Development of a single helical baffle to increase CO2 gas and microalgal solution mixing and Chlorella PY-ZU1 biomass yield

Abstract

A single helical baffle (SHB), consisting of twisted turns, was developed to convert straight flow into spiral flow in a Chlorella PY-ZU1 open raceway pond (ORWP) bubbled with 15% CO2. Microalgal solution flowing through the SHB alternative helical interspaces generated whirling flow both vertically and horizontally, which decreased mixing and increased mass transfer rates. The optimized SHB had a pitch length to total SHB length ratio of 0.13 and SHB diameter to ORWP single channel width ratio of 0.30, which decreased mixing times and increased mass transfer coefficients by 41.1% and 38.4% respectively. SHB moved Chlorella PY-ZU1 from the ORWP bottom to the top, increasing light exposure for photosynthesis. Cellular electron transfer rates and photochemical efficiency (φPSII) increased by 18%, chlorophyll a content increased by 16% and variable to maximum fluorescence ratio increased by 13%. The microalgal biomass of SHB ORWP was 23% higher than that of conventional ORWP.