Evaluation of the Compost Produced from Mixed Sludge of Municipal Wastewater Treatment Plant and Pistachio Hull Waste

Background and Direct application of sewage sludge in agriculture is limited due to the presence of pathogens¡ improper fermentation of organic waste and heavy metals in the sludge. Co-composting of sewage sludge and other waste is a method for safe and healthy disposal to reuse sewage sludge. This study investigated the possibility of producing compost from sewage sludge and pistachio hull waste.
Material and A cross-sectional study was conducted in the winter of 2014 at the Environmental Health Engineering Research Center affiliated to Kerman University of Medical Sciences. First¡ a cylindrical reactor was made which was 30liters in volume¡ 30cmdiameter in dimensions¡ 45cm depth¡ and wall thickness of 6 mm. Pistachio hull waste with sewage sludge was mixed in a ratio of 1 to 4 and C/N ratio of 25. Reactor started with aeration rate of 5 liters per minute. The reactor content was mixed every five days¡ and the resulting compost samples were measured for moisture content¡ pH¡ electrical conductivity¡ organic carbon¡ total nitrogen¡ phosphorus¡ potassium¡ cadmium¡ and lead.
After 30 days from the start of composting process¡ the carbon to nitrogen ratio decreased to 16.5. During the composting process¡ pH increased but the amounts of electrical conductivity¡ total nitrogen¡ organic carbon¡ phosphorus¡ potassium¡ lead¡ and cadmium decreased. The maximum temperature reached 63ºc.
The properties of the produced compost including temperature¡ pH¡ electrical conductivity¡ moisture ratio¡ C/N¡P¡ K¡ and heavy metals were in category 1 and 2 of the standard compost of Iran.