Experimental and model-based characterisation of Bacillus spizizenii growth under different temperature, pH and salinity conditions prior to aquacultural wastewater treatment application

Abstract

Aquacultural production generates large amounts of wastewater with all its negative effects on life and the environment, particularly caused by elevated amounts of salt and organic matter. Within the natural microflora of such wastewaters, Bacillus spp. are largely present and therefore also actively used within biological treatment. The study conducted here followed work done in Ho Chi Minh City, Vietnam, that examined local aquacultural wastewater samples and identified different strains including species of Bacillus. More specifically in this study, the recently reclassified species Bacillus spizizenii was investigated in closer detail to quantitatively characterise its growth under different temperature, pH and salinity conditions. The strain was grown in flask and lab-scale batch bioreactor cultures. The experimental data obtained was subjected to mathematical modelling to estimate specific growth parameters. The modelling covers, in a newly combined form, logistic and delayed growth as well as growth dependency on temperature, pH and salinity. Major results obtained quantify the best growth conditions at temperature 38.7∘C, pH 7.5 and salinity 6.6 g l−1, although the organism was experimentally shown here to grow delayed at salinities of 54.7 g l−1, with a likely growth at even higher salinities. The results obtained can be used to grow Bacillus spizizenii under best conditions in bioreactors to high biomass to finally apply it to aquacultural wastewater sites.