Effect of the hydraulic retention time on the anaerobic biofilm reactor efficiency applied to screened cattle waste treatment

Summary It was found that the increase of the hydraulic retention time improved the organic matter removal and the conversion of organic to ammonia nitrogen. Methane concentration in the biogas was not affected by the hydraulic retention time.The reactor in operation during one year was not clogged.     

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.     

Kinetic modelling and performance prediction of a hybrid anaerobic baffled reactor treating synthetic wastewater at mesophilic temperature

A modelling study on the anaerobic digestion process of a synthetic medium-strength wastewater containing molasses as a carbon source was carried out at different influent conditions. The digestion was conducted in a laboratory-scale hybrid anaerobic baffled reactor with three compartments and a working volume of 54 L, which operated at mesophilic temperature (35 °C). Two different kinetic models (one model was based on completely stirred tank reactors (CSTR) in series and the other an axial diffusion or dispersion model typical of deviations of plug-flow reactors), were assessed and compared to simulate the organic matter removal or fractional conversion. The kinetic constant (k) obtained by using the CSTR in series model was 0.60 ± 0.07 h⁻¹, while the kinetic parameter achieved with the dispersion model was 0.67 ± 0.06 h⁻¹, the dispersion coefficient (D) being 46. The flow pattern observed in the reactor studied was intermediate between plug-flow and CSTR in series systems, although the plug-flow system was somewhat predominant. The dispersion model allowed for a better fit of the experimental results of fractional conversions with deviations lower than 8% between the experimental and theoretical values. By contrast, the CSTR in series model predicted the behaviour of the reactor somewhat less accurately showing deviations lower than 10% between the experimental and theoretical values of the fractional conversion.     

Effect of hydraulic retention time on inorganic nutrient recovery and biodegradable organics removal in a biofilm reactor treating plant biomass leachate

A fixed-film (biofilm) reactor was designed and its performance was determined at various retention times. The goal was to find the optimal retention time for recycling plant nutrients in an advanced life support system, to minimize the size, mass, and volume (hold-up) of a production model. The prototype reactor was tested with aqueous leachate from wheat crop residue at 24, 12, 6, and 3 h hydraulic retention times (HRTs). Biochemical oxygen demand (BOD), nitrates and other plant nutrients, carbohydrates, total phenolics, and microbial counts were monitored to characterize reactor performance. BOD removal decreased significantly from 92% at the 24 h HRT to 73% at 3 h. Removal of phenolics was 62% at the 24 h retention time, but 37% at 3 h. Dissolved oxygen concentrations, nitric acid consumption, and calcium and magnesium removals were also affected by HRT. Carbohydrate removals, carbon dioxide (CO2) productions, denitrification, potassium concentrations, and microbial counts were not affected by different retention times. A 6 h HRT will be used in future studies to determine the suitability of the bioreactor effluent for hydroponic plant production.     

Effects of nitrobenzene concentration and hydraulic retention time on the treatment of nitrobenzene in sequential anaerobic baffled reactor (ABR)/continuously stirred tank reactor (CSTR) system

The effects of increasing nitrobenzene (NB) concentrations and hydraulic retention times (HRT) on the treatment of NB were investigated in a sequential anaerobic baffled reactor (ABR)/aerobic completely stirred tank reactor (CSTR) system. In the first step of the study, the maximum COD removal efficiencies were found as 88% and 92% at NB concentrations varying between 30 mg L^?1 and 210 mg L^?1 in ABR. The minimum COD removal efficiency was 79% at a NB concentration of 700 mg L^?1. The removal efficiency of NB was nearly 100% for all NB concentrations in the ABR reactor. The methane gas production and the methane gas percentage remained stable (1500 mL day^?1 and 48–50%, respectively) as the NB concentration was increased from 30 to 210 mg L^?1. In the second step of the study it was found that as the HRT decreased from 10.38 days to 2.5 days the COD removal efficiencies decreased slightly from 94% to 92% in the ABR. For maximum COD and NB removal efficiencies the optimum HRT was found as 2.5 days in the ABR. The total COD removal efficiency was 95% in sequential anaerobic (ABR)/aerobic (CSTR) reactor system at a minimum HRT of 1 day. When the HRT was decreased from 10.38 days to 1 day, the methane percentage decreased from 42% to 29% in an ABR reactor treating 100 mg L^?1 NB. Nitrobenzene was reduced to aniline under anaerobic conditions while aniline was mineralized to catechol with meta cleavage under aerobic conditions.     

Novel mathematical modeling on pilot-scale of plug-flow aerated submerged biofilm reactor for dissolved organic matter and nitrogen removal

The investigation aimed to present mathematical models for describing the dynamic behavior of the dissolved organic matter removal and nitrification in the Aerated Submerged Bio-Film (ASBF) for a plug-flow reactor. Based on the experimental data from the batch system of the ASBF pilot plant, mathematical models for the plug-flow reactor were developed to predict dissolved organic matter and ammonia nitrogen removal rates as a function of heterotrophic and autotrophic bacteria populations, dissolved organic matter concentrations, ammonia nitrogen concentrations, dissolved oxygen concentrations, and temperature. The mathematical models for dissolved organic matter and ammonia nitrogen removal in ASBF include two differential equations reflecting heterotrophic and autotrophic bacteria populations, and a number of kinetic parameters. Consequently, the results present a better insight into the dynamics behavior of heterotrophic and autotrophic biofilm growth and their practical application to wastewater for dissolved organic matter and ammonia nitrogen removal process. The mathematical model for ammonia nitrogen and dissolved organic matter removals present good results for the plug-flow reactor.     

Ultrasonic sludge disintegration for enhanced methane production in anaerobic digestion: effects of sludge hydrolysis efficiency and hydraulic retention time

Hydrolysis of waste activated sludge (WAS) has been regarded as the rate limiting step of anaerobic sludge digestion. Therefore, in this study, the effect of ultrasound and hydraulic residence time during sludge hydrolysis was investigated with the goal of enhancing methane production from anaerobic digestion (AD). WAS was ultrasonically disintegrated for hydrolysis, and it was semi-continuously fed to an anaerobic digesters at various hydraulic retention times (HRTs). The results of these experiments showed that the solids and chemical oxygen demand (COD) removal efficiencies when using ultrasonically disintegrated sludge were higher during AD than the control sludge. The longer the HRT, the higher the removal efficiencies of solids and COD, while methane production increased with lower HRT. Sludge with 30% hydrolysis produced 7 × more methane production than the control sludge. The highest methane yields were 0.350 m(3)/kg volatile solids (VS)(add) and 0.301 m(3)/kg COD(con) for 16 and 30% hydrolyzed sludge, respectively. In addition, we found that excess ultrasound irradiation may inhibit AD since the 50% hydrolyzed sludge produced lower methane yields than 16 and 30% hydrolyzed sludge.     

Effects of internal recycling time mode and hydraulic retention time on biological nitrogen and phosphorus removal in a sequencing anoxic/anaerobic membrane bioreactor process

This study investigated the effects of internal recycling time mode and hydraulic retention time (HRT) on nutrient removal in the sequencing anoxic/anaerobic membrane bioreactor process. Denitrification and phosphorus release were reciprocally dependent on the anoxic/anaerobic time ratio (Ax/An). As Ax/An increased, nitrogen removal rate increased but phosphorus removal rate decreased. The increasing Ax/An provided the longer denitrification period so that the organic substrate were consumed more for denitrification rather than phosphorus release in the limited condition of readily biodegradable substrate. Decreasing HRT increased both nitrogen and phosphorus removal efficiency because as HRT decreased, food-to-microorganism loading ratio increased and thus enhanced the biological capacity and activity of denitrifying bacteria. This could be verified from the observation mixed liquor suspended solids concentration and specific denitrification rate. The change of Ax/An and HRT affected phosphorus removal more than nitrogen removal due to the limitation of favourable carbon source for phosphorus accumulating organisms.     

处理印染废水的厌氧折流板反应器中的微生物种群组成及分布规律

设计出一个由12个隔室组成的厌氧折流板反应器(ABR),并将其应用于高浓度、高色度的印染废水生物处理,取得了良好效果。研究着重考察该反应器在处理印染废水过程中不同隔室的微生物种群构成,并分析与印染废水处理效率密切相关的具有脱色功能和苯胺降解功能的两类细菌的分布规律。结果表明,在处理印染废水的ABR反应器中,可培养的优势菌群以芽孢杆菌属(Bacillus)、不动杆菌属(Acinetobacter)、丛毛单胞菌属(Comamonas)、假单胞菌属(Pseudomonas)和水螺菌属(Aquaspirillum)为主,且在ABR的前段、中段及后段隔室中不同种类的优势菌群存在数量差异;好氧及兼性厌氧优势菌群的数量随着废水在ABR隔室中的折流前进而逐渐减少;厌氧微生物的数量变化规律则是先增多,后减少;产甲烷活性在前段隔室中相对较低,后段隔室则相对较高。脱色菌在ABR的前段隔室中分布相对较多,后段隔室中分布相对较少;苯胺降解菌则呈现出在前段隔室中分布相对较少,后段隔室中分布相对较多的规律,这两类功能菌的分布与ABR不同隔室中色度下降、苯胺产生和消减之间密切相关。     

Effect of influent nutrient ratios and hydraulic retention time (HRT) on simultaneous phosphorus and nitrogen removal in a two-sludge sequencing batch reactor process

A laboratory-scale anaerobic–anoxic/nitrification sequencing batch reactor (A₂N-SBR) fed with domestic wastewater was operated to examine the effect of varying ratios of influent COD/P, COD/TN and TN/P on the nutrient removal. With the increased COD/P, the phosphorus removals exhibited an upward trend. The influent TN/P ratios had a positive linear correlation with the phosphorus removal efficiencies, mainly because nitrates act as electron acceptors for the phosphorus uptake in the A₂N-SBR. Moreover, it was found that lower COD/TN ratio, e.g. 3.5, did not significantly weaken the phosphorus removal, though the nitrogen removal first decreased greatly. The optimal phosphorus and nitrogen removals of 94% and 91%, respectively were achieved with influent COD/P and COD/TN ratios of 19.9 and 9.9, respectively. Additionally, a real-time control strategy for A₂N-SBR can be undertaken based on some characteristic points of pH, redox potential (ORP) and dissolved oxygen (DO) profiles in order to obtain the optimum hydraulic retention time (HRT) and improve the operating reliability.     

A tracer study for assessing the interactions between hydraulic retention time and transport processes in a wetland system for nutrient removal

In this study, a new-generation subsurface upflow wetland (SUW) system packed with the unique sorption media was introduced for nutrient removal. To explore the interface between hydraulic and environmental performance, a tracer study was carried out in concert with a transport model to collectively provide hydraulic retention time (7.1 days) and compelling evidence of pollutant fate and transport processes. Research findings indicate that our pollution-control media demonstrate smooth nutrient removal efficiencies across different sampling port locations given the appropriate size distribution conversant with the anticipated hydraulic patterns and layered structure among the sorption media components. The sizable capacity for nutrient removal in this bioprocess confirms that SUW is a promising substitute for an extension of traditional on-site wastewater treatment systems.     

Enhancing digestion efficiency of POME in anaerobic sequencing batch reactor with ozonation pretreatment and cycle time reduction

Ozonation pretreatment was applied to palm oil mill effluent (POME) prior to anaerobic digestion using the anaerobic sequencing batch reactor (ASBR). Ozonation increased BOD/COD by 37.9% with a COD loss of only 3.3%. At organic loads of 6.48-12.96 kg COD/m³/d, feeding with non-ozonated POME caused a system failure. The ozonated POME gave significantly higher TCOD removal at loadings 6.52 and 9.04 kg COD/m³/d but failed to sustain the operation at loading 11.67 kg COD/m³/d. Effects of cycle time (CT) and hydraulic retention time (HRT) were determined using quadratic regression model. The generated response surface and contour plot showed that at this high load conditions (6.52-11.67 kg COD/m³/d), longer HRT and shorter CT gave the ASBR higher organic removal efficiency and methane yield. The model was able to satisfactorily describe the relationship of these two key operating parameters.     

The kinetics of the removal of nitrogen and organic matter from parboiled rice effluent by cyanobacteria in a stirred batch reactor

The aim of this research was to evaluate the kinetics of the removal of nitrogen and organic matter from parboiled rice effluent by the cyanobacteria Aphanothece microscopica Nägeli. From the results obtained, it was verified that maximum efficiency for the removal of organic matter expressed as COD and total nitrogen (N-TKN) occurred after 15 h of cultivation, being 83.44% and 72.74, respectively. The scale-up process indicated that the volume of the estimated reactor would be 100.2 m³, containing parboiled rice effluent and biomass.     

Biomass retention in a glucose acidifying anaerobic gas-lift reactor: isolation of the organism responsible for granule formation

Summary A study was undertaken of the microbial composition of aggregates from an acidifying anaerobic gas-lift reactor. For this purpose a simple 100 ml anaerobic gas lift reactor was developed. It was found that the predominant organism in the aggregates was Selenomonas ruminantium. Both, microscopical observations and a newly developed enumeration technique led to the conclusion that the mixed granules consisted mainly of this organism. Grown in pure culture, S. ruminantium was capable of forming aggregates. These aggregates resembled the mixed aggregates both macro- as well as microscopically. Furthermore the fermentation pattern of this pure aggregated culture was similar to that of a mixed aggregated culture.     

Ethanol and toluene removal in a horizontal-flow anaerobic immobilized biomass reactor in the presence of sulfate

In this study it is reported the operation of a horizontal-flow anaerobic immobilized biomass (HAIB) reactor under sulfate-reducing condition which was also exposed to different amounts of ethanol and toluene. The system was inoculated with sludge taken from up-flow anaerobic sludge blanket (UASB) reactors treating refuses from a poultry slaughterhouse. The HAIB reactor comprised of an immobilized biomass on polyurethane foam and ferrous and sodium sulfate solutions were used (91 and 550 mg/L, respectively), to promote a sulfate-reducing environment. Toluene was added at an initial concentration of 2.0 mg/L followed by an increased range of different amendments (5, 7, and 9 mg/L). Ethanol was added at an initial concentration of 170 mg/L followed by an increased range of 960 mg/L. The reactor was operated at 30(+/-2) degrees C with hydraulic detention time of 12 h. Organic matter removal efficiency was close to 90% with a maximum toluene degradation rate of 0.06 mg(toluene)/mg(vss)/d. Sulfate reduction was close to 99.9% for all-nutritional amendments. Biofilm microscopic characterization revealed a diversity of microbial morphologies and DGGE-profiling showed a variation of bacterial and sulfate reducing bacteria (SRB) populations, which were significantly associated with toluene amendments. Diversity of archaea remained unaltered during the different phases of this experiment. Thus, this study demonstrates that compact units of HAIB reactors, under sulfate reducing conditions, are a potential alternative for in situ aromatics bioremediation.     

Evaluation of the microbial diversity in a horizontal-flow anaerobic immobilized biomass reactor treating linear alkylbenzene sulfonate

The purpose of this work was to assess the degradation of linear alkylbenzene sulfonate (LAS) in a horizontal-flow anaerobic immobilized biomass (HAIB) reactor. The reactor was filled with polyurethane foam where the sludge from a sanitary sewage treatment was immobilized. The hydraulic detention time (HDT) used in the experiments was of 12 h. The reactor was fed with synthetic substrate (410 mg l⁻¹ of meat extract, 115 mg l⁻¹ of starch, 80 mg l⁻¹ of saccharose, 320 mg l⁻¹ of sodium bicarbonate and 5 ml l⁻¹ of salt solution) in the following stages of operation: SI—synthetic substrate, SII—synthetic substrate with 7 mg l⁻¹ of LAS, SIII—synthetic substrate with 14 mg l⁻¹ of LAS and SIV—synthetic substrate containing yeast extract (substituting meat extract) and 14 mg l⁻¹ of LAS, without starch. At the end of the experiment (313 days) a degradation of ∼35% of LAS was achieved. The higher the concentration of LAS, the greater the amount of foam for its adsorption. This is necessary because the isotherm of LAS adsorption in the foam is linear for the studied concentrations (2 to 50 mg l⁻¹). Microscopic analyses of the biofilm revealed diverse microbial morphologies, while Denaturing Gradient Gel Eletrophoresis (DGGE) profiling showed variations in the population of total bacteria and sulphate-reducing bacteria (SRB). The 16S rRNA gene sequencing and phylogenetic analyses revealed that the members of the order Clostridiales were the major components of the bacterial community in the last reactor operation step.