Assessing Heavy Metal Contamination in Urban River Water: An Experimental Evaluation of Low-Cost Biochar Adsorption for Water Pollution Reduction

Abstract

Urban rivers often receive untreated wastewater, stormwater, and industrial discharge. These flows can carry lead, cadmium, chromium, arsenic, copper, and other metals. Heavy metals do not break down like many organic pollutants. They can stay in water, settle in sediment, and move through food chains. This study evaluates low-cost biochar as an adsorbent for reducing heavy metal pollution in urban river water. The paper uses a secondary experimental design. It combines field water-quality data from the Sabarmati River at Ahmedabad with published adsorption experiments. The experiments used banana stem and leaf biochar, coconut husk biochar, rice husk biochar, corn husk biochar, date palm biochar, and urban biowaste biochar. The Sabarmati data showed severe downstream pollution at Site F. Chromium reached 52.84 ug/L in summer and 76.03 ug/L in winter. Cadmium reached 3.66 ug/L in summer. These values exceeded important drinking-water guideline values. Published biochar experiments showed strong removal of Pb, Cd, Cr, Cu, and Fe under controlled conditions. Banana stem and leaf biochar removed Pb and Cd with maximum capacities of 302.20 and 32.03 mg/g. Urban biowaste biochars removed some metals above 99%. Coconut husk biochar also removed Cd, Cr, and Pb with high efficiency. The findings show that biochar can support decentralized river-pollution control. Yet site testing is needed before full use.