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.
Conventional wastewater treatment plants (CWWTPs) play a key role in reducing the environmental impact of urban wastewater. But nowadays, this role goes even further with climate change, water scarcity, and the current energy crisis. After the thickening of the secondary sludge, a wastewater flow is generated, which is normally recirculated to the plant head for further treatment. This work aims to use secondary thickener wastewater (STW) as a culture medium for Chlorella vulgaris, Neochloris oleoabundans and Scenedesmus quadricauda growth. These microalgae have the capacity to remove organic and inorganic matters, particularly, in wastewater rich in nitrogen and phosphate compounds. The experiments have been carried out in stirred photobioreactors with 1 L capacity under the following common operating conditions pH 8, mechanical agitation = 200 rpm, air supply rate = 0.5 L/min, continuous artificial illumination intensity = 359 ?E m-2 s-1, and non-sterilized conditions. The net biomass generated for C. vulgaris, N. oleoabundans, and S. quadricauda was 1.89 g/L, 2.73 g/L, and 2.52 g/L, respectively. The kinetic growth study showed a maximum specific growth rate, volumetric biomass productivity and culture duration for C. vulgaris (0.0128 h-1, 0.00583 g/(L h), and 429 h), for N. oleoabundans (0.0151 h-1, 0.00456 g/(L h), and 429 h), and for S. quadricauda (0.0146 h-1 and 0.007362 g/(L h), and 509 h). The microalgae biochemical composition determined biomass rich in energetic compounds (carbohydrates and lipids contents) between 70.9 % and 86.8 % with lower proteins and lipids contents between 9.17 % and 11.5 % and 6.29 % and 13.9 %, respectively. The final water quality registered lower chemical oxygen demand (COD) less than 157 mg O2/L. The final treated water can be direct discharge or used for irrigation.
The worldwide olive oil sector is a strategic sector for olive oil producing countries due to olive oil nutrition and health benefits. With what is being produced of olive oil, it continues to produce wastewater with a significant environmental impact due to the high organic load and the biochemical composition of this wastewater, particularly, the presence of microbial growth inhibiting compounds such as phenolic compounds, which makes its biological treatment difficult. On other way, red mud, the main leaching residue resulting from the alkaline treatment of bauxite (Bayer process), can be used as catalyst in chemical processing. Bayer red mud reveals high alkalinity, strong water absorption, and a large content of iron. The presence of metals in the composition of the red mud, such as iron dioxide (hematite), titanium dioxide, etc. allows its use as a catalyst in advanced oxidation processes. In this work, red mud has been revalued as a catalyst in the treatment of olive mill wastewater (OMW) by Fenton reaction. All experiments were carried out at laboratory scale in reactor with capacity of 500 cm3. Experiments have been carried out at different concentrations of red mud 0.05, 0.10, 0.5, 1.0, 2.0, 4.0, 5.0, 20, and 30 g/L. In parallel, three control experiments were carried out using only hydrogen peroxide or hydrochloric acid or red mud without pH adjustment (adsorption experiment). Experimental results have determined that the introduction of red mud as a catalyst in the like Fenton reaction (H2O2/red mud) with concentrations higher than 0.05 g/L has allowed the increase of the degradation percentages until reaching stable values at red mud concentrations higher than 5 g/L. The removal percentages at 0.5 g/L of red mud were COD = 47.1 %, total organic carbon (TOC) = 58.1 %, total carbon (TC) = 66.8 %, total nitrogen = 44.1 %, and total phenolic compounds (TPCs) = 63.5 % versus 57.2 % for COD, 74.4 % for TOC, 79.9 % for TC, 70.7 % for TN, and 66.0 % for TPCs in Fenton like reaction with 5 g/L of red mud. The common operating conditions were initial COD of OMW = 6171.9 mg O2/L, initial TOC of OMW = 3253.7 mg/L, pH = 3, magnetic agitation speed = 460 rpm, environment temperature, and the H2O2 at 10 % (w/v) added to the OMW according to the stoichiometry of the reaction. Given these results, it can be concluded that red mud can be a promising catalyst in oxidation systems based on the Fenton reaction allowing the incorporation of wastes into new green processes leading to the achievement of circular economy in industrial processes.
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