Session- Fate of Pathogens in Specific Feedstocks
E. Coli Survival in Compost Tea Using Different Nutrient Substrates
VICKI H. BESS, Misty Manes, Brantlee S. Richter, Jennifer L. Snodgrass
BBC Laboratories, Inc., Tempe AZ, USA
Compost tea, a product made by the aqueous extraction of compost, is increasingly being used by more growers to deliver the microbial and soluble nutrient components of compost through irrigation systems or as a foliar application. Compost tea is used for various purposes including disease suppression and nutrient delivery to the plant. Several companies worldwide now make commercially available machines specifically for the production of compost tea on a scale ranging from the backyard gardener to growers with greater than 1000 acres. Recipes for producing compost tea have been devised to increase microbial numbers in the final product for potential increase in the compost tea impact. These formulations, frequently containing simple and easily available carbon sources, may unintentionally enrich for the growth of human pathogens such as E. coli during the production of the compost tea. This study investigates nutrient additions during the production of compost tea and the influence of these carbon sources on the survival and growth of E. coli. A commercially available compost tea "brewer" was used for compost tea production and the nutrients tested include molasses, liquid barley malt, seaweed extract, yeast extract and fish emulsion at concentrations of 2g/l. Samples taken on a time line between 8 and 24 hours into compost tea production indicate that the addition of simple sugars enhance the growth of E. coli, analyzed by AOAC 991.15, while the elimination of sugars can reduce or eliminate the pathogen even though it is present in the starting compost.
Composting Sheep Offal in an Aerated Bunker System
DONNA CHAW (1)
(1) Olds College Centre for Innovation, Composting Technology Center, Canada
This project was initiated when a federally inspected sheep slaughtering facility in Alberta, Canada was unable to slaughter mature sheep because of the difficulty associated with the disposal of offal and waste. Despite strict survelliance and disease prevention program in Alberta the renderers would not accept sheep into their facilities due to the stigma associated with Scrapie (a transmissable spongiform encephalothy (TSE) of sheep). Alberta and many other provinces in Canada are faced with the need to develop responsible and efficient ways to dispose of mature sheep offal and waste. A comprehensive investigation for diposal options for mature sheep offal concluded that composting was the most promising option. A pilot project was conducted at the Composting Technology Centre (CTC) at the Olds College Centre for Innovation over a one year period. Offals and condemned carcasses were delivered to the CTC weekly. An average of 50 mature sheep were slaughtered once a week and the offals were blended with wood shavings and sawdust, prior to placing in an outdoor composting system. The aerated bunker system consisted of four bunkers and materials rotated through the system every four weeks. The aerated bunker system proved to be the appropriate choice of technology for composting the offal and waste. Rapid degradation of the soft tissue was observed and fresh materials readily maintained thermophilic temperatures within the bunkers independent of sub-zero ambient temperatures in the winter. This paper presents the composting parameters and microbiological data collected from the pilot trial summarizing the effectiveness of the system to treat this type of residual, and the technology transfer information that has resulted.
Pathogen Regrowth in Compost Teas and Transfer to Vegetables
Brion DUFFY (1), Ryan Stevenson (1), Chester Sarreal (1), Subbarao Ravva (1), Larry Stanker (1)
(1) Food Safety and Health Research Unit, US Department of Agriculture, Agricultural Research Service, Albany, CA, USA
Composting is an effective approach to reduce pathogen numbers in manure. We are concerned with potential regrowth of pathogens when composts are handled inappropriately. Processing of composts to produce watery extracts called compost teas is gaining in popularity among organic growers and home gardeners. Preparation methods often call for the addition of carbon sources such as molasses to stimulate a rapid increase in microbial populations. Recipes calling for as much as 2% of such amendments are common in trade literature. Our work monitored the risk potential for regrowth of E. coli O157:H7 and Salmonella Thompson in teas made from various types of compost. We used outbreak strains marked with antibiotic resistance and carrying stable GFP plasmids. Teas were prepared by soaking 20 g compost solids for 3 days in 180 ml sterile water in a 500 ml flask with shaking at 20 C. Molasses was added at a range of concentrations from 0 to 1% v:v. Teas were inoculated with either bacterium to give 1 CFU/ml. Amendments greatly increased regrowth of both bacteria in dairy compost, yard waste compost, and chicken manure compost teas (approximately 2.5 log increase with 0.5% molasses in most cases). However, regrowth potential depended on the pathogen and also on the type of compost used to prepare teas. For example, with 0.5% molasses, Salmonella increased from 1 to over 1000 CFU/ml in teas made from dairy or yard waste compost but exceeded 350,000 in chicken manure compost tea, whereas, E. coli regrowth was the same in all types of compost teas. Using Confocal Laser Scanning Microscopy, we observed that GFP marked pathogens were transferred to tomato foliage by spray application of contaminated teas, and that pathogen populations proliferated in veins and on glandular trichomes. Results with other amendments and with transfer to flowers and fruits will be discussed.
Reduction of Fecal Streptococci and Strongyle Eggs during Small-Scale Composting of Horse Manure Mixed with Wood Shavings
Uta KROGMANN (1), Paul V Romano (1), Michael L Westendorf (2)
(1) Dept Environ Sci, Rutgers University, (2) Dept Animal Sci, Rutgers University, USA
Construction activities, urban runoff, and horse farms are the predominant sources of non-point source pollution in the coastal Monmouth County drainage basin in New Jersey (US). We proposed to implement Best Management Practices for manure composting on small horse farms (1-5 horses). Horse manure composting reduces pathogens in the manure, produces a storable end product for on- and off- farm use and therefore lowers nonpoint source pollution from horse farms. Most horse farmers are pleasure farmers and will only implement simple, cost-effective composting methods. It was known that simple composters used in the backyard do not efficiently reduce pathogens due to their small scale. However, it was not clear if small-scale composting on horse farms could ensure pathogen reduction during all seasons. The objective of this study was to evaluate pathogen reduction in a simple shed composter during various seasons. A 6-bay composter (2.3 m x 2.1 m each bay) was constructed and covered by a shed roof. Horse manure mixed with wood shavings (bedding) has been composted for 4-8 weeks in the fall, winter and spring. The heights of the weekly turned piles were 1.2 m and 1.6 m, respectively. The moisture content ranged between 50% and 65%. Temperature, oxygen levels, moisture content, bulk density, pH, organic matter and respiration rate were monitored. Fecal streptococci and strongyle eggs, eggs of a horse parasite, were used as pathogen indicator organisms. Compost quality, including nutrient contents, was determined for selected samples. Results of this study will be presented and the implications for composting horse manure on small horse farms will be discussed.