Ph.D Thesis


Ph.D StudentAviezer Yaron
SubjectSupercritical Water Oxidation of Contaminants of Emerging
Concern in Secondary Municipal Effluents RO
Retentates
DepartmentDepartment of Civil and Environmental Engineering
Supervisors PROF. Ori Lahav
ASSOCIATE PROF. Yael Dubowski


Abstract

Secondary municipal effluents contain tens of thousands of contaminants of emerging concern (often termed also micro-pollutants) at 2-5% (w/w) of their overall Total Organic Carbon (TOC) concentration, leading to a typical concentration range of 200- 5 00 μg/L. These pollutants currently reach the environment, e.g., the aquifers, surface waters and soils, and as a result, the food and water chain. The primary required separation is reverse osmosis filtration, which concentrates the pollutants into 10-20% of their initial volume. The present work investigated, for the first time, the application of supercritical water oxidation (SCWO), as a generic sole application, enabling the mineralization of >99% of the effluent retentate TOC and full decomposition of model micro-pollutants (carbamazepine and estrogens). The research was divided into four stages. First, I conducted batch SCWO experiments of synthetic solutions of the model pollutants and real effluent retentate solutions. The results of these experiments laid the basis for the understanding and quantification of the feasibility for decomposing and mineralizing the chosen pollutants and solutions under subcritical and supercritical conditions. Second, I applied sets of continuous SCWO of model pollutants synthetic solutions and developed a kinetic investigation methodology, which enabled generating a set of empirical power low kinetic equations for predicting the decomposition and mineralization of both model pollutants, and with regard to later stages, enables me to focus on the range of the operating conditions that was relevant for the continuous SCWO experiments of real matrix solutions. Third, a set of qualitative salts solubility quartz capillaries experiments were conducted, which investigated the salts' onset time of precipitation, under hydrothermal conditions, enabling to set 200 °C as the required preheating temperature that would increase the heat load in the subsequent continuous SCWO reactor of real matrix solution on the one hand, and reduce the risk of salts' plugging on the other. Finally, two set of continuous SCWO experiments of real secondary municipal effluents RO retentate matrix were conducted to further examine the application of the findings on the treatment of secondary effluents RO retentates form a city of 100,000 PE. It was determined that SCWO is a feasible method for full mineralization of TOC and the model pollutants present in the feed stream, with an efficiency >99%, at operating conditions of 450 °C, oxidant dosage of 5-10 of the stoichiometric COD, hydraulic residence time of 1 minute and addition of 100 mg/L of IPA, a homogenous catalyst. Furthermore, the city size SCWO model demonstrated that a very high thermal efficiency and full pressure recovery could be attained by the suggested installation of a pressure recovery unit that is common in seawater desalination but has not been suggested or installed so far within SCWO systems. The evaluated total OPEX and CAPEX of the proposed plant may be lower than $5. 9 ±2.5m3 of secondary effluent, which is two orders of magnitude lower than the reported shadow price of the contaminants of emerging concern in the original secondary municipal effluent.