Experiment Research And Mechanism Analysis Of Sewage Sludge Conditioning With Coal Fly Ash Modified By Sulfuric Acid

Activated sludge process to treat municipal and industrial wastewater produces huge amounts of excess sludge. As this was high moisture content, its treatment become the bottleneck problem of Municipal Wastewater Treatment Plant. Chemical condition has been employed widely to improve sludge mechanical dewatering, but the cost is high, thus it is very important to find cheap and effective conditioners.This paper was to explore the possibility of improvement of the excess sewage sludge dewaterability by coal fly ash modified by sulfuric acid. Coal fly ash is the waste product of coal-buring power plants. After modified, coal fly ash could effectively condition sludge, improving of sludge dewaterability. The optimal conditions of coal fly ash modification were determined by orthogonal tests. The optimal conditions of conditioning and dewatering and related mechanisms were investigated. The results could provide a new approach for the practice of sewage sludge conditioning and coal fly ash utilization. Through orthogonal experiments with specific resistance to filtration (SRF) as the target index, acid concentration and soaking time were verified to be the important influencing parameters in coal fly ash modification. The optimal modification conditions were: acid concentration, 4 mol/L; ratio of acid to coal fly ash, 5:1 ml/g; and soaking time, 3 h. The dewaterability and the settleability of the conditioned sludge were investigated with vacuum filtrating dewatering tests, centrifugal dewatering tests and settling experiments. The results showed that SRF of the sludge significantly decreased with coal fly ash addition, and MCFA showed much stronger conditioning capacity than non-modified coal fly ash (NMCFA). Under a MCFA dosage of 30 g/L, SRF of the sludge decreased from 1.86×10¹³ m/kg to 4.23×10¹¹ m/kg, and the filter cake moisture decreased from 86.90% to 56.52%. The sludge conditioning before and after, the composition and content of Extracellular Polymeric Substances (EPS) and the Zeta potential were measured. The Field Emission Scanning Electron Microscope(FESEM) images of the MCFA, the changed of Zeta potential and micrographs of the conditioned sludge suggested that the conditioning mechanisms with MCFA might be charge neutralization and adsorption bridging. All these provided a theoretical basis for sludge conditioning with coal fly ash modified by sulfuric acid in practical.