| dc.description.abstract | This study focuses on a chemical plant that provides electronic-grade chemicals for the semiconductor and optoelectronic industries. It explores the feasibility and effectiveness of using different advanced oxidation processes as pre-treatment for high-concentration chemical waste liquids. The motivation for this study stems from the inadequate results obtained when using the existing ozone equipment alone for wastewater treatment. The final chemical oxygen demand (COD) was still as high as 3,000 mg/L with a removal rate of only 49.2%. Therefore, this study attempts to enhance the efficiency of the existing ozone equipment by integrating it with other commonly used advanced oxidation methods, including UV/H2O2 and Fenton reactions. The experimental results show that in terms of COD removal rate, the treatment effectiveness follows the order of UV/H2O2/O3 > UV/H2O2 > UV/H2O2/Fe2+ > UV/O3, indicating that the UV/H2O2/O3 integrated system is most suitable for removing high-concentration organic chemical mixtures in the plant. The optimal operating conditions for this UV/H2O2/O3 system are as follows: initial COD = 6,060 mg/L, UV wavelengths of 185 nm and 254 nm, initial pH = 7.63, O3 = 32 g/hr, flow rate = 2 L/min, and H2O2 addition amount = 72.72 g/L. After 8 hours of reaction, the COD removal rate reaches 98.2%. Furthermore, this study finds that in addition to achieving COD removal close to the desired effluent standard, the process has insignificant degradation effects on nitrate nitrogen and ammonia nitrogen under initial pH conditions of 4 to 7. This is likely because the nitrate in the waste liquid belongs to highly oxidized nitrogen-containing species, making it no longer susceptible to oxidation by free radicals. Within the 8-hour reaction time, the optimal ammonia nitrogen removal rate obtained is 45%.
Additionally, a study on parameter adjustment using different advanced oxidation processes shows a decreasing trend in pH during the initial stage of the reaction. This may be due to the accumulation of acids caused by the oxidation of Fe2+ to Fe3+ in the Fenton reaction, which readily reacts with hydroxide ions. In the later stage of the reaction, bicarbonate ions are produced, leading to an increase in pH to around 8. Changes in sulfate ions indicate that adjusting the initial pH can result in a relatively high residual sulfate concentration of up to 4,200 mg/L. The presence of sulfite ions in the waste liquid is likely a byproduct of DMSO decomposition, making the monitoring of sulfate ion changes a reference for deodorization. In conclusion, if designed with a batch capacity of 1 ton and a monthly treatment capacity of 22 tons, the UV/H2O2/O3 system has an investment payback period of approximately 1.45 years, making it more beneficial than outsourcing treatment. | en_US |