XA Equilibrium equivalent fraction of species A in the liquid YA Equilibrium equivalent fraction of species A in. Large parts of heavy metals are released into the environment from industrial water through inefficiencies built into the technological activities used directly in the processing of metals or via other pathways. Given the number of metals and different biosorbent materials of interest, in the absence of theoretical apparatus, experimental testing of these effects requires a large amount of laboratory work [6].
Floating masses of Sargassum form the Sargasso Sea, which is also very common on the Brazilian coast. All Sargassum species contain floating bubbles, which are responsible for their reduced density and thus contribute to their presence in the marine environment. Quantitatively, alginic acid is the most abundant polysaccharide in the cell wall of brown seaweed.
Alginic acid usually occurs in this seaweed as calcium, magnesium, sodium and potassium salts, mainly in the cell wall. The compound toxic effects of heavy metals in the environment are recognized and their dangerous impact is better understood.
Conventional metal-removal technologies
Technologies currently used to remove heavy metals from industrial effluents appear to be inadequate, often causing secondary problems with sludges containing metals that are extremely difficult to remove. Currently available "best treatment technologies" for metal-containing wastewater are either insufficiently efficient or prohibitively expensive and inadequate for the enormous volumes of wastewater [3]. Ultrafiltration: These are pressurized membrane operations that use porous membranes to remove heavy metals.
Chemical precipitation: Precipitation of metals is achieved by adding coagulants such as alum, lime, iron salts and other organic polymers. The large amount of sludge containing toxic compounds produced during the process is the main disadvantage. Phytoremediation: Phytoremediation is the use of certain plants to clean soil, sediment and water contaminated with metals.
The disadvantages include that it takes a long time for the removal of metals and a regeneration of the plant for further biosorption is difficult. Therefore, the disadvantages such as incomplete metal removal, high reagent and energy requirements, the generation of toxic sludge or other waste products that require careful disposal made it essential for a cost-effective treatment method capable of removing heavy metals from aqueous effluent.
Advantages of Adsorption on biomass
It is often associated with an active defense system of the macroorganism, which reacts to the presence of toxic metals. Metal transport systems can be perturbed by the presence of heavy metal ions with the same charge and ionic radius associated with essential ions. Ion exchange: Cell walls of polysaccharide-containing microorganisms exchange divalent metal ions with polysaccharide counterions.
In the first case, the metal removal from the solution is often accompanied by an active defense system of the micro-organisms. In the case of precipitation that is not dependent on cellular metabolism, this may be a consequence of the chemical interaction between the metal and the cell surface. The values of the specific uptake q are plotted as a function of the metal concentration Ceq.
Cross-linking: The addition of the cross-linker leads to the formation of stable cellular aggregates. The desorption of the adsorbed Hg(ll) from the biosorbent - immobilized and heat-inactivated Trametes versicolor and Pleurotus sajur-caju were studied in a batch system [50]. Effect of pretreatment on heavy metal biosorption: The metal affinity for the biomass can be manipulated by pretreating the biomass with alkalis, acids, detergents and heat, which can increase the amount of metal sorbed.
Over the past twenty years, there has been increasing awareness about the ecological effects of toxic heavy metals. Since (qA/Q) represents the fraction of binding sites occupied by A, equation (7) can be used to evaluate the decrease in equilibrium uptake of species A by the biosorbent due to the presence of species B. Equation (7) shows that whenCB= 0, (qAIQ) ~ 1, regardless of the absolute value of the final concentration ofA, CA.
The efficiency of a biomass to adsorb heavy metals is related to the chemical composition of the biomass [8, 9, 10]. Since cost is the big factor in dealing with wastewater, the cheaper the source of the biosorbent, the better. Due to the higher 'affinity' of the sorbent for the sorbate species, the latter are attracted to the solid and bound to it by different mechanisms.
The extent of the sorbent's 'affinity' for the sorbate determines its distribution between the solid and liquid phases. For this purpose, it is customary to determine the metal uptake (q) by the biosorbent as the amount of sorbate bound by the unit of solid.
EXPERIMENTAL
The sargassum was then dried in an oven at a temperature of 60°C for 24 hours. To determine the contact time required for the sorption equilibrium experiments, the sorption dynamics experiments were first performed. The O.IN HCl or O.IN NaOH solution was added to maintain the pH value of the reacting solution at the level of the designed end point.
A simple preliminary test of sorption kinetics determined the exposure time required for given sorbent particles to reach the equilibrium state characterized by constant sorbate concentration in solution. Its advantage is the highest possible packing density of the sorbent, giving a high volumetric productivity. Both curves are a function of column flow parameters, sorption equilibrium, and mass transport factors [27, 28].
The column experiments were carried out in a packed-bed column with an inner diameter of 30 mm and a length of 500 mm (Figure 2), uniformly packed with 38 g (dry basis) acid-treated biomass (see section 3.2). During the column sorption, an aqueous solution containing 35 mg/l copper (from CuSO4.5H20) at pH 4 was continuously pumped through the column at a constant flow rate (15 ml/min). The samples were collected from the column outlet at different times and analyzed for copper effluent concentration using an atomic absorption spectrophotometer.
After the biomass in the column was saturated, the column was washed at the same rate with distilled water for several hours, before a. The reason for washing the column for several hours was to ensure that all Cu ion solutions were removed. Outlet sample collection and analysis was the same as that used in the biosorption intake stream.
The amount of (bio)sorbent solids (S) to be used was accurately weighed for each contact test and recorded. If too much solids are added, there may be almost no sorbate left in the solution for a reliable analysis [22]. At the end of the contact period, solids were separated from liquids by decantation or filtration.
RESULTS AND DISCUSSION
The same conditions were also applied to determine the contact time at pH 4 and it was observed that 3 hours is sufficient for the system to reach equilibrium (Figure 4). The equilibrium time is a function of many factors, such as the type of biomass (number and type of biosorption sites), the size and shape of the biomass, the physiological state of the biomass (active or inactive, free or immobilized), as well as the metal involved is. the biosorption system. The experimental results indicate that the size of the biosorbent did not affect the capacity and rate of copper biosorption.
Although this is contrary to what is expected for an intraparticle diffusion controlled process, it is necessary to point out that the two sizes of biomass are actually of the same thickness (dimension that determines the diffusion distance). This behavior has been reported by other researchers, although it has been shown that larger biomass particles of Sargassum fluitans and Ascophylum nodosum had higher metal uptake than smaller particles in the case of cadmium, nickel, lead and zinc [2, 27]. At pH in the range 3.5–5.0, these groups generate a negatively charged surface, and electrostatic interactions between cationic species and this surface are responsible for metal uptake [ 19 ].
It is shown that as the pH increases, the adsorption rate also increases with the optimum pH of 4 for copper biosorption. At pH values lower than 2.5, the removal of copper (Il) was inhibited, possibly as a result of the competition between hydrogen and copper ions on the sorption sites, with an apparent predominance of hydrogen ions, limiting the influx of metal cations as a result. of the repulsive force [63]. The sorption process was stopped after reaching 35 mg of Cull in the effluent and the regeneration solution of O.IN HCI was pumped through the bed.
The breakthrough point is the time (tb) when the sorbate appeared in the effluent stream at some predetermined concentration, which was 1 mg Cull. The time interval between tb and 1st corresponds to the length of the mass transfer zone of the bed as shown in figure 8. To determine the weight loss after the 6th cycle, the biomass was washed with distilled water and dried in the oven at 45°C overnight.
The reason for the shortened breakthrough time was apparently not a decrease in equilibrium uptake capacity, but a slight change in the overall adsorption rate of the column. It can be caused by changes in the chemistry and structure of the biosorbent, as well as by flow changes within the column. The deterioration of absorption properties may be due to chemical changes of cell wall components such as alginate and sulfated polysaccharides, which play a major role in absorption by seaweed [25, 28].
CHAPTERS CONCLUSION
Cotoras, D., and Viedma, P., A microbial; Technology for Removing Metal Ions from Mining and Industrial Wastewaters, Environmental Publications, Karad (1989). Mahan, C.A. and Holcombe, J.A. Immobilization of algal cells on silica gel and their characterization for trace metal preconcentration. Removal of metal ions from aqueous solutions by Pencillium biomass: Kinetic and uptake parameters, water, air and soil pollution.
