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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.

Pentachlorophenol is the most toxic and recalcitrant chlorophenol because both aspects are directly proportional to the halogenation degree. Biological and abiotic pentachlorophenol degradation generates p-chloranil, which in neutral to lightly alkaline environmental conditions is hydrolyzed to chloranilic acid that present a violet-reddish coloration in aqueous solution. Several genes of the degradation pathway, cadR-cadCDX, as well as other uncharacterized genes (ORF5 and 6), were isolated from a chloranilic acid degrading bacterium, Pseudomonas putida strain TQ07. The disruption by random mutagenesis of the cadR and cadC genes in TQ07 resulted in a growth deficiency in the presence of chloranilic acid, indicating that these genes are essential for TQ07 growth with chloranilic acid as the sole carbon source. Complementation assays demonstrated that a transposon insertion in mutant CAD82 (cadC) had a polar effect on other genes contained in cosmid pLG3562. These results suggest that at least one of these genes, cadD and cadX, also takes part in chloranilic acid degradation. Based on molecular modeling and function prediction, we strongly suggest that CadC is a pyrone dicarboxylic acid hydrolase and CadD is an aldolase enzyme like dihydrodipicolinate synthase. The results of this study allowed us to propose a novel pathway that offers hypotheses on chloranilic acid degradation (an abiotic by-product of pentachlorophenol) by means of a very clear phenotype that is narrowly related to the capability of Pseudomonas putida strain TQ07 to degrade this benzoquinone.