The feasibility of improving biodegradability induced from the structural conversion of refractory pollutants by hydrothermal reaction was investigated in order to develop a new pretreatment method for the following conventional biological treatment m...
The feasibility of improving biodegradability induced from the structural conversion of refractory pollutants by hydrothermal reaction was investigated in order to develop a new pretreatment method for the following conventional biological treatment methods. Besides, the application of hydrothermal reaction was mainly considered on the viewpoint of treatment of refractory pollutants, treated reactant reuse and enhancing biological treatment process.
At first, the feasibility of improving biodegradability of polyvinyl alcohol (PVA) representing for high-molecular-weight refractory pollutants was evaluated under various hydrothermal conditions (Chapter 2). The structural conversion of PVA was obtained from hydrothermal reaction without much reduction of carbon contents. The change of molecular weight distribution and ultraviolet (UV) absorbance collected by gel-permeation chromatography (GPC) system was corresponding to the biodegradability improvement of PVA. Biodegradable low-molecular-weight products from high-molecular-weight refractory pollutants such as PVA could be secured by using hydrothermal reaction.
Then, the reaction mechanism of biodegradability improvement induced from the structural conversion of chloroacetic acids (CAAs) by hydrothermal reaction was investigated (Chapter 3). CAAs were used as test materials for linear hydrocarbon structured refractory pollutants involving recalcitrant parts. The production of biodegradable products followed by the elimination of recalcitrant chlorine atoms from CAAs was obtained at the beginning of hydrothermal reaction. Hydrothermal reaction might be possibly applied to the pretreatment of refractory pollutants prior to conventional biological treatment method, due to very simple apparatus, easy control and extremely short reaction time with exception of the heat-up time of reactor.
Finally, hydrothermal reaction was applied to excess sludge in order to verify its applicability on the viewpoint of treatment of refractory pollutants and reuse of treated reactant for enhancing biological treatment methods (Chapter 4). The readily biodegradable substrate was produced from the content change of excess sludge by hydrothermal reaction. The usability of treated excess sludge as a carbon source in biological phosphorus removal (BPR) process was demonstrated in Chapter 4. During hydrothermal reaction, the control of content change of excess sludge was the most important factor on the viewpoint of excess sludge reuse. Recycling of excess sludge treated by hydrothermal reaction indicates not only a decrease of excess sludge amount discharged but also an improvement of conventional biological treatment methods including BPR process.