Avaliação energética e experimental da secagem em baixa temperatura de lodo sanitário com o uso de energia heliotérmica

Abstract

The development of an efficient and low-cost treatment for sanitary sludge meets the 6th UN objective that aims to and provide sanitation for the world population by the year 2030. In view of the above, this study evaluated, by means of a thermodynamic model, the drying of sanitary sludge at low temperature by the method of the granular bed, previously centrifuged, which was integrated into a heliothermic system with thermal storage. Scenario 1 was modeled with the dryer operating for 9h.d-1 and scenario 2 for 24 h.d-1 (continuous operation), and the same amount of sludge per day was processed in each scenario. Experimental assays were also conducted on the mixture of wet and thermally treated sludge to study the influence of the mixture on the drying process. The results showed that, in the conditions studied, the contents of 50 and 90% of total solids are the most suitable for sludge, respectively, in the inlet and outlet of the sludge dryer. While the drying temperature was defined at 80°C, as the tests did not indicate the advantage over any temperature within the range evaluated (60 to 104°C). The drying method of the granular bed, produced a less coarse profile sludge and with drying rates of up to 3.10 times higher than the convective method. The modeling achieved thermodynamic viability for the integration of the heliothermic system when scenarios 1 and 2 presented, respectively, a mirrored area of 3,848 and 3,345m², thermal demand (with global losses of the model) of 3.23 and 2.81GJ.tv -1 and thermal storage of 1,594 and 4,550kWht, demonstrating that the size of the modeled system is employed commercially in several countries and that scenario 2 is the most interesting for indicating a smaller plant. The model still showed that it is possible to produce condensed water naturally to maintain a cycle of cleaning the solar concentrators with periodicity less than 2 days. In view of the above, it is concluded that the integration of the drying with the heliothermic energy is feasible from a technical and energetic standpoint and still presents the benefit of producing water for cleaning or other non-potable purposes, mitigating one of the main impacts environment of this technology and becoming attractive in regions of water stress. It was also demonstrated that the sludge mixing technique can to modify the morphological and rheological characteristics of the material, improving the permeability and drying rate, in addition to reducing the plasticity of the original sludge. Finally, it is proved that the drying method of the granular bed is able to produce an attractive granular, dry, possibly sanitized biosolid, suitable for use in various production processes.