Physicochemical characterization of sewage sludge and green waste for agricultural utilization

In order to valorize the organic wastes, a mixture composed of 60 kg of thick sewage sludge from a wastewater treatment plant, 30 kg of green wastes (made of 10 kg straw of wheat, 10 kg manure farm wastes, and 10 kg of dead leaves), and 10 kg of wood chips was prepared. The organic wastes were mixed and put into a wooden cubic composter having a volume of 1.5 m3. Physicochemical analyses were made every 30 days for five months. The results of the analyses showed that the obtained compost had good physicochemical quality and can be used as an organic fertilizer. The main characteristics of this compost were distinguished by its pH from 7.4 to 7.8, with a ratio of organic matter of 40-42%. During composting, the humification process led to an increase in humic acids from 29.5 to 39.1 mg g(-1), a decrease in fulvic acids from 32.1 to 10.9 mg g(-1), and a global decomposition of hemicellulose, cellulose, and lignin. The obtained results show that a period of 150 days of composting gave a C/N ratio of 15.4. The total metal content in the final compost was much lower than the standard toxic levels for composts to be used as good soil fertilizers. The germination index for the two plants Cicer arietinum and Hordeum vulgare was 93% after the same period of composting, showing that the final compost was not phytotoxic. The study showed the possibility of valorization of the compost and its possible use in the domain of agriculture.