Authors: Dolak, Ivan; Murthy, Sudhir; Bauer, Tim

Source: Proceedings of the Water Environment Federation, WEF/AWWA/CWEA Joint Residuals and Biosolids Management 2001 , pp. 960-977(18)

Publisher: Water Environment Federation

Abstract:

Heat drying of sewage solids from municipal wastewater treatment plants is becoming increasingly prevalent in North America as regulations for wastewater solids disposal become more restrictive. The material derived from heat drying typically meets federal regulations for land application, and it is often easier to store, transport, and apply than wet biosolids.

A successful heat drying operation is largely dependent upon the handling and processing of the solids prior to drying. The eventual management options and “value” of the final dried material are dependent on its “quality.” Quality, in this case, is defined through regulatory as well as physical properties. Regulations dictate the rules governing the ability to land apply the dried biosolids, and physical properties dictate the ability and desirability to use the dried product.

A common goal of a solids drying operation is to generate a revenue stream from the sale of the dry material to help in offsetting the capital cost of the heat drying system. The level of success in achieving this goal, or the revenue value of the material, depends to a large degree on the quality of the dried biosolids.

Nearly all of the treatment processes employed to the wastewater in the municipal wastewater treatment plant, and even upstream of it, impact the eventual quality and marketability of the dried product. In addition, these processes influence the economic practicality of heat drying. Influential processes include pretreatment, screening and grit removal, primary and secondary treatment, upstream solids handling and digestion, and the thickening and dewatering systems employed.

To provide insight and guidelines to assist in evaluation of heat drying as a solids handling practice, we compare dried biosolids and present data from several North American wastewater treatment facilities employing varying upstream treatment processes. Material properties such as metal concentrations, volatile solids concentrations, odor potential, and chemical nutrient content are also compared as are the impacts from upstream treatment. Additionally, quantitative relationships between the upstream processes, size of the heat drying system, and its energy consumption are presented in this paper.

Document Type: Research article

DOI: http://dx.doi.org/10.2175/193864701784993605

Publication date: 2001-01-01

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