Characterization of the immobilized algae-based bioreactor with external ceramic ultrafiltration membrane to remove nutrients from the synthetic secondary wastewater effluent

Abstract

Abstract In this study, alginate-immobilization of microalgae combined with continuous/intermittent algae-based membrane bioreactor (A-MBR) and external ceramic membrane was developed to investigate the effect of immobilization on algal growth, nutrient removal, algal organic matter (AOM) and membrane fouling control in synthetic secondary wastewater effluent treatment. First, Chlorella vulgaris and Scenedesmus quadricauda were selected to investigate the treatment performance, AOM characteristics and membrane fouling control between suspended and immobilized microalgae. The results showed the effect of immobilization on two microalgae growth was not significant and nearly complete NO3−-N and PO43−-P removals were achieved by both immobilized microalgae in batch experiments, contributing from algal uptake as well as chemical precipitation. In addition, fluorescence excitation-emission matrix spectra indicated specific intensity of protein- and soluble microbial byproduct-like peaks in AOM derived from immobilized S. quadricauda was lower than C. vulgaris and reduced recently produced AOM from two immobilized microalgae was observed, which would improve membrane fouling control. After 35-day intermittent A-MBR operation with immobilized S. quadricauda, higher concentration of microalgal biomass and 63% NO3−-N and 58% PO43−-P removals were achieved. In addition, alginate-immobilization and intermittent operation for relaxation of membrane showed slower decline of permeate flux under constant pressure mode and therefore, were beneficial for membrane fouling control. Hence, the intermittent A-MBR with immobilized microalgae has potential to cultivate microalgae, provide stable treatment performance to remove nutrients and limit membrane fouling in secondary wastewater effluent treatment.