Biochar shows substantial potential to contribute as a globally applicable adsorbent to decontaminate the water system due to the ample availability of feedstocks and valuable physio-chemical surface properties. This review aims to highlight the modification technologies of biochar, the alteration of characteristics after modification, and the eliminating of organic, inorganic, antibiotics and other pollutants from water systems by modified biochar. Alkali-acid modified and metal-loaded biochar possesses the superior surface functionality; these modifications are greatly favorable for improving the removal of different pollutants from water systems. Acidic- alkaline and metal treatment provides more diverse functional groups on biochar surfaces e.g. produces ample oxygenated functional groups, improve the surface attributes, generates high ratios of surface aromaticity and N/C, these changes provide the more adsorption sites and increase the removal of pollutants. This review also demonstrates the existing problems and future research direction related to modified biochars by acidic and alkaline agents as well as metal loaded composite in the remediation of the pollutants.