Mitigating membrane fouling in an internal loop airlift membrane photobioreactor containing Spirulina platensis: effects of riser cross-sectional area and hydrophilic baffles

Membrane photobioreactors (MPBRs) have gained significant attention due to their ability to support microalgae activities such as cultivation, harvesting, and production of beneficial products. Despite various efforts to mitigate membrane fouling, a fundamental issue in membrane processes, in these systems, a cost-effective and less energy-consuming method is still needed. This study examines the impact of the cross-sectional area of the riser and the baffle material on membrane fouling in an internal loop airlift MPBR. The use of hydrophilic polyester-polypropylene (PES-PP) baffles proves to be more effective than plexiglass baffles. Specifically, in configurations with d = 0.7 cm and d = 1.4 cm, RC/RT decreased by approximately 20% and 13%, respectively, compared to plexiglass baffles. As for the values of RP/RT at a distance of d = 0.7, nearly a 5% increase was observed, and at a distance of d = 1.4, an increase of approximately 11% was observed. This is due to the development of the cake layer on the matrix structure of the PES-PP baffles instead of the membrane itself. The most optimal outcomes were reached while working with PES-PP at a distance of 0.7 cm, as it prolonged the membrane fouling time to 46 h.

The comparison between two methods of membrane cleaning to control membrane fouling in a hybrid membrane photobioreactor (HMPBR)

In this study, the effect of two membrane cleaning methods, such as aeration and addition of granular particles in a hybrid membrane photobioreactor (HMPBR) including Spirulina sp. with the concentration of 1.5 g·L^-1 was investigated. Three different spargers [i.e., different diameters of orifice (d_o): 0.5, 1, and 1.5 mm] and granular particles (i.e., three packing ratios of 0.5, 1, and 1.5%) were used. The results showed that with the increase in granular packing ratio, R_c/R_t decreased significantly. The best result was achieved by combining aeration with an orifice diameter of 1.5 mm and a granular packing ratio of 1.5%, which led to the lowest R_c/R_t value (0.38), while R_c/R_t value with a d_o of 1.5 mm was 0.68 without particles. In contrast, the ratio of pore blocking resistance to total resistance (R_p/R_t) increased by 4.2% under the combined application of 1.5 mm of orifice diameter and 1.5% of granular packing ratio. The results from protein concentrations in the cake layer showed that as the d_o became larger, cake protein concentration decreased by 40%, whereas increasing the granular packing ratio from 0.5 to 1.5% increased protein concentration by 60% in the cake layer.