Jiménez P., Ortiz O., Tarrasón D., Ginovart M., Bonmatí M. (2007) Effect of differently post-treated dewatered sewage sludge on β-glucosidase activity, microbial biomass carbon, basal respiration and carbohydrates contents of soils from limestone quarries. Biology and Fertility of Soils. 44: 393-398.EnllaçDoi: 10.1007/s00374-007-0220-z
This work has evaluated the effects of thermally dried (TDS) or composted (CDS) dewatered sewage sludge on β-glucosidase activity, total (TCH) and extractable (ECH) carbohydrate content, microbial biomass carbon and basal respiration of soils from limestone quarries under laboratory conditions. Two doses (low and high) of the dewatered sludge (DS) or of the respective TDS or CDS were applied to a clayey and a sandy soil, both coming from working quarries. The soil mixtures and the controls (soils with no added sludge) were incubated for 9 months at 25°C and 30% of field capacity. The addition of sludge increased all the studied soil parameters, and the increase depended on the amount of sludge. Except in the case of TCH and ECH, the enhancing effect decreased with time, but at the end of incubation, parameters of the treated soils were higher than those of the control. The rank order of the initial stimulating effect was soil-TDS ≥ soil-DS ≥ soil-CDS, and probably, this order depended on the proportion of stable organic matter, which was the lowest in the TDS. Values of metabolic quotient (qCO2) were higher at the lower dose, and they did not change during incubation in the CDS-treated soils. Both TCH and ECH were the parameters with the greatest significant sludge and dose effects. Basal respiration, microbial biomass carbon and β-glucosidase activity were the best measured parameters in distinguishing the long-term effects of the three sludge types over the soils. © 2007 Springer-Verlag.
Tarrasón D., Ortiz O., Alcañiz J.M. (2007) A multi-criteria evaluation of organic amendments used to transform an unproductive shrubland into a Mediterranean dehesa. Journal of Environmental Management. 82: 446-456.EnllaçDoi: 10.1016/j.jenvman.2006.01.002
Environmental and health problems associated with the use of digested sewage sludge hinder its application and encourage the introduction of additional treatments such as composting and thermal drying. The aim of this paper is to assess the possibility of using three different types of sewage sludge (digested, composted and thermally dried) to improve soil fertility and enhance the transformation of an unproductive shrub land into a Mediterranean dehesa for grazing purposes and also to reduce wildfire risk. In total, 10 t ha-1 of dry matter of three types of sewage sludge were spread on the soil surface of 4×5 m field plots, and then seeded with a mixture of grasses. Effects on soil fertility and plant growth were monitored over 2 years. The results show that all three types of sludge application had a significant effect on vegetation cover, herbaceous biomass (2767.7±716.1 and 1735.0±299.7 kg ha-1 for digested sludge amended and control plots, respectively) and tree growth (0.41±0.108 cm year-1 on amended trees, 14.6% more than control trees). This study proposes the use of multi-criteria analysis to identify the most suitable fertilization alternatives and to assist in the decision-making process of sludge recycling. Because of the high degree of uncertainty and conflicting objectives associated with these decisions, multi-criteria evaluation tools make a valuable contribution to decision-making processes concerning sewage sludge applications. According to multi-criteria results, the composted sludge alternative is the most suitable. This is because all the objectives are achieved: an improvement in the properties and functions of the soil with a positive vegetation response as well as minimal economic cost and risk of toxicity. © 2006 Elsevier Ltd. All rights reserved.
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