The Experimental Study On Gamma-ray Irradiation Treatment Of Residual Sewage Sludge

In order to achieve reduction, stabilization, harmlessness and recycling ofresidual sewage sludge, many sludge treatment processes have been developed in thepast decades, such as anaerobic digestion, mechanical dewatering and incineration,etc. While these traditional processes always have disadvantages of high energyconsumption, low treatment efficiency and secondary pollution, etc. It’s time todevelop an efficient, economical and environmental-friendly sludge treatment process.The effects of gamma-ray irradiation on residual sewage sludge in municipalwastewater treatment plant were studied by measuring pH, alkalinity, ORP,sedimentation-thickening property, dewatering property, TS, VS, TSS, VSS and EPS,etc. in this paper.The results showed that at an absorbed dose of0to15kGy, the pH of sludgeremained constant (around7.5), while the alkalinity increased markedly, which couldimprove the acid-resistance impact performance in the follow-up sludge treatmentproceses. ORP also remained constant (-30mV to-21mV) and sludge was reductiveas a whole. After irradiation, sedimentation-thickening property enhanced, initialsettling velocity and thickening ratio increased, SV decreased and these effects weremore obvious with irradiation dose increased. After15kGy irradiation, the initialsettling velocity increased from initial0.5156cm·min-1to1.4136cm·min-1, and theincreasing rate was174.17%；SV decreased from initial44to31, and thickening ratioincreased from2.27to3.22, TS, VS, TSS and VSS all decreased with increasingirradiation dose from0to15kGy, and the decease of VSS was the most remarkable.CSM test indicated that sludge dewatering rate, dewatering extent and irradiation doseappeared positive correlation, respectively. UV-vis spectra showed that after alkaline pretreatment and gamma-ray irradiation, sludge flocs and cells were broken and theoutflow of sludge inclusion increased the concentration of protein and nucleic acid,etc. in EPS. The extractable EPS from treated initial sludge was higher than ofuntreated sludge by101%at the dose of15kGy. Alkaline pretreatment andgamma-ray irradiation could generate pronounced synergistic effects, while strongacid condition was against to sludge irradiation solubilization. FTIR spectra resultsrevealed that alkaline and irradiation treatment could change EPS’s major functiongroups, such as protein groups and polysaccharide groups which could enhance thecharacteristics of sewage sludge. SEM images demonstrated that a lot of sludge cellswere deformed and sludge flocs were broken under irradiation condition leading tothe increase of extractable EPS, while irradiation didn’t do obvious damage to sludgeflocs and cells under strong acid condition.According to the experimental results, sludge treatment by gamma-rayirradiation could promote sludge disintegration and solubilization, which could bebeneficial to sludge reduction, stabilization and follow-up treatment and disposal.