Characteristics of whole and scraped swine waste as substrates for contiinuously expanding anaerobic digestion systems

A study was performed using continuously expanding anaerobic digestion to determine the operating and performance characteristics of two types of swine waste. The two types of manure were a scraped manure, from a sloping concrete floor where the urine fraction of the waste drained into gutters, and a whole waste, collected using a pan under a slatted-floor production facility. There exists a possibility of considerable differences in the methane production capability of these two waste types. Identical runs employing the continuously expanding digestion (CED) technology were made using the two waste types. Operating parameters for both runs were a 70-day cycle time, a 35°C temperature and a Volatile Solids (VS) loading concentration of 81 g of Volatile Solids per liter. The study used 378 liter bench scale reactors which were replicated. Due to the identical operating parameters, the differences noted in methane production between the two waste types can be attributed only to characteristics of the raw waste. The operating characteristics noted include a lower acid level and higher alkalinity and pH levels for the whole waste. Almost identical ammonia levels for the two runs were noted. Performance characteristics are quite different. Whole waste produced a 65·3% VS reduction while the VS reduction for scraped waste was 50·9% and total methane production was 24·4% higher using the whole waste. Gas quality for both waste types was approximately 60% methane while specific methane productivity (liter of CH₄ per gram of Volatile Solids destroyed) was not significantly (p > 0·05) different between the two waste types.