Chlorine Removal from Agrictultural Watewater using Sugarcane Bagasse Magnetic Nano Biochar

Introduction

Irrigation water salinity is a very serious problem in different parts of the world, especially in arid and semi-arid regions. The increased fresh-water demand due to population growth cause the pressure on water resources to increase in the future causing the water supply through saline and unconventional water to become a serious issue, especially in areas facing water scarcity. On the other hand, agriculture is the greatest water consumer in the world where saline water not only reduces the products but also destroys the soil structure and damages the environment

Wastewater desalination and its reuse is a relatively new approach in the water industry that solves saline-water problems through various methods, but it is uneconomical due to high equipment costs and energy consumption especially in agriculture where water consumption and costs are much higher.

To remove pollutants, various studies have used different adsorbents such as biochar, activated carbon, zeolite and resin among which biochar can effectively remove pollutants from aquatic environments because it is an effective, inexpensive, polar, high-porosity adsorbent. Ion exchange, complex formation, surface adsorption, electron sharing and biochar (carboxylic and pHenolic) - functional group interaction are among various mechanisms where the presence of negative charge on the biochar surface and positive charge on metal ions improve the adsorption process . As the activated carbon is made from such inexpensive materials as wood, coal, oil, coke, sawdust and plant waste, it is quite economical and highly capable of removing a wide range of organic and inorganic pollutants from aquatic and gaseous environments.

Materials and Methods

To prepare biochar, this research used the sugarcane bagasse as a primary biomass by 1) washing it several times with ordinary and distilled water and drying it in the open air to remove its remaining salts, 2) crushing it with an industrial mill and placing it in an oven at 60 °C for 24 hrs to remove its excess moisture, 3) grinding the crushed bagasse with a small mill for further milling, 4) passing it through 60 and 100 mesh sieves in two stages for more uniformity and 5) placing it in closed containers. Biomass was converted to biochar (BC) using a heat-programmable electric furnace where the temperature rise was set at 5 ° C/min for a uniform heat distribution. Bagasse was placed inside a steel reactor into which nitrogen gas was injected at a fixed flow-rate and prevented it from oxidation. Biomass was kept at 600 ° C for 2 hrs thereafter the furnace was turned off, while nitrogen gas was injected, and the temperature was slowly lowered to that of the lab. Considering the sizes of the furnace and reactor, each time 20 g biomass was placed in the reactor and about 5 g biochar was produced after the carbonization process; the biochar production efficiency under these conditions was about 25%.

Nano biochar (N-BC) was produced by a planetary ball mill with ceramic cup and bullets where the bullet-to-biochar weight ratio was 15-to-1 and the rotation speed was 300 rpm. The good mill-activity time was 2, 4 and 6 hrs and it worked for 3 min and rested for 1 min to prevent the temperature to rise and cohesive masses to form in the samples; as size and uniformity of particles were important, use was made of a gradation device.

Results and Discussion

In all treatments, by increasing the initial Chlorine concentration,the Chlorine removal had an increasing trend. on average, this was, using activated nano biochar 74.4% more than activated non-nano biochar. Magnetizing nano-absorbents reduced the Chlorine removal by 18.8%, on average. The highest and lowest Chlorine removal reductions due to the adsorbent magnetization were 31.6 and 10.9%, respectively. The highest Chlorine removal in all three activated non-nano, activated nano and magnetic activated nano adsorbents (200 and 400 W treatments) was measured for an activator-to-biochar ratio of 3. According to the results, Chlorine adsorption by magnetic activated nano absorbent reached equilibrium after 480 min in the treatment with 200 and 700 W microwave power and after 540 min in treatment with 400 W microwave power. Increasing the initial Chlorine concentration from 3 to 25 g/l, increased the Chlorine removal by the magnetic activated nano absorbent by 3, 3.5 and 2.6 times in 200, 400 and 700 W microwave power treatments, respectively.



Conclusion

The pseudo-first-order kinetic model had a good correlation with the data and the pseudo-second-order kinetic model did not correlate well with the data in times less than 60 min; hence, the dominating adsorption mechanism was not chemical in this interval. Intraparticle diffusion was an effective Chlorine-adsorption factor from the beginning of the adsorption process. Considering the correlation coefficient and sum of squared errors, the pseudo-first-order kinetic model and the intraparticle diffusion model had the highest correlation with the measured data. The average correlation coefficient for Langmuir and Freundlich models was found to be 0.9938 and 0.886, respectively. Therefore, the Langmuir isothermal model conformed better to the measured data than the Freundlich model.