Biomethanization of mixtures of fruits and vegetables solid wastes and sludge from a municipal wastewater treatment plant

Abstract

The possible management of Fruit and Vegetable Solid Wastes (FVSWs) through their simultaneous digestion with the primary sludge of Municipal Wastewater Treatment plants is investigated. This alternative allows the recovery of energy and a solid product that can be used as an amendment for soils that generated the residue, while is not expensive. Results indicate that the ratio of FVSWs to sludge and the pH control are the main variables determining the methane production and concentration. NaHCO₃ was selected to achieve the pH control. The results for a ratio of 50% sludge together with 10 g NaHCO₃/kg of residue are among the best obtained, with a methane yield of about 90 L per kg of volatile solids, and a methane concentration of 40% (v/v) of the biogas. A 50% reduction of the total solids; 21% reduction of the volatile solids (in terms of total solids); and a pH value of the sludge, which is 6.9 indicate that the digested sludge can be a good material for soil amendment.

Keywords:

• Anaerobic digestion
• recycling
• energy recovery
• soil amendment
• waste management.

Acknowledgments

Authors acknowledge Mercadona SA for providing the funds for the Research Project “Aprovechamiento energético de subproductos vegetales de la industria agroalimentaria,” which shows their interest on the promotion of the scientific research on environmental issues related with the food sector. CGL and CVA also acknowledge the economic support from the Secretaria General de Universidades, Investigación y Tecnologia, of the Junta de Andalucia (Spain), through the Program “Medidas de Impulso de la Sociedad del Conocimiento en Andalucia.”

Notes

*6 NaHCO₃ + 4 Ca(OH)₂.