Environmental benefits of a hybrid system for algal biomass production, harvesting and nutrient recovery under a life-cycle assessment

Abstract

Biofilm reactors (BRs) are being studied as a means to optimize microalgae biomass production and overcome harvesting bottlenecks. This has led to the development of hybrid systems (HS), which combine BRs with conventional systems. However, for this technology to be implemented on a large scale, environmental viability must be ensured for its various configurations. To this end, a study was conducted using two life cycle assessments (LCAs) based on primary data. The study evaluated different support materials (cotton, nylon, and polyester) and investigated the impact of coupling a BR to a high-rate pond (HRP) during domestic wastewater treatment for biomass production and harvesting. The LCAs were conducted by SimaPro® software using the ReCiPe 2016 midpoint and endpoint methods. Results of the environmental performance of the BR operation with different support materials revealed that the production of fabrics was not the most impactful stage, except for cotton, in which this stage was responsible for >90 % of the environmental impacts in the Land use, Freshwater ecotoxicity and Marine ecotoxicity categories. The environmental impact contribution of the production stage of nylon and polyester fabrics in all categories did not exceed 26 %. Despite requiring more energy and support material, the hybrid system showed a reduction of around 28 % across all environmental categories compared to a system consisting only of a HRP and settling tank (ST). This is due to the HS's higher biomass recovery efficiency. Additionally, increasing the number or surface area of BRs to encourage attached growth is a strategy that can lower environmental impacts by approximately 40 %. Therefore, the HS, composed of an HRP and a BR, proved to be a promising alternative for wastewater treatment and algal biomass production and harvesting.