Anaerobic Degradation Kinetics Research Articles

Restructuring anaerobic hydrolysis kinetics in plant-wide models for accurate prediction of biogas production

In this study, the effect of anaerobic hydrolysis rate on biogas production was investigated with mesophilic digesters in seven large-scale wastewater treatment plants. A linear correlation was determined between the percentage of primary sludge mass in the total sludge fed to the digester and the overall anaerobic hydrolysis rate. The anaerobic hydrolysis rate of primary sludge was determined to be three times higher than that of biological sludge. The reduction factors for anaerobic hydrolysis (ηHYD,ana) were identified in the range of 0.11–0.30 which is lower compared to the recommended range (0.30–0.50) given in the literature. This study proposes a new model approach where anaerobic degradation kinetics of influent originated (XB) and decay originated (XB,E) particulate biodegradable organics are separated. Current plant-wide models with a single kinetic expression required recalibration of the model for calculating biogas flowrate for each treatment facility with different primary and secondary sludge ratios fed to the digesters. The new model structure is able to predict biogas production of all wastewater treatment plants without any recalibration effort by segregating degradation kinetics of two particulate biodegradable organic fractions (XB, XB,E).

Anaerobic biodegradation and detoxification of chloroacetamide herbicides by a novel Proteiniclasticum sediminis BAD-10T

Chloroacetamide herbicides (CAAHs) are important herbicides that were widely used to control agricultural weeds. However, their mass applications have seriously contaminated environment, and they are toxic to living beings. CAAHs are easy to enter anoxic environments such as subsoil, wetland sediment, and groundwater, where CAAHs are mainly degraded by anaerobic organisms. To date, there are no research on the anaerobic degradation of CAAHs by pure isolate and toxicity of anaerobic metabolites of CAAHs. In this study, the anaerobic degradation kinetics and metabolites of CAAHs by an anaerobic isolate BAD-10T and the toxicity of anaerobic metabolites were studied. Isolate BAD-10T could degrade alachlor, acetochlor, propisochlor, butachlor, pretilachlor and metolachlor with the degradation kinetics fitting the pseudo-first-order kinetics equation. The degradation rates of CAAHs were significantly affected by the length of N-alkoxyalkyl groups, the shorter the N-alkoxyalkyl groups, the higher the degradation rates. Four metabolites 2-ethyl-6-methyl-N-(ethoxymethyl)-acetanilide (EMEMA), N-(2-methyl-6-ethylphenyl)-acetamide (MEPA), N-2-ethylphenyl acetamide and 2-ethyl-N-carboxyl aniline were identified during acetochlor degradation, and an anaerobic catabolic pathway of acetochlor was proposed. The toxicity of EMEMA and EMPA for zebrafish, Arabidopsis and Chlorella ellipsoidea were obviously lower than that of acetochlor, indicating that the anaerobic degradation of acetochlor by isolate BAD-10T is a detoxification process. The work reveals the anaerobic degradation kinetics and catabolic pathway of CAAHs and highlights a potential application of Proteiniclasticum sediminis BAD-10T for bioremediation of CAAHs residue-contaminated environment.

Anaerobic Degradation of Dairy Wastewater in Intermittent UASB Reactors: Influence of Effluent Recirculation

This work studied the influence of effluent recirculation upon the kinetics of anaerobic degradation of dairy wastewater in intermittent UASB (Upflow Anaerobic Sludge Bed) reactors. Several laboratory-scale tests were performed with different organic loads in a UASB reactor inoculated with flocculent sludge from an industrial wastewater treatment plant. The data obtained were used for determination of specific substrate removal rates and specific methane production rates and adjusted to kinetic models. A high initial substrate removal was observed in all tests due to adsorption of organic matter onto the anaerobic biomass which was not accompanied by biological substrate degradation as measured by methane production. Initial methane production was about 45% of initial soluble and colloidal substrate removal rate. This discrepancy was observed mainly in the first day of all experiments and was attenuated in the second day. Effluent recirculation raised significantly the rate of removal of soluble and colloidal substrate and methane productivity as compared to literature results for batch assays without recirculation.

Anaerobic Degradation of Dairy Wastewater in Intermittent UASB Reactors: Influence of Effluent Recirculation

This work studied the influence of effluent recirculation upon the kinetics of anaerobic degradation of dairy wastewater in intermittent UASB (Upflow Anaerobic Sludge Bed) reactors. Several laboratory-scale tests were performed with different organic loads in a UASB reactor inoculated with flocculent sludge from an industrial wastewater treatment plant. The data obtained were used for determination of specific substrate removal rates and specific methane production rates and adjusted to kinetic models. A high initial substrate removal was observed in all tests due to adsorption of organic matter onto the anaerobic biomass which was not accompanied by biological substrate degradation as measured by methane production. Initial methane production was about 45% of initial soluble and colloidal substrate removal rate. This discrepancy was observed mainly in the first day of all experiments and was attenuated in the second day. Effluent recirculation raised significantly the rate of removal of soluble and colloidal substrate and methane productivity as compared to literature results for batch assays without recirculation.

Potentiality of municipal sludge for biological gas production at Soba Station South of Khartoum (Sudan)

Potentiality of municipal sludge for biological gas production at Soba Station South of Khartoum (Sudan)

Anaerobic co-digestion of agro-food waste mixtures in a fed-batch basis

ABSTRACTThe agro-food industry (including livestock) generates millions of tonnes of waste products. A solution to this sector's waste disposal challenges was explored by a joint treatment model of organic waste products from several industries. An inventory of agro-food industry organic waste streams with high potential for biogas production was carried out in a logistically viable area (Cider Region, Asturias, Spain). Three industries were selected as those with the higher potential for this study: livestock, dairy and beverage. The kinetics of anaerobic degradation and methane production of four mixtures of selected waste streams were investigated. The specific methane production at five different substrate-to-inoculum ratios (0.50, 0.75, 1.00, 1.50 and 2.00) showed a slightly decreasing trend at the higher ratios. Some hints of a synergistic effect have been observed in mixtures with higher content in milled apple waste, while antagonistic symptoms were noted in mixtures mainly composed of dairy wastes. The estimation of fluxes of waste and methane potentials in the Cider Region suggests centralised anaerobic digestion as a sustainable solution for the valorisation of livestock and agro-food wastes generated in this area. Sector-specific waste streams (livestock and agro-food industry) could cover up to 12% of regional total energy demand.

Determining anaerobic degradation kinetics from batch tests

Data obtained from a biomethane potential (BMP) test were used in order to obtain the parameters of a kinetic model of solid wastes anaerobic degradation. The proposed model considers a hydrolysis step with a first order kinetic, a Monod kinetic for the soluble organic substrate degradation and a first order decay of microorganisms. The instantaneous release of methane was assumed. The parameters of the model are determined following a direct search optimization procedure. A 'multiple-shooting' technique was used as a first step of the optimization process. The confidence interval of the parameters was determined by using Monte Carlo simulations. Also, the distribution functions of the parameters were determined. Only the hydrolysis first order constant shows a normal distribution.

Anaerobic degradation of dairy wastewater in intermittent UASB reactors: influence of effluent recirculation

This work studied the influence of effluent recirculation upon the kinetics of anaerobic degradation of dairy wastewater in the feedless phase of intermittent upflow anaerobic sludge bed (UASB) reactors. Several laboratory-scale tests were performed with different organic loads in closed circuit UASB reactors inoculated with adapted flocculent sludge. The data obtained were used for determination of specific substrate removal rates and specific methane production rates, and adjusted to kinetic models. A high initial substrate removal was observed in all tests due to adsorption of organic matter onto the anaerobic biomass which was not accompanied by biological substrate degradation as measured by methane production. Initial methane production rate was about 45% of initial soluble and colloidal substrate removal rate. This discrepancy between methane production rate and substrate removal rate was observed mainly on the first day of all experiments and was attenuated on the second day, suggesting that the feedless period of intermittent UASB reactors treating dairy wastewater should be longer than one day. Effluent recirculation expressively raised the rate of removal of soluble and colloidal substrate and methane productivity, as compared with results for similar assays in batch reactors without recirculation. The observed bed expansion was due to the biogas production and the application of effluent recirculation led to a sludge bed contraction after all the substrates were degraded. The settleability of the anaerobic sludge improved by the introduction of effluent recirculation this effect being more pronounced for the higher loads.

Application of Anaerobic Digestion Model No. 1 for describing anaerobic digestion of grass, maize, green weed silage, and industrial glycerine

Anaerobic digestion of organic waste plays an important role for the development of sustainable energy supply based on renewable resources. For further process optimization of anaerobic digestion, biogas production with the commonly used substrates, grass, maize, and green weed silage, together with industrial glycerine, were analyzed by the Weender analysis/van Soest method, and a simulation study was performed, based on the International Water Association’s (IWA) Anaerobic Digestion Model No. 1 (ADM1). The simplex algorithm was applied to optimize kinetic constants for disintegration and hydrolysis steps for all examined substrates. Consequently, new parameters were determined for each evaluated substrate, tested against experimental cumulative biogas production results, and assessed against ADM1 default values for disintegration and hydrolysis kinetic constants, where the ADM1 values for mesophilic high rate and ADM1 values for solids were used. Results of the optimization lead to a precise prediction of the kinetics of anaerobic degradation of complex substrates.

Effect of inoculum to substrate ratio (I/S) on municipal solid waste anaerobic degradation kinetics and potential

The goal of this study is to evaluate the impact of the inoculum to substrate ratio (I/S) on the anaerobic degradation potential of municipal solid waste (MSW). Reconstituted MSW samples were thus incubated under batch anaerobic conditions and inoculated with an increasing amount of inoculum originating from a mesophilic sludge digester. I/S tested values were 0 (no inoculum added), 0.015, 0.03, 0.06, 0.12, 0.25, 1, 2 and 4 (gVMinoculum/gVMwaste). The results indicate that the apparent maximal rate of dissolved organic carbon accumulation is reached at I/S=0.12. Under this level, the hydrolysis process is limited by the concentration of biomass and can thus be described as first order kinetics phenomena with respect to biomass for I/S ratios below 0.12. The maximum methane production rate and the minimal latency are reached at a ratio of 2. In addition to that, both methane signature and ARISA show a shift in the methanogenic populations from hydrogenotrophic to acetoclastic.

Evaluation of pre-treatment processes for increasing biodegradability of agro-food wastes

Anaerobic digestion (AD) technology can be employed for treating sewage sludge, livestock waste or food waste. Generally, the hydrolysis stage is the rate-limiting step of the AD processes for solid waste degradation. Therefore, physical, chemical and biological pre-treatment methods or their combination are required, in order to reduce the rate of such a limiting step. In this study, four methods (mechanical shredding, acid hydrolysis, alkaline hydrolysis and sonication) were tested to improve methane production and anaerobic biodegradability of different agro-food wastes and their mixtures. The kinetics of anaerobic degradation and methane production of pre-treated individual wastes and selected mixtures were investigated with batch tests. Sonication at lower frequencies (37 kHz) proved to give the best results with methane productivity enhancements of over 100% in the case of pig manure and in the range of 10–47% for the other wastes assayed. Furthermore, the ultimate methane production was proportional, in all the cases, to the specific energy input applied (Es). Sonication can, thus, enhance waste digestion and the rate and quantity of biogas generated. The behaviour of the other pre-treatments under the conditions assayed is not significant. Only a slight enhancement of biogas production (around 10%) was detected for whey and waste activated sludge (WAS) after mechanical shredding. The lack of effectiveness of chemical pre-treatments (acid and alkaline hydrolysis) can be justified by the inhibition of the methanogenic process due to the presence of high concentrations of sodium (up to 8 g l−1 in some tests). Only in the case of WAS did the acid hydrolysis considerably increase the biodegradability of the sample (79%), because in this case no inhibition by sodium took place. Some hints of a synergistic effect have been observed when co-digestion of the mixtures was performed.

Kinetics of anaerobic degradation of screened dairy manure by upflow fixed bed digesters: Effect of natural zeolite addition

The effect of the hydraulic retention time (HRT) on the performance of two up-flow anaerobic fixed bed digesters (UFAFBDs) packed with waste tire rubber (D1) and waste tire rubber and zeolite (D2) as micro-organism immobilization supports was studied. It was found that a first-order kinetic model described well the experimental results obtained. The kinetic constants for COD, BOD5, total solids (TS) and volatile solids (VS) removal were determined to be higher in digester D2 than in digester D1 or control. Specifically, they were 0.28 ± 0.01, 0.32 ± 0.02, 0.16 ± 0.01 and 0.24 ± 0.01 d− 1 respectively for D1 and 0.33 ± 0.02, 0.40 ± 0.02, 0.21 ± 0.01 and 0.28 ± 0.01 d− 1 respectively for D2. This was significant at the 95% confidence level. In addition, the first-order model was also adequate for assessing the effect of the HRT on the removal efficiency and methane production. Maximum methane yield and the first-order constant for methane production were determined and the results obtained were comparable with those obtained by other authors but operating at higher HRTs. Maximum methane yields and the kinetic constant for methane production were 11.1% and 29.4% higher in digester D2 than in D1.

Kinetics of syntrophic acetogenesis in a saline medium

AbstractBACKGROUND: The anaerobic degradation kinetics of volatile fatty acids (VFA) in a saline (24 g NaCl dm−3) and mesophilic (37 °C) medium was studied under batch test conditions. The acetate production kinetics without inhibition by propionic, butyric and valeric acids was determined. The inhibition of acetate production during syntrophic acetogenesis by VFA and pH was studied. The acetogenesis without inhibition was modelled using a Monod equation. The pH inhibition was represented by a Michaelis pH function, while the inhibition by acetic acid (HAc) was represented by a non‐competitive model.RESULTS: The specific maximum degradation rate and saturation constant (kmax, VFA, KS, max) values were (5.89, 15.95), (7.97, 25.99) and (7.75 g VFA g−1 volatile suspended solids day−1, 11.52 mg VFA dm−3) for propionic, butyric and valeric acids respectively, with maximum velocity at pH 7. The inhibition constants (KI, HAc) were 1295, 671 and 572 mg HAc dm−3 for propionic, butyric and valeric acids respectively.CONCLUSION: VFA and pH can be inhibitory for acetogenesis under these conditions. Copyright © 2008 Society of Chemical Industry

Analysis of the methodology to determine anaerobic toxicity: evaluation of main compounds present in wastewater treatment plants (WWTPs)

The influence of the concentration of biomass on the level of inhibition and anaerobic degradation kinetics in batch systems was studied with toxic compounds that can generate destabilization in the operation of sludge anaerobic digesters. The compounds were grouped in four families; long chain fatty acids, polycyclic aromatic hydrocarbons, linear alkylbenzene sulphonates and organic acids. For the organic acids, there is no effect due to the biomass concentration variation, therefore it is a competitive inhibition; but that doesn't happen with the remaining compounds, where there is a dependence on the complexity of their structure, becoming a non-competitive inhibition. In addition, it was observed that the degradation kinetics is affected, whether diminishing the methane production (polycyclic aromatic hydrocarbons, linear alkylbenzene sulphonates, organics acids) or increasing the initial latency time (long chain fatty acids) without this becoming an obstacle to obtain the maximum methane productions for the latter ones.

Anaerobic degradation kinetics of particulate organic matter in untreated and sonicated sewage sludge: Role of the inoculum

Degradation kinetics of particulate matter in anaerobic digestion of secondary sludge, untreated and sonicated, was investigated by carrying out batch tests at different feed/inoculum ratio ( F/ I) (in the range of 0.1–4.0). Particulate COD degradation data were analysed using the four equations most widely utilized to model the hydrolysis process and the related kinetic parameters were evaluated. The increase of F/ I results in a correspondent increase of the process rate up to one order of magnitude in the investigated interval for both untreated and sonicated sludge. The maximum step increase is observed in the range of 0.1–2.0 while for F/ I varying from 2.0 to 4.0 only a modest enhancement of the process kinetics is detected. The effect of sonication on kinetics is not appreciable at low F/ I, due to the low fraction of fed sludge and to the consequent strong substrate limitation, whereas at high F/ I a slight increase is evidenced.

Kinetics of anaerobic degradation of glycol-based type I aircraft deicing fluids.

The kinetics of anaerobic degradation of glycol-based Type I aircraft deicing fluids (ADFs) were characterized using suspended-growth fill-and-draw reactors. Both Type I ADFs tested showed near-complete anaerobic degradability. First-order degradation rate constants of 3.5 d(-1) for the propylene glycol-based Type I ADF and 5.2 d(-1) for the ethylene glycol-based Type I ADF were obtained through continuous-culture means under mesophilic conditions (35 degrees C). Fill-and-draw operation at lower temperatures affected anaerobic degradability only minimally down to 25 degrees C but substantially below 25 degrees C. High Type I ADF feed concentrations substantially affected degradability. Batch testing of fill-and-draw reactors resulted in first-order degradation rate constants of 1.9 d(-1) for propylene glycol-based Type I ADF and 3.5 d(-1) for ethylene glycol-based Type I ADF.

Upgrade of a petrochemical wastewater treatment plant by an upflow anaerobic pond

A petrochemical plant producing terephthalic acid faced a saturation of its wastewater treatment facilities due to an increase in production. In fact, the plant has been growing in recent years, and the effluents have been treated by reproducing the original activated sludge design. However, owing to lack of space, as well as energy consumption and sludge production reaching a certain level, the plant considered other options for coping with the new effluent flow and organic load. Based on the authors' previous experience with this wastewater, the consultant designed a process consisting of modifying an existing pond, in order to add an anaerobic step before the aerobic tanks already in operation. The anaerobic pond is a three-stage process, all included in the same adapted basin, with a distribution system in the bottom of each stage that creates an upflow pattern. Terephthalic acid wastewater is a mixture of several organic acids, with different anaerobic degradation kinetics, acetic and benzoic acids being more rapidly removed; the staged design takes this into account. The first two stages have a plastic floating cover (5,813 m3 and 8,719 m3 volume, respectively), while the third one is a conventional UASB type reactor (6,276 m3 volume) with a gas-liquid-solid separation device on top. The design wastewater flow is 230 m3/h, with 10,300 mg/l COD, a pH of 4.5 and a temperature of 40 °C. There is an effluent recycling pump (510 m3/h) to control upflow velocities and eventual acidification problems in the first two stages. The reactor, seeded with anaerobically adapted waste sludge from the aerobic plant, is now under start up, with the expected performance.

Anaerobic degradation kinetics of acetic acid in the presence of 2,4-dichlorophenol (2,4-DCP)

Anaerobic degradation kinetics of acetic acid (HAc) in the presence of 2,4-DCP were investigated, using 2,4-DCP acclimated anaerobic granules. The effect of HAc on 2,4-DCP dechlorination was minimal. On the basis of model discrimination, the degradation kinetics of HAc were found to follow uncompetitive inhibition with 2,4-DCP as an inhibitor.

Anaerobic degradation kinetics of acetic acid in the presence of 2,4-dichlorophenol (2,4-dcp)

Anaerobic degradation kinetics of acetic acid (HAc) in the presence of 2,4-DCP were investigated, using 2,4DCP acclimated anaerobic granules. The effect of HAc on 2,4-DCP dechlorination was minimal. On the basis of model discrimination, the degradation kinetics of HAc were found to follow uncompetitive inhibition with 2,4-DCP as an inhibitor.

Anaerobic degradation kinetics of particulate organic matter: a new approach

The development of a reliable model of anaerobic hydrolysis is of primary importance for improving modeling and design of anaerobic treatment for wastewaters and slurries with high suspended solids concentration. Michaelis-Menten, substrate first order, substrate and biomass first order and substrate first order and biomass half order equations have been compared using experimental data from a series of anaerobic degradation batch tests on cellulose particles of known size. A general kinetic equation [dS/dt=−KHASXA] which may include all the four considered kinetics, is presented. This general equation allows for a more accurate mathematical representation of the hydrolysis process. Analysing data from a series of batch tests, the best fit value of A was found to be in the range 0.42 to 0.64. This approach could reduce the choice of anaerobic degradation kinetics of particulate organic matter to the calculation of the kinetic constant KHA and of the related power coefficient A.