Estimation of heavy metals loading of anaerobic digested animal manure slurry
2009
Irie, M. | Ochiai, M. | Yamaguchi, T. | Ushikubo, A.
Closed-system anaerobic digestion has the potential to eliminate most of the lagoon emissions while conserving more nutrients and producing a renewable energy source as an additional benefit. In addition, the anaerobic digestion process creates potentially valuable by-products with available nutrients and animal manure is a significant source of heavy metal input such as copper (Cu) and Zinc (Zn) which have been used as a feed additives. This study aims to estimate the heavy metal balances in anaerobic digested slurry ADS, grass and forage crops, and grassland soil accumulation based on the loads of heavy metal from animal digested slurry to grassland and forage cropping area, and the uptake of these elements by grass and forage crops. Three feed crops; Lolium perenne L. (PRG), Phleum pratense L. (TY) and Lolium multiflorum Lam. (IRG) were grown. Feed crop field plots (la turf-type) had been treated 2 years with dairy manure ADS, swine manure ADS, and chemical fertilizer included no added fertilizer as a control for each crop. Fertilizer application amounts 200 kgN/ha/y was determined by equalizing the ammonium nitrogen contained within the recommended commercial fertilizer with the ADS for each. Potassium (K) 320 kg K2O/ha/y and phosphorus (P) 240 kg P2O5 ha/y were applied following regional recommended rate; however in ADS, K exceeded the application rate because of the high contents in ADS. Fertilizers were applied three times per year, 1/2 in spring and 1/4 in summer and fall after harvesting. The loads of Cu and Zn from ADS to grassland and forage cropping area were 1474 and 2033 g/ha/y from dairy manure ADS, 11,344 and 12,972 g/ha/y from swine manure ADS, respectively. The Cu and Zn uptake in IRG and TY applied dairy manure ADS were greater than that of PRG; applied dairy manure ADS, swine manure ADS and TY applied dairy manure ADS. The upper layer soil contained 58.5 kg/ha Cu and 40.0 kg/ha Zn. To keep the environmental quality standards for soil pollution, dairy manure ADS could be applied 43 years, and swine manure ADS could be applied 6 years to grassland soil.
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