Fabrication and characterization of low-cost kaolin based tubular ceramic membrane for microalgal harvesting

Abstract

Tubular membranes with natural kaolin as a key precursor were fabricated in this study. Membranes with five different compositions were prepared, and the optimized membrane (77% kaolin, 2% boric acid, 2% sodium metasilicate, 4% sodium carbonate, and 15% calcium carbonate) was used to harvest microalgal culture. The pore size, porosity, water permeability, chemical and mechanical strength of the membranes were investigated. An assessment of the cost related to the membrane fabrication was also conducted. The fabricated membranes had porosity of ∼26–47%, a pore diameter of 0.123–0.182 µm, water permeability of 4.2 × 10−8 – 17.1 × 10−8 m3 m−2 s−1 kPa−1, along with good mechanical and chemical strength. The optimized membrane was tested for microfiltration of microalgae Monoraphidium sp. KMC4 with 1.5 g L−1 of initial concentration at a persistent cross-flow rate (1.11 × 10−5 m3 s−1) and various transmembrane pressures (69 kPa - 345 kPa). The separation results yielded an average permeate flux of 1.85 × 10−5 m3 m−2 s−1 at 276 kPa transmembrane pressure. Complete algal cell recovery and substantial nutrient passage (>88%) were observed within the pressure range of 69 kPa to 345 kPa. Fouling mechanism was explained by fitting four distinct pore-blocking models, of which the cake filtration model provided the most accurate fit as compared to the complete, intermediate and standard pore-blocking models. Additionally, the total organic carbon varied in the range of 31.6–63.2 mg L−1. This essentially explained the source of pore blocking.