw-packed-bed reactor, a glass packed-bed reactor and a reactor containing suspended plastic carriers. The reactor with the packed straw bed showed the best results. It had the highest methane production, 5.4 11(-1) d(-1), and the chemical oxygen demand (COD) removal ranged from 73-50% at organic loading rates from 2.4-25 g COD l(-1) d(-1). The degradation pattern of volatile fatty acids showed that the degradation of propionate and longer-chain fatty acids was limiting at higher organic loading rates. A stable effluent pH showed that the packed-bed reactors had good ability to withstand the variations in load and volatile fatty acid concentrations that can occur in the two-stage process. The conclusion is that straw would work very well in the intended application. A further benefit is that straw is a common agricultural waste product and requires only limited resources concerning handling and cost.     

A hybrid anaerobic solid-liquid bioreactor for food waste digestion

A hybrid anaerobic solid-liquid (HASL) bioreactor is an enhanced two-phase anaerobic system, that consists of a solid waste reactor as the acidification reactor and a wastewater reactor, i.e. an upflow anaerobic sludge blanket (UASB) reactor as the methanogenic reactor. Food waste digestion in HASL bioreactors with pre-acidification and HASL operation stages was investigated in two separate runs. After 8 days of pre-acidification in Run A and 4 days in Run B, total volatile fatty acid (TVFA) and chemical oxygen demand (COD) concentrations in the leachates of both acidification reactors were similar. During HASL operation stage, TVFA and COD removal in the methanogenic phase were 77–100% and 75–95%, respectively. Some 99% of the total methane generated was from the methanogenic phase with a content of 68–70% methane. At the end of operation, about 59–60% of the added volatile solids (VS) were removed with a methane yield of 0.25 l g^–1 VS.     

Impact of ozonation pre-treatment of oil sands process-affected water on the operational performance of a GAC-fluidized bed biofilm reactor

Treatment of oil sands process-affected water (OSPW) using biodegradation has the potential to be an environmentally sound approach for tailings water reclamation. This process is both economical and efficient, however, the recalcitrance of some OSPW constituents, such as naphthenic acids (NAs), require the pre-treatment of raw OSPW to improve its biodegradability. This study evaluated the treatment of OSPW using ozonation followed by fluidized bed biofilm reactor (FBBR) using granular activated carbon (GAC). Different organic and hydraulic loading rates were applied to investigate the performance of the bioreactor over 120 days. It was shown that ozonation improved the adsorption capacity of GAC for OSPW and improved biodegradation by reducing NAs cyclicity. Bioreactor treatment efficiencies were dependent on the organic loading rate (OLR), and to a lesser degree, the hydraulic loading rate (HLR). The combined ozonation, GAC adsorption, and biodegradation process removed 62 % of chemical oxygen demand (COD), 88 % of acid-extractable fraction (AEF) and 99.9 % of NAs under optimized operational conditions. Compared with a planktonic bacterial community in raw and ozonated OSPW, more diverse microbial communities were found in biofilms colonized on the surface of GAC after 120 days, with various carbon degraders found in the bioreactor including Burkholderia multivorans, Polaromonas jejuensis and Roseomonas sp.     

Organic Matter Degradation Kinetics in an Anaerobic Thermophilic Fluidised Bed Bioreactor

This paper describes the thermophilic anaerobic biodegradation of wine distillery wastewater (vinasses) in a laboratory fluidised bed reactor (AFB) with a porous support medium. The experimental protocol was defined to examine the effect of increasing organic loading rate on the efficiency of AFB and to report on its steady-state performance. Moreover, in order to evaluate treatment efficiency and to investigate fermentation kinetics in an AFB reactor, experimental data were used to estimate the ‘active biomass’ concentration using an autocatalytic kinetic model proposed in this paper, since viable biomass in AFB reactors is very difficult to measure experimentally. The AFB reactor was subjected to a program of steady-state operation over a range of hydraulic retention time (HRTs) of 2.5–0.37 days and organic loading rate (OLRs) up to 5.88 kgCOD/m³/day in order to evaluate its treatment capacity. The AFB reactor was initially operated with organic loading rate of 5.88 kgCOD/m³/day and HRT of 2.5 days. The chemical oxygen demand (COD) removal efficiency was found to be 96.5% in the reactor while the methane content of biogas produced in the digester reached 1.08 m³/m³digester/day. Over 94 days operating period, an OLR of 32 kgCOD/m³/day at a food-to-micro-organisms (F:M) ratio of 0.55 kgCOD/kgVS_att/day was achieved with 81.5% COD removal efficiency in the experimental AFB reactor. At this moment, the methane content of biogas produced in the digester reached 9.0 m³/m³digester/day. The proposed kinetic model is able to estimate kinetic constants of the biodegradation process: non-biodegradable substrate (S_nb) and active adhered biomass concentration (X_a). The parameters of the model were obtained by the curve-fitting method to the proposed kinetic model using the COD as substrate of the anaerobic process and assuming a maximum specific μ_max: 0.72 per day. The comparison of the measured concentration of volatile attached solids (VS_att) with the estimated ‘active’ biomass concentration indicated that extremely high ‘active biomass’ concentrations can be maintained in the system because biofilm thickness is limited by the liquid flow rate applied. This is due to the fact that the anaerobic fluidised bed system retains the growth support medium in suspension by drag forces exerted by upflowing wastewater, and the distribution of biomass holdup (in the form of a biofilm) is thus relatively uniform.     

Anaerobic treatment of synthetic medium-strength wastewater using a multistage biofilm reactor

A laboratory-scale multistage anaerobic biofilm reactor of three compartments with a working volume of 54-L was used for treating a synthetic medium-strength wastewater containing molasses as a carbon source at different influent conditions. The start-up period, stability and performance of this reactor were assessed at mesophilic temperature (35 °C). During the start-up period, pH fluctuations were observed because there was no microbial selection or zoning, but as the experiment progressed, results showed that phase separation had occurred inside the reactor. COD removal percentages of 91.6, 91.6, 90.0 and 88.3 were achieved at organic loading rates of 3.0, 4.5, 6.75 and 9.0 kg COD/m³ day, respectively. A decrease in HRT from 24 to 16 h had no effect on COD removal efficiency. When HRT decreased to 8 h, COD removal efficiency was still 84.9%. Recirculation ratios of 0.5 and 1.0 had no effect on COD removal but other factors such as the volatile fatty acid (VFA) content were affected. The effect of toxic shock was also investigated and results showed that the main advantage of using this bioreactor lies in its compartmentalized structure.