As pollution escalates, water purification is becoming crucial, with adsorption emerging as an efficient technique. This study aimed to evaluate the effectiveness of iron-modified rice husk biochar as an adsorbent for water pollutants. The biochar was produced at a pyrolysis temperature of 500 °C and modified by FeSO₄·7H₂O. Diverse adsorbent dosages were introduced to simulated wastewater containing aldrin, mercury (Hg²⁺), lead (Pb²⁺), and cadmium (Cd²⁺). The solution was agitated for 60 min, then filtered, and the samples were sent for analysis. The results were promising; aldrin had a removal efficiency of 100%. The removal efficiency for Hg²⁺ ranged from 99.80% to 99.96%, for Pb²⁺ from 88.90% to 99.56%, and for Cd²⁺ from 78.90% to 99.98%. The Freundlich adsorption isotherm best described the mono- and quaternary component systems, while the Langmuir isotherm was the best fit for the binary system. Therefore, iron-modified rice husk biochar shows potential as a sustainable and efficient adsorbent for wastewater treatment.

Assessments of the spatiotemporal distribution of livestock manure and its risk to the watershed are important to prevent water pollution. In this work, the spatiotemporal livestock manure distribution and its risk for the Chaohu lake basin were evaluated based on the excretion coefficient method and ArcGIS technology. In detail, the amounts of livestock manure and its associated pollutants, including chemical oxygen demand (COD), five-day biochemical oxygen demand (BOD₅), ammonia (NH₄⁺-N), total nitrogen (TN), and total phosphorus (TP), were calculated from 2009 to 2019. Then, the diffusion concentrations of COD, BOD₅, NH₄⁺-N, TN, and TP and the water pollution risk index from livestock manure were estimated and predicted for the Chaohu lake basin. The results indicated that the mean amount of livestock manure had reached 1.04 × 10⁷ t in the Chaohu lake basin in the studied decade. The COD, BOD₅, NH₄⁺-N, TN, and TP from livestock manure in Feixi and Feidong contributed 54.26% and 54.40% of the total in the whole basin. These results demonstrate the potential pollution risk of livestock manure for the Chaohu lake basin. Moreover, the diffusion concentrations of COD, BOD₅, NH₄⁺-N, TN, and TP for the lake basin were from highest to lowest as follows: Feixi > Feidong > Chaohu > Lujiang > Wuwei > Shucheng > Hefei. The water pollution risk index was more than 20 in Feixi and Feidong, indicating that these areas were heavily affected by local livestock manure. The water pollution risk index will be approximately 18 for the Chaohu lake basin in 2030, implying that the Chaohu lake watershed will suffer moderate pollution from animal manure. These results provide scientific support for policymakers to enhance manure utilization efficiency and control livestock manure loss, causing water eutrophication in Chaohu lake basin or other similar watersheds.