Process modelling and techno-economic analysis of anaerobic digestion of sewage sludge integrated with wet oxidation using a gravity pressure vessel and thermal hydrolysis.

Anaerobic digestion (AD) of sewage sludge is used to biodegrade sewage sludge into biomethane and digestate. With the addition of thermal processes such as thermal hydrolysis (TH) and wet oxidation (WO), AD biodegradability generally improves. Implementation of additional treatment is challenging due to the limitation in the mass and energy balances. Hence, tools such as process simulation can be utilized to predict the input and output around the process. In addition, an economic analysis needs to be conducted to check the economic feasibility. The techno-economic analysis (TEA), an integrated method to evaluate a process scheme through simulation and subsequent economic analysis, is effective in providing a systematic understanding of economic implications and the feasibility of a process by identifying the bottlenecks and uncertainties that have a significant impact on the technology. TEA of AD, especially incorporating the TH or WO using gravity pressure vessel (GPV) technology, is limited in the literature. A comprehensive TEA of the AD and the pre- and post-treatment schemes can be utilized to determine the most feasible pathway for sludge treatment for implementation in the wastewater industry. In this study, TEA for four different scenarios of AD was conducted using Aspen Plus and economic analysis tools: (1) without any pre- or post-treatment, (2) with TH pre-treatment, (3) with 100 % WO post-treatment, and (4) with 20 % partial wet oxidation (PWO) and acid hydrolysis pre- or post-treatment. A simulation model (GPVM) was developed using Aspen Plus to mimic the GPV reactor. The study outcomes showed that Scenario 3 with 100 % WO post-treatment was the most suitable for processing parameters and sludge treatment cost. The sensitivity analysis concluded that operating cost and plant capacity are the dominant factors that impact the plant feasibility significantly.

Plastic pollution risks in bioretention systems: a case study.

We investigated plastic pollution in soil-based stormwater bioretention systems (BRS), which are potentially important pollutant receptors and pathways. Our integrated study is the first of its kind, focusing on plastic abundance, size fractionation, composition, and interactions with urban metrics (including housing density and auxiliary stormwater treatment infrastructure) in BRS filter media. Our results revealed that mesoplastic (MEP) and microplastic (MP) concentrations in BRS are comparable with those reported in other stormwater systems (e.g. wetlands) as well as soils in other land use areas (e.g. agriculture). Distributional sampling within the BRS revealed MP abundances do not change with horizontal distance from the inlet to the outlet. However, MEP abundances drastically decreased towards the outlet, indicating plastic accumulation within BRS. This is important because MEPs can breakdown into MPs which can affect BRS function as well as mobilise downstream. Yet our data uncovered more complex mechanisms involved in BRS plastic fate, with composition data revealing that MPs are not simply breakdown products of MEPs but are instead derived from different sources. Composition, morphology and colour analysis confirmed that BRS polymer liners are a key source of MPs and MEPs in soil filter media. Multivariate analysis of the data with urban design metrics showed gross pollutant traps are effective at decreasing MP concentrations in BRS but not as effective at controlling MEPs. Our results point to complex plastic transmission and accumulation pathways in BRS. Interception measures can partially alleviate plastic risk, but more work is needed to elucidate plastic long-term fate in BRS.

Deploying two-stage anaerobic process to co-digest greasy sludge and waste activated sludge for effective waste treatment and biogas recovery.

High-strength waste activated sludge (WAS) and greasy sludge (GS) were largely generated from canned tuna processing. This study reports the performance of the two-stage anaerobic process for co-digesting WAS and GS. Various WAS:GS mixing ratios of 0:100, 10:90, 20:80, 30:70, 40:60, 50:50, 60:40, 70:30, 80:20, 90:10, and 100:00 (volatile solids (VS) basis) were investigated in batch acidogenic stage at ambient (30 °C ± 3 °C), 55 °C, and 60 °C temperatures. Subsequently, the effluents from the first stage were used to produce methane in the second methanogenic stage at an ambient temperature. The highest methane yield of 609 mL CH4/g-VSadded was achieved using acidogenic effluents generated from a WAS:GS mixing ratio of 40:60 at an ambient temperature. The first-order kinetic constants (k) for the first (k1) and second (k2) stages were subsequently estimated to be 0.457 d-1 and 0.139 d-1, respectively. The obtained k constants were further used to predict the hydraulic retention time (HRT) for the two continuously stirred tank reactors (CSTR) in series. Consequently, the calculated 4-day HRT and 20-day HRT for 50-L CSTR1 and 250-L CSTR2, respectively, were used to operate the continuous two-stage process at an ambient temperature by feeding with a 40:60-WAS:GS mixing ratio. A satisfactory methane yield of 470-mL CH4/g-VS along with 75% chemical oxygen demand (COD) removal was generated. Furthermore, the predicted methane yield of 450-mL CH4/g-VS obtained from the simple kinetic CSTR model resembled the experimental yield with 96% accuracy. The obtained experimental results demonstrate that WAS and GS co-digestion could be successfully accomplished using a practical two-stage anaerobic process operated at an ambient temperature.

Performance of pilot scale two-stage anaerobic co-digestion of waste activated sludge and greasy sludge under uncontrolled mesophilic temperature.

Waste-activated sludge (WAS) and greasy sludge (GS) discharged from the canned tuna industry are considerably characterized as harsh organic wastes to be individually treated by using traditional anaerobic digestion. This study was attempted to anaerobically co-digest WAS and GS in continuous pilot scale two-stage process, comprising the first 50 L continuous stir tank reactor (CSTR1) and the second 250 L continuous stir tank reactor (CSTR2). The two-stage co-digesting operation of dewatered WAS:GS ratio of 0.4:1 (g-VS) at ambient temperature with the organic loading rate (OLR) of 12.6 ± 0.75 g-VS/L·d and 2.26 ± 0.13 g-VS/L·d, corresponding to 3-day and 17-day hydraulic retention time (HRT) for the first and second stage, respectively generated highest methane production rate of 957 ± 86 mL-CH4/L·d, corresponding to methane yield of 423.4 ± 36 mL-CH4/g-VS. Organic removal efficiency obtained was around 67.5% on COD basis. The microbial diversity was depended on the process's activity. Bacteria were mostly detected in the CSTR1, dominating with the phylum Firmicutes and Proteobacteria, whereas genus Methanosaeta archaea were found dominantly in the CSTR2. The economic analysis of process shows payback period (PBP), internal rate of return (IRR), and net present value (NPV) of 3 years, 30%, and 250,177 USD, respectively. This study demonstrated the potential approach to applying the two-stage anaerobic co-digestion process to stabilize both WAS and GS along with generating valuable bioenergy carriers.

Effects of pretreatment methods on biomethane production kinetics and microbial community by solid state anaerobic digestion of sugarcane trash.

Solid state anaerobic digestion (SS-AD) of lignocellulose is effective in improving biomethane productivity but is limited by low biomass digestibility and lack of substrate-specific working microorganisms. In this study, the effects of different pretreatment methods on biomethane production by SS-AD of sugarcane trash were studied. The biomethane production, fitted to a modified Gompertz's model, predicted a maximum methane yield of 214.2 L/kg volatile solids (VS) and productivity of 6.9 L/kg VS/day from KOH-pretreated trash, respectively. Microbial community analysis showed that bacterial community was significantly associated with volatile acids and pretreatment types while archaeal community was significantly associated with methane yield. Microbial community dynamics was revealed in SS-AD. Main genera related to pretreatment method were identified and discussed. This study generated important information on SS-AD of lignocellulosic biomass pretreated by different methods, which is useful for developing bioaugmentation strategies to improve biomethane production by SS-AD.

Impact of Operational Factors, Inoculum Origin, and Feedstock Preservation on the Biochemical Methane Potential.

Anaerobic digestion for the valorization of organic wastes into biogas is gaining worldwide interest. Nonetheless, the sizing of the biogas plant units require knowledge of the quantity of feedstock, and their associated methane potentials, estimated widely by Biochemical Methane Potential (BMP) tests. Discrepancies exist among laboratories due to variability of protocols adopted and operational factors used. The aim of this study is to verify the influence of some operational factors (e.g., analysis frequency, trace elements and vitamins solution addition and flushing gas), feedstock conservation and the source of inoculum on BMP. Among the operational parameters tested on cellulose degradation, only the type of gas used for flushing headspace of BMP assays had shown a significant influence on methane yields from cellulose. Methane yields of 344 ± 6 NL CH4 kg-1 VS and 321 ± 10 NL CH4 kg-1 VS obtained from assays flushed with pure N2 and N2/CO2 (60/40 v/v). The origin of inoculum (fed in co-digestion) only significantly affected the methane yields for straw, 253 ± 3 and 333 ± 3 NL CH4 kg-1 VS. Finally, freezing/thawing cycle effect depended of the substrate (tested on biowaste, manure, straw and WWTP sludge) with a possible effect of water content substrate.

Enzymatic purification of microplastics in soil.

Accurate and effective analysis of microplastics depends on the purification of any biogenic matter present in the environmental sample. Within the soil environment, the presence of biogenic materials (living and non-living) obstruct reliable identification of microplastics. However, while conventional acidic, alkaline, and wet peroxidation methods are often used for microplastics purification, they can result in significant alteration to the polymer integrity. To overcome this issue of polymer damage, we have developed a more efficient protocol using enzymes to eliminate organic materials from soil media without affecting the synthetic polymers. This method describes a simple enzymatic protocol that eliminates the organic matter based on the application of enzymes that target the three natural components of lignocellulosic biomass (cellulose, hemicellulose, and lignin). The enzymatic protocol introduced in this study allows for the use of an oxidizing agent for the pre-treatment of samples and density separation step. Additionally, this method was used to determine the enzymatic digestion efficiencies of soil organic matter and recovery rates of microplastics. Finally, the recovered microplastics were characterized by techniques including stereomicroscopy, FT-IR, and SEM. This method proved to be effective in reducing approximately >90% of organic materials in soil samples. After showing a high digestion efficiency the method was applied to spiked microplastic soil samples where high recovery rates were established and plastic characteristics were conserved. Despite being a time consuming and expensive method when compared to other purification methods. The key benefits of this methodology are:•Minimal sample preparation•Representative purification of microplastic from diverse soil media; and•Most importantly, preservation of polymer integrity aiding requirements needed for particle identification (e.g.,% mass polymer remaining, SEM images revealing no obvious polymer morphology change after enzyme treatment).

The rise of artificial soil carbon inputs: Reviewing microplastic pollution effects in the soil environment.

The surge in the use of plastic materials, its poor handling and disposal have led to an increase in microplastic pollution in terrestrial environments. Microplastic pollution in soils is of concern due to potential influences on soil properties which play a critical role in plant growth and soil fertility. Moreover, the soil environment is a key nexus linking the atmosphere, hydrosphere, biosphere and lithosphere, and thus represents a crucial conduit for pollutant migration from the anthroposphere. In this review we evaluate the effects of microplastics in the soil environment with a specific focus on physical properties and biological function in the rhizosphere. Our review reveals that agricultural sources, particularly plastic mulches and waste applications, represent the main source of soil microplastic inputs. Once in the soil environment, microplastic effects on soil properties are highly variable depending mainly on soil type and microplastic characteristics. Soil properties relating to erosion-risk (i.e., bulk density), structural integrity (i.e., aggregate stability, particularly micro-aggregate stability), and water-storage capacity (i.e., evaporation rate, desiccation) are generally adversely impacted by soil microplastic inputs. Soil microplastic effects on rhizosphere function (i.e., plant health and microbial activity) are remarkably varied with some studies revealing positive impacts, such as enhanced plant-symbiotic fungi associations, from soil plastic additions. However, all identified publications reported at least one detrimental MP-induced impact on plant responses. Finally, our review revealed associations between microplastic properties and soil functional parameters - in particular, polymer size and morphology control soil water-holding properties whereas polymer type influences plant response. These associations will be helpful in targeting future research directions on this important topic that intersects all of the Earth's spheres.

Prediction of methyl orange removal by iron decorated activated carbon using an artificial neural network.

Date Stones were used as a bio-degradable waste source for preparing iron impregnated activated carbon. The prepared activated carbon-containing oxides of iron were characterized using SEM, XRD, FTIR, and BET. The specific surface area of the iron decorated activated carbon was 738.65 m2/g. The XRD confirmed the presence of magnetite and hematite while the SEM images assured the presence of pores. The prepared activated carbon was used to remove methyl orange from wastewater. Genetic Algorithm was used to develop a model which could predict the removal efficiency of the dye. The ANN model was validated and the effect of different parameters like adsorbent dosage (0.1-1 g/L), initial dye concentration (2-20 mg/L), pH (2-11), time (10-55 min) and temperature (30-75°C) was estimated both experimentally and predicted using the model. The adsorption process follows the Freundlich isotherm and pseudo-second-order kinetic model. The values of 1/n and KF obtained from the Freundlich isotherm designate good adsorption capacity. Both experimental and model-predicted data agrees with the kinetic model. The adsorption rate is proportionate to the square of the number of vacant adsorption sites. From the thermodynamic study, the positive worth of ΔH° indicates the energy-absorbing nature of the surface assimilation method and the process is endothermic in nature. The low values of each ΔG° (-200 to 0 kJ/mol) and ΔH° correspond to physical surface assimilation. A positive worth of ΔS° reflects the inflated randomness at the solid-aqueous interface with some structural changes in adsorbate and adsorbent.

A systematic evaluation of biomethane production from sugarcane trash pretreated by different methods.

Biomethane production was systematically evaluated with sugarcane trash pretreated by liquid hot water (LHW), dilute acid (DA) and KOH solutions. Multiple linear regression analysis identified glucan in pretreated solid residue as well as C5 sugars and acetic acid in pretreatment hydrolysate as the key parameters affecting biomethane potentials. Moreover, biomethane production was best simulated using Chen & Hashimoto model with a predicted highest methane yield of 187 mL/g initial total solids (TS) based on LHW (130 °C for 15 min) and KOH (10% on trash, 150 °C for 60 min) pretreatments. KOH pretreatment led to a biomethane yield of 167 mL/g initial TS at day 25, 82%, 34% and 33% higher than those achieved with untreated and pretreated trash samples with optimal LHW and DA conditions, respectively. This study led to the identification of best kinetic model and pretreatment condition for biomethane production from sugarcane trash through a systematic evaluation.

Effect of macro- and micro-nutrients addition during anaerobic mono-digestion of grass silage in leach-bed reactors.

The effect of macro- (NH4Cl) (set I) and micro-nutrients (Fe, Ni, Co and Mo) (set II) addition on chemical oxygen demand (COD) solubilisation during anaerobic mono-digestion of grass silage was investigated in two sets of leach bed reactor experiments at 35°C. Results showed that addition of NH4Cl and micro-nutrients improved COD solubilisation by 18% (0.56 g SCOD g-1 volatile solids) and 7% (0.45 g SCOD g-1 VS), respectively than control. About 20-50% of the added micro-nutrients were bioavailable in the produced leachates, while the rest (50-80%) were adsorbed onto the grass silage. Results of biological methane potential assays showed that, specific methane yields of grass silage were improved by 17% (0.36 ± 0.02 m3 CH4 kg-1 VSadded) when NH4Cl was supplemented while Fe, Ni, Co and Mo addition improved methane yields by 15% (0.33 ± 0.005 m3 CH4 kg-1 VSadded) when compared to control.

Method for the technical, financial, economic and environmental pre-feasibility study of geothermal power plants by RETScreen - Ecuador's case study.

RETScreen presents a proven focused methodology on pre-feasibility studies. Although this tool has been used to carry out a number of pre-feasibility studies of solar, wind, and hydropower projects; that is not the case for geothermal developments. This method paper proposes a systematic methodology to cover all the necessary inputs of the RETScreen-International Geothermal Project Model. As case study, geothermal power plant developments in the Ecuadorian context were analysed by RETScreen-International Geothermal Project Model. Three different scenarios were considered for analyses. Scenario I and II considered incentives of 132.1 USD/MWh for electricity generation and grants of 3 million USD. Scenario III considered the geothermal project with an electricity export price of 49.3 USD/MWh. Scenario III was further divided into IIIA and IIIB case studies. Scenario IIIA considered a 3 million USD grant while Scenario IIIB considered an income of 8.9 USD/MWh for selling heat in direct applications. Modelling results showed that binary power cycle was the most suitable geothermal technology to produce electricity along with aquaculture and greenhouse heating for direct use applications in all scenarios. Financial analyses showed that the debt payment would be 5.36 million USD/year under in Scenario I and III. The correspindig values for Scenario II was 7.06 million USD/year. Net Present Value was positive for all studied scenarios except for Scenario IIIA. Overall, Scenario II was identified as the most feasible project due to positive NPV with short payback period. Scenario IIIB could become financially attractive by selling heat for direct applications. The total initial investment for a 22 MW geothermal power plant was 114.3 million USD (at 2017 costs). Economic analysis showed an annual savings of 24.3 million USD by avoiding fossil fuel electricity generation. More than 184,000 tCO2 eq. could be avoided annually.

Assessment of hydrothermal pretreatment of various lignocellulosic biomass with CO2 catalyst for enhanced methane and hydrogen production.

Hydrothermal pretreatment of five lignocellulosic substrates (i.e. wheat straw, rice straw, biomass sorghum, corn stover and Douglas fir bark) were conducted in the presence of CO2 as a catalyst. To maximize disintegration and conversion into bioenergy (methane and hydrogen), pretreatment temperatures and subsequent pressures varied with a range of 26-175 °C, and 25-102 bars, respectively. Among lignin, cellulose and hemicelluloses, hydrothermal pretreatment caused the highest reduction (23-42%) in hemicelluloses while delignification was limited to only 0-12%. These reductions in structural integrity resulted in 20-30% faster hydrolysis rates during anaerobic digestion for the pretreated substrates of straws, sorghum, and corn stover while Douglas fir bark yielded 172% faster hydrolysis/digestion due to its highly refractory nature in the control. Furans and phenolic compounds formed in the pretreated hydrolyzates were below the inhibitory levels for methane and hydrogen production which had a range of 98-340 ml CH4/g volatile solids (VS) and 5-26 ml H2/g VS, respectively. Results indicated that hydrothermal pretreatment is able to accelerate the rate of biodegradation without generating high levels of inhibitory compounds while showing no discernible effect on ultimate biodegradation.

Mesophilic co-digestion of dairy manure and lipid rich solid slaughterhouse wastes: process efficiency, limitations and floating granules formation.

Lipid and protein rich solid slaughterhouse wastes are attractive co-substrates to increase volumetric biogas production in co-digestion with dairy manure. Addition of decanter sludge (DS), containing 42.2% of lipids and 35.8% of proteins (total solids basis), up to 5% of feed mixture resulted in a stable process without any indication of long chain fatty acids (LCFA) or free ammonia (NH3) inhibition and in 3.5-fold increase of volumetric biogas production. Contrary, only lipids addition as technical fat (TF) at over 2% of feed mixture resulted in formation of floating granules (FG) and process efficiency decrease. Formed FG had low biodegradability and its organic part was composed of lipids and calcium salts of LCFAs. Anaerobic digestion process intentionally directed to FG formation, could be a viable option for mitigation and control of lipids overload and derived LCFA inhibition.

Co-digestion of sewage sludge and sterilized solid slaughterhouse waste: methane production efficiency and process limitations.

The rendering product of Category 2 and 3 Animal By-Products is known as sterilized mass (SM) and it is mainly composed of fat and proteins, making it interesting substrate for anaerobic digestion. Batch and semi-continuous laboratory experiments were carried out to investigate the effect of SM addition in co-digestion with sewage sludge on methane production and possible process limitations. Results showed that SM addition in the feed mixture up to 5% (w/w), corresponding to 68.1% of the organic loading, increased methane production 5.7 times, without any indication of process inhibition. Further increase of SM addition at 7.5% (w/w) caused methane production decrease and volatile solids removal reduction, that was mainly related to remarkably increased free ammonia concentration in the digester of 596.5±68.6 gNH3 L(-1). Sterilized mass addition of 10% (w/w) caused intensive foaming, LCFA accumulation of 9172±701.2 mgCOD-LCFA g(-1) sample and termination of the experiment.

Effect of additives on process stability of mesophilic anaerobic monodigestion of pig slaughterhouse waste.

The effect of two additives on anaerobic monodigestion of pig slaughterhouse waste was studied in three laboratory scale continuously stirred tank reactors (CSTRs) operated for 242-284 days at 35°C. A higher organic loading rate (OLR), namely 2.25 kg volatile solids (VS)/m(3)d with a hydraulic retention time (HRT) of 30 d was feasible with an additive containing Fe, HCl and trace elements while an OLR of 1.5 kg VS/m(3)d (HRT 30 d) led to instabilities in CSTR with an additive consisting of Fe and HCl and in CSTR without additives. Methane yields of ca. 700 dm(3) CH(4)/kg VS(fed) were obtained in all reactors under stable conditions. Both additives decreased H(2)S concentration of the biogas below detection limit 0.5 ppm while in a control reactor H(2)S concentration was up to 1900 ppm. In conclusion, the results suggest the possibility that additives may facilitate higher OLRs in monodigestion of pig slaughterhouse waste.

Methane potential of sterilized solid slaughterhouse wastes.

The aim of the current study was to determine chemical composition and methane potential of Category 2 and 3 solid slaughterhouse wastes rendering products (SSHWRP) viz. melt, decanter sludge, meat and bone meal (MBM), technical fat and flotation sludge from wastewater treatment. Chemical analyses showed that SSHWRP were high in protein and lipids with total solids (TS) content of 96-99%. Methane yields of the SSHWRP were between 390 and 978 m(3) CH(4)/t volatile solids (VS)(added). Based on batch experiments, anaerobic digestion of SSHWRP from the dry rendering process could recover 4.6 times more primary energy than the energy required for the rendering process. Estonia has technological capacity to sterilize all the produced Category 2 and 3 solid slaughterhouse wastes (SSHW) and if separated from Category 1 animal by-products (ABP), it could be further utilized as energy rich input material for anaerobic digestion.

Agricultural potential of anaerobically digested industrial orange waste with and without aerobic post-treatment.

The potential of anaerobically digested orange waste with (AAD) and without (AD) aerobic post-treatment for use in agriculture was evaluated through chemical analyses, short-term phytotoxicity and long-term plant assays. Chemical analyses showed that AD contained ammonia and organic acids, and aerobic post-treatment did not significantly remove these phytotoxins. The N:P2O5:K2O ratio in AD was 1:0.26:0.96 and aerobic post-treatment did not change the composition in AAD except for K2O (1:0.26:1.24). Heavy metal contents in AD and AAD were more or less the same and were below the upper limit recommended for non-sewage sludge application on agricultural soils. Short-term phytotoxicity tests showed that seed germination and root elongation of Chinese cabbage and ryegrass were severely inhibited at digestate concentrations of 60-100%. Germination index values were well below the score of 50% required to indicate the phytotoxic-free nature of compost. Long-term plant assays showed that AD and AAD, when supplemented with a base fertilizer, resulted in higher plant growth, and fresh weight and dry matter production than AD without base fertilizer. The results thus indicate that aerobic post-treatment did not have any significant beneficial effect on reducing phytotoxicity, and AD could be used as such on agricultural soils, especially with high P.

Mesophilic and thermophilic anaerobic co-digestion of rendering plant and slaughterhouse wastes.

Co-digestion of rendering and slaughterhouse wastes was studied in laboratory scale semi-continuously fed continuously stirred tank reactors (CSTRs) at 35 and 55 °C. All in all, 10 different rendering plant and slaughterhouse waste fractions were characterised showing high contents of lipids and proteins, and methane potentials of 262-572 dm(3)CH(4)/kg volatile solids(VS)(added). In mesophilic CSTR methane yields of ca 720 dm(3) CH(4)/kg VS(fed) were obtained with organic loading rates (OLR) of 1.0 and 1.5 kg VS/m(3) d, and hydraulic retention time (HRT) of 50 d. For thermophilic process, the lowest studied OLR of 1.5 kg VS/m(3) d, turned to be unstable after operation of 1.5 HRT, due to accumulating ammonia, volatile fatty acids (VFAs) and probably also long chain fatty acids (LCFAs). In conclusion, mesophilic process was found to be more feasible for co-digestion than thermophilic process, methane yields being higher and process more stable in mesophilic conditions.

Two-stage anaerobic digestion of tomato, cucumber, common reed and grass silage in leach-bed reactors and upflow anaerobic sludge blanket reactors.

Anaerobic digestion of tomato, cucumber, common reed and grass silage was studied in four separate two-stage reactor configuration consisting of leach bed reactor (LBR) and upflow anaerobic sludge blanket reactor (UASB). LBR studies showed that COD solubilization for cucumber and grass silage was higher (50%) than tomato (35%) and common reed (15%). Results also showed that 31-39% of initial TKN present in tomato and cucumber was solubilized in the leachates and 47-54% of the solubilized TKN was converted to NH(4)-N. The corresponding values for common reed and grass silage were 38-50% and 18-36%, respectively. Biomethanation of the leachates in UASB reactors resulted in methane yields of 0.03-0.14 m(3) CH(4) kg(-1)VS(fed) for the studied crop materials. Thus, high COD solubilization, high nitrogen mineralization and solubilization rates were feasible during anaerobic digestion of lignocellulosic materials in a two-stage LBR-UASB reactor system.