Processed milk waste recycling via thermal pretreatment and lactic acid bacteria fermentation

Abstract

Processed milk waste (MW) presents a serious problem within the dairy industries due to its high polluting load. Its chemical oxygen demand (COD) can reach values as high as 80,000 mg O₂ L⁻¹. This study proposes to reduce the organic load of those wastes using thermal coagulation and recover residual valuable components via fermentation. Thermal process results showed that the COD removal rates exceeded 40% when samples were treated at temperature above 60 °C to reach 72% at 100 °C. Clarified supernatants resulting from thermal treatment of the samples at the temperatures of 60 (MW₆₀), 80 (MW₈₀), and 100 °C (MW₁₀₀) were fermented using lactic acid bacteria strains without pH control. Lactic strains recorded important final cell yields (5–7 g L⁻¹). Growth mediums prepared using the thermally treated MW produced 73% of the bacterial biomass recorded with a conventional culture medium. At the end of fermentation, mediums were found exhausted from several valuable components. Industrial scale implementation of the proposed process for the recycling of industrial MWs is described and discussed.

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