Research On Biofilm Carriers As Carbon Source And Application On Treatment Of Low C/N Ratio Wastewater

Considered of the technology and economy, the waste water discharged by many enterprises in our country is treated only by simple biochemical methods, so the content of nitrate in the waste water goes beyond the standard. The waste water which discharged into rivers or lakes has resulted in the large area of water eutrophication. It makes the water smelt fishy, the quality of water depravation or the lake degenerate, seriously the water becomes black and olid. However, the concentration of nitrate in the water discharged by these enterprises varies from several tens to several thousands per liter, and most of the water is a kind of low concentration. So part of the rivers and lakes has the characteristic of high concentration of nitrate and low concentration of COD, which results in the difficulty of the treatment of this water.Generally, nitrogen removal technology can be disparted two kinds: physical chemistry method or biology method. Physical chemistry method includes air blowing off, adding chlorine, flocculating and deposition, manual marsh. Now the biology method is the main method to remove the nitrogen in treating the waste water which is recognized the most economic, effect and development future method. Traditional removing nitrogen theory considers that ammonia nitrogen can be wipe off through nitrify moment and denitrification moment. Nitrification process happens in the activity of nitrobacteria which is a kind of chemoautotroph, has no use for 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 theelectron 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 Denitrification. Simultaneous Nitrification 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 biomembrane thickness, the organism diffused by concentration gradient to the biomembrane 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 biomembrane 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 by ourselves which can be used in simultaneous nitrification and denitrification watertreatment, and analyzed the function parameters further.In the experiment, starch and disused fast food containers modified especially made into a new kind of starch based degradable carriers. These carriers are white, bacilliform, well biodegradable and can supply enough organic carbon resources for denitrobacteria; they have high surface roughness and porosity which is good for the growing of denitrobacteria; their high specific surface area could contain amount of microorganism. Because of the low cost, this kind of carrier could be applied abroad.In the view of the problem of low C/N ratio in the process of biodenitrification in wastewater, the effect of NH₄⁺—N removal by biofilm with the starch based biodegradable carrier was studied. Some factors, which affected the simultaneous nitrification and denitrification, such as pH, DO and temperature, were investigated. The results showed that the starch based degradable carrier could provide plenty of organic carbon source for denitrifying microorganism on the carrier and gain a good effect of nitrate removal. The removal efficiencies of NH₃—N and TN reached 93% and 76% respectively in the conditions of pH 8～8.5, DO=1mg/L and temperature 28℃.The organism removal ratio could keep in round about 90%. 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 avoids 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.