| In recent years, global warming and environmental deterioration have not been controlled effectively. Algal bloom break-out still occurs frequently in natural water system, which affects the water ecosystem and drinking water safety seriously. It is urgent to develop new technologies for denitrification and algal removal in polluted raw water. Based on the raw water quality characteristics with high concentration of algae and ammonia nitrogen in Eastern China, this thesis developed a new biological aerated filter mixed with three filter materials of zeolite, granular activated carbon (GAC) and suspended biological carrier. The optimization of filtration parameters and the discharge risk of disinfection by-products during long-term operation were studied. Meanwhile, the adsorption and biodegradation characteristics of regular pollutants and algal toxins with different filter materials and the removal mechanism of microcystin-LR were investigated. The main results are as follows:1. Based on the raw water quality of high concentration of algae and ammonia nitrogen in Eastern China, a novel biological aerated filter (BAF) was developed with three different filter materials of zeolite, GAC and suspended biological carriers. At the reactor start-up phase, the average removal efficiencies of NH4+-N for R1, R2 and R3 were 84.8±10.5%,95.6±2.5% and 97.9±2.3%. The average TOC removal efficiencies were 47.9±24.6%,54.4±22.9% and 63.4±12.6% and the average algal cells removal efficiencies were 47.8±29.1%、59.2±25.1% and 69.3±29.3%, respectively. When HRT reduced to 4h and the gas-water-ratio reduced to 4:1, the average NH4+-N removal rates reached to up 90% in R2 and R3 reactors. The results showed that R2 and R3 reactors with suspended biological carriers were more stable than Rl reactor. The R2 and R3 bioreactors achieved a higher removal efficiency of NH4+-N. The potential formation risks of disinfection by-products were also studied. During the chlorinating disinfection process, the algae organic matter (AOM) formed dichloroacetic acid (DCA), trichloroacetic acid (TCA) and trichloromethane (THM) easily. After BAF treatment, the removal efficiency of halogen acid was very high. However the potential of trichloromethane risks was still high.2. Based on operating results of the reactors, the adsorption and biodegradation performances for pollutants using different filter materials were studied. The results showed that the algal cells were mainly absorbed by filtration materials. There were no obviously differences among three materials on algal cells removal. The removal efficiencies by zeolite, GAC or suspended biological carrier were about 72%. Batch experiments showed the TOC removal efficiency was 40% by zeolite and 60% by GAC. Zeolite alao had good adsorption properties to NH4+-N. NH4+-N adsorption efficiency by zeolite was as high as 30% in 4h. GAC had good NH4+-N removal efficiency of 29.9% by nitrification. The NH4+-N adsorption process by zeolite and nitrification process by GAC followed by first-kinetics equation. The adsorption kinetics constant of Ka was 0.105h-1 while biodegradation kinetics constant of Kb was 0.008 h-1. Results showed that the removal efficiencies of NH4+-N and TOC by mixed filter materials was superior to the cumulation of three single filter materials. The combination of three filter materials obvious reinforced the removal effect.3. Considering the risk of the formation of cyanotoxins, the effect of filter materials on the adsorption and biodegradation of cyanotoxins was studied. The results showed that all three materials had good adsorptive capacity of MC-LR within 7 hours. GAC showed the best adsorptive effect of MC-LR among the three materials and the adsorption rate by GAC reach to 88% after 7h. GAC also had good biodegradation performence for MC-LR and the remowal efficiency was 96.8% after 48h. According to the LC/MS analysis of MC-LR biological degradation products, the intermediate products were mainly linear MC-LR, four peptide compounds and Adda. Therefore, the degradation mechanism of MC-LR is mainly according to the removal and mineralization of Adda. |
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