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The increasing demand for methane production cannot be satisfied by the use of anaerobic digestion only from waste/wastewater treatment. Perennial energy crops, such as miscanthus and willow, as well as agricultural residues can be considered as options for increasing the methane production through biomass digestion, due to their high organic content and biomass yield. These materials present a great potential, which is only limited by the rigid lignocellulosic structure. In this case, it is possible to apply a pretreatment step in order to achieve increased biogas production. In the present study, aqueous ammonia soaking (AAS) has been investigated as a method to disrupt the lignocellulosic structure and increase the methane yield of wheat straw, miscanthus and willow. Among the three biomasses tested, wheat straw and miscanthus were the most promising in terms of methane production, yielding around 200 and 230 ml of methane per gram of total solids. In all three cases, AAS resulted to an increase in methane yield of 37-41%, 25-27% and 94-162% for wheat straw, miscanthus and willow, respectively. A comparison of the methane yields after 20 and 50 days of anaerobic digestion revealed that AAS affected positively the methane production rate as well. AAS also resulted to a low solubilization of sugars, with a 15.4% and 8.9% increase in soluble xylose concentration in miscanthus and willow, respectively, and a 5% solubilization of glucose in AAS-pretreated miscanthus.

Abstract:The continuously increasing demand for renewable energy sources renders anaerobic digestion one of the most promising technologies for renewable energy production. Due to the animal production intensification, manure is being used as the primary feedstock for most biogas plants. Thus, their economical profitable operation relies on increasing the methane yield from manure, and especially of its solid fraction which is not so easily degradable. In the present study, aqueous ammonia soaking (AAS) at six different concentrations in ammonia (5%, 10%, 15%, 20%, 25% and 32%) and for 1, 3 and 5 days at 22 °C was applied on digested fibers separated from the effluent of a manure-fed, full-scale anaerobic digester. A methane yield increase from 76% to 104% was achieved during the first series of experiments, while the difference in reagent concentration did not considerably affect the methane yield. It was shown that the optimal duration was three days for both 5% and 25% w/w reagent concentrations in ammonia tested. Carbohydrates and phosphorus content remained unaffected, while a slight decrease in Klason lignin and non-soluble organic nitrogen content was observed after AAS. It is concluded that AAS is a very promising treatment resulting to an overall increase of the methane yield of digested manure fibers from 76% to 265% depending on the conditions and the batch of digested fibers used (an even higher increase of 190%-265% was achieved during the 2nd series of OPEN ACCESSEnergies 2014, 7 4158 experiments, where different AAS durations were tested, compared to the 1st series were different ammonia concentrations were applied).

Continuous anaerobic digestion of swine manure: ADM1-based modelling and effect of addition of swine manure fibers pretreated with aqueous ammonia soaking Jurado, E.; Antonopoulou, G.; Lyberatos, G.; Gavala, Hariklia N.; Skiadas, Ioannis V.

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