鸟粪石法回收养猪废水中磷时pH对沉淀物组分的影响

Effect of pH on Precipitate Composition During Phosphorus Recovery as Struvite from Swine Wastewater

采用鸟粪石沉淀法对养猪废水中的磷进行回收,应用红外光谱和X射线衍射法,并结合物料衡算研究pH变化对沉淀物组分的影响.结果表明,当pH由8.0升至9.0时,磷去除率从85%增加到94%;pH在9.0～11.0范围,磷去除率稳定在94%左右;当pH升高至12.0,磷去除率急剧下降至70%.沉淀物组分为鸟粪石(MgNH4PO4.6H2O)、钾型鸟粪石(MgKPO4.6H2 O)、Ca3(PO4)2.xH2 O和Mg(OH)2,不含有硫酸盐和碳酸盐.当pH<9.0,沉淀物组分主要为鸟粪石;pH在9.0～10.0范围时,鸟粪石含量降低,钾型鸟粪石、Ca3(PO4)2.xH2O含量呈逐渐增加趋势;pH由10.0升至12.0时,鸟粪石含量急剧下降,Ca3(PO4)2.xH2 O和Mg(OH)2含量快速增加,而钾型鸟粪石快速增加并在pH 11.0达到最大后急剧下降.因此,回收养猪废水中的磷时要获得纯度高的鸟粪石产品,pH值应控制在8.0～9.0.

Phosphorus recovery as struvite from swine wastewater was carried out.Fourier transform infrared spectroscopy（FTIR）,X-ray diffraction（XRD） and mass balance analysis were utilized to analyze the species of precipitated minerals under different pH conditions.Results showed that increasing pH from 8.0 to 9.0 resulted in the increase of phosphorus removal efficiency from 85% to 94%.A relatively stable phosphorus removal at 94% was observed at pH 9.0-11.0,whereas a drastic decline to 70% was detected when pH increased to 12.0.The minerals precipitated in the deposits were struvite（MgNH4PO4·6H2O）,K-struvite（MgKPO4·6H2O）,amorphous calcium phosphate [Ca3（PO4）2·xH2O,ACP] and Mg（OH）2.Struvite was the dominant species in the precipitate at pH 8.0-9.0.Enhancing pH from 9.0 to 10.0 resulted in struvite decline and gave rise to K-struvite and ACP steadily.With regard to highly alkaline conditions at pH above 10,drastic decrease of struvite and rapid increase of ACP and Mg（OH）2 were observed.Maximum concentration of K-struvite was obtained at pH 11.0,following a sharp decline to pH 12.0.Controlling pH between 8.0 and 9.0 could inhibit other minerals formation and obtain the highly pure struvite crystal product.