Long-term evolution of the composition of surface water from the River Gharasoo, Iran: a case study using multivariate statistical techniques

Bio-sorption of toxic metals from industrial wastewater by algae strains Spirulina platensis and Chlorella vulgaris: Application of isotherm, kinetic models and process optimization

The present study evaluates the effect of an acidic treatment on the improvement of the percentage removal of toxic metal (%TM_rem) from wastewater by algae strains (Spirulina platensis (SP) and Chlorella vulgar (CV)) under different adsorbent dosages (0.2-2.5 g), a pH of (4-8) and contact time (5-100 min). The acidic treatment (Ac-T) altered the functional groups on the surface of algae promoting more electronegative groups and improved the %TM_rem of Al, Ni and Cu. Treated SP removed up to 95.0 ± 0.3% (Std. Dev = 0.24), 87.0 ± 0.2% (Std. Dev = 0.34)%, and 63.0 ± 0.3% (Std. Dev = 0.14) of Al, Ni, and Cu at the optimum pH of 5.5, 6.0, and, 7.0 and an adsorbent dosage of = 2.5 ± 0.1 g/L (Std. Dev = 0.14) g/L, respectively. Lower %TM_rem of 87.0% ± 0.2 (Std. Dev = 0.09), 79.1 ± 0.4% (Std. Dev = 0.08), and 80.0 ± 0.2% (Std. Dev = 0.04) were achieved with treated CV, respectively. The optimum operational conditions for maximum %TM_rem were determined at (C_algae = 4.8 ± 0.2 g_MNPs.L^-1, C_t = 88 ± 1, and pH = 6) using the response surface methodology (RSM). The adsorption of TMs on algae is endothermic, spontaneous, and follows Langmuir and second-order kinetics. Zeta potential measurements indicated that the adsorption mechanism between the toxic metal (TM) and algal strains is controlled by electrostatic interaction. As such, bio-sorption is a sustainable and efficient technology for the removal of TM from wastewater.

Effect of light/dark cycle on nitrate and phosphate removal from synthetic wastewater based on BG11 medium by Scenedesmus sp

In this study, microalgae growth in the synthetic wastewater and their ability to remove nutrients under different light levels was investigated. For this purpose, a comparative study was conducted on freshwater microalgae Scenedesmus sp. to evaluate their performance to remove nitrate and phosphate from both slaughterhouse and dairy synthetic treated wastewaters, under different light/dark cycles (12/12, 16/8 and 24/0 h), in Erlenmeyer flasks. The best light/dark cycles in Erlenmeyer flasks for nitrate and phosphate removal and growth were obtained at 24/0 h. Moreover, nitrate and phosphate removal under light conditions at 24/0 h light/dark cycles were tested in a designed open raceway pond. The maximum nitrate removal in slaughterhouse and dairy synthetic wastewater was 78% and 99.7%, and the phosphate removal was 31% and 68%, respectively. Furthermore, the highest biomass productivity in dairy and slaughterhouse synthetic wastewater during 9 days was 0.65 g L^-1 and 1.5 g L^-1, respectively. Thus, Scenedesmus sp. could be potential candidates by showing their intrinsic merit, for the reduction of nitrate and phosphate residue levels from dairy and slaughterhouse synthetic wastewaters in open raceway ponds.