Macroalgae, during their growth, have the capacity to assimilate nutrients and thus subsequent harvesting of the algal biomass recovers the nutrients from biowaste sources. Therefore, the use of biowaste as algae nutrient during the growing phase, will give the possibility to transform negative environmental externalities in positive mainly in terms of eutrophication and climate change impact categories. Meantime the direct use of CO2 produced during the plant processes is becoming a large factor for the daily growing rate of algae. The first calculations and assumptions for the Life Cycle Inventory and the preliminary results of Life Cycle Assessment are presented in the paper in order to evaluate the final impact assessment of the plant. The analyses quantify the theoretical production of biogas and biomethane using marine macroalgae Ulva Prolifera cultivated in open ponds, the amount of biowaste (poultry manure) used as nutrient for algae, and will start to characterize the environmental inputs and outputs of the seaweed cultivation based on literature studies and experimental analysis. The final intention of the research is to identify environmental indicators and a benchmarking threshold.