Submerged microfiltration membrane performances of microalgal biomass cultivated in secondary effluent

Abstract

This study was conducted to investigate the feasibility of submerged microfiltration process to separate microalgal biomass in the growth reactor fed by a secondary wastewater effluent. Both nitrogen and phosphorous were utilized by microalgae as nutrient. The results showed that almost 90 % of N and total P content of secondary effluent were consumed by microalgae in the first six days. It was observed that the phosphorus was the limiting nutrient. The growth rate was also a function of pH and optimum pH was determined as 6.0 to 6.5. High growth rate at that pH values was likely due to the fact that CO2 was present mostly in soluble form; whereas, at higher pH CO2 was in bicarbonate form. Membrane filtration experiments were conducted using polyethersulfone (PES) membranes with 0.1 mu m, 1.2 mu m and polycarbonate (PC) membranes with 0.1 mu m, 1.0 mu m pore sizes. The results showed that the use of submerged microfiltration membranes allowed continuous operation for microalgal growth reactor. Membranes effectively separated biomass from the reactor. The stead-ystate flux values were almost independent of the type and the pore size of the membranes. More than 90% of the total resistance was due to cake formation. Since the cake layer controlled the filtration rate, the average flux values as well as the decline pattern remained largely independent of pore size and the membrane types. The physical surface cleaning experiment conducted for PC 1.0 mu m showed that the fouling layer could easily be removed, resulting similar filtration performance to the new membranes.