The raw and activated biomass of a green microalga, Chlamydomonas variabilis, were investigated as adsorbents for the removal of methylene blue (MB) dye from aqueous solutions. Chlamydomonas variabilis was isolated and cultivated to obtain a sufficient algal biomass. The collected biomass was first oven-dried and then activated by H2SO4. The results obtained showed that the optimum adsorption of MB occurred over 30 min of contact time at pH 7 and an biosorbent dose of 1.5 and 1.0 g·L−1 of dried biomass and activated biosorbent, respectively. Point of zero charge (pHpzc) was recorded at pH 6.8 and 6.9 for dried and activated biomass, respectively. The activated biomass was a more effective biosorbent than was the dried biomass: At a MB concentration of 82.4 mg·L−1, the minimum removal was greater than 98% using 1 g·L−1 activated biomass with a maximum adsorption capacity (qmax) of 115 mg·g−1, whereas at a MB concentration of 56.4 mg·L−1, the maximum removal did not exceed 80.8% using 1.5 g·L−1 raw biomass with a qmax of 18.3 mg·g−1. Furthermore, the Freundlich and Langmuir isotherm models of adsorption showed a better model fit when using activated biomass than when using raw biomass, with the former yielding R2 values greater than 0.9. The kinetic data suggest that the adsorption of MB follows the pseudo-second-order equation better than the pseudo-first-order one. This study demonstrates that the activated biomass of Chlamydomonas variabilis can be used as an effective biosorbent for the treatment of dye-containing wastewater streams.

In the last decade, studies have focused on identifying microalgal species responsible for wastewater treatment in high rate algal pond (HRAP). In this study, investigation of the microalgal community composition in Pilot-scale Race way-type high rate algal pond through study period of 24 months, chlorophyll “a” content was estimated, Physico-chemical parameters were analyzed, light intensity and temperature also measured, and the biomass productivity was calculated. It was found from the recorded results that, more than 19 genera of phytoplankton belonging to 4 divisions were identified with dominance variation throughout the study period. The presence of the species inside the pond is dependent on seasonal variation. Chemical analysis data exhibit a significant increase of COD, BOD, and TSS concentration with the temperature increase. There is an obvious impact of light intensity and temperature on the growth rate, where the highest growth response of 3.5 mg/l Chl. (a) was achieved at the highest light intensity of 1900 lux with a temperature degree of 39 °C. The average algal biomass produced from HRAP 0.99 kg algae/m3/d. This study demonstrates that the predominance of algal community structure affected by seasonal variations, and there are clear light intensity and temperature impact on the growth rate, as well as there was a promising production of algal biomass can be used in different aspects.