| In recent years, the amount of total sludge generated in China has risen dramatically, and this trend is expected to increase many folds in the coming time. Sewage sludge in the wastewater treatment plants always has the prosperities of huge volume and complex compositions, which play a negative role in volume reduction and resource ultilization. Sewage sludge contains a high water content which leads to a huge volume and brings a difficult task to us. Sludge dewatering has been pointed out as the most expensive and least understood process. The treatment and disposal of excess activated sludge account for 35-50% of the entire operating cost of wastewater treatment plants. Therefore, excess activated sludge treatment has become a serious environmental problem in wastewater treatment plants.Bioleaching-Fenton oxidation was used to condition sewage sludge. In this study, depending on the sulfate production of Thiobacillus thiooxidans to reduce sludge system pH to meet the requirement of Fenton reaction, different H2O2/Fe2+ dosages and Fenton reaction time were also used to investigate the dewaterability of excess activated sludge to optimize reaction conditions of bioleaching-Fenton oxidation. Specific resistance to filtration (SRF), Sludge settling property, VSS reduction and the moisture content of sludge cake were used to evaluate the improvement of dewatering property in experimental processes. The results showed that with a fixed sulfur power dosage of 3g/L, the bioleaching lasted 2.0d to decrease the sludge pH about 2.5. Bioleaching significantly improved the sludge dewaterability with a specific resistance to filtration (SRF) reduction of 70% from 6.45x1010s2/g to 2.05×1010s2/g, but the bioleached sludge was still difficult to be dewatered. At the same time, the stability of sewage sludge was improved. The results also showed that the dewaterability was improved with increasing the amounts of H2O2 and Fe2+ in a certain range. In terms of SRF value for economical point of view, the optimal H2O2/Fe2+ ration and concentrations of H2O2 and Fe2+were 2,4g/L and 2g/L, respectively, and the optimum reaction time was 60min. At optimal conditions, sludge became easy to dewater, SRF, SV and the moisture content of sludge cake changed from 6.45×1010s2/g,97.0% and 91.42% to 3.56×108s2/g,59.0% and 79.47%, respectively; the stability of sludge was also improved significantly and the reduction of volatile suspended solids (VSS) was up to 41.93%. Furthermore, in the bioleaching-Fenton oxidation process, a low SV value of sludge will result in high dewaterability of sludge when reaction time is less than 60min; on the contrary, when the reaction time is beyond 60min, the high dewaterability means a high SV value, which may be resulted from the reduction of sludge particle size.Bioleaching-dual polyaluminum chloride (PAC) and polyacrylamide (PAM) addition was used to condition sewage sludge. The results showed that FeSO4·7H2O addition obviously improved the bioleaching rate with a fixed sulfur power dosage of 3g/L; when the FeSO4·7H2O dosage was 8g/L the bioleaching lasted 1.5d to decrease the sludge pH below 2. Bioleaching significantly improved the sludge dewaterability with a specific resistance to filtration (SRF) reduction of 77.52% from 6.45×1010s2/g to 1.45×1010s2/g, but the bioleached sludge was still difficult to be dewatered. After adjusting the bioleached sludge pH to 6, PAC and PAM were used to enhance conditioning of the bioleached sludge. The results indicated that the optimal dosage was 200mg/L for PAC or 50mg/L for PAM when single chemical was used. When PAC and PAM were dually used, the optimal dosage of PAC and PAM was 100mg/L and 25mg/L, respectively; SRF and moisture of sludge cake reduced to 2.02x108s2/g and 74.81%, respectively, showing good dewaterability of the treated sludge. Compared with the single use of PAC and PAM, the dual use of PAC and PAM showed the advantages of lower cost and better conditioning effect.
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