Investigating the effect of solids retention time on pesticides removal in an activated sludge process
2022
Kocaman, Kumru | Yetis, Ulku | Dilek, Filiz B.
The levels of pesticides reaching the biological wastewater treatment plants have been increasing. Operational conditions leading to the most efficient removal of pesticides in these plants should be evaluated first before attempting tertiary-level treatment options. This study investigated the influence of solids retention times (SRTs) on the removal of three pesticides (carbendazim, imidacloprid, and aclonifen) in the activated sludge process. Laboratory-scale reactors receiving these pesticides (0–400 μg/L) were operated at five different SRTs (3, 8, 10, 20, and 30 d). When the pesticides were present individually, all of the reactors were capable of removing carbendazim up to 25 μg/L, imidacloprid, and aclonifen up to 10 μg/L, by almost 100%, regardless of SRT. When the pesticides were present in combination, higher pesticide removals were generally attained, although there was no clear correlation between SRT and removal efficiency. Aclonifen being the least soluble one was removed more efficiently, either individually or in a mixture, when the SRT was set to 3 or 30 d. The COD removal efficiency was not impaired at all until 50, 10, and 10 μg/L of individual carbendazim, imidacloprid, and aclonifen levels, respectively, at all SRTs. When the pesticides were present in combination, each 50 μg/L, there were no adverse effects on COD removal, provided that SRT is 30 d. The competitive inhibition of COD removal was evident. The obtained results demonstrated that the activated sludge process receiving pesticides in combination could be operated with better pesticide and COD removal performances if SRT is closely controlled.
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