Effects of Biological Molecules on Calcium MineralFormation Associated with Wastewater Desalination as Assessed usingSmall-Angle Neutron Scattering.

Calcium phosphate scale formationon reverse osmosis (RO) membranesis one of the main limitations on cost-effective desalination of domesticwastewater worldwide. It has been shown that organic agents affectmineralization. In this study, we explored mineralization in the presenceof two biofilm-relevant organic compounds, the proteins bovine serumalbumin (BSA) and lysozyme, in a simulated secondary effluent (SSE)solution using small-angle neutron scattering (SANS), and appliedthe results to analyses of mineral precipitation in RO desalinationof secondary effluents of wastewater. The two proteins are prominentmembers of bacterial extracellular polymeric substances (EPSs), formingbiofilms that are frequently associated with RO-membrane fouling duringwastewater desalination. Laboratory experiments showed that both proteinsin SSE solution are involved in complex mineralization processes.Only small portions of both protein fractions are involved in mineralizationprocesses, whereas most of the protein fractions remain as monomersin solution. Contrast variation showed that composite particles ofmineral and protein are formed instantaneously to a radius of gyrationof about 300 Å, coexisting with particles of about μm size.After about one day, these large particles start to grow again atthe expense of the 300 Å particles. The volume fraction of the300 Å particles is of the order of 2 × 10–4, which is too large to represent calcium phosphate such as hydroxyapatiteas the only mineral present. Considering the data of mineral volumefraction obtained here as well as the solubility product of possiblemineral polymorphs in the SSE solution, we suggest the formation ofprotein-mineral particles of hydroxyapatite and calcium carbonateduring scale formation. [ABSTRACT FROM AUTHOR]