Anaerobic co-digestion of dairy manure and sugar beets

Bioenergy from dairy manure: technologies, challenges and opportunities

Dairy manure (DM) is a kind of cheap cellulosic biomass resource which includes lignocellulose and mineral nutrients. Random stacks not only leads damage to the environment, but also results in waste of natural resources. The traditional ways to use DM include returning it to the soil or acting as a fertilizer, which could reduce environmental pollution to some extent. However, the resource utilization rate is not high and socio-economic performance is not utilized. To expand the application of DM, more and more attention has been paid to explore its potential as bioenergy or bio-chemicals production. This article presented a comprehensive review of different types of bioenergy production from DM and provided a general overview for bioenergy production. Importantly, this paper discussed potentials of DM as candidate feedstocks not only for biogas, bioethanol, biohydrogen, microbial fuel cell, lactic acid, and fumaric acid production by microbial technology, but also for bio-oil and biochar production through apyrolysis process. Additionally, the use of manure for replacing freshwater or nutrients for algae cultivation and cellulase production were also discussed. Overall, DM could be a novel suitable material for future biorefinery. Importantly, considerable efforts and further extensive research on overcoming technical bottlenecks like pretreatment, the effective release of fermentable sugars, the absence of robust organisms for fermentation, energy balance, and life cycle assessment should be needed to develop a comprehensive biorefinery model.

Agricultural Residue Management for Sustainable Power Generation: The Poland Case Study

The European Union has set targets for renewable energy utilization. Poland is a member of the EU, and its authorities support an increase in renewable energy use. The background of this study is based on the role of renewable energy sources in improving energy security and mitigation of climate change. Agricultural waste is of a significant role in bioenergy. However, there is a lack of integrated methodology for the measurement of its potential. The possibility of developing an integrated evaluation methodology for renewable energy potential and its spatial distribution was assumed as the hypothesis. The novelty of this study is the integration of two renewable energy sources: crop residues and animal husbandry waste (for biogas). To determine agricultural waste energy potential, we took into account straw requirements for stock-raising and soil conservation. The total energy potential of agricultural waste was estimated at 279.94 PJ. It can cover up to 15% of national power generation. The spatial distribution of the agricultural residue energy potential was examined. This information can be used to predict appropriate locations for biomass-based power generation facilities. The potential reduction in carbon dioxide emissions ranges from 25.7 to 33.5 Mt per year.

Sugar beet silage as highly flexible feedstock for on demand biogas production

On demand biogas production is a great option to complement solar and wind power for the energy revolution. Alternatives like feedstock management are important in order to avoid expensive and complex adjustments for gas storage systems. The use of sugar beet silage (S) is a good option because it mainly contains carbohydrates that are easily degradable. Anaerobic digestion was performed for 63 days in four completely stirred tank reactors (CSTR) with different ratios of maize silage (M) and S. M given every hour was used as a base load for the fermentation and S was given two times a day every 12h. Biogas and methane production rates were measured every 5min in order to achieve data with high resolution. Also, pH value, VFA/TIC values and volatile fatty acids were measured during the experiment. The process remained stable in CSTR1 (M:S1:0), CSTR2 (M:S6:1) and CSTR3 (M:S3:1). Instabilities occurred in CSTR4 (M:S1:3) after an operation time of 33 days. Nevertheless, methane yields more than doubled for CSTR3 within 5min after the input of S. Use of sugar beet as a feedstock for biogas production is a further application for this agricultural commodity.

Influence of total solids concentration on the anaerobic co-digestion of sugar beet by-products and livestock manures

A series of batch anaerobic digestion assays were implemented to determine the influence of total solids concentration on the anaerobic digestion of sugar beet by-products and their co-digestion with two kind of livestock manures (pig and cow manures). The two total solid concentrations studied were 8% and 5%. Total solids contents above 8% were not evaluated because of the inappropriate rheological behaviour of sugar beet by-products at these concentrations. The best total solid content tested corresponded to 8%, achieving specific methane yields of 464.3 and 451.4mL/g VS_added for co-digestion with pig manure and cow manure respectively. These data were 1.5 times higher than that obtained for reactors operating with 5% total solids content. For individual digestion of sugar beet by-products, final methane yields operating at 8% were also higher than those measured at 5% total solids concentration. However, in these tests, a large delay in the start of biogas production was registered due to the inhibition caused by the accumulation of volatile fatty acids. No significant differences in the organic matter removal efficiencies were observed for the two total solids contents studied.

Co-Digestion of Sugar Beet Silage Increases Biogas Yield from Fibrous Substrates

This study tested the hypothesis that the easily degradable carbohydrates of the sugar beet silage (S) will improve the anaerobic digestion of grass silage (G) more profoundly compared to co-digestion of sugar beet silage with maize silage (M). M : S and G : S mixtures were tested in two continuous laboratory-scale AD experiments at volatile solid ratios of 1 : 0, 6 : 1, 3 : 1, and 1 : 3 at organic loading rates of 1.5 kgVS m⁻³ day⁻¹. While the sugar beet effects in mixtures with maize silage were negligible, co-digestion with grass silage showed a beneficial performance. There, the specific methane production rate was 0.27 l_N kg⁻¹VS h⁻¹at G : S ratio of 6 : 1 compared to G : S 1 : 0 with 0.14 l_N kg⁻¹VS h⁻¹. In comparison to G : S 1 : 0, about 44% and 62% higher biogas yields were obtained at G : S 6 : 1 and 3 : 1, respectively. Also, the highest methane concentration was found in G : S at ratio of 1 : 3. Synergistic increase of methane yield was found in co-digestion in both experiments, but higher effect was realized in G : S, independently of the amount of sugar beet silage. The findings of this study emphasize the improvement of AD of grass silage by even low addition of sugar beet silage.

Biomethanization of sugar beet byproduct by semi-continuous single digestion and co-digestion with cow manure

Dried pellet of exhausted sugar beet cossettes were digested alone and combined with cow manure as co-substrate in a mesophilic semi-continuous anaerobic system. In single digestion assay, the stable biogas production and stable reactor operation was observed at the hydraulic retention time (HRT) of 20days (OLR: 3.26gVS/Lreactord) which was the minimum HRT tolerated by the system. However, co-digestion with cow manure allowed to decrease the HRT until 15days (OLR: 4.97gVS/Lreactord) with 32% higher biogas generation and efficient reactor operation. Propionic acid was the predominant VFA observed during single digestion assay failure, while acetic acid accumulation was observed in the co-digestion assay. In both single and co-digestion assays, the recovery of digesters was possible by ceasing the feeding and re-inoculation with a well-adapted inoculum.

Anaerobic co-digestion of forage radish and dairy manure in complete mix digesters

Pilot-scale digesters (850 L) were used to quantify CH4 and H2S production when using forage radish cover crops as a co-digestion feedstock in dairy manure-based digesters. During two trials, triplicate mixed digesters were operated in batch mode with manure-only or radish+manure (27% and 13% radish by wet weight in Trial 1 and 2, respectively). Co-digestion increased CH4 production by 11% and 39% in Trial 1 and 2, respectively. As H2S production rapidly declined in the radish+manure digesters, CH4 production increased reaching high levels of CH4 (⩾67%) in the biogas. Over time, radish co-digestion lowered the H2S concentration in the biogas (0.20%) beyond that of manure-only digestion (0.34-0.40%), although cumulative H2S production in the radish+manure digesters was higher than manure-only. Extrapolated to a farm-scale (200 cows) continuous mixed digester, co-digesting with radish could generate 3150 m(3) CH4/month, providing a farmer additional revenue up to $3125/month in electricity sales.

Towards eliminating systematic errors caused by the experimental conditions in Biochemical Methane Potential (BMP) tests

The Biochemical Methane Potential (BMP) test is increasingly recognised as a tool for selecting and pricing biomass material for production of biogas. However, the results for the same substrate often differ between laboratories and much work to standardise such tests is still needed. In the current study, the effects from four environmental factors (i.e. ambient temperature and pressure, water vapour content and initial gas composition of the reactor headspace) on the degradation kinetics and the determined methane potential were evaluated with a 2(4) full factorial design. Four substrates, with different biodegradation profiles, were investigated and the ambient temperature was found to be the most significant contributor to errors in the methane potential. Concerning the kinetics of the process, the environmental factors' impact on the calculated rate constants was negligible. The impact of the environmental factors on the kinetic parameters and methane potential from performing a BMP test at different geographical locations around the world was simulated by adjusting the data according to the ambient temperature and pressure of some chosen model sites. The largest effect on the methane potential was registered from tests performed at high altitudes due to a low ambient pressure. The results from this study illustrate the importance of considering the environmental factors' influence on volumetric gas measurement in BMP tests. This is essential to achieve trustworthy and standardised results that can be used by researchers and end users from all over the world.

Factors in the determination of methanogenic potential of manure

The influence of the substrate concentration, the micro and macro nutrients and buffer requirements, the sludge origin (biomass that is acclimatized or not acclimatized to waste) and the inoculum/substrate ratio (ISR) were studied to determine their effects in the methanogenic potential of turkey manure, which is a solid waste. According to the results obtained, the methane production determination does not require the addition of nutrients (additional to the contents in the waste) and a buffer for this type of assay. The methane yield (γ(CH) ₄) performance is given by the substrate concentration and the sludge origin, therefore it is better to carry out the assay with biomass that is already adapted to the waste. The methanogenic potential of this type of waste is not determined by the amount of sludge and it does not need an external inoculum (external to the waste contents).

Anaerobic co-digestion of by-products from sugar production with cow manure

Sugar beet leaves (SBL), sugar beet top (SBT), sugar beet pulp (SBP) and desugared molasses (DM) are by-products from the sugar production. In the present study we investigated the potential of SBL, SBT and SBP as feedstock for biogas production. The maximum methane potential of SBL, SBT and SBP determined by batch assays was found to be 490, 500 and 240 mL-CH(4)/gVS-added respectively. Three reactor experiments were carried out to investigate the effect of co-digestion of SBP, DM and manure at different ratios, on biogas process efficiency and stability. The results showed that DM was potentially inhibiting the biogas process and the co-digestion of SBP and DM was only successful at high dilution with manure or water. In contrast, SBP was shown to be a good substrate for biogas production and the methane yield of 280 mL-CH(4)/gVS-added was obtained in a thermophilic continuously operated reactor, co-digesting 50% of SBP with cow manure.

Physical-anaerobic-chemical process for treatment of dairy cattle manure

An overall treatment process for the removal of nitrogen, methane production and obtention of valuable fertilizers from dairy manure has been investigated in laboratory scale. Solid and liquid fractions were separated by flocculation and screening. The solid fraction contained 81.6%, 84.4%, 58.6% and 85.2% of TS, VS, TKN-N and P(T) originally present in manure. Batch anaerobic digestion of this solid fraction at 50°C resulted in methane production of 29.0 L CH(4)/kg. The liquid fraction, free of suspended solids, was satisfactorily treated at 35°C in an upflow anaerobic sludge blanket reactor operating stably at an organic loading rate of 40.8 g COD/(L·d) reaching a methane production of 10.3 L CH(4)/(L·d). Accumulation of volatile fatty acids did not occur. Ammonia nitrogen concentration in the anaerobic effluent fluctuated between 850-1170 mg NH(4)(+)-N/L and was reduced to values less than 100mg NH(4)(+)-N/L by struvite precipitation.

Evolution of composition of dairy manure supernatant in a controlled dung pit

Anaerobic conversion of dairy manure into biogas is an attractive way of managing this waste. It is well known that the hydrolysis of large molecules into small, directly biodegradable ones is the rate limiting step of the overall anaerobic process. The present work studies the development of the hydrolytic and acidogenic stages of dairy manure with different solid concentrations (40, 60 and 80 g VS/L) at ambient temperature (20 degrees C). The purpose was to determine the operational conditions that provide a liquid fraction with a high soluble chemical oxygen demand (COD) and a high volatile fatty acids (VFA) content in manure before the methanogenic stage starts up. At 20 degrees C, the evolution of the studied parameters showed that, in a controlled plug-flow dung pit, the hydrolytic and acidogenic stages progressed moderately in a continuous way during the 25 days that the experimentation lasted, whereas no methanization was observed. Supernatant COD and VFA concentrations increased 30% and 107%, respectively, for the 60 g VS/L samples. Manure was also operated at 35 degrees C with a similar increase in supernatant COD but a higher increase in VFA, 154%. For both operational temperatures, the predominant VFAs were, in this order, acetic, propionic and butyric acids. During the operation at 35 degrees C, the methanogenic stage started between days 20 and 25 for the samples with lower solids content, i.e. 40 and 60 g VS/L.

Co-digestion of grass silage and cow manure in a CSTR by re-circulation of alkali treated solids of the digestate

Three laboratory, continuously stirred tank reactors (CSTRs) co-digesting grass silage and cow manure (forming 30% and 70% of substrate volatile solids (VS), respectively) were operated to evaluate the effects of re-circulating an alkali-treated and untreated solid fraction of the digestate back to the reactors. The CSTRs were operated at an organic loading rate (OLR) of 2 kg VS m(-3) day(-1) and hydraulic retention time (HRT) of 20 days with a semi-continuous mode of feeding. The feasibility of co-digestion with substrate VS containing 30% VS of crop was reinforced, resulting in average specific methane yield of about 180-185 1 CH4 kg(-1) VS. Re-circulation of the solid fraction of digestate back to the reactors in both alkali-treated and untreated forms decreased the methane yield by 11% and 21%, respectively, and resulted in operational problems such as scum formation and accumulation of the reactor materials. Batch studies were conducted to evaluate (i) the methane potentials of the solid fraction of digestate, and whole digestate with alkali treatments ranging from 20-60 g NaOH kg(-1) VS of substrate, and (ii) methane potentials of the accumulated reactor materials as top, middle and bottom layers. The solid fraction of digestate treated with 20 g NaOH kg(-1) VS showed higher specific methane yield (340 l CH4 kg(-1) VS) than the higher range of alkali treatments. The bottom layers of the control reactor and the reactor fed with alkali-treated solids gave a higher specific methane yield (93 and 85 l CH4 kg(-1) VS, respectively), and all three layers of untreated solids gave similar methane potentials.