RESUMEN
Wastewater treatment and simultaneous production of value-added products with microalgae represent a sustainable alternative. Industrial wastewater, characterized by high C/N molar ratios, can naturally improve the carbohydrate content in microalgae without the need for any external source of carbon while degrading the organic matter, macro-nutrients, and micro-nutrients. This study aimed to understand the treatment, reuse, and valorization mechanisms of real cooling tower wastewater (CWW) from a cement-processing industry mixed with domestic wastewater (DW) to produce microalgal biomass with potential for synthesis of biofuels or other value-added products. For this purpose, three photobioreactors with different hydraulic retention times (HRT) were inoculated simultaneously using the CWW-DW mixture. Macro- and micro-nutrient consumption and accumulation, organic matter removal, algae growth, and carbohydrate content were monitored for 55 days. High COD (> 80%) and macronutrient removals (> 80% of N and P) were achieved in all the photoreactors, with heavy metals below the limits established by local standards. The best results showed maximum algal growth of 1.02 g SSV L-1 and 54% carbohydrate accumulation with a C/N ratio of 31.24 mol mol-1. Additionally, the harvested biomass presented a high Ca and Si content, ranging from 11 to 26% and 2 to 4%, respectively. Remarkably, big flocs were produced during microalgae growth, which enhanced natural settling for easy biomass harvesting. Overall, this process represents a sustainable alternative for CWW treatment and valorization, as well as a green tool for generating carbohydrate-rich biomass with the potential to produce biofuels and fertilizers.
RESUMEN
Contaminants from cooling water waste (CWW) generated by industries represent an environmental hazard if discharged into aquatic bodies and soil without treatment. Most treatment strategies are energy-demanding and costly; hence, low-cost and sustainable treatment alternative technologies are needed. The present study proposed cyanobacteria culture as a low-cost biological method to treat cooling water waste (CWW) while simultaneously producing carbohydrates. For this purpose, CWW from a cooling tower was evaluated in different dilutions with domestic wastewater (DW) (DW25% -CWW75%, DW50% -CWW50%, DW25% -CWW75%, DW100%, and CWW100%) (v/v). The CWW provided a high content of inorganic carbon and low content of N and P, which resulted in a high C/N ratio promoting a fast carbohydrate accumulation but low biomass production. In contrast, cultures with higher DW concentrations achieved similar results in 14 days. The best results were obtained with DW25% -CWW75%, achieving up to 52 ± 18% carbohydrate content on day 8, with the highest biomass concentration of 1.7 ± 0.12â g L-1 on day 14. This culture removed >94% of TAN, N-NO3- and P-PO43-, and 84 ± 10.82% of COD. This strategy could be a promising approach to treating CWW and DW from the same industry and producing value-added products and bioenergy.
RESUMEN
Cyanobacterial biomass has constituted a crucial third and fourth-generation biofuel material, with great potential to synthesize a wide range of metabolites, mainly carbohydrates. Lately, carbohydrate-based biofuels from cyanobacteria, such as bioethanol, biohydrogen, and biobutanol, have attracted attention as a sustainable alternative to petroleum-based products. Cyanobacteria can perform a simple process of saccharification, and extracted carbohydrates can be converted into biofuels with two alternatives; the first one consists of a fermentative process based on bacteria or yeasts, while the second alternative consists of an internal metabolic process of their own in intracellular carbohydrate content, either by the natural or genetic engineered process. This study reviewed carbohydrate-enriched cyanobacterial biomass as feedstock for biofuels. Detailed insights on technical strategies and limitations of cultivation, polysaccharide accumulation strategies for further fermentation process were provided. Advances and challenges in bioethanol, biohydrogen, and biobutanol production by cyanobacteria synthesis and an independent fermentative process are presented. Critical outlook on life-cycle assessment and techno-economical aspects for large-scale application of these technologies were discussed.