Study On The Carrier As Carbon Source And Application On The Treatment Of Urban Rivers And Lakes

Nowadays, with the rapidly development of the economy and the process of urbanization, the eutrophicated phenomenon of rivers, oceans, especially urban rivers and lakes are getting more and more serious. Water Blooms and red tide occur continually. Most of the urban rivers and lakes are closed, slowly fluid waters, they are stillness and bad fluidness. They usually have the characteristics of easily polluted, low self-purification capacity, etc. Urban rivers and lakes are including all the rivers or reservoirs that have the function of sightseeing, entertainment, water supply or holding dirt, they usually locate in the city or near the countryside. Commonly, urban rivers and lakes have low water level, evaporation is the mainly effect. Meanwhile, as the containers of rain and city wastewater, urban rivers and lakes are surrounded by blocks, which hold a large amount of city wastewater. Recently, a kind of special waters has been found in many cities, these waters have the characteristics of high concentration of nitrite and low concentration of COD, which results in the difficulty of the treatment of the water.Traditional removing nitrogen theory considers that ammonia nitrogen can be wiped off through nitrify moment and denitrification moment. Nitrification process happens in the activity of nitrobacteria which is a kind of chemoautotroph, it makes no use of organic nutrition, gets carbon recourses from carbon dioxide and obtains energy though inorganic matter oxidation; denitrobacteria is used in denitrification process which reduces nitrate nitrogen into nitrogen. Denitrobacteria is a kind of heterotrophic facultative anaerobic bacteria, makes the nitrate nitrogen as the electron acceptor and the organism as the electron donor in anaerobic conditions. So if the ratio of C/N is too low in waste water, the organic carbon recourses is needed from outside. This method may result in the quality of the outflow unstable and increase the investment expenses.Recently, the new nitrogen removal technology is Shortcut Nitrification Denitrification and Simultaneous Nitrification and Denitrification. Simultaneous Nitrification and Denitrification use the impersonality phenomena that the oxygen can not be supplied asymmetry, form a structure of anaerobe inside and aerobe outside which supplies a favorable reproducing environment for denitrobacteria and nitrobacteria to make the nitrification reaction and denitrification reaction happen in the same time and space.But in the process of Simultaneous Nitrification and Denitrification, since the effect of the biofilm thickness, the organism diffused by concentration gradient to the biofilm inside is few, especially for the low C/N ratio waste water. Denitrobacteria which is lack of organism can not reproduce either. In the view of this problem, many researchers are finding some cheap solid organisms both as carbon recourse and biofilm carrier and they have gained some fruit. Recent years, there is a new kind of Simultaneous Nitrification and Denitrification techniques using Biodegradable Polymers (BDPs) as microorganism carrier and solid carbon resource. This technique is no need of organism from outside, and BDPs is degraded by enzyme in the body of microorganism, supplies carbon resource for denitrobacteria. This method can resolve the problem of be lack of carbon source in low COD waste water.This experiment developed a kind of biodegradable substance on our own. Fused modified starch and disused fast food containers under the heat of 175—185℃, then let the mixture through the special mould machine, there we got a new kind of starch based degradable carriers. Through screen, the experiment finally decided to use the thermoplastic starch in which the ratio of the starch, elasticizer, water is 70:25:5, and to compose the carriers in the ratio of 30% thermoplastic starch to 70% biodegradable containers. The carriers are white, bacilliform, well biodegradable. These carriers have suited water absorption, so the microorganism can grow well on the surface of the carriers. Under the natural condition, the carrier is heavier than water, so if the carriers were fastened with a rope, they can suspend in the water well without affecting the fixation of the microorganism. They have high surface roughness which is good for the growing of denitrobacteria. Because of the low cost, this kind of carrier could be applied abroad.In the experiment, starch based carriers are used in the courses of Simultaneous Nitrification and Denitrification as the biofilm carriers, and we made a primary research on the function parameters. Through the research, we draw the conclusion that the best HRT is 6h. Meanwhile, the Biofilm Simultaneous Nitrification and Denitrification experiments were carried through using the starch based carriers. Some factors, which affected the simultaneous nitrification and denitrification, such as C/N, pH, DO and temperature, were investigated. The results showed that the starch based degradable carriers which acted as the organic carbon source for denitrifying microorganism can gain a good effect of nitrate removal in the courses of Simultaneous Nitrification and Denitrification. The removal efficiencies of NH3—N and TN reached 90% and 70% respectively in the conditions of HRT=6h, pH=8, DO=1mg/L and temperature=30℃. The experimental research proved that in the low C/N ratio condition, starch based biodegradable carrier could supply enough carbon source for the growing membrane. This method solves the problem of secondary pollution from pulling in carbon sources directly, simplifies the technological process, and reduces the cost of the nitrate removal water treatment.