Microalgae offer great potential as a second-generation biofuel feedstock. Microalgae are attractive because they require minimal nutrient inputs, can capture atmospheric CO2, and can be grown in fresh, brackish, or salt water. Additionally, they do not compete with current food, feed or fiber feedstock needs, and can be grown on non-arable lands. However, limited water supplies and nutrient sources can significantly add to microalgae production costs.
Currently, municipal wastewater treatment facilities spend millions of dollars each year to remove abundant nitrogen and phosphorus from wastewater. In lieu of traditional treatments, microalgae can be used to effectively and efficiently remove these compounds, while simultaneously producing biofuel feedstocks. Preliminary research has demonstrated that some microalgal species can be grown successfully on centrate, the liquid fraction remaining after dewatering anaerobically digested wastewater sludge.
This project evaluates the potential for growth on centrate of over forty microalgae strains from fresh, brackish, or salt water genera. Generally, freshwater strains were able to grow in higher centrate concentrations, with two species, Neochloris pseudostigmata and N. conjuncta, demonstrating growth with up to 40 vol% centrate. Nine of eighteen salt water Dunaliella spp. also demonstrated growth in centrate levels exceeding 25 vol%. The use of UV sterilization for centrate sterilization was also evaluated. UV dosage requirements were significantly higher than those used in traditional drinking water treatment plants due to coloration and high TSS/TDS levels.
The lipid profiles of strains with high centrate tolerance were determined and compared against growth on defined maintenance media using GC-MS. The major lipid compounds were found to be palmitic (16:0), oleic (18:1), and linoleic (18:2) acids for all strains grown on either centrate or their respective maintenance medium.