Optimization Of The Intimated Coupled Photocatalysis-biodegradation System And Co-metabolic Degradation Regulation

Phenol and chlorophenols, as the typical pollutants in phenolic wastewater, are highly inhibitory, widely available and easy to change with environmental migration and transformation. They have become a direct threat to water use security and the surroundings. Intimate coupling of photocatalysis and biodegradation technology(ICPB) innovatively integrate advantages of high efficiency, economic and security, while significantly weakening their limitations about biodegradability, input costs and terms of the reaction cycle. Relative to other advanced oxidation–biodegradation technologies, ICPB utilizes space more intensively and requires simpler regulation, thus it has earned a lot of attraction in inhibitive wastewater field in recent years. However, studies about ICPB are all dependent on UV radiation, only 4% of the solar spectrum. Additionally, it has been found that biofilm prone to break and cracking under UV irradiation, affecting water quality. It is the first time to propose the use of the rich resources of the visible excitation in ICPB in this paper. It is aimed atadjusting catalytic activity to optimize ICPB treating ability and to protect biofilm. Based on that, we further investigate suitable co-metabolism substrates to enhance 4-chlorophenol(4CP).The main contents are as following. The intimate coupling of visible-light-induced photocatalysis and biodegradation system(VPCB) was established and compared with intimate coupling of ultralight-induced photocatalysis and biodegradation system(UPCB). The removal efficiency, the dissolved organic carbon concentration(DOC), intermediates changes were analyzed in order to examine 50 mg/L phenol degradation behavior in different systems. We observed biomass, biofilm distribution, extracellular polymeric substances(EPSs) and the bacterial species to learn about the biofilm responses to different conditions, from microbes to the microbial structure level. Eventually, different phenomena of VPCB and its advantages over UPCB were illustrated by water sample biodegradability. Experimental results showed that the ICPB reflected obvious advantages over single photocatalysis like VPC or UPC and biodegradation(B). No stagnation was found in ICPB.VPCB exerted notable advantages over UPCB. At 16 h, phenol removal in VPCB reached 98.8%, while UPCB was only 67.7%. UPCB had a poor DOC for the existence of more intermediate products difficult to be absorbed by sponge carriers and the release of large amounts of soluble products(SMPs) resulting from broken biofilm and cell lysis under UV irradiation. In contrast, visible light catalysis provides not only more mild and efficient oxidation environment, and avoid the harm from light to microbes. Biomass and microbial structure were well protected and exert great effect on degradation. DOC removal efficiency was 64% in VPCB with better biodegradability, 42.3% higher than that of UPCB.Under VPCB system with Ag-TiO2, phenol, catechol and sodium acetate(NaAc) were selected to investigate the effects of different co-metabolism substrates on degradation of 20 mg/L 4CP. Degradation efficiency and pathway were analyzed and the biomass, biofilm distribution and biological activity were compared to elaborate different influence from substrates on 4CP degradation. In VPCB with Ag- TiO2 as catalyst, the protection to biofilm from the system was verified fundamentally because all four metabolic systems possessed relatively high microbial activity. However, co-metabolic systems presented different 4CP degradation behaviors. The addition of NaAc to 4CP accelerated removal rate initially due to its high biodegradability, but the rate slowed down short after with removal efficiency 69.4% in the end. While catechol co-metabolic system only showed 56.2 %. Phenol co-metabolic system shared a similar removal rate trend with solo 4CP. For the addition of phenol accelerated 4CP removal, it earned removal efficiency of 71.8% and dechlorination degree of 62.6%, 15.9% higher than that of solo 4CP system. However, catechol co-metabolic system obviously dragged down 4CP degradation with more recalcitrant intermediates produced. Its removal efficiency remained at rather low level about 56.2% and the dechlorination degree was14.3%, one third to that of solo 4CP system. According to the above, it is concluded that not all substrates will enhance pollutant degradation. In VPCB system, phenol accelerated but catechol inhibited 4CP degradation.