Abstract
Global eutrophication degrades water quality in freshwater ecosystems and limits the availability of freshwater for human consumption. While current wastewater treatment facilities (WWTF) remove pathogens and pollutants, many US WWTF continue to discharge nutrients that contribute to eutrophication. Traditional nutrient removal technologies can effectively reduce eutrophication risk, but can have unintended negative consequences on human and environmental health. Alternatives, such as algae-based treatment systems, improve the sustainability of the nutrient recovery process by producing biomass that can be converted to biofuel. However, research is needed to increase the productivity of algal treatment systems to improve their economic viability. Because algae in wastewater treatment systems are grown in wastewater rich in nutrients, the algae could become limited by dissolved inorganic carbon. This hypothesis was tested in 1.2 m long recirculating floways (n = 8 for each treatment/control) by quantifying algal dry mass and wastewater nutrient concentrations in 3 independent experiments: (1) carbon dioxide gas infused vs air infused control; (2) hydrochloric acid acidified vs neutralized solution control vs no chemical addition control; and (3) sodium bicarbonate addition vs no chemical control. Results showed increases in algal biomass after 18 days in wastewater augmented with dissolved inorganic carbon (carbon dioxide or sodium bicarbonate). In contrast, maintaining wastewater at near neutral pH with hydrochloric acid reduced algal productivity relative to controls. Nutrient reductions generally paralleled algal biomass increases except in the bicarbonate addition experiment. These findings provide evidence for the importance of carbon limitation in algal wastewater treatment floways. These results could help explain why carbon dioxide infusions stimulate algae in treatment systems. Furthermore, these results suggest that algae in nutrient enriched, sun-exposed streams (e.g., agricultural ditches or urbanized streams) may become carbon limited during peak periods of productivity. These findings could have important implications for ecosystems undergoing eutrophication as atmospheric carbon dioxide concentrations continue to rise.
Highlights
Cultural eutrophication, anthropogenic nutrient over-enrichment of natural waters, has degraded aquatic ecosystems globally [1]
The temperature of water used in the pH variable experiment averaged 20.1 ± 0.5 ̊C, significantly lower compared to the carbon dioxide or sodium bicarbonate experiments (Fig 2, Tukey, p < 0.001 for all)
While several studies have reported that carbon dioxide infusions in algal wastewater treatment systems stimulate algal productivity [33, 51, 50, 52], few studies have identified the causal mechanism [see 31 for exception]
Summary
Anthropogenic nutrient over-enrichment of natural waters, has degraded aquatic ecosystems globally [1]. Phosphorus, a limiting nutrient often involved in eutrophication, has increased by 75% globally compared to preindustrial levels in terrestrial and freshwater ecosystems [2]. This phosphorus loading translates into ~13 Tg/yr of phosphorus accumulating in freshwaters and surface soils, effecting marine environments [2]. Nutrient over-enrichment can cause algal blooms, reduce water quality, and decrease aquatic biodiversity [3]. To protect the quality of surface waters, EPA mandated that total maximum daily loads be set to limit nutrients, sediments, and effluent temperatures, for all impaired state waters [6]. The Clean Water Act mandates that wastewater treatment facilities (i.e., point sources) have a permit to discharge nutrients, chemicals, and biological material from their effluent [7]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
