Production of microalgal-based carbon encapsulated iron nanoparticles (ME-nFe) to remove heavy metals in wastewater

Abstract

The integration of microalgae-bacteria consortia within existing wastewater treatment plants as alternative biological treatment could be an interesting option to improve the sustainability of these facilities. However, the fate of the produced biomass is decisive to make that option economically attractive. The present study aimed to valorize the microalgae grown at a pilot scale and used for the treatment of the centrate from municipal sewage sludge, producing microalgal-based iron nanoparticles (ME-nFe), by hydrothermal carbonization. The final product had high carbon content, strong sorbent power, and reducing properties, due to the presence of zerovalent iron. Different synthesis conditions were tested, comparing iron (III) nitrate nonahydrate (Fe (NO3)3·9H2O) and ammonium iron (III) sulfate dodecahydrate (NH4 Fe (SO4)2·12 H2O) as iron sources, four different Fe/C molar ratios (0.02, 0.05, 0.1, 0.2), and three process temperatures (180, 200, 225 °C). Based on the characterization of all the prototypes, the best one (having a specific area of 110 m2g−1) was chosen and tested for the removal of selected heavy metals by Jar tests. The removal of copper, zinc, cadmium, and nickel from the treated effluent from the wastewater treatment plant was 99.6%, 97.8%, 96.4%, and 80.3%, respectively, also for very low starting concentrations (1 mg L−1). The removal of total chromium, on the contrary, was only 12.4%. Thanks to the magnetic properties, the same batch of ME-nFe was recovered and used effectively for three consecutive Jar tests.

Nutrients recovery from dairy wastewater by Chlorella vulgaris and comparison of the lipid’s composition with various chlorella strains for biodiesel production

“…Regarding the observed variabilities of the fatty acid profiles, it is known that the chemical composition of microalgae sensibly varies from species to species. However, environmental factors, among which, the composition of the growth medium also play a considerable role in this variability [ 51 ]. The accumulation of higher amounts of saturated fatty acids under nitrogen deficiency has been observed when comparing the two samples of C .…”

Reparation of nano-FeS by ultrasonic precipitation for treatment of acidic chromium-containing wastewater

“…S 2− also forms a form of Cr 2 S 3 precipitation with free Cr 3+ , which blocks the pores inside the particles and affects the rate of material transfer between immobilized particles, leading to poor removal of Cr(III) in the later stages of the reaction, resulting in a continuous decrease in the total chromium removal rate of the 2# dynamic column. Mantovani et al 42 used microalgae-modified nano-zero-valent iron to remove 12.4% of total chromium in 54 h. Gajaraj et al 43 removed 66.2% and 56.7% of total chromium from wastewater after 50 days with the help of microbial electrolytic cell and microbial fuel cell, respectively. Sahinkaya 44 et al used elemental sulfur as an electron acceptor and through this technique, the removal rate of total chromium reached 85% after 250 d. This result was lower than the current experiment and this might be due to the halting of the production of HS gas 45 that could lower Cr(VI).…”

Reparation of Nano-FeS by Ultrasonic Precipitation for Treatment of Acidic Chromium-Containing Wastewater

“…As the reaction proceeds, Fe 2+ and H + are gradually consumed. A passivation film adheres to the surface of the particles in neutral or alkaline solutions [29] .S 2also forms a form of Cr2S3 precipitation with free Cr 3+ , which blocks the pores inside the particles and affects the rate of material transfer between immobilized particles, leading to poor removal of Cr(III) in the later stages of the reaction, resulting in a continuous decrease in the total chromium removal rate of the 2# dynamic column.Mantovani et al [33] used microalgae-modified nano-zero-valent iron to remove 12.4% of total chromium in 54 h. Gajaraj et al [34] removed 66.2% and 56.7% of total chromium from wastewater after 50 days with the help of microbial electrolytic cell and microbial fuel cell, respectively. Erkan [35] et al used elemental sulfur as an electron acceptor and through this technique, the removal rate of total chromium reached 85% after 250 d. This result was lower than the current experiment and this might be due to the halting of the production of HS gas [36] that could lower Cr(VI).…”