Closing the Water-Energy-Nutrient Loop Using Anaerobic Membrane Biorector Coupled with Algae Photobioreactor

Recovery of resources has been steadily growing in the wastewater treatment industry. Biosolids are land applied and reclaimed water is piped throughout many municipalities. Methane recovery for energy production is a common practice at anaerobic digestion facilities throughout the developed world. Most “recovery” efforts result from convenient byproducts of the removal process, and are not the focus of technology development. However, with rising energy costs, depletion of mineral reserves, increasing fertilizer costs, and increasing population stress on resources, society is on the cusp of a paradigm switch where recovery of resources from wastewater is not only sustainable but also makes good business sense. Focused efforts to recover renewable resources such as clean water, energy, nitrogen and phosphorus, from sewage are now becoming the basis of new technology innovation.Algae cultivation in wastewater is one potential solution for nutrient and energy recovery. Algal biomass grown in wastewater can be used as a renewable fertilizer or fermented to produce biogas. Some species also produce significant quantities of lipids per dry cell weight, which can be turned into biofuel. Instead of losing nutrients through chemical precipitation or release to the atmosphere, as occurs in traditional wastewater treatment, incorporating algae into the process helps to close the nutrient loop and concentrate the energy source for subsequent use. Previous lab experiments suggested that the green microalgae Chlorella sorokiniana was able to rapidly adjust to the different effluents from treatment stages in a wastewater treatment plant. With dissolved nutrient concentration as high as 680 mg/l N and 34 mg/l P, this algae was able to grow at biomass concentration of 1.003 Kg/m3 as dry weight from the press filtrate of the sludge dewatering process. This outcome only confirms the great potential embedded in wastewater towards biofuel production from algae.With the premise of the technology development for resource recovery, the effluent from a gas lift anaerobic membrane bioreactor (Gl-AnMBR) was used as a primary substrate for a biofuel producing algal photo-bioreactor. In this study, synthetic sewage was treated in a lab-scale AnMBR where waste organic matter is converted to biogas (methane and carbon dioxide) via hydrolysis, acidogenesis and methanogenesis. While capturing organic matter, particulates and even pathogens in the membrane, excess dissolved nutrients from the anaerobic process pass through to the algal photobioreactor, where they are assimilated by algae. Additionally, the produced biogas could be potentially recycled for membrane scrubbing (gas-lift) and further serves as carbon source for the algal culture. Results of the preliminary operation of the sequential AnMBR -algae photobioreactor will be shown in this presentation.