Treatment of raw mixed dairy wastewater using an attached-growth biological filter

The bioremediation of mixed dairy wastewater was examined using an attached-growth aerobic biological filter. The influent consisted of two distinct dairy wastewater streams in equal proportions: second cheese whey (SCW) and traditional Greek pudding dessert wastewater (PDW). Both streams had similar initial organic loads and were used in their raw, non-sterilized form.

A pilot-scale attached growth bioreactor, inoculated with indigenous microorganisms, was used with a working volume of 7 L. The batch reactor operated in recirculation mode at a flow rate of 1.0 L min^-1 and was tested under five different initial concentrations of dissolved chemical oxygen demand (d-COD), ranging from 1000 to 12500 mg L^-1.

The removal of both organic and inorganic components was investigated, including d-COD, sugars, nitrogen species, phosphorus and solids. The d-COD removal rates ranged from 115.5 to 194.6 mg L^-1 h^-1, while d-COD removal of 81.4% to 92.3% was achieved. N-NH₄ exhibited exceptionally high removal efficiencies, up to 99,9 %, while N-NO₃^- removal was more variable, ranging from 29.4% to 89.3%. Significant reductions in solids were also observed, with removal efficiencies of 92.8% for total dissolved solids and 93.9% for total suspended solids.

Notably, the final d-COD concentration in the experiment with an initial 1000 mg L⁻¹ d-COD was below the regulatory limit for discharge into natural water bodies (125 mg L⁻¹ COD). In all other cases, the final d-COD remained about or below 1000 mg L⁻¹, even at the highest initial load, indicating suitability for disposal into municipal sewage systems. These findings confirm the effectiveness of the proposed biological method in significantly reducing organic load and solids. The use of mixed dairy wastewater enhances microbial activity and process stability due to its balanced nutrient profile. This demonstrates the system’s adaptability to diverse and variable real-world dairy effluents.