Nitrate Nitrogen Compound Catalytic Reduction Of Sound Principles And Technical Research

Contamination of nitrate in surface water and groundwater is increasing gradually in many areas. Since nitrate can cause methaemoglobinaemia in infants, the removal of nitrate has become a key concern. Industrial wastewaters that contain high concentration of nitrate is hard to removal. The most promising treat techniques are biological and selective catalytic denitrification. Biological denitrification have some disadvantage such as the possible bacterial contamination to treated water, the presence of residual organics in treated water, and the possible increase in chlorine demand in chlorinating operation of raw water in later stage. Furthermore, the presence of aged sludge could lead to the formation of nitrite. The chemical catalytic reduction, therefore, is now regarded as the most promising approaches for removal of nitrate. 1.In this paper, a direct method for preparing large pore volume, large specific surface area and ultra-pure pseudo-boehmite from sodium meta-aluminate solution of Shanxi Aluminium Plant was provided. With laboratory-made desilication agent, the ratio of SiO₂/Al₂O₃ and Fe2O3/Al₂O₃ in solution could be reduced to below 0.01%. The pseudo-boehmite was obtained by depositing from buffer solution with ammonia gas circulated medium. The specific surface area of product reached up to 300m2/g and pore volume reached about 0.7ml/g. The produced pseudo-boehime was treated by laboratory-made desodium agent (I and II). The content of sodium could be reduced to below 0.005%. The characteristics of the product meet the index of SB powder produced by Germany. After calcinations(560℃/3 h) according to certain temperature rising rate, the producing pseudo-boehime was commendably turned into gamma alumina ,It can keep biggish specific surface area. 2. Catalysts prepared by double impregnation can effectively remove nitrite. With platinum catalysts, the reduction of nitrite is high activity. The activity and selectivity of catalysts is difference with various carriers. Considering activity and selectivity of nitrite reduction, Pd/γ-Al2O3 is basically suitable. 3. Laboratory-made ultra-pureγ-Al₂O₃ -supported palladium–copper catalysts, prepared by double impregnation with different palladium and copper proportion, were used for the reduction of aqueous nitrate and nitrite solutions. Experiments were performed in a batch reactor at atmospheric pressure and room temperature using formic acid as pH buffer. The results demonstrated that catalysts with different ratios of palladium to copper ,and with an addition of small quantity of Pt (2% of Pd) can effectively remove nitrate in 40 minute. The total nitrogen removal efficiency is 95%. The activity and selectivity of the catalysts were also enhanced 4. With the catalyst consisted of Pd-Cu /TiO₂ (anatase)/molecular sieve, nitrite is selective reduced, and only 6% of the initial nitrite content is converted to ammonium ions. 5. Nitrate is removed by ion exchanger. The nitrogen-containing regenerated water can be treated by Pd-Cu-deposited strong-base anion resin. The combined treatment system avoids direct contact between the denitrification reactor and the water treated. 6. The selectivity and activity of Pd-Cu doping adsorbing resin, as catalyst for the nitrate reduction are elevated. It can remove 100²00mg/L initial nitrate in 40 minute and only 2% of the initial nitrate content is converted to ammonium ions. The selectivity of nitrate reduction decreased with increasing temperature. 7. Catalytic nitrate reduction was investigated in catalytic tubular membrane reactor with combined treatment system of Pd-Cu/ tubular Al2O3 membrane and Pd-Cu /adsorbing resin. The selectivity and activity of the combined treatment system are effectively improved due to its high effective gas/liquid/soild interface. This system can continuously treat wastewater contaminated by nitrate . 8. This paper introduce a new procedure to prepare anion exchange fiber from cotton cellulose and ethylene dichioride. All the best conditions of this reaction were studied. The preparing procedure avoided using strong carcinogenic compounds, such as chloromethylether (CME) or bis-chlormethylether (BCME) and had a shorter reaction time than the traditional technology. Besides, every step response of two kinds of traditional technologies and optimum condition have also been compared. The technical improvement is superior to two kinds of traditional technologies in the capacity, the exchanging speed and the selectivity to NO3-. This is a promising method for removal nitrate and nitrite, especially for the small-scale application in the rural area.