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Thesis Format

Integrated Article

Degree

Doctor of Philosophy

Program

Chemical and Biochemical Engineering

Supervisor

Ray Madhumita B

2nd Supervisor

Dagnew Martha

Co-Supervisor

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.

Summary for Lay Audience

Micropollutants and microplastics, are two kinds of contaminants in environment, which come from many sources closely related to daily life. Micropollutants refer to industrial chemicals, pharmaceuticals, and personal care products such as antibiotics, hormones such as estrogen, synthetic musk, cleaners, and disinfectants. Microplastics are tiny plastic pieces with a diameter less than 5 mm from direct plastic fragments or breakdown of larger plastic pieces under environmental weathering activities. Both micropollutants and microplastics are regarded as global environmental problems due to their possible negative effects on human health and ecosystems. Generally, wastewater treatment plants (WWTPs) play an important role on protecting human and environment from contaminants as barriers. Therefore, the removal of several micropollutants and microplastics were studied in this work.

This research aimed at investigating various treatment processes in WWTPs related to the elimination of micropollutants and microplastics including coagulation, anaerobic digestion, post-treatment of anaerobic digestion, and UV disinfection. The results indicated coagulation as a process in primary treatment in WWTP, can remove over 90% microfibers by adding coagulants. Most of microfibers retained in sludge and enhanced methane production in anaerobic digestion. Furthermore, post-treatment with thermal-alkaline at pH 11.0 removed 40% of target micropollutant. This is beneficial for reuse of biosolids as fertilizer or other land applications.

UV disinfection is a promising process for potable reuse application. Selected micropollutants were removed efficiently by direct UV photolysis, in which pH affected the UV photodegradation performance. The results in this work are useful for understanding the treatment performance of coagulation, thermos-alkaline treatment, and UV photolysis for the removal of micropollutants and microplastics in WWTPs.

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