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An innovative symbiotic microalgae-IFAS process for nutrient removal and photo-oxygenation: Multi-scale investigations using microelectrodes and next-generation molecular tools
Citation:
Church, J., H. Ryu, AND W. Lee. An innovative symbiotic microalgae-IFAS process for nutrient removal and photo-oxygenation: Multi-scale investigations using microelectrodes and next-generation molecular tools. To be Presented at WEFTEC 2017, Chicago, IL, September 30 - October 04, 2017.
Impact/Purpose:
Given that sustainable energy production and advanced wastewater treatment are two major challenges faced by modern society, microalgae make a desirable wastewater treatment alternative. A combination treatment of wastewater, utilizing the interaction of algae and bacteria, can offer lower energy consumption using photosynthetic aeration while also providing algal biomass for biofuel production.
Description:
A consortium of algae and bacteria is known to be effective in removing nitrogen (N) and phosphorus (P) from wastewater; however, the concept has largely been limited to suspended processes and fixed filmed (biofilm) processes have not fully been explored. Here we demonstrate the successful algal-bacterial biofilm where an algal biofilm present on top of the bacterial biofilm can assist in photo-aeration for nitrification. The algal-driven direct denitrification without additional carbon sources was also observed. Nutrient removal was stabilized after 36 days with ammonia removal reaching 100% and 57% for the microalgae-IFAS and suspended reactors, respectively. Microalgae-IFAS and suspended reactors were able to remove 51 and 49% of P, respectively. Furthermore, the algae bacteria consortia showed excellent settling with an SVI ranging from 74 to 111 and less than 1 mg/L Chl. α in the effluent. Microelectrode investigations clearly demonstrated algal biofilm photo-aeration as an alternative to costly mechanical aeration. DO concentrations in bulk solutions reached 1.3 mg O2/L and 0.6 mg O2/L in the microalgae-IFAS and suspended reactors under light only, respectively. DO concentration microprofiles showed oxygen concentrations reached 6.8 mg O2/L at the surface of the microalgal biofilm and 0.9 mg O2/L at the substratum which means the underlying nitrifying biofilm has ample supply of oxygen for nitrification. pH and ammonia microprofiles also showed a decrease in pH and ammonia at the bottom layers of the biofilm, indicating well-defined nitrification. Candidatus Accumulibacter known having the capability of phosphorus removal in wastewater was highly enriched within the microalgae-IFAS biofilms. Interestingly, C. Accumulibacter was predominant in the RNA libraries (about 50%) whereas its population substantially decreased to about 10% in the DNA libraries, indicating that C. Accumulibacter is metabolically active on the algae-bacteria consortium biofilms. In addition, microbial community analyses confirmed the presence of nitrifying bacteria such as Nitrosomonas and Nitrospria within the biofilm. Overall, this research is the first to show that the cohabitation of microalgal and bacterial biofilm enables an efficient symbiotic process for reducing the energy requirements for N and P removal from wastewater.