Evaluation of chemical treatments for control of ciliate grazers in algae cultures: A site study

Algal cultivation and biomass production for biofuels and other products have many advantages over terrestrial crops. However, algal production is often negatively affected by zooplankton grazers resulting in a culture crash within days of detection. Controlling zooplankton is critical for sustainable algal productivity. In this study, we evaluated several chemical techniques to monitor and control ciliate grazers in algae cultures in flasks, columns, and small outdoor raceways. Eliminating CO2 addition in small outdoor raceways led to a maximum pH of 9.5, which was not high enough to inhibit the ciliate (Vorticella sp.) in Scenedesmus acutus LRB-0424 cultures; however, laboratory conditions that reached pH > 10 successfully inhibited ciliate growth. Application of 10.0 mg-Cl L-1 of hypochlorite application in outdoor raceways eliminated 95% of the ciliate (Colpoda sp.) in the Chlorella vulgaris LRB-1201 culture and 65% of the Vorticella sp. in the S. acutus culture. Application of 20.0 mg L-1 of quinine sulfate in raceways eliminated 85% of the Colpoda sp. in the C. vulgaris culture for 2 weeks and 55% of the Vorticella sp. in the S. acutus culture for 1 week. Copper concentrations of 10.0 mg-Cu L-1 in raceways eradicated all the ciliates in C. vulgaris and S. acutus cultures, but also inhibited algal growth, which was not observed in 24-h flask/column tests with copper sulfate.