Evaluation of liquid ferrate role on controlling assimilable organic carbon (AOC) formation for seawater desalination pretreatment during harmful algal blooms

Abstract

Understanding the growth potential of assimilable organic carbon (AOC) is important to manage bacterial regrowth in the water treatment process. Bacterial growth in seawater during desalination is mainly impacted by the available nutrients and pretreatment chemicals. One of the commonly used chemicals in pretreatment is a coagulant. In this study, the impact of coagulants in AOC formation was investigated. Two different coagulants were studied, including ferric chloride Fe(III) and liquid ferrate Fe(VI). The study investigated two different source waters, namely raw seawater and seawater spiked with algal organic matter (AOM). Flow-cytometry (FCM) and adenosine triphosphate (ATP) were used to evaluate the growth potential of different microbial communities indigenous to the samples as carbon concentrations were increased (0, 100, 300 ug of sodium acetate). The AOC measurements as represented by bacterial and ATP concentrations in seawater proved that Fe(VI) is effective at reducing the potential for bacterial growth. The treated raw seawater with the use of Fe(VI) coagulant eliminated the bacterial concentration and reduced ATP concentrations by more than 89.28%. Use of Fe(III) was not as effective in reducing bacterial concentration and ATP. In certain experiments (with the addition of sodium acetate), Fe(III) increased the bacterial and ATP concentrations. likely caused by the presence of excess iron as a micronutrient.