Dynamics of Bacterial Abundance,Biomass, Activity,and Community Composition in the Oligotrophic Traunsee and the Traun River (Austria)

The holomictic Traunsee is the deepest and second largest lakein Austria. The special characteristic of this ecosystem isthe fact that local salt and soda industries presumably alterthe lake by the discharge of waste materials. Since thebeginning of the 20th century salt and soda works areannually releasing up to 50,000 tons of solid wastes and up to150,000 tons of chloride into Traunsee. To assess potentialeffects of these anthropogenic impacts on the bacterioplanktonthree sampling sites, influenced as well as not influenced bythe industrial discharge, were chosen for comparison andsampled monthly from November 1997 to October 1998. Bacterialabundance ranged between 0.4 to 3.0 × 10⁶ cells ml^-1 with decreasing numbers along the depth profile. Theproportion of actively respiring bacteria, i.e. INT [2-(4-iodophenyl)-3-(4-nitrophenyl)-5-phenyltetrazolium chloride]reducing cells, never exceeded 10% of DAPI (4',6'-diamidino-2-phenylindole) stained cells. Fluorescence in situ hybridization (FISH) was used to examine the seasonal and spatial distribution of dominant phylogenetic groups of thebacterioplankton. Up to 84% of bacteria detected with DAPIcould be detected via FISH applying the universal bacterialprobe EUB338. Percentages of alpha- and beta-Proteobacteriaand members of the Cytophaga-Flavobacterium cluster did notexceed 60% of DAPI-stained cells.Beta-Proteobacteriaappeared to be the most abundant group, not only in Traunsee butalso in two reference lakes, Attersee and Hallstättersee. No significant differences in any of the bacterial parameters couldbe detected between the three sampling sites and all measurementswere found in the range reported for oligotrophic lakes. The highdischarge of the Traun River, resulting in a lake water renewaltime of only one year, may diminish possible effects of industrial waste discharge in the pelagic zone.     

Industrial Tailings in Traunsee (Austria) Revisited: The Status of 1999

Alkaline tailings from a salt work and a soda plant have been pumped into the southernmost part of Traunsee at Ebensee for many decades. A survey in 1981 showed an accumulation of more than 3 × 10⁶ m³ alkaline mud in the Bay of Ebensee and the existence of slumping structures and turbidites in the profundal zone of the lake. A new survey of the industrial tailings has been performed in 1999. Compared to the earlier survey, the accumulation in the Bay of Ebensee has grown to >4 × 10⁶ m³, which suggests an average yearly input of 90 000 m³. Slumping structures and turbidites document the unstable situation of the tailings near the waste inlet. The lake area occasionally affected by the turbidity currents in the profundal zone has increased to 19%. Within the central profundal area these tailings reach <1 m in thickness.     

Variations in the Epiphytic Invertebrate Community Structure on Potamogeton Perfoliatus L. in Traunsee (Austria): Patchiness versus Impacts by Industrial Tailings

The epiphytic invertebrates found on Potamogetonperfoliatus L. in Traunsee, an oligotrophic Alpine lake inAustria, were investigated in August and October 1998 in orderto study the impact of industrial tailings discharged into thelake. 113 taxa were found, 54 could be identified to thespecies level. Their total abundance varied between ca.190,000 and 1,138,000 ind. m^-2 lake bottom area. Thisepiphytic assemblage was dominated by Dreissenapolymorpha and Sida crystallina, which resulted in avery low overall species diversity. Multivariate statisticalanalyses revealed significant differences in the communitystructure between three sites, each of them was located at adifferent distance from the site of industrial waste emission.These differences were interpreted as variations which reflectthe patchiness within highly structured habitats rather thanas being the result of the industrial pollution.     

Protozooplankton in the Deep Oligotrophic Traunsee (Austria) Influenced by Discharges of Soda and Salt Industries

Traunsee is a deep oligotrophic lake in Austria characterised by an artificial enrichment of chloride in the hypolimnion (up to 170 mg L^-1) caused by waste disposal of soda and salt industries. Protists were collected monthly over one year, observed alive and after Quantitative Protargol Staining (ciliates) or via epifluorescence microscopy (heterotrophic flagellates). Three sites within the lake (0–40 m depths) were compared to deeper water layers from 60–160 m depths where chloride concentrations and conductivity were increased. In addition, we observed the protozooplankton of two neighbouring lakes, i.e. reference systems, during one sampling occasion. In Traunsee the abundance of ciliates was low (200–36 600 cells L^-1) in contrast to high species diversity (at least 60 different species; H_S = 2.6) throughout the year. The main pelagic species in terms of abundance were small oligotrichs and prostomatids like Rimostrombidium brachykinetum/hyalinum, Balanion planctonicum and Urotricha spp. throughout the investigation period. Among free-living heterotrophic flagellates, which occurred at densities of 40–2800 cells mL^-1, small morphotypes dominated in the pelagial. No differences at the community level between the three lakes could be observed and pelagic ciliates and flagellates seemed not to be affected by increased chloride concentrations or by enhanced conductivity.     

Assessment of the Ecological Integrity of Traunsee (Austria) Via Analysis of Sediments and Benthic Microbial Communities

Since nearly one hundred years Traunsee experiences the import of tons of liquid and solid waste originating from salt and soda production. Today, the lake exhibits chloride concentrations of up to 170 mg L^-1 and 19% of the lake floor are directly or indirectly influenced by industrial deposits (ID). Based on the comparison of several microbial parameters in unaffected, directly affected and intermediate lake bottom sediments, the ecological integrity of the lake was evaluated. The highly alkaline ID, which were exclusively colonized by microorganisms, harbored a bacterial community reduced by a factor of 10 in abundance and biomass compared to undisturbed sediment areas within the lake. The bacterial community of ID was furthermore characterized by a reduced content of actively respiring cells (INT-formazan reduction), a lower frequency of dividing cells (FDC) and a significantly reduced cell and biomass production. A 80 to 90% reduction in carbon recycling is estimated for the area exclusively covered by ID. Protists, although occasionally absent from the industrial sediments, were in general found to be less sensitive to the contaminant stress. Differences in alkalinity and dissolved organic carbon (DOC) concentrations of sediment porewaters as well as the total organic content and C/N ratios of sediments partly explain the microbial pattern observed at the various sampling sites. Possible consequences of the continuous industrial tailings for the whole lake ecosystem and the validation of the ecological integrity are discussed.     

Distribution Pattern of Benthic Invertebrate Communities in Traunsee (Austria) in Relation to Industrial Tailings and Trophy

Traunsee, an oligotrophic Alpine lake, has suffered from inputsof industrial tailings (soda- and salt-mining industries) forseveral decades. The effects of the industrial sludges on thespatial distribution of the littoral and profundal invertebratefauna was investigated along three transects at five dates. Inthe littoral zone, no negative impacts were found. A distinctgradient in faunal composition and diversity was, however,observed along a profundal transect relative to the distance fromthe waste emission. Near the industrial input, the enhanced pH,the substrate instability, and the poor sediment quality forsubstrate- and deposit-feeders were the main factors that loweror prohibit colonization of the industrial sludges. Along atransitional zone between the waste emission and the deepestbasin, recolonization was delayed, but did occur as soon aslayers of a few mm natural sediment seal the sludge. Mobile,epibenthic organisms are the first to settle these areas, whereasrecolonization by tube-building oligochaetes and chironomidsrequires thicker sealings of the industrial sludges. Differencesin the abundance of benthic invertebrates at different profundalsites were not only related to the waste emission, but also tothe influence of the main tributary, the River Traun. Theenhanced availability of allochthonous organic matter wasprobably responsible for high densities of tubificids near theinlet in the South of Traunsee. Moreover, a higher proportion oftolerant oligochaete and ostracod species in the lower profundaloutside the influence of the industrial tailings was interpretedas reflecting the increased trophy of Traunsee in the 1970s,which forced sensitive species to shift to the upper profundalwhen the oxygen climate deteriorated.     

Picocyanobacteria – Sensitive Bioindicators of Contaminant Stress in an Alpine Lake (Traunsee Austria)

The abundance and photosynthetic activity ofpicocyanobacteria in the oligotrophic alpine lake Traunseewere measured at a station located close to the outlet ofindustrial soda waste and at a mid-lake reference stationduring spring, 1999 through to autumn, 2000.Picocyanobacterial numbers measured by flow cytometry inTraunsee (0.7–13.2 × 10⁴ ml^-1) were comparable tothose of other oligotrophic lakes, and there was nosignificant difference between the contaminated and thereference sampling location. Picoplankton (<2 m)photosynthetic rates measured in vitro by the ¹⁴C-technique were significantly reduced at the contaminated siterelative to the reference station at low photosyntheticallyavailable radiation (10 E m^-2 s^-1), while nodifference between these two stations was found at moderatelyhigh light intensity (100 E m^-2 s^-1). Theinvestigation was complemented by laboratory experiments withcultured picocyanobacteria. Three Synechococcus spp.strains were exposed to water taken from either of the twoTraunsee stations and from a control station located inneighbouring Attersee. Cell-specific photosynthetic activitymeasured by 4-h in vitro incubations revealed no significantdifference among the three stations investigated. Growthrates of the same three Synechococcus spp. strains weremeasured by flow cytometry over several days in thelaboratory. One strain, in particular, was sensitive to watertaken from the contaminated site; growth rate of this strainwas significantly reduced, relative to when exposed to watertaken from the reference station. Taken together, our resultsdemonstrate that picocyanobacteria are highly sensitivebioindicators of contaminant stress. The overall impact ofthe emissions from the industrial outlet on thepicocyanobacteria was, however, relatively minor.     

Species Composition of Freshwater Invertebrates in Relation to Chemical and Physical Factors in High Mountains in Soutwestern Norway

The composition of benthic invertebrates was investigated in three Norwegian alpine watersheds during the period 1991–1997. The watersheds represented an environmental gradient in chemical factors. The Kvenna watershed was relatively well buffered, Lake Øvre Neådalsvatn was poorly buffered, but receives low inputs of atmospheric pollution while Lake Stavsvatn has low buffering capacity and receives larger inputs of acidifying components. Qualitative samples were taken in the inlet rivers, lake littoral zone, lake outlet and in the outlet rivers of the lakes for analyses of species composition. In Ø. Neådalsvatn the water chemical data showed strong seasonal variations with waters of low ionic content during snowmelt and summer, while increased ion concentrations build up during winter. The time of ice break and/or water temperature rise during the growing season affected the life cycle of Siphlonurus lacustris and Parameletus chelifer. Even small changes in pH or ANC seemed to have a strong effect on Baetis rhodani. In the Kvenna watershed eight very sensitive species were found at sites with pH 6.5, Ca 1.2 mg L^-1 and LAl < 10 eq L^-1. Only two highly sensitive species, B. rhodani and Capnia sp. were recorded when pH was 6, concentration of calcium 0.8 mg L^-1 and low labile aluminium < 10 eq L^-1. None of the highly sensitive species occurred in Stavsvatn, a formerly acidified area, where LAl concentrations ranged between 25–40 eq L^-1. Low ionic content and elevated concentrations of labile aluminium are suggested to exclude sensitive invertebrates in alpine lakes. Synergistic effects of dilute water and harsh climate are assumed to increase sensitivity of invertebrates to acid water. Global warming will result in higher precipitation and more snow in the west Norwegian alpine area. This will shorten the growing season, increase the amount of dilute water and consequently threaten invertebrate species living close to their tolerance limits.     

14C-Photosynthesis of Phytoplankton in an Oligotrophic Alpine Lake (Traunsee,Austria) and its Response to Turbidity Caused by Industrial Tailings

The influence of industrial tailings on the biological integrity of the phytoplankton was assessed from annual measurements of photosynthetic rates in the alpine lake Traunsee. The mean annual integral production of 21 mmol C m^-2 d^-1 corresponded to the oligotrophic nature of the lake. Effects of effluents were tested by comparing photosynthesis at a station close to the industrial outlet (EB) and at a reference site with a maximum depth of 190 m (VI). Between-site optical properties (vertical attenuation coefficient, euphotic depth) were statistically significant different. The euphotic zone at the impacted station was on average 2 m shallower than at the reference site, owing to turbidity emanating from the industrial plant. The adaptation to low light intensities by the algal community at this station was evident from a high maximum light utilisation coefficient (^* at low light saturation (E _K). Algae at the deep reference site were photosynthetically less efficient but adapted to high light intensities. Photosynthetic adaptation to different light climates in the euphotic zone without significant quantitative biomass alterations at the impacted site gave a clear signature of biological integrity of the phytoplankton in the oligotrophic Traunsee.     

The Application of Stable Isotopes for Assessing the Hydrological, Sulfur, and Iron Balances of Acidic Mining Lake ML 111 (Lusatia, Germany) as a Basis for Biotechnological Remediation

Stable isotope (¹⁸O–H₂O, ²H–H₂O ³⁴S–SO₄ ^2-) andhydrochemical data (SO₄ ^2-, Fe-concentrations) have beenused to estimate the annual groundwater inflow and outflow of mining lake ML 111 and to calculate the total amount of dissolvedsulfate and iron that is carried into the lake by groundwater. The hydrological balance suggests an annual groundwater inflow of 23 700 m³ and an annual groundwater outflow of 15 700 m³. The calculation of the sulfur and iron balances yielded an annual sulfate input of 37 800 kg and an annual iron input of 7000 kg with the groundwater inflow. Furthermore it was shown that significant fluxes of these elements go into the lake sediments which results in continuous release of acidity in the lake water.     

WSH-2型催化剂在环氧丙烷/苯乙烯装置废气处理中的工业应用

介绍了WSH-2型催化剂在环氧丙烷（PO）/苯乙烯（SM）装置废气处理中的应用。工业化装置的运行结果表明，在废气处理量86 000 Nm³/h、设定反应器进口温度250~300 ℃、设定进口非甲烷总烃（NMHC）质量浓度1 000~2 200 mg/m³的条件下，无论单系列还是双系列运转，采用WSH-2型催化剂均可对废气进行有效处理。处理后气体中的NMHC、苯、甲苯、乙醛、SM等的含量均符合GB 16297—1996《大气污染物综合排放标准》和GB 14554—1993《恶臭污染物排放标准》中的相关规定。NMHC去除率达到92.9%以上，装置运行稳定。按照目前的废气排放工况推算，预计催化剂的使用寿命可达5 a。     

Metabolic and Environmental Control on Methane Emission from Soils: Mechanistic Studies of Mesotrophic Fen in West Siberia

The biological mechanisms regulating methane emission fromnatural wetlands are the focus of this article. A novel techniqueprovides estimates of the distribution of CH₄ sources withinan undisturbed soil profile by recording the transient gasdynamics after soil enclosure by deep (50 cm) chamber. Thecombined use of conventional surface and soil chambers across a200-m fen transect allowed us to relate the observed methaneemission to its instant generation and uptake. Surprisingly, themethane generation was relatively constant (9–12 mg CH₄-C hr^-1 m^-2) and highly variable net emission (0.2–20 mg CH₄-C hr^-1 m^-2) was closely correlated (r = –0.809)with methane uptake. In laboratory incubations, CH₄ uptakefollowed Michaelis-Menten kinetics. Added chloride and nitrateirrespective of the cation's nature suppressed uptake as a strongnoncompetitive inhibitors (K _i 0.5 mM). The methaneformation turned out to be unstable and under anaerobicincubation, the formation of CH₄, CO₂ andH₂displayed sustained weekly oscillations. We conclude that effectsof environmental factors alone are not sufficient topredict the variation in emission, which depends also on metabolic control of respective soil organisms. The multitude ofsuch controls is dependent on diversity of respective soilorganisms and could be grouped into a limited number ofcategories considerably simplifying large-scale simulations.     

Gas production, composition and emission at a modern disposal site receiving waste with a low-organic content

AV Miljø is a modern waste disposal site receiving non-combustible waste with a low-organic content. The objective of the current project was to determine the gas generation, composition, emission, and oxidation in top covers on selected waste cells as well as the total methane (CH₄) emission from the disposal site. The investigations focused particularly on three waste disposal cells containing shredder waste (cell 1.5.1), mixed industrial waste (cell 2.2.2), and mixed combustible waste (cell 1.3). Laboratory waste incubation experiments as well as gas modeling showed that significant gas generation was occurring in all three cells. Field analysis showed that the gas generated in the cell with mixed combustible waste consisted of mainly CH₄ (70%) and carbon dioxide (CO₂) (29%) whereas the gas generated within the shredder waste, primarily consisted of CH₄ (27%) and nitrogen (N₂) (71%), containing no CO₂. The results indicated that the gas composition in the shredder waste was governed by chemical reactions as well as microbial reactions. CH₄ mass balances from three individual waste cells showed that a significant part (between 15% and 67%) of the CH₄ generated in cell 1.3 and 2.2.2 was emitted through leachate collection wells, as a result of the relatively impermeable covers in place at these two cells preventing vertical migration of the gas. At cell 1.5.1, which is un-covered, the CH₄ emission through the leachate system was low due to the high gas permeability of the shredder waste. Instead the gas was emitted through the waste resulting in some hotspot observations on the shredder surface with higher emission rates. The remaining gas that was not emitted through surfaces or the leachate collection system could potentially be oxidized as the measured oxidation capacity exceeded the potential emission rate. The whole CH₄ emission from the disposal site was found to be 820 ± 202 kg CH₄ d⁻¹. The total emission rate through the leachate collection system at AV Miljø was found to be 211 kg CH₄ d⁻¹. This showed that approximately ¼ of the emitted gas was emitted through the leachate collections system making the leachate collection system an important source controlling the overall gas migration from the site. The emission pathway for the remaining part of the gas was more uncertain, but emission from open cells where waste is being disposed of or being excavated for incineration, or from horizontal leachate drainage pipes placed in permeable gravel layers in the bottom of empty cells was likely.     

Hysteresis in Reversal of Central European Mountain Lakes from Atmospheric Acidification

Extremely high emissions of S and N compounds in Central Europe (both 280 mmol m^-2 yr^-1) declined by 70and 35%, respectively, during the last decade. Decreaseddeposition rates of SO₄ ^-2, NO₃ ^-, and NH₄ ⁺ in the region paralleled emission declines. The reduction in atmospheric inputs of S and N to mountain ecosystemshas resulted in a pronounced reversal of acidification in the Tatra Mountains and Bohemian Forest lakes. Between the 1987–1990and 1997–1999 periods, concentrations of SO₄ ^-2 and NO₃ ^- decreased (average ± standard deviation) by 22±7 and 12±7 mol L^-1, respectively, in theTatra Mountains, and by 19±7 and 15±10 mol L^-1, respectively, in the Bohemian Forest. Their decrease was compensated in part (1) by a decrease in Ca²⁺ + Mg²⁺ (17±7 mol L^-1) and H⁺ (4±6 mol L^-1), and an increase in HCO₃ ^-(10±10 mol L^-1) in the Tatra Mountains lakes, and (2) by a decrease in Al (7±4 mol L^-1), Ca²⁺ + Mg²⁺ (9±6 mol L^-1), and H⁺ (6±5 mol L^-1), in Bohemian Forest lakes. Despite the rapid decline in lake water concentrations of SO₄ ^-2 and NO₃ ^- in response to reduced S and N emissions, their present concentrations in some lakes are higher than predictionsbased on observed concentrations at comparable emission rates during development of acidification. This hysteresis in chemical reversal from acidification has delayed biological recovery of the lakes. The only unequivocal sign of biological recovery hasbeen observed in erné Lake (Bohemian Forest) where a cladoceran species Ceriodaphnia quadrangular has recentlyreached its pre-acidification abundance.     

Analysis of the St. Petersburg Traffic Data using the OSPM Model

Since October 1998 two DOAS instruments were installed at the level of the first floor and at the top of a building located in St. Petersburg at Pestelya Street. The collected datacovers the time period of December 1998–March 2001, and include concentrations of benzene, toluene, NO and NO₂, ozone and SO₂. There is also an additional information about the traffic intensity and meteorological conditions. The results of the analysis of this data set, using the OSPM model, are presented here with the goal to understand the features of the air pollution dispersion in this street canyon and to analyse the information about the emission factors of the vehicles. In particular, the model results are used for the solution of the inverse problem of reconstructing the emission factors from measured concentrations. The results obtained indicate that most of the concentrations are well inside the Russian standards with the only exception of NO₂ (mean and 98-th percentile are equal to 57.8 and 119.2 g m^-3 for the street level). The same values for benzene are 18.5 and 62.6, respectively. Emission estimates show that there is a possibility that the NO_x and benzene basic emission factors recommended by the Russian national guidelines could result in overestimating the traffic emissions. These considerations are supplemented with the model sensitivity tests carried out in connection with the problem of predictability of NO₂ concentrations in the street canyon. Tests indicate that NO₂ concentrations are not very sensitive to NO_x emissions because of the usually low urban background ozone levels.     

纯碱生产废水的综合治理

介绍了纯碱生产过程中产生的蒸氨废清液和生产下水的综合治理情况。将废清液晒盐回收ＮａＣｌ,然后从母液中回收ＣａＣｌ２。在雨季等情况下对废清液的治理措施是,将其两次兑海水,使其各项指标达到国家排放标准。     

Pore structure and adsorption properties of activated carbon prepared from granular molded waste paper

We have previously manufactured activated carbon using waste paper board, which was prepared by adding 8% phenol resin adhesive to torn waste newspaper and hot-pressing. In this study, the pretreatment process of the raw material was simplified; the waste paper was extruded to form granules. The activated carbon was manufactured by the carbon dioxide activation method using the granules as the raw material. The properties of the activated carbon were evaluated based on the pore structure, the iodine adsorption number, and the adsorption of toluene vapor in a sealed chamber. The activated carbon, which was manufactured at an activation temperature of 1100°C and a treatment time of 60min, exhibited a specific surface area of 1241m²/g and an iodine adsorption number of 1120mg/g. These results were similar to those obtained for two commercially available activated carbons. The extent of toluene vapor adsorption by this activated carbon was similar to that observed for the two commercial activated carbons over a period of 130min.     

Monitoring and Modelling of Ammonia Concentrations and Deposition in Agricultural Areas of The Netherlands

Passive samplers were used from 1996 to 1999 in a dense network to monitorthe concentrations of ammonia in air, in four agricultural areas in The Netherlands. To show representative patterns, sampling was not made within 50 m of livestock buildings and stores. The concentration of ammonia varies typically between 10 and 40 g m^-3 within a few kilometres in these areas. The interpretation of the measurements was supported by calculations with OPS, a Lagrangian dispersion model. Model calculations were based on a high-resolution database that included estimates of the ammonia emission of each farm in the area and emissions from surface application of manure at a 250 × 250 m scale. The model underestimated the observed ammonia concentrations by nearly a factor of two over most of the area. This result was attributed to underestimation of the ammonia emission in the models. And the ammonia emissions from field application of manure seem to be seriously underestimated. A detailed analysis of model results and measurements showed that the observed decrease of the ammonia concentration in the study period was partly due to changes in meteorological conditions during the study period and partly due to the reduced amount of manure applied in 1998.     

Aerobic in situ stabilization of Landfill Konstanz Dorfweiher: Leachate quality after 1 year of operation

Modern landfill understanding points out controlled operation of landfills. Emissions from landfills are caused mainly by anaerobic biodegradation processes which continue for very long time periods after landfill closure. In situ landfill stabilization aims controlled reduction of emissions towards reduced expenditures as well as aftercare measures. Since April 2010, a new in situ stabilization technique is being applied at a pilot scale landfill (BAIV) within Landfill Konstanz Dorfweiher. This new method utilizes intermittent aeration and leachate recirculation for waste stabilization. In this study, influence of this technique on leachate quality is investigated. Among many other parameters, leachate analyses were conducted for COD, BOD₅, NH₄–N, NO₂–N, NO₃–N, TKN and chloride besides continuously on site recorded pH, electrical conductivity and oxidation–reduction potential (ORP). Results from leachate quality analyses showed that biological activity in the landfill was accelerated resulting in initial higher leachate strength and reduced emission potential of landfill. During full scale in situ aeration, ambient conditions differ from optimized laboratory scale conditions which mainly concern temperature increase and deficient aeration of some landfill parts (Ritzkowski and Stegmann, 2005). Thus, as a field application results of this study have major importance on further process optimization and application.     

Enhancement of biogas production potential from <Emphasis Type="Italic">Acacia</Emphasis> leaf waste using alkaline pre-treatment and co-digestion

The objective of this research was to evaluate possibility of utilizing Acacia leaves (A. mangium and A. auriculiformis), which is an agro-industrial waste from the pulp and paper industry. The effects of alkaline pre-treatment and co-digestion with Napier grass for the enhancement of biogas production from Acacia leaf waste (ALW) were investigated. Six continuous stirred tank reactors with a working volume of 5 L were carried out at the laboratory scale. The results showed that pre-treatment of Acacia leaf waste (pretreated ALW) by soaking in 3 % NaOH for 48 h increased the biogas and methane productivity to 0.200 and 0.117 m³/kgVS_added compared to 0.098 and 0.048 m³/kgVS_added of raw ALW digestion, respectively. Meanwhile, the co-digestion of Acacia leaves with different proportions of Napier grass at ratios of 1:1–1:3 in volatile solid basis also increased the production of biogas and its productivity. The maximum gas production yields of 0.424 and 0.268 m³/kgVS_added for biogas and methane were obtained at 1:3 ratio. This finding affirms the potential of ALW and its possibility to use as biogas feedstock in both single and co-substrate with Napier grass.