Rapid evaluation of algal and cyanobacterial activities through specific oxygen production rate measurement

- An SOPR procedure was established to determine the phototrophic activity and decay rate.
- Microcystis aeruginosa had a higher specific growth rate than did algae Chlorella vulgaris.
- No significant difference of the decay rate between Microcystis aeruginosa and Chlorella vulgaris.
- Ammonium was the preferred nitrogen source for Microcystis aeruginosa and Chlorella vulgaris.
- Microcystis aeruginosa was more susceptible than Chlorella vulgaris to copper inhibition.

Extant respirometry enables rapid determination of sludge decay coefficients and chemical biodegradability in wastewater treatment systems. This study extends its use to phototrophic systems to determine phototrophic decay rate and photosynthetic activity through the measurements of specific oxygen uptake rate (SOUR) and specific oxygen production rate (SOPR), respectively. With a sufficient CO2 supply (4.0 mM of NaHCO3) and pH control (from 7 to 8) at the light intensity of 50 ± 5 μmol m−2 s−1 and the temperature of 23 ± 1 °C, the specific growth rates of cyanobacteria (Microcystis aeruginosa) and green algae (Chlorella vulgaris) were 0.92 ± 0.11 and 0.79 ± 0.14 d−1, respectively. The decay coefficients of M. aeruginosa and C. vulgaris were 0.08 ± 0.04 and 0.08 ± 0.03 d−1, respectively. Compared to batch phototrophic growth studies that often last longer than 10 days, the proposed SOPR measurement enables rapid determination of algal/cyanobacterial growth kinetics within minutes and is capable of determining phototrophic growth under different environmental and stress conditions (e.g., pH, nitrogen sources, chemical and metal exposure). As demonstrated here, ammonium was a preferred nitrogen source for the growth of M. aeruginosa and C. vulgaris because reducing power (energy) is needed to convert nitrate to ammonium before nitrogen uptake by the phototrophs. M. aeruginosa was more susceptible than C. vulgaris to inhibition by heavy metal copper. At the concentration of 10 mg Cu2+/L, cupric ions had no effect on algal growth but inhibited cyanobacterial growth by 66.4%.