Irrigation of agricultural land with wastewater is beneficial because it incorporates organic matter into the soil, as well as organic ions (such as nitrates, sulfates, and phosphates). However, long-term application causes negative effects such as the accumulation of heavy metals. The wastewater used in the agricultural soils, also incorporates organic refractory compounds, which affect the microbial population and fertility. This chapter aimed to identify the chromium species present in agricultural soil irrigated with wastewater (679.6 mg/L for total chromium and 559.5 mg/L for Cr VI), and characterize the dissolved organic matter in the saturated solution soil. In the soil-saturated solutions (pH 6), the most stable Cr (III) species was Cr2O3. These species precipitate and accumulate in the soil in combination with natural organic matter. The highest accumulation of chromium occurred in the first 10 cm of the soil column. The 3D fluorescence analysis exposes the presence of aromatic proteins, microbiological degradation products, and humic and fulvic acids in the soil profile. The excitation-emission matrix (EEM) showed that Cr (VI) species were complexed with humic acids. In the X-ray diffraction analysis, the species Cr2O5, Cr5O12, CrO2, and Cr7C3 were found at depth with the greatest amount of organic matter.
Part of the book: Agricultural Waste and Residues