Analysis of 1H-benzotriazole removal efficiency from wastewater in individual process phases of a sequencing batch reactor SBR

The research focused on a very dangerous and commonly used compound which has carcinogenic and mutagenic impact on living organisms. 1H-benzotriazole (1H-BTR) is used as a corrosion inhibitor for installations in industrial plants, in the production of biocides, detergents, drugs, tires, rubber, in refrigeration systems and de-icing substances, while its derivates are UV stabilizers in plastics, paints, films and sunscreens. It is also an additive in petroleum products (lubricants, hydraulic fluids). The paper presents quantitative changes of 1H-BTR after sequencing batch reactor (SBR) process. The studies have been carried out for 411 cycles of SBR during which concentration of 1H-BTR was changed in the range of 50–1000 μg L⁻¹. SBR operating cycle consisted of 6 phases: filling (dilution-40 min), mixing I (dephospatation-20 min), aeration with stirring (nitrification and oxidation of organic compounds-300 min), mixing II (denitrification-30 or 60 min), settling and decantation (separation-40 min), downtime (90 or 60 min). The technological parameters of the activated sludge (sludge volume index, solids and hydraulic retention time) were as similar as possible to those maintained in the real wastewater treatment plant (WWTP). Mixed liquor suspended solids concentration was 3.50 kg m⁻³. Conducted studies showed that industrial wastewater containing 1H-BTR can be effectively treated in SBR. The conducted studies showed that removal of 1H-BTR with more than 80% efficiency is possible at effluent concentrations not exceeding 200 μg L⁻¹. Higher concentrations of 1H-BTR in wastewater lead to a sharp decrease in removal efficiency. The lowest removal efficiency (56.6%) was recorded at the initial 1H-BTR concentration of 100 μg L⁻¹. On the other hand, the highest efficiency (88.2%) at the initial concentration of 1000 μg L⁻¹. The concentration of 1H-BTR in treated wastewater was 1.1 μg L⁻¹ in the control reactor and from 7.2 to 434.0 μg L⁻¹ for an initial concentration from 50 to 1000 μg L⁻¹, respectively. The aeration phase was superior in terms of 1H-BTR removal, regardless of the benzotriazole doze in the raw wastewater. In the anaerobic mixing phases I and II in the SBR, the decomposition of the 1H-BTR was 5.3 and 4.9 times slower, respectively, compared to aerobic conditions.