Phosphorus and Nitrogen Adsorption Capacities of Biochars Derived from Feedstocks at Different Pyrolysis Temperatures

This study investigates the P and NO3- adsorption capacities of different biochars made from plant waste including rice straw (RSB), Phragmites communis (PCB), sawdust (SDB), and egg shell (ESB) exposed to a range of pyrolysis temperatures (300, 500 and 700 degrees C). Results indicate that the effect of pyrolysis temperature on the physiochemical properties of biochar varied with feedstock material. Biochars derived from plant waste had limited adsorption or even released P and NO3-, but adsorption of P capacity could be improved by adjusting pyrolysis temperature. The maximum adsorption of P on RSB700, PCB300, and SDB300, produced at pyrolysis temperature of 700, 300 and 300 degrees C, was 5.41, 7.75 and 3.86 mg g(-1), respectively. ESB can absorb both P and NO3-, and its adsorption capacity increased with an increase in pyrolysis temperature. The maximum NO3- and P adsorption for ESB700 was 1.43 and 6.08 mg g(-1), respectively. The less negative charge and higher surface area of ESB enabled higher NO3- and P adsorption capacity. The P adsorption process on RSB, PCB, SDB and ESB, and the NO3- adsorption process on ESB were endothermic reactions. However, the NO3- adsorption process on RSB, PCB and SDB was exothermic. The study demonstrates that the use of egg shell biochar may be an effective way to remove, through adsorption, P and NO3- from wastewater.