Evaluation of the effect of reaction time on nutrients removal from secondary effluent of wastewater: Field demonstrations using algal-bacterial photobioreactors.

Real field demonstrations to assess the removal efficiency of nutrients and organic matter from domestic wastewater were carried out using algal-bacterial photobioreactors. The reactors which consisted of three basins of 200 L were fed with secondary effluent of domestic wastewater and operated under natural day light/dark cycles. The results demonstrated that reaction time (RT) has a substantial role on the whole process performance. Whereas inoculation with nitrifiers affected the process only in some aspects. The enhancement in the dissolved oxygen production rate (1.15 mg O. L.h) was in alignment with growing higher algal biomass concentrations due to the increase in RT. COD removal rates were significantly increased (p < 0.05) with increasing the RT, and removal rates of 27%, 46% and 50% were obtained under RTs of 2, 3 and 4hrs. respectively. Meanwhile, 30%, 84% and 95% of the phosphorus was removed under the same studied RTs. No significant effect was recorded due to the addition of nitrifying bacteria on the removal of both COD and phosphorus. Ammonium (NH -N) removal rates were also increased with increasing RT and by the addition of nitrifiers, such that removal rates of 13%, 21% and 31% were obtained in basins inoculated with nitrifiers, but 11%, 14% and 19.5% were obtained in non-inoculated basins under RT of 2, 3, and 4 hrs. respectively. These results provide some new insights into algal-bacterial symbiosis systems under real field conditions which could be helpful for further process development.