| Phosphorus is both a nonrenewable resource and one important factor leading water to eutrophication. Facing the increasing demand from industry and agriculture to phosphorus and the fact that high quality phosphorite is to be exhausted in 100 years, it is very urgent to find new phosphorus resource. The synthetic Tobermorite, a by-product produced when potassium feldspar was hydrothermally decomposed to prepare highly pure potassium carbonate, was employed as seed to recover phosphorus from wastewater as the material contains neither heavy metals nor phosphorus and can decrease chemical reagent costs by supporting OH- and Ca2+.Batch experiments showed the pH=8, Ca/P=2 (mole ratio), 2～2.4g/L seed concentration and 140r/min shaking speed were preferable. Under the optimized conditions, the residual phosphorus can be below the first class standard of national sewage discharging criteria. Calcium phosphate crystallization favors high temperature. Some ions such as Mg2+, NH4+ , CO32- and citric acid may block the crystallization. Among them, citric acid has much more influence than the others on the same concentration.The comparison between synthetic water with high quantity phosphorus content and low content with the same Ca/P showed that high contents was preferable. The experiments of repetitious seed usage showed a satisfied result after the seed being employed continuously for 18th times in wet status under optimized conditions. Compared with some other seed materials such as calcite, optimized calcite and apatite which are usually used as seed in phosphorus recovery process, Tobermorite is the most efficient. The characteristics of the products were determined by Powder X-ray Diffraction (XRD), Fourier Transform Infrared (FTIR), Scanning ElectronMicroscopy (SEM) and EDS analytic techniques. The results showed that the main recovered product was hydroxyapatite with lower crystallization degree.The results simulating potato waste water of one starch factory showed the residual phosphorus could be controlled under 0.5mg/L by adding calcium or improving seed concentration. The preferable pH value between simply synthetic water and living sewage even after rapid infiltration was different and the residual phosphorus of the living sewage was 2.83mg/L after 24 hours. So in practical application, trials of finding optimized conditions are needed when specific sewage is treated .In column experiment, it was found that hydraulic residence time (HRT) had little impacts on residual phosphorus when HRT exceeded 1hour. Drying of seed during use did harm to phosphorus recovery. Chemical analysis were exerted on recovery seed and found what located in input and middle part reached high grade P rock standard. |
