Abstract. At an alpine grassland cambisol, one site had been intensely fertilized with urban sewage sludge for 10 years of 7.5 tons/ha annually, whereas an adjacent site had been left untreated. A model column experiment was set up to investigate changes of permeabilities and trace element retentions at 0–20 cm and 20–60 cm layers thereof. The particular goal was to monitor losses of nutrients to deeper soil layers or aquifers from biogas residues deposited on site. Residual slurry after biogas production or equivalent amount of water were added on top of the model columns, followed by gradual elution with de-ionized water at amounts of expected rainfall at the sampling site (1000 mm). Long-term sludge treatment changed organic carbon, soil nutrients as well as Ba, Cu, Pb, and Zn significantly, resulting in different vertical migration and elution of applied substances. Differences between the mobilities of P, Fe, S, Cu, B, as well as nitrate and ammonia losses were much more affected by the long-term sludge pretreatment than by the characteristics of the biogas residue or just de-ionized water applied on top of the columns. Largest differences between biogas residue addition and water only were noticed for zinc and ammonia. The addition of iron salts in order to increase sulfide precipitation, had measurable but low effects.
The feasibility of trace element supplementation for stable operation of wheat stillage-fed biogas tank reactors
