Effect of sodium alginate on phosphorus recovery by vivianite precipitation

There are good prospects for phosphorus recovery from excess sludge by vivianite crystallization while a large number of extracellular polymeric substances in sludge will have impact on vivianite precipitation.In this study,as a representative of extracellular polymeric substance,the effect of sodium alginate(SA)on phosphorus recovery by vivianite precipitation under different initial SA concentrations(0–800 mg/L),p H values(6.5–9.0)and Fe/P molar ratios(1:1–2.4:1)was investigated using synthetic wastewater.The results showed that SA in low concentrations(≤400 mg/L)had little inhibitory effect on the phosphorus recovery rate.However,when the concentration of SA was larger than 400 mg/L,the phosphorus recovery rate decreased significantly with increasing SA concentrations.The inhibition rate of 800 mg/L SA was about 3 times as large as that of 400 mg/L SA.It was worth noting that the inhibitory effect of SA on vivianite precipitation decreased with increasing initial p H and Fe/P molar ratios.Additionally,SA has no obvious influence on the composition of products,but the morphology of harvested crystals was transformed from branches to plates or rods in uneven sizes.