Græs er ægte grøn energi

Græs fra engarealer kan mere end fordoble produktionen af biogas, og energibalancen er markant bedre end ved traditionelle landbrugsafgrøder som majs og korn. Samtidig får man fjernet næringsstofferne fra de følsomme områder, og man undgår, at arealerne ender med at blive til skov

The Effect of Low-Temperature Thermal Pre-Treatment on Methane Yield of Pig Manure Fractions

Abstract.  The aim of the present study was to evaluate the effect of low-temperature thermal pre-treatment on the methane yield of pig manure fractions. Four different temperatures ranging from 65°C to 80°C were applied for 20 h to whole pig manure and the solid fraction of pig manure derived from solid-liquid manure separation. The results showed significant improvements in methane yield both in pig manure and solid-fraction pig manure at 11 d of the batch digestion test. The improvement was between 9.5-22.5% for pig manure and 6.1-25.3% for solid fraction pig manure. However, at 90 d of the batch digestion assay the effect of low-temperature pre-treatment on methane yield was significant only for the 65°C treatment. Application of low-temperature thermal pre-treatment appears to be a promising method to improve methane yield of pig manure fractions, particularly when surplus thermal energy is available. Key words: biogas, anaerobic digestion, thermal pre-treatment, pig manure, methane. Abstrak.   Penelitan ini bertujuan untuk mengevaluasi pengaruh pre-treatment pada suhu rendah terhadap produksi methan dari bagian manure babi. Perlakuan pre-treatment yang digunakan berupa empat level temperatur mulai dari 65°C sampai dengan 80°C selama 20 jam yang diterapkan pada manure babi dan bagian padat manure babi yang diperoleh dari pemisahan bagian cair dan bagian padat manure babi. Hasil penelitian menunjukkan adanya peningkatan produksi methan secara signifikan setelah 11 hari inkubasi dengan digester model batch. Produksi methane meningkat antara 9,5-22,5% pada manure babi dan 6,1-25,3% pada bagian padat manure babi. Namun demikian setelah 90 hari inkubasi, pengaruh dari penggunaan pre-treatment pada suhu rendah hanya berpengaruh siginifikan pada temperatur 65°C saja. Penggunaan pre-treatment pada suhu rendah menunjukkan bahwa metode tersebut merupakan metode yang menjanjikan untuk meningkatkan produksi methan dari manure babi khususnya apabila terdapat surplus energi. Kata kunci : biogas, digesti secara anaerob, pre-treatment dengan pemanasan, manure babi, metha

Improved anaerobic biodegradability of wheat straw, solid cattle manure and solid slaughterhouse by alkali, ultrasonic and alkali-ultrasonic pre-treatment

Wheat straw and animal wastes are important feedstock for biogas production in Europe. Yet, the high content of lignocellulosic and refractory materials causes the process to be relatively slow. Therefore, pretreatment methods have been proposed to shorten the hydrolysis phase. The present study examined the effectiveness of alkali pre-treatment (AP), ultrasonic pre-treatment (UP), and alkali-ultrasonic pre-treatment (AUP) applied on wheat straw (WS), solid fraction of cattle manure (SCM) and solid fraction of slaughterhouse waste (SSHW), by monitoring solubilisation ratio, anaerobic biodegradability and methane yield. The results indicate that the solubilisation ratio of the substrates improved regardless of the types of pre-treatment applied. Though, AP was more effective on WS and SSHW than other pre-treatments (UP and AUP), with approximately 47% and 17% extra methane, respectively. Moreover, AP of SCM caused an increased in methane production rate by 100% and minimised lag phase from 16 days to 1 day during anaerobic digestion. Based on Danish conditions, only AP of WS was economical prior to the biogas process due to high extra methane yield. A positive energy budget of 8 € t−1 VS was calculated. High-energy consumption during UP and AUP in laboratory scale hindered the positive benefits of these pre-treatments.info:eu-repo/semantics/acceptedVersio

Effects of electrokinetic and ultrasonication pre-treatment and two-step anaerobic digestion of biowastes on the nitrogen fertiliser value by injection or surface banding to cereal crops

Biogas production from anaerobic digestion (AD) of biowastes is restricted by the recalcitrant nature of many substrates, and this may also reduce the fertiliser value of the produced digestate. The degradability of substrates can potentially be enhanced by physico-chemical pre-treatments before AD, and/or the degradation can be increased by a longer digestion time. In this study, we evaluated the effects of electrokinetic (high voltage) and ultrasonication pre-treatments of biowastes in a two-step AD process on nitrogen fertiliser replacement value (NFRV) of digestates obtained from two biogas plants with contrasting hydraulic retention time (HRT) in the primary AD step. The fertiliser value was tested by direct injection to spring barley and surface-banding to winter wheat, and the ammonium N was 15N-labelled to evaluate ammonia losses. The electrokinetic pre-treatment step significantly (p < 0.05) increased the NH4+-N/total N in the digestates before the second AD step but had an insignificant effect on the fertiliser value in winter wheat and spring barley. Ultrasonication pre-treatment had also no significant effect on the fertiliser value. The two-step AD significantly (p < 0.001) increased 15N recoveries and mineral fertiliser equivalence of labelled ammonium-N in winter wheat and reduced ammonia losses, with a significant effect (p < 0.001) observed in digestates sourced from a shorter HRT biogas reactor. The fertiliser equivalence of labelled ammonium-N in the digestates was 80–88% after injection, indicating relatively low N immobilisation with all the digestates. NFRV in the crops was mainly explained by the NH4+-N/total N ratio, C/N ratio and dry matter content of the digestates. The findings suggest that electrokinetic and ultrasonication pre-treatments combined with a second AD step have no considerable impact on the fertiliser value of digestates, whereas a second AD step significantly reduced ammonia losses after application by surface-banding in winter wheat

Nitrogen dynamics and carbon sequestration in soil following application of digestates from one- and two-step anaerobic digestion

Anaerobic digestion (AD) is an important tool for reducing greenhouse gas emissions from agricultural production. A prolonged retention time by adding an extra anaerobic digestion step can be utilized to further degrade the digestates, contributing to increased nitrogen mineralisation and reducing decomposable organic matter. These modifications could influence the potential N fertiliser value of the digestate and soil carbon sequestration after field application. This study investigated the effects of prolonging retention time by implementing an additional anaerobic digestion step on carbon and nitrogen dynamics in the soil and soil carbon sequestration. Two digestates obtained from two biogas plants operating at contrasting hydraulic retention times, with and without an additional digestion step, were applied to a loamy sand soil. N mineralisation dynamics were measured during 80 days and C mineralisation during 212 days. After 80 days of incubation, the net inorganic N release from digestates obtained from a secondary AD step increased by 9–17 % (% of the N input) compared to corresponding digestates obtained from a primary AD step. A kinetic four-pool carbon model was used to fit C mineralisation data to estimate carbon sequestration in the soil. After 212 days of incubation, the net C mineralisation was highest in undigested solid biomass (68 %) and digestates obtained from the primary AD step (59–65 %). The model predicted that 26–54 % of C applied is sequestered in the soil in the long-term. The long-term soil C retention related to the C present before digestion was similar for one- and two-step AD at 12–16%. Weconclude that optimizing the anaerobic digestion configurations by including a secondary AD step could potentially replace more mineral N fertiliser due to an improved N fertiliser value of the resultant digestate without affecting carbon sequestration negatively