Confined animal production is an efficient way to produce meat, but creates a number of problems, one being the large amount of manure. Composting is one method of waste handling that allows its use as fertilizer. Hog manure can difficult to compost due to the high moisture level. In China, dry ingredients (bulking agents) are typically added to hog manure to reduce the water content from 75% to 60% or below. Bulking agents can be costly and dilute the fertilizer value of the resulting compost. House flies will lay their eggs and develop in manure. A group of Chinese scientists asked, “Can house fly maggots be used to quickly reduce the water content of pig manure to facilitate composting?”*
The scientists innoculated a 7 cm thick layer of pig manure with a series of maggot concentrations and found a concentration that optimized drying times and production of maggots. Suitable concentrations of maggots could dry the manure in 6 days or less. Using maggots to compost manure could create an unwanted problem: adult flies. Therefore they collected maggots from the manure by repeatedly skimming a thin layer at the top. Maggots respond by tunneling down into the manure so that eventually the manure is removed and only the maggots remain. The maggots were collected and killed by microwave. Analysis of the maggots determined that the protein concentration was high enough and the heavy metals concentrations low enough to meet the standards for commercial fish food.
Their process could improve the ability to compost manure and at the same time contribute to the protein production that will be needed to feed the expanding human population. The resulting compost has a better fertilizer value (NPK) that compost from manure treated with bulking agents. New and creative uses of insects can help address some of our technical challenges.
*Feng-Xiang Zhu, Yan-Lai Yao, Su-Juan Wang, Rong-Guang Du, Wei-Ping Wang, Xiao-Yang Chen, Chun-Lai Hong, Bing Qi, Zhi-Yong Xue & Hong-Quan Yang. 2015. Housefly maggot-treated composting as sustainable option for pig manure management. Waste Management. 35: 62–67.