Intensive aquaculture releases large quantities of nutrients into aquatic bodies, which can lead to eutrophication.
The objective of this study was the development of a biological recirculatory wastewater treatment
system with a diazotrophic cyanobacterium, Aulosira fertilissima, and simultaneous production of valuable
product in the form of poly--hydroxybutyrate (PHB). To investigate this possible synergy, batch scale tests
were conducted under a recirculatory aquaculture system in fiber-reinforced plastic tanks enhanced by several
manageable parameters (e.g., sedimentation, inoculum size, depth, turbulence, and light intensity), an adequate
combination of which showed better productivity. The dissolved-oxygen level increased in the range of 3.2
to 6.9 mg liter1 during the culture period. Nutrients such as ammonia, nitrite, and phosphate decreased to
as low as zero within 15 days of incubation, indicating the system’s bioremediation capability while yielding
valuable cyanobacterial biomass for PHB production. Maximum PHB accumulation in A. fertilissima was found
in sedimented fish pond discharge at 20-cm culture depth with stirring and an initial inoculum size of 80 mg
dry cell weight (dcw) liter1. Under optimized conditions, the PHB yield was boosted to 92, 89, and 80 g m2,
respectively for the summer, rainy, and winter seasons. Extrapolation of the result showed that a hectare of
A. fertilissima cultivation in fish pond discharge would give an annual harvest of 17 tons dry biomass,
consisting of 14 tons of PHB with material properties comparable to those of the bacterial polymer, with
simultaneous treatment of 32,640 m3 water discharge.