Static Low Density Media (SLDM) Filters have been used since the early 1970's for the treatment of recirculating aquacultural waters, concurrently providing nitrification and solids removal. Recently the application of SLDM filters to domestic wastewater treatment has been suggested.
This strategy would allow for both organic and particulate removal by a single, compact unit. Data collected from early bench scale units recirculated with aid of airlift pumps is reported. The pneumatically-washed units employed a modified shape media and a high backwashing frequency to enhance
biofiltration capacities. The units were fed primary effluents with mean CBOD5 (carbonaceous biochemical oxygen demand) of 100 and 150 mg/L. Mean influent TSS (total suspended solids) values for the two units tested were 60 and 90 mg/L. The airlift/bead filter combination
was able to maintain mean hydraulic filtration rates in the range of 11-14 m/hr and always kept the bed in an aerobic state. Findings indicate the unit's ability to produce CBOD5 and TSS effluent qualities in the 10-20 mg/l range when subject to organic loadings between
1 and 3.5 kg/m3.day. In this study, effluent CBOD5 levels were closely correlated with effluent TSS levels. Although no problems with media caking was observed, at times poor backwash interval selection did lead to severe oxygen depression within the bead bed. It
is concluded that SLDM show promise for application in the domestic wastewater arena, particularly where the scale of the operation places a premium on simple operation.
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