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Integrated treatment of non-ionic surfactant containing industrial wastewater: process optimization, material selection and life cycle analysis

Boek - Dissertatie

Endocrine-disrupting compounds are increasingly recognized as a severe threat to aquatic (micro-)organisms and public health. One class of components that have distinct endocrine disruptive properties are non-ionic surfactants, such as alkylphenol ethoxylates (APEOs). Nonyl- and octylphenol ethoxylates are the most well-known APEOs used as non-ionic surfactants and are applied as cleaning, washing and surface-active agents in the textile industry. To date, such non-ionic surfactants are still produced and transported in bulk, and one particular type of discharge is as a residual load during the tank cleaning process by the tank truck cleaning industry. The produced wastewater, containing the APEOs, is typically treated in a combined physicochemical/biological on-site wastewater treatment facility. However, endocrine disruptive properties do not decrease significantly due to the formation of biodegradation products having similar properties. Alkylphenols are common biodegradation products that are produced during the biological treatment of wastewater APEOs. Intensive research has already been carried out on the removal of these surfactants themselves, but research on further alkylphenol degradation is scarce. However, alkylphenols such as nonyl- and octylphenols, still possess estrogenic activities and interfere with the endocrine systems of living organisms. Research on the further degradation of these compounds is, therefore, necessary. The most frequently encountered alkylphenol is nonylphenol (NP). Advanced Oxidation Processes (AOP) are shown to be highly effective for the removal of various classes of recalcitrant pollutants. These are all based on the oxidation of the organics by OH-radicals (OH*). Various types of AOPs have been developed (e.g., ozone and hydrogen peroxide based), which differ in the production pathway of the OH*. Their use for the degradation of detergents has already been reported in the scientific literature. In this work, the implementation of AOPs as post- or pre-treatment technique for NP removal is investigated on lab-scale. Also, pilot-scale experiments were performed to assess the NP removal by an integrated treatment of AOPs and conventional biological treatment. Hence, the scope of the PhD covers the removal of NP by various AOP treatments and the effect of daily fresh industrial wastewater on the removal of NP by a pilot-scale AOP unit. For example, a combined biological-ozone unit was operated. During the ozonation period, the average NP concentration of the ozonated wastewater was 0.27 µg/L, compared to 1.89 µg/L for the effluent obtained after a sole biological treatment, resulting in an improved average removal efficiency of 32%. Highly corrosion resistant materials are generally recommended in AOP installations, particularly in the presence of chloride contamination (e.g., super duplex or 6Mo stainless steels, nickel-based alloys, etc.). However, these alloys can be very expensive while the applicability of less expensive (leaner) duplex stainless steel grades can be considered under certain conditions. Therefore, in this work, electrochemical and immersion experiments were performed to assess the corrosion of lean duplex stainless steel and define their limits of use in different AOP treatment plants. The corrosion experiments suggest that dissolved ozone at the tested levels does not result in a higher pitting susceptibility for the tested base metal alloys. Contrarily, the addition of Fenton reagents leads to pitting corrosion of the studied lean duplex alloys. The immersion experiments show that crevice corrosion is a serious problem in wastewater treated with both ozone and Fenton reagents. For welded samples, it was confirmed that higher pit depths were observed in the Fenton-treated water than in the ozone environment. The maintenance of piping systems (WWTPs) and its effect on the LCA and LCC for both austenitic and duplex stainless steel grades is evaluated. Additionally, all data are combined into a user-friendly tool, which can be used in industry for an appropriate grade selection for pipes in a WWTP. The results show that the duplex stainless steel alloy EN 1.4462 has a lower GWP and PED than austenitic stainless steel alloy EN 1.4404 after the total WWTP's service life of 40 years due to multiple replacements of pipes required for wastewater with high chloride levels (> 3000 ppm).
Jaar van publicatie:2021
Toegankelijkheid:Closed