| Ammonia contamination of source water is universal in China. The effective biological treatment of ammonia would lead to limited processing capacity at low temperature phase (<5℃) due to the reduced biological activity. Although the representative ammonia removal method of zeolite adsorption would not be affected by temperature, zeolite adsorption has the following disadvantages, such as limited capacity, needs of periodical regeneration, complicated operation, high maintenance cost. So solving the low-temperature ammonia pollution of drinking water is very important and urgent, research of physiochemical-biochemical coupling system to remove ammonia will be of more value.In this paper, aiming at the control of ammonia in drinking water at low temperature, a Biological Aerated Filter (SZBAF) with suspended filler as the lower layer and zeolite as the upper layer was established. Performance of SZBAF at short-term low-temperature period was systematically studied for treating polluted source water in South China. Removal of organic matter, manganese and ammonia by SZBAF were researched and compared with a single layer BAF. To furtherly study the mechanisms of SZBAF, Songhua river with longer low-temperature period was chosen. Ammonia removal and bacteria community response mechanisms of SZBAF were studied at low-temperature period. In the last, impacting factors and adsorption-desorption law of biological zeolite were researched at complicated bulk-water environment, and nitrogen transfer promotion mechanism in SZBAF were explained.For source water polluted with multiple contaminants, SZBAF and LBAF presented limited removal of organic matters, but a very good control of phthalates, odor substances and disinfection byproducts formation potential. SZBAF and LBAF could also give a good removal of manganese through biological oxidation with an average removal rate of over80%at stable period, and synchronized efficient removal of ammonia and manganese can be achieved. At high ammonia loading period and low-temperature period, SZBAF was better than LBAF. Additionally, SZBAF presented longer backwashing period and lower backwashing intensity than LBAF, so the former is more suitable for handling high ammonia and high turbidity polluted water.For treating longer period of low-temperature Songhua River water, SZBAF had a stable removal of ammonia at low-temperature restart period, high ammonia loading period and temperature transition period, by synergetic biological oxidation mechanism and zeolite adsorption mechanism. At long-term low-temperature (about1～5.5℃), average removal rate of ammonia by SZBAF was77.08%, and nitrification mechanism became stronger and stronger along with the running time. When water environment was transited from normal temperature to low temperature, nitrification mechanism was actually weakened, and while re-entry of common temperature period from the low temperature period, the system still had stable ammonia removal efficiency, with the presence of similar nitrogen physicochemical transfer. Performance about removal efficiency of ammonia by SZBAF is consistent with microbial community succession law, although the bacteria diversity at normal temperature was higher than low temperature, but after a long period of nitrifying bacteria acclimation and proliferation at cold time, the number of Nitrospiraceae_Nitrospira and Nitrosomonas and the types of bacteria were both higher than that in normal temperature period. The quantitative real-time Polymerase Chain Reaction (PCR) results also demonstrated that the number of ammonia oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB) at low temperature period was significantly higher than that at room temperature period. However, the original domesticated low-temperature nitrifying bacteria were re-weakened after the normal temperature period. Low temperature also made niche separation between suspended media in the lower layer and zeolite media in the upper layer, nitrification bacteria were more collected on the upper zeolite layer.The aeration system in SZBAF would promote the bio-zeolite adsorption of ammonia, and hydraulic retention time (HRT) at30～60min can ensure completed biol-zeolite adsorption of ammonia. Cation coexisted in water, humic acid and kaolin particles will all affect zeolite adsorption rate of ammonia, and the greatest one was the coexisted cation. Bio-zeolite adsorption rate of ammonia would also be affected by the presence of biofilm and low temperature, but the adsorption capacity could not be impacted. Bio-zeolite adsorption of ammonia was accorded with the Langmuir adsorption model. With the change of the ammonia concentration gradient, when the ammonia concentration in source water became smaller, ammonia would be released from the bio-zeolite to ensure the use of nitrogen sources by nitrifying bacteria on the zeolite surface. By adjusting operation mode (e.g. prolonging HRT), it can accelerate the nitrogen transfer in SZBAF to achieve sustainability and efficiency of ammonia removal.In this paper, efficient removal of ammonia by SZBAF at <5℃was achieved, ammonia removal mechanism at low temperature was revealed. The proliferation of nitrifying bacteria at low temperature was proposed and validated; this would be of significance and provide theoretical foundation for fundamentally solving ammonia pollution problem of drinking water in long-term low–temperature period. |
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