Climatic changes and the increased air pollution intensify the atmospheric degradation of stone, affecting the aspect and integrity of valuable historical buildings constructed using limestone and located in tropical coastal sites. This paper analyzes limestone degradation process due to air pollution and humidity in tropical humid conditions in historical buildings located in the cities of Havana, Cuba and San Francisco de Campeche, Mexico. Havana shows higher pollution level than San Francisco de Campeche, which presents pollution levels as a consequence of a multipollutant situation along with the presence of airborne salinity. Temperature and humidity data were recorded from the walls of historical buildings in the city of Havana: the Minor Basilica and the convent of San Francisco. Changes in dry/wet cycles due to the absence of direct sun radiation as well as a high level of SO 2 allow the formation of a black crust (mainly composed of gypsum) in the lower part of the surface of the facade of the Basilica Minor in Havana; however, crusts formed in historical buildings located in San Francisco de Campeche City are mainly composed of calcium carbonate, indicating the importance of natural degradation mechanisms mainly due to dissolution in water. In the last case, the influence of water plays an important role in the development of biodegradation, which induces the formation of calcium oxalates. Caves and cracks were found in the walls of military buildings caused by water infiltration. The influence of air contamination, humidity, and construction materials determine the type of degradation that historical buildings undergo.

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In this work the dynamic study of EPS (Extracellular Polymeric Substances) concentration and distribution during the operation of two different reactor configurations (UASB and EGSB) is presented, treating medium (5 g COD/l) and low-concentrated (0.5 g COD/l) wastewater. Medium-concentrated wastewater was supplied for granules maturation as well as for stabilisation of the process. The effect of substrate change on granule characteristics was followed in both reactors. Total concentration of EPS associated to steady operation, was higher in the UASB reactor. The change to a low-concentrated substrate led to an increased difference, promoting a sharp destabilisation of the EGSB reactor, observing an increment in filamentous structures, causing biomass flotation and wash out. Although total concentration of EPS remained almost constant in the UASB reactor, their composition and distribution presented significant differences. The ratio of protein/polysaccharides as well as acidic-polysaccharides/total (neutral + acidic) polysaccharides decreased drastically in the EGSB reactor, while in the UASB reactor, the decrease was not so important and not enough for destabilisation of granule structure. Moreover, polysaccharides distribution seemed to have an important role in granule stability being enough to maintain granule cohesion only in the case of the UASB reactor. These observations point to composition and distribution of EPS rather than their total concentration as key parameters for granule stability and settleability.