Microbial and photolytic degradation of benzothiazoles in water and wastewater

Abstract

In the present study, an analytical method for the determination and extraction of benzothiazoles in water and wastewater was developed. Because bacteria are important agents in transforming most organic compounds, their specific roles in biotransformation of benzothiazole compounds in water was explored. The biodegradability of these compounds by using aerobic and anaerobic conditions was investigated. Additionally, the photochemical degradation of benzothiazoles was studied. The polar benzothiazole compounds such as benzothiazole sulfonic acid (BTSA) and hydroxybenzothiazole (OHBT) are well recovered from the polar polymer phases. The other analytes show good recoveries on the silicagel-cartridges. Based on their high capacity, RP 18 and EN were chosen for a sequential solid phases-extraction of benzothiazoles. The recovery rates of the solid-phase extraction (SPE) from sewage treatment plants effluents and influents are slightly decreased compared to those obtained with tap water but remained acceptable and are full satisfied. Aerobic mixed cultures are capable of utilising benzothiazoles as a sole source of carbon, nitrogen and energy. Benzothiazole (BT), hydroxybenzothiazole (OHBT), mercaptobenzothiazole (MBT) and methylthiobenzothiazole (MTBT) were investigated in separate batch tests. Benzothiazole and hydroxybenzothiazole can be microbially degraded in water in a relatively short time, whereas methylthiobenzothiazole was proved to be stable under aerobic conditions. Mercaptobenzothiazole was methylated to methylthiobenzothiazole. By using the Sequencing Batch Reactor (SBR), mercaptobenzothiazole was transformed to benzothiazole sulfonic acid (BTSA), methylthiobenzothiazole (MTBT) and traces of dithiobisbenzothiazole (MBTS). Anaerobic treatment revealed no transformation of hydroxybenzothiazole whereas, methylthiobenzothiazole was partly degraded. Mercaptobenzothiazole was partly metabolised to BT and BTSA was partially transformed to OHBT, which was not observable earlier than 5 weeks together with other unknown substances that were not identified. Concerning thiocyanomethylthiobenzothiazole (TCMTB), BT is beside MBT an important metabolite. Under photolytic conditions in water and wastewater, both mercaptobenzothiazole and methylthiobenzothiazole revealed the formation of two stable photoproducts: benzothiazole (BT) and hydroxybenzothiazole (OHBT).