Production of Biogas from Wastewaters of Food Processing Industries

Abstract

An Upflow Anaerobic Sludge Blanket Process used in converting biodegradable, soluble, organic pollutants in industrial wastewaters to a directly-burnable biogas composed mainly of methane has been developed, tested, and commercially applied in Holland. Operations on wastewater from the processing of sugar beets have shown hydraulic retention times of less than 10 hours with reactor loadings of at least 10 Kg COD per m3 digester volume per day and purification efficiencies exceeding 90%. Biogas production is at a rate of about 1 therm (100000 BTU) per 10 Kg COD treated. A moderately sized (1000 m3) wastewater treatment plant processing the order of 10000 Kg COD per day will, therefore, produce the order of 1000 therms of energy per day while, at the same time, reducing the COD level in the effluent by an order of magnitude.

The set of conditions required for efficient operation of this anaerobic process will be discussed. The process is unique in its mixed sludge bed approach allowing for tolerance of swings in Ph (6-8) at relatively low temperatures (32 C - 38 C) which can be readily achieved from most wastewater streams with little expenditure of additional energy. Sludge production is remarkably low, only about 5% of the COD loading, greatly alleviating disposal problems. These characteristics are conducive for the use of the anaerobic process to recover energy from a variety of wastewaters rich in carbohydrate-type substances as produced routinely as a by product of many types of food processing activities.