High rate anaerobic digestion of a petrochemical wastewater using biomass support particles

Anaerobic digestion of wastewater from a dimethyl terephthalate plant was studied in continuously stirred tank reactors with plastic net biomass support particles (BSP) at a level of 20% (v/v). The experimental results showed that the BSP system could treat the wastewater at a hydraulic retention time as low as 1.5 d, organic loading as high as 20 kg COD/m3/d and at acidic feed pH as low as 4.5 with 95% COD reduction and biogas production of about 8l/l/d, while the control system without support particles could not treat the wastewater above a 5-d hydraulic retention time, 5 kg COD/m3/d organic loading and a feed pH of 6.0. Thus, augmentation of BSP upgraded the performance of the conventional suspended growth system to an equivalent level to advanced reactors.     

Maximization of acetic acid production in partial acidogenesis of swine wastewater.

Swine wastewater was biologically treated to produce short-chain volatile organic acids (VOAs) in laboratory-scale continuously stirred tank reactors. The maximum production rates of acetic and butyric acids associated with simultaneous changes in pH and hydraulic retention time (HRT) were investigated, in which the degree of acidification of swine wastewater to the short-chain VOAs was <25% of influent chemical oxygen demand (COD) concentration. A constant inoculum system was used to minimize the experimental error due to the use of inconsistent inoculum. The inoculum system was operated with synthetic wastewater at 6000 mg soluble chemical oxygen demand per liter (pH 6.0) and 35 degrees C at 0.5 day hydraulic retention time. Response surface methodology was applied successfully to determine the optimum physiological condition for which the maximum rate of acetic acid production occurred, which was pH 5.90 and 0.88 day hydraulic retention time at 35 degrees C. The partial acidification process to manage swine waste should be operated in the optimum condition for acetic acid production because the optimum operating condition for butyric acid production approached the washout point.     

Design of acidogenic reactors for the anaerobic treatment of the organic fraction of solid food waste

Volatile Fatty Acids (VFA) production by anaerobic fermentation of organic solid wastes was studied at laboratory scale. The influence of initial substrate concentration was evaluated on VFA production. Completely mixed reactors (0.9?l) were used at mesophilic temperature (35?°C). Food wastes had 43.8% Total Solids content. Three dilutions of substrate (1/25, 1/10 and 1/5) corresponding to 1.75%, 4.38% and 8.76% of Total Solids and five values of Organic Loading Rates: 2, 5, 10, 12.5 and 25?kg COD/m³?d were studied. It was found that substrate 1/10 led to 14?g VFA/l at a loading rate of 12.5?kg COD/m³?d and an hydraulic retention time of 3.7 d. The main VFA produced were especially acetate and butyrate. Substrate diluted 1/5 led to 26.1?g VFA/l at a loading of 5?kg COD/m³?d and an hydraulic retention time of 15.1 d, but biomass production was not optimal. In a second study, a cascade of three reactors was used. An effluent with 42?g VFA/l was obtained at steady-state conditions at a loading of 12.5?kg of COD/m³?d and an hydraulic retention time of 12.5?d. The distribution of VFA was the following: 36% of propionate, 34% of acetate and 22.5% of butyrate.     

A comparison of analytical techniques for evaluating food waste degradation by anaerobic digestion

Organic matter contained in food waste was degraded by anaerobic digestion under mesophilic and thermophilic conditions at two hydraulic retention times. Evolution of the digestion process was followed by thermogravimetry analysis, fluorescence spectroscopy and ¹H nuclear magnetic resonance. All analytical methods suggested that longer retention times might be required for food waste stabilization under mesophilic conditions as compared to thermophilic stabilization. All the analytical methods showed that the stabilization process consisted of two steps, where complex organic molecules were formed during initial stabilization and then digested providing sufficient hydraulic retention time. Longer hydraulic retention times were required for food waste stabilization under mesophilic conditions. Overall, thermal and ¹H NMR analyses of the digestate samples might be recommended if more detailed analysis is required, while fluorescence measurements can be used as a fast screening technique, which provides qualitative assessment of the stabilization process.     

Performance of anaerobic thermophilic fluidized bed in the treatment of cutting-oil wastewater

This paper examines the effect of organic loading rate on the removal efficiency of COD and TOC anaerobic thermophilic fluidized bed reactor (AFBR) in the treatment of cutting-oil wastewater at different hydraulic retention time (HRT) conditions. The essays are development at laboratory scale using a porous support medium. The AFBR reactor was subjected to a programme of steady-state operation over a range of hydraulic retention times, HRTs, in the range 12-2h and organic loading rates, OLRs, between 11.9 and 51.3kgCOD/m(3)d. The highest efficiency was 95.9% for an OLR of 13kgCOD/m(3)d and HRT of 11h. Over an operating period of 92 days, an OLR of 51.3kgCOD/m(3)d was achieved with 67.1% COD removal efficiency (71.3% TOC) in the experimental AFBR reactor. Although the level of biogas generation was not high, the anaerobic fluidized bed technology provided significant advantages over the conventional physico-chemical treatment applied in the factory. The effluent had a better quality (lower organic loading) and it was possible to reuse it in different applications in the factory (e.g., irrigation of gardens). The biological treatment did not lead to the generation of oily sludge, which is considered as hazardous waste by legislation. Furthermore, a continuous stream is produced and this reduced the impact of large flows discharged 4-5 times per week to the urban collector and MWWTP (municipal wastewater treatment plant).     

Anaerobic acidogenesis of a complex wastewater: I. The influence of operational parameters on reactor performance

The influence of operational, parameters, such as hydraulic retention time, organic loading rate, influent substrate concentration, pH, and temperature, on the performance of the first phase of anaerobic digestion has been investigated. A complex substrate based on beef extract was used, and six series of experimental runs were conducted, each one showing the effect of one operational variable. The predominant fermentation products were always acetic and propionic acid, independent of the values of the operational parameters. For initial COD concentrations and hydraulic retention times above the critical values identified as 3 g/L and 6 h, respectively, the degree of acidification achieved was between 30 and 60%. The degree of acidification was found to increase with the hydraulic retention time and decrease with the influent substrate concentration and organic loading rate, while the opposite held true for the rate of product formation. Furthermore, it has been demonstrated that acidification is primarily determined by the hydraulic retention time and the rate of product formation by the influent substrate concentration. The concentration of the acetic acid produced was found to depend on the operational parameters. However, the concentration of propionic acid produced depended only on the substrate availability with a consistent proportion of 8% initial COD converted to it. The optimum pH and temperature were 7 and 40 degrees C, respectively. The percentage of acetic acid as a proportion of the total volatile fatty acids produced was found to increase with increasing pH and temperature, while the percentage of propionic acid seemed to decrease accordingly. Finally the effect of the temperature on the rate of acidification followed an Arrhenius type equation with an activation energy equal to 4739 cal/mol.     

Evaluation of a new fixed-bed digester design utilizing large media for flush dairy manure treatment

A new anaerobic digester design for the treatment of diluted (<2% solids) flush dairy manure was evaluated. The new design was developed as an economic alternative for enhancing the performance of anaerobic lagoon systems in cold weather areas. The digester employed used automobile tires as fixed-bed media to improve bacterial retention. The digester was heated by steam injection and built underground to enhance insulation. The tires were sorted in a unique pattern for improving mixing and uniform temperature distribution. The system was tested on a pilot-scale. The treatment mechanism was explored by mathematical modeling. The observed treatment efficiency of the new design was comparable to that of conventional digesters operating at higher total solids concentrations (>4%). With a hydraulic retention time (HRT) of 17 days, the measured removal rates were 30-50% and 40-60% of TVS and COD, respectively. The new digester maintained longer solids retention time (SRT) as estimated using the model, supported by the observed thick biofilm formation and resistance to hydraulic overload. The model was used to analyze different operation scenarios varying both the organic and hydraulic loads.     

Treatment of low strength industrial cluster wastewater by anaerobic hybrid reactor

The study was aimed at treating the complex, combined wastewater generated in Mangolpuri industrial cluster. It was considered as a low strength wastewater with respect to its organic content. Anaerobic treatment of this wastewater was studied using an anaerobic hybrid reactor (AHR) which combined the best features of both the upflow anaerobic sludge blanket (UASB) reactor and anaerobic fluidized bed rector (AFBR). The performance of the reactor under different organic and hydraulic loading rates were studied. The COD removal reached 94% at an organic loading rate (OLR) of 2.08 kg COD m(-3)d(-1) at an hydraulic retention time (HRT) of 6.0 h. The granules developed were characterized in terms of their diameter and terminal settling velocity.     

Anaerobic treatment of distillery spent wash - a study on upflow anaerobic fixed film bioreactor

Anaerobic digestion of wastewater from a distillery industry having very high COD (1,10,000-1,90,000 mg/L) and BOD (50,000-60,000 mg/L) was studied in a continuously fed, up flow fixed film column reactor using different support materials such as charcoal, coconut coir and nylon fibers under varying hydraulic retention time and organic loading rates. The seed consortium was prepared by enrichment with distillery spent wash in a conventional type reactor having working capacity of 3 L and was used for charging the anaerobic column reactor. Amongst the various support materials studied the reactor having coconut coir could treat distillery spent wash at 8d hydraulic retention time with organic loading rate of 23.25 kg COD m(-3)d(-1) leading to 64% COD reduction with biogas production of 7.2 m3 m(-3)d(-1) having high methane yield without any pretreatment or neutralization of the distillery spent wash. This study indicates fixed film biomethanation of distillery spent wash using coconut coir as the support material appears to be a cost effective and promising technology for mitigating the problems caused by distillery effluent.     

Kinetics of organic removal in fixed-bed aerobic biological reactor

The process kinetics of a lab-scale upflow aerobic immobilized biomass (UAIB) reactor using simulated sugar-manufacturing wastewater as feed was investigated. The experimental unit consisted of a 22l reactor filled with high porosity pumice stone. The UAIB reactor was tested under different organic loads and different hydraulic retention times (HRT) and the substrate loading removal rate was compared with prediction of Stover-Kincannon model, second-order model and the first order substrate removal model. After obtaining steady-state conditions, organic loading rate was increased from 750 to 4500 g COD/m(3) day to resemble wastewater from sugar production lines, and hydraulic retention time was decreased from 1 to 0.5 days, stepwise. Nine different operational conditions were applied changing these two parameters in a certain program. As a result of the calculations, Stover-Kincannon model and second-order model known as "Grau" model were found to be the most appropriate models for this reactor. Stover-Kincannon model and Grau second-order model gave high correlation coefficients, which were 99.7% and 99.4%, respectively. Therefore, these models could be used in predicting the behavior or design of the UAIB reactors.     

Immobilization of anaerobic bacteria on rubberized-coir for psychrophilic digestion of night soil

Low-ambient temperatures, <30 degrees C, are known to cause drastic reduction in the efficiency of anaerobic biodigesters due to low-growth rate of the constituent bacterial consortium. Immobilization of anaerobic bacteria has been attempted in the biodigester operating at 10 degrees C. Various matrices were screened and evaluated for the immobilization of bacteria in digesters. Anaerobic digestion of night soil was carried out with hydraulic retention time in the range of 9-18 days. Among the tested matrices, rubberized-coir was found to be the most useful at 10 degrees C with optimum hydraulic retention time of 15 days. Optimum amount of coir was found as 25 g/L of the working volume of biodigesters. Immobilization of bacteria on the coir was observed by scanning electron microscopy and fluorescent microscopy. The study indicates that rubberized-coir can be utilized to increase biodegradation of night soil at higher organic loading. Another advantage of using this matrix is that it is renewable and easily available in comparison to other synthetic polymeric matrices.     

Microstructure and molecular microbiology of rapidly formed hydrogen‐ and methane‐producing granules in a phase‐separated anaerobic environment

Hydrogen and methane were simultaneously produced in a two‐phase reactor, operated to separate the reactions of hydrogen and methanogen production. Each reactor was inoculated with a seed enriched with different microbial consortia. The first phase was operated with a hydraulic retention time of 7 days and at an organic loading rate of 7.7 g VS L^?1 d^?1 that produced a stable pH of 5.5. This suppressed the growth of methanogens and as a result, the off gas contained up to 27% hydrogen. The second phase was operated with a hydraulic retention time of 12 days and at an organic loading rate of 3.6 g VS L^?1 d^?1. This permitted the growth of hydrogenotrophs and methanogens to produce methane at a concentration of 60%. Examination of the microbial population of the two reactors both microscopically and using PCR, showed an effective separation of hydrogen‐ and methane‐producing microbial communities. The study revealed that the suppression of hydrogentrophs and methanogens can be achieved by adopting rapid method that leads the growth of hydrogen‐ and methane‐producing granules in phase‐separated anaerobic environment.     

Two-stage anaerobic fermentation of organic waste in CSTR and UFAF-reactors.

The mechanically separated liquid fraction of organic waste from households was used as a substrate for anaerobic fermentation. A two-step system consisting of a 2001 continuously stirred tank reactor (CSTR) and a 501 upflow anaerobic filter filled with glass foam pearls was constructed. The CSTR was operated for 5 months with a loading rate of 9.8 kg CSB m(-3) day(-1). At a resulting hydraulic retention time (HRT) of 24 days, 68% COD was degraded and a gas productivity of 4.0 m3 m(-3) day(-1) was achieved. Further digestion of the CSTR output was separately optimised in a 20 l-UFAF and based on these results a 50 l-UFAF was connected to the CSTR. At a resulting hydraulic retention time (HRT) of 6 days 38% COD was degraded and a gas productivity of 1.8 m3 m(-3) day(-1) was achieved with the 50 l-UFAF. Thus, the overall degradation efficiency of the two-phase system was 80%. The methane content (61%) of the biogas produced in the 50 l-UF     

A comparison of the performance of mesophilic and thermophilic anaerobic filters treating papermill wastewater

Two anaerobic filters, one mesophilic (35 degrees C) and one thermophilic (55 degrees C), were operated with a papermill wastewater at a series of organic loadings. The hydraulic retention time (HRT) ranged from 6 to 24 h with organic loading rates (OLR) 1.07-12.25 g/l per day. At loading rates up to 8.4 g COD/l d, there was no difference in terms of the removal of soluble COD (SCOD) and gas production. At the higher organic loading rate, the SCOD removal performance of thermophilic digester was slightly better compare to mesophilic digester. Similar trend was also observed in terms of the daily methane production. The stability of thermophilic digester was also better than mesophilic digester particularly for the higher organic loadings. Volatile fatty acid accumulation was observed in the effluent of the mesophilic filter at the higher organic loading rates. The Stover-Kincannon model was applied to both digesters and it was found that model was applicable to both digesters for papermill wastewater. K(B) and U(max) constants from the Stover-Kincannon model were also derived.     

Thermodynamic Analysis of Energy Transfer in Acidogenic Cultures

A global thermodynamic analysis, normally used for pure cultures, has been performed for steady‐state data sets from acidogenic mixed cultures. This analysis is a combination of two different thermodynamic approaches, based on tabulated standard Gibbs energy of formation, global stoichiometry and medium compositions. It takes into account the energy transfer efficiency, ?, together with the Gibbs free energy dissipation, ΔG_o, analysis of the different data. The objective is to describe these systems thermodynamically without any heat measurement. The results show that ? is influenced by environmental conditions, where increasing hydraulic retention time increases its value all cases. The pH effect on ? is related to metabolic shifts and osmoregulation. Within the environmental conditions analyzed, ? ranges from 0.23 for a hydraulic retention time of 20 h and pH 4, to 0.42 for a hydraulic retention time of 8 h and a pH ranging from 7–8.5. The estimated values of ΔG_o are comparable to standard Gibbs energy of dissipation reported in the literature. For the data sets analyzed, ΔG_o ranges from –1210 kJ/mol_x, corresponding to a stirring velocity of 300 rpm, pH 6 and a hydraulic retention time of 6 h, to –20744 kJ/mol_x for pH 4 and a hydraulic retention time of 20 h. For average conclusions, the combined approach based on standard Gibbs energy of formation and global stoichiometry, used in this thermodynamic analysis, allows for the estimation of Gibbs energy dissipation values from the extracellular medium compositions in acidogenic mixed cultures. Such estimated values are comparable to the standard Gibbs energy dissipation values reported in the literature. It is demonstrated that ? is affected by the environmental conditions, i.e., stirring velocity, hydraulic retention time and pH. However, a relationship that relates this parameter to environmental conditions was not found and will be the focus of further research.     

Effects of support material on the pattern of volatile fatty acid accumulation at overload in anaerobic digestion of semi-solid waste

Anaerobic degradation of a semi-solid waste with a total solids content of 4% particulate matter, much of it insoluble, was investigated in four laboratory-scale reactors. Two of the reactors were equipped with different textile materials for immobilisation of microorganisms, while the other two were used as continuously-stirred-tank reactor references. A constant organic loading rate and hydraulic retention time were used in the start-up period; the hydraulic retention time was then decreased and the effects of this change were monitored. Volatile fatty acid (VFA) concentration and pH were chosen as indicators of the microbial status in the reactors. The reactors with support material showed a greater resistance to overload than did the continuously-stirred-tank reactors. This is in agreement with many studies undertaken on the anaerobic treatment of wastewater. However, no problems with clogging occurred, showing that a support material is also applicable in systems treating waste containing large amounts of insoluble, particulate matter. The pH was comparable to VFA for indicating an approaching process failure. However, the pattern of VFA accumulation was qualitatively different between the reactors with and without support material. Obviously the metabolic pattern of mixed cultures changes when the microorganisms are immobilised. Received: 3 December 1996 / Received revision: 7 February 1997 / Accepted: 14 February 1997     

Bioaugmentation and treatment of cephalexin drug-based pharmaceutical effluent in an upflow anaerobic fluidized bed system

Cephalexin is a constituent of the cephalosporin group used for the treatment of bronchitis and other heart diseases due to its enhanced oral activity. The effluent from these industries contains a disintegrated form of the drug contributing high chemical oxygen demand (COD), volatile solids and organic solvent. A laboratory-scale study was conducted to evaluate the efficiency of a fluidized bed reactor operated under anaerobic condition with bioaugmentation to treat the cephalexin containing pharmaceutical factory effluent. The main objective of the study was to show that bioaugmentation could be used to promote biological treatment to applications where conventional operation might be difficult or unfavourable. The effluent, with COD of 12,000-15,000 mg/l, was diluted and studied in single and multiple inoculation experiments with hydraulic retention times of 3-12 h. The removal efficiency after inoculation from an anaerobic sequencing batch reactor was related to influent concentration, mass of inoculum and hydraulic retention time characterized by calculating the initial food to microorganism ratio. Continuous COD removal efficiency attained a maximum value of 88.5% using bioaugmentation through periodic addition of acclimated cells every 2 days with 30-73.2 g of cells from an off-line enricher-reactor.     

Impact of spruce forest and grass vegetation cover on soil micromorphology and hydraulic properties of organic matter horizon

Two organic matter horizons developed under a spruce forest and grass vegetation were chosen to demonstrate the impact of a different vegetation cover on the micromorphology, porous system and hydraulic properties of surface soils. Micromorphological studies showed that the decomposed organic material in the organic matter horizon under the grass vegetation was more compact compared to the decomposed organic material in the organic matter horizon under the spruce forest. The detected soil porous system in the organic matter horizon under the spruce forest consisted of two clusters of pores with different diameters that were highly connected within and between both clusters. The soil porous system in the organic matter horizon under the grass vegetation consisted of one cluster of pores with the larger diameters and isolated pores with the smaller diameter. The retention ability of the organic matter horizon under the grass vegetation was higher than the retention ability of the organic matter horizon under the spruce forest. Presented at the International Conference on Bioclimatology and Natural Hazards, Poľana nad Detvou, Slovakia, 17–20 September 2007.     

Performance of anaerobic contact filter in series for treating distillery spentwash

Investigations were carried out by using rigid polyurethane foam as a packing material in the anaerobic contact filter (series) to treat distillery spentwash. The effect of hydraulic retention time (HRT) in treatment efficiency of reactor (I) and (II) was evaluated at different initial substrate concentrations ranging from 1500 mg/l to 19,000 mg/l. The effect of toxic parameters such as sulphate present in the distillery spentwash and the corresponding parameters such as total sulphide and un-ionized hydrogen sulphide generated during digestion of wastewater were evaluated to assess the reactor performance. The results showed that at 4 d HRT the overall COD removal percent ranged from 98% to 73% for an influent COD of 1500 mg/l to 19,000 mg/l. The overall performance of COD removal percent in reactor (I) and (II) at 2, 3 and 4 d HRT's were investigated. At 3 d HRT the reactor (II) showed a higher COD removal percent when compared to reactor (I), which clearly shows the role of hydraulic retention time in degradation of the organic matter present in the wastewater above an influent COD concentration of 5000 mg/l.     

Treatment of brewery wastewater using anaerobic sequencing batch reactor (ASBR)

Brewery wastewater was treated in a pilot-scale anaerobic sequencing batch reactor (ASBR) in which a floating cover(@) was employed. Long time experiments showed that the reactor worked stably and effectively for COD removal and gas production. When the organic loading rate was controlled between 1.5 kg COD/m3 d and 5.0 kg COD/m(3)d, and hydraulic retention time one day, COD removal efficiency could reach more than 90%. Sludge granulation was achieved in the reactor in approximately 60 days, which is much less than the granulation time ever reported. In addition, high specific methanogenic activity (SMA) for formate was observed. The study suggests that the ASBR technology is a potential alternative for brewery wastewater treatment.