Phosphorus Speciation Provides Direction to Produce 10 μg/L


Increasing demand to achieve very low effluent total phosphorus due to more stringent discharge limits have raised questions on the limits of available technologies and presented challenges of how to further the removal of phosphorus to extremely low levels (e.g 10 μg/L). This study investigated the phosphorus speciation in effluents from various available technologies, including both conventional secondary chemical P or biological P removal processes, and more
advanced tertiary treatment processes at full-scale or pilot-scale. Phosphorus speciation analysis in effluents from different treatment processes showed various fractions and composition that seem to be associated with fundamental mechanisms of each processes. Effluent from chemical P removal process consists mainly of soluble reactive P and refractory organic P, while effluent from biological P removal process (EBPR) showed presence of hydrolysable polyP at nearly 20 percent in the effluent, in addition to the other two fractions. Advanced tertiary treatment process that have multiple stages and apply filtration, coagulation and adsorption, showed very efficient TP removal down to approximately 20 μg/L level. P speciation analysis of these tertiary effluents shows that dissolved (soluble) refractory organic P (rDOP) is the dominant component. Refractory organic phosphorus, ranged from 0.01 to 0.05 mg/L, was present in all secondary and tertiary effluents studied and they seem to be mostly in “soluble” form (pass 0.45 um filter). Enhanced removal of rDOP observed with coagulant additions indicates that most rDOP are likely in colloidal form and they are susceptible to coagulation/flocculation. Membrane microfiltration process showed very efficient particulate phosphorus removal; however, the removal of soluble P fractions including both soluble reactive P (ortho-P) and rDOP were not as effective as other tertiary treatment processes studied. rDOP are the residual refractory P that is shown to be difficult to remove even in advanced tertiary treatment processes. Investigation on the characterization and treatability of rDOP is, therefore, necessary for developing technologies to further the removal of TP to extremely low levels, which may be imposed by more stringent P limits.

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