Biodiversity and disease risk in an algal biofuel system: An experimental test in outdoor ponds using a before-after-control-impact (BACI) design

feedstocks from prior work, and single best algal polyculture (Selenastrum capricornutum, Chlorella sorokiniana, and Scenedesmus obliquus) were selected to pit against each other in out- door raceway cultivation that is more realistic to that of commercial scale production. Experimental units The study site was located at the Arizona Center for Algae Technology and Innovation (AzCATI) at Arizona State University’s Polytechnic campus in Mesa, AZ (Fig 1). Six identical raceway ponds measuring 3.5m by 1.5m (approximately 4.2m2 surface area) filled to a depth of 10cm to produce a 400-L capacity were utlized. Each pond at AzCATI was equipped with a mechanical paddle wheel to constantly mix the algal cultures (flow rate of 9.3 cm s-1), an air stone to bubble CO2 into solution (5 L min-1 based on measured pH so that a constant pH could be maintained), and a YSI 5200A-DC (YSI Inc., Yellow Springs, OH, USA) probe to measured physical and chemical conditions of the ponds (temperature, salinity, conductivity, dissolved oxygen, oxygen saturation, and pH) at 15 minute intervals. Each 400-L raceway was initiated with the 2 time the standard concentration of constituents of BG-11 growth media [37], which is a common media for growth of algal feedstocks. As will be shown (Section Physi- cal and chemical conditions of raceways) physical and chemical conditions among replicates were statistically similar between Control-monoculture and Impact-polyculture treatments. Experimental design This experiment used a BACI design (Before, After, Control, Impact) to determine if algal

polycultures (the ‘Impact’ group) increase the production and stability of algal feedstock Fig 1. Experimental set-up of outdoor cultivation ponds. Photographs of 400-L experimental outdoor raceways located at Arizona Center for Algal Technology and Innovation (AzCATI) in Mesa, Arizona. Inset text summarizes experimental design. https://doi.org/10.1371/journal.pone.0267674.g001 PLOS ONE Biodiversity, biofuel and disease: Ecological engineering in algal feedstocks PLOS ONE | https://doi.org/10.1371/journal.pone.0267674 April 28, 2022 4 / 15