How to remove phosphorus in sludge energy-saving treatment
1. Chemical phosphorus removal method: the basic theory of this method is to add chemical drugs to formulate insoluble phosphate sediments. And the phosphorus can be removed by the ways of solid-liquid separation. The main research content focuses on the selection of the optimal chemical drugs. This chemical sediments method features many advantages, including easy operations, better phosphorus removal effect with remove ratio up to 80%～90%, high stability and will not discharge phosphorus to cause the second pollutions. With the inlet water concentration fluctuates greatly, the removal effect will not be influenced. But the method is expensive due to large amount of chemical drugs and will produce a great deal of chemical sludge.
2. Biological phosphorus removal method: This method is a kind of economical way to remove phosphorus and will not affect the total amount of the nitrogen. It can reduce the cost and prevent the chemical sludge resulted from the chemical phosphorus removal. The current research focus is denitrifying phosphorus removal process. Delft University of Technology and University of Tokyo jointly name the Biological phosphorus removal/uptake of denitrifying bacteria the “denitrifying dephosphatation”. Denitrifying Phosphorus removing Bacteria (DPB) regards the O2 or NO3 as electron acceptor. Under anaerobic conditions, COD can be degraded into low molecular weight aliphatic acids such as HAC that can be absorbed and bred by DPB. In the meantime, Poly- P inside the cell can be hydrolyzed and be discharged in the form of inorganic phosphate. Under hypoxic conditions, DPB uses nitrate nitrogen as the electron acceptor to cause biological phosphorus take-up effect and nitrate nitrogen will be reduced to nitrogen. The denitrifying phosphorus removal process after the combination of the DPB can save a considerable amount of COD and aeration rate and lead to a small amount of thecells synthesizing. The study of the denitrifying phosphorus removal started early in foreign countries. Compared with the traditional process of biological nitrogen and phosphorus removal, it can reduce the COD quantity by 30%(counted as sanitary sewage). The technical of denitrifying phosphorus removal has been developed from the basic research step into the actual application. The representative process that can meet the requirements of the environment and matrix are unipolar process (BCFS) and bipolar process (A2N).
3. Chemistry assisted biological phosphorus removal. Due to low stability and flexibility for the biological phosphorus removal, it will be affected by some factors such as carbon source and PH value. Therefore, the phosphorus content of the outlet water cannot meet the national emission standards. The chemical method can help to increase the stability of biological phosphorus removal. The study of the biological phosphorus removal together with the chemical ways attracts more attentions, among which the process of the Phostrip is deeply concerned. Phostrip can ensure the outlet water of the phosphorus below the value of 1mg/L. Although the result cannot reach A standard of national one level, but it has its own advantages other processes don’t have, such as a better stability in phosphorus removal, a high efficient of phosphorus removal, an easier way to dispose the sludge and a low cost.
4. The recycle of phosphorous in the sewage. The phosphorous removal method with struvite (MgNH4PO4·6H20) sediments can get rid of and recycle the phosphorous and nitrogen at the same time, especially for some waste water that contains phosphorous and nitrogen. You should only add the magnesium and adjust the PH value to recycle the phosphorous. The struvite is a high quality phosphatic fertilizer. Sewage of100m3 can crystallize 1kg of the struvite. If each country starts collecting the struvite, the whole world can obtain 63,000 t phosphorus (calculated by P205) and save 1.6% of the total phosphorusexploitation. The related research shows that recycling the phosphorus from the sludge can reduce the sediment quantity as well as the ash content from the burning of the sludge. The volume of the sludge from the phosphorus removal process using struvite is only 49% of that from the chemical phosphorus removal method.
