Primary and secondary sludge treatment using ionizing radiation technology in Alexandria, Egypt

Improving the treatment efficiency of sludge in Alexandria, Egypt, was studied to improve the primary and secondary sludge treatment efficiency, different doses ranging from 0.25 to 6 kGy of ionizing radiation were proposed and evaluated. The scope of This study is to assess the radiation-based treatment efficiency from physical, chemical, and biological perspectives and to compare between the conventional treatment method and the radiation-based treatment technology. To evaluate the performance of each treatment system, pH, oil and greases concentrations, total solid concentrations, BOD concentrations, COD concentrations, parasites, and microorganisms were assessed in the primary and secondary samples at different radiation doses (from 0.25 to 6 KGy), and in the conventionally treated samples. Irradiation by gamma radiation with a dose ranging from 0.25 to 6 kGy was efficient in reducing some of the physical contaminants. Oil & greases, Total Solids, BOD, COD concentrations were reduced significantly (p < 0.001) in a dose-dependent manner. Either primary or secondary sludge samples, total solid reduced significantly to about one-third of control concentration at six kGy. Six kGy able to reduce the BOD and COD concentrations in the primary sludge samples to that of the treated (after sludge dewatering) samples or less respectively and saved the secondary treatment stage. In primary and secondary sludge samples culture, E. coli, Staphylococcus aureus, and Vibrio spp were isolated as heavy growth on different culture media in the samples before radiation. After exposure to increasing doses of radiation, the number of isolated organisms decreased, however, the growth of Proteus, Acinetobacter, and vipro organisms was detected but in small numbers. No growth of any organism was noted at 5 kGy. On the other hand, in the secondary sludge samples, Proteus was isolated as heavy growth before radiation and After exposure to increasing doses of radiation, Moraxella spp. organisms were detected but in small numbers. By increasing the radiation doses, the free-living ciliates were decreased in the primary and secondary sludge samples. The free-living ciliates disappeared completely at 3 kGy. In the primary and secondary sludge samples, free-living ciliates reduction efficiency at 0.25 kGy was equivalent to the conventional treatment methods. So, we can conclude that radiation technology using Gamma rays at a dose higher than 5 kGy with a dose rate of 1.095 kGy/h is an effective technology for domestic and industrial waste sludge treatment from the environmental perspective and an experimental pilot plant study is required to optimize the cost of wastewater treatment through the use of irradiation technology.