Treatment of cooling tower blowdown water by using adsorption-electrocatalytic oxidation: Technical performance, toxicity assessment and economic evaluation

[Display omitted] •An eco-friendly process was adopted to treat cooling tower blowdown water.•PANI/TiO2 exhibits excellent performance in the removal of organics and P.•Electrocatalytic oxidation is an effective method for desorbed eluate.•TELI method was applied to assess the toxicity of effluent and oxidized eluate.•A reasonable operation cost of the treatment loop was estimated. An eco-friendly process was adopted to treat cooling tower blowdown water (CTBD) and the toxicity of correspondingly produced water/eluate was evaluated using the transcriptional effect level index (TELI) based on toxicogenomics. The objective of the work is to provide a feasible treatment loop including adsorption to remove organics and phosphorus from CTBD, electrocatalytic oxidation to improve the biodegradability of the eluate after desorption. Results showed that PANI/TiO2 was a promising adsorbent in the removal of organics and phosphorus from CTBD and exhibited a satisfied regeneration ability beyond 30 times of reuse. During the electrocatalytic oxidation process the biodegradability of desorption eluate was gradually increasing and BOD5/COD of the oxidized eluate reached 0.4 after 4.8 h of treatment, indicating that the treated wastewater could be returned to the biological treatment loop for further processing. The analysis of the quantitative toxicogenomics assay revealed that the toxicity of CTBD was mainly caused by oxidizing biocides of trichloroisocyanuric acid (TCCA), leading to a significant membrane stress response of bacteria. And the toxicity level of CTBD decreased after adsorption treatment while the desorption eluate experienced increase and then decrease during the electrocatalytic oxidation, meaning that certain oxidation duration was needed to keep the eluate safe for biological treatment. According to economic analysis, the operation cost of treatment loop was estimated at around 0.6 dollars/m3, ensuring high reuse water quality and safe eluate for further biological treatment.