Enhancement of cell production in photosynthetic bacteria wastewater treatment by low-strength ultrasound

The present study is aimed at enhanced cell production in together with pollution removal in photosynthetic bacteria wastewater treatment through low-strength ultrasound stimulation. The ultrasound strength was 0.3 W/cm2 with 40 kHz frequency. Results showed 1–10 min sonication significantly improved the cell production. The optimal sonication time was 2 min. When the irradiation period was over 10 min, a strong mechanical damage occurred. These phenomena could be explained by the changes of PSB dehydrogenase activity. Sonication stimulated the initial dehydrogenase activity; moderate sonication increased the cell activity while too-long sonication led to quick enzyme activity decrease. The optimal sonication strategy was 1 min at the 0th hour and 1 min at the 27th hour. The corresponding cell production and cell yield increased by 110% and 93% respectively, and the COD removal reached 98%. The cost of low-strength ultrasound was only 1% of the incremental sales value of cells.