Efficient phosphate removal in swine wastewatewater using Fe-Mn-modified pyro/hydrochar from swine manure

Phosphorus in wastewater is one of the main causes of water eutrophication. Phosphorus removal from swine wastewater is always a challenge. To achieve on-site recycling of swine farm waste, the low-cost pyro/hydrochars and their Fe-Mn-modified form were prepared from swine manure as an efficient adsorbent for phosphate removal. The results showed that the phosphate removal efficiency of unmodified pyro/hydrochars was less than 7.77%, which was significantly increased to 58.21–83.76% for the Fe-Mn-modified-pyro/hydrochars. The maximum adsorption capacity of pyrochar was found on the Fe-Mn-modified-pyrochar (PC-600M) with a surface area of 102.03 m2/g and a micropore volume of 0.25 cm3/g. The PC-600M exhibited high adsorption capacity (26.07 mg/g) in a low concentration of phosphate (50 mg/dm3), and its removal efficiency reached up to 83.76% within 24 hours. Furthermore, the adsorption of phosphate on biochars without modification (HC-210 and PC-600) was validated using a first-order kinetic model, and the adsorption of phosphate on modified biochars (HC-210M and PC-600M) was well described by the second-order kinetic model and Langmuir isotherm. In addition, there is no significant difference in the adsorption of phosphorus between pyrochars and hydrochars, but the preparation cost of hydrochars is lower than that of pyrochars. It was confirmed that the low-cost Fe-Mn-modified pyro/hydrochar from swine manure had potential for efficient phosphate removal in wastewater treatment and would facilitate value-added utilization of swine manure.