Organic material decomposition and nutrient dynamics in a mulch system enriched with leguminous trees in the Amazon

As novas técnicas propostas para a agricultura na Amazônia incluem sistema de rotação de capoeira enriquecido com árvores leguminosas e transformando a queima da biomassa em cobertura morta sobre o solo. A decomposição e a liberação de nutrientes da cobertura morta foram estudadas usando sacos de liteira com malha fina que continham cinco tratamentos com diferentes espécies de leguminosas em comparação a um tratamento-controle com vegetação natural. As amostras para cada tratamento foram analisadas para conteúdos de C total, N, P, K, Ca, Mg, lignina, celulose e polifenóis solúveis em diferentes tempos de amostragem durante um ano. A razão constante de decomposição variou com a espécie e com o tempo. A perda de massa nos sacos de decomposição foi de 30,1 % para Acacia angustissima, de 32,7 % para Sclerolobium paniculatum, de 33,9 % para Inga edulis e para a vegetação secundária, de 45,2 % para Acacia mangium e de 63,6 % para Clitoria racemosa. Foi observada imobilização de N e P em todos os tratamentos, sendo a mineralização do N negativamente correlacionada com o fenol, razão C/N, razão (lignina + fenol)/N, razão fenol/P e o conteúdo de N nos sacos de liteira. Depois de 362 dias de incubação no campo, 3,3 % de K, 32,2 % de Ca e 22,4 % de Mg permaneceram no material em decomposição. Os resultados evidenciaram que a baixa qualidade mineral e a alta quantidade de carbono orgânico e aplicado como cobertura morta podem limitar a quantidade de energia disponível para os microrganismos resultando em uma competição por nutrientes com as plantas agrícolas.

Kinetic study on thermal decomposition of woods in oxidative environment

The purpose of this work is to gain knowledge on kinetics of biomass decomposition under oxidative atmospheres, mainly examining effect of heating rate on different biomass species. Two sets of experiments are carried out: the first set of experiments is thermal decomposition of four different wood particles, namely aspens, birch, oak and pine under an oxidative atmosphere and analysis with TGA; and the second set is to use large size samples of wood under different heat fluxes in a purpose-built furnace, where the temperature distribution, mass loss and ignition characteristics are recorded and analyzed by a data post-processing system. The experimental data is then used to develop a two-step reactions kinetic scheme with low and high temperature regions while the activation energy for the reactions of the species under different heating rates is calculated. It is found that the activation energy of the second stage reaction for the species with similar constituent fractions tends to converge to a similar value under the high heating rate.

森林生态系统的养分循环-一个温带落叶阔叶林生态系统的研究

l、有机质和全N在草甸土壤的不同层次之间呈现明显的差异，表现力随着土壤深度的增加，含量逐渐降低。无机N包括NH4+-N和No3--N在土层之闻的差异并没有象全N和有机质那么显著。NH4+-在表面30Cm的土壤中明显高于NO3--N的。全P在各层土壤中的含量差异并不显著，但有效p在三层土壤中表现出明显的差异，表现为随土壤深度的增加而降低。 K、Na、Ca、Mg、Fe和AI等6种金属元素的可交换成分在革甸土壤中的含量除K表现出明显的土层间的差异外，在表层30cm的土壤中并没有明显的随土壤深度变化的趋势。 有机质和全N在东灵山地区主要森林土壤中的含量以0~lOcm土层中的显著高于10~20cm的土层中的。20cm的土层中无机N中也以NH4+-为主，这与草甸土壤中的一致。全p和有效P在两个土层之间的差异并不十分显著，而以0^lOcm土层略高于10～20Cm土层的。 K、Na、Ca、Mg、Fe和AI等6种金属元素的可交换成分在不同土层间的差异以K和Ca较为明显，K和Ca在O—1Ocm的土层中要高于lO-20cm的。 森林土壤中的有机质、全N（包括NH4+-N）、全p（包括有效P)都表现为低于亚高山草甸土壤中的，主要原因是亚高山革甸分布于海拔1800cm至2300m，而主要森林类型则基本分布在海拔120m至1500m，亚高山草甸较为恶劣的气候条件明显不利于有机质的矿化，因而分解速率较低，积聚了较多的有机质．而森林土壤中较低的NH4+-N和有效P则可能是由于森林中旺盛的生命活动，尤其是微生物的活动，而大量被植物和微生物固持，因而，即使在森林土壤中有较高的矿化速率，但仍具有较低的NH4+-N和有效p的含量． 不同类型的森林土壤之间各化学成分并没有发现有明显的变化趋势，即使森林类型差异较大的落叶阔叶林和针叶林之间也并没有发现十分显著的差异，这说明各森林类型土壤之间养分特征的一致性。两种针叶林均为人工林，林龄不超过30，而在这之前推测也是以落叶阔叶林为主，森林土壤在这30年间并没有发生十分明显的变化。 在l100m至I500m之间的各种森林类型的土壤也没有表现出十分明显的与海拔高度的相关性。同一森林土壤在不同时间的采样之间，各化学成分也没有表现出明显的差异。 2、降水引起的树干茎流水分中全N的含量在降水季节的初期的含量略高于大量降水期间的。而在降水季节后期，随着每次降雨量的减少，降水间隔时间的增加，树干茎流中N的含量明显地有很大幅度的升高。NO3-N在树干茎流中的含量也同样受到了降水量的影响，表现在后期也发生显著的升高，但升高的幅度没有全N的大。受到降水量影响的元素还有S。 全p在树干茎流水分中含量随降水时间的变化，在各个树种之间有很大的差异。 其它几种元素的可交换态在茎流水分中的含量以K的含量为最高;其次是S、ca、Mg，AI在所有分析的元素中含量最低。不过，AI在降水初期(6月22日)的取样中，含量在几个树种的茎流水分样品中普遍较高，Ca和Mg也被发现有类似的情形。 穿透雨中全N的含量在降水初期略高于降水中期的，而至降水末期时又略有升高，这种格局与树干茎流水分中的具有一致性。全P、K、Ca、Mg、S．ＡＩ等包括全N及其无视成分与树干茎流中的含量的差异并不显著． 地表径流中的全N含量在去除枯枝落叶层的径流场的变化格局与树干茎流和穿透雨中的较为一致．表明这三者之间存在一定的相关性．但与未去除枯枝落叶层的径流场的径流水分中全N和NO３－Ｎ的含量并不十分一致，全N和NO３－N的含量有时较高． 取自马牙石沟流水堰口的集水区水样中全N和NO３-N的含量均变化在l～3ｍｇ／L之间;而取自南沟流水堰口的集水区水样中的全N和N03-N的含量均在l～2mg／L之间，但在这两者之间并没有十分显著的差异，说明取自两个集水区溪流水分中的全N和N03-N的含量基本一致。 3、通过对三个森林立地乔木层生物量的两次调查（相隔6年），发现尽管以辽东栎为主要优势树种的暖温带落叶阔叶混交林（91- 03）第一次调查的生物量低于辽东栋林（91 - 02）和桦木林（91 - 04)的，但在生长6年后，该立地的乔木层生物量已明显超过桦木林的，其增长速率在三个样地中为最高。 根据两次调查的结果，三个样地中出现的11种乔木树种胸径的增加可以分成两组，第一组包括北京花楸、糠椴、白桦和辽东栎，另一组则由山杨、五角枫、棘皮桦、大叶白蜡、蒙椴、黄花柳和沙涞组成。6年中，第一组树种的胸径增加量在1.O～l.4em之间，而第二组的增量在0.2~O.9cm之间，两者之间具有显著的差异。 常用的生物量预测模型包括两个因子，即胸径(D)和树高(H)。D通常可以实测得到，但H大部分只能估计得到。本研究通过比较6年前后两次树高的实际估测结果，证明用D和H共同建立的模型预测结果可能会产生较大的人为误差，建议改用D的单因子预测模型。 无论是实测结果还是树木年轮分析结果，都表明处于目前径级水平的暖温带地区分布的这几个树种还处在不断生长的过程中，随着年龄的增加，表现为胸径还有很大程度的增加，因为这些树种目前的大径级个体的年平均增加速率大于小径级的． 树木年龄与胸径的相互关系的分析结果表明，树木年龄和胸径可以很好地用饱和模型Y=a-be－ｃｘ来拟合． 4、通过近5年对辽东栎枝条( D<0.5cm)和叶片凋落物分解的观察和分析，发现辽东栎枝条的总失重率达到了43%，分解速率常数k为2.713x10－3／周，而叶的总失重率则可以达到70%，分解速率常数k为6.234xl0-3/周. 枝条分解过程中的有机质含量变化可以分为三种类型，一种是单调上升型的，如蛋白质，其含量从3.5%增加到约6%;-种是单调下降型的，如半纤维素，约从15%降低至7%;另一种则是相对变化不大，如粗纤维（包括纤维素和木质素），粗纤维的含量变化在58％±3%，木质素变化在56%±2.5%，纤维素则变化在1%～3%之间。 用Olson指数方程拟合，结果表明粗纤维、木质素和半纤维素三者的分解以半纤维素为最快，分解速率常数为5.693xl0-3／周，其次是木质素和粗纤维，分别为2.461x10-3/周和2.352xl0-3／周．而蛋白质和纤维素的拟合结果较差或根本无法拟合． 用Olsoｎ指数方程拟合的结果表明，有些元素在凋落物分解过程中可以很好地用该方程拟合，如K，Na、Mn和C，p和N，Mg，Zn，而一些元素如Ca和Cu没有取得很好的拟合效果。 几种元素在叶片凋落物分解过程过程的丢失速率也以K为最快，其它元素的顺序为，e，N，p，Na，Mn，Mg和Ca（Ca的拟合效果较差），而Cu、Zn也不能很好地用Olson指数方程拟合。 5、根据对东灵山地区6年(199l~1997)的气象观测结果，可得到该地区的年平均降水量和总降水量，用1994年分析的降水中养分含量的数据可以近似计算得东灵山地区每年通过降水进入该暖温带落叶阔叶林生态系统的几种养分输入量。同理可以计算降水输入养分在树干茎流和穿透雨中的分配，还可以计算养分从地表径流中的输出。通过对这几个水分循环的主要环节中养分输入或输出量的计算，发现每年通过降水而进入系统的养分，大部分将积累在系统中，而输出份额只占很小的一部分。 K和Mg两种养分元素在降水通过林冠和树干表面时，将产生大量的淋溶，而Ca的淋溶较小．N、P和AI则产生少量的吸附或吸收。对于S来说，淋溶和吸收或吸附作用相当，或两者都很小。 通过生物量的年平均增量和生物量中的养分含量可以计算得到每年积累在生物量中的养分量即存留量，同理可以计算年凋落物中的养分量、归还量及生物系统从土壤中吸收的养分量，每年养分的存留率．通过以上计算，发现该落叶阔叶林对养分的存留率较低，这可能是由于该落叶阔叶林森林生态系统每年具有较高的养分归还量，对于一些元素来说，还具有较高的淋溶量，尤其是K和Mg．

Estudo da decomposição de plantas aquáticas em função das quantidades depositadas, da umidade e do tipo de disposição no solo

Um estudo foi realizado com a finalidade de avaliar a decomposição da biomassa de plantas aquáticas, incorporadas ou não ao solo, provenientes do controle mecânico, no reservatório da UHE Americana. O ensaio foi realizado em casa de vegetação, localizada no Núcleo de Pesquisas Avançadas em Matologia (NUPAM) da FCA/Unesp-Botucatu. A avaliação foi conduzida em vasos contendo 14 kg de solo, simulando descartes de 50, 100, 150 e 200 t MF de plantas ha-1 e avaliando o processo de decomposição através da liberação de CO2, divididos em duas etapas: a primeira em solo seco e, a segunda, na seqüência, com o solo úmido. A quantificação do CO2 liberado foi realizada através de titulação de solução adicionada ao processo de incubação de 24 horas dos vasos. Os dados foram interpolados e analisados seguindo modelo de Mitscherlich, com algumas modificações. Na primeira etapa, foi observada uma rápida liberação de CO2 até o décimo dia, seguida de estabilização. O maior teor de CO2 liberado foi observado no tratamento com descarte de 200 t MF ha-1 incorporado ao solo. Os dados avaliados durante a segunda fase do ensaio representaram uma maior linearidade no processo de liberação de CO2, indicando um período mais longo do processo de degradação da biomassa descartada.

Two structurally discrete GH7-cellobiohydrolases compete for the same cellulosic substrate fiber

Background: Cellulose consisting of arrays of linear beta-1,4 linked glucans, is the most abundant carbon-containing polymer present in biomass. Recalcitrance of crystalline cellulose towards enzymatic degradation is widely reported and is the result of intra-and inter-molecular hydrogen bonds within and among the linear glucans. Cellobiohydrolases are enzymes that attack crystalline cellulose. Here we report on two forms of glycosyl hydrolase family 7 cellobiohydrolases common to all Aspergillii that attack Avicel, cotton cellulose and other forms of crystalline cellulose. Results: Cellobiohydrolases Cbh1 and CelD have similar catalytic domains but only Cbh1 contains a carbohydrate-binding domain (CBD) that binds to cellulose. Structural superpositioning of Cbh1 and CelD on the Talaromyces emersonii Cel7A 3-dimensional structure, identifies the typical tunnel-like catalytic active site while Cbh1 shows an additional loop that partially obstructs the substrate-fitting channel. CelD does not have a CBD and shows a four amino acid residue deletion on the tunnel-obstructing loop providing a continuous opening in the absence of a CBD. Cbh1 and CelD are catalytically functional and while specific activity against Avicel is 7.7 and 0.5 U. mg prot-1, respectively specific activity on pNPC is virtually identical. Cbh1 is slightly more stable to thermal inactivation compared to CelD and is much less sensitive to glucose inhibition suggesting that an open tunnel configuration, or absence of a CBD, alters the way the catalytic domain interacts with the substrate. Cbh1 and CelD enzyme mixtures on crystalline cellulosic substrates show a strong combinatorial effort response for mixtures where Cbh1 is present in 2: 1 or 4: 1 molar excess. When CelD was overrepresented the combinatorial effort could only be partially overcome. CelD appears to bind and hydrolyze only loose cellulosic chains while Cbh1 is capable of opening new cellulosic substrate molecules away from the cellulosic fiber. Conclusion: Cellobiohydrolases both with and without a CBD occur in most fungal genomes where both enzymes are secreted, and likely participate in cellulose degradation. The fact that only Cbh1 binds to the substrate and in combination with CelD exhibits strong synergy only when Cbh1 is present in excess, suggests that Cbh1 unties enough chains from cellulose fibers, thus enabling processive access of CelD.

Potassium catalysis in the pyrolysis behaviour of short rotation willow coppice

Short rotation willow coppice (SRC) and a synthetic biomass, a mixture of the basic biomass components (cellulose, hemicellulose and lignin), have been investigated for the influence of potassium on their pyrolysis behaviours. The willow sample was pre-treated to remove salts and metals by hydrochloric acid, and this demineralised sample was impregnated with potassium. The same type of pre-treatment was applied to components of the synthetic biomass. Characterisation was performed using thermogravimetric analysis with measurement of products by means of Fourier transform infrared spectroscopy (TGA-FTIR) and pyrolysis-gas chromatography-mass spectrometry (PY-GC-MS). A comparison of product distributions and kinetics are reported. While the general features of decomposition of SRC are described well by an additive behaviour of the individual components, there are some differences in the magnitude of the influence of potassium, and on the products produced. For both SRC and the synthetic biomass, TGA traces indicate catalytic promotion of both of the two-stages of biomass decomposition, and potassium can lower the average apparent first-order activation energy for pyrolysis by up to 50 kJ/mol. For both SRC and synthetic biomass the yields and distribution of pyrolysis products have been influenced by the presence of the catalyst. Potassium catalysed pyrolysis increases the char yields markedly and this is more pronounced for synthetic biomass than SRC. Gas evolution profiles during pyrolysis show the same general features for both SRC and synthetic biomass. Relative methane yields increase during the char formation stage of pyrolysis of the potassium doped samples. The evolution profiles of acetic acid and formaldehyde change, and these products are seen in lower relative amounts for both the demineralised samples. A greater variation in pyrolysis products is observed from the treated SRC samples compared to the different synthetic biomass samples. Furthermore, substituted phenols from lignin pyrolysis are more dominant in the pyrolysis profiles of the synthetic biomass than of the SRC, implying that the extracted lignins used in the synthetic biomass yield a greater fraction of monomeric type species than the lignocellulosic cell wall material of SRC. For both types of samples, PY-GS-MS analyses show that potassium has a significant influence on cellulose decomposition markers, not just on the formation of levoglucosan, but also other species from the non-catalysed mechanism, such as 3,4-dihydroxy-3-cyclobutene-1,2-dione. © 2007 Elsevier Ltd. All rights reserved.

Produção e purificação de biogás utilizando microalga spirulina sp. LEB-18

O crescimento da população mundial e a tentativa de substituição parcial dos combustíveis fósseis por novas fontes de energia têm levado a uma maior atenção quanto à possível escassez de alimentos e a carência de grandes áreas disponíveis para agricultura. Microalgas, por meio do metabolismo fotossintético, utilizam energia solar e gás carbônico como nutrientes para o crescimento. A microalga Spirulina pode ser utilizada como suplemento alimentar, na biofixação de CO2, como fonte de biocombustíveis e no tratamento de efluentes. A digestão anaeróbia da biomassa microalgal produz biogás e os resíduos deste processo podem ser utilizados como substrato para novos cultivos da microalga. O objetivo deste trabalho foi estudar a conversão de Spirulina sp. LEB-18 em biogás em escala piloto e produzir biomassa microalgal utilizando os efluentes bicarbonato e dióxido de carbono do processo anaeróbio como fonte de nutrientes. Spirulina foi utilizada como substrato na digestão anaeróbia para produção de biogás em escala piloto sob temperaturas variáveis (12- 38 °C). Efluente do processo anaeróbio foi adicionado (20 %, v/v) como fonte de carbono no cultivo da microalga para avaliar o crescimento e a composição da biomassa. A seguir foi avaliada a capacidade da microalga de remover CO2 presente no biogás através de biofixação para obtenção do biocombustível purificado. O biogás produzido sob as diferentes temperaturas apresentou entre 72,2 e 74,4 % de CH4, quando realizado nas temperaturas 12 a 21 °C e 26 a 38 °C, respectivamente. A redução na temperatura do processo anaeróbio provocou um decréscimo na conversão de biomassa em biogás (0,30 para 0,22 g.g-1 ), ocorrendo dentro da faixa adequada e segura para as bactérias metanogênicas (pH 6,9; alcalinidade entre 1706,0 e 2248,0 mg.L-1 CaCO3 e nitrogênio amoniacal 479,3 a 661,7 mg.L-1 ). Os cultivos de Spirulina sp. LEB-18 em efluente anaeróbio contendo 20 % (v/v) e meio Zarrouk modificado (NaHCO3 2,8 e 5,3 g.L-1 ) apresentaram velocidade específica máxima de crescimento entre 0,324 e 0,354 d-1 , produtividade volumétrica entre 0,280 e 0,297 g.L-1 .d-1 e produtividade areal entre 14,00 e 14,85 g.m-2 .d-1 , sem diferenças significativas (p > 0,05) entre as diferentes condições estudadas. Lipídios variaram entre 4,9 e 5,0 % com proporção de ácido linoleico maximizada nos meios com efluente e ácido alfa-linolênico reduzida nesses meios em comparação ao meio Zarrouk completo. Nos ensaios para avaliar a capacidade da microalga Spirulina sp. LEB-18 de remover CO2 contaminante no biogás, as máximas concentrações celulares e produtividades de biomassa variaram, respectivamente, entre 1,12 e 1,24 g.L-1 e 0,11 e 0,14 g.L-1 .d-1 , não apresentando diferenças significativas (p > 0,05) entre os ensaios. A maior fixação diária total (FDT) de dióxido de carbono obtida foi 58,01 % (v/v) em cultivos com adição de biogás contendo 25 % (v/v) CO2. Obteve-se biogás com 89,5 % (v/v) de CH4 após injeção em cultivos de Spirulina, no qual aproximadamente 45 % (v/v) do CO2 injetado foi fixado pela microalga, gerando biomassa para diversas aplicações e biogás purificado.

Pyrolysis decomposition of mahogony seeds (Swietenia macrophylla) for alternative fuel oil

A fixed bed pyrolysis has been designed and fabricated for obtaining liquid fuel from Mahogany seeds. The major components of the system are fixed bed pyrolysis reactor, liquid condenser and liquid collectors. The Mahogany seed in particle form is pyrolysed in an externally heated 10 cm diameter and 36 cm high fixed bed reactor with nitrogen as the carrier gas. The reactor is heated by means of a biomass source cylindrical heater from 450oC to 600oC. The products are oil, char and gas. The reactor bed temperature, running time and feed particle size are considered as process parameters. A maximum liquid yield of 54wt% of biomass feed is obtained with particle size of 1.18 mm at a reactor bed temperature of 5500C with a running time of 90 minutes. The oil is found to possess favorable flash point and reasonable density and viscosity. The higher calorific value is found to be 39.9 MJ/kg which is higher than other biomass derived pyrolysis oils.

Effect of preparation method of palygorskite-supported Fe and Ni catalysts on catalytic cracking of biomass tar

In this study, the effect of catalyst preparation and additive precursors on the catalytic decomposition of biomass using palygorskite-supported Fe and Ni catalysts was investigated. The catalysts were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). It is concluded that the most active additive precursor was Fe(NO3)3·9H2O. As for the catalyst preparation method, co-precipitation had superiority over incipient wetness impregnation at low Fe loadings.

Regional contingencies in the relationship between aboveground biomass and litter in the world’s grasslands

Based on regional-scale studies, aboveground production and litter decomposition are thought to positively covary, because they are driven by shared biotic and climatic factors. Until now we have been unable to test whether production and decomposition are generally coupled across climatically dissimilar regions, because we lacked replicated data collected within a single vegetation type across multiple regions, obfuscating the drivers and generality of the association between production and decomposition. Furthermore, our understanding of the relationships between production and decomposition rests heavily on separate meta-analyses of each response, because no studies have simultaneously measured production and the accumulation or decomposition of litter using consistent methods at globally relevant scales. Here, we use a multi-country grassland dataset collected using a standardized protocol to show that live plant biomass (an estimate of aboveground net primary production) and litter disappearance (represented by mass loss of aboveground litter) do not strongly covary. Live biomass and litter disappearance varied at different spatial scales. There was substantial variation in live biomass among continents, sites and plots whereas among continent differences accounted for most of the variation in litter disappearance rates. Although there were strong associations among aboveground biomass, litter disappearance and climatic factors in some regions (e.g. U.S. Great Plains), these relationships were inconsistent within and among the regions represented by this study. These results highlight the importance of replication among regions and continents when characterizing the correlations between ecosystem processes and interpreting their global-scale implications for carbon flux. We must exercise caution in parameterizing litter decomposition and aboveground production in future regional and global carbon models as their relationship is complex.

Biomethanation of herbaceous biomass residues using 3-zone plug flow like digesters - A case study from India

Biomethanation of herbaceous biomass feedstock has the potential to provide clean energy source for cooking and other activities in areas where such biomass availability predominates. A biomethanation concept that involves fermentation of biomass residues in three steps, occurring in three zones of the fermentor is described. This approach while attempting take advantage of multistage reactors simplifies the reactor operation and obviates the need for a high degree of process control or complex reactor design. Typical herbaceous biomass decompose with a rapid VFA flux initially (with a tendency to float) followed by a slower decomposition showing balanced process of VFA generation and its utilization by methanogens that colonize biomass slowly. The tendency to float at the initial stages is suppressed by allowing previous days feed to hold it below digester liquid which permits VFA to disperse into the digester liquid without causing process inhibition. This approach has been used to build and operate simple biomass digesters to provide cooking gas in rural areas with weed and agro-residues. With appropriate modifications, the same concept has been used for digesting municipal solid wastes in small towns where large fermentors are not viable. With further modifications this concept has been used for solid-liquid feed fermentors. Methanogen colonized leaf biomass has been used as biofilm support to treat coffee processing wastewater as well as crop litter alternately in a year. During summer it functions as a biomass based biogas plants operating in the three-zone mode while in winter, feeding biomass is suspended and high strength coffee processing wastewater is let into the fermentor achieving over 90% BOD reduction. The early field experience of these fermentors is presented.

Solid phase fermentation of leaf biomass to biogas

This paper describes a simple technique for the fermentation of untreated or partly-treated leafy biomass in a digester of novel design without incurring the normal problems of feeding, floating and scum formation of feed, etc. The solid phase fermentation studied consists of a bed of biomass frequently sprinkled with an aqueous bacterial inoculum and recycling the leachate to conserve moisture and improve the bacterial dispersion in the bed. The decomposition of the leaf biomass and water hyacinth substrates used in this study was rapid, taking 45 and 30 days for the production of 250 and 235 l biogas per kg total solids (TS) respectively, for the above mentioned substrates at a daily sprinkled volume of 26 ml cm−2 of bed per day sprinkled at 12 h intervals. Very little volatile fatty acid (VFA) intermediates accumulated in the liquid sprinkled, suggesting acidogenesis to be rate-limiting in this process. From the pattern of VFA and gas produced it is concluded that most of the biogas produced is from the biomass bed, thus making the operation of a separate methanogenic reactor unnecessary.