Estudio de aditivos para la optimización de procesos de digestión anaerobia

Laburpena

Abstract. The aim of this work is to explore the improvement of both biogas production as well as anaerobic digestion process itself of sewage sludge (EDAR). More specifically, the addition of nutrients, or non-hazardous waste, allows the use of biogas farms exploitation for the production of electricity in cogeneration system. Moreover, this second case ensures that they are properly managed. In the phase of bibliographic research, a comprehensive review (of the state of the art) of the anaerobic digestion of sewage sludge from waste-water treatment plant has been made. Moreover, its specific application for the search of nutrients or waste which fostered the growth of Methanosarcinas bacterial species was also investigated due to the fact that they are the only known anaerobic methanogenic capable of producing methane using the three viable methanogenic routes. The search of possible waste addiction to anaerobic digesters has a dual objective. On one hand, the improvement of the anaerobic digestion. On the other hand, a new activity for EDAR could be possible given that they could become management companies of these wastes. Two work lines have been developed at the experimental part. One of them consists of laboratory experiments with the use of a Bioprocess Control equipment which operates with 15, 0.5 liters batch bioreactors. The other one is an experimental pilot plant using two ten-liters digesters which operate in semi-continuous regime. In both cases, there are economic technical feasibility studies that allow us to actually simulate and calculate the global process to establish if this waste water process adding additives is cheaper, than the standard procedure of anaerobic digester without them. The first experimental step, operating in discontinuous regime consists of six test series using alternatively sludge produced in three water treatment plants and, as additives: yeast, methanol, cattle manure, leachate, slaughter waste and industrial waste, respectively. On the other hand, the experimental step operating in semi-continuous regime was developed using the two most favorable additives from the discontinuous experimentations (yeast and industrial waste) in two test set with sludge from the three named water treatment plants. The measured magnitudes in each test series of the six studied in discontinuous regime have been, respectively, the % of elimination of volatile solid, the biomethanation potential (MLCH4/gSVadditives) and the volume of methane produced referred to the content of volatile solid in the feeding (MLCH4/gSVfeed). Likewise, all biodegradability curves of evolution of accumulated volume of CH4 v.s. time in each experiment have made possible to detect the cases in which there is inhibition of the process as well as situations with positive economic performance in the simulation of a real plant, according to the results, operating with each sludge under such conditions. All additives and sludge at the beginning, and the end, of the experiments have been typified, referred to total solids, volatile solids, pH, conductivity, DQO, total nitrogen, volatile fatty acid and alkalinity, respectively. Most of the tests (discontinuous and continuous regime) have verified the applicability and efficiency of the used nutrients and waste in real plants, thanks to an Excel simulation with the real data of the plants used at the same time that the ones obtained in this experimentation.