Abstract
Sludge dewatering systems are important for sludge recycling and lowering sludge disposal costs in sewage works. Currently, these systems use flocculants for sludge dewatering, but their high cost is problematic. Therefore, several researchers have used medium made of fibers or woodchips as alternatives. In river works, weed growth on riverbanks causes problems due to disposal costs of the grass clippings, amongst others. Grass clippings from public spaces have been attracting attention as a source of biomass in sewage works.
We assessed the feasibility of using grass clippings to reduce the water content of sewage sludge. Four sludge samples from three treatment plants (A-C) were used to investigate the effect of grass clippings on sludge water content: digestion sludge and concentrated sludge from the standard activated sludge method (A) and concentrated sludge from the oxidation ditch method (B and C). Sludge samples from each plant were mixed with grass clippings in ratios of 0, 10, 30, and 50% to sludge total solids (TS). The content rates of the flocculants were 0, 0.5, 1, and 2% to sludge TS.
We found that sludge mixed with 1% flocculant and 10% grass clippings reduced sufficiently the water content compared to that without grass clippings. Furthermore, in all sludge samples, sludge mixed with 1% flocculant and 10% grass clippings had a lower disposal cost than that without grass clippings. Therefore this technique can be considered effective and can be applied to both sewage and river works.
