Effect of structural features of plant biomass as a dewatering aid for digested sludge from a wastewater treatment plant

Abstract

Large amounts of plant biomass are produced by public work projects. This plant biomass was evaluated as an aid for the dewatering of sludge from a sewage treatment plant. The relationships were investigated between the different structural types of plant biomass (grass clippings, pruned branches of Japanese black pine, and bamboo powder) and their dewaterability potential in digested sludge. Microscopic observations revealed that grass fibrous materials and Japanese black pine needles had hollow structures. However, xylem, bark parts of Japanese black pine, and bamboo culms exhibited woody cell structures. The difference in water retention value of grass clippings after filtration and centrifugation was higher than that of Japanese pine and bamboo, indicating that the water present within the pores of grass fibrous materials could be easily removed. Plant biomass was captured inside the floc when digested sludge was mixed with plant biomass and flocculation was performed by adding a flocculant. The addition of grass clippings exhibited better dewaterability compared with both Japanese black pine and bamboo. The grass fibrous materials used as a dewatering aid effectively improved the dewaterability of the digested sludge because the water in a sludge floc may be drained from within the grass fibrous materials.