Effect of Organic Matter on Struvite Precipitation of Phosphorus Contained in Tapioca-starch Wastewater

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Chutarat Khaita
Chongchin Polprasert


Phosphorus (P) recovery receives more attention as a means to curb water pollution caused by discharge of nutrient-laden effluent.  This study was conducted so as to investigate the effect of organic matter on P recovery from raw tapioca-starch wastewater and anaerobically-digested effluent. With total COD of 17,907 mg/L, 40 mg P/L, molar ratios of Mg:Ca = 0.4:1 and Mg:N:P = 0.4:17:1, P precipitation in raw starch wastewater was found to be impeded, resulting in low P recovery efficiency of 18.2, 23.4 and 40.4% at pH = 7, 9 and 11, respectively.  This may be due to low concentrations of Mg and P available for the precipitation reaction as they were bound in the organic solids. In the anaerobically-digested effluent with total COD of 4,181 mg/L, 68.mg P/L, the molar ratio of Mg:N:P was found to be 1.5:11.8:1, leading to increased P recovery efficiency of 56.5, 83.5 and 91.2% at pH = 7, 9 and 11, respectively. Overall, findings of this study reveal that the anaerobically-digested effluent is preferable to raw starch wastewater for P recovery since most P and other relevant precipitating ions (Mg2+ and NH4+) are liberated from organic solids and are readily available for chemical precipitation. Consequently, struvite precipitates formed could be used to produce a good-quality product as slow release fertilizer.


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