| Municipal wastewater treatment plants (WWTPs) produce large amounts of sludge. Large amount of sludge has been a great trouble of the current domestic wastewater treatment. To reduce the sludge volume, the sludge deeply dewatering is the key fator. And the sludge characteristics differ between various WWTPs.And the sludge pretreatment has a significant impact on the sludge dewatering. Nowadays, polyacrylamide (PAM) as a chemical conditioner is frequently used in the sludge conditioning. With this treatment, the water beam structures of sludge are destroyed and the sludge is in a viscoelastic status, which is difficult to further compress and dewater. Thus, it is necessary to find out an applicable and effective conditioning technology to change the characteristics of sludge in the industrial practice.This study systematically researched the effect of experiments conditions and the organic matter content (VSS%) on the dewaterability of typical five sewage sludges via conditioning with a combination of Fenton oxidation and quicklime. And the dewatering mechanism of Fenton oxidation and quicklime on five sewage sludges was investigated. Moreover, based on the the optimal dewatering conditioning, the pilot-scale experiments were conducted by a novel ultrahigh pressure filtration system and the sludge dewatering efficiency and depth were researched with the Fenton oxidation and quicklime treatment.The dewaterability of five VSS% sludges with Fenton oxidation and quicklime treatment was investigated. The results showed that sludge conditioning with Fenton’s reagent and quicklime is a valid method for sludge dewatering and the specific resistance to filterability (SRF) of sludge was reduced efficiently by approximately 90%.Moreover, the optimal dewatering conditioning of sludges with various VSS% was concluded. Meanwhile, sludge VSS% had the positive correlation with the sludge dewaterability including the SRF and the filtrate total organic carbon (TOC).Besides, the correlations were found between the sludge VSS% and the optimal Fenton reaction time, the consumption of sulfuric acid, the molar ratio of Fe2+ and H2O2.The dewatering mechanism of Fenton oxidation and quicklime on five sewage sludges was researched. The results demonstrated that the Extracellular Polymeric Substances (EPS) and the bound water might be the key factors to sludge dewatering. The sludge VSS% had the positive correlation with the EPS and the bound water content of sludge, in other words, the sludge VSS% was the main influence factors of sludge dewaterability. The high content EPS and bound water cause release of the free water difficultly. After conditioning with Fenton oxidation and quicklime, the EPS content and the bound water content of sludge were decreased sharply. And the particle size of conditioned sludge became smaller, while the zeta potentials had a tendency to increase. Meanwhile, the scattered particles were flocculated and a rigid skeleton structure was constructed with calcium sulfate and ferric hydroxide, resulting in improving the sludge dewatering efficiency.Based on the above experiments, the pilot-scale experiments were conducted by an ultrahigh pressure filtration system. The results indicated that the mechanical pressure dewatering efficiency and depth including the sludge cake water content, the filtration rate and the compress time was related to the sludge VSS%. The high VSS% sludge had the poor dewaterability and it needed longer time to feed and compress. However, the novel ultrahigh pressure filtration system can enhance the mechanical pressure dewatering efficiency and depth. After conditioning, the filtration rater was improved and the compress time was reduced. The water content of the dewatered sludge cakes was lower than 50% and the estimated prices of the reagents were below 350 yuan/t DS. In conclusion, it is an economical and viable way to apply the technique (Fenton oxidation and quicklime combined with ultrahigh pressure filtration system) to sludge dewatering in the full-scale WWTPs of Guangzhou. |
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