This research determines the techno-economic feasibility of valorizing as biofertilizer the nitrogen (N) and the phosphorus (P) from a municipal wastewater effluent using the microalgae Scenedesmus sp., contributing to phosphorus recycling, resource optimization, and diminishing eutrophication by capturing 74% of N, 97% of P, and 41% of chemical oxygen demand in effluents. The inoculum was conditioned in 20 L photobioreactors by weekly harvesting and refilling at room temperature (25 °C day, 12 °C night) with a 12:12 photoperiod and 4 L/min atmospheric air bubbling. The improved operational conditions were obtained using a Box–Behnken experimental design, establishing that 70% wastewater concentration (vol./vol.), 4.5% nutrient addition, and 3 days’ harvesting time were the best conditions. The estimated biomass production was 176 tons/year, and this represents a maximum net present value of 1.5 MUSD for a 6.8 Ha plant, capturing 10% of municipal wastewater effluent, which serves 64000 inhabitants. The representative operational costs (OPEX) were 32% for utilities, 30% labor costs, and 25% for raw materials, and the required capital expenditures (CAPEX) were 11 MUSD and are related to photobioreactors (64%) and land (21%). The findings demonstrate the potential of microalgae-based systems as a feasible and profitable approach to wastewater valorization, while also highlighting the need for scale-up validation and integration with existing treatment infrastructures, where land requirements and photobioreactor installation will be relevant for financial feasibility.

This research aims to propose management strategies to mitigate eutrophication caused by inefficient wastewater treatment plants in Colombia. The information analyzed was provided by environmental authorities such as IDEAM, CORANTIOQUIA, and CORNARE in Antioquia, where the average concentrations of phosphorus in wastewater from municipal, livestock, and industrial activities are 5.1, 30.6, and 29.1 mg P/L. The total nitrogen concentrations are 77, 143, and 121 mg N/L, respectively, surpassing the limit concentrations stated by the European Union, the United States, and Mexico, among others, while Colombia has not established its own limits. Including limitations for nutrient concentrations will align Colombia with the 2050 Sustainable Development Goals (SDGs), where microalgae species like Chlorella or Scenedesmus could be used in wastewater treatment systems for municipalities and industries. These microalgae can capture organic matter, nutrients, and greenhouse emissions and reduce the concentrations observed in natural water. They could also be an alternative for capturing heavy metals and some pollutants of emerging concern. In addition to the ecological and social benefits, the algal biomass could be valorized by transforming it into biological products such as fuels, fertilizers, and pigments when micropollutants are not present, reducing operational costs for treatment systems.

This study presents a comprehensive life cycle assessment of the production of biofuels from microalgae by hydrothermal liquefaction, focusing on the valorization of CO₂ emitted by the cement industry, which represents about 8% of global anthropogenic emissions. The results demonstrate that hydrothermal liquefaction is a promising option for producing biofuels and highlight the importance of understanding its environmental impact in order to ensure its sustainability. OpenLCA 2.6 software was used to analyze the greenhouse gas (GHG) emissions associated with the process, and it was found that it can capture 3.91 kg of CO₂ per kg of biofuel produced compared to 0.286 kg of CO₂ per kg of fuel emitted by petrochemical diesel. This article also discusses the financial potential of the technology through the reduction in capital costs due to the elimination of taxes and tariffs under the current policies in Colombia, including the benefits of carbon credits, and finds that the classification of these processes as environmental facilitates their implementation at the industrial level. In conclusion, the capital investment can be reduced by about 15% with an estimated MUSD 165, and the project would be profitable, producing around 850 barrels/day of biofuel under a medium scenario with a carbon bond price of 5 USD/ton CO₂, capturing an estimated 20% of the CO₂ emitted at the Cementos Argos plant in Cartagena, Colombia.