| With the development of human society and industrialization, water contaminations have severely restricted the increasing of the world economics and menaced the survival and development of human being. Therefore, to improve water environments and solve all the problems related to water contaminations, researchers are seeking for a more efficient water disposal method at all times. As an economical and efficient water treatment technology, Photocatalysis develops rapidly in recent years. Since Phenols is the main contaminant in wastewater, the research of photocatalyticdegradation of wastewater with phenols is indispensable. Currently, most research is focused on the analysis of degradation results, intermediates, courses of reactions and influencing factors. The harm to the environment and human body health caused by the treated water is barely considered.The dissertation summaries the previous experimental methods and effecting factors in the research of photocatalytic degradation of wastewater contained phenols, concludes the distributing principles of main existing materials affected by different factors. Based on the primary standard of "Integrated Wastewater Discharge Standard" (GB8978-1996), we made the risk assessment of intermediate outcomes brought by the process of photocatalytic degradation of wastewater with phenols, and illustrated a variety of potential harms in current processing procedures.In photocatalytic degradation of wastewater with phenols, the main intermediates of phenol is catechol, hydroquinone and quinine, where the concentration of catechol is the most and hydroquinone is the second. The main intermediates of2-Chlorophenol are catechol, chlorohydroquinone and chloroquinine, where the concentration of catechol is the most great. In addition, there are some higher carbon intermediates in degradation, which are hard to be detected due to the low quantities.In the normal process, although phenols in wastewater can meet the standard requirement, there are many intermediates, which maybe have more toxicity and result in more pollution. Furthermore, because the photocatalytic process is affected by many factors such as reaction time, initial concentration, pH, catalyst kind, O2 concentrations and additive substances, the degradation rates of the substances and distribution of the intermediates are various in the different conditions. As a result, it will bring up different levels of harm.In this research, we found that the reaction time (90 min. -150 min.), when phenol meets the water standard requirement, is the most dangerous period of intermediates. Less than 90min., the concentration of phenol is over water standard and the harm is always great. In the period between90min. and 150min., phenol value is fair, but the quantity of the intermediates is over safety range. If the reaction was stopped during this time, there would be lots of potential harm. More than 150min. phenol and its intermediates are fully degraded and have little harm.Meanwhile, when phenol or 2-chlorophenol meets the standard, the harm of the intermediates is greatest under initial concentration 80mg/L, pH=7, pure TiO2 catalyst, O2 concentration 10.13kPa or no acetone additive. In contrast, under initial concentration lOmg/L, pH=9 or 11, TiO2/ACM catalyst, O2 concentration l.OlkPa or no acetone additive harm is smallest. At last, considering reaction time and risk increasing rate etc., we showed that concentration 60mg/L (between lOmg/L and 80mg/L), pH=3, TiO^ACu catalyst, O2 concentration 20.26kPa and no additive are the most conformable and economical reaction conditions of phenols.Even although most researchers agree that the photocatalytic technology has many advantages such as simplicity of operation, moderation of react condition,reduction of recontamination and so on. But the photocatalysis produces different harm due to many effects and the current restrictions of the practical implements. Hence, it still needs great efforts to explore and research in applying photocatalysis.
|
PDF Full Text Request