RESUMO
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.
RESUMO
This study aimed to investigate a mixed microalgae culture's capacity to simultaneously remove nutrients and organic matter from industrial effluents while producing carbohydrate-rich biomass. A culture initially dominated by filamentous cyanobacteria Geitlerinema sp. was inoculated in a lab-scale stirred tank photobioreactor, operating at 10, 8, and 6 days hydraulic retention time (HRT). The results show that different HRT led to different inorganic carbon profiles and N:P ratios in the culture, influencing microbial changes, and carbohydrate content. Hence, higher N-NH4+ removal efficiencies were obtained at HRT of 10 d and decreased with decreasing HRT. Whereas, complete depletion of P-PO43- was achieved only at HRT of 8 d and 6 d. Also, the highest COD removal efficiency (60%) was achieved at 6 d of HRT. The maximum accumulation of carbohydrates was achieved at HRT of 8 d, which presented an N:P ratio of 22:1 and carbon availability, recording a constant carbohydrate content of 57% without any additional carbon source. Furthermore, this operational condition reached the best biomass production of 0.033 g L-1d-1 of easy-settling cyanobacteria dominated culture. According to the results, this process presents an alternative to recycling industrial effluents and, at the same time, grow valuable biomass, closing a loop for sustainable economy.
Assuntos
Microalgas , Águas Residuárias , Biomassa , Reatores Biológicos , Carboidratos , FotobiorreatoresRESUMO
Microbial mineralization of atrazine was characterized in soils and liquid media in the presence of nitrogen fertilizer concentrations representing typical field applications. The mineralization of atrazine in soils varied between 6 and 99% after 18 d of incubation. Half-lives of between 0.99 and more than 18 d were obtained. Mineralization kinetics and degree are related by a reciprocal trend to concentrations of available nitrogen in the soil. In liquid media, half-lives were calculated as 0.12 d in the absence of fertilizer nitrogen and as 79 d in the presence of 1,000 mg/L of KNO3-N. Only 20% of atrazine was mineralized after 18 d of incubation in the presence of this concentration of KNO3-N, whereas greater than 90% mineralization occurred after 2 d of incubation in liquid medium without KNO3-N. The results demonstrate that the mineralization of atrazine is inhibited even at fertilizer nitrogen levels lower than typical field applications. Inhibition in soil is lower than that in liquid medium, possibly because of the higher complexity of the soil system. This may explain why atrazine that infiltrates to the groundwater is persistent. The microbial consortium of the soils was characterized, and seven species were identified. The degrading capacity of these species suggests that only three species are involved in the degradation of atrazine.