Development of marine activated algal-bacterial granule: A novel replacement to the conventional algal remediation processes

A self-sustained waste treatment technology entails the integration of various cultivation and harvesting processes cost-effectively. Activated algae are a unique microalgae-based technological platform with diverse applications and superior performance compared to the conventional methodologies. An attempt has been made to develop marine activated algae using targeted microalgal species (Synechococcus elongates, Chroococcus minor, Chroococcus sp., Phormidium sp., and Spirulina platensis) and activated bacterial sludge cultured in a customized sequential batch reactor (SBR). The activated marine granules attained a sturdy structural configuration with further inclusion of filamentous cyanobacterium Phormidium sp. A complete marine activated algal-bacterial granule was formed in 40 days however; the maturation phase was prolonged to 90 days for its robustness. A progressive decline in turbidity and dissolved solids accompanied by the maturation of the granules further affirmed its remediation potential. Pronounced reduction in total nitrogen and phosphorus levels (similar to 75 %) was observed from the wastewater growth medium. The matured marine granules rapidly removed the enhanced nitrate concentrations (500 mg L-1 of NO3 in 32 h) from the simulated wastewater accompanied by rapid increase in the settling velocity (5.8 m/h) suggesting that granules can be harvested precipitously. The present work is a novel attempt using specific marine algae and is a viable bio-remediating technology with minimal cost inputs for sustainable treatment of complex loadings. Extracellular Polymeric Substances (EPS) secretion and quorum sensing (QS) mediated interaction among the algal-bacterial relationship widely influenced the community organization, population structure, etc., and was instrumental in the granule formation.