Application of Nordic microalgal-bacterial consortia for nutrient removal from wastewater

Abstract

Organic waste recycling is an important emergent technology in development to combat the growing crisis of nutrient scarcity. Many waste streams and effluents contain high concentrations of valuable nutrients, but chemical treatments and recovery processes are both fiscally and energetically expensive. Microalgae are well-studied for use in biological nutrient recovery systems, but conventional culture techniques still have significant shortcomings, especially regarding energy balancing. This study sampled microalgae and photosynthetic consortia from the local environment and artificially adapted them to blended, untreated wastewaters using a stepwise bioprospecting approach. Liquid biogas digestate (BD) was selected for its high phosphorus (P) and nitrogen (N) concentrations and difficulties associated with recycling, while aquaculture effluent (ACE) was selected to dilute BD for its slightly acidic pH, low turbidity, and sheer volume produced in Finland. Mixed consortia showed 2 × greater biomass production than cultures containing only eukaryotic microalgae under concentrations of 10–25% BD. At 5% and 10% BD, all experimental consortia removed enough dissolved P to satisfy EU wastewater discharge standards (<2 mg/L); however, only 5% BD results met N discharge standards. (<15 mg/L) by the end of the cultivation period (10–12 d). In contrast with nutrient removal findings, higher BD concentration resulted in more efficient removal of dissolved inorganic carbon (DIC, >93% removal). Biomass accumulation and removal of P and N were enhanced by the addition of plastic mesh “scaffolding”; cultures grown with scaffold demonstrated an increase of 0.48 g/L biomass and >60% higher rates of N and P removal than cultures grown without scaffolding. Taken together, these results provide the foundation for a circular bioeconomy approach for integrated biomass production, wastewater remediation, and removal of nutrients and carbon.