The Influence of Forward Osmosis Module Configuration on Nutrients Removal and Microalgae Harvesting in Osmotic Photobioreactor

Abstract

Microalgae have attracted great interest recently due to their potential for nutrients removal from wastewater, renewable biodiesel production and bioactive compounds extraction. However, one major challenge in microalgal bioremediation and the algal biofuel process is the high energy cost of separating microalgae from water. Our previous studies demonstrated that forward osmosis (FO) is a promising technology for microalgae harvesting and dewatering due to its low energy consumption and easy fouling control. In the present study, two FO module configurations (side-stream and submerged) were integrated with microalgae (C. vulgaris) photobioreactor (PBR) in order to evaluate the system performance, including nutrients removal, algae harvesting efficiency and membrane fouling. After 7 days of operation, both systems showed effective nutrients removal. A total of 92.9%, 100% and 98.7% of PO4-P, NH3-N and TN were removed in the PBR integrated with the submerged FO module, and 82%, 96% and 94.8% of PO4-P, NH3-N and TN were removed in the PBR integrated with the side-stream FO module. The better nutrients removal efficiency is attributed to the greater algae biomass in the submerged FO-PBR where in situ biomass dewatering was conducted. The side-stream FO module showed more severe permeate flux loss and biomass loss (less dewatering efficiency) due to algae deposition onto the membrane. This is likely caused by the higher initial water flux associated with the side-stream FO configuration, resulting in more foulants being transported to the membrane surface. However, the side-stream FO module showed better fouling mitigation by simple hydraulic flushing than the submerged FO module, which is not convenient for conducting cleaning without interrupting the PBR operation. Taken together, our results suggest that side-stream FO configuration may provide a viable way to integrate with PBR for a microalgae-based treatment. The present work provides novel insights into the efficient operation of a FO-PBR for more sustainable wastewater treatment and effective microalgae harvesting.

Evaluation of Osmotic Photobioreactor (OPBR) For the Removal of Nutrients from Anaerobic Digestion Effluents

“…However, harvesting and dewatering microalgae for bioenergy is energy intensive process, which accounts for about 20 -30% of the operational cost. Therefore, it is necessary to develop a harvesting method that is less energy intensive [2].…”

Microalgae-Enabled Wastewater Remediation and Nutrient Recovery through Membrane Photobioreactors: Recent Achievements and Future Perspective

“…As the efficiency of membrane filtration deteriorates over time due to membrane fouling, this phenomenon has been identified as the main contributor of the total operational cost in MPBRs. For a membrane system operated under low The effects of sidestream and submerged FO module configurations on nutrient removal efficiency and microalgal growth have been evaluated, as illustrated in Figure 2d [111]. A higher algae biomass was obtained in the submerged OMPBR, hence leading to a higher nutrient removal efficiency of 100% for NO 3 --N and 92.9% for PO 4 3--P compared with the sidestream counterpart, which had a removal efficiency of 96% for NO 3 --N and 82% for PO 4…”

“…(c) Removal efficiencies of (i) NO 3 − -N and (ii) PO 4 3− -P in the MPBR and OMPBR as a function of hydraulic retention time [110]. (d) Illustrations of (i) sidestream and (ii) submerged FO modules in the OMPBR[111] (Reprinted with permission).…”