Removal Of Nitrogen And Phosphorus From Domestic Sewage By Constructed Wetland Containing Titanium Blast Furnace Slag

As a new type of wastewater treatment technology, the constructed wetlands have advantages of small investment, easy management and beautiful landscape. Substrate is the framework of constructed wetlands, of which the chemical composition and particle size are two important factors affecting the wetland purification effect. The blast furnace slag of Pangang Group is high titanium bearing blast furnace slags, which has great potential values.However, a large amount of high titanium bearing blast furnace slag is extensively used only as building material additives every year. The titanium cannot be taken full used of, which causes a huge waste of resources.The titanium bearing blast furnace slag's adsorptive property to ammonia nitrogen and phosphorus is studied in this paper through the static adsorption experiment. The wastewater purifying effect of titanium bearing blast furnace slag,converter steelmaking slag and stones is also studied. The wastewater photo-catalytic degradation performance of titanium mineral phase of titanium bearing blast furnace slag is tested through experiments. The removal mechanism of different substrates are analyzed by representing the substrates before and after the experiment with XRF?FT-IR?DTA-TG methods. The main conclusions of the research are as follows:(1) The adsorption of ammonia nitrogen and phosphorus of titanium bearing blast furnace slag can be described by the pseudo-second-order model properly. The Langmuir isotherm model can provide a better description of the adsorption process of ammonia nitrogen and phosphorus. The adsorption of ammonia nitrogen of the titanium bearing blast furnace slag can occur spontaneously at room temperature, but the adsorption capacity is small. When the concentration changes strongly, it is hard to maintain the removal effect;the adsorption of phosphorus can occur spontaneously at room temperature and maintain a good removal effect despite the concentration change.(2) The removal effects of ammonia nitrogen, total nitrogen and total phosphorus adsorption of constructed wetlands with several substrates show different variation trends along with the increase of hydraulic retention time. When HRT=5d, the effluent concentration of ammonia nitrogen and total nitrogen of the TZ system achieves stability,concentrations are 7.44mg/L and 14.17mg/L, removed rates are 74.5% and 70.77%, the concentrations can meet the emission standard for municipal wastewater treatment plants in the ammonia and total nitrogen level emissions standards (15mg/L). Total phosphorus effluent concentration, although there is some fluctuation, is under 0.3mg/L of different hydraulic retention time, removal rate is almost 100%, in full compliance with the urban wastewater treatment plant emission standards of total phosphorus in wastewater discharge standards (0.5mg/L). During the testing process of wetlands, the calamus has effect on the removal of ammonia nitrogen, but has no significant effect on the removal of total nitrogen,and total phosphorus in the small test system. In summer, the removal of ammonia nitrogen,total nitrogen and total phosphorus in upper system is superior to spring.(3) The nitrogen in wetland mainly exists in the form of organic nitrogen and ammonia nitrogen, and organic nitrogen originates come from soil. In the spring, there is little change in ammonia nitrogen of different system, the concentration of organic nitrogen along the way in TZ and SZ system do not changed much. The upper concentration of organic nitrogen in the GZ system is lower than the below. The total phosphorus concentration of different system decreased gradually from left to right as the flow direction, and the upper removal rate is 80%.In the summer, the upper concentration of ammonia nitrogen in TZ and GZ system is lower than the below, the concentration of ammonia in ammonia in the SZ system do not changed much. The concentration of organic nitrogen in different system do not changed much, the below concentration of the total phosphorus is slightly higher than the upper.(4) Photocatalytic results showed that under the condition of no light, the upper ammonia nitrogen concentration in different system is 7.94-10.01 mg/L; under the condition of light, the upper ammonia nitrogen concentration in different system is 6.22-7.68 mg/L;and potassium nitrogen, nitrate nitrogen and organic nitrogen concentration in different system don not changed much. Thus assumes that under natural light conditions, titanium bearing blast furnace slag has a certain photocatalytic degradation ability of nitrogenous compounds, mainly on the degradation of ammonia nitrogen, also includes the reduction of nitrate at the same time.(5) The results of before and after the experiment data of XRF, FT-IR and DTA-TG show that compared with the experiments before, there is a significant improvement in the content of P in titanium bearing blast furnace slag and steel-making slag, but the content of P in stone basically remain unchanged. The vibration peak of CO32- is in the titanium bearing blast furnace slag. The vibration-peak strength of the Ca-0 in steel-making slag is weakened and there is a vibration peak of N-H. There is no new bond generation in the stone. Within 25?200?, the weight loss of titanium bearing blast furnace slag and steel slag increase after experiments, the weight loss of stones basically remain unchanged. It shows that the removal of nitrogen and phosphorus by titanium bearing blast furnace slag and steel-making slag is mainly dependent on the chemical adsorption, and the stone is mainly dependent on the physical intercept.