| 1. |
- Gissén, Charlott, et al.
(författare)
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Comparing energy crops for biogas production Yields, energy input and costs in cultivation using digestate and mineral fertilisation
- 2014
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Ingår i: Biomass & Bioenergy. - : Elsevier BV. - 1873-2909 .- 0961-9534. ; 64, s. 199-210
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Tidskriftsartikel (refereegranskat)abstract
- Analyses of six crops grown in southern Sweden for biogas production (hemp, sugar beet, maize, triticale, grass/clover ley, winter wheat) showed varying performance regarding methane yield per hectare and energy input and costs in the production and supply of crops as biogas feedstock. The highest biomass and biogas yield was observed for sugar beet. Crops with lower risk of negative environmental impact in cultivation, such as ley and hemp, produced less than half the methane energy yield per hectare. Triticale, also having less risk of negative environmental impact, gave an energy yield similar to that of winter wheat grain and maize. Replacing most of the mineral fertiliser with biogas digestate did not, with the exception for hemp, influence crop yields per hectare, but energy input in cultivation decreased by on average 34% for the six crops tested. For hemp and sugar beet the biogas feedstock costs for the freshly harvested crop per GJ methane were close to that of the economic reference crop, winter wheat grain. For maize, beet tops and first and second year ley, the feedstock costs were lower, and for triticale much lower. When ensiled crops were used for biogas the feedstock costs increased and only those of triticale silage remained slightly lower than the cost of dried wheat grain. However, all feedstock costs were so high that profitable biogas production based solely on ensiled crops would be difficult to achieve at present Swedish biogas sales prices. (c) 2014 Elsevier Ltd. All rights reserved.
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| 2. |
- Ivo Achu, Nges
(författare)
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Anaerobic digestion of crop and waste biomass: Impact of feedstock characteristics on process performance
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Anaerobic digestion provides an array of positive environmental benefits such as reducing greenhouse gas emissions, replacing mineral fertilizers, producing renewable energy and treating waste. However, pitfalls in anaerobic digestion such as poor methane yields, process instability, process failure and regional shortages of feedstock have limited the full exploitation of the anaerobic digestion process. The research presented in this thesis deals with the assessment of the possible negative or positive impacts of feedstock characteristics on the efficiency of anaerobic digestion. In addition, it investigates ways of enhancing the methane yield of the feedstock by improving the feedstock characteristics. The feedstocks investigated were various energy crops, food industrial waste and sewage sludge. The improvement methods investigated were ensiling, nutrient supplementation, co-digestion and anaerobic pretreatment. It was found that ensiling crops results in insignificant losses in energy, total solid and wet weight. In addition, no significant difference was found in methane yields between the ensiled and fresh crop samples. The importance of correcting for losses of volatiles in total solids determination was pointed out and it was shown that failing to do so could be the main reason why many previous publications report increased total solid based methane yields after ensiling. Increased methane yield in silages may therefore be an effect of an analytical error rather than an effect of using ensiling as a pretreatment prior to anaerobic digestion. Anaerobic digestion of crop biomass is known to be particularly limited by nutrient availability. Direct nutrient supplementation in crop mono-digestion in this research demonstrated an efficient biogas process at the shorter hydraulic retention times commonly applied in co-digestion of crop biomass and manure. The high degradation efficiency was evidenced by high methane yields, comparable to maximum expected yields generated under controlled conditions, and low volatile fatty acids accumulation. As a result of nutrient addition, the digestate could comply with certification standards for bio-fertilizer. Also, viscosity problems commonly reported for crop mono-digestion were not observed in this study, which could be another effect of nutrient addition. Co-digesting of waste biomass and crop biomass led to significant improvement in methane yield per ton of feedstock and carbon to nitrogen ratio as compared to digestion of only the waste biomass. Biogas production from crops in combination with waste biomass also eliminated the need for addition of micronutrients normally required in crop mono-digestion. Co-digestion was also presented as a means of feedstock supplementation to curb feedstock shortages in waste-based anaerobic digestion processes. In addition, inhibitors in anaerobic digestion such as free ammonia and light metal ions were diluted, a condition which can lead to an overall viable biogas process Anaerobic pre-treatment led to the solubilisation of particulate organic matter in sewage sludge. This solubilisation could have led to the improved methane yield, methane production rate and reduction in volatile solids. Applying different feedstock improvement solutions to the various feedstocks investigated, i.e. nutrient addition, co-digestion and pretreatment, were demonstrated as effective means of enhancing the methane yield of the feedstock thereby improving the overall anaerobic digestion process.
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| 3. |
- Ivo Achu, Nges, et al.
(författare)
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Benefits of supplementing an industrial waste anaerobic digester with energy crops for increased biogas production.
- 2012
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Ingår i: Waste Management: international journal of integrated waste management, science and technology. - : Elsevier BV. - 1879-2456. ; 32:1, s. 53-59
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Tidskriftsartikel (refereegranskat)abstract
- Currently, there is increasing competition for waste as feedstock for the growing number of biogas plants. This has led to fluctuation in feedstock supply and biogas plants being operated below maximum capacity. The feasibility of supplementing a protein/lipid-rich industrial waste (pig manure, slaughterhouse waste, food processing and poultry waste) mesophilic anaerobic digester with carbohydrate-rich energy crops (hemp, maize and triticale) was therefore studied in laboratory scale batch and continuous stirred tank reactors (CSTR) with a view to scale-up to a commercial biogas process. Co-digesting industrial waste and crops led to significant improvement in methane yield per ton of feedstock and carbon-to-nitrogen ratio as compared to digestion of the industrial waste alone. Biogas production from crops in combination with industrial waste also avoids the need for micronutrients normally required in crop digestion. The batch co-digestion methane yields were used to predict co-digestion methane yield in full scale operation. This was done based on the ratio of methane yields observed for laboratory batch and CSTR experiments compared to full scale CSTR digestion of industrial waste. The economy of crop-based biogas production is limited under Swedish conditions; therefore, adding crops to existing industrial waste digestion could be a viable alternative to ensure a constant/reliable supply of feedstock to the anaerobic digester.
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| 4. |
- Ivo Achu, Nges, et al.
(författare)
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Digestate liquor recycle in minimal nutrients-supplemented anaerobic digestion of wheat straw
- 2015
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Ingår i: Biochemical Engineering Journal. - : Elsevier BV. - 1369-703X. ; 94, s. 106-114
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Tidskriftsartikel (refereegranskat)abstract
- Anaerobic digestion (AD) of minimal nutrient-supplemented wheat straw and digestate liquor recycle was evaluated in semi-continuous processes using a novel BioReactor Simulator developed for easy accurate online normalised-gas measurement. Three scenarios (i) no recycle (NR), (ii) recycle of soluble nutrient (RSN), and (iii) recycle of nutrient and microbes (RNM) were investigated in order to evaluate their respective efficiencies. Although mono-digestion of lignocellulosic biomasses are often performed with very long solid retention times (SRT), the present study demonstrated an efficient process operating with a 30-day SRT and an organic loading rate of 4 gVS/L d. The best methane yield was 303 mLCH(4)/g VS achieved in the RSN process showing a 21% improvement as compared to the NR process. The methanogenic potential of the digestates from the RSN and RNM processes was comparable to fresh inoculum indicating efficient processes. The RNM and RSN processes showed superior process stability evidenced by minimal volatile fatty acid accumulation (<0.5 g/L). As compared to the RNM process, RSN demonstrated the best performance. The improved process performance was probably due to higher nutrient and microbial concentration in the digestate-recycled processes. This study confirms the feasibility of digestate recycle in AD as an appropriate technology for treating nutrient-deficient substrates.
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| 5. |
- Ivo Achu, Nges, et al.
(författare)
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Effects of anaerobic pre-treatment on the degradation of dewatered-sewage sludge
- 2009
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Ingår i: Renewable Energy. - : Elsevier BV. - 0960-1481. ; 34:7, s. 1795-1800
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Tidskriftsartikel (refereegranskat)abstract
- Effects of anaerobic pre-treatment were evaluated on the dewatered-sewage sludge from a municipal wastewater treatment plant in order to improve its biodegradability through anaerobic digestion. The pre-treatment was conducted in laboratory scale at 25, 50 and 70 degrees C for an incubation time of two days. As a reference, sludge sample was also autoclaved at 121 degrees C for 20 min to determine the thermal effect to the subsequent sludge digestion. Characteristics of dewatered-sludge such as viscosity, pH and soluble chemical oxygen demand (SCOD) were affected by the pre-treatment. A higher SCOD after the pretreatment did not necessarily imply an increase in methane yield, although initial biodegradability rate was improved. In fact, a 'great' improvement in SCOD concentration (up to 27%) was translated in only 8% increase in the methane yield (298 +/- 9 and 276 +/- 6 Nml CH4 gVS(added)(-1) for pre-treated and untreated samples, respectively). Increasing the anaerobic pre-treatment time from 12 h to 2 days at 50 degrees C led to an 11% improvement in methane yield. Methane content in biogas increased from an average of 65-69% for the pre-treated and untreated substrates, respectively. Volatile solids (VS) reduction increased from 42% to 51%. The overall digestion time was not affected by the pre-treatment but 90% of methane was produced in the first 12 days of incubation for 50 degrees C pre-treated samples whereas it took 2-5 days more for 25, 70 degrees C pre-treated and untreated sludge samples. In this study, thermophilic digestion was also found to be a better option in terms of faster digestion and higher VS-reduction, but it showed lower methane yield as compared to mesophilic digestion, i.e. 9% and 11% increment in methane yields for thermophilic and mesophilic digestions, respectively. (C) 2008 Elsevier Ltd. All rights reserved.
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| 6. |
- Ivo Achu, Nges, et al.
(författare)
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Effects of solid retention time on anaerobic digestion of dewatered-sewage sludge in mesophilic and thermophilic conditions
- 2010
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Ingår i: Renewable Energy. - : Elsevier BV. - 0960-1481. ; 35:10, s. 2200-2206
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Tidskriftsartikel (refereegranskat)abstract
- Anaerobic digestion of dewatered-sewage sludge using continuous stirred tank reactors (CSTRs) in duplicates was evaluated under thermophilic (50 degrees C) and mesophilic (37 degrees C) conditions over a range of nine solid retention times (SRTs). The 35- and 30-day SRTs were designed to simulate a full-scale plant operation while 25-, 20-, 15- and 12-day SRTs were planned to evaluate process performance at the various SRTs. The 9-, 5- and 3-day SRTs were performed to push the reactors to extend their degradation capacity and test the threshold for process imbalance. The corresponding organic loading rates (OLR) varied from 1.6 to 20.5 kg VS m(-3) Biogas production rate could be tripled when the SRT was shortened from 30 to 12 days and more than doubled from 35- to 15-day SRT because of a concomitant increase in OLR. In general, higher biogas productivity was realized under thermophilic, but methane yields were comparable due to the higher methane content in the biogas under mesophilic digestion. The methane content in biogas fluctuated between 55 and 65% and the methane yield ranged from 0.314 to 0.348 Nm(3) CH4 kg VSadded-1 day(-1) for both thermophilic and mesophilic digestion. The VS-reduction at 12- and 15-day SRT ranged from 45 to 52% and there was no accumulation of VFAs. Increasing concentrations of VFAs, decreasing concentration of partial alkalinity and decrease in pH were noted as signs of reactor instability. Process imbalance started at 9-day SRT, souring of the reactors, cell wash-out and foaming was noted as the principal causes of process failure under both thermophilic and mesophilic conditions. This study projected the possibility of using CSTRs in treating dewatered-sewage sludge at a shorter SRT to achieve reasonable biogas production and VS-reduction without encountering adverse operation conditions as foaming and wash-out of cells. Crown Copyright (c) 2010 Published by Elsevier Ltd. All rights reserved.
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| 7. |
- Ivo Achu, Nges, et al.
(författare)
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High methane yields and stable operation during anaerobic digestion of nutrient-supplemented energy crop mixtures
- 2012
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Ingår i: Biomass & Bioenergy. - : Elsevier BV. - 1873-2909 .- 0961-9534. ; 47, s. 62-70
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Tidskriftsartikel (refereegranskat)abstract
- The feasibility of digesting energy crops supplemented with macro- and micronutrients instead of manure, without the commonly applied long hydraulic retention time (HRT), was investigated in long-term, single-stage continuous stirred tank processes. The crops used were mixtures of sugar beets, maize and whole crop triticale. The organic loading rate (OLR) measured as a total solid (TS) was 1.5-5.5 kg m(-3) d(-1) and the HRT from 30 to 40 days. The results showed high methane yields, comparable to those in batch digestion, and high stability. The digestion of beets only was most stable, and showed the highest average TS-based methane yield (383 +/- 26 m(3) kg(-1)) at an OLR of 4.5 kg m(-3) d(-1) and a HRT of 40 days. No significant difference in methane yield was found for all the crop mixtures during stable operation. Nutrient addition therefore showed the same stimulatory and stabilising effects as manure with high methane yields achieved at relatively short HRTs. (c) 2012 Elsevier Ltd. All rights reserved.
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| 8. |
- Ivo Achu, Nges, et al.
(författare)
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Improved utilization of fish waste by anaerobic digestion following omega-3 fatty acids extraction.
- 2012
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Ingår i: Journal of Environmental Management. - : Elsevier BV. - 0301-4797. ; 110, s. 159-165
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Tidskriftsartikel (refereegranskat)abstract
- Fish waste is a potentially valuable resource from which high-value products can be obtained. Anaerobic digestion of the original fish waste and the fish sludge remaining after enzymatic pre-treatment to extract fish oil and fish protein hydrolysate was evaluated regarding the potential for methane production. The results showed high biodegradability of both fish sludge and fish waste, giving specific methane yields of 742 and 828 m(3)CH(4)/tons VS added, respectively. However, chemical analysis showed high concentrations of light metals which, together with high fat and protein contents, could be inhibitory to methanogenic bacteria. The feasibility of co-digesting the fish sludge with a carbohydrate-rich residue from crop production was thus investigated, and a full-scale process outlined for converting odorous fish waste to useful products.
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| 9. |
- Ivo Achu, Nges, et al.
(författare)
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Physio-chemical pretreatments for improved methane potential of Miscanthus lutarioriparius
- 2016
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Ingår i: Fuel. - : Elsevier BV. - 1873-7153 .- 0016-2361. ; 166, s. 29-35
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Tidskriftsartikel (refereegranskat)abstract
- Bio-energy production from lignocelluloses biomass has gained a lot of interest in recent years. Miscanthus sp. are high lignocelluloses biomass yielding with relatively high carbohydrate content cultivable on different soils and under climatic conditions. However, the lignocellulosic nature means that cellulose and hemicellulose are cover by lignin network that might limit hydrolysis. In this study, physical pretreatments (size reduction), physiochemical (steam expulsion) and chemical pre-treatments (mild acid and alkaline) were investigated in a view to improve the anaerobic biodegradability of Miscanthus lutarioriparius for biogas production. Prior to the pretreatment and methane potential test, the compositional analyses of M. lutarioriparius was performed in order unveil the carbohydrate (cellulose and hemicelluloses), protein and lignin contents. From these analyses, the maximum theoretical methane potential was estimated. All pretreatments led to solubilisation of organic matter as was evidenced by increase dissolve COD and ammonium nitrogen. There was a positive correlation between dissolved COD and methane yields meanwhile a negative correlation was observed for reducing sugar and methane yields. The achieved methane yields ranged from 121 to 238 ml CH4/g VS. Steam explosion, 0.3 M NaOH treatment and 0.5 mm size reduction led to the highest increases in methane yields, which was in the order of 57% with regard to the untreated samples. These improvements resulted in 71% of theoretical methane yield of M. lutarioriparius. Alkaline pretreatment in particular also improve the rate of methane production as was evidenced by the fact that as high 15% of the final methane yield that was achieve on the first day as compared to only 3% for the untreated sample. Indeed, the time to reach 90% of the ultimate methane yield was reduced by 13 days following 0.3 M NaOH treatment. M. lutarioriparius may therefore represent an interesting candidate as a lignocellulosic feedstock for biogas production after suitable pretreatment. (C) 2015 Elsevier Ltd. All rights reserved.
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| 10. |
- Ivo Achu, Nges, et al.
(författare)
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Stable operation during pilot-scale anaerobic digestion of nutrient-supplemented maize/sugar beet silage
- 2012
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Ingår i: Bioresource Technology. - : Elsevier. - 0960-8524 .- 1873-2976. ; 118, s. 445-454
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Tidskriftsartikel (refereegranskat)abstract
- Biogas production from maize/sugar beet silage was studied under mesophilic conditions in a continuous stirred tank reactor pilot-scale process. While energy crop mono-digestion is often performed with very long hydraulic retention times (HRTs), the present study demonstrated an efficient process operating with a 50-day HRT and a corrected total solids (TScorr) based organic loading rate of 3.4 kg/m3×d. The good performance was attributed to supplementation with both macro- and micronutrients and was evidenced by good methane yields (318 m3/ton TScorr) which were comparable to laboratory maximum expected yields plus low total volatile fatty acid concentrations (< 0.8 g/L). A viscoplastic and thixotropic digester fluid behaviour was observed, and the viscosity problems common in crop mono-digestion were not seen in this study. The effluent also complied with Swedish certification standards for bio-fertilizer for farmland application. Nutrient addition thus rendered a stable biogas process, while the effluent was a good quality bio-fertilizer.
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