Sustainable use of rice husk powder and bamboo powder as sludge deep dewatering conditioners in pilot-scale application: Feasibility for incineration and potential application for land use

Abstract

Conventional conditioners are not conducive to the sludge separate incineration process. The agricultural wastes bamboo powder (BP) and rice husk powder (RHP) have strong toughness and porosity, which has the potential to replace quicklime as a sludge conditioner. When the dosage of BP and RHP is 30 % of the sludge dry solids, the dewatering performance of sludge was greatly improved after sludge was conditioned with BP and RHP respectively, where the specific resistance of sludge was reduced from 4.6 × 1012 m/kg to 1.3 × 1012 and 0.9 × 1012 m/kg. In addition, the sludge conditioned by BP and RHP acquired better filtrate quality, which is conducive to the stable operation of the wastewater treatment plants (WWTPs). The components of extracellular polymer substances (EPS) showed that the tightly bound-EPS (TB-EPS) decreased by 36.6 % after conditioning with quicklime, while the TB-EPS maintained with BP and RHP conditioning, indicating that the dewatering mechanism of BP and RHP involves physical activities to work as the skeleton builder. The use of BP and RHP increased the enrichment effect of nitrogen and phosphorus in the sludge cake, yet the contents of heavy metals Cd, Pb and Zn were below the sludge land use limit. Combined with the ecological risk assessment by the methods of the Geoaccumulation index (Igeo), the Nemerow pollution index (PI) and the potential ecological risk index (RI), the ecological risk index of quicklime-conditioned sludge is higher when the dewatered sludge is composted and applied for land use, while the ecological risk after conditioning by BP and RHP is in a slightly polluted or non-polluted state, therefore the application of BP and RHP as the deep dewatering conditioners possesses practical potential for land use.