Electrodewatering of sewage sludge - Pilot scale studies

The dewatering of digested sewage sludges in Australia is a difficult and important problem since products derived from applying conventional technology contain only 14-20 wt% solids. This leads to excessive downstream costs of many millions of dollars per year in handling, transport and re-use/disposal of the dewatered sludges. CSIRO is' developing electrodewatering (EDW), which involves the application of an electric field to a filter cake during pressure filtration to increase the solids content of products from belt press filters. The technique is showing promise, with EDW bench scale tests increasing product solids from a typical maximum of 20 wt% up to 40-50 wt%, equivalent to removing at least 2.5 tonnes of water for every tome of dry solids. This paper initially describes an attempt to mathematically simulate the application of EDW to sewage sludge, based on a model developed by Iwata et sal, and then goes on to compare the performance of EDW on a bench scale filter press, a pilot scale filter press and finally on a pilot-scale semi-continuous prototype rig, which contains many of the features of a belt press filter. The model gave a reasonable simulation of experimentally determined kinetics of moisture reduction. The cake solids were consistently:underestimated but this was not surprising given some of the model's underlying assumptions. The development of EDW from bench to pilot scale proved very successful, with both the filter press and belt press configurations providing similar cake solids contents to the bench scale but at much lower power consumption.