Effect of hydraulic retention time on anaerobic hydrogenesis in CSTR

The objective of this work was to evaluate the production of hydrogen in a continuous system as a function of hydraulic retention time (HRT). The intermediates accumulated and other parameters of pH, oxidation-reduction potential were quantified. The heat treatment (103 degrees C for 24 h) of the compost from a cattle dung composting facility was able to select H2-producing spores; this product was used as a seed for continuous systems. The brewery waste was used as substrate. For the eight runs with combinations of five HRTs and four pHs, the results indicate that at pH=5.5, a maximum H2 production of 47% H2 concentration, 43 ml H2/g COD(added), and 3.1 l H2/l reactor d was achieved at HRT=18 h. Nevertheless, at HRT=18 h, pH 5.5 was also the optimum pH for the maximum H2 production among four pHs evaluated from 5 to 6.5. There was a significant accumulation of volatile acid and alcohols during the entire study.     

Performance of sulfidogenic anaerobic baffled reactor (ABR) treating acidic and zinc-containing wastewater

The applicability of anaerobic baffled reactor (ABR) was investigated for the treatment of acidic (pH 4.5–7.0) wastewater containing sulfate (1000–2000 mg/L) and Zn (65–200 mg/L) at 35 °C. The ABR consisted of four equal stages and lactate was supplemented (COD/SO₄²⁻ = 0.67) as carbon and energy source for sulfate reducing bacteria (SRB). The robustness of the system was studied by decreasing pH and increasing Zn, COD, and sulfate loadings. Sulfate-reduction efficiency quickly increased during the startup period and reached 80% within 45 days. Decreasing feed pH, increasing feed sulfate and Zn concentrations did not adversely affect system performance as sulfate reduction and COD removal efficiencies were within 62–90% and 80–95%, respectively. Although feed pH was steadily decreased from 7.0 to 4.5, effluent pH was always within 6.8–7.5. Over 99% Zn removal was attained throughout the study due to formation of Zn-sulfide precipitate.     

Treatment of low strength complex wastewater using an anaerobic baffled reactor (ABR)

Treatment of a low strength complex wastewater of chemical oxygen demand (COD) around 500mg/L was studied in a 10L capacity laboratory scale anaerobic baffled reactor (ABR). It was operated at hydraulic retention times (HRTs) of 20, 15, 10, 8 and 6h. Corresponding organic loading rates (OLRs) were 0.6, 0.8, 1.2, 1.5 and 2kg COD/m(3)d. At every HRT (or OLR), pseudo steady state (PSS) was achieved. Even at maximum OLR of 2kg COD/m(3)d, COD and biochemical oxygen demand (BOD) removals exceeded 88%. Removal of particulate fraction of organics was found to be greater than soluble fraction. Compartment-wise studies of various parameters revealed that if the OLR was larger, the number of initial compartments played significant role in the removal of organics. The values of volatile fatty acids (VFA) demonstrated that hydrolysis and acidogenesis were the main biochemical activities in the initial few compartments. Based on the tracer studies, dead space in the ABR was found to range from 23% to 34%. The flow pattern in the ABR was classified as intermediate between plug flow and perfectly mixed flows. Observations from scanning electron micrographs (SEM) also suggested that distinct phase separation takes place in an ABR. Study of organic and hydraulic shock loads revealed that ABR was capable of sustaining the type of shock loads generally experienced at a sewage treatment plant (STP).     

Performance of anaerobic baffled reactor (ABR) treating synthetic wastewater containing p-nitrophenol

In this study, the effect of increasing p-nitrophenol (PNP) concentrations on the performance of anaerobic baffled reactor (ABR) (chemical oxygen demand (COD), removals, volatile fatty acid (VFA), p-aminophenol (PAP) and methane gas productions) was investigated through 240 days. The PNP concentrations were raised to 700 from 10 mg/L corresponding to PNP loading rates of 0.97 and 67.9 g/m³ day. The PNP and COD removal efficiencies were 99 and 90% at PNP loading rates as high as 33.9 g/m³ day, respectively, through the acclimation of anaerobic granular sludge. After this loading rate, the removal efficiencies decreased to 79%. The COD removal efficiencies were high in compartment 1 (E = 78–93%) while a small amount of COD removal was achieved in compartments 2 and 3. The PNP removal efficiencies were approximately 90% in all PNP loading rates except for loading rate of 0.97 g/m³ day. The maximum PNP removal efficiency was measured as 99% at a loading rate of 8.32 g/m³ day. The optimum PNP loading rate for maximum COD, PNP removals and methane yield was 8.32 g/m³ day. The total, methane gas productions and methane percentages were approximately 2160–2400 mL/day and 950–1250 mL/day and 44–52% for the PNP loading rates varying between 4.36 and 33.9 g/m³ day, respectively. For PNP loading rates varying between 33.9 and 67.9 g/m³ day, the total, methane gas productions and methane percentages were approximately 2160 and 960 mL/day and 44%, respectively. The highest total volatile fatty acid (TVFA) concentrations were found in the first compartment with fluctuated values varied between 50 and 200 mg/L indicating the acidogenesis. p-Aminophenol was found as the main intermediate through anaerobic degradation of PNP which later was broken down to phenol and ammonia.     

Microbial community structure in anaerobic co-digestion of grass silage and cow manure in a laboratory continuously stirred tank reactor

The impacts of feeding ratio and loading rate on the microbial community during co-digestion of grass silage with cow manure in an anaerobic laboratory continuously stirred tank reactor were investigated by 16S rRNA gene-based fingerprints. The microbial community remained stable when the reactor was fed with cow manure alone and with up to 20% of grass silage in feedstock at an organic loading rate (OLR) of 2 kg VS m⁻³ day⁻¹. Large changes in the bacterial community were observed when the loading ratio of grass was increased to 40%, while there was little change in the archaeal community. During the increase in OLR from 2 to 4 kg VS m⁻³ day⁻¹ the bacterial community structure showed few differences, whereas Archaea was undetectable. Sequencing of the major DGGE bands indicated that the phylum Bacteriodetes predominated in the bacterial community. Two unclassified bacteria with high abundance survived throughout the operation of the reactor.     

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 two mathematical models for correlating the organic matter removal efficiency with hydraulic retention time in a hybrid anaerobic baffled reactor treating molasses

A modelling of the anaerobic digestion process of molasses was conducted in a 70-L multistage anaerobic biofilm reactor or hybrid anaerobic baffled reactor with six compartments at an operating temperature of 26 °C. Five hydraulic retention times (6, 16, 24, 72 and 120 h) were studied at a constant influent COD concentration of 10,000 mg/L. Two different kinetic models (one was based on a dispersion model with first-order kinetics for substrate consumption and the other based on a modification of the Young equation) were evaluated and compared to predict the organic matter removal efficiency or fractional conversion. The first-order kinetic constant obtained with the dispersion model was 0.28 h⁻¹, the Peclet dispersion number being 45, with a mean relative error of 2%. The model based on the Young equation predicted the behaviour of the reactor more accurately showing deviations lower than 10% between the theoretical and experimental values of the fractional conversion, the mean relative error being 0.9% in this case.     

Study of archaea community structure during the biodegradation process of nitrobenzene wastewater in an anaerobic baffled reactor

Nitrobenzene (NB) is an important industrial raw material in organic synthesis. However, successful biological treatment is challenging since NB wastewater is biologically toxic. During the experiment, the performance was examined during the acclimation process of NB in an anaerobic baffled reactor (ABR). The removal efficiencies of NB and chemical oxygen demand were 98% and 90%, respectively. Furthermore, by applying polymerase chain reaction-denaturing gradient gel electrophoresis (DGGE) technology of 16SrDNA, this paper analyzes the structural change of the archaea community in the ABR before and after NB acclimation and identifies the dominant community. The sequence structure analysis of archaea 16S rDNA in DGGE profiles shows that after NB biodegradation, the archaea-dominant community primarily consists of Methanothrix soehngenii from Methanosarcina, Methanosaeta concilii from Methanosaeta, Methanobacterium beijingense 8-2, uncultured Archaeon TA04, and uncultured Methanobacterium sp. isolated from environmental samples, which may be the important functional archaea in an ABR for NB biodegradation. The study of the population structure distribution and the dominant archaea community is helpful for elucidating the mechanisms of the anaerobic biodegradation mechanism of NB.     

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.     

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。     

Effects of hydraulic retention time and sulfide toxicity on ethanol and acetate oxidation in sulfate-reducing metal-precipitating fluidized-bed reactor

The effects of hydraulic retention time (HRT) and sulfide toxicity on ethanol and acetate utilization were studied in a sulfate-reducing fluidized-bed reactor (FBR) treating acidic metal-containing wastewater. The effects of HRT were determined with continuous flow FBR experiments. The percentage of ethanol oxidation was 99.9% even at a HRT of 6.5 h (loading of 2.6 g ethanol L(-1) d(-1)), while acetate accumulated in the FBR with HRTs below 12 h (loading of 1.4 g ethanol L(-1) d(-1)). Partial acetate utilization was accompanied by decreased concentrations of dissolved sulfide (DS) and alkalinity in the effluent, and eventually resulted in process failure when HRT was decreased to 6.1 h (loading of 2.7 g ethanol L(-1) d(-1)). Zinc and iron precipitation rates increased to over 600 mg L(-1) d(-1) and 300 mg L(-1) d(-1), respectively, with decreasing HRT. At HRT of 6.5 h, percent metal precipitation was over 99.9%, and effluent metal concentrations remained below 0.08 mg L(-1). Under these conditions, the alkalinity produced by substrate utilization increased the wastewater pH from 3 to 7.9-8.0. The percentage of electron flow from ethanol to sulfate reduction averaged 76 +/- 10% and was not affected by the HRT. The lowest HRT did not result in significant biomass washout from the FBR. The effect of sulfide toxicity on the sulfate-reducing culture was studied with batch kinetic experiments in the FBR. Noncompetitive inhibition model described well the sulfide inhibition of the sulfate-reducing culture. (DS) inhibition constants (K(i)) for ethanol and acetate oxidation were 248 mg S L(-1) and 356 mg S L(-1), respectively, and the corresponding K(i) values for H(2)S were 84 mg S L(-1) and 124 mg S L(-1). In conclusion, ethanol oxidation was more inhibited by sulfide toxicity than the acetate oxidation.     

Influence of step increases in hydraulic retention time on (RS)-MCPP degradation using an anaerobic membrane bioreactor

The effects of different hydraulic retention time (HRT) on (RS)-MCPP utilisation was investigated by decreasing the feed flow rate in an anaerobic membrane bioreactor (AnMBR). Results showed an average COD removal efficiency of 91.4%, 96.9% and 94.4% when the reactor was operated at HRT 3, 7 and 17 d, respectively. However, when the HRT was reduced to 1d, the COD removal efficiency declined to just only 60%, confirming the AnMBR is stable to a large transient hydraulic shock loads. The (RS)-MCPP removal efficiency fluctuated from 6% to 39% at HRT 3 d, however when it was increased to 7 and 17 d, the removal efficiency increased to an average of 60% and 74.5%. In addition, (RS)-MCPP specific utilisation rates (SUR) were dependent on the HRT and gradually improved from 18 to 43 μg mg VSS(-1) d(-1) as flow rate increased.     

Development of a stirred tank reactor system for the production of lignin peroxidases (ligninases) byPhanerochaete chrysosporium BKM-F-1767

Summary Lignin peroxidases produced byPhanerochaete chrysosporium have several important potential industrial applications based on their ability to degrade lignin and lignin-like compounds. A stirred tank reactor system for the production of lignin peroxidases is described here. Included in this study is an examination of the mechanics of pellet biocatalyst formation and the optimization of an acetate buffered medium. Higher levels of lignin peroxidase were obtained with acetate buffer compared to the other buffer systems tested. Concentrations of 0.05% (w/v) Tween 80 and 0.4 mM veratryl alcohol gave optimal lignin peroxidase activity in acetate buffered medium. In shake flask cultures, mycelial fragments in the inoculum aggregated into pellets during the first eight hours of incubation and thereafter increased in size through the eighth day. The agitation rate in shake flask cultures affected pellet size, the number of pellets formed, and lignin peroxidase activity. Transfer of fungal pellets from shake flask culture to a continuously oxygenated baffled stirred tank reactor (STR) resulted in production of high lignin peroxidase titres comparable to those of shake flask cultures when the agitation rate, oxygen dispersion and foaming were closely controlled.     

Methane from cattle waste: Effects of temperature, hydraulic retention time, and influent substrate concentration on kinetic parameter (k)

The effects of temperature (35 and 55 degrees C), influent volatile solids (VS) concentration (S(0) = 43, 64, 82, 100, and 128 kg VS/m(3)) and hydraulic retention time (HRT = 4, 5, 8, 10, 15, and 25 days) on methane (CH(4)) production from cattle waste were evaluated using 3-dm(3) laboratoryscale fermentors. The highest CH(4) production rate achieved was 6.11 m(3) CH(4) m(-3) fermentor day(-1) at 55 degrees C, four days HRT, and S(0) = 100 kg VS/m(3). Batch fermentations showed an ultimate CH(4) yield (B(0)) of 0.42 m(3) CH(4)/kg VS fed. The maximum loading rates for unstressed fermentation were 7 kg VS m(-3) day(-1) at 35 degrees C and 20 kg VS m(-3) day(-1) at 55 degrees C. The kinetic parameter (K, an increasing K indicates inhibition of fermentation) increased exponentially as S(0) increased, and was described by: K = 0.8 + 0.0016 e(0.06S(0) ). Temperature had no significant effect on K for S(0) between 40 and 100 kg VS/m(3). The above equation predicted published K values for cattle waste within a mean standard error of 7%.     

Anaerobic baffled reactor (ABR) for treating heavy oil produced water with high concentrations of salt and poor nutrient

The start-up and operational performance (total 212 days, including the start-up of 164 days) of an anaerobic baffled reactor (ABR), which is used to treat heavy oil produced water, was studied without the temperature control. Inoculums were mixtures of acclimated sediment taken from a heavy oil produced water treatment plant and digested sludge from a sewage wastewater treatment plant. The rod-shaped and spherical granules with colors of henna and black, in which Clostridia, Methanosarcina and Methanothrx sp. were main populations, were observed in each compartment of ABR after the reactor's successful start-up (day 164). Rhodopseudomonas with the activity of lipase and halotolerant, as a kind of photosynthetic bacteria, was also observed in the first five compartments. X-ray diffraction (XRD) showed that the spherical granule sludge was compact and contained a large amount of organics, amorphous materials, and crystals of Fe(2)O(3), FeS, and CaCO(3), whereas the rod-shaped granule sludge was incompact without crystals of Fe(2)O(3), FeS, and CaCO(3). Scanning electron microscope (SEM) showed that the skeleton construction of this rod-shaped granule was filamentous bacteria and amount of extracellular polymeric substances (EPS). The ABR, after successful start up, can achieve high average chemical oxygen demand (COD) and oil removals of 65% and 88% for heavy oil produced water with poor nutrient (COD:TN:TP, 1200:15:1) and high salt concentration (1.15-1.46%), respectively. Furthermore, ABR kept stable during 2.5 times the COD level shock load (0.50 kg COD m-3 d-1) for four days.     

The effects of hydraulic retention time and sludge retention time on the fate of di-(2-ethylhexyl) phthalate in a laboratory-scale anaerobic-anoxic-aerobic activated sludge system

A laboratory-scale anaerobic-anoxic-aerobic (AAA) activated sludge wastewater treatment system was employed to investigate the effects of hydraulic retention time (HRT) and sludge retention time (SRT) on the removal and fate of di-(2-ethylhexyl) phthalate (DEHP). In the range from 5 to 14h, HRT had no significant effect on DEHP removal. However, longer HRT increased DEHP accumulation in the system and DEHP retention in the waste sludge. When SRT was increased from 15 to 25d, DEHP removal efficiency stayed above 96%. Compared to the removal of only 88% at SRT of 10d, longer SRT enhanced DEHP degradation efficiency. The optimal HRT and SRT for both nutrients (nitrogen and phosphorus) and DEHP removal were 8h and 15d. At these retention times, about 71% of DEHP was degraded by the activated sludge process, 26% was accumulated in the system, 2% was released in the effluent, and 1% remained in the waste sludge. The anaerobic, anoxic and aerobic reactors were responsible for 15%, 19% and 62% of the overall DEHP removal, respectively.     

On the behavior of the periodic anaerobic baffled reactor (PABR) during the transition from carbohydrate to protein-based feedings

The influence of the organic substrate composition in the feed of an innovative reactor, the periodic anaerobic baffled reactor (PABR) is examined. A laboratory-scale PABR fed on a synthetic medium composed of mixtures of glucose (a carbohydrate) and gelatin (a protein) in various ratios performed well. The PABR seemed to be minimally affected during the gradual substitution of glucose by gelatin. In fact, the reactor performance remained at an optimal level (approximately 98%), while operated under an organic loading rate of 3.125 gCOD/l/d.