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Clemson scientist reducing risk from compost


May 14, 2009
By Marg Land

May 14, 2009, Clemson, SC — Heat-treating animal manure does not sound like spellbinding science, but it can save lives.

May 14, 2009, Clemson, SC — Heat-treating animal manure does not sound like spellbinding science, but it can save lives.

A Clemson University food safety researcher has been awarded $222,000 to reduce illness-causing bacteria from getting into farms and gardens through manure used as fertilizer.

A teaspoon of fertile soil can have as many as 1 billion bacteria. Some bacteria are harmful to humans, causing gut-wrenching sickness and even death among the very young, very old or very weak. By raising temperatures and using other approaches, Xiuping Jiang has been lowering bacterial counts in compost.

The Center for Produce Safety at the University of California in Davis is funding the research by Jiang, an associate professor in Clemson’s food science and human nutrition department. The microbiologist works on microbial safety, the control and source of food pathogens. Pathogens are microorganisms that cause disease. Some pathogens, including salmonella and E. coli (Escherichia coli 0157:H7), have been linked to using manure.

The research goals for Jiang and her colleagues Jinkyung Kim in food science and Feng Luo in the computer sciences department are to:

  • understand how human pathogens react to heat in compost,
  • use biological controls to reduce pathogen re-growth in compost,
  • develop a sensitive pathogen detection method and
  • apply mathematical modeling to simulate the effect of heat on pathogen growth.

The relationship between livestock production, manure management and human health has been in the news. Organic and commercial vegetable growers are using fresh and composted animal feces — manure — as fertilizer and soil enrichment for farms, gardens, nurseries and greenhouses. Livestock and poultry manure naturally contain a wide range of bacteria as well as viruses and protozoa. Some cause illnesses: E. coli is most common in cattle manure; salmonella is most common in poultry manure. Food-related sicknesses have been linked to E. coli and salmonella on apples, lettuce, spinach, cantaloupe and sprouts. Root crops and leafy vegetables have a greater risk of infection from manure application to soil.

Composting often is used to reduce the spread of pathogens before mixing into the soil, but it must be done correctly. Bacteria are survivors, some lasting more than year under the right conditions. For example, E. coli survives cold temperatures and tolerates acidic, salty and dry conditions. Fortunately, it is easily destroyed by heat, provided temperature and duration are sufficient.

Jiang’s research team also is studying biological controls, such as other bacteria in the compost that can grow more rapidly and out-compete harmful pathogens for nutrients. Additionally, the researchers are devising an improved ways to find harmful bacteria, enabling farmers and growers to more confidently identify and count pathogen populations in manure-based compost.


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