Determination of optimal conditions for 5-methyl-benzotriazole biodegradation with activated sludge communities by dilution of the inoculum

The aerobic biodegradation of 5-methyl-benzotriazole (5-TTri) was optimized using lab-scale setups and activated sludge communities (ASC) collected from three wastewater treatment plants (WWTP) MBR-MH, CAS-E and CAS-M being different in their treatment technologies. ASC inocula were diluted to rule out non-biodegrading species and incubated under two nutrient conditions: A) mineral salt media (MSM) and B) carbon and nitrogen supplied MSM giving MSM-CN. 5-TTri removal with the ASC ranged from 60% to 100% in only 10days. 100μL suspended biomass from the biodegrading setups was subsequently plated on solid media to eliminate possible activated sludge remnants. After growth occurred, mixed colonies were harvested and inoculated in fresh liquid MSM containing 20mgL^-1 5-TTri. These bacterial consortia showed good 5-TTri removal in MSM-CN rather than in MSM, indicating nutrient supply being required for efficient biodegradation. In addition, experiments with high 5-TTri concentrations ranging from 20 to 1000mgL^-1 were conducted in both, MSM and MSM-CN and the maximal 5-TTri removal capacity of the ASC evaluated. 50mgL^-1 5-TTri was still removed in both media whereas 100mgL^-1 was solely removed in MSM-CN. 5-TTri biodegradation patterns also indicated that 5-TTri might be co-metabolized by microbial consortia. Furthermore, experiments with gradient-solid-media-plates showed 5-TTri to be inhibitory for the ASC in concentrations above 50mgL^-1 and revealed the optimal conditions regarding carbon and nitrogen concentration and pH value for effective 5-TTri biodegradation by ASC. Nitrogen proved a crucial factor for enhancing organisms' biodegradation capacity with an optimal pH around 7 while carbon showed no such effect.