Preliminary Study On The Removal Of Steroidal Estrogens In Wastewater By Embedded Nitrobacteria Pellets

In recent years, the pollution of steroid estrogens has caused the attention of many researchers overseas and they have begun to study the removal of steroid estrogens in the environment. A large number of studies found that the correlation was strong between nitrification process and steroid estrogen biodegradation, and steroid estrogen can be removed by embedded nitrobacteria pellets in wastewater depth treatment. This paper focuses on steroidal estrogens in artificial sewage. In this study, the preliminary study on the removal of steroidal estrogens by embedded nitrobacteria pellets acclimated in air-lift inner circulated aerobic fluidized bed reactor is executed. This research is about the following fields: the effect of different temperatures on embedded nitrobacteria pellets acclimated; the spatial distribution of embedded nitrobacteria in pellets; the removal of E1, E2 and EE2 by embedded nitrobacteria pellets and corresponding biodegradation kinetics; static adsorption for E1, E2 and EE2 by PAC(contain carbon but not bacteria) and CPM(no carbon and bacteria). The main results of the research are listed as follows:1) At high temperature, the system had some advantages such as starting fast, high nitrification activity and impact resistance. After 9 days, the acclimation of embedded nitrobacteria pellets could be completed in air-lift inner circulated aerobic fluidized bed reactor. Compared with the high temperature, the system had some drawbacks such as starting slowly and low nitrification activity at low temperature. After 29 days, the acclimation of embedded nitrobacteria pellets were only completed in air-lift inner circulated aerobic fluidized bed reactor. If the temperature drops below 12 ℃, the effluent ammonia concentration will not meet the urban sewage treatment plant pollutant level A standards due to the activity of embedded nitrobacteria inhibited severely. The scanning electron microscopy confirmed that the spatial distribution of embedded nitrobacteria in pellets had changed a lot after embedded nitrobacteria were acclimated. They have been uniformly distributed in pellets before embedded nitrobacteria were not acclimated. After a period of acclimation, light yellow biofilm with the depth of 1-2mm on the surface of embedded nitrobacteria pellets appeared. In fact, the biofilm consisted of a large number of rod-like and ellipsoidal nitrobacteria.2) Preliminiary study on the removal of steroidal estrogens by embedded nitrobacteria pellets was executed. The removal rates of E1, E2 and EE2 were 65.6%, 98.8% and 72.0% under controlled conditions in BAC(contain carbon and bacteria) reactor. The mechanisms were based on biodegradation of nitrobacteria and physical adsorption of embedded material. The removal rates of E1, E2 and EE2 were 39.4%, 45.2% and 71.3% under controlled conditions in PAC(contain carbon but not bacteria) reactor. The mechanisms were based on physical adsorption of embedded material. E1 and E2 were able to be biodegradated largely by embedded nitrobacteria. Meanwhile, E1 was an intermediate metabolite for E2. In contrast, the research showed biodegradation of EE2 was very weak by embedded nitrobacteria.3) Biological degradation linear regression results showed that the degradation rates of E1, E2 and EE2 by embedded nitrobacteria were different. The relationship was as follows: E2(0.0935/h)>E1(0.0365/h)>EE2(0.0008/h). Compared with E1 and EE2, The degradation rate of E2 was 2.6 times and 116.9 times than theirs. It also showed that nitrification existed under autotrophic conditions, and biodegradation rates were consistent with the characteristic of three steroid estrogens. The most stable steroid estrogen was EE2 and the most unstable was E2.4) The research used PAC and CPM as adsorbate of E1, E2 and EE2. The static adsorption experiment results showed adsorption capacity of PAC for E1, E2 and EE2 were 1.1-1.9 times, 1.1-1.8 times and 1.1 times than CPM. Compared with the CPM, PAC could significantly improve adsorption capacity when small amount of powdered activated carbon were added to pellets. The mechanisms were based on filled micropores and gains and losses electron between carbonyl group and the benzene ring. At the same time, Freundlich equation could be a good fit for adsorption isotherms of E1, E2 and EE2. The adsorption capacity K and adsorption intensity 1/n of PAC were higher than CPM. The relationship was as follows: EE2(PAC)>E2(PAC)>E1(PAC)>EE2(CPM)>E2(CPM)>E1(CPM). PAC and CPM adsorption for E1, E2 and EE2 were consistent with their Kow values. The easiest assignment to a solid phase was EE2 and the least was E1.5) The steroid estrogens(E1, E2 and EE2) can be removed strongly by embedded nitrobacteria pellets. The mechanisms are based on biodegradation of autotrophic nitrobacteria and physical adsorption of embedded material. The method of embedded nitrobacteria pellets removing steroid estrogens in wastewater is feasible. It can not only reduce the expensive cost of the use of physical and chemical means, but also provide an affordable means to remove steroid estrogen in wastewater depth treatment effectively. In short, the technology has a very important theoretical significance and practical value.