Treatment of high‐fat‐containing dairy wastewater in a sequential UASBR system: influence of recycle

BACKGROUND: Raw cheese whey originating from white cheese production results in a strong and complex wastewater excessively rich in organic matter (chemical oxygen demand, COD = 28–65 g L^?1), fatty matter (14–24.5 g L^?1) and acidity (3.9–6.1 g L^?1). It was treated in a three‐stage configuration consisting of a pre‐acidification (PA) tank and sequential upflow anaerobic sludge bed reactors (UASBRs) at 2.8–7 g COD L^?1 day^?1 organic loading rates, during which the effects of effluent recycling at low rates and promoted SRB activity were investigated. Acidification, volatile fatty acids (VFA), COD and fatty matter removal and volatile solids were monitored throughout the system during the study. RESULTS: Recycling of the effluent promoted VFA and COD removal as well as pH stability in both stages of the UASBRs and the effluent where high alkalinity levels were recovered reducing alkali requirement to 0.05 g OH g^?1 COD_applied. Higher removal rates of 71–100 and 50–92% for VFA and COD were obtained by use of recycling. Fatty matter was removed at 63–89% throughout the study. Volatile solids build‐up was significant in the inlet zones of the UASBRs. CONCLUSIONS: The system produced efficient acidification in the PA tank, balanced pH levels and an effluent high in alkalinity and BOD/COD ratio. Efficient VFA removal and solids immobilization was obtained in both stages up to the highest loading rate. Recycling improved the system performance under high fatty matter loading conditions. A major advantage of the sequential system was that the second stage UASBR compensated for reduced performance in the first stage. Copyright © 2010 Society of Chemical Industry     

Effect of coagulation on palm oil mill effluent and subsequent treatment of coagulated sludge by anaerobic digestion

A new effluent treatment scheme is proposed for treating palm oil mill effluent based on coagulation and anaerobic digestion of coagulated sludge. The effectiveness of anionic (N9901) and cationic (N9907) polyelectrolytes manufactured by NALCO (Malaysia) was evaluated both as coagulant and coagulant aid. The results showed that the anionic and cationic polyelectrolytes were best suited as a coagulant aid, and the cationic polyelectrolyte showed better performance than the anionic polyelectrolyte. For an influent chemical oxygen demand (COD) concentration of 59 700 mg L^?1 at an alum dosage of 1700 mg L^?1, the residual COD, suspended solid removal, sludge volume and pH were found to be 39 665 mg L^?1, 87%, 260 mL L^?1 and 6.3, respectively. For the above influent COD and alum dosage with the addition of 2 mg L^?1 of cationic polyelectrolyte as coagulant aid, the results were 30 870 mg L^?1, 90%, 240 mL L^?1 and 6.2, respectively. The sludge resulting from the coagulation process using alum as coagulant and cationic polyelectrolyte as coagulant aid was tested for its digestibility in an anaerobic digester. The quantity of biogas generated per gram of volatile solids (VS) destroyed at a loading rate of 26.7 ± 0.5 and 35.2 ± 0.4 g VS L^?1 d^?1 was found to be 0.68 and 0.72 L g^?1 VS destroyed. The anaerobic biomass when subjected to varying alum dosage in the coagulated palm oil sludge did not exhibit inhibition as the digester performance was in conformity with the regular treatment process Copyright © 2006 Society of Chemical Industry     

Batch treatment of saline wastewater by Halanaerobium lacusrosei in an anaerobic packed bed reactor

BACKGROUND: This study considers batch treatment of saline wastewater in an upflow anaerobic packed bed reactor by salt tolerant anaerobic organisms Halanaerobium lacusrosei . RESULTS: The effects of initial chemical oxygen demand (COD) concentration (COD₀ = 1880–9570 mg L^?1), salt concentration ([NaCl] = 30–100 g L^?1) and liquid upflow velocity (V_up = 1.0–8.5 m h^?1) on COD removal from salt (NaCl)‐containing synthetic wastewater were investigated. The results indicated that initial COD concentration significantly affects the effluent COD concentration and removal efficiency. COD removal was around 87% at about COD₀ = 1880 mg L^?1, and efficiency decreased to 43% on increasing COD₀ to 9570 mg L^?1 at 20 g L^?1 salt concentration. COD removal was in the range 50–60% for [NaCl] = 30–60 g L^?1 at COD₀ = 5200 ± .100 mg L^?1. However, removal efficiency dropped to 10% when salt concentration was increased to 100 g L^?1. Increasing liquid upflow velocity from V_up = 1.0 m h^?1 to 8.5 m h^?1 provided a substantial improvement in COD removal. COD concentration decreased from 4343 mg L^?1 to 321 mg L^?1 at V_up = 8.5 m h^?1, resulting in over 92% COD removal at 30 g L^?1 salt‐containing synthetic wastewater. CONCLUSION: The experimental results showed that anaerobic treatment of saline wastewater is possible and could result in efficient COD removal by the utilization of halophilic anaerobic bacteria. Copyright © 2008 Society of Chemical Industry     

The effect of organic loading rate on the anaerobic digestion of two‐phase olive mill solid residue derived from fruits with low ripening index

A study of the effect of organic loading rate on the performance of anaerobic digestion of two‐phase olive mill solid residue (OMSR) was carried out in a laboratory‐scale completely stirred tank reactor. The reactor was operated at an influent substrate concentration of 162 g chemical oxygen demand (COD) dm^?3. The organic loading rate (OLR) varied between 0.8 and 11.0 g COD dm^?3 d^?1. COD removal efficiency decreased from 97.0% to 82.6% when the OLR increased from 0.8 to 8.3 g COD dm^?3 d^?1. It was found that OLRs higher than 9.2 g COD dm^?3 d^?1 favoured process failure, decreasing pH, COD removal efficiency and methane production rates (Q_M). Empirical equations described the effect of OLR on the process stability and the effect of soluble organic matter concentration on the total volatile fatty acids (TVFA)/total alkalinity (TAlk) ratio (ρ). The results obtained demonstrated that rates of substrate uptake were correlated with concentration of biodegradable COD, through an equation of the Michaelis–Menten type. The kinetic equation obtained was used to simulate the anaerobic digestion process of this residue and to obtain the theoretical COD degradation rates in the reactor. The small deviations obtained (equal to or lower than 10%) between values calculated through the model and experimental values suggest that the proposed model predicts the behaviour of the reactor accurately. Copyright © 2007 Society of Chemical Industry     

Investigation of soluble microbial products in anaerobic wastewater treatment effluents

BACKGROUND: Anaerobic treatment of distillery wastewater, purified terephthalic acid (PTA) wastewater and synthetic glucose wastewater was conducted and the soluble microbial products (SMPs) in the anaerobic effluent were investigated. RESULTS: Gas chromatography‐mass spectrometry (GC‐MS) analysis showed that apart from the degradation residuals, the long chain alkanes, esters and acids totally accounted for the majority of the low molecular weight (MW) SMPs in the effluents. The sum of protein and polysaccharide SMPs in the effluent increased from 50 to 323 mg L^?1 when organic loading rate (OLR) was increased from 2.5 to 10.5 kg m^?3 d^?1; when influent COD changed from 5000 to 10 000 mg L^?1, the sum increased from 54 to 98 mg L^?1 at about the same OLR of 5 kg m^?3 d^?1. CONCLUSION: The results showed that SMPs made up an important proportion of organic compounds in the anaerobic effluents; the main low MW SMPs were long chain alkanes, esters and acids. The protein and polysaccharide SMPs increased with the increasing OLR, while higher influent concentrations led to higher concentrations of SMPs at the same OLR. From the variation of protein and polysaccharide SMPs along the height of the anaerobic reactors, it could be inferred that the methanogens might have contributed more in SMP consumption. Copyright © 2010 Society of Chemical Industry     

Anaerobic and aerobic treatment of a simulated textile effluent

A simulated textile effluent (STE) was generated for use in laboratory biotreatment studies; this effluent contained one reactive azo dye, PROCION Red H‐E7B (1.5 g dm⁻³); sizing agent, Tissalys 150 (1.9 g dm⁻³); sodium chloride (1.5 g dm⁻³) and acetic acid (0.53 g dm⁻³) together with nutrients and trace elements, giving a mean COD of 3480 mg dm⁻³. An inclined tubular anaerobic digester (ITD) was operated for 9 months on the STE and a UASB reactor for 3 months. For a 57 day period anaerobic effluent from two reactors, a UASB and an ITD, was mixed and treated in an aerobic stage. In days 77–247 68% of the true colour of PROCION Red H‐E7B was removed by anaerobic treatment with no colour removal aerobically and up to 37% COD was removed anaerobically, with a corresponding BOD removal of 71%. For combined anaerobic and aerobic treatment a mean COD removal of 57% and BOD removal of 86% was achieved. Operation of the ITD at a 2.8 day HRT (volumetric loading rate (B _v) 1.24 g COD dm⁻³day⁻¹) and the UASB at a 2 day HRT (B _v 1.74 g COD dm⁻³day⁻¹) gave comparable COD removals but the UASB gave better true colour removal. Effluent from the combined process operating on this simulated waste still contained an average 1500 mg COD dm⁻³, and further treatment would be required to meet consent standards. © 1999 Society of Chemical Industry     

Treatment of settled piggery waste by a down‐flow anaerobic fixed bed reactor

A study of the effect of organic volumetric loading rate (B_V) on the performance of a down‐flow anaerobic fixed bed reactor (DFAFBR) treating settled piggery waste was carried out at a range of between 1.1 and 6.8 g COD dm^?3 d^?1. The reactor operated at good removal efficiencies and stability under the operational conditions studied. Logarithmic empirical equations described adequately the removal efficiency for different parameters studied (COD, SCOD, BOD, TS, VS, TSS, VSS and phosphorous). Although process stability was affected by the increase of B_V, process failure was not observed. A logarithmic relationship was found to describe the influence of B_V on the TVFA/alkalinity ratio (p). A linear correlation was found between the effluent substrate concentration and the values of p and between p and the CO₂/CH₄ ratio in the biogas. The effect of the hydraulic volumetric loading rate (H_V) on the flow pattern of the reactor was evaluated. Dispersion number (D_n) was in the range of 0.17–0.37 for the maximum and minimum values of H_V studied, respectively. The ratio between the real and theoretical HRT increased as the H_V decreased. These results demonstrate that axial dispersion increased as the H_V and the Reynolds number decreased. Due to the hydraulic behaviour of the reactor, the kinetic model developed by Lawrence and McCarty was used for describing the experimental results obtained. Maximum specific substrate removal rate (K), specific organic loading rate constant (K_L), microbial decay coefficient (K_d), microbial yield coefficient (Y), maximum microbial growth rate (U_M) and saturation constant (K_S) were found to be: 3.1 (g COD g VSS^?1 d^?1), 3.0 (g COD g VSS^?1 d^?1), 0.062 (d^?1), 0.15 (g VSS g COD removed^?1), 0.39 (d^?1) and 2.6 (g SCOD dm^?3), respectively. Copyright © 2004 Society of Chemical Industry     

Anaerobic acidogenesis of dairy wastewater: the effects of variations in hydraulic retention time with no pH control

The performance of a laboratory‐scale mesophilic acidogenic reactor was evaluated in this study, in terms of volatile fatty acid production and distribution, with respect to variations in hydraulic retention time (HRT). The continuous flow‐completely mixed anaerobic reactor, coupled with a conventional gravity settling tank and a continuous recycling system, was operated in a hydraulic retention time ranging between 24 and 12 h, and up to an organic loading rate of about 9.3 kg COD m^?3 d^?1, without pH control. The acid production gradually increased proportionally to the organic loading rate, with decrease in hydraulic retention time. The highest degree of acidification and the rate of acid production were 56% and 3.1 g dm^?3 d^?1 at 12 h of HRT. Variations in hydraulic retention time affected volatile fatty acid production and distribution substantially, for the range investigated. Acetic, propionic, butyric and valeric acids were commonly produced during acidogenesis of dairy wastewater. Copyright © 2004 Society of Chemical Industry     

Start‐up and recovery of a biogas‐reactor using a hierarchical neural network‐based control tool

Due to its intricate internal biological structure the process of anaerobic digestion is difficult to control. The aim of any applied process control is to maximize methane production and minimize the chemical oxygen demand of the effluent and surplus sludge production. Of special interest is the start‐up and adaptation phase of the bioreactor and the recovery of the biocoenose after a toxic event. It is shown that the anaerobic digestion of surplus sludge can be effectively modeled by means of a hierarchical system of neural networks and a prediction of biogas production and composition can be made several time‐steps in advance. Thus it was possible to optimally control the loading rate during the start‐up of a non‐adapted system and to recover an anaerobic reactor after a period of heavy organic overload. During the controlled period an optimal feeding profile that allowed a minimum loading rate of 6 kg COD m^?3 d^?1 to be maintained was found. Maximum loading rates higher than 12 kg COD m^?3 d^?1 were often reached without destabilizing the system. The control strategy resulted simultaneously in a high level of gas production of about 3 m³_biogas m^?3_reactor and a methane content in the biogas of about 70%. To visualize the effects of the control strategy on the reactor's operational space the data were processed using a data‐mining program based on Kohonen Self‐Organizing Maps. Copyright © 2003 Society of Chemical Industry     

The Anaerobic Biodegradation of a Bagasse-Based Paper-Mill Waste in Fixed-Film Reactor

The high concentration of biodegradable constituents in waste-water derived from bagasse-based paper mills warrants the consideration of an anaerobic biotechnology process to recover biogas and reduce the pollution load. An anaerobic down-flow fixed-film bark reactor process was studied to treat waste-water generated from bagasse-based paper mills. At the anaerobic stage, 90–95% of the total chemical oxygen demand (COD) was removed at loading rates of 3–18 kg COD m%^?3 day%^?1 without supplying any nutrients or trace elements. A yield coefficient of 0.156 g cells (g COD) %^?1 was calculated at a high COD loading rate of 18 kg COD m%^?3 day%^?1. With the anaerobic treatment process it is estimated that 1 m³ of bagasse waste-water with a COD content of 13000 mg dm%^?3 can produce about 3.5 m³ of methane. Intermittent checks on the system alkalinity revealed that feed neutralization to maintain alkalinity would be necessary with sodium bicarbonate at approximately 2500 mg dm%^?3 for achieving steady-state high treatment efficiency.     

新型厌氧反应器COD去除影响因素研究

以模拟高浓度有机废水为研究对象,采用新型厌氧反应器对COD去除影响因素进行了为期4个月的试验研究,考察了污泥负荷、水力停留时间(HRT)、容积负荷、进水COD、VFA、出水SS等因素对COD去除的影响。结果表明,影响COD去除的主要因素是污泥负荷、HRT和容积负荷,次要因素是进水COD、VFA和出水SS,当反应器内COD污泥负荷在0.297 2～0.464 7 kg.kg-1.d-1之间、HRT=7 h时,COD的去除效率维持在72%～90%。     

Biodegradability of slaughterhouse wastewater with high blood content under anaerobic and aerobic conditions

In this work, the biodegradability of wastewater from a slaughterhouse located in Ke?an, Turkey, was studied under aerobic and anaerobic conditions. A very high total COD content of 7230 mg dm^?3 was found, due to an inefficient blood recovery system. Low BOD₅/COD ratio, high organic nitrogen and soluble COD contents, were in accordance with a high blood content. A respirometry test for COD fractionation showed a very low readily biodegradable fraction (S_S) of 2%, a rapidly hydrolysable fraction (S_H) of 51%, a slowly hydrolysable fraction (X_S) of 33% and an inert fraction of 6%. Kinetic analysis revealed that hydrolysis rates were much slower than these of domestic sewage. The results underlined the need for an anaerobic stage prior to aerobic treatment. Tests with an anaerobic batch reactor indicated efficient COD degradation, up to around 80% removal. Further anaerobic degradation of the remaining COD was much slower and resulted in the build up of inert COD compounds generated as part of the metabolic activities in the anaerobic reactor. Accordingly, it is suggested that an appropriate combination of anaerobic and aerobic reactors would have to limit anaerobic degradation to around 80% of the tCOD and an effluent concentration above 1000 mg dm^?3, for the optimum operation of the following aerobic stage. © 2003 Society of Chemical Industry     

Anaerobic digestion of Aegean olive mill effluents with and without pretreatment

BACKGROUND: Olive oil production is an important economical activity in the Aegean region of Turkey. However, the effluents of the olive oil producing mills with their high organic loads and toxic compounds are causing serious environmental problems. The anaerobic biological treatment of olive mill wastewater (OMWW) using the treatment plants of the regional industries could be a method of choice and within the scope of this study floccular and granular sludges were investigated in batch mode for their success in the treatment of OMWW while producing biogas. The major limitation of this treatment is the inhibition of methanogenic bacteria by the phenolic compounds in OMWW. Thus an integrated solution was suggested in which a pre‐treatment step (dephenolization) was also introduced before biological step. RESULTS: The effluents of 27 olive mills out of 47 were found to have total phenolics (TP) less than 3 g L^?1 and could be treated anaerobically after simple dilution. The biogas production for the untreated OMWW was higher for floccular sludge than for the granular sludge (68.5 mL and 45.7 mL respectively). Combined pre‐treatment experiments, first coagulation with polyaluminum chloride, followed by flocculation with cationic polyelectrolyte and finally Fenton's oxidation, could remove 80% of TP and 95% of the total suspended solids. CONCLUSION: OMWW having TP values less than 3 g L^?1 can be treated anaerobically using floccular sludge after simple dilution and biogas can be produced. For OMWW samples having higher TP values pre‐treatment is necessary and the pre‐treatment given in this study may be used effectively. Copyright © 2010 Society of Chemical Industry     

Anaerobic biodegradability and toxicity of eucalyptus fiber board manufacturing wastewater

Wastewater from eucalyptus fiber board manufacturing (EFBM) was characterized and studied for its treatability by anaerobic digestion. The characteristics of the wastewater (in mg dm^?3), are as follows: COD (42 000), SS (550), SO (1200), PO.P (50), NH.N (15), VFA (710), phenol (20), p-cresol (125), tannin COD (1460) and pH 2.8. Approximately 60% of the COD is composed of carbohydrates. The continuous treatment of EFBM wastewater resulted in 93% COD removal and 78% COD methanogenized, with influent COD values of 20 g dm^?3 and OLR of 17 kg COD m^?3 d^?1. The biodegradation reached 94% of influent COD and 74% of influent ultraviolet absorbance (215 nm). EFBM wastewater supplied at 20 g COD dm^?3 (1:1 tap water diluted) caused 50% methanogenic toxicity, which did not disappear when tannins were removed by adsorption on PVP (polyvinylpyrrolidone). The toxicity decreased to 25% once the wastewater was autoxidized with air at high pH values. However, the effluent of the continuously fed column didn't show methanogenic toxicity, therefore the main toxic compounds in the wastewater were removed during anaerobic treatment.     

Anaerobic digestion of alkaline black liquor using an up-flow anaerobic sludge blanket reactor

The anaerobic digestion of alkaline black liquor from a cereal straw pulping mill was studied in batch (serum bottles) and continuous systems (up-flow anaerobic sludge blanket reactor—UASB). The batch digestion studies confirmed that lignin and related compounds (LRC) in the alkaline black liquor were the main inhibitory substances and could not be decomposed by anaerobic bacteria. At organic loading rates of 5–10 kg COD m^?3 day^?1, the UASB reactor achieved 50–60% COD removal efficiencies. Gas production was 2–3 dm³ per dm³ of alkaline black liquor. Two different sludge types were examined in the reactor: granular and cluster-like sludges. Sludge in a cluster, which involved many small granules and flocs, tended to form larger aggregates and possessed good settling ability.     

The effect of solids on the electrochemical treatment of olive mill effluents

The electrochemical oxidation of an olive mill effluent over Ti–Pt anodes was studied. The effluent had an average total chemical oxygen demand (COD) value of 234 g L^?1, soluble COD of 61 g L^?1, soluble phenolic content 3.4 g L^?1, total solids of 80 g L^?1 and pH = 5.1. Experiments were conducted in a 10 L vessel with the effluent recirculating at 1 L s^?1. The applied current was varied between 5 and 20 A, the salinity between 1 and 4% NaCl, and experiments were performed with the effluent diluted with water to achieve the desired initial concentration. Emphasis was given to the effect of the presence of solids as well as of varying operating conditions on process performance as assessed in terms of COD, color and phenols removal. In general, degradation of phenols occurred relatively fast with conversion increasing with increasing applied current and decreasing initial organic loading and this was accompanied by low COD removal levels and moderate decolorization. The presence of solids had practically no effect on phenols removal, which, in most cases, was complete in less than about 180 min of reaction. However, oxidation in the presence of solids resulted in a substantial solid fraction being dissolved and this consequently increased sample color and the soluble COD content. The solid content typically found in olive mill effluents may partially impede its treatment by electrochemical oxidation, thus requiring more severe operating conditions and greater energy consumption. Copyright © 2007 Society of Chemical Industry     

Effects of butyric acid stress on anaerobic sludge for hydrogen production from kitchen wastes

BACKGROUND: Anaerobic digestion is an alternative technology to achieve the dual benefits of hydrogen production and waste stabilization from kitchen wastes. In this work, the butyric acid stress on anaerobic sludge was investigated in order to improve the tolerance of sludge against organic acids, and to enhance hydrogen accumulation. RESULTS: The tolerance of butyric acid in anaerobic sludge increased with the stress concentration, however, it decreased at concentrations greater than of 4.0 g L^?1. The maximum hydrogen yield reached 63.72 mL g^?1 VS at 4.0 g L^?1 stress, representing an increase of 114% compared with the control group. The concentration of volatile solids (VS) of the sludge and SCOD increased steadily with time up to 20 h. At 4.0 g L^?1 butyric acid stress, the maximum activity of β‐glucosidase, BAA‐hydrolysing protease and dehydrogenase enzyme were 14912.1 µmol PNP g^?1 TS h^?1, 134.14 µmol NH₄‐N g^?1 TS h^?1 and 7316.42 µg TF g^?1 TS h^?1, which were 2.78, 1.90 and 2.01 times that of the control, respectively. CONCLUSIONS: The feasibility of butyric acid stress on anaerobic sludge to increase hydrogen production from kitchen wastes was demonstrated. Remarkably, 4.0 g L^?1 butyric acid stress was found to be favorable for improving the tolerance of butyric acid in sludge as well as hydrogen yield in the experiment. Copyright © 2010 Society of Chemical Industry     

The influence of influent distribution and blood content of slaughterhouse wastewater on the performance of an anaerobic fixed‐film reactor

This paper evaluates the performance of a laboratory‐scale anaerobic fixed‐film reactor (AFFR) with arranged media treating slaughterhouse wastewater. The reactor was operated at 20 °C, its organic loading rate was increased from 1.8 to 9.2 kg COD m^?3 d^?1, and it had a short hydraulic residence time (5–9 h). The influence of wastewater concentrations on its performance was studied by artificially increasing the blood content of the wastewater. The efficiency of the removal of organic matter decreased from 70% to 54% as the superficial velocity increased from 0.12 to 0.97 m h^?1, due mainly to distribution defects, as had been confirmed experimentally by tracer tests. The kinetics of the anaerobic processes was limited by substrate availability, even at high COD concentrations (between 700 and 1100 mg dm^?3) due to a high content of slowly biodegradable and inert compounds present in the wastewater from the slaughterhouse. It was observed that a large amount of the organic matter had accumulated inside the reactor instead of being removed by methanogenic digestion. Furthermore, the fraction of organic matter held inside the reactor varied significantly in relation to the blood content of the wastewater. Copyright © 2005 Society of Chemical Industry     

Simultaneous removal of TOC and TSS in swine wastewater using the partial nitritation process

BACKGROUND: Considering biological nitrogen removal, the partial nitritation connected with the anaerobic ammonium oxidation (anammox) process is a promising alternative for nitrogen elimination at high loading rates. The objective of the present study was to evaluate the establishment and operation of a partial nitritation process in an airlift reactor with simultaneous removal of total organic carbon and suspended solids using swine wastewater. RESULTS: The partial nitritation reactor was inoculated with a nitrifying sludge at 2.1 gTSS L^?1 and fed with an UASB reactor effluent. High organic carbon loading rates, above 2 kgTOC m^?3 d^?1 have been shown to be potential inhibitors of the partial nitritation process due to competition between autotrophic and heterotrophic bacteria. In this study, the partial nitritation process was established using undiluted swine wastewater, with HRT of 24 h, 1.84 mgO₂ L^?1 (SD = 0.41) DO, loading rate of 1.14 gTOC L^?1 d^?1 and 0.91 gN‐NH₃ L^?1 d^?1 for more than 100 consecutive days. At the same time, the system proved to be an effective tool in TOC and TSS removal, reaching 84.9% (SD = 9.3) and 83.1% (SD = 0.1), respectively. CONCLUSION: This result enhances partial nitritation application as a technology for high load nitrogen converting, and allows the possibility of connection with anammox reactors. Copyright © 2012 Society of Chemical Industry     

Mesophilic anaerobic digestion of corn thin stillage: a technical and energetic assessment of the corn‐to‐ethanol industry integrated with anaerobic digestion

BACKGROUND: The purpose of this study was to reduce the VS (volatile solid) and recover energy (methane) from thin stillage through mesophilic anaerobic digestion in corn–ethanol plants. The performance of a continuously stirred tank reactor (CSTR) with different hydraulic retention times (HRTs) was evaluated in this study. RESULTS: The results show no differences in volatile solid (VS) destruction (82–83%) in the reactor with HRTs ranging from 25 to 40 days. The maximum volumetric methane production rate of 1.41 L L^?1 day^?1 was produced at 25‐day HRT, whereas the maximum methane yield of approximately 0.63 L CH₄ g^?1 VS_fed (0.77 L g^?1 VS_removed) was achieved with HRTs between 30 and 40 days. Simulation results using a kinetic model indicate that the reactor needs to be operated for longer than 23 days in order to achieve 80% of maximum methane yield. The techno‐economic potential of a corn–ethanol facility to produce an estimated 57% energy recovery using mesophilic anaerobic digestion has long been overlooked. A corn–ethanol plant integrated with mesophilic anaerobic digestion increases the net energy balance ratio from 1.26 to 1.80. CONCLUSION: Mesophilic anaerobic digestion complements the corn–ethanol business so that the sustainable energy obtained from corn recovery is made more lucrative and renewable. Copyright © 2011 Society of Chemical Industry