Solar Drying Technologies in Pathogen Reduction in Biosolids

摘要

Many small wastewater treatment plants in the United States and in developing countries utilize solar drying to dewater sewer sludge for economical transportation to landfills. Integrating engineering methods into the solar drying cycle can enhance dewatering and disinfection of the sewer sludge for the purpose of safely recycling the biosolids onto agricultural fields or land application onto sites needing remediation such as mine tailings or burned forest land. Experimental solar drying beds were set-up in arid and semi-arid locations in Arizona, Mexico and Jordan to study the pathogen inactivation. Desiccation rates were also documented. Experimental treatments included mechanical and hand tilling, solar assisted passive heat gain, and provisionsfor a controlled structure to prevent wetting throughout the drying cycle. Generated biosolids were studied until the microbial quality reached Class A criteria. The results indicated that mechanical tilling significantly increases drying bed efficiencyand pathogen inactivation during hot, dry periods. Hand-tilling improved the rate of parasite inactivation, passive solar heat gain effectively doubled the rate of pathogen inactivation, and a retractable automated shield maintained pathogen indicator bacteria at levels near or below Class A criteria throughout the monsoon season. However during cold and wet winter seasons, tilling provides limited measurable benefits. The seasonal studies suggest that best management practices associated with the drying and disinfection of biosolids in open solar drying beds is to provide an enclosed structure with a retractable roof, till during hot arid months and leave the biosolids untreated during cold and wet seasons.