Abstract
This study investigated the synergetic effect of the combined calcium peroxide (CaO2) and microwave (MW) treatment on waste active sludge dewatering properties and organic contaminants’ removal. The optimal sludge dewaterability was obtained at CaO2 (20 mg/gVSS)/MW (70°C), and the capillary suction time decreased by 52% compared with raw sludge. Further investigation indicated that total extracellular polymeric substances (EPS), tightly bound EPS, total protein, and protein present in tightly bound EPS were closely correlated with sludge dewaterability. Tryptophan, aromatic protein–like substances and humic acid–like substances were the key compounds that affect sludge dewaterability. The charge neutralization and bridge effect of cation ions were strengthened when combined with MW irradiation. In addition, it was revealed that MW facilitated CaO2 to produce more hydroxyl and superoxide anion radicals. This study confirmed CaO2/MW to be an effective way to improve sludge dewatering and remove organic pollutants from sludge.
Highlights
The growing population and rising requirement for human activities have caused an increased yield of waste-activated sludge with high moisture content in wastewater treatment plants (WWTPs) in recent years (Liu et al, 2021)
DDSCOD is the ratio of the increment of soluble chemical oxygen demand (COD) (SCOD) in the CaO2/MW treatment group to the biggest increment of SCOD, which can be calculated with the following formula: DDSCOD(%)
The test with single CaO2 at room temperature shows that the Capillary suction time (CST) decreased from 47.1 to 44.2, 39.3, 36.1, and 42.1 s at the CaO2 dosages of 10, 20, 30, and 40 mg/gVSS, respectively, whereas at the CaO2 dosage of 50 mg/gVSS, the CST again increased to 50.2 s
Summary
The growing population and rising requirement for human activities have caused an increased yield of waste-activated sludge with high moisture content in wastewater treatment plants (WWTPs) in recent years (Liu et al, 2021). Treatment and disposal of sludge accounts for about 60% of the operating cost of WWTPs, which has become a critical issue (Kim et al, 2016; Liu et al, 2017). Dewatering is an important step in sludge treatment because proper dewatering can reduce the volume of sludge, reducing the cost of sludge transportation and disposal (Cao et al, 2021; Anjum et al, 2016). It makes a strong economic incentive itself to improve the sludge dewaterability. Common organic pollutants in sludge include traditional persistent organic
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