Co-composting of Olive Industry Wastes with Poultry Manure and Evaluation of the Obtained Compost Maturity

Abstract

The objective of this study is to examine the viability of recycling olive industry wastes by co-composting with poultry manures, describe the evolution of the physic-chemical and microbiological composting parameters, and evaluate the maturity of the obtained compost. The co-composting process applied was a windrow composting process. A pile was prepared by mixing olive mill pomace (OMP) and olive mill solid husk (OMSH) as carbon source, poultry manure (PM) as nitrogen source, green wastes (GW) as bilking agents and olive mill wastewater (OMW) as humidifier. The mixture was prepared based on fresh weight (FW) according to the following proportions: OMP + OMSH = 51.72% FW; GW = 27.58% FW; PM = 20.68% FW and C/N ratio = 29.25. The windrow was arranged in a pile of 1.5 m height, 2 m wide and 2 m length. Results showed that during the composting process, a high microbiological activity was depicted by a quickly increase in temperature (65 °C) in 09 days. An exponential increase in the number of aerobic microorganisms in the pile with a maximum (156 × 108 CFU g−1 FM) after 09 days of incubation and a progressive decrease in the C/N ratio over time were recorded. The obtained compost had a homogeneous particle size with a fine majority fraction (70.41% < 2 mm), a neutral pH (6.69) and a C/N ratio close to 10. It was also rich in minerals fertilizers (P, K, Ca). Finally, the germination tests carried out on 04 different seeds (tomato (Solanum lycopersicum), cresson (Lepidium sativum), sorghum (Sorghum bicolor) and alfalfa (Medicago sativa) showed that the obtained compost allowed germination index (GI%) values that exceeded 85%, which confirms the non-phytotoxicity of the product.