Modeling the carbon cycle in Lake Matano

Lake Matano, Indonesia, is a stratified anoxic lake with iron‐rich waters that has been used as an analogue for the Archean and early Proterozoic oceans. Past studies of Lake Matano report large amounts of methane production, with as much as 80% of primary production degraded via methanogenesis. Low δ¹³C values of DIC in the lake are difficult to reconcile with this notion, as fractionation during methanogenesis produces isotopically heavy CO₂. To help reconcile these observations, we develop a box model of the carbon cycle in ferruginous Lake Matano, Indonesia, that satisfies the constraints of CH₄ and DIC isotopic profiles, sediment composition, and alkalinity. We estimate methane fluxes smaller than originally proposed, with about 9% of organic carbon export to the deep waters degraded via methanogenesis. In addition, despite the abundance of Fe within the waters, anoxic ferric iron respiration of organic matter degrades <3% of organic carbon export, leaving methanogenesis as the largest contributor to anaerobic organic matter remineralization, while indicating a relatively minor role for iron as an electron acceptor. As the majority of carbon exported is buried in the sediments, we suggest that the role of methane in the Archean and early Proterozoic oceans is less significant than presumed in other studies.     

Binding of phosphate in sediment accumulation areas of the eastern Gulf of Finland,Baltic Sea

The relationships between P and components binding P were studied by analysing the concentrations of N, P, Fe, Mn, Ca and Al in sediments and pore water along the estuarine transect of the River Neva in August 1995. The high sediment organic matter concentration resulted in low surface redox potential and high pore-water o-P concentration, whereas the abundance of amphipods resulted in high surface redox potentials and low pore-water o-P concentration. However, despite the variation in sediment organic matter and the abundance of amphipods, very reduced conditions and slightly variable concentrations of Tot-P (0.7–1.1 mg g^–1 DW) were observed in the 10–15 cm sediment depth along the estuarine gradient, indicating that the pools of mobile P were largely depleted within the depth of 0–15 cm. Multiple regression analysis demonstrated that organic matter and Tot-Fe concentration of the sediment were closely related to the variation in Tot-P concentration of the sediments (r ² = 0.817, n=32). In addition, the high total Fe:P ratio suggested that there is enough Fe to bind P in sediments along the estuarine gradient. However, low Fe_diss concentrations in the pore water of reduced sediment (redox-potential <–50 mV) indicated efficient precipitation of FeS (FeS and FeS₂), incapable to efficiently bind P. Consequently, the low Fe_diss:o-P ratio (< 1) recorded in pore water in late summer implied that Fe³⁺ oxides formed by diffusing Fe_diss in the oxic zone of the sediments were insufficient to bind the diffusing o-P completely. The measured high o-P concentrations in the near-bottom water are consistent with this conclusion. However, there was enough Fe_diss in pore water to form Fe³⁺ oxides to bind upwards diffusing P in the oxic sediment layer of the innermost Neva estuary and the areas bioturbated by abundant amphipods.     

Soil Characteristics and Vegetation Structure in a Heavily Deteriorated Mangrove Forest in the Caribbean Coast of Colombia

Mass mortality and biomass of mangrove trees are related to soil factors in the Caribbean Coast of Colombia. Soil properties measured were particle size distribution, bulk density, organic matter, total nitrogen, total phosphorus, pH, redox potential, salinity, and extractable nitrogen (NO₂, NO₃, NH₄) and phosphorus (PO₄). Sampling was performed at three locations along two 50 m transects at each site. Soil nutrient concentrations of either exchangeable nitrogen or phosphorus were comparable to other reported values. Redox potentials (E_h) were variable probably due to microtopographic conditions and to the amount of water and organic matter present in the soil. Hydrogen potentials (pH) are within the range reported as normal for mangrove soils. Locations with highest biomass had an average soil salinity of 35 with a range of 20 to 53. Sites with dead or dwarfed vegetation had an average soil salinity of 74 and minimum and maximum values observed were 52 and 100 respectively. Statistical analysis exhibited temporal and spatial differences in soil salinity and suggest that this parameter is most correlated to the development and distribution of mangrove vegetation in the area indicating that basal area and biomass volume are inversely correlated with soil salinity.     

Effect of glyphosate contaminated feed on rumen fermentation parameters and in sacco degradation of grass hay and corn grain

Four rumen fistulated wethers were used to investigate the effect of glyphosate contaminated feed on rumen fermentation. The rations were based on corn silage, urea and a vitamin-mineral premix, either in the absence or presence of 0.77?g glyphosate per kg DM. Furthermore, rations were fed either with or without aromatic amino acid supplementation. During four periods of 28 days, sheep received each of the four dietary treatments according to a Latin square. After 14 days of adaptation rumen fermentation parameters (pH, ammonia, volatile fatty acids) were measured on day 15 over a five-hour period after the morning feeding. The remaining 13 days served for in sacco degradation studies with grass hay and corn grain. Ammonia (NH₃) and pH of rumen fluid were within the normal range for all dietary treatments (NH₃: 9.1 – 32.3?mmol·l^???1, pH: 6.2 – 6.7). Neither rumen fermentation parameters nor in sacco DM and NDF degradation of incubated feedstuffs were significantly affected by glyphosate, with or without aromatic amino acid supplementation. Kinetic profiles of the in sacco dry matter and NDF degradation of grass hay were almost identical for the dietary treatments.     

Origin and fate of acetate in an acidic fen

Acetate is a central intermediate in the anaerobic degradation of organic matter, and the resolution of its metabolism necessitates integrated strategies. This study aims to (1) estimate the contribution of acetogenesis to acetate formation in an acidic fen (pH ~ 4.9), (2) assess the genetic potential for acetogenesis targeting the fhs gene encoding formyltetrahydrofolate synthetase (FTHFS) and (3) unravel the in situ turnover of acetate using stable carbon isotope pore-water analysis. H(2)/CO(2)-supplemented peat microcosms yielded (13)C-depleted acetate (-37.2‰ vs. VPDB (Vienna Peedee belemnite standard) compared with -14.2‰ vs. VPDB in an unamended control), indicating the potential for H(2)-dependent acetogenesis. Molecular analysis revealed a high diversity and depth-dependent distribution of fhs phylotypes with the highest number of operational taxonomic units in 0-20 cm depth, but only few and distant relationships to known acetogens. In pore waters, acetate concentrations (0-170 μM) and δ(13)C-values varied widely (-17.4‰ to -3.4‰ vs. VPDB) and did not indicate acetogenesis, but pointed to a predominance of sinks, which preferentially consumed (12)C-acetate, like acetoclastic methanogenesis. However, depth profiles of methane and δ(13)C(CH4) revealed a temporarily and spatially restricted role of this acetate sink and suggest other processes like sulfate and iron reduction played an important role in acetate turnover.     

Seasonal variation in sulfate reduction and methanogenesis in peaty sediments of eutrophic Lake Loosdrecht,The Netherlands

During one year, concentration profiles of sulfate and methane were measured in sediment cores of eutrophic Lake Loosdrecht. Sulfate concentrations decreased exponentially with depth towards a constant threshold value of 7.6 ± 6.1 μM. Concentration profiles were used to calculate fluxes of sulfate and methane and to estimate the anaerobic mineralization rate. Anaerobic mineralization was highest in autumn which was probably due to an increased sedimentation of easily degradable organic carbon. At high rates (>600 μ mol organic carbon .m⁻².h⁻¹), sulfate reduction appeared to be limited by sulfate and methanogenesis accounted for over 80% of the anaerobic mineralization. At low anaerobic mineralization rates, measured in winter and spring, sulfate reduction was predominant. There was little methanogenesis below 5 cm depth in the sediment which indicated a rapid decrease of degradable organic matter with depth. There was a remarkable difference, especially in winter, between methane fluxes which were measured in batch experiments and those calculated from the concentration profiles in the sediment. These differences may be due to methane diffusing upward from deep layers.     

Spatial variation of dissolved gas concentrations in a willow vegetation filter treating landfill leachate

Membrane inlet mass spectrometry (MIMS) was used to monitor continuously and simultaneously the concentrations of dissolved gases (O₂, CO₂, CH₄) within the treatment bed of a willow vegetation filter treating leachate at a landfill site in mid Wales. The distribution of dissolved gasses within the bed was shown to be highly heterogeneous at the small spatial scale with considerable variation between vertical profiles measured simultaneously at different locations. In general, aerobic conditions were observed above the water table with reduced levels of oxygen and increasing levels of carbon dioxide and methane below it. Distinct pockets of oxygen (up to 200 μM) were observed in anaerobic zones and pockets of reduced oxygen and elevated carbon dioxide were observed in the aerobic zone. Pockets of methane were observed in some profiles coexisting with up to 200 μM oxygen at 5 cm depth. These observations confirm the hypothesis that micro-sites exists within the soil/root matrix where aerobic organic matter decomposition and anaerobic processes such as methanogenesis can occur in relatively close proximity to each other. We hypothesise that the distribution of dissolved gases is determined by rapid diffusion of air maintaining aerobic conditions above the water table, removal of oxygen by microbial processes creating anaerobic conditions below the water table and the distribution of willow roots in the soil which create local aerobic zones by oxygen release.     

A laboratory study on biochemical degradation and microbial utilization of organic matter comprising a marine diatom,land grass,and salt marsh plant in estuarine ecosystems

We studied the biochemical degradation of organic matter comprising marine diatom, land grass, and salt marsh plant in estuarine ecosystems in two laboratory microcosms consisting of estuarine sediments and coastal seawater. The materials were incubated separately and together under controlled oxic and anoxic conditions to test effects of co-metabolism and redox on overall degradation of organic matter. We followed variations of bulk parameters [total organic carbon (TOC), total nitrogen (TN), C/N ratio, δ¹³C_TOC, and δ¹⁵N_TN], fatty acid concentrations, and compound-specific δ¹³C values over 3 months. Coexistence of marine diatom (relatively labile) with land grass/salt marsh plant (relatively refractory) in the microcosms yielded a negative co-metabolism effect (retardation rather than acceleration) on the overall degradation of organic matter. The ratios of oxic to anoxic degradation rate constants (k _ox/k _an) of TOC and most fatty acids were in a range of 1.1–1.7, implying that redox conditions per se had a limited influence on degradation of fresh organic materials in estuarine ecosystems. Variations of two bacteria-specific fatty acids (iso- and anteiso-15:0) and their δ¹³C values indicated that bacterial metabolism could use organic carbon (OC) from any available material when only one single-source material was dominant in the ecosystems. However, bacteria probably utilized OC preferentially from labile marine diatom when multiple-source materials were almost equally present in the ecosystems.     

A simulation model of organic matter and nutrient accumulation in mangrove wetland soils

The distribution and accumulation of organic matter, nitrogen (N) and phosphorus (P) in mangrove soils at four sites along the Shark River estuary of south Florida were investigated with empirical measures and a process-based model. The mangrove nutrient model (NUMAN) was developed from the SEMIDEC marsh organic matter model and parameterized with data from mangrove wetlands. The soil characteristics in the four mangrove sites varied greatly in both concentrations and profiles of soil carbon, N and P. Organic matter decreased from 82% in the upstream locations to 30% in the marine sites. Comparisons of simulated and observed results demonstrated that landscape gradients of soil characteristics along the estuary can be adequately modeled by accounting for plant production, litter decomposition and export, and allochthonous input of mineral sediments. Model sensitivity analyses suggest that root production has a more significant effect on soil composition than litter fall. Model simulations showed that the greatest change in organic matter, N, and P occurred from the soil surface to 5 cm depth. The rapid decomposition of labile organic matter was responsible for this decrease in organic matter. Simulated N mineralization rates decreased quickly with depth, which corresponded with the decrease of labile organic matter. The increase in organic matter content and decrease in soil bulk density from mangrove sites at downstream locations compared to those at upstream locations was controlled mainly by variation in allochthonous inputs of mineral matter at the mouth of the estuary, along with gradients in mangrove root production. Research on allochthonouns sediment input and in situ root production of mangroves is limited compared to their significance to understanding nutrient biogeochemistry of these wetlands. More accurate simulations of temporal patterns of nutrient characteristics with depth will depend on including the effects of disturbance such as hurricanes on sediment redistribution and biomass production.     

Physicochemical Conditions and Microbial Activities in the Highly Alkaline Gut of the Humus-Feeding Larva of Pachnoda ephippiata (Coleoptera: Scarabaeidae)

The soil macrofauna plays an important role in the carbon and nitrogen cycle of terrestrial ecosystems. In order to gain more insight into the role of the intestinal microbiota in transformation and mineralization of organic matter during gut passage, we characterized the physicochemical conditions, microbial activities, and community structure in the gut of our model organism, the humus-feeding larva of the cetoniid beetle Pachnoda ephippiata. Microsensor measurements revealed an extreme alkalinity in the midgut, with highest values (pH > 10) between the second and third crown of midgut ceca. Both midgut and hindgut were largely anoxic, but despite the high pH, the redox potential of the midgut content was surprisingly high even in the largest instar. However, reducing conditions prevailed in the hindgut paunch of all instars (E_h ~ −100 mV). Both gut compartments possessed a pronounced gut microbiota, with highest numbers in the hindgut, and microbial fermentation products were present in high concentrations. The stimulation of hindgut methanogenesis by exogenous electron donors, such as H₂, formate, and methanol, together with considerable concentrations of formate in midgut and hemolymph, suggests that midgut fermentations are coupled to methanogenesis in the hindgut by an intercompartmental transfer of reducing equivalents via the hemolymph. The results of a cultivation-based enumeration of the major metabolic groups in midgut and hindgut, which yielded high titers of lactogenic, propionigenic, and acetogenic bacteria, are in good agreement not only with the accumulation of microbial fermentation products in the respective compartments but also with the results of a cultivation-independent characterization of the bacterial communities reported in the companion paper (M. Egert, B. Wagner, T. Lemke, A. Brune, and M. W. Friedrich, Appl. Environ. Microbiol. 69:6659-6668, 2003).     

Determination of isotope fractionation factors and quantification of carbon flow by stable carbon isotope signatures in a methanogenic rice root model system

Methanogenic processes can be quantified by stable carbon isotopes, if necessary modeling parameters, especially fractionation factors, are known. Anoxically incubated rice roots are a model system with a dynamic microbial community and thus suitable to investigate principal geochemical processes in anoxic natural systems. Here we applied an inhibitor of acetoclastic methanogenesis (methyl fluoride), calculated the thermodynamics of the involved processes, and analyzed the carbon stable isotope signatures of CO₂, CH₄, propionate, acetate and the methyl carbon of acetate to characterize the carbon flow during anaerobic degradation of rice roots to the final products CO₂ and CH₄. Methyl fluoride inhibited acetoclastic methanogenesis and thus allowed to quantify the fractionation factor of CH₄ production from H₂/CO₂. Since our model system was not affected by H₂ gradients, the fractionation factor could alternatively be determined from the Gibbs free energies of hydrogenotrophic methanogenesis. The fractionation factor of acetoclastic methanogenesis was also experimentally determined. The data were used for successfully modeling the carbon flow. The model results were in agreement with the measured process data, but were sensitive to even small changes in the fractionation factor of hydrogenotrophic methanogenesis. Our study demonstrates that stable carbon isotope signatures are a proper tool to quantify carbon flow, if fractionation factors are determined precisely.     

Biogeochemical changes at the sediment–water interface during redox transitions in an acidic reservoir: exchange of protons,acidity and electron donors and acceptors

Redox transitions induced by seasonal changes in water column O₂ concentration can have important effects on solutes exchange across the sediment–water interface in systems polluted with acid mine drainage (AMD), thus influencing natural attenuation and bioremediation processes. The effect of such transitions was studied in a mesocosm experiment with water and sediment cores from an acidic reservoir (El Sancho, SW Spain). Rates of aerobic organic matter mineralization and oxidation of reduced inorganic compounds increased under oxic conditions (OX). Anaerobic process, like Fe(III) and sulfate reduction, also increased due to higher O₂ availability and penetration depth in the sediment, resulting in higher regeneration rates of their corresponding anaerobic e^? acceptors. The contribution of the different processes to oxygen uptake changed considerably over time. pH decreased due to the precipitation of schwertmannite and the release of H⁺ from the sediment, favouring the dissolution of Al-hydroxides and hydroxysulfates at the sediment surface. The increase in dissolved Al was the main contributor to water column acidity during OX. Changes in organic matter degradation rates and co-precipitation and dissolution of dissolved organic carbon and nitrogen with redox-sensitive Fe(III) compounds affected considerably C and N cycling at the sediment–water interface during redox transitions. The release of NO₂^? and NO₃^? during the hypoxic period could be attributed to ammonium oxidation coupled to ferric iron reduction (Feammox). Considering the multiple effects of redox transitions at the sediment–water interface is critical for the successful outcome of natural attenuation and bioremediation of AMD impacted aquatic environments.     

Anaerobic biodegradation of sugar beet pulp

Sugar beet pulp is a by-product of sugar production and consists mainly of cellulose, hemicellulose and pectin. Its composition is suitable for biological degradation. A possible alternative for the utilization of this material (besides cattle feeding) can be anaerobic methanogenic degradation. It has an additional advantage – biogas production. Beet pulp was treated by a two-step anaerobic process. The first step consisted of hydrolysis andacidification. The second step was methanogenesis. In this paper, observation ofthe process of anaerobic degradation and determination of optimal parameters is discussed. A laboratory-scale model for sugar beet pulp anaerobic biodegradation was operated. Results of model performance have shown very good pulp digestion characteristics. In addition, high efficiency removal of organic matter was achieved. Methane yield was over 0.360 m³ kg^-1 dried pulp and excess sludge production was 0.094 g per gram COD added.     

Temperature regulation of anaerobic degradation of organic matter

Anaerobic degradation of organic matter follows similar pathways in digesters and anaerobic freshwater sediments. The responsible microorganisms are linked in a complex food web, where short chain fatty acids and H₂ are important intermediates. Degradation of short-chain fatty acids is endothermic under standard conditions and is only possible at low H₂ partial pressures maintained by exothermic methanogenesis. The coupling between these endothermic and exothermic processes is delicate, and hence sensitive to environmental changes such as temperature variations. The effect of temperature on thermodynamics and on kinetics of these and other anaerobic degradation processes with emphasis on freshwater ecosystems is discussed.The author is with the Department of General Microbiology, Institute of Molecular Biology, University of Copenhagen, Sølvgade 83 H, DK-1307 Copenhagen K, Denmark     

Crystalline iron oxides stimulate methanogenic benzoate degradation in marine sediment-derived enrichment cultures

Elevated dissolved iron concentrations in the methanic zone are typical geochemical signatures of rapidly accumulating marine sediments. These sediments are often characterized by co-burial of iron oxides with recalcitrant aromatic organic matter of terrigenous origin. Thus far, iron oxides are predicted to either impede organic matter degradation, aiding its preservation, or identified to enhance organic carbon oxidation via direct electron transfer. Here, we investigated the effect of various iron oxide phases with differing crystallinity (magnetite, hematite, and lepidocrocite) during microbial degradation of the aromatic model compound benzoate in methanic sediments. In slurry incubations with magnetite or hematite, concurrent iron reduction, and methanogenesis were stimulated during accelerated benzoate degradation with methanogenesis as the dominant electron sink. In contrast, with lepidocrocite, benzoate degradation, and methanogenesis were inhibited. These observations were reproducible in sediment-free enrichments, even after five successive transfers. Genes involved in the complete degradation of benzoate were identified in multiple metagenome assembled genomes. Four previously unknown benzoate degraders of the genera Thermincola (Peptococcaceae, Firmicutes), Dethiobacter (Syntrophomonadaceae, Firmicutes), Deltaproteobacteria bacteria SG8_13 (Desulfosarcinaceae, Deltaproteobacteria), and Melioribacter (Melioribacteraceae, Chlorobi) were identified from the marine sediment-derived enrichments. Scanning electron microscopy (SEM) and catalyzed reporter deposition fluorescence in situ hybridization (CARD-FISH) images showed the ability of microorganisms to colonize and concurrently reduce magnetite likely stimulated by the observed methanogenic benzoate degradation. These findings explain the possible contribution of organoclastic reduction of iron oxides to the elevated dissolved Fe²⁺ pool typically observed in methanic zones of rapidly accumulating coastal and continental margin sediments.Subject terms: Biogeochemistry, Microbial ecology     

Rapid reworking of subtidal sediments by burrowing spatangoid urchins

The mixing and displacement of sediment by benthic macrofauna (bioturbation) has major biogeochemical implications, and can control rates of organic matter degradation and carbon burial. Large, abundant, mobile macrofauna often dominate sediment bioturbation, and heart urchins of the genus Echinocardium are regarded as key sediment bioturbators in marine systems throughout the world. To better understand the bioturbation potential and functional role of Echinocardium, we developed a mathematical model and parameterized it with field data from six locations in northern New Zealand in order to estimate bioturbation rates in these places. Although urchin sizes and densities were measured in consecutive years at all six locations, we obtained a third model parameter, urchin movement rate, from one time and place only (Site OB5). Because confidence in model output was greatest at OB5, and since OB5 had the highest sediment reworking rate of all sites, our model yielded a good upper bound estimate for the bioturbation potential of Echinocardium in the areas examined. The volume of sediment displaced by Echinocardium populations reached 20,000 cm³ m⁻² d⁻¹ at OB5, suggesting that surface sediment is reworked about every 3 days at sites where Echinocardium is abundant. Experimental work with a fluorescent tracer at OB5 suggested limited downward particle movement as a result of Echinocardium bioturbation, though vertical profiles of chlorophyll a and organic matter content indicated well mixed sediment. The loss of Echinocardium because of broad-scale anthropogenic disturbance to the seabed could have major consequences on marine ecosystem functioning.     

Methane Metabolism in a Temperate Swamp

Comparisons between in situ CH₄ concentration and potential factors controlling its net production were made in a temperate swamp. Seasonal measurements of water table level and depth profiles of pH, dissolved CH₄, CO₂, O₂, SO₄^2-, NO₃^-, formate, acetate, propionate, and butyrate were made at two adjacent sites 1.5 to 2 m apart. Dissolved CH₄ was inversely correlated to O₂ and, in general, to NO₃^- and SO₄^2-, potential inhibitors of methanogenesis. At low water table levels (August 1992), maximal CH₄ (2 to 4 μM) occurred below 30 cm, whereas at high water table levels (October 1992) or under flooded conditions (May 1993), CH₄ maxima (4 to 55 μM) occurred in the top 10 to 20 cm. Higher CH₄ concentrations were likely supported by inputs of fresh organic matter from decaying leaf litter, as suggested by high acetate and propionate concentrations (25 to 100 μM) in one of the sites in fall and spring. Measurements of potential CH₄ production (and consumption) showed that the highest rates generally occurred in the top 10 cm of soil. Soil slurry incubations confirmed the importance of organic matter to CH₄ production but also showed that competition for substrates by nonmethanogenic microorganisms could greatly attenuate its effect.     

Determination of total destruction of organic matter in sediments of water bodies

A new scheme for determining the destruction of organic matter in bottom sediments with an account of methanogenesis and the dark assimilation of CO₂ is suggested. The values of the total destruction calculated according to the new methodical scheme increases by 30–60%.     

Effects of added organic matter on iron and manganese redox systems in sediment

Addition of five types of organic matter to Lake Washington sediments resulted in release of high concentrations of iron, organic carbon, and manganese into the interstitial water, and caused an increase in observed sediment oxygen consumption rates. The depressed electrode potentials (E_h < —150 mV) that should accompany such reduction processes did not occur, indicating that E_h was being poised by redox systems present in the sediment. Iron redox systems [Fe(OH)₃‐Fe²⁺, Fe₃(OH)₈‐Fe²⁺, and Fe(OH)₃‐Fe₃(OH)₈] were shown to be poising the E_h of control sediments throughout 13 weeks of incubation and dominating the potential of several of the organically amended sediments following the first three weeks of incubation. Depression of calculated iron system E_o values relative to that of the control sediment early in the incubation appeared to be due to the decreased pH and non‐equilibrium conditions in the organic matter‐amended sediment during the first weeks of incubation. Manganese redox systems exerted no discernable impact on the E_h of the sediment.     

The effect of methanogenesis inhibition,inoculum and substrate concentration on hydrogen and carboxylic acids production from cassava wastewater

Manipueira is a carbohydrate-rich agro-industrial waste from cassava processing. It is considered well suitable for biotechnological processes, such as hydrogen and carboxylic acids production, due to the high content of easily degradable organic matter. However, the proper methanogenesis inhibition method, inoculum type, and organic loads are factors still limiting the processes. The objective in this work was to evaluate the effects of such factors on byproducts production in anaerobic reactors. Batch experiments were conducted with 2.3-L flasks during two operational phases. In the first phase (P1), inhibition of methanogens in the sludge was evaluated using acetylene (1% v/v of headspace) and heat treatment (120 °C, 1 atm for 30 min). In the second phase (P2), three inoculum types obtained from common anaerobic sludges (bovine rumen and sludges from municipal and textile industrial wastewater treatment plants) were individually assayed. P2 aimed to identify the best inoculum, based on hydrogen production ability, which was tested for three initial concentrations of manipueira in terms of chemical oxygen demand (COD) (10, 20 and 40 g O₂/L). Results of P1 indicated that either acetylene or heat treatment efficiently inhibited methanogenesis, with no methane production. However, the maximum H₂ production potential by applying heat treatment (~ 563 mL) was more than twice compared with that by acetylene treatment (~ 257 mL); and butyrate was the main carboxylic acid by-product (~ 3 g/L). In P2 experiments after sludge heat treatment, the highest hydrogen yield (1.66 ± 0.07 mol H₂/mol glucose) and caproic acid production (~ 2 g/L) were observed at 20 g O₂/L of manipueira COD, when bovine rumen was the inoculum. The primary metabolic degradation products in all P2 experiments were ethanol, acetic, butyric, propionic and caproic acids. The finding of caproic acid detection indicated that the applied conditions in manipueira anaerobic degradation favored carbon chain elongation over methanogenesis.