Solids Removal Methods

5.1.1 Introduction

The occasional high concentration of total suspended solids (TSS), which can exceed 100 mg/L, in the effluent is the major disadvantage of pond systems. The solids are primarily composed of algae and other pond detritus, not wastewater solids. These high concentrations are usually limited to 2 to 4 months during the year. Solids removal methods that are discussed in this chapter include intermittent sand filters, recirculating sand filters, rock filters, coagulation-flocculation, and dissolved-air flotation. The rock filter is not a true filter but is included because of its association with filters when discussing solids removal from lagoon effluents. Further details for all methods can be found in the references at the end of the chapter. Although slightly dated, an excellent introduction to the design and performance of intermittent sand filters and rock filters is presented in the U.S. Environmental Protection Agency's Design Manual: Municipal Wastewater Stabilization Ponds (USEPA, 1983). Information on both processes can also be found in a document published by the Water Environment Federation (2001). A literature search on the application of recirculating sand filters to the removal of TSS from lagoon effluents was unsuccessful, but several references to their application in treating septic tank effluents were found. This lack of information may be attributable to concern about the accumulation of algae in the media. Nolte & Associates (1992) conducted a review of the literature covering recirculating sand filters and intermittent sand filters.

5.1.2 Intermittent Sand Filtration

Intermittent sand filters have a long and successful history of treating wastewaters (Furman et al., 1955; Grantham et al., 1949; Massachusetts Board of Health, 1912). Table 5.1 presents a summary of the design characteristics and performance of several systems employed in Massachusetts around 1900. These systems

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