Reclamation of nutrients, carbon, and metals from compromised surface waters fated to the Salton Sea: Biomass production and ecosystem services using an attached periphytic algae flow-way

Abstract

The Salton Sea in the Imperial Valley of California is a threatened ecosystem. To address the challenges related to trace element accumulation and eutrophication, a 270 m long attached periphytic algae flow-way was deployed at the Alamo River Wetlands, a tributary of the Salton Sea. To assess opportunities for efficient generation of biomass from reclamation of run-off-derived nutrients, the quantities of available and biosorpbed nutrients, organics, and trace elements were monitored. Over the course of 2 years, persistent algal biomass production was achieved at an average ash-free biomass productivity of 5.8 ± 2.7 g/m2/day for the full flow-way length. Overall, harvested biomass consisted of high ash (76.3 ± 5.4%) and low lipid (1.1 ± 1.0%) content, which are typical of periphytic algal biomass. Nitrogen removal rates of 530 ± 190 mg N/m2/day, phosphorous removal rates of 14 ± 6 mg P/m2/day, and 73 ± 25% of BOD (Biological Oxygen Demand) removal rates were achieved. Furthermore, spatial variations of the biomass productivity along with nutrient removal rates were observed to have a decreasing trend over the length of the flow-way, while N and P contents of the biomass showed increasing trend, indicating variable nutrient utilization efficiency as an important factor for system scaling. Temperature and solar irradiation were found to be key environmental factors for biomass productivity and nutrient removal rates. However, stable uptake of nutrients, organics, and metals in the biomass, despite intermittent variation of the analyte concentrations in the source water, indicate the resilience of attached periphytic algae biomass production at dilute nutrient concentration regimes. Trace metal analysis of the water from the surrounding area revealed levels exceeding federal toxicity guidelines for Selenium and Copper. Significant bioaccumulation of these and other metals contaminants were also identified in the harvested biomass, including Nickel, Chromium, Cadmium and Lead. Together these findings demonstrate several potential value propositions for attached algae cultivation from agricultural runoff-impacted surface waters, including remediation of N/P nutrients, organics, and common toxic metals, concomitant with biomass production.