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Hexavalent chromium Cr (VI) is a toxic heavy metal that discharged by many industries into the water streams. It is the most toxic form of chromium compound, which causes significant damage to receiving ecosystems. A microalgal species, Chlorella sp., was used as a biosorbent material to remove Cr (VI) from Cr-contaminated effluents. Furthermore, different variables: pH, temperature, contact time, Cr (VI) concentration and algal dose, were optimized in order to determine the optimum conditions that achieve the highest removal efficiency. The optimization process was achieved through two steps: one factor at a time (OFAT) experiments followed by 25 general full factorial. Moreover, molecular identification was performed using 18S rRNA in order to demonstrate the species of Chlorella, and it was identified as Chlorella sorokiniana. The highest chromium removal efficiency of 99.6793% was achieved at 100 ppm Cr (VI) after three days' contact time. Chlorophyll ‘a’ estimation as a growth indicator stated that Chlorella sorokiniana can tolerate 100 ppm Cr (VI) for three days' exposure. The results suggested that Chlorella sorokiniana is a good biosorbent material and it distinguished by its high ability to uptake Cr (VI) from solutions.

Biosorption is a bioremediation approach for the removal of harmful dyes from industrial effluents using biological materials. This study investigated Methylene blue (M. blue) and Congo red (C. red) biosorption from model aqueous solutions by two marine macro-algae, Ulva fasciata and Sargassum dentifolium, incorporated within acrylic fiber waste to form composite membranes, Acrylic fiber-U. fasciata (AF-U) and Acrylic fiber-S. dentifolium (AF-S), respectively. The adsorption process was designed to more easily achieve the 3R process, i.e., removal, recovery, and reuse. The process of optimization was implemented through one factor at a time (OFAT) experiments, followed by a factorial design experiment to achieve the highest dye removal efficiency. Furthermore, isotherm and kinetics studies were undertaken to determine the reaction nature. FT-IR and SEM analyses were performed to investigate the properties of the membrane. The AF-U membrane showed a significant dye removal efficiency, of 88.9% for 100 ppm M. blue conc. and 79.6% for 50 ppm C. red conc. after 240 min sorption time. AF-S recorded a sorption capacity of 82.1% for 100 ppm M. blue conc. after 30 min sorption time and 85% for 100 ppm C. red conc. after 240 min contact time. The membranes were successfully applied in the 3Rs process, in which it was found that the membranes could be used for five cycles of the removal process with stable efficiency.

New composite adsorptive membranes were prepared from non-living Ulva fasciata (U), marine algae and cellulose acetate (CA) as polymer matrix to develop CA-U composite membranes with different ratios using the phase inversion technique. These CA-U membranes were used for cadmium (Cd 2+ ) and zinc (Zn 2+ ) ion removal from aqueous media. The prepared membranes were characterized via different instrumental techniques as ATR-FTIR, SEM and EDX in addition to swelling and porosity measurements. Afterwards, they were optimized for Cd 2+ and Zn 2+ removal through one factor at a time (OFAT) trials followed by full factorial design. The morphology and porosity measurements were highly affected by the addition of Ulva fasciata biosorbent and showed a large increase of the size and density of pores of the CA-U membrane. Maximum adsorption capacities (q max ) of 95.2 and 91.7 mg/g were obtained for Cd 2+ and Zn 2+ ions, respectively. Results established that all isotherm models attained R 2 more than 0.9, where the Langmuir isotherm achieved the highest one with R 2 0.9993 for Cd 2+ and 0.9965 for Zn 2+ , and the adsorption process belongs to the pseudo-1st-order kinetic model. The CA-U membrane displayed a higher affinity for Cd 2+ and Zn 2+ ion removal by three to four times than the blank CA membrane. Furthermore, 3R processes (removal, recovery and re-use) were applied and indicated the suitability of this system in heavy metal removal with high efficiency.

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