Algal bioreactors for nutrient removal and biomass production during the tertiary treatment of domestic sewage

摘要: This thesis covers work carried out on algae bioreactors as a tertiary treatment process for wastewater treatment. The was primarily assessed by the removal of Phosphorus and Nitrogen an alternative to chemical and bacterial removal. Algal would have added advantage carbon sequestration by-product in energy rich algal biomass that should be exploited existing AD capacity. Laboratory scale were run (4.5-30L) using secondary treated final effluent from local Loughborough sewage works. In preliminary series experiments several different bioreactor designs tested. These included both batch feed continuous flow configurations. The all agitated keep algal cells suspension. results demonstrated most effective easy operate with the biomass harvested simple gravitational settling. Experiments also compared artificial light source with natural outdoor experiments. Outdoor summer produced greater growth rates but could not sustained natural UK winter light. Light intensity is proportional productivity require minimum around 97W/m2 grow, overcast day (the worst case scenario) typically around 78W/m2, however this only available for few hours per during Nov-Jan. The process would better suited areas world receive year round sunlight. It shown phosphorus totally removed from wastewater in less than 24 depending other operating variables. With optimisation addition of more carbon, HRT 10-12 predicted achieve EU WFD / UWWTD standard. It further economically sustainably more attractive alternatives small medium sized Biomass 3 concentrations between 1-2g/L found best these removals produce the fastest average 125-150mg/L/d. uptake of phosphorus nitrogen dependent type present the bioreactor. less when filamentous bluegreen algae whilst almost completely stopped compared to unicellular green achieved 5.3mg/L/d phosphorus uptake 8mg/L/d. Soluble concentrations Fe, Ni Zn also reduced 60% in the standard 10 HRT. The predominant depend largely nitrogen, strain specific nutrient or temperature environment dominated. Nutrient linked which correlated the availability Carbon CO2. CO2 limiting factor growth; becoming exhausted within causing pH rise above 10.5. literature showed this common result use sparging double performance making good candidate waste sequestration. Heat generated combustion or generators exhaust ideal maintain a constant temperature 20-25°C bioreactors. A number of possible uses generated examined currently most feasible option wet anaerobic co-digestion. Further economic analysis recommended balance land area and complementary generation AD. suggested given interest algae as future fuel source, adapted large and algal production where available.