The Various Forms of Cow Manure Waste as Adsorbents of Heavy Metals

In recent years, the application of cow manure waste as an adsorbent of heavy metals in water and soil has increased. The analysis of the most effective adsorbents from cow manure as materials that can reduce heavy metals, while being low-cost and easy to produce, is important in the agricultural field. This study investigated adsorbents from cow manure, such as compost, biochar and humic acid, and analyzed the capability of the adsorption mechanisms of Cr, Pb and Cd. The experiments were performed as a function of pH, adsorbent dose, initial metal ion concentration, and contact time. To investigate the mechanism of the adsorption process, the Langmuir and Freundlich models were used. The results showed that the optimum conditions of Cr, Cd and Pb ions were achieved by compost, biochar and humic acid with 83–99% removal. An adsorption isotherm model for compost, biochar and humic acid generally followed the Langmuir and Freundlich models. This study ranks the different forms of cow manure waste in the following order based on their ease of production, high adsorption capacity, and low cost: biochar > compost > humic acid.