Combined photo-assisted and biological treatment of industrial oily wastewater

In this paper we analyze the relationship between the distribution of firm size and stochastic process of growth. Three main models have been suggested by Gibrat (1931), Kalecki (1945), Champernowne (1973). The first two lead to lognormal distribution and the last to Pareto distribution. We fitted lognormal and Pareto distribution two Italian sectors: ICT and mechanical. For ICT we found that lognormal distribution must be rejected and Pareto fits reasonably well to the last 30% of largest companies. For mechanical sector we can not reject lognormal distribution. Furthermore, we perform some experiments to corroborate the theoretical models. By means of transition matrices we found that ICT shows features very close to Gibrat’s and Champernowne’s models, while Kalecki’s model strongly fits to mechanical