2.0 Introduction

Biosolids are the residual solids generated from the processing of municipal wastewater (excluding grit and bar screenings) and domestic septage that meet the regulatory requirements for recycling (i.e., beneficial use) specified in the 40 CFR Part 503 rule. Once generated, beneficial use (i.e., land application of biosolids for agricultural or aesthetic purposes) represents a cost-effective disposal option for biosolids. To properly design biosolids beneficial-use systems, it is important to understand the impact of wastewater quality objectives on biosolids characteristics and production rates (Fig. 2.1).

Figure 2.1: ( a) Schematic diagram of municipal wastewater treatment facility. ( b) Photograph of oxidation ditch wastewater treatment plant. ( Courtesy of I. Kruger, Inc.)

Municipal wastewater consists of liquid wastes produced in residences, commercial establishments, industries, and any subsurface, surface, or storm water that enters the municipal wastewater collection system. Depending on the type and extent of wastewater treatment, any of the materials that enter the municipal wastewater collection system ultimately may find their way into biosolids.

2.1 Wastewater Quality

Effective treatment of wastewater requires an accurate knowledge of its influent quality. Since wastewater influent is not constant in character from place to place nor from time to time, the biosolids resulting from its treatment would be expected to vary as well. The principal constituents of wastewater are summarized in Table 2.1.