An Effective Passive Solar Dryer for Thin Layer Drying of Poultry Manure

Abstract

Animal and poultry manures have been recognized for centuries as organic fertilizers providing essential nutrients to crops and improving soil structure due to their large input of organic matter. Increasing demand for poultry and egg products has led to intensification of the poultry rearing process, resulting in large amounts of poultry manure. Drying can be used to reduce the environmental impact of poultry manure and create a value added product for the farmers (animal feed or organic fertilizer). The aim of this study was to investigate the effect of solar heated air drying on the chemical and biological characteristics of poultry manure and develop a suitable manure solar dryer. The effects of temperature (40-60°C) and manure layer depth (1-3 cm) were evaluated. At the three temperature levels studied, the time required to dry poultry manure in the 1 cm-deep layer was the shortest, followed by the 2 and 3 cm-deep layers, respectively. The optimum depth to dry manure (at which the highest drying effectiveness occurred) was 3 cm. The manure drying rate increased with increasing temperature and was the fastest at 60°C for all manure depths studied. A drying temperature-depth combination of 60°C and 3 cm was the most efficient for the thin layer drying of poultry manure. Drying poultry manure at these conditions provided an effective means of removing moisture and odor and destroying microorganisms, thereby allowing the production of a value added product. This temperature range is feasible with a solar dryer operating in the tropics. A solar dryer operating at a 3 cm manure depth would be capable of drying 336 kg/h. Drying poultry manure with solar heated air resulted in a slight decrease in protein content (from 42 to 41%), a decrease in pH (from 8.4 to 6.6), removal of Salmonellae and a 99% reduction in numbers of total bacteria, yeast, mold and E. coli. Thin layer solar drying of poultry manure proved to be an effective means of converting poultry manure into a value added product while reducing the environmental and health problems that are associated with current disposal options.