Zeolite combined with alum and polyaluminum chloride mixed with agricultural slurries reduces carbon losses in runoff from grassed soil boxes

Carbon (C) losses from agricultural soils to surface waters can migrate through water treatment plants and result in the formation of disinfection by-products, which are potentially harmful to human health. This study aimed to quantify total organic carbon (TOC) and total inorganic C losses in runoff after application of dairy slurry, pig slurry, or milk house wash water (MWW) to land and to mitigate these losses through coamendment of the slurries with zeolite (2.36-3.35 mm clinoptilolite) and liquid polyaluminum chloride (PAC) (10% Al₂O₃) for dairy and pig slurries or liquid aluminum sulfate (alum) (8% Al₂O₃) for MWW. Four treatments under repeated 30-min simulated rainfall events (9.6 mm h^-1) were examined in a laboratory study using grassed soil runoff boxes (0.225 m wide, 1 m long; 10% slope): control soil, unamended slurries, PAC-amended dairy and pig slurries (13.3 and 11.7 kg t^-1, respectively), alum-amended MWW (3.2 kg t^-1), combined zeolite and PAC-amended dairy (160 and 13.3 kg t^-1 zeolite and PAC, respectively) and pig slurries (158 and 11.7 kg t^-1 zeolite and PAC, respectively), and combined zeolite and alumamended MWW (72 and 3.2 kg t^-1 zeolite and alum, respectively). The unamended and amended slurries were applied at net rates of 31, 34, and 50 t ha^-1 for pig and dairy slurries and MWW, respectively. Significant reductions of TOC in runoff compared with unamended slurries were measured for PACamended dairy and pig slurries (52 and 56%, respectively) but not for alum-amended MWW. Dual zeolite and alum-amended MWW significantly reduced TOC in runoff compared with alum amendment only. We conclude that use of PAC-amended dairy and pig slurries and dual zeolite and alum-amended MWW, although effective, may not be economically viable to reduce TOC losses from organic slurries given the relatively low amounts of TOC measured in runoff from unamended slurries compared with the amounts applied.