BioCycle Magazine

Soil organic matter quality as affected by sewage sludge or as a compost application

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Sewage sludge (SS) or sewage sludge compost (SSC) were applied to soil under controlled conditions, at rates of 0 or 200 Mg ha-1, to investigate changes in dissolved organic matter (DOM), humic acids (HA), and Pb and Zn sorption in the soil. Infrared spectroscopy, visible spectrophotometry, and sorption isotherms (mono-metal and competitive sorption systems) methods were used to assess the changer. The E4/E6 ratio (l at 465 / l at 665 nm) and the infrared spectra of DOM and HA showed aromatic behaviour in compost-soil (SSC-S); in contrast sewage sludge-soil (SS-S) showed an aliphatic behaviour.

Application of either SS or SSC increased the Pb and Zn sorption capacity of soil. The Pb and Zn sorption increased in soil and soil mixtures with a competitive metal system. The metal affinity sequence for soil, SS-S, and SSC-S was compared with the predicted affinity sequences obtained from metal properties. Poor correspondence was observed between the metal affinity sequence and the metal affinity sequence predicted by ionic potential, indicating that metals bonding to soils were not predominantly electrostatic. An affinity sequence based on Pearson’s theory agreed with the metal affinity sequences for soils. A statistical analysis showed that the bands assigned to esters (1080 cm-1) of DOM, phenolic OH (1420 cm-1), amide I (1650 cm-1), carboxyl and carbonyl C=O stretches of different nature, C=O stretch of aromatic esters, aliphatic cetone, aldehyde (1720 cm-1), ethers and esters (1230 cm-1), aliphatic alcohols (1125 cm-1), and lignin (1380 cm-1) of HA were correlated with Zn constants of Langmuir adsorption isotherm (P < 0.05).

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