Field test of sodium dodecyl benzene sulfonate (SDBS) as a pesticide to control predatory flagellate and ciliate contaminations

SDBS was used as a pesticide to control Poterioochromonas sp. and Hemiurosomoida sp. in Chlorella mass cultivation. The field test was conducted at the microalgal mass culture test station at Yunnan province, China (26°29′29.6′′ N; 100°40′56.12′′ E). Detailed information about the raceway ponds and general cultivation parameters can be seen in our previous study [37]. Chlorella pyrenoidosa XQ-20044 was firstly cultivated in greenhouse-covered raceway ponds (5 m², 1000 L). Then, approximately 2 L of the Poterioochromonas sp./Hemiurosomoida sp. culture suspension was added empirically into each pond on the 2nd or 3rd day. The grazer cultures acted as seeds to bring about Poterioochromonas sp./Hemiurosomoida sp. contamination, which was validated later by microbial community analysis using metagenomics data. 1 − 2 days after the addition, the predators increased in density and could be easily observed under the microscope and counted using a counting chamber. After several days of cultivation, the predator density had a marked increase, and then 10 mg L⁻¹ SDBS was added to the ponds. For the control experiments, the development of the two predators was not interfered with by any extra operation. The experiments were conducted in parallel. Chl a content and predator density were monitored every day to indicate Chlorella growth and predator development, respectively.

The SDBS pesticide was also applied in a 20–200 m² cascade culture of Chlorella in October 2019. The cultivations were performed according to our previous study [37] and continued for 20 days. For the first 10 days, the cultivation was conducted in a greenhouse-covered 20-m² raceway pond (4000 L cultural volume) and then the culture suspension was transferred to a 200-m² open raceway pond (40,000 L cultural volume) to inoculate a new cultivation. The cascade culture was microscopically monitored twice a day and two rounds of naturally occurring bio-contamination were observed. The SDBS pesticide (10 mg L⁻¹) was used to control these contaminations.