During the anaerobic digestion process, a significant part of the organic matter in sewage sludge is decomposed to form other organic and inorganic compounds in dissolved form. This biological transformation of a substantial part of the organic solids has, certainly, a strong influence on the rheological characteristics of the sludge. In this paper a test facility was set up to simulate sewage sludge digestion and periodic observations on the evolution of the sludge characteristics were carried out. Results of this study show that important changes on the sludge rheological behaviour occur during anaerobic digestion and that the evolution of those changes is related to the degree of digestion. Moreover, it is shown that the verified high degree of physical changes can not be explained only by the total solids concentration variation and two hypotheses are proposed to explain those changes.

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This paper examines the relationship between trade and investment in technology adoption when firms face demand uncertainty. Our model predicts that, for a given overall market size, exporting to several countries reduces firms' demand uncertainty and, hence, raises incentives to invest in productivity improvements. The effects of diversification are heterogeneous across firms: An additional foreign market matters more for firms exporting to fewer destinations. We test the proposed theory using a large sample of Argentinean manufacturing exporters. The predictions of the model find strong support in the data.

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Employment volatility is larger for young and old workers than for the prime aged. At the same time, in countries with high tax rates, the share of total hours supplied by young/old workers is lower. These two observations imply a negative correlation between government size and business cycle volatility. This paper assesses in a heterogeneous agent OLG model the quantitative importance of these two facts to account for the empirical relation between government size and macroeconomic stability.