Improving dewaterability of waste activated sludge through advanced oxidization process

Abstract

The production of excess sludge in biological wastewater treatment processes has been a serious issue for the operation of wastewater treatment plants (WWTPs) on both economic and environmental sides. To reduce the volume of sludge to be disposed of, the sludge dewaterability needs to be improved through conditioning processes. Many conditioning methods have been developed and applied for this purpose. Among them, the advanced oxidization process is a promising technique due to its high efficiency, and economical and environmental advantages. The aim of this thesis is to apply a series of novel advanced oxidization techniques on sludge conditioning process for the improvement of sludge dewaterability, such as the indigenous iron activated peroxidation and zero-valent iron (ZVI)/hydrogen peroxide, zero-valent iron/persulfate. Also, the role of extracellular polymeric substances (EPS) during the advanced oxidization process was also investigated to expand the knowledge of basic mechanism on the sludge dewaterability.Capillary suction time stands for the time needed for completing the filtration of sludge, is used as quantitative indexes for the evaluation of the sludge dewaterability.The indigenous iron was firstly utilized as the substitute for externally supplied iron salt to improve dewaterability of waste activated sludge through catalysing the hydrogen peroxide. Significant improvement in sludge dewaterability was attained after the addition of hydrogen peroxide at 30 mg/g total solid (TS) and 28 mg/g TS under acidic conditions (pH = 3.0), with the highest reduction of capillary suction time being 68% and 56%, respectively, for sludge containing an iron concentration of 56 mg Fe/g TS and 25 mg Fe/g TS, respectively. The observations were due to Fenton reactions between the iron contained in sludge (indigenous iron) and hydrogen peroxide. For the sludge with an insufficient level of indigenous iron, the addition of iron salt was found to be able to improve the sludge dewaterability.To expand the understanding of the indigenous iron activated advanced oxidization process, the effect of indigenous iron activated peroxidation on methane production from waste activated sludge was also investigated. Pre-treatment of waste activated sludge for 30 min at 50 mg H 2 O 2 /g TS and pH 2.0 (iron concentration in sludge was 7 mg/g TS) substantially enhanced waste activated sludge solubilization. Biochemical methane potential tests demonstrated that methane production was II improved by 10% at a digestion time of 16 d after incorporating the indigenous iron activated peroxidation pre-treatment.The combined conditioning process with zero-valent iron and hydrogen peroxide was applied to improve dewaterability of a full-scale waste activated sludge. The combination of ZVI and hydrogen peroxide at pH 2.0 substantially improved the waste activated sludge dewaterability due to Fentonlike reactions. The highest improvement in waste activated sludge's dewaterability was attained at 500 mg ZVI/L and 250 mg hydrogen peroxide/...