Biological Purification of Chemically Pre-Treated Dairy Wastewater Before Discharge into a Municipal Sewage Systems

Abstract

Dairy production is one of the most inefficient processes with respect to water usage in the food industry. It was estimated that the production of a litre of milk creates three to four litres of wastewater. Dairy wastewater contains a high amount of dissolved and suspended solids. Moreover, it contains high concentrations of fat, protein, and carbohydrate. Consequently, the dairy wastewater content of organic compounds is high and so is its chemical oxygen demand. The majority of organic compounds are biodegradable with a high biological and chemical oxygen demand ratio. In this work, we examined the biological purification of physico-chemically pretreated wastewater from a Hungarian milk-processing factory before it was discharged into the public sewage system. The chemical oxygen demand of the pre-treated wastewater ranged from 500 to 2500 mg dm-3. We found that it was possible to achieve efficient organic material removal from nutrient-poor wastewater without nutrient dosage contrary to the literature. The activated sludge system manifested efficient organic material removal that required a smaller biological volume. Experiments with biofilms have shown that a thicker biofilm needs more dissolved oxygen, which dictates oxygen input levels to be sufficient for creating an aerobic environment.