Effect of Aqueous Ammonia Soaking on the Methane Yield and Composition of Digested Manure Fibers Applying Different Ammonia Concentrations and Treatment Durations

Abstract

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).

AMMONOX: Ammonia for Enhancing Biogas Yield and Reducing NOx—Analysis of Effects of Aqueous Ammonia Soaking on Manure Fibers

“…Finally, wet explosion of digested manure fibers resulted in a 136 % increase of CH 4 yield [27]. In comparison to the results obtained so far from these pretreatments, AAS of digested manure fibers has achieved an increase of CH 4 yield up to 205 % (265 % at 17 days of digestion) when compared to nontreated fibers [9]. In order to identify the important factors that affected the performance of AAS on digested manure fibers, a statistical tool was used for analyzing the results obtained up to now.…”

“…All the experimental data used in this analysis originate from research at Aalborg University and are published in Jurado et al [17] and Mirtsou-Xanthopoulou et al [9]. The data consist of CH 4 yields of digested swine manure fibers pretreated with AAS under two different temperatures (22 and 55°C), three different pretreatment durations (1, 3 and 5 days) and six different NH 3 concentrations of the reagent (5, 10, 15, 20, 25 and 32 % w/w).…”

“…The data consist of CH 4 yields of digested swine manure fibers pretreated with AAS under two different temperatures (22 and 55°C), three different pretreatment durations (1, 3 and 5 days) and six different NH 3 concentrations of the reagent (5, 10, 15, 20, 25 and 32 % w/w). All pretreatment mixtures were further used for experiments after a distillation step where the NH 3 concentration was reduced to belowinhibition levels [9]. Two data sets were formed for the data exploration analysis, both originating from the same experiments.…”

“…Jurado et al [17] have performed AAS of digested manure fibers under different levels of temperature and duration achieving an increase of methane yield between 30 and 80 %. Further experiments with lower ammonia concentrations led to a higher increase of methane yield (up to 205 %) [9]. Batch experiments for the determination of the methane potential of AAS-pretreated raw manure fibers showed that AAS pretreatment increased the methane yield by 178 % compared to non-pretreated fibers [17].…”

“…Various researchers have used different approaches for pretreating manure fibers in order to make them more easily degradable and increase the methane yield. According to a recent survey [9], aqueous ammonia soaking (AAS) has achieved the highest increase of methane yield of manure fibers, both of raw (separated from manure) and digested (separated from the effluent after a first digestion).…”