Adsorptive Removal Of Atrazine From Aqueous Solution By Various Types Of Biochars

Nowadays the extensive use of chemicals in agriculture, fisheries, animalprotection and in other areas has raised global concerns because of the environmentalproblems resulting from these practices. Atrazine (2-chloro-4-ethylamino-6-isopro-pylamine-s-triazine) is pre-and post-emergence herbicide widely used in agriculturefor broadleaves weed control in several crops such as coffee, sugar cane, bananas,soybeans, maize, wheat, sorghum, and pineapples. Atrazine is highly mobile undercertain environmental conditions, so it can be found in groundwater, surface water,and wells used to provide drinking water. However, the high concentration of atrazinein surface and ground water can cause severe problems to the environment, humanhealth (developmental, cancer and reproductive damages), aquatic species(feminization, intoxication demasculinization of male gonads) and plant growth.Finding ways to remove atrazine from contaminated water and soil have been theconcerns of many researchers. Biochar has been used as a potential alternative foratrazine removal. Biochar is a bioresidue generated from heating biomass underoxygen limited conditions, resulting in a rich and porous material which nowadays iswidely used for the removal of pollutants from soil and water.Biochar samples were prepared from six different feedstocks, and the sampleswere (1) soybean biochar (SBB),(2) corn stalk biochar (CSB),(3) rice stalk biochar(RSB),(4) poultry manure biochar (PMB),(5) cattle manure biochar (CMB), and (6)pig manure biochar (PgMB). The biochars were characterized by determining theirphysical and chemical properties (elemental composition, surface morphology,surface functional groups, specifc surface area, average pore diameter, total porevolume, etc). The effects of the four key controlling parameters (pesticideconcentration, dosage of adsorbent, temperature, and pH) on atrazine adsorption ontothe biochars were studied using batch experiments. The equilibrium isotherms andkinetic models for atrazine adsorption onto the different biochars were investigated.Then, the biochar with the best adsorptive removal performance was chosen (amongthe six biochar types) for the optimization study using response surface methodology(RSM). The main findings of this study are described below: (1) The biochars adsorption capacity increased as the initial pesticideconcentration, adsorbent dosage and temperature increased. The adsorption affectedby pH (4.5–11) was characterized by variations of solution pH (into basic,8.17–9.33) and atrazine concentration. Atrazine removal was favored in both acidic andbasic solutions. More atrazine was removed from basic solutions than acidic solutions,and this was attributed to the effects of adsorption and hydrolysis.(2) The Freundlich isotherm adsorption parameters indicated that the adsorptioncapacity decreased in the order SBB> RSB> CMB> CSB> PMB> PgMB. All ofthe parameters related to the atrazine adsorption capacity that were determinedshowed that the SBB was a better adsorbent for atrazine than the other biochars. Thetotal pore volumes were between0.05cm3/g (for PgMB and PMB) and0.19cm3/g(for SBB). The SBB had more pores than the other biochars, with the microporevolume in the SBB contributing12.5%of the total pore volume. Our study found outthat the total pore volume and biochar pH play important roles in determining theadsorption capacity, and might have contributed to the physical adsorptionmechanisms dominating the overall adsorption process (the activation energy was <42kJ/mol for all of the biochars).(3) Five kinetic models, pseudo-frst-order, pseudo-second-order, Elovich, andintra-particle diffusion (IPD) models and a modified Freundlich model, were used todescribe the time-dependence of atrazine adsorption onto the biochars. The correlationcoefficients (R2) that were found indicated that the modified Freundlich and IPDmodels fitted the experimental data better than did the other models.(4) The optimization analysis found that the optimum operating condition toyield higher adsorptive removal percentage of92.18%is at pH6.67,7.75g/L SBBdosage,5mg/L and a temperature of32oC. Moreover, the analyze of statisticalsignificance of the model terms at95%confidence level found significant effects ofindividual independent variables (pH, dosage, concentration, and temperature withP-values0.005,0.000,0.000and0.000, respectively), the square effect of dosage ofadsorbent (P=0.009), and the interaction initial pH-to-initial concentration (P=0.034).The correlation factor (R2=0.94) is close to1, and lack of fit values of F=169.660and P=0.000were statistically significant, indicating that the quadratic modelobtained is significant (fitted the data well).In sum, the findings of this study suggested that biochar (SBB) can be veryeffective in both water treatment and remediation of ecosystems contaminated by atrazine.