Abstract
Two stages anaerobic digestion of the organic fraction of municipal solid wastes (OFMSW) is proposed using a batch anaerobic trickling bed (BATB) reactor in the first hydrolysis and acidogenesis stage. At total solids loading of 135 g/L and reaction times around 30 days, total solids (ηTS) and chemical oxygen demand (ηCOD) removal efficiencies above 46% were obtained independently of pH (between 4.1 and 6.4). Dependent on pH were methane production, four times more at pH 6.4 than at 4.8 and four times more volatile fatty acids (VFA) production at 6.4 than at 4.1 and twice than at 4.8. Leachates generated in the BATB reactor were diluted with municipal wastewater and fed to an upflow anaerobic sludge blanket (UASB) reactor at volumetric organic loading rates from 11 to 28 g/L.d where 90% COD removal efficiencies (ηCOD) and 11.4 g CODCH4./L.d were obtained. Two stages anaerobic digestion results in high rates of solids removal and methane production (0.63 kWhr/kg TS fed).
Highlights
The total generation of municipal solid wastes in Mexico reached 40 million tons in 2010, where the organic fraction (OFMSW) was 53%
Two stage anaerobic digestion of OFMSW in compact and controlled reactors is a sustainable treatment, because they can be installed in small plants within the cities reducing transportation costs and using in the surroundings methane, to produce enough energy to carry out the entire management of the municipal solid wastes [2]
All the reported two stage processes are based on the use of water, to obtain slurries to produce volatile fatty acids (VFA) which need to be neutralized and supplemented with nutrients in order to be methanized. For these reasons this study aimed to evaluate the anaerobic digestion in two stages of OFMSW (15 % TS): hydrolysis and acidogenesis in a batch anaerobic trickling bed (BATB) reactor to maintain the normal humidity of the OFMSW by trickling of a small amount municipal wastewater (MWW) over the solids bed; and acetogenesis and methanogenesis of the leachate, diluted as needed with MWW, in a upflow anaerobic sludge bed (UASB) reactor, in order to use the waste generated in cities
Summary
The total generation of municipal solid wastes in Mexico reached 40 million tons in 2010, where the organic fraction (OFMSW) was 53%. Landfilling in Mexico is not a sustainable alternative to dispose of the OFMSW because due to the extended treatment area they need can only be located in the outer reaches of the cities where transportation of wastes is expensive and use of delayed and uncontrolled methane production is inefficient. Two stage anaerobic digestion of OFMSW in compact and controlled reactors is a sustainable treatment, because they can be installed in small plants within the cities reducing transportation costs and using in the surroundings methane, to produce enough energy to carry out the entire management of the municipal solid wastes [2]. In a second methanogenic stage these VFA can be transformed to methane in an upflow anaerobic sludge bed (UASB) reactor
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