Modelling and application of an uncovered freezing bed technology for septage treatment

Abstract

A series of pilot scale freezing bed experiments were conducted to evaluate and model the freeze–thaw treatment of septic tank sludge (septage). Filtrate quality is similar to a low strength domestic wastewater and the sludge cake has a dry matter content of 25% with E. coli numbers below 2.0 × 106 CFU/g dry solids. Experimental results showed no impact of snow cover on bed performance in a region with moderate snowfall (1.3–1.6 m) as new layers of sludge effectively melted any accumulated snow; suggesting that it is not necessary to cover the bed or remove the snow in areas where sludge dosing exceeds snowfall. Both freezing and thawing processes were successfully modelled with readily available climatic data. Model output for North American climatic conditions indicates that the freezing bed technology can be widely applied throughout the northern United States and Alaska and most of Canada with the exception of coastal areas and southern Ontario.