Study On The Process Of MAP And HAP Crystallization For Phosphorus Removal

Phosphorus is one of the major factors leading to eutrophication.Controlling the phosphorus content is a long-term task in water pollutioncontrol and environment quality improvement in our country. Phosphorus isnot only a main pollutant, but also an important strategic resource. Today onehot topic is to develop the new process: combining phosphorus removal withrecovery in wastewater treatment. Focused on the MAP and HAP technologywhich have the potential for phosphorus removal and recovery，the thesiscarry out the characteristics of the technology based on different Magnesiumsource and crystal seed. The specific content as follows:We choose MgO which has unique nature and is less studied asMagnesium source to form MAP crystal, and study the process characteristicsin this situation. The following conclusions were drawn:1. MgO is a kind of high quality Magnesium source which is suitable forMAP de-phosphorus technology, because it could provide Mg2+as well asOH-.Both heavy magnesium oxide and light magnesium oxide can obtaingood effect on removing phosphorus. However, compared with the lightmagnesium oxide, the heavy magnesium oxide has advantages of less usedamount and low cost. So the heavy magnesium oxide is more suitable forintermittent or continuous process of the MAP crystallization technology.2. In the continuous operated fluidized bed reactor of MAPcrystallization de-phosphorus process, which was dosed heavy magnesiumoxide as Magnesium source to control Mg:N:P=2.7:1:1or1.3:2:1(mol ratio),HRT=6h, the TP with the concentration of130mg/L can be treat to the DPconcentration in the effluent below5mg/L, and the solubility phosphorusremoval rate can be up to96%. During the process, the pH value ranges from8.8to9.4, the sludge volume is (0.8~2.78)‰of the wastewater quality. After drying at60℃, the phosphorus content in the sludge is more than13%, whichequals to the phosphorus content of the natural struvite.3. Using MgO as the Magnesium source to deal with the wastewater ofthe anaerobic processing effluent of the Soybean protein wastewater(TP=105mg/L) with MAP de-phosphorus process which doses MgO as,controlling Mg:P=3:1(mol ratio),HRT=4.8h, the TP concentration couldreduce to0.23~4.7mg/L and the TP removal rate can be above95%, pH in thereaction is around8.5. The effluent TP concentration reaches to the first graderequirement of “Integrated Wastewater Discharge Standard”(GB8978-1996).In addition, we chooses natural coral sand and oyster shells as the crystalseed which are rich in calcium, to study on the process characteristics of HAPtechnology. Specific content as follows: It’s possible to use coral sand andoyster shells as the crystal seed in the HAP process. Modified coral sand andoyster shells can quickly completed HAP induced crystallization process. Inthis process phosphorus removal efficiency is closely related to Ca/P molratio. The test showed to control Ca:P=1.9:1(mol ratio),pH≈8,HRT=6h,thesolubility phosphorus removal rate is up to95%,the effluent solubilityphosphorus concentration can be treated to1.88mg/L (modified coral sand)and6mg/L (oyster shell) respectively (the TP concentration of the influencewas130mg/L).