Co-composting of Olive Mill Waste and Wine-Processing Waste: An Application of Compost as Soil Amendment

In order to decrease the environmental harm produced by the agro industries' wastes', an investigation of the co-composting of olive mill waste (olive mill wastewater (OMW), olive mill sludge (OMS)) and wine by-products (grape marc and winery wastewater) was done. Three aerated windrows of variable compositions were performed; these windrows differ in terms of their initial composition and the liquid used for their humidification; OMW and wastewater winery were used for humidification to replace water for windrow moistening. Moreover, the main physicochemical parameters (temperature, pH, electrical conductivity, and C/N) were monitored to evaluate the co-composting process. The latter lasted around three months. The elaborated composts were characterized by low C/N ratio, and they were rich in fertilizing and nutriment elements and of low heavy metal contents. The humidification of the windrows with OMW showed effectiveness in improving the windrows temperature, reflected by the high temperatures monitored during the composting process in comparison with the windrow humidified with winery wastewater. Furthermore, a longer thermophilic phase was held in windrows carrying OMS. The valorization of the produced composts for soil amendment significantly improved the soil fertility. Indeed, field experiments showed an increase in radish yield by 10%, the composts were harmless and did not have any phytotoxic effect on radish growth.