工艺条件对鸟粪石法回收磷耗碱量的影响及其理论计算

Effect of process condition on alkali consumption in phosphorus recovery by struvite and its theoretical calculation

通过分析磷回收过程中存在的各种耗碱因素,推导出耗碱量的理论计算公式,计算出了不同工艺条件下的理论耗碱量,并与小型连续搅拌反应-沉淀磷回收过程的实验实测值进行比较。结果表明,耗碱量的理论计算值与实验测定值的平均相对误差为13.20%,说明计算方法可用于耗碱量的工程估算;耗碱量随出水pH值的增大而急剧增加,随废水中氨氮含量和磷初始浓度的增加都近似于线性增加,但随镁磷比的增加基本不变。因此,从节约废水处理成本的角度看,磷回收过程中pH值应控制在9.2-9.3,氮磷比控制在3.0-5.0,镁磷比控制在1.1-1.2为佳。磷回收过程的药剂消耗量与废水中磷的浓度和工艺条件有关,以磷初始浓度为124 mg/L,N/Mg/P=5∶1.2∶1,出水pH值为9.20的回收过程为例,处理毎吨废水需消耗片碱0.5313 kg,成本约为1.328元,需消耗氯化镁（含六个结晶水）0.9758 kg,成本约为0.634元。因此,处理每吨废水的药剂成本约为1.962元,其中耗碱约占67.7%。

Base on the theoretical analysis of every item of alkali needed in phosphorus recovery process by struvite,calculation formula for the of alkali consumption was derived out,and the values under different process conditions were calculated by the formula,which was compared with the experimental results measured in a continuous stirred phosphorus recovery pilot unit.It was showed that the average relative error between the theoretical calculated values and experimental measured results was 13.20%,which indicated that the theoretical calculation is reliable,and can be used in the estimation of alkali needed in the engineering.The alkali needed increases linearly with the pH,molar ratio of ammonia nitrogen to phosphorus and the initial concentration of phosphorus.However,it should be noted that the effect of the increasing of molar ratio of magnesium to phosphorus was weak.The results indicate that the optimal operation conditions for saving the treatment costs should be chosen as： pH 9.20 - 9.30,the molar ratio of ammonia nitrogen and magnesium to phosphorus in 3.0 - 5.0 and 1.1 - 1.2,respectively.Reagents consumption in the phosphorus recovery process are related to the initial concentration of phosphorus in the wastewater and its process conditions.For example,when the initial concentration of phosphorus is 124 mg / L,N / Mg / P = 5∶ 1.2∶ 1,pH = 9.20,the alkali needed is 0.5313 kg and magnesium chloride（which has six crystallization water） needed is 0.9758 kg for treating 1 ton of wastewater,costs are about ￥ 1.328 and ￥ 0.634,respectively,and ￥ 1.962 as total,in which the cost of alkali takes about 67.7%.