Cultivation on Sewage of Microalgae Harvestable by Microstrainers. Progress Report

摘要

The development of biomass production technology for planktonic microalgae was studied. Two methods of algal species control are presented in detail--the theory of size selective biomass recycle and the selection and cultivation of nitrogen-fixing blue-green algae. In the outdoor experiments, circular 3 m exp 2 ponds were used and were fed daily settled sewage, were mixed with paddle wheels, and were maintained at a variable detention time and fixed depth (10 inches). The ponds were inoculated with the filamentous blue-green Oscillatoria. Due to poor growth, the Oscillatoria culture could not be maintained for long against an invading Scenedesmus sp. The naturally appearing alga--Micractinium, a colonial, spiny green algae which harvested well with microstrainers--was much more successful in maintaining itself in the experimental ponds. However, even this species could not survive adverse conditions despite extensive recycling. Selective biomass recycle is not a sufficient tool in itself for sustained species control. Laboratory experiments concentrated on demonstrating the selective recycle theory. A mixture of Spinulina (a filamentous blue-green algae) and a small unicellular green algae could be maintained with either organism predominating depending on recycling. The growth requirements of two Spirulina species were studied in batch cultures in the laboratory where they were found to be similar to other blue-green algae. Tolerance of high salts and alkalinities accounts for the predominance of Spirulina under these conditions. Small outdoor sewage ponds inoculated with Spirulina confirm these findings as well as the effect of long detention times on culture maintenance. Algal harvesting by microstraining is an economically favorable method for small-scale waste treatment systems (10 MGD) and could become sufficiently inexpensive for large-scale systems (100 MGD) to allow algal biomass production with minimal waste treatment credits. (ERA citation 03:021311)