Abstract
Currently, most wastewater treatment plants do not meet the legal requirements, especially regarding phosphorus and nitrogen contents. In this work, real primary urban wastewater (P-UW) was used as culture medium for the growth of Chlorella vulgaris. Experiments were carried out in batch photobioreactors at laboratory scale. To determine the maximum nutrient removal levels and the optimal pH value for C. vulgaris growth, the following pH values were studied: 5, 6, 7, 8, 9, 10, and 11. Additionally, two control experiments were conducted using UW and tap water at the same conditions but without microalgae inoculation. The operational conditions were agitation rate = 200 rpm, T = 25 °C, aeration rate = 0.5 L/min, and continuous light with illumination intensity = 359 µE m−2 s−1. Significant higher growth was obtained at pH = 7. The direct use of C. vulgaris for P-UW treatment demonstrated high removal percentages of organic (COD and BOD5 removal = 63.4% and 92.3%, respectively) and inorganic compounds (inorganic carbon removal = 99.6%). The final biomass was characterized by an accumulation of high energetic compounds, mainly carbohydrates, which ranged between 63.3% (pH = 5) and 82.8% (pH = 11) and represent a source of biofuels. These new achievements open up the possibility of new horizons in urban wastewater treatment.
Highlights
Global population is estimated to be increased to nine billion people by 2050
The urban wastewater used in this work was obtained in a WWTP after a pre-treatment based on the separation of large particles as wet wipes, wood, leaves, stones, etc., and after natural sedimentation in a settling tank where primary sludge and clear (P-urban wastewaters (UW)) fractions were obtained
In the primary urban wastewater (P-UW) is lower than that determined for tap water, 8.2 mg O2 /L, which is due to the presence of the organic matter in the P-UW
Summary
The continuous population growth, urbanization, industrial development, and diversification of human activities has resulted in a water crisis that affects, nowadays, 4000 million people around the world, who undergo water scarcity [1,2]. Urban wastewaters (UW) are generated by industrialized countries as a combination of liquid and solid residues from domestic and commercial activities, and sometimes from pre-treated industrial activities [4]. Physicochemical characteristics of these effluents are related to the standard of living, behavior, and lifestyle of the inhabitants of the regions where UW are generated. Numerous pathogens microorganisms are commonly found in untreated UW, representing a major health risk for natural environments [6]
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