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ARS Home » Plains Area » Bushland, Texas » Conservation and Production Research Laboratory » Soil and Water Management Research » Research » Publications at this Location » Publication #310310

Title: Impacts of tilling and covering treatments on the biosolids solar drying conversion from Class B to Class A

item SONG, INHONG - Seoul National University
item O`Shaughnessy, Susan
item CHOI, CHFISTOPHER - University Of Wisconsin
item GERBA, CHARLES - University Of Arizona

Submitted to: Environmental Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/8/2014
Publication Date: 5/19/2014
Citation: Song, I., Oshaughnessy, S.A., Choi, C.Y., Gerba, C.P. 2014. Impacts of tilling and covering treatments on the biosolids solar drying conversion from Class B to Class A. Environmental Technology. 35(20):2610-2618. Available:

Interpretive Summary: Treatment of sewage sludge by small public wastewater treatment plants is economically challenging. To help small treatment plants develop inexpensive methods to treat sewage sludge, information concerning the effectiveness of alternative treatments to reduce pathogen levels is necessary. The impacts of solar heating using a permanent cover and tillage on pathogen reduction in sewage sludge on drying beds was investigated during winter and summer seasons. The results indicate that during seasons of high ambient temperatures, solar heating under a covered structure provides fast inactivation to acceptable levels, while tillage accelerates inactivation over no-till treatment. A retractable cover reduced pathogen indicator regrowth after rainfall events. However, during the winter seasons, the rate of pathogen reduction was not improved using these alternative treatments.

Technical Abstract: The objective of this study was to evaluate the effects of tillage and cover treatments of solar drying on the conversion of Class B treated sewage sludge to a Class A product. The experiments were performed over two years at Green Valley, Arizona in steel-constructed sand-filled drying beds of 1.0m (width) x 3.0m (length) x 0.6m (depth). Freshly produced aerobically and anaerobically digested biosolids from nearby wastewater treatment plants received tillage and cover treatments to expedite solar drying and microbial inactivation. During the summer drying, covering the drying beds increased the fecal coliform inactivation rate by 26 percent over other treatments and an automated rain shield abated fecal coliform regrowth from summer rains. Tilling accelerated evaporation of moisture from the biosolids and increased the inactivation rate of fecal coliforms during the summer season. An automated retractable roof to protect the biosolids from rain aided in maintaining Class A criteria by preventing re-wetting from rainfall events. However, results from tilling and passive solar heating during the cold winter season did not improve the fecal coliform inactivation rate due mainly to lower ambient air temperatures. Thus, tilling and cover treatments can be effective in accelerating biosolids solar drying and enhance pathogen inactivation during the summer season. Investigation on the effects of tillage depth and frequency is recommended to determine optimal tilling practices.