Study On Ionizing Radiation Treatment Of Residual Sludge

Reducing and detoxifying sludge, which is operated by development of efficient, economic, and operable sludge treatment process, is the key element to solve the problem of excess sludge, and it has become one of the very pressing issues of environmental control in China.Theγ-ray and electron beam radiation effects on residual sludge in municipal wastewater treatment plant with different moisture content were studied by measuring soluble COD (SCOD), UV-vis spectra, total nitrogen(TN), endogenous respiration oxygen uptake rate (OUR), mixed liquor suspended solid(MLSS), and zeta potential.The results show that a new absorption band near 240nm-300nm for all irradiated samples indicated that cellular components of the sludge were broken to smaller molecules. SCOD and TN concentration increased with the increasing radiation dose afterγ-ray irradiation, and more SCOD, TN were generated by sludge with lower moisture content. With all the original SCOD less than 100mg/L, SCOD was increased to 348,1120,1774 and 2050 mg/L after 20kGy irradiation with the moisture content of 99%,97%,96% and 90%, respectively. TN increased from the original TN of less than 10mg/L to 41.95,72.99 and 94 mg/L after 30kGy irradiation with the moisture content of 99%,97%, and 90%, respectivelyEndogenous respiration oxygen uptake rate (OUR) of the irradiated sludge decreased rapidly with the increasing of radiation dose, and were all near 0 after 30kGy radiation for sludge with moisture content of 99%,97% and 90%, which showed that the majority of the microorganisms in the residual sludge were killed by y-ray. With the increasing of the radiation dose, zeta potential showed an increasing tendency, while MLSS decreased due to the lysis of sludge microorganisms. When the radiation dose went up to 30kGy, MLSS decreased 2.4g/L,3.7g/L,6.7 g/Land 9.2 g/L.The results showed that SCOD, TN and UV-Vis absorption had the similar trend after the electron beam irradiation. For sludge with moisture content of 99%,97% and 90%, SCOD, TN and UV-Vis absorption all increased with the increasing of the radiation dose, more SCOD, TN were generated by sludge with lower moisture content. And they all decreased with the sludge thickness of 0.5cm,0.3cm and 1.0cm, respectively. Endogenous respiration OUR of the irradiated sludge decreased with increased irradiation dose, and decreased with the sludge thickness of 0.5cm,0.3cm and 1.0cm under the same radiation dose. When the moisture content of sludge was 97%, MLSS decreased 7.0g/L,7.5 g/L and 6.5g/L after 20kGy radiation with the sludge thickness of 0.3cm,0.5cm and 1.0cm, respectively, and MLSS decreased 7.7g/L,10.2 g/L and 7.9g/L when the moisture content of sludge was 90%. Zeta potential showed an increasing tendency with the increasing of the radiation dose, zeta potential increased 2.36 mV and 2.04 mV after 20kGy irradiation with the moisture content of 99% and 97%.And zeta potential had a trend that increased from the negative to zero with different sludge thickness, when the moisture content of sludge was 97%, it increased 4.16mV,2.04mV and 4.59mV after 20kGy irradiation with the sludge thickness of 0.5cm,0.3cm and 1.0cm, respectively.According to experimental results, sludge treatment through ionizing radiation improves treatment effect, it can also helps in subsequent disposal of sludge.