Study On The Mechanism Of 4-t-Octylphenol Removal By Using Biological Wastewater Treatment Processes

In resent years, alkylphenols(APs) as an important class of endocrine disrupting chemicals (EDCs) has been paid intensive attention to in environmental science research. Nonylphenol(NP) and octylphenol(OP) are most toxic compounds among the APs, and have been widely detected in the environment.At first, we took the influent of Anting Wastewater Treatment Plant as an example to study the kinds of EDCs in the influent of typical municipal wastewater in Shanghai, and investigated the removal performance of EDCs in chem-bioflocculation (CBF) treatment process. We have detected 8 kinds of EDCs, mainly including 4-t-OP(OP for short) and phthalates (PAEs). The results showed that all EDCs have been detected could partly be removed by CBF treatment process. The removal rate of the alkylphenols ranged from 60% to 99%, while the removal rate of the esters was 30%-34%. It shows that biosorption and flocculation play the central role of the removal of EDCs in CBF treatment process.For OP has been detected in the influent, we decided to take it as our target compound. Recently, activated-sludge process is the most popular process for the municipal wastewater treatments which are important sources of EDCs in the environment. So we mainly researched the removal capability of OP in activated sludge process. There are absorption and biodegradation characters for OP in different process, and the removal performance by aerobic,anoxic and anoxic-aerobic SBR reactors were studied.The process of OP absorption by activated sludge could be divided into two steps, one was quick absorption period, and the other was slow absorption period. The quick absorption period fits the first-order kinetics. As the concentration of the sludge increase, the absorption speed became slower, and the equilibrium time went longer The relationship between distribution coefficient (K_p) and the concentration of the sludge could be described by the equation K_p=a(SC)^b. Low temperature benefited the absorption function. When the pH value belonged to 5.0 to 9.0, the pH value could barely affect adsorption. K_p has negative relativity with the diameter of activated sludge, so we think it probably turn out to be a surface adsorption.In comparison, OP degradation rate in activated sludge under aerobic condition was higher than that under anaerobic condition. The degradation rate decreased with the increase of the initial OP concentration. The optimal pH values for OP degradation were 8.0 and 7.0 under aerobic and anaerobic condition, respectively. Addition of yeast extract enhanced the OP degradation, and under aerobic condition, phenol could also enhance the degradation. After incubated with OP as a main carbon source, the major species of activated sludge were identified asγ-proteobacteria. Furthermore, we also found major species identified as firmicutes under aerobic condition.We simulated OP removal performance in municipal wastewater by activated-sludge process through reactors in our lab. The result showed that the activated-sludge process could remove OP efficiently, and increasing of OP concentration did not affect the removal of other pollutants. There were many protozoa in activated sludge systems, such as vorticella and so on. The removal rate of OP went higher with the C/N decreased. And the longer the residence time was, the higher the removal rate became. When OP concentration was 50-150μg/L in the influent, the volume load became higher with OP concentration increased. When OP concentration was 150μg/L in the influent, the volume load of the anoxic-aerobic SBR reactor could achieve 85.1μgL^-1d^-1, which was the most efficient reactor on OP removal among the three kinds of reactors studied in this paper, second was the aerobic reactor and the third was the anoxic reactor. We investigated microbial community in the three different activated sludge systems, and found that most major species separated identified asβ-proteobacteria which was the same as traditional activated sludge system. This indicated the toxicity of OP did not obversly change the main major species in the sludge. Besides, we also found major species identified asγ- proteobacteria andδ- proteobacteria in aerobic reactor andγ- proteobacteria and firmicutes in anoxic reactor.In recent years, aerobic granular sludge process has been developed quickly. Compared to traditional activated sludge, granular sludge has special particular granular structures which could improve the environment for varieties of bacterium. So we studied the degradation of OP in granular sludge process, too, and got the same result as activated sludge. After incubated with OP as a main carbon source, the biological diversity decreased obviously. The major species found in granular sludge were identified asγ-proteobacteria under aerobic condition, while the major species were identified as firmicutes under anaerobic conditionAfter separation and purification, two different strains were obtained for OP degradation. Both of them were identified asγ-proteobacteria. Strain OP-1 belong to Pseudomonas, and strain OP-2 belong to pantoea agglomeran which hasn't been reported as OP degradation bacteria before. The optimal pH value for strain OP-1 degrading OP was 7.0 and was 8.0 for strain OP-2. Strain OP-1 degraded OP more efficiently by adding glucose as a carbon source.