Addressing wastewater challenges in the dairy industry: a focused case study

This Research Paper addresses the hypothesis that wastewater characteristics in the dairy industry vary with product type and operational procedures, and that current treatment methods face limitations in managing such variability. The study examined raw and clean-in-place (CIP) wastewater from a Serbian dairy plant over three years. Physico-chemical and microbiological analyses included pH, protein, fat, carbohydrates, total solids, total microorganisms, <i>E. coli</i>, Enterobacteriaceae, chemical oxygen demand (COD), total suspended solids (TSS), nitrogen (N), phosphorus (P), and dissolved oxygen (O₂).Dairy plants produced 0.2-10 L wastewater per litre of milk. Protein content ranged 0.07-0.31 g/100 ml, fat 0.01-0.19 g/100 ml, and carbohydrates up to 1.37%. Total solids were 0.13-2.95%. pH varied from 4.41 to 12.76, affected by lactic fermentation and cleaning agents. COD values (529-12,476 mg/l) indicated strong organic loads. Microbiological counts were highly variable, with <i>E. coli</i> up to 10³ cfu/ml and total microorganisms up to 1 × 10⁸ cfu/ml. Nitrogen ranged 36-104 mg/l and phosphorus reached 10.91 mg/l, sometimes exceeding limits. Principal component analysis (PCA) explained 61.86% of variance, driven by N, pH, P, <i>E. coli</i>, Enterobacteriaceae, and oxygen content. Seasonal patterns were identified: higher TSS during spring and summer, and increased microbial loads, COD, and oxygen fluctuations in autumn and winter. The findings demonstrate that dairy wastewater is complex and variable, requiring adaptive treatment strategies. Optimised management, including pH control, nutrient removal, and combined biological and advanced technologies, can improve treatment efficiency, support reuse, and mitigate environmental impact.