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