Hydrodynamic granulation of oxygenic photogranules

Abstract

Oxygenic photogranules (OPGs), granular assemblages of phototrophic and chemotrophic microbes, offer a promising biotechnology for wastewater treatment with self-aerating potential. Currently, the seed OPG is produced under hydrostatic conditions with activated-sludge inoculum. We investigated the development of OPGs under hydrodynamic conditions employing batches with different light, shear, and inoculum conditions. The results demonstrated hydrodynamic granulation of OPGs from activated sludge, presenting opportunities for rapid (less than 8 days) and bulk development. From the matrix of conditions investigated, we found that granulation occurs only with some combinations of different magnitudes of these input energies. For example, ×4 dilute inoculum combined with low light supported granulation under the different shear conditions utilized. However, ×4 dilution inoculum with high light and high shear did not support granulation. This observed disparity in applied conditions suggests that OPG granulation ensues only with favorable interaction of variable induced energy pressures coupled with biological response selecting for spheroidal aggregates. Multi-regression analysis on temporal changes in the ratio of sludge volume index for 5 min to 30 min settling, a metric for granulation, confirmed the intercorrelation of these energy inputs on OPG granulation. This granulation scheme, dependent on goldilocks interaction of selection pressures, can potentially be extended to other granules applied in wastewater treatment.