Treatability of Micropollutants and Microplastics using Selected Wastewater Treatment Processes
Abstract
Micropollutants and microplastics are ubiquitously detected in environment, which are directly linked to human health and ecosystems safety. Conventional wastewater treatment plants (WWTPs) are regarded as a major source for discharging these contaminants into environment. Therefore, it is of great significance to study the behavior of these pollutants and their removal potential in WWTPs. This work investigated specific treatment processes to determine their efficiency in removing target micropollutants and microplastics.
Primary treatments in WWTPs are first step to removal solid particle and other floated materials from the water stream. Therefore, the process is important for microplastics particles. The behavior of microplastic, especially for microfiber from laundry water were investigated in coagulation process. Over 90% removal efficiency of microfibers in pure water and laundry wastewater occurred by ferric chloride and poly aluminum chloride. As 90% of microfibers transferred into primary sludge after coagulation, the effect of microfibers on anaerobic digestion was explored. Microfibers have showed positive effect on anerobic digestion with methane production increased 6% to 35%.
Micropollutants are frequently found at µg/L-ng/L in wastewater. Many hydrophobic organics tend to adsorb on primary and secondary sludge (biosolids), however show poor removal in anaerobic digestion. Thermal alkaline hydrolysis (TAH) as a pretreatment method for removal of several commonly found micropollutants in biosolids was investigated for improving the safety of biosolid reuse as fertilizer or other land applications. Optimum detection methods for simultaneous detection of five micropollutants from water and biosolids using LC-MS were established. The TAH was found as an effective process to remove micropollutants in biosolids with an average 40% removal efficiency for the target micropollutants.
Additionally, micropollutants also are frequently detected in secondary effluent. The effluent after reverse osmosis can drop to pH 5 to 5.5. Therefore, the pH could be a factor in UV photolysis efficiency of micropollutants for potable reuse of municipal wastewater. Direct UV photolysis was evaluated to remove target micropollutants at varying pH 5.0-8.0. Sulfa, fluroquinolones, and tetracycline group are sensitive to pH and sulfa group showed a high photodegradation rate.