SUITMA 2005 Cairo - Use of environmentally sound waste mixtures for land application
SUITMA 2005 Cairo
| This abstract is about one of the papers of the Cycling of city fluids and solid refuse theme of the SUITMA 2005 symposium. |
| Marta Camps Arbestain,i | Urko Santisteban,i |
| Susana Virgel,i | F. Macías,ii |
| Miriam Pinto.i |
- ii - Departamento de Edafología e Química Agrícola, Universidad de Santiago de Compostela, Santiago de Compostela, Spain.
The major drawbacks associated with the use of waste products (either organic, such as sewage sludge, or inorganic, such as coal combustion by-products) as fertilizers have been :
- the commonly imbalanced source of plant nutrients,
- the presence of toxic elements.
The objective of this study was to prepare mixtures of different organic and inorganic waste products in order to balance essential nutrient concentrations and immobilize heavy metals. The mixtures used were:
- sewage sludge + foundry sand
- sewage sludge + wood combustion ash
- sewage sludge + type A metal scrap
- sewage sludge + type B metal scrap
- sewage sludge + Linz-Donawitz (LD) slag
- sewage sludge + barley straw.
Waste materials were mixed in two proportions: 90:10 and 75:25 (wet weight basis), except for the sewage sludge + barley straw mixture in which the ratios used were 99:1 and 98:2 (wet weight basis). Different types of sewage sludge were also tested – anaerobic (AN), aerobic (AE), and a 50:50 (dry weight basis) mixture of both (AN+AE) - and three replicates per treatment were used. The waste mixtures were weighed and irrigated daily with distilled water (to keep soil moisture to field capacity) during 4 weeks and samples were taken on weeks 1, 2, and 4. Values of pH of the inert residues used (foundry sand, wood combustion ash, metal scrap A, metal scrap B, and LD slag) were 9.6, 8.6, 8.2, 9.6, and 12.1, respectively. Values of pH of the sewage sludges used (AN, AE, AN+AE) were 6.8, 11.4, and 10.5, respectively. The pH analysis carried out to present (samples of weeks 1 and 2) indicate that the type of sewage sludge is the most determinant factor influencing the pH of the waste mixtures during the first weeks of incubation, although a liming effect of the LD slag has been detected in the AN and AN+AE mixtures.
We are currently analyzing the samples of residue mixtures for total elemental concentration, electrical conductivity, organic C, total N, and available P. Major and heavy metal cations and anions in a mixture of 1:5 residues to deionized water will also be determined, and the solid phase will be characterized using FTIR and XRD.
Results of this experiment could provide data for predicting nutrient availability and heavy metal mobility in order to undertake environmental risk assessment of waste mixtures application to soils
