Cu and Zn Accumulations in Myriophyllum spicatum for Purification of Pig Farm Biogas Slurry

The ability of Myriophyllum spicatum to absorb and accumulate Cu and Zn from pig farm biogas slurry was studied. Hydraulic residence time (HRT) of 20, 40 and 60 d were applied for the plants in the study. It was found that the maximum biomass of the plants in 40 d of HRT reached 1 475.00 g, which was 7.40 times higher than that of control. More importantly, the Cu and Zn accumulations in the plants were 7.66 mg·kg^-1 and 64.18 mg·kg^-1, respectively, which were significantly greater than those in control. The metal removal from the slurry by the plants was at the highest levels when 40 d HRT was applied as well. The reductions on COD, ammonia nitrogen and total phosphorus on the slurry were 92.40%, 92.03% and 74.39%, respectively. After the HRT test the plants had increases of 7.62%-12.57% on organic matters, 30.62%-69.38% on N, 5.88%-12.94% on P, and 3.85%-21.15% on K, as well as contents of 6.76-10.78 mg·kg^-1 of Cu and 77.63-130.60 mg·kg^-1 of Zn. The increases of metal contents met the levels set forth by the national GB26419-2010 and the Agricultural Industry Standard of NY929-2005. Furthermore, the harvested M. spicatum could be used for fodder to effectively avoid the concern of secondary pollution after the biogas slurry purification.