Abstract Microalgae cultivation at biogas plants creates joint benefits for using liquid digestate and exhaust gas from the CHP unit as nutrient and carbon sources for microalgae growing. This circular approach increases biogas production’s sustainability towards a bioeconomy and zero-waste perspective. This study aims to evaluate the potential environmental impacts in connection to a novel microalgae growing technology named Stacked Modular Open Raceway Pond (SMORP) as a side-stream process coupled with centrate and exhaust gases from a biogas plant. A comparative LCA according to ISO 14044 is performed between the innovative SMORP concept at the pilot level and a hypothetical scaled-up system. Primary data for the inventory are directly gathered from the microalgae growing test performed at the biosystems laboratory of the Institute of Energy Systems and Environment of the Riga Technical University. Secondary data are collected from literature mostly in terms of mass and energy balances considering the SMORP pilot project design. The results of the LCA include the main findings both at mid and endpoint categories according to the IMPACT 2002+ method. In addition, a sensitivity analysis for several different parameters has been investigated. Results show the feasibility of the coupled system and the possibility of having benefits once the system is scaled up. Nevertheless, the results show a critical dependency of the environmental performance on the local conditions, potentially affecting too high cultivation costs.