Introduction: The use of natural adsorbents in wastewater treatment is one of the efficient methods that, due to the availability of raw materials, the cost of the process is significantly reduced. Various natural organic and inorganic compounds can be used as adsorbents in this field. Contamination of water resources with aromatic compounds is one of the environmental problems that has attracted the attention of researchers. In general, phenolic compounds and their derivatives have harmful effects on living organisms even in low concentrations because the nitro aromatic componds have toxicity and mutagenic nature. According to the studies conducted in this field, the adsorption method using biochar can be a suitable method for removing aromatic compounds from the aqueous media.
Materials and Methods: In this study, due to the production of a large amount of biomass in Iran, the use of these compounds in the preparation of biochar as an adsorbent and its application to remove nitro phenol from water have been investigated. For this purpose, straw and stubble of pirozi garden of Tehran has been used as biomass. A laboratory system that is designed and constructed for this purpose, was used to prepare biochar. Biochar was prepared at a temperature of 350 °C and was used as an adsorbent after washing and drying. In order to assesse the general characteristics of the prepared biochar, surface morphology was performed by SEM analysis, surface chemical characteristics was assessed by FTIR analysis, heavy metal content was investigated by MOOPAM method using atomic absorption spectroscopy, and specific surface area of the produced biochar was checked by BET analysis. Also, the process has been modeled and optimized statistically using the CCD method.
Results: Examining the characteristics of the prepared biochar showed that the prepared biochar has nano structure, which will lead to an increase in the surface area. Based on the results, specific surface area was 0.42 m²/g, the porosity volume was 0.04 cm³/g, and the average diameter of the holes was 361.76 nm. Also, the analysis of heavy metals in the produced biochar showed that the measured metal values are less than the allowable range of presence of heavy metals in biochar based on the IBI standard. After designing the experiment and performing the relevant experiments, statistical analysis was performed on the results. The results of statistical analysis showed that the process is well fitted with a quadratic model and has good accuracy. According to the prediction of the model, after 60 minutes of the process, this adsorbent can remove about 84.8% of nitrophenol with an initial concentration of 16.2 ppm, at pH = 4.2, using 47.12 mg of adsorbent per 100 ml of solution. In order to confirm the correct performance of the model, the process was experimentally checked under optimal conditions, and the average removal efficiency was 82.7%.
Discussion: According to the obtained results, biochar as a natural material can be used as an adsorbent to remove nitroaromatic compounds. Also, the use of biochar, in addition to wastewater treatment, it leads to biomass waste management.