Wastewater renovation in buried and recirculating sand filters

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A replicated, multiyear field study was conducted to assess the reduction of N, P and microbial indicators by a recirculating sand filter (RSF) and a buried multilayer sand filter patterned after the RUCK filter. The RSF's received 38 L m-2 d-1 of septic tank effluent, while the buried sand filters were loaded at 76 L m-2 d-1. The RSF's had significantly greater reductions of N and P (21 and 31%, respectively) than the buried filters (8 and 1%, respectively); however, N reduction was not significantly different per unit area. The lower daily loading rate and even distribution of effluent on the recirculating filters may have contributed to the elevated P reductions noted. Total Kjeldahl N (TKN) reductions in the RSF's were markedly lower during the cold season (≤10 °C) than the warm season. In contrast, TKN reductions in the buried sand filters were relatively constant, except during the coldest periods of winter. Substantial TKN reductions occurred under acidic conditions. During warm weather sampling, both types of filters dramatically reduced levels of fecal coliform, enterococci, and F male-specific bacteriophage. During cold conditions, the buried sand filters produced greater reductions of fecal coliforms and enterococci levels, while neither filter consistently reduced the levels of Clostridium perfringens or F phage. Increased reductions in fecal coliform, enterococci and F phage were associated with lower effluent pH for both sand filters.

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Journal of Environmental Quality