Escherichia coli inactivation kinetics in anaerobic digestion of dairy manure under moderate, mesophilic and thermophilic temperatures

Pramod K Pandey 0 Michelle L Soupir 0 0 Agricultural and Biosystems Engineering Department, Iowa State University , Ames, 50011, USA Batch anaerobic digestion experiments using dairy manure as feedstocks were performed at moderate (25C), mesophilic (37C), and thermophilic (52.5C) temperatures to understand E. coli, an indicator organism for pathogens, inactivation in dairy manure. Incubation periods at 25, 37, and 52.5C, were 61, 41, and 28 days respectively. Results were used to develop models for predicting E. coli inactivation and survival in anaerobic digestion. For modeling we used the decay of E. coli at each temperature to calculate the first-order inactivation rate coefficients, and these rates were used to formulate the time - temperature - E. coli survival relationships. We found the inactivation rate coefficient at 52.5C was 17 and 15 times larger than the inactivation rate coefficients at 25 and 37C, respectively. Decimal reduction times (D10; time to achieve one log removal) at 25, 37, and 52.5C, were 9 -10, 7 - 8 days, and < 1 day, respectively. The Arrhenius correlation between inactivation rate coefficients and temperatures over the range 25 -52.5C was developed to understand the impacts of temperature on E. coli inactivation rate. Using this correlation, the time - temperature - E. coli survival relationships were derived. Besides E. coli inactivation, impacts of temperature on biogas production, methane content, pH change, ORP, and solid reduction were also studied. At higher temperatures, biogas production and methane content was greater than that at low temperatures. While at thermophilic temperature pH was increased, at mesophilic and moderate temperatures pH were reduced over the incubation period. These results can be used to understand pathogen inactivation during anaerobic digestion of dairy manure, and impacts of temperatures on performance of anaerobic digesters treating dairy manure. - Introduction In the United States, combined livestock production of cattle, swine, and sheep generates 49% of the total farm income, which is nearly 241 billion dollars (US Census Bureau 2010,). The practice of applying livestock manure to recycle waste to enhance crop yield is more than 4,000 years old, and this practice continues to reduce farm fertilization costs in the developing as well as the developed world (WHO 2010,; USEPA 2010,). However, land application of manure can damage environmental ecosystems (USEPA, 2010,) and create a risk to human health if not applied properly. Runoff from fields where manure has been applied can be a source of pathogen contamination in ambient water bodies including streams lakes and reservoirs and groundwater systems (Brennan et al. 2010,; Gerba and Smith 2005,; Mawdsley et al.1995,; Pell 1997,; Tyrrel and Quinton 2003,; Unc and Goss 2004,), particularly if a rainfall event occurs soon after application (Soupir et al. 2006). Manure can contain numerous pathogenic organisms that are associated with human diseases including salmonella, E. coli O157:H7, Yesinia, campylobacter, guardia, and cryptosporidium (Klein et al. 2010,; Ltourneau et al. 2010,; Mass et al. 2010,; Ziemer et al. 2010,). Treating manure before land application can greatly reduce the number of viable pathogens, and various methods such as drying (Amin-Nayyeri et al. 2010,), composting (Maeda et al. 2010,), heat treatment (Shepherd Jr et al. 2010,), radiation treatment (Farag and Mohamed 1999,; Sinton et al. 2007,), aerobic digestion (Bortone 2009,; Dumas et al. 2010,; Shen et al. 2010,), and anaerobic digestion (Aitken et al. 2005,; Aitken et al. 2007,; Lang and Smith 2008,; Popat et al. 2010,; Sung and Santha 2003,; Wagner et al. 2009) are typically used. Of these, anaerobic digestion is crucial as it produces biogas, a source of energy, in addition to reducing pathogens. The use of anaerobic digesters for biogas production and manure treatment is well established and has been implemented all over the world. A tremendous amount of research has been conducted on the anaerobic digestion process to enhance biogas production (Climent et al. 2007,; He et al. 2008,; Kim et al. 2010,; Pandey et al. 2010,; Yilmaz and Demirer 2008,; Zaher et al. 2008,), increase nutrient recovery (Banu et al. 2009,; Carrere et al. 2010,; Jin et al. 2009,; Novak et al. 2010,; Prapaspongsa et al. 2010,; Wang et al. 2010,), and reduce solids content (Forster-Carneiro et al. 2010,; Gilroyed et al. 2010,; Gong et al. 2010,; Riau et al. 2010,; Rubio-Loza and Noyola 2010). Batch reactors are a useful tool to improve understanding of the outcomes of anaerobic digestion processes. Masse et al. (2010) evaluated efficiency of commercial-scale psychrophilic anaerobic digestion in sequencing batch reactors, operated at 7 or 14 days hydraulic retention time and 24C. The authors found that the concentrations of fecal coliforms, E. coli, Salmonella, Campylobacter spp., and Y. enterocolitica were reduced to undetectable levels in pig manure. Ct et al. (2006) found nearly complete reduction of total coliforms and E. coli by anaerobic digestion at 20C for 20 days while Baert et al. (2010) observed a 4 log decrease of Murine Norovirus-1 at 37 and 52C after 13 and 7 days, respectively. Several studies have focused on pathogen inactivation in sludge anaerobic digestion at thermophilic temperatures to achieve Class A (complete pathogen inactivation) and Class B (incomplete pathogens removal) classification (Aitken et al. 2005,; Popat et al. 2010,; Puchajda et al. 2006,; Smith et al. 2005,; Wagner et al. 2009,). For example, Shin et al. (2010), used the batch process to show decreases in bacteria 16S rRNA gene concentrations and organic removal efficiency in anaerobic digestion of secondary sludge, while Aitken et al. (2005) measured the inactivation of vaccine - strain poliovirus and eggs from helminth Ascaris suum at temperatures from 49 to 55C in biosolids. Popat et al. (2010) used the batch process to estimate the inactivation kinetics of Ascaris suum and poliovirus type 1 (PVS -1) at temperatures ranging from 51 to 56C. Despite previous studies to determine pathogen decay under anaerobic conditions, no information exists on the performance of anaerobic digestion in reducing pathogen concentrations in dairy manure. Aitken et al. (2005), and Popat et al. (2010) provided important information about pathogen inactivation kinetics in anaerobic digestion. However, both of these studies are focused on anaerobic digestion of sludge obtained from municipal waste treatment facilities, and inactivation kinetics were determined at temperatures ranging from 49 to 56C (thermophilic). Both studies emphasized the need for improving EPAs time - temperature relationships. Our objective is to determine the E. coli inactivation kinetics in dairy manure at moderate (25C), mesophilic (37C) and thermophilic (52.5C) temperatures, and use the inactivation kinetics at these temperatures to derive the time - temp (...truncated)