Effects of the Shapes and Materials of Fluidised Carriers on the Distribution and Settleability of Microalgal–bacterial Consortia for Wastewater Treatment

Microalgal–bacterial consortia (MBC) are expected to be utilised for wastewater treatment. This study investigated MBC cultivation using primary treated wastewater and various fluidised carriers based on the hypothesis that dual control of the hydraulic retention time (HRT) and carrier retention time (CRT) can achieve the flocculation of suspended MBC regardless of the carrier shape and material. Polyurethane carriers with different shapes and carriers made from loofah, konjac and cellulose sponge were tested at an HRT of 1.2 d. Cultivation with polyurethane and loofah carriers was successfully accomplished without carrier replacement and with a CRT of 27 d, respectively. The konjac and cellulose carriers are unsuitable because of their immediate dissolution. A large majority of the total MBC in each reactor attached on the carriers. Floc formation in the cultures, likely resulting from carrier detachment of MBC clusters, achieved the superior settleability of suspended MBC in each culture, regardless of the shapes and materials of the carriers. MBC cultivated with the polyurethane and loofah carriers maximised the removal rates of organic matter and nitrogen, respectively. These results confirm the feasibility of various carriers for cultivating MBC, which is expected to promote the adoption of MBC for wastewater treatment.