| Constructed wetlands system is a low-cost investing, energy consumption saved and effective systems engineering for treatment and reclamation of wastewater, which has an obvious result of nitrogen and phosphorus removal. When constructed wetland system is used for 1-2 years, the system removal efficiency of phosphorus will remarkably decreased. So choosing plants and fillings that have high purifying capacity is the guarantee to remain the system long-term efficiency.In first period test, 4 minitype simulating artificial wetlands are constructed, which are filled with soil, sand and detritus, and one is without plants, the others are planted reeds, acorus gramineus and canna. Investigate the effect of hydraulic load, inflow water TP and COD concentration, hydraulic retention time, dry and wet changes, season changes, pH value on TP removal efficiency to pick out plant which works best for removing the phosphorus. The main conclusions include:1. The effect of plants. The TP removal efficiency of different plant systems becomes worse with the hydraulic load increases when the inflow TP concentration was 3.9～5mg/L. The removal efficiency of TP of blank system declines remarkably when hydraulic load increases.2. The effect of hydraulic load. In acorus gramineus system and canna system, when hydraulic load is below 0.2m3/m2·d, the highest TP removal efficiency attains at the inflow TP concentration is 7mg/L. And when hydraulic load exceeds 0.2 m3/m2·d, the highest TP removal efficiency is about 5mg/L.3. The effect of hydraulic detention time. As hydraulic detention time increases, the TP removal efficiency increases, especially when hydraulic detention time changes from 17.2h to 21.6h, although detention time increases only 4.4h, TP removal efficiency of systems grows from less than 70% to over 82%. But when hydraulic detention time continues to increase, TP removal efficiency grows little.4. Recover the phosphorus removal ability of wetland. The TP removal efficiency becomes worse with the consecution circulate. But after two days cease work, TP removal efficiency has been effectively recovered.5. The effect of seson. The circulating data of two system shows TP removal efficiency in the middle of August is the highest, and the lowest in the middle of December with the motion range <10%.6. The effect of pH. The best pH value range for TP removal efficiency was 7-8.When pH value 8, it reaches the best TP removal efficiency.In second period test, the effects of fillings to phosphorus removal are discussed. Besides soil, sand and detritus as fillings, ash fly and cinders are taken as phosphorus removal material to progress efficiency of wetland. The main conclusions include:1. This test takes the system with fillings sand and detritus used in common currently as reference system (A0) in contrast to system with new-type fillings. The result indicates that the treatment efficiency of sand-detritus simulating constructed wetland (A0) is better than that of any other system (A1, A2, A3) at the early stage of test. But operating for some time, the treating effect of reference system is lower than that of any other system with new-type fillings, has an obvious downward trend. It shows that the adsorption capacity of new-type fillings is larger than that of such ordinary fillings as sand and detritus. The longer the filling reaches adsorption saturation point, the more the system's durable years are. This is very important directing significance for practice.2. Fly ash and cinders are alkaline, so combine them with sand and detritus. The plant is growing well, and the pH of water discharge is between 7 and 9.3. System with the optimal combination of substrates, which is the combination of small detritus, sand, cinders and big detritus and in condition of phosphorus concentration of 4 mg/L and detention time of 24 hours has the highest efficiency (considered removal of COD, TP and ammonia nitrogen). When operating in shorter detention time, the purifying effect is similar to that in above condition, and shorter detention time will reduce the occupation area and cut down the run cost. So taking economy, practicality into account, we choose 15-hour detention time.4. The effect of phosphorus concentration of inflow water. While treating wastewater of high concentration of phosphorus, the higher concentration, the better removal effect will be reached, and the same time the removal rates of COD and ammonia nitrogen drop just a little, but also achieve a relatively good level (respectively 86.27%, 95.30%).5. Take three different load (1.15m3/m2·d, 2.30 m3/m2·d, 4.60 m3/m2·d) to conduct test separately with intermittent inflow. The average time interval between two inflows is about 1 hour. The pollutants concentrations of the raw water are as follows: COD varies from 158 mg/L to 179 mg/L, TP from 3.9 mg/L to 4.8 mg/L and ammonia nitrogen from 18 mg/L to 22 mg/L. When applied loading of system increases, the removal rates of pollutants fluctuate somewhat, however, also remain above 80%, and most of them are higher than 95%, which means the system is far below purifying capacity. In this test, simulating constructed wetlands with new-type fillings are proved to be able to treat high-load wastewater efficiently. |
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