Which of the following methods is primarily used for the removal of contaminants in wastewater treatment?

The method primarily used for the removal of contaminants in wastewater treatment is adsorption. This process involves the adhesion of molecules from a liquid to a solid surface, where contaminants are captured and held, effectively cleaning the water. Adsorption is particularly effective for removing organic compounds, heavy metals, and other pollutants from wastewater.

In wastewater treatment, activated carbon is commonly employed as an adsorbent due to its high surface area and porosity, which enhances its ability to attract and hold various contaminants. This method is valuable because it can significantly reduce the concentration of specific pollutants, allowing treated water to meet regulatory standards for discharge or further use.

Other methods listed, such as thermal decomposition and hydraulic fracturing, are not primarily focused on contaminant removal in the context of wastewater treatment. Thermal decomposition involves breaking down materials using heat, which is not the central method used in wastewater processes. Similarly, hydraulic fracturing is a technique used in extracting oil and gas, not in treating wastewater contaminants. Landfilling involves the disposal of waste and is not a treatment method for removing contaminants from water. Therefore, adsorption stands out as the key method for effectively treating and purifying wastewater.