UC Davis

Dairy industry is important for milk production and has substantial contribution to the California’s economy, however, dairy farms also produce manure, which impacts the environment. Dairy manure contains carbon, nitrogen and phosphorus, which are beneficial to soil. Manure also contains many bacteria including human pathogen, such as Salmonella and Escherichia coli (E. coli) which poses risk to public health. In this research, an intensive reconnaissance survey of manure stored in dairy lagoon was conducted to determine the prevalence of E. coli and Salmonella. In addition, an attempt was made to develop the ozone and air-based treatment method to reduce pathogen in liquid manure. First a comprehensive review on microbial pollution of manure, and various control method was performed (Chapter 1). Secondly, a field study was undertaken to collect dairy manure from 20 dairy farms to determine the prevalence of indicator E. coli, Shiga toxin producing E. coli (STEC), and E. coli O157:H7 (Chapter 2). Finally, a lab scale experiment was developed to determine the impact of ozone and air injection on E. coli inactivation in liquid manure (Chapter 3). The first chapter addresses the issues of microbial pathogen in manure and associated risk to human, animal and environment and impacts of various treatment methods on bacteria control. Previous studies showed that anaerobic digestion reduces E. coli and Salmonella under prolonged incubation and high temperature conditions, however, many anaerobic pathogens such as Clostridium survive anaerobic environment. In anaerobic incubation, E. coli level is reduced, but these bacteria are not eliminated completely. In the second chapter, several bacteria testing methods were used to determine the prevalence of E. coli, Salmonella, STEC and E. coli O157:H7 which are common pathogens in dairy manure. About 177 manure samples were collected from 20 dairy farms from primary and secondary lagoons to test the bacteria using agar culture-based methods, polymerase chain reaction (PCR) method for detection of E. coli and Salmonella. In addition, a real- time PCR based method was used to determine the presence of E coli O157:H7. Results showed that the prevalence of Salmonella in manure sample is lower than E. coli. The bacteria detection approach presented here could reduce the number of testing required during downstream confirmation process. The presence of Salmonella was found in 2.26 % of the samples, and both the culture-based and PCR methods yielded comparable outcomes in detecting Salmonella. Moreover, approximately 11.30% of the total samples out of the 177 were identified as positive for STEC by qPCR. None of the lagoon samples were positive to E coli O157:H7 by qPCR. The outcomes of this study hold substantial importance to determine the microbial quality of lagoon manure, and aid in the selection of appropriate methodologies for determining the prevalence of pathogenic organisms in dairy manure. In the third chapter, lab scale experiments were conducted to determine the impacts of ozone injection (Ozonation) and air injection (Aeration) in liquid dairy manure on E. coli reduction. Liquid manure was exposed to ozone and air for multiple durations (0 min, 60 min, 120 min, and 240 min) and E. coli levels were determined. Further, manure samples were analyzed for pH, salt content, potassium (K+), sodium (Na+), nitrate (NO3-), calcium (Ca2+), and electrical conductivity (EC, mS/cm). Results showed that Ozonation can be an effective treatment method to reduce E. coli levels in liquid manure. Further nitrate ions were reduced substantially by Ozonation. The analysis of variance (one way and two way) revealed significance difference in E. coli and nitrate reductions in liquid slurry among ozone and air treatments (p <0.05). The study's results carry significance importance in terms of developing a simple field-scale method for reducing microbial and nutrient pollutions from dairy lagoon manure.