Membrane-based Algal Harvesting Process: Process design and Nutrient recovery

Abstract

Utilization of microalgae has gained popularity in recent years due to microalgal diverse properties. For example, microalgae-derived bioproducts such as lipids, proteins and antioxidants have been utilized to produce biofuel and food supplements. During the algal culturing process, separation of algal cells from culture solution is required. Common methods for algal separation include centrifugation and flotation which is either energy intensive or chemical intensive. Alternatively, membrane filtration is feasible for microalgal harvesting as this process requires lower energy and less chemicals. Gravity-driven membrane (GDM) filtration is an extremely low energy process but is prone to lower productivity, while crossflow filtration requires relatively higher energy consumption but in turn has higher productivity. This study aims to determine the suitable membrane filtration process and favorable operation conditions for harvesting Haematococcus pluvialis algal cells, and examine the feasibility of utilizing the permeate from GDM and crossflow filtration of algal solution as liquid fertilizer for culturing edible vegetables. The results revealed that intermittent crossflow filtration at 15 min filtration with 5 min clean water (50°C) flushing condition displayed the best performance for long term filtration of algal solutions among the tested membrane processes and operation conditions.The filtrated algal solution was suitable as liquid fertilizer for plant cultivation with additional Nitrogen source. However, the accumulation amount of Hg in the whole vegetable (edible part and root) were beyond the WHO recommendation level. Further analysis of the edible part of the vegetables was thus needed. Finally, cost analysis predicts that crossflow-based filtration for algal harvesting was more feasible than GDM-based filtration, especially for higher treatment capacity.