Abstract
Agricultural runoff is a major cause of degradation to freshwater sources. Nitrate is of particular interest, due to the abundant use of nitrogen-based fertilizers in agricultural practices globally. This study investigated the nitrate removal of biochar produced from an agricultural waste product, macadamia nutshell (MBC). Kinetic experiments and structural analyses showed that MBC pyrolsed at 900 °C exhibited inferior NO3− removal compared to that pyrolsed at 1000 °C, which was subsequently used in the column experiments. Concentrations of 5, 10 and 15 mg/L, with flowrates of 2, 5 and 10 mL/min, were examined over a 360 min treatment time. Detailed statistical analyses were applied using 23 factorial design. Nitrate removal was significantly affected by flowrate, concentration and their interactions. The highest nitrate removal capacity of 0.11 mg/g MBC was achieved at a NO3− concentration of 15 mg/L and flowrate of 2 mL/min. The more crystalline structure and rough texture of MBC prepared at 1000 °C resulted in higher NO3− removal compared to MBC prepared at 900 °C. The operating parameters with the highest NO3− removal were used to study the removal capacity of the column. Breakthrough and exhaustion times of the column were 25 and 330 min respectively. Approximately 92% of the column bed was saturated after exhaustion.
Highlights
IntroductionOne of the main contributors to the contamination is agricultural runoff
Contamination of freshwater sources is a serious issue worldwide
This study aims to fill this gap by thoroughly investigating the use of macadamia nutshell biochar produced at 900 ◦ C and 1000 ◦ C for nitrate removal from synthetic samples at a concentration range similar to that commonly present in agricultural runoff
Summary
One of the main contributors to the contamination is agricultural runoff. It is of particular concern given the high level of nutrients contained, such as phosphorus and nitrogen compounds [1,2]. Nitrogen compounds such as nitrate can be problematic due to the widespread use of nitrogen based fertilizers and soil instability [3]. Nitrogen fertilizers undergo several chemical transformation processes such as ammonification, nitrification, de-nitrification, nitrogen fixation and immobilization in soil [4]. Nitrate has a weak affinity to form surface complexes and this makes it readily available for dissolution into agricultural runoff [5]
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