Effect of swine waste concentration on energy production and profitability of aerobic thermophilic processing

Abstract

Improvements to aerobic thermophilic processing have led to the ability to recover significant amounts of energy as hot water (∼55°C). This energy can easily be made useful in swine production facilities as a source of heating for farrowing or nursery buildings, aquaculture tanks or greenhouses for most of the year. Work is underway to investigate alternative uses for the energy in the hot months. Potentially, the energy may be used to dry the residual solids from the process (∼40% of the original amount of solids) and these solids may be used for application as: (1) field fertilizer in the non-growing season, (2) a high value organic food fertilizer, and (3) dry solids for co-firing in electric power stations. Heat produced may also be used to generate induced draught in chimneys to aid in building ventilation, reducing electric power consumption, and also to power state-of-the-art refrigeration/chilling systems for cooling production buildings. This work makes use of a design and economic model for a given configuration of aerobic thermophilic treatment suitable for swine production facilities to evaluate the effects on economics and energy production of various swine waste concentrations. While actual waste from the animal may be in the 130 g l −1 dry solids range, waste for treatment is often diluted based on hog watering rates and building cleanout and flush systems. Some concentrations are as low as 15 g l −1 . Lower waste concentrations require larger initial expenditures related to increased reactor volumes and tend to strongly affect the profitability of the process. Straightforward engineering design considerations permit profitable use of this technology even in these low concentration ranges.