Abstract: Based on a theoretical analysis for every items of alkali needed in phosphorus recovery process by struvite, a formula for calculation of alkali amount needed was established, and used for estimating the alkali amount at different process conditions.The values calculated were compared with the experimental one measured and obtained in a double pipes/CO₂ stripping packed layer phosphorus recovery pilot unit, and the results showed that average relative error between them was 18.73%, indicating that the theoritical calculation is reliable and the formula can be used for engineering estimation of alkali needed. Due to CO₂ and NH₃ stripping with packed layer and air, alkali amount needed saved about 20% for the double pipes/CO₂ stripping packed layer phosphorus recovery unit.The alkali needed increases linearly with pH, ammonia-nitrogen/phosphorus molar ratio and the initial concentration of phosphorus.However, it should be noted that the effect of magnesium/phosphorus molar ratio was weak.The optimal operation conditions for reducing treatment costs could be as:pH9.20—9.30, molar ratio of ammonia-nitrogen/phosphorus and magnesium/phosphorus 3.0—5.0 and 1.1—1.2 respectively.Reagents consumption for phosphorus recovery process depends on initial concentration of phosphorus in wastewater and process conditions.For example, when initial concentration of phosphorus is 77.5 mg·L^-1, N∶Mg∶P=5∶1.2∶1, pH=9.20, alkali amount needed is 0.3315 kg and magnesium chloride containing six crystallization water is 0.6099 kg for treating 1 ton of wastewater, the cost about ￥0.828 and ￥ 0.396 respectively, and ￥1.224 as total, in which cost of alkali takes about 67.6%.

Key words: phosphorus recovery;struvite;amount of alkali needed, theoretical calculation

摘要： 从分析磷回收过程中的各种耗碱因素入手，推导出耗碱量的理论计算公式，计算出不同工艺条件下的理论耗碱量，并与小型套管式空气脱气填料层磷回收过程的实测值进行比较。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18.73%，说明计算方法可用于耗碱量的工程估算；在套管式空气脱气填料层磷回收装置中，由于填料和空气对二氧化碳和氨气的脱气作用，耗碱量可节省约20%；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，从节约处理成本的角度看，磷回收过程中pH值应控制在9.20～9.30，氮磷比控制在3.0～5.0，镁磷比控制在1.1～1.2为宜。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77.5 mg·L^-1，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0.3315 kg，成本约为0.828元，需消耗氯化镁（含6个结晶水）0.6099 kg，成本约为0.396元。因此，处理每吨废水的药剂成本约为1.224元，其中耗碱约占67.6%。

关键词: 磷回收, 鸟粪石法, 耗碱量, 理论计算