Preparation and application of lightweight chemical sludge fillers

Fillers in 10-20 mm diameter were made via drying, preheating and sintering with chemical sludge combustion ash, clay, dry chemical sludge and formulated stabilizer of heavy metals(S01) as raw materials. The effects of ratio of raw materials, preheating time and sintering temperature on the performance of fillers were discussed by testing the bulk density and water-absorption. The optimum preparation conditions for fillers could be obtained at 1 150℃ after preheating for 30 min with 20%wt drying sludge, 40%wt sludge combustion ash and 5%wt S01. Under these conditions, the bulk density and water-absorption of fillers were 569.11 kg/m³ and 9.84%, respectively. Meanwhile, the leaching concentrations of heavy metals were much lower than the limit value in Identification Standards for Hazardous Wastes-Identification for Extraction Toxicity(GB5085.3-2007). Furthermore, the microstructures and characters of fillers were observed by scanning electron microscope(SEM) and it was found that the surface of fillers was coarse and the inner space was porous. Besides, the formation process of biofilm on the fillers was also investigated. The results showed that the removal rate of COD and NH₄⁺-N in the chemical sludge filler biofilter maintained at 95.6% and 71.8%, respectively, after 13 days, which were slightly better than the commercially available filler biofilter. It verifies that the application of chemical sludge fillers in biofilter is feasible.