The concept of a â??simulated lichen systemâ? was recently developed by our UMN research group in which we can select different desired microalgae and fungal combinations which can be grown on the surface of specific polymers to form a biofilm. This technology can be extended to aquaculture wastewater bioremediation in order to recycle the nutrients as a proteinaceous microbial biomass
feed for the reared aquatic animals. This process modification could make aquafarming more efficient as commercial feeds account for up to 50% of total production costs. The â??mycoalgae biofilmâ? utilizes photosynthetic aeration to replace the conventional and energy intensive mechanical aeration for biological processes. By using the mycoalgae biofilm in aquaculture production, farmers will realize lowered costs for feed and reduced costs for maintenance and cleaning of the aquaculture water. Microalgae cultivation has been heavily researched to treat nutrient-rich water; however, the process is limited by problems associated with the settling and separation of small microalgae cells downstream of the treatment site. The proposed methodology of using a bioaugment of filamentous fungi in the lichen biofilm overcomes this limitation. The fungi efficiently retain algae and can also aid in the recovery and recycling of nutrients in the wastewater. The fungi retaining the algae allows for a less energy intensive harvesting process as a singular solid biofilm is produced. The strains complement each other by the exchange of required respiratory gases. The biofilm composition can be tailored based on the influent stream components, feasibility of the strains to grow together and its nutritional value as animal feed.
The effect of different initial levels of ammonia were tested in synthetic aquaculture wastewater to study the removal efficiency of nutrient pollutants by our biofilm. Starting ammonia levels were chosen based on a literature review of effluent discharge from various cultured aquatic species. Ammonia levels were reduced to undetectable limits in the medium to low initial levels of ammonia trials. At high levels of ammonia a set ammonia removal rate was observed, independent of total ammonia present in the system. We suspect the removal rate is dependent on nutrient availability and can be optimized in the future. The mycoalgae biofilm outperformed mono-cultures of fungi and algae at every level of ammonia tested in regards to total nutrients removed from the media. Combined biomass production was also higher in the co-cultures than in mono-cultures at all ranges of ammonia tested. The biomass has added value as feed for the cultured fish, thus making the process more economically advantageous. The biomass generated will be high in polyunsaturated fatty acids, proteins, and carbohydrates thus enabling robust fish growth. The biofilmâ??s nutritional properties, low energy harvesting method, and effective nutrient removal abilities make it a promising system for wastewater remediation.