Algal softening followed by ozonation: The fate of persistent micropollutants and natural organic matter in groundwater.

A proof-of-concept study evaluates the performance of a novel strategy using photosynthetic microorganisms to soften groundwater instead of using caustic chemicals. The microalga Scenedesmus quadricauda was used to increase the pH of the groundwater via natural photosynthesis. This work applied softening as a pretreatment to ozonation of hard groundwater and mainly focused on investigating the multiple effects of algal softening on the degradation of persistent micropollutants upon subsequent ozonation. The algae-induced alkaline conditions (pH > 10) were favorable to catalyze the formation of OH radicals directly from O3 molecules. Moreover, algal softening removed the strong radical-scavenging carbonate species (HCO3- and CO32-) to a much greater extent than that achieved by chemical softening, which was attributed to the combination of mineral carbonation and metabolic CO2 reduction. The fate of the natural organic matter (NOM) was characterized with spectroscopy, chromatography, and bioassay, which indicates that algal treatment decomposed the NOM to be less susceptible to attack by OH radicals. Consequently, the ozonation of alkaline groundwater achieved a better removal of the micropollutant residues in groundwater. Carbamazepine and diclofenac were used as model chemicals of persistent groundwater contaminants and were almost completely removed with an addition of 1.25 mg O3 L-1 (0.63 mg-O3 mg-C-1).

Treatment of reverse osmosis concentrate using an algal-based MBR combined with ozone pretreatment.

Algal treatment was combined with ozone pretreatment for treatment of synthetic reverse osmosis concentrate (ROC) prior to microfiltration. The research mainly focused on minimizing the fouling of polyvinylidene-fluoride membranes and maximizing the restoration of membrane permeability. The algal treatment alone was only moderately effective for the mitigation of fouling in microfiltration, while a markedly improved performance was achieved when the algal treatment followed ozonation. The combination of ozonation and algal treatment reduced membrane permeability decline and significantly (p < 0.05) increased the reversibility of fouling after hydraulic washing. A longitudinal evaluation was also performed with a goal of achieving a robust removal of contaminants. Ozonation followed by algal treatment was very effective in attenuating both caffeine and carbamazepine, as well as removing organic matter and inorganic nutrients from ROC in a single bioreactor. In this study, an alkaline condition (∼pH 12), produced by microalgae in the light without supplemental aeration was applied for in-situ cleaning of fouled membranes. The result showed that the algal-induced cleaning successfully restored the permeability of organic-fouled membranes during the filtration of both raw and algal-treated ROC. This in-situ strategy offers a novel option for periodic cleaning of fouled membranes while maintaining operational simplicity, especially for existing submerged membrane filtration facilities.