Batch culture screening of marine microalgal nutrient removal from primary sewage effluent

Abstract

A total of 102 marine microalgal species (including 66 isolates from a sewage outfall site in St Andrews Bay, Scotland) were screened for their ability to remove ammonium and phosphate from primary treated sewage. Primary effluent was diluted 1:1 with sterile seawater, to which the test alga was added for batch culture experiments under controlled environmental conditions of seven or two days duration. The results demonstrated that although microalgae vary in their treatment capabilities, some species were able to remove >90% of both the ammonium and phosphate after seven and even two days culture. All of these best-treating species were found to be unialgal after sequential culture, indicating their potential value for further screening under continuous culture conditions, and over half were isolates from the outfall site. The best-treating algal species showed a variety of growth responses to changes in salinity between 32 and 0‰, but all had similar growth responses to a series of sewage:seawater dilutions, suggesting that for some species, other properties of the diluted sewage had more effect on algal growth than salinity. These results demonstrate that a contact time of two days was adequate for >90% removal of ammonium and phosphate by some species of marine microalgae, and that limitations on their growth were not a result of the hyposalinity of the diluted sewage compared to seawater.