(553f) Pretreatment of Hog Manure Prior to Anaerobic Digestion

Hog farming is a significant agricultural activity in Canada, with the size of operations expected to increase substantially in the near future, increasing the generation of hog originated organic waste. Canada produces 24.4 million tons of manure annually, which is traditionally disposed as in crop applications.

However, the concern is that pig manure can contain high concentrations of endocrine-disrupting chemicals, including natural estrogens. These chemicals have been proven through various studies to have long-term adverse effects on the growth and toxicity, development and reproduction of fish and wildlife. Runoff from fields treated with pig manure can enter adjacent streams or other bodies of water, resulting in eutrophication or even acute toxicity.

Recently the interest of using hog manure in farms for energy has substantially increased. Anaerobic digestion, which is the most widely used sludge stabilization process worldwide, utilizes anaerobic bacteria to break down about 40-50% of the organic matter of the sludge to form valuable biogas (methane) and to reduce pathogen content of the sludge prior to disposal. A disadvantage of the digestion process is the slow sludge hydrolysis rate requiring large volume digesters. Anaerobic processes are also hindered by high oil and grease concentrations, especially present in high strength food processing wastewaters. The biodegradability and dewaterability of biosolids as well as destruction of pathogens and odorous compounds can be improved by the pretreatment of sludge. In this work, advanced oxidation processes (AOPs) that are characterized as producers of hydroxyl radicals in practical quantities are used for hog waste pretreatment. Research has been conducted using hog waste and different schemes of AOPs namely ultrasonication to determine the pretreatment efficiency of hog waste prior to anaerobic digestion. The efficacy of pretreatment processes is evaluated with respect to the extent of hog waste solubilization, particle size distribution, and biogas production. The effect of pretreatment on the destruction of odor precursors specifically on protein compounds is also evaluated. Pretreatment methods are optimized in batch studies with respect to various process parameters such as acoustic power density (power per unit reactor volume), and sonication time..

Key words: Anaerobic digestion, hog waste pretreatment, advanced oxidation, gas production, pathogen reduction.