Mixed results have been obtained with rock filters. The most successful ones have been located in Veneta, Oregon, and West Monroe, Louisiana. Performance data from a study by Swanson and Williamson (1980) for the Veneta system are shown in Figure 5.4. Performance data for 1994 are shown in Table 5.10. After approximately 20 years of operation, the system was producing an effluent meeting secondary standards with regard to BOD5, TSS, and fecal coliforms (FC). During the winter months, high ammonia nitrogen concentrations were observed in the effluent. Stamberg et al. (1984) presented performance results for the two rock filters operating in West Monroe (Figure 5.5). The systems were loaded at higher hydraulic loading rates than that used at the Veneta facility (<0.3 m3 of
wastewater per d per m3 of rock), and the TSS removals were less than those reported for the Veneta system. In general, the West Monroe systems produced effluent BOD5 and TSS concentrations less than 30 mg/L, but these concentrations
^CO ^O) ^CN in IO ^ CO in T-cm cm cm c<o — oo — oo — 00 _ CO _ CO _ CO 222222
FIGURE 5.4 Performance of Veneta, Oregon, rock filter. (From Swanson, G.R. and Williamson, K.J., J. Environ. Eng. Div. ASCE, 106(EE6), 1111-1119, 1980. With permission.)
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