Abstract
This work reports on municipal sludge hygienization using electron beams. Three types of sewage sludge from two municipal wastewater treatment plants were tested: preliminary sludge with 4% TS, postflotation sludge with 2.5% TS and thickened preliminary sludge with 10% TS. The analysis of reference samples demonstrated the presence of bacteria and helminths ova in all examined samples. For the study of hygienization, electron beams from two types of accelerators, linear (Elektronika 10/10) and single cavity (ILU-6), were applied. For each type of accelerator, different irradiation methods were used: irradiation in sealed polyethylene bags using conveyor and flow irradiation installation. Experiments showed that the doses necessary for the elimination of mentioned pathogens were 4 kGy for preliminary sludge, 4 kGy for postflotation sludge and 5.5 kGy for preliminary sludge. The differences between the amounts of initial pathogens in preliminary and thickened preliminary sludge were marginal. It is possible that the higher irradiation dose required to hygienize thickened sludge resulted from higher TS concentration.
Highlights
Sewage sludge is a waste formed in the process of municipal and industrial wastewater in wastewater treatment plants (WWTP)
The obtained results showed that, for the preliminary sludge from WWTP 1 (Table 1), thedose postflotation sludge the dose for hygienization was agai the required to remove all (Table observed3), bacteria was 4required kGy
The results obtained for sludge hygienization related to living helminths eggs are provided in the Tables below
Summary
Sewage sludge is a waste formed in the process of municipal and industrial wastewater in wastewater treatment plants (WWTP). The water phase is directed to an aerobic biological purification process while sediment is removed from the settler as primary sludge. In the aerobic biological purification process, organic pollutants containing carbon and sometimes nitrogen and phosphorus are removed by biological processes in aerated reactors. Bacteria cells are produced, and a suspension is obtained which is directed to a settler where a separated water phase with low COD is removed outside of the WWTP, sludge is removed from the settler and partially recirculated to the aerobic biological reactor as a source of microorganisms, and the rest is removed as excess sludge. Some WWTPs can operate some custom installations, where different types of sludge can be obtained [1]
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