Evaluation Biosorption of Cadmium (II) from Aqueous Solution by Modified Ceratophyllum demersum L.

In recent years, concern over the long-term effects of heavy metals has been increased as environmental pollutants. Environmental pollution of heavy metals is one of the major environmental issues. Unfortunately, due to the uncontrolled entry of various types of industrial waste, their input is increasing into air, water and soil sharply. Heavy metals are irresolvable and tend to accumulate in the organs and tissues of living organisms that cause a variety of diseases and disorders for humans and other living organisms. Recently, biological methods and technologies such as biosorbent and bio-accumulation have been used to help researchers to confront the problem of removing heavy metals from sewage. In bio-accumulation technology is used living biota to remove metals. However, in the second method, or biological absorption is used of dead or inactive biologically is this purpose. The main objective of this research is to determine the capability of the storage of cadmium as heavy metal by modified Ceratophyllum demersum biomass. In addition, the effect of pH on adsorption rate, contact time on adsorption rate, adsorbent adsorption, initial concentration of adsorbant (cadmium) were evaluated on adsorption. Also, kinetic and isotherm models of absorption were determined.

In the present study, the effect of modification of Ceratophyllum demersum on the removal of Cadmium from aqueous solution was investigated. Ceratophyllum demersum or blue fork is a submerged plant that is commonly found in aqueous humorous streams containing moderate to high levels of nutrients. One of the suitable environments for growth of Ceratophyllum demersum is low depth and laminar flow of water channels. In this regard, a search was conducted on irrigation channels inside Shahid Chamran University of Ahvaz and large quantities of this plant were observed in many parts of these channels. The plant was collected from the entrance channel of the Karoon River to the university. After collecting the plant and washing it with urban water and distilled water and drying it in free air was dried at 70 ° C. After that the dry matter was milled and it passed through the standard No. 50 sieve. In this study, alkaline solutions (0.5M NaOH solution) were used to modify biomass. This method has been shown to be effective in similar studies, and has greatly increased the absorption capacity of adsorbents. Preparation of cadmium storage solution was performed based on the methods presented in the standard reference for water and wastewater testing.

The morphology characteristics of biosorbent surface by Scanning Electron Microscope (SEM) were studied and desirable effects of modification on characteristics of biosorbent surface were proved. The result of study showed that by increasing pH from 3 to 8, the removal efficiency increased from 93% to 97% at pH 7, and then decreased to 85% at pH 8. In addition, adsorption capacity, in similar way, increased from 7.04 to 7.35 and then decreased to 6.44 mg/g. Therefore, pH 7 was determined as optimum pH. Increasing contact time, from 5 to 240 minute, caused changes in removal efficiency from 67% to 98% after 180 minute, and then decreased slightly. Adsorption capacity, in similar way, increased from 6.25 to 9.13 mg/g and then decreased slightly and contact time of 60 minute was determined as equilibrium time. Increasing dose of biosorbent from 0.02 to 4 g/L, causing increase of removal efficiency from 37% to 99% and decrease of adsorption capacity from 169.5 to 2.35 mg/g and finally dose of 10 mg/L was determined as proper dose of biosobent. Increasing of initial concentration of Cadmium solution from 10 to 200 mg/L led to decrease in removal efficiency from 96% to 31%, and increase in adsorption capacity from 9.18 to 59.7 mg/g, and concentration of 10 mg/L was determined as optimum initial concentration of Cadmium. Finally, kinetic and isotherm adsorption models were studied. In kinetic models, pseudo-second order kinetic model, with correlation coefficient of 0.99 described biosorption better than pseudo-first order. In isotherm models, the Langmuir isotherm with correlation coefficient of 0.99 described biosorption process such better than other models. Based on results obtained in this study, the high capability of modified Ceratophyllum demersum, as a favorable biosorbent for cadmium removal from aqueous solution was proved.

The images from the SEM device showed that adsorption modification increased the absorption capacity to absorb cadmium ions. The highest efficiency was achieved in pH equal to seven. According to the economic considerations and optimum consumption of the energy 60 minutes was determined as the time of equilibrium. Kinetic modeling shows that Pseudo second order has the best matching with experimental data.