Reuse of expired dairy products and sewage in the production of biogas by anaerobic digestion

Abstract

Dairy industry is a prominent sector of the agro-industry with global production of 906 million tonnes of milk. Several dairy products are wasted due their high perishability. Anaerobic digestion is a sustainable alternative for reducing this waste aiming biogas production. This study evaluated the co-digestion of expired dairy products (EDP) with synthetic sewage from two assays using two types of dairy waste, separately: Assay I (EDP mixture of 80% of milk + 15% of yogurt + 5% of milk cream) and Assay II (industrial raw mixture of EDP). Both assays were composed of 20 g COD L-1 (Chemical Oxygen Demand per Liter) using anaerobic batch reactors (1.0 L) assembled in duplicates with 0.5 L headspace (N2) and working volume of 0.5 L with initial pH 8.2, at 37 °C, in a static mode. The cumulative CH4 productions were 2722.5 NmL in 31 days of operation (Assay I) and 3140.0 NmL in 25 days of operation (Assay II). Equivalent CH4 yields were obtained for the both assays with ~330 NmLCH4 g CODrem-1. Carbohydrates and COD removals were 96.8% and 98.0%; 87.3% and 89.4%, respectively. The co-digestion of EDP with sewage was effective to CH4 production with efficient organic matter removal. These results encourage new strategies for reuse of expired dairy products by the use of anaerobic digestion.