Performance of a new low-cost Zn/Fe-layered double hydroxide-modified ceramsite for the removal of P from agricultural runoff

Abstract

Modified ceramsite has been widely reported as a P adsorbent in wastewater treatments; however, its performance in removing P from agricultural runoff is unclear. A new low-cost ceramsite is modified in this study applying Zn/Fe-layered double hydroxides (LDHs; CZF) to investigate its practicality in treating P-polluted agricultural runoff. The results revealed that the CZF has a theoretical maximum P-adsorption capacity of 11.2 mg-P g−1. Various factors in P-adsorption performance followed the order of pH value (−22.6) > Ca2+ (21.5) > Mg2+ (19.9) > CO32− (−14.5) > SO42− (−13.3) > humic acid (−10.7) > NO3− (−5.57) > Cl− (−2.93) > Na+ (0.32) > NH4+ (0.19). Through iterant adsorption/regeneration, CZF cyclically reduced P concentration in agricultural runoff from 0.58 mg-P L−1 to below 0.1 mg-P L−1 under the preferred parameters of 20 g L−1 dosage, 2 h adsorption time at pH 7.2, and 1 h desorption time at pH 13.0. The treated water has low luminescence toxicity as well as low leaching risks of embedded Zn and adsorbed P in the spent CZF. Additionally, the CZF packing module significantly decreased P in agricultural runoff within four weeks. The CZF dosage and hydraulic retention time (HRT) prolonged the effective operating time (EOT) for P removal, whereas the total organic carbon (TOC) concentration had a negative impact. The cost of CZF for removing P from agricultural runoff was as low as 0.45 ¥ m−3. Overall, this research indicates that using CZF as the adsorption substrate in a ditch purification system is an effective approach for mitigating P pollution in agricultural runoff.