Comparative Analysis of Wastewaters from Three Bulgarian Dairy Multiproduct Plants

Abstract

The growing sector of dairy industry in Bulgaria leads to large waste stream formation with high pollution variation, which require specific treatment application. In the present research different fractions and wash waters from the production of kashkaval and white brined cheese, milk curd, strained yoghurt manufactured in three medium-type Bulgarian milk processing plants were studied. The basic indicators for wastewater quality: total solids (TS), total suspended solids (TSS), active reaction, fat, oil and grease (FOG), 5-day biological oxygen demand (BOD5), chemical oxygen demand (COD), total nitrogen (TN) and total phosphorus (TP) were analysed by standard procedures. The obtained results indicate that kashkaval whey from the sheep’s milk processing was the most contaminated effluent, reaching COD more than 68,000 mg O2/dm3 and BOD5 – up to 37,000 mg O2/dm3. Such high concentrated wastewaters can be treated only by anaerobic methods. Secondary cheese whey (SCW) has less impurities than cheese whey, but its soluble milk fractions are difficult to biodegrade, resulting in BOD5:COD ratio lower than 0.40. Application of membrane technologies in milk co-product processing remove totally FOG from the SCW, where BOD5 and COD values are around 950 and 2.500 mg O2/dm3, respectively. However, the TN concentration in it is not enough to apply directly aerobic utilization. This method is the most appropriate for washing waters, which occupy both the largest volume and the cleanest fractions of all milk effluents. Future combinations of different dairy wastewaters will show the best utilization protocol for each of the milk processing plant.