Performance Of Denitrification And Dephosphorization Of Composite Artificial Zeolite Granule

Zeolite has high performance of adsorption and ion exchange due to its structure features and physical and chemical properties. At present, zeolite was used to remove nitrogen and phosphorus, which are the main pollutants in the sewage, was paid more and more attention by people. Zeolite was modified by certain physico-chemical method and granulation after treatment can improve the capability of denitrification and dephosphorization and is beneficial to dehydration in order to application in industry.Natural zeolite was modified by different concentrations of acid, alkali, salt and roasting under a certain temperature in the experiment, and adsorption experiments were conduceed. The results showed that zeolite’s performance of denitrification was the best after modified by NaOH solution and NaCI solution in turn. Ammonia nitrogen removal rate was 95.9%, which is 41.4% higher than natural zeolite, when NaOH solution concentration was 1.0 mol·L-1, NaCl solution concentration was 0.25 mol·L-1, roasting temperature was 300℃ and roasting time was 2h. Then the modified zeolite was regulated further in different species and concentrations of salt solution and roast after that. The results showed the best dephosphorization ability was 93.8%, which was 91.9% higher than natural zeolite, when LaCl3 solution concentration was 0.015 mol·L-1, pH value was 9 and roasting temperature was 300℃, as well as roasting time was 2h.Then, artificial granules were made with three kinds of raw materials, which were modified zeolite by NaOH and NaCl as well as regulated by LaCl3, modified zeolite and steel slag mixture, modified zeolite and activated carbon mixture. Some factors which influence adsorption property and granule intensity were investigated in the experiment, which were binder type and content, particle granularity, roasting temperature, roasting time and granule shape and size. The results showed the new type binder, KD1 work well, and the best granulation conditions of the three kinds of guanule were as follows. Coarse grained content was 40%, KD1 additive amount was 4%, roasting temperature was 200℃, roasting time was 2h. Steel slag content was 20%, KD1 additive amount was 4%, roasting temperature was 200℃, roasting time was 2h. Activated carbon content was 20%, additive amount was 6%, roasting temperature was 300℃, roasting time was 1.5h. And the guanules with the shape and size of of φ1.5mm×2.5mm. Then, ammonia nitrogen and phosphorus removal rate of the three kinds of guanles were 86.1%、87.3%、0,69.2%、79.8%、0 and 71.2%、66.8%、0。Next, the adsorption performance of the three kinds of guanules were tested by the conditions of dosage, adsorption time, oscillation rate, pH value and foreign ion.The results showed that the three kinds of granules’adsorption were all high when the dosage was 3.0g·L-1,The adsorption time was 2h, oscillation rate was 150r·min-1, and pH Value was 6-7. The application experiment was done to the municipal secondary effluent with the modified zeolite granule, and result shows the concentration indexes of ammonia nitrogen and phosphorus after adsorptioned by zeolite granule conform to V standard of Surface Water Environment Quality Standard. Ammonia nitrogen removal process of the zeolite granule conform to Langmuir adsorption isotherm and pseudo-second order reaction kinetics equation, and the removal process was mainly controlled by membrane diffusion and internal diffusion process together. The test of adsorption thermodynamics showed that ammonia nitrogen removal process of the zeolite granule belong to endothermic process, and adsorbing capacity increase with the temperature rise. Ammonia nitrogen removal mechanism of zeolite artificial granule in the wastewater is mainly ion exchange, complexation reaction and adsorption, as well as phosphorus removal mechanism is complexation reaction by lanthanum oxide, cation of steel slag, iron loaded in activated carbon with phosphate in the sewage.