Stability of a percolating anaerobic downflow fixed film reactor under overloading conditions

Summary An anaerobic downflow fixed film (DSFF) reactor was used to treat cheese whey. The reactor was initially operated flooded (DSFF mode) and then the liquid level reduced by 67% (ATF mode); thus, the packing support was completely submerged and one third submerged respectively. The partly submerged anaerobic culture had higher gas production, and was more resistant to general and localized high VFA levels; methanogenic bacteria were acclimated to VFA levels as high as 3000 mg/l of propionate and 1600 mg/l of acetate (pH near neutrality) whilst the reactor remained stable.     

Mixing characteristics and startup of anaerobic downflow stationary fixed film (DSFF) reactors

Tests to determine the mixing characteristics of the anaerobic downflow stationary fixed film (DSFF) reactor during startup showed that mixing characteristics affected performance. Different mixing profiles were obtained by keeping the same flow distribution system and by varying the number of clay channels (1, 4, and 25) in the DSFF reactors (2-32 L). Results with a clean bed reactor indicated a plug flow pattern with a relatively large extent of dispersion. Recirculation dramatically improved the mixing and the residence time distribution (RTD) changed to that of the completely mixed type. Multiple-channel reactors exhibited a dead space of ca. 12% of the total volume, likely a result of a less than optimally designed flow distributor. A startup period of 90 days was necessary to achieve a maximum loading rate of between 10 and 15 kg COD/m(3) day, a volumetric methane production rate of up to 3 m(3) (STP)/m(3) day and a COD reduction efficiency of up to 90%. For the first 50 days of operation, the difference in achievable volumetric loading rate and volumetric methane production rate was only related to the surface-to-volume ratio of the reactors and was not affected by the number of channels present. After 90 days, the bacterial growth on the support material was sufficient to dramatically increase the amount of dead space in the reactors, especially in multiple-channel reactors (up to 55% of their volume). As a result, the performance of these reactors deteriorated and overloading characteristics were observed. Other results showed that biogas production alone was not sufficient to improve reactor mixing and that little or no shortcircuiting or channelling occurred. Furthermore, the nonmethanogenic bacterial activity in the liquid phase was not affected by the degree of mixing but acetoclastic methanogenic and hydrogenophilic methanogenic activity in the liquid phase were reduced as the fluid flow pattern in the reactor improved.     

Startup of anaerobic downflow stationary fixed film (DSFF) reactors

One of the serious problems limiting the application of full-scale anaerobic fixed film processes is reactor startup. To better understand startup, studies with downflow stationary fixed film (DSFF) reactors were conducted to characterize the effects of influent concentration, support material, and surface-to-volume ratio on biofilm development and overall reactor performance. Materials with roughened surfaces gave the best startup performance and as expected increased surface area in the reactors led to more rapid increases in loading rates and higher ultimate loadings. Soluble influent COD concentrations between 5 x 10(3) and 2 x 10(4) mg/L influenced the rate of biofilm development. Lower COD concentrations resulted in faster development of the biofilm, even though ultimate loadings were not necessarily achieved as rapidly as in reactors fed higher strength wastes. No decrease in specific activity of the biofilms in each reactor was observed as the thickness of the biofilms increased to their maximum value at the ultimate loadings. The operation of reactors fed lower strength wastes was more stable than reactors receiving higher strength feeds at comparable loadings. Biofilm yield and activity, COD removals, suspended growth and activity, and other system parameters are discussed.     

Treatment of fish processing waste using the downflow stationary fixed film (DSFF) reactor

Summary The DSFF reactor has been shown to be capable of treating a wide variety of wastes. In this study, a high protein fish processing waste was treated at several influent concentrations. Chemical oxygen demand (COD) removal efficiencies of up to 90% were achieved at loading rates in excess of 10 kg COD/m³/day.     

Changes in microbial ecology in an anaerobic reactor

This study examined the behaviour of the microbial population in an anaerobic reactor, in terms of changes in numbers of total bacterial community, autofluorescent methanogens, non-methanogens and morphology of the autofluorescent methanogens, using epifluorescence microscopy and microbiological enumeration techniques. A laboratory-scale, continuous flow-completely mixed anaerobic reactor, coupled with a conventional gravity settling tank and a continuous recycling system, was operated at an HRT range between 24 and 12 h, using dairy wastewater as the substrate. The numbers of the total bacterial community and autofluorescent methanogens both decreased during start-up. Also, the proportion of the number of autofluorescent methanogens in the total bacterial community varied from 5% to 16% during operation. In particular, the activity of the methane-forming bacteria decreased significantly at HRTs of 16 and 12 h. A membrane module, instead of a conventional settling tank, would obviously have been a more effective method if recycling were required in the anaerobic treatment system.     

Biomethanation of cheese whey using anaerobic upflow fixed film reactor

Performance of anaerobic upflow fixed film reactors for biomethanation of high-strength cheese whey using different support material such as charcoal, gravel, brick pieces, PVC pieces and pumice stones at 37°C has been studied. Among them the charcoal fixed film reactor showed the best performance when operated at 2 d hydraulic retention times (HRT), achieving maximum COD removal of 81% (COD influent=70 g/l) and improved total gas production (6.7 l/d/l digester) with high methane content (72%).     

Effect of hydraulic and organic overloading on thermophilic downflow stationary fixed film (DSFF) reactor

Summary Tests to determine the stability of thermophilic DSFF reactors using bean blanching waste as substrate, showed them to become unstable at 30 to 40 kg/m³/day whether hydraulically or organically overloaded. This level is significantly less than mesophilic reactors could handle (90 kg/m³/day).     

Stability of a downflow anaerobic fixed-film reactor to feed change

Summary A stepped-loading start-up regime utilising volatile fatty acids as carbon and energy sources was applied to a downflow anaerobic fixed-film reactor operated at 37°C. A steadystate was attained with over 90% COD reduction at an organic loading rate of 6.1 Kg COD/m³·day. A complex wastewater coming from a citrus processing plant was then used to test the feasibility of feeding changes as well as the stability of the reactor performance. A final COD reduction of 60% was achieved with hydraulic retention times down to 1.5 days.     

The influence of different substrate pH values on the performance of a downflow anaerobic fixed bed reactor treating a petrochemical effluent

Summary Neutralizing requirements for the anaerobic treatment of an acidic petrochemical effluent in a downflow anaerobic fixed bed reactor were examined. Neutralization (pH 6.0 with NaOH) of the effluent prior to digestion resulted in a Na⁺ concentration of over 3 g/l which was detrimental. Decreasing the Na⁺ concentration and subsequent replacement of NaOH by a mixture of Ca(OH)₂, NaOH and KOH resulted in an increase in reactor performance. The addition of different alkalines resulted in the best loading rates thusfar applied in the anaerobic treatment of this petrochemical effluent. During the final stages of this study, the effluent (pH 3.95) was treated at a loading rate of 10.37 kg COD/m³. d (HRT=1.35 d) with more than 94% fatty acid removal.     

Effect of effluent recirculation on start-up and steady state operation of the downflow stationary fixed film (DSFF) reactor

Biotechnology Letters - In this study, the effect of effluent recirculation on the start-up and steady state operation of the DSFF is reported. Recirculation had little effect on start-up; however,...     

Use of fixed film and CSTR reactor for anaerobic treatment of stillage of wood hydrolysate

Summary The application of fixed film and CSTR reactor-systems for the treatment of stillage from wood hydrolysates was studied in laboratory units at 35° and 55°C. Organic loads of 10.7 (10) gCOD/l/d with COD-reduction of 86.6 (84.4)% and a biogas production rate of 400 (380) ml/ gCOD with 63 (62) % methane were feasible using fixed film systems, whereas organic loads with CSTR reactor-systems were only 2.4 gCOD/l/day.     

Mixing characteristics of fixed film anaerobic reactors

Summary Since the mixing characteristics of anaerobic reactors would appear to have an effect on their operational performance, lithium tracer studies were made on two different digester types; the upflow sludge blanket and the expanded bed reactors. The mixing characteristics of both types of reactor, defined by this technique, were found to be of the intermediate type with a bias towards good mixing.     

Effect of reactor height on mixing characteristics and performance of the anaerobic downflow stationary fixed-film (DSFF) reactor

Three anaerobic downflow stationary fixed-film (DSFF) reactors using multiple vertical clay channels of different heights (31, 92 and 183 cm) and treating bean blanching waste showed improved performance and mixing characteristics with increased reactor height. A start-up period of 100 days was necessary to achieve the best performance in terms of loading rate (up to 9.5 kg Chemical Oxygen Demand (COD) m^?3 d^?1) and methane production rate (up to 2.7 m³ m^?3 d^?1). During this period, differences in performance could only be related to the surface-to-volume ratio. At steady-state, mixing analysis indicated that the reactors deviated from the perfect-mixed pattern. Some dead space and shortcircuiting occurred. The amount of dead space due to biomass accumulation decreased as the reactor height increased (up to 44% for the shortest reactor). The COD removal efficiency was dependent on loading rate, decreasing from 90% at a loading rate of 1.0 kg COD m^?3 d^?1 to 75% at 7.0 kg COD m^?3 d^?1. However, the effect was more pronounced in the shortest reactor than in the tallest one. The improvement in mixing characteristics in the tallest reactor could be related to the higher liquid velocity inside channels which in turn permitted better support utilization and concomitant better COD removal. Data also suggest that it may be preferable to scale-up vertically rather than horizontally in order to maximize the liquid velocity in the channels.     

Perchlorate reduction by a mixed culture in an up-flow anaerobic fixed bed reactor

Wolinella succinogenes HAP-1 is a Gram-negative microaerophile which reduces perchlorate to chloride by the proposed pathway ClO₄ to ClO₃ to ClO₂ to Cl + O₂. A cost-effective perchlorate treatment process has been established using a consortium of facultative anaerobic organisms and W. succinogenes HAP-1. The mixed anaerobic bacterial culture containing W. succinogenes HAP-1 was examined for the ability to form a biofilm capable of perchlorate reduction. An up-flow anaerobic fixed bed reactor (UAFBR) was packed with diatomaceous earth pellets and operated at residence times of 1.17 and 0.46 h to insure a viable biofilm had attached to the diatomaceous earth pellets. Reduction rates of perchlorate to chloride in the UAFBR could be maintained at 1 g of perchlorate reduced h⁻¹ L⁻¹. Studies with the same bacterial consortium in continuously stirred tank reactors (CSTR) generally reduced 0.5–0.7 g of perchlorate h⁻¹. Viable cell counts were performed periodically on the diatomaceous earth pellets and demonstrated that the W. succinogenes HAP-1 population was maintained at 28–47% of the total microbial population. Scanning electron micrographs demonstrated that the external and internal surfaces of the diatomaceous pellets were densely colonized with microbial cells of multiple cell types. This is the first report of an anaerobic mixed culture forming a biofilm capable of perchlorate reduction. Received 22 May 1997/ Accepted in revised form 07 January 1998     

Continuous vs slug loading of downflow stationary fixed film reactors digesting piggery waste

Downflow stationary fixed film reactors successfully digested piggery waste at retention times down to 2.6 days either loaded continuously or once-a-day. Daily methane production rates of up to 2.6 m³/m³ were recorded for both loading methods. The rate for the slug loaded reactor peaked within 2–6 hours after being loaded.     

Proposed pathways for the reduction of a reactive azo dye in an anaerobic fixed bed reactor

Some process has been proposed for azo dye degradation and anaerobic bioreactors are one of them, since for their reduction, the dye has to be the electron acceptor. An anaerobic fixed bed bioreactor packed with activated carbon (AC) is proposed to degradate the Reactive Red 272 azo dye. In the present paper a dye degradation mechanism in an anaerobic environment is explained. It is very important to consider the interaction dye-microorganism-AC, because the groups in the AC surface take part in the reaction besides being an excellent carrier for microorganism and an adsorbent for the dye. The aromatic compounds produced in the dye reduction are partially degraded as a function of inlet dye concentration and reactor residence time. In anaerobic environment the aromatic compounds are decomposed through hydroxylation, carboxylation and redox reactions, due to enzymatic reactions.     

Comparison of startup and anaerobic wastewater treatment in UASB, hybrid and baffled reactor

An experimental study was carried out to compare the performance of selected anaerobic high rate reactors operated simultaneously at 37?°C. The three reactors, namely upflow anaerobic sludge bed reactor (UASB), hybrid of UASB reactor and anaerobic filter (anaerobic hybrid reactor – AHR) and anaerobic baffled reactor (ABR), were inoculated with the anaerobic digested sludge from municipal wastewater treatment plant and tested with synthetic wastewater. This wastewater contained sodium acetate and glucose with balanced nutrients and trace elements (COD 6000?mg?·?l^?1). Organic loading rate (B _v ) was increased gradually from an initial 0.5?kg?·?m^?3?·?d^?1 to 15?kg?·?m^?3?·?d^?1 in all the reactors. From the comparison of the reactors' performance, the lowest biomass wash-out resulted from ABR. In the UASB, significant biomass wash-out was observed at the B _v 6?kg?·?m^?3?·?d^?1, and in the AHR at the B _v 12?kg?·?m^?3?·?d^?1. The demand of sodium bicarbonate for pH maintenance in ABR was two times higher as for UASB and AHR. The efficiency of COD removal was comparable for all three reactors – 80–90%. A faster biomass granulation was observed in the ABR than in the other two reactors. This fact is explained by the kinetic selection of filamentous bacteria of the Methanotrix sp. under a high (over 1.5?g?·?l^?1) acetate concentration.     

固定载体卧式厌氧反应器处理糖蜜废水的快速启动

为高效处理高浓度有机废水而设计了固定载体卧式厌氧反应器R1和R2, 它是厌氧折流板反应器(ABR)的改进, 以活性炭纤维作为生物膜载体固定并充当反应器的折流板, 在实验室规模上对R1和R2处理糖蜜废水进行快速启动运行。HRT和ORL是影响R1和R2稳定高效运行及启动的2个重要工艺参数。实验证明: HRT为2 d时, 反应器运行最佳。在第30天时, R1的COD去除率达到84.88%, R2达到81.72%。随着进水ORL由1.25 kg/(m3·d)提升到10 kg/(m3·d), 沼气容积产气率由0.35 L/(L·d)逐渐增加到4.98 L/(L·d)。进水pH值为3.9?4.5之间, 整个启动运行过程中, 未调节pH值, R1和R2的出水pH值均在6.7?7.6之间, 2个反应器均有较强的抗酸能力, R1的pH波动更为平缓。在整个实验过程中, 污泥流失量小, 没有发生堵塞现象, 在处理酸性高浓度有机废水时, 2个反应器均表现出较强的抗负荷冲击能力。     

Growth characteristic of anaerobic ammonium-oxidizing bacteria in an anaerobic biological filtrated reactor

The doubling time of anaerobic ammonium-oxidizing (anammox) bacteria in an anaerobic biological filtrated (ABF) reactor was determined. Fluorescence in situ hybridization analysis was used to detect and count anammox bacteria cells in anammox sludge. As a result, the populations of anammox bacteria at 14th and 21st days were 1.1×10⁶ and 1.7×10⁷ cells/ml reactor, respectively. From these results, the doubling time of anammox bacteria was calculated as 1.8 days, and the specific growth rate (μ) was 0.39 day⁻¹. This result indicated that the anammox bacteria have higher growth rate than the reported value (doubling time, 11 days). Furthermore, it was clearly demonstrated that nitrogen conversion rate was proportional to the population of anammox bacteria. Maintaining the ideal environment for the growth of anammox bacteria in the ABF reactor might lead to faster growth. This is the first report of the growth rate of anammox bacteria based on the direct counting of anammox bacteria.