Monitoring: Physic‐Chemical, Microbiological, and Phytotoxic Parameters of Mixed Oil Mill Waste and Green Waste Composts Moistened with Treated Urban Wastewater and Tap Water

Abstract In Tunisia, on‐site co‐composting of oil mill waste would overcome environmental issues and valorize renewable resources. The authors' goal was to determine the physic‐chemical and microbiological properties and nutrient supply characteristics of mixed oil mill waste and green waste compost. Two piles of the same raw materials (2/3 oil mill waste–1/3 green waste, w/w) were moistened with two kinds of water: treated urban wastewater (A1) and tap water (A2). Results showed the following: (i) produced compost decreased in C/N from 32 to 12.30 ± 0.89 (A1) and 11 ± 0.89 (A2); (ii) major elements (P and K) were within acceptable limits; (iii) A1 and A2 had potentially lower heavy metal contents than the limits established by the second draft of the Biological Treatment of Biowaste of the European Commission and microbial load values below the limit N FU 44‐051 values; (iv) A1 and A2 had, respectively, 93 and 89.67% as germination index Gl values, which confirmed the composts' maturity and safety; (v) for both composts, A1 and A2, culture potting made up of half compost and half soil revealed the highest bean leaves' number; and (vi) the less richness in minerals and organic compounds of A2 compared to A1 gave better germination results for white wheat and bean leaves' number for A2. Even moistened with treated urban waste water, oil mill wastes proved to be very interesting for co‐composting with green waste.