Cultivation Of Nitrifying Granular Sludge And Interaction Between Granules And Tetracycline

Antibiotics, with potential physiological effects, is one kind of emerging organic pollutants and has been applied widely. Most of the antibiotics has toxic effect on organism and has direct effect on keys processes of biotransformation and wastewater treatment processes. Biological wastewater treatment technology is the most economic method for wastewater treatment and it is still the first choice for PPCPs removal in environment. Studies show that nitrification is the main driving force for estrogen removal. Aerobic granular sludge has lots of advantages, such as long SRT, high MLSS and nitrifying bacteria enrichment. In this study, aerobic granular sludge with short-cut nitrification ability was cultivated; short-cut nitrification granular sludge was used for adsorption and degradation of tetracycline (TC); the effect of TC on operation of reactors as well as the physiological and biochemical characteristics of granules was investigated; the interaction of tetracycline and granular sludge was also evaluated. Main contents and results are as follows:1. Aerobic granular sludge with short-cut nitrification was cultivated and microbial compositions as well as denitrification ability of the granules were studied. Short-cut nitrification granules could be cultivated by stepwise increasing ammonium concentration in influent. SEM analysis showed that the main components in granules were coccus and bacillus and FISH showed that AOB were in the outer part of granules with a percent of45±1.5%, while nitrite oxidizing bacteria (NOB) were in the inner part of granules with a percent of3±1.2%. Batch experiments demonstrated a high denitrification ability of the granules and the low total nitrogen removal may be due to the limited organics in the reactor. N2O production was not increased in the short-cut nitrification system (1.74%of total nitrogen in influent).2. The adsorption and biodegradation processes of TC by shortcut-nitrification granules were characterized. The removal process of TC was a process of quick chemical adsorption and slow biodegradation. TC sorption was an endothermic process, with a complex mechanism of surface adsorption and intra-particle diffusion. Data fit pseudo-second-order adsorption kinetic well, which showed this was a chemical adsorption and Van der Waals force and covalent force played an important role. Presence of COD and NH4+-N enhanced the removal of TC, while presence of ATU (AMO inhibitor) greatly decreased TC degradation, which showed that TC biodegradation was achieved by multi-microbes.3. The effects of TC on microbial activity as well as the reactor operation were discussed in this study. With TC addition, granules both in nitrifying granules (NG) and conventional granules (CG) brokeup into small fractions. TC had toxic effect on AOB and NOB, but higer toxicity were found for NOB and there were nitrite accumulation in NG system. Specific oxygen uptake rate (SOUR) tests showed a3.3%decrease of AOB activity and25.7%decrease of NOB activity after TC addition, which meant a higher toxicity on NOB. Both NG and CG were sensitive to the presence of TC and produced more EPS to protect themselves from the TC toxicity, with higher production of protein (PN) than that of polysaccharide (PS). The fluorescence of EPS was quenched by TC addition and there may be new complex produced after TC addition.4. Three-dimensional excitation-emission matrix fluorescence spectroscopy (3D-EEM) was used to investigate the interaction of granular sludge EPS and TC for further. Both nitrifying granules and conventional granules had two fluorescent groups, which belonged to protein-like substances. TC had quenching effect on these two protein-like peaks, which showed a complexation between EPS and TC and production of complex without fluorescence. Modified Stern-Volmer equation fit the interaction of sludge and TC quite well and showed this quenching process was static quenching. There were more than one binding sites in this process and atable complexes produced. In wastewater treatment system, the combinantion of EPS with TC could not only protect sludge microbes from the toxicity of TC but also decreased free TC in aquatic environment, and thus decreasing environmental toxicity effect of TC.