Medium factors on anaerobic production of rhamnolipids by <Emphasis Type="Italic">Pseudomonas aeruginosa</Emphasis> SG and a simplifying medium for in situ microbial enhanced oil recovery applications

Aerobic production of rhamnolipid by Pseudomonas aeruginosa was extensively studied. But effect of medium composition on anaerobic production of rhamnolipid by P. aeruginosa was unknown. A simplifying medium facilitating anaerobic production of rhamnolipid is urgently needed for in situ microbial enhanced oil recovery (MEOR). Medium factors affecting anaerobic production of rhamnolipid were investigated using P. aeruginosa SG (Genbank accession number KJ995745). Medium composition for anaerobic production of rhamnolipid by P. aeruginosa is different from that for aerobic production of rhamnolipid. Both hydrophobic substrate and organic nitrogen inhibited rhamnolipid production under anaerobic conditions. Glycerol and nitrate were the best carbon and nitrogen source. The commonly used N limitation under aerobic conditions was not conducive to rhamnolipid production under anaerobic conditions because the initial cell growth demanded enough nitrate for anaerobic respiration. But rhamnolipid was also fast accumulated under nitrogen starvation conditions. Sufficient phosphate was needed for anaerobic production of rhamnolipid. SO₄ ^2? and Mg²⁺ are required for anaerobic production of rhamnolipid. Results will contribute to isolation bacteria strains which can anaerobically produce rhamnolipid and medium optimization for anaerobic production of rhamnolipid. Based on medium optimization by response surface methodology and ions composition of reservoir formation water, a simplifying medium containing 70.3 g/l glycerol, 5.25 g/l NaNO₃, 5.49 g/l KH₂PO₄, 6.9 g/l K₂HPO₄·3H₂O and 0.40 g/l MgSO₄ was designed. Using the simplifying medium, 630 mg/l of rhamnolipid was produced by SG, and the anaerobic culture emulsified crude oil to EI₂₄ = 82.5 %. The simplifying medium was promising for in situ MEOR applications.     

Process contribution evaluation for COD removal and energy production from molasses wastewater in a BioH<Subscript>2</Subscript>–BioCH<Subscript>4</Subscript>–MFC-integrated system

In this study, a three-stage-integrated process using the hydrogenic process (BioH₂), methanogenic process (BioCH₄), and a microbial fuel cell (MFC) was operated using molasses wastewater. The contribution of individual processes to chemical oxygen demand (COD) removal and energy production was evaluated. The three-stage integration system was operated at molasses of 20 g-COD L^?1, and each process achieved hydrogen production rate of 1.1 ± 0.24 L-H₂ L^?1 day^?1, methane production rate of 311 ± 18.94 mL-CH₄ L^?1 day^?1, and production rate per electrode surface area of 10.8 ± 1.4 g m^?2 day^?1. The three-stage integration system generated energy production of 32.32 kJ g-COD^?1 and achieved COD removal of 98 %. The contribution of BioH₂, BioCH₄, and the MFC reactor was 20.8, 72.2, and, 7.0 % of the total COD removal, and 18.7, 81.2, and 0.16 % of the total energy production, respectively. The continuous stirred-tank reactor BioH₂ at HRT of 1 day, up-flow anaerobic sludge blanket BioCH₄ at HRT of 2 days, and MFC reactor at HRT of 3 days were decided in 1:2:3 ratios of working volume under hydraulic retention time consideration. This integration system can be applied to various configurations depending on target wastewater inputs, and it is expected to enhance energy recovery and reduce environmental impact of the final effluent.     

Differential production yet chemical similarity of dissolved organic matter across a chronosequence with contrasting nutrient availability in Hawaii

Dissolved organic matter (DOM) is a critical phase in terrestrial carbon and nutrient cycling forming the basis of many ecosystem functions, yet the primary drivers controlling its flux from organic horizons and resultant chemical composition remain only partially understood. We studied dissolved organic matter production and chemistry from organic soil horizons across a 4.1 My old well-constrained chronosequence in Hawaii. Controlled soil column irrigation and leaching experiments were conducted on field moist organic soil horizons to quantify microbial activity, DOM production and chemistry. Both microbial activity (defined as CO₂ production per unit substrate C) and DOM production were found to be lowest in the youngest (0.3 ky) and oldest (4.1 My) sites of the chronosequence, where nutrients (N and P respectively) were most limiting. By contrast, DOM production and microbial activity was greatest at the intermediate-aged (20–350 ky) sites where nutrients were least limiting, unrelated to the mass of organic matter found in the organic horizons. While differences in production rates were found, ¹³C NMR spectroscopic results indicated that there was a convergence of chemistry from the solid to the dissolved phase at all sites. In particular, all DOM samples were found to have a high proportion of aromatic acids. With supporting data from a diverse range of ecosystems, we postulate that chemical homogenization of DOM relative to source material is a common feature of many ecosystems due to two microbially mediated processes: (1) similar extracellular enzymatic oxidation conferring solubility to a subset of degradation products; and (2) the rapid selective consumption of the more labile organic compounds in the soil solution.     

Leaf Litter Fuels Methanogenesis Throughout Decomposition in a Forested Peatland

Decomposing leaf litter is a large supply of energy and nutrients for soil microorganisms. How long decaying leaves continue to fuel anaerobic microbial activity in wetland ecosystems is poorly understood. Here, we compare leaf litter from 15 tree species with different growth forms (angiosperms and gymnosperms, deciduous, and longer life span), using litterbags positioned for up to 4 years in a forested peatland in New York State. Periodically, we incubated partially decayed residue per species with fresh soil to assess its ability to fuel microbial methane (CH₄) production and concomitant anaerobic carbon dioxide (CO₂) production. Decay rates varied by leaf type: deciduous angiosperm > evergreen gymnosperm > deciduous gymnosperm. Decay rates were slower in leaf litter with a large concentration of lignin. Soil with residue of leaves decomposed for 338 days had greater rates of CH₄ production (5.8 µmol g^?1 dry mass d^?1) than less decomposed (<0.42 µmol g^?1 dry mass d^?1) or more decomposed (2.1 µmol g^?1 dry mass d^?1) leaf residue. Species-driven differences in their ability to fuel CH₄ production were evident throughout the study, whereas concomitant rates of CO₂ production were more similar among species and declined with degree of decomposition. Methane production rates exhibited a positive correlation with pectin and the rate of pectin decomposition. This link between leaf litter decay rates, biochemical components in leaves, and microorganisms producing greenhouse gases should improve predictions of CH₄ production in wetlands.     

Treatment of thin stillage by Aspergillus oryzae and its effect on alcoholic fermentation in syrup liquid

The microbial degradation of thin stillage for environment-friendly treatment has been studied extensively in recent years, and useful compounds in the treated-thin stillage are expected to be utilized in the subsequent fermentation. In this study, an Aspergillus oryzae H18, suitable for growing in thin stillage, was isolated from soil and served to degrade the organic matter in thin stillage, with the increase in pH (from 3·75 to 4·8) and decrease in chemical oxygen demand (COD, 81·3% removal rate). The effect of thin stillage as backset water after degradation of the strain H18 on alcohol production in syrup liquid was investigated. Compared with zero addition of thin stillage, the alcohol yield in mixed syrup liquid increased by 8·6% when the concentration of treated-thin stillage was 20%. After the addition of nutrients at proper concentration (0·5% urea, 1% molasses, 0·25% NaCl, 0·2% NaH₂PO₄, 0·3% MgSO₄ and 0·25% CaCl₂) in thin stillage, the alcohol yield in yeast fermentation was increased by 32·7% when mixed syrup liquid (with 40% thin stillage treated by H18) was employed, in comparison to control group without thin stillage addition. Meanwhile, the fermentation time was shortened, and alcohol production rate was enhanced.     

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.     

Transport,anoxia and end-product accumulation control carbon dioxide and methane production and release in peat soils

Anaerobic respiration and methanogenesis have been found to slow-down in water saturated peat soils with accumulation of metabolic end-products, i.e. dissolved inorganic carbon (DIC) and methane (CH₄), due to a lack of solute and gas transport. So far it is not well understood how solute and gas transport may control this effect. We conducted a column experiment with homogenized ombrotrophic peat over a period of 300 days at 20 °C. We specifically evaluated the effects of diffusive flux as control, downward advective water flux, intensified ebullition by conduit gas transport and diffusive oxygen supply on controlling anaerobic decomposition rates and carbon (C) turnover. To simulate advective flux, water and solutes were recirculated downward through the column after stripping of dissolved gases. We analyzed DIC and CH₄ concentrations, production rates and fluxes, gas filled porosity, oxygen profiles (O₂) and microbial C biomass over time. DIC residence time thereby served as proxy to characterize transport. A slowdown of anaerobic respiration and methanogenesis evolved with the accumulation of the end-products DIC and CH₄ and set in after 150 days. This slow-down was accompanied by a decrease in the distribution of microbial biomass C with depths. Anaerobic DIC and CH₄ production rates were fastest close to the water table and sharply slowed with depth. Accumulation of DIC and CH₄ in the homogeneous peat material throughout the column decreased decomposition constants from about 10^?5 near the surface to 10^?9 year^?1 deeper in the profile. Advective water transport extended the zone of active methanogenesis compared to a diffusive system; experimental enhancement of ebullition had little or no effect as well as strictly anoxic conditions. DIC residence time was negatively correlated to anaerobic respiration suggesting this parameter to be a predictor of anaerobic peat decomposition in peatlands. Overall, this study suggests that burial of peat and accumulation of metabolic end-products effectively slows decomposition and that this effect needs to be considered to explain peat accumulation and the response of peat mineralization rates to changes in environmental conditions.     

Predicting long‐term carbon mineralization and trace gas production from thawing permafrost of Northeast Siberia

The currently observed Arctic warming will increase permafrost degradation followed by mineralization of formerly frozen organic matter to carbon dioxide (CO₂) and methane (CH₄). Despite increasing awareness of permafrost carbon vulnerability, the potential long‐term formation of trace gases from thawing permafrost remains unclear. The objective of the current study is to quantify the potential long‐term release of trace gases from permafrost organic matter. Therefore, Holocene and Pleistocene permafrost deposits were sampled in the Lena River Delta, Northeast Siberia. The sampled permafrost contained between 0.6% and 12.4% organic carbon. CO₂ and CH₄ production was measured for 1200 days in aerobic and anaerobic incubations at 4 °C. The derived fluxes were used to estimate parameters of a two pool carbon degradation model. Total CO₂ production was similar in Holocene permafrost (1.3 ± 0.8 mg CO₂‐C gdw^?1 aerobically, 0.25 ± 0.13 mg CO₂‐C gdw^?1 anaerobically) as in 34 000–42 000‐year‐old Pleistocene permafrost (1.6 ± 1.2 mg CO₂‐C gdw^?1 aerobically, 0.26 ± 0.10 mg CO₂‐C gdw^?1 anaerobically). The main predictor for carbon mineralization was the content of organic matter. Anaerobic conditions strongly reduced carbon mineralization since only 25% of aerobically mineralized carbon was released as CO₂ and CH₄ in the absence of oxygen. CH₄ production was low or absent in most of the Pleistocene permafrost and always started after a significant delay. After 1200 days on average 3.1% of initial carbon was mineralized to CO₂ under aerobic conditions while without oxygen 0.55% were released as CO₂ and 0.28% as CH₄. The calibrated carbon degradation model predicted cumulative CO₂ production over a period of 100 years accounting for 15.1% (aerobic) and 1.8% (anaerobic) of initial organic carbon, which is significantly less than recent estimates. The multiyear time series from the incubation experiments helps to more reliably constrain projections of future trace gas fluxes from thawing permafrost landscapes.     

Intensifying Clean Energy Production Through Cultivating Mixotrophic Microalgae from Digestates of Biogas Systems: Effects of Light Intensity,Medium Dilution,and Cultivating Time

High-strength wastewaters after being digested for biogas production in anaerobic digesters still contain substantial nutrients and organics. The anaerobic digestates from four major industries in Thailand were tested with batch cultivation of Chlorella sp. for oil production potentials. Pig farm digestate was found most suitable as the growth medium generating 0.95 g/L_medium (dry biomass), which was 1.16–3.06 times of other digestates tested. Considerable removals of nitrogen and phosphorus achieved were an added benefit to the goal of ultimate treatment of these wastewaters. Light intensity had strong influence on growth and heterotrophic metabolism up to 78 μmol/m²/s, while the dilution of digestate above 2.4× diminished growth potential and lipid production. A quadratic regression model was constructed to describe interaction of light intensity, dilution factor, and time of cultivation to lipid production with a satisfactory precision. Light intensity could influence fatty acid composition, although palmitic acid was found predominant at 47.1 %. The algae oil generated could potentially increase the total energy output from anaerobic digesters of a typical pig farm by 22 %.     

Will CO<Subscript>2</Subscript> Emissions from Drained Tropical Peatlands Decline Over Time? Links Between Soil Organic Matter Quality,Nutrients, and C Mineralization Rates

Conversion, drainage, and cultivation of tropical peatlands can change soil conditions, shifting the C balance of these systems, which is important for the global C cycle. We examined the effect of soil organic matter (SOM) quality and nutrients on CO₂ production from peat decomposition using laboratory incubations of Indonesian peat soils from undrained forest in Kalimantan and drained oil palm plantations in Kalimantan and Sumatra. We found that oil palm soils had higher C/N and lower SOM quality than forest soils. Higher substrate quality and nutrient availability, particularly lower ratios of aromatic/aliphatic carbon and C/N, rather than total SOM or carbon, explained the higher rate of CO₂ production by forest soils (10.80 ± 0.23 µg CO₂–C g C h^?1) compared to oil palm soils (5.34 ± 0.26 µg CO₂–C g C h^?1) from Kalimantan. These factors also explained lower rates in Sumatran oil palm (3.90 ± 0.25 µg CO₂–C g C h^?1). We amended peat with nitrogen (N), phosphorus (P), and glucose to further investigate observed substrate and nutrient constraints across the range of observed peat quality. Available N limited CO₂ production, in unamended and amended soils. P addition raised CO₂ production when substrate quality was high and initial P state was low. Glucose addition raised CO₂ production in the presence of added N and P. Our results suggest that decline in SOM quality and nutrients associated with conversion may decrease substrate-driven rates of CO₂ production from peat decomposition over time.     

Anaerobic Soil Disinfestation (ASD) Combined with Soil Solarization as a Methyl Bromide Alternative: Vegetable Crop Performance and Soil Nutrient Dynamics

Background and Aims

Soil treatment by anaerobic soil disinfestation (ASD) combined with soil solarization can effectively control soilborne plant pathogens and plant-parasitic nematodes in specialty crop production systems. At the same time, research is limited on the impact of soil treatment by ASD?+?solarization on soil fertility, crop performance and plant nutrition. Our objectives were to evaluate the response of 1) soil nutrients and 2) vegetable crop performance to ASD?+?solarization with differing levels of irrigation, molasses amendment, and partially-composted poultry litter amendment (CPL) compared to an untreated control and a methyl bromide (MeBr)?+?chloropicrin-fumigated control.

Methods

A 2-year field study was established in 2008 at the USDA-ARS U.S. Horticultural Research Lab in Fort Pierce, Florida, USA to determine the effectiveness of ASD as an alternative to MeBr fumigation for a bell pepper (Capsicum annum L.)-eggplant (Solanum melongena L.) double crop system. A complete factorial combination of treatments in a split-split plot was established to evaluate three levels of initial irrigation [10, 5, or 0 cm], two levels of CPL (amended or unamended), and two levels of molasses (amended or unamended) in combination with solarization. Untreated and MeBr controls were established for comparison to ASD treatments.

Conclusions

Results suggest that ASD treatment using molasses as the carbon source paired with solarization can be an effective strategy to maintain crop yields in the absence of soil fumigants. For both bell pepper and eggplant crops, ASD treatments with molasses as the carbon source had equivalent or greater marketable yields than the MeBr control. The application of organic amendments in ASD treatment (molasses or molasses?+?CPL) caused differences in soil nutrients and plant nutrition compared to the MeBr control that must be effectively managed in order to implement ASD on a commercial scale as a MeBr replacement.     

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.     

Nutrient stocks and phosphorus fractions in mountain soils of Southern Ecuador after conversion of forest to pasture

Understanding pasture degradation processes is the key for sustainable land management in the tropical mountain rainforest region of the South Ecuadorian Andes. We estimated the stocks of total carbon and nutrients, microbial biomass and different P fractions along a gradient of land-uses that is typical of the eastern escarpment of the Cordillera Real i.e., old-growth evergreen lower montane forest, active pastures (17 and 50 years-old), abandoned pastures 10 and 20 years old with bracken fern or successional vegetation. Conversion of forest to pasture by slash-and-burn increased the stocks of SOC, TN, P and S in mineral topsoil of active pasture sites. Microbial growth in pasture soils was enhanced by improved availability of nutrients, C:N ratio, and increased soil pH. Up to 39 % of the total P in mineral soil was stored in the microbial biomass indicating its importance as a dynamic, easily available P reservoir at all sites. At a 17 years-old pasture the stock of NH₄F extractable organic P, which is considered to be mineralisable in the short-term, was twice as high as in all other soils. The importance of the NaOH extractable organic P pool increased with pasture age. Pasture degradation was accelerated by a decline of this P stock, which is essential for the long-term P supply. Stocks of microbial biomass, total N and S had returned to forest levels 10 years after pasture abandonment; soil pH and total P 20 years after growth of successional bush vegetation. Only the C:N ratio increased above forest level indicating an ongoing loss of N after 20 years. Soil nutrient depletion and microbial biomass decline enforced the degradation of pastures on the investigated Cambisol sites.     

The growth of <Emphasis Type="Italic">Chlorella sorokiniana</Emphasis> as influenced by CO<Subscript>2</Subscript>, light,and flue gases

In order to achieve recognition as environmentally friendly production, flue gases should be used as a CO₂ source for growing the microalgae Chlorella sorokiniana when used for hydrogen production. Flue gases from a waste incinerator and from a silicomanganese smelter were used. Before testing the flue gases, the algae were grown in a laboratory at 0.04, 1.3, 5.9, and 11.0 % (v/v) pure CO₂ gas mixed with fresh air. After 5 days of growth, the dry biomass per liter algal culture reached its maximum at 6.1 % CO₂. A second experiment was conducted in the laboratory at 6.2 % CO₂ at photon flux densities (PFD) of 100, 230, and 320 μmol photons m^?2 s^?1. After 4 days of growth, increasing the PFD increased the biomass production by 67 and 108 % at the two highest PFD levels, as compared with the lowest PFD. A bioreactor system containing nine daylight-exposed tubes and nine artificial light-exposed tubes was installed on the roof of the waste incinerator. The effect of undiluted flue gas (10.7 % CO₂, 35.8 ppm NO _x , and 38.6 ppm SO₂), flue gas diluted with fresh air to give 4.2 % CO₂ concentration, and 5.0 % pure CO₂ gas was studied in daylight (21.4?±?9.6 mol photons m^?2 day^?1 PAR, day length 12.0 h) and at 135 μmol photons m^?2 s^?1 artificial light given 24 h day^?1 (11.7?±?0.0 mol photons m^?2 day^?1 PAR). After 4 days’ growth, the biomass production was the same in the two flue gas concentrations and the 5 % pure CO₂ gas control. The biomass production was also the same in daylight and artificial light, which meant that, in artificial light, the light use efficiency was about twice that of daylight. The starch concentration of the algae was unaffected by the light level and CO₂ concentration in the laboratory experiments (2.5–4.0 % of the dry weight). The flue gas concentration had no effect on starch concentration, while the starch concentration increased from about 1.5 % to about 6.0 % when the light source changed from artificial light to daylight. The flue gas from the silicomanganese smelter was characterized by a high CO₂ concentration (about 17 % v/v), low oxygen concentration (about 4 %), about 100 ppm NO _x , and 1 ppm SO₂. The biomass production using flue gas significantly increased as compared with about 5 % pure CO₂ gas, which was similar to the biomass produced at a CO₂ concentration of 10–20 % mixed with N₂. Thus, the enhanced biomass production seemed to be related to the low oxygen concentration rather than to the very high CO₂ concentration.     

α-Ketoglutaric acid production from rapeseed oil by Yarrowia lipolytica yeast

The possibility of using rapeseed oil as a carbon source for microbiological production of α-ketoglutaric acid (KGA) has been studied. Acid formation on the selective media has been tested in 26 strains of Yarrowia lipolytica yeast, and the strain Y. lipolytica VKM Y-2412 was selected as a prospective producer of KGA from rapeseed oil. KGA production by the selected strain was studied in dependence on thiamine concentration, medium pH, temperature, aeration, and concentration of oil. Under optimal conditions (thiamine concentration of 0.063 μg?g cells^?1, pH?3.5, 30 °C, high dissolved oxygen concentration (pO₂) of 50 % (of air saturation), and oil concentration in a range from 20 to 60 g?l^?1), Y. lipolytica VKM Y-2412 produced up to 102.5 g?l^?1 of KGA with the mass yield coefficient of 0.95 g?g^?1 and the volumetric KGA productivity (Q _KGA) of 0.8 g?l^?1?h^?1.     

Anaerobic digestion of swine manure under natural zeolite addition: VFA evolution, cation variation, and related microbial diversity

Batch experiments were carried out on anaerobic digestion of swine manure under 10 % of total solids and 60 g/L of zeolite addition at 35 °C. Four distinctive volatile fatty acid (VFAs) evolution stages were observed during the anaerobic process, i.e., VFA accumulation, acetic acid (HAc) and butyric acid (HBu) utilization, propionic acid (HPr) and valeric acid (HVa) degradation, and VFA depletion. Large decreases in HAc/HBu and HPr/HVa occurred respectively at the first and second biogas peaks. Biogas yield increased by 20 % after zeolite addition, about 356 mL/g VS_added with accelerated soluble chemical oxygen demand degradation and VFA (especially HPr and HBu) consumption in addition to a shortened lag phase between the two biogas peaks. Compared with Ca²⁺ and Mg²⁺ (100–300 mg/L) released from zeolite, simultaneous K⁺ and NH₄ ⁺ (580–600 mg/L) adsorptions onto zeolite particles contributed more to the enhanced biogasification, resulting in alleviated inhibition effects of ammonium on acidogenesis and methanogenesis, respectively. All the identified anaerobes could be grouped into Bacteroidetes and Firmicutes, and zeolite addition had no significant influence on the microbial biodiversity in this study.     

Nanoscale structure of organic matter could explain litter decomposition

Soil organic matter (SOM) turnover is crucial for soil quality and fertility in biogeochemical carbon cycle dynamics that can influence the fluxes of greenhouse gases. This research was focused to acquire deeper understanding of the mechanisms leading to decomposition of plant tissue and SOM persistence against both aerobic and anaerobic biodegradation. Decomposition rates of a various biomass types were studied conducting experiments in both aerobic and anaerobic environments. Different analytical approaches were applied in order to characterize biomass at chemical and physical levels. Combined statistical approaches were used to examine the relationships between carbon mineralization and chemical/physical characteristics. The obtained results revealed that degradation was significantly and negatively correlated with the micro-porosity surface (surface of pores of 0.3–1.5 nm of diameter). The multiple regressions performed by using partial least squares modelling enabled describing biomass biodegradability under either aerobic and anaerobic condition by using micro-porosity and aromatic-C content (assumed to be representative of lignin) as independent variables (R² = 0.97, R _cv ²  = 0.95 for aerobic condition; R² = 0.99, R _cv ²  = 0.98 for anaerobic condition, respectively). These results corroborate the hypothesis that plant tissues are physically protected from enzymatic attack by a microporous “sheath” that limits enzyme penetration into cell wall, and demonstrate the key role played by aromatic carbon, because of its chemical protection of the other cell wall polymers and its contribution to the three-dimensional (3D) cell wall structure.     

The effect of temperature and retention time on methane production and microbial community composition in staged anaerobic digesters fed with food waste

Background

Food waste is a large bio-resource that may be converted to biogas that can be used for heat and power production, or as transport fuel. We studied the anaerobic digestion of food waste in a staged digestion system consisting of separate acidogenic and methanogenic reactor vessels. Two anaerobic digestion parameters were investigated. First, we tested the effect of 55 vs. 65 °C acidogenic reactor temperature, and second, we examined the effect of reducing the hydraulic retention time (HRT) from 17 to 10 days in the methanogenic reactor. Process parameters including biogas production were monitored, and the microbial community composition was characterized by 16S amplicon sequencing.

Results

Neither organic matter removal nor methane production were significantly different for the 55 and 65 °C systems, despite the higher acetate and butyrate concentrations observed in the 65 °C acidogenic reactor. Ammonium levels in the methanogenic reactors were about 950 mg/L NH₄ ⁺ when HRT was 17 days but were reduced to 550 mg/L NH₄ ⁺ at 10 days HRT. Methane production increased from ~ 3600 mL/day to ~ 7800 when the HRT was decreased. Each reactor had unique environmental parameters and a correspondingly unique microbial community. In fact, the distinct values in each reactor for just two parameters, pH and ammonium concentration, recapitulate the separation seen in microbial community composition. The thermophilic and mesophilic digesters were particularly distinct from one another. The 55 °C acidogenic reactor was mainly dominated by Thermoanaerobacterium and Ruminococcus, whereas the 65 °C acidogenic reactor was initially dominated by Thermoanaerobacterium but later was overtaken by Coprothermobacter. The acidogenic reactors were lower in diversity (34–101 observed OTU_0.97, 1.3–2.5 Shannon) compared to the methanogenic reactors (472–513 observed OTU_0.97, 5.1–5.6 Shannon). The microbial communities in the acidogenic reactors were > 90% Firmicutes, and the Euryarchaeota were higher in relative abundance in the methanogenic reactors.

Conclusions

The digestion systems had similar biogas production and COD removal rates, and hence differences in temperature, NH₄ ⁺ concentration, and pH in the reactors resulted in distinct but similarly functioning microbial communities over this range of operating parameters. Consequently, one could reduce operational costs by lowering both the hydrolysis temperature from 65 to 55 °C and the HRT from 17 to 10 days.

     

Hydrocarbon Degradation and Biosurfactant Production by an Acenaphthene-degrading Pseudomonas Species

An acenaphthene-degrading bacterium putatively identified as Pseudomonas sp. strain KR3 and isolated from diesel-contaminated soil in Lagos, Nigeria was investigated for its degradative and biosurfactant production potentials on crude oil. Physicochemical analysis of the sampling site indicates gross pollution of the soil with high hydrocarbon content (2100 mg/kg) and detection of various heavy metals. The isolate grew luxuriantly on crude oil, engine oil and acenaphthene. It was resistant to septrin, amoxicillin and augmentin but was susceptible to pefloxacin, streptomycin and gentamycin. It was also resistant to elevated concentration of heavy metals such as 1–15 mM lead, nickel and molybdenum. On acenaphthene, the isolate exhibited specific growth rate and doubling time of 0.098 day^?1 and 3.06 days, respectively. It degraded 62.44% (31.2 mg/l) and 91.78% (45.89 mg/l) of 50 mg/l acenaphthene within 12 and 21 days. On crude oil, the specific growth rate and doubling time were 0.375 day^?1 and 1.85 days with corresponding percentage degradation of 33.01% (903.99 mg/l) and 87.79% (2403.71 mg/l) of crude oil (2738.16 mg/l) within 9 and 18 days. Gas chromatographic analysis of residual crude oil at the end of 18 days incubation showed significant reductions in the aliphatic, alicyclic and aromatic fractions with complete disappearance of benzene, propylbenzene, pristane, phytane, and nC₁₈-octadecane fractions of the crude oil. The isolate produced growth-associated biosurfactant on crude oil with the highest emulsification index (E₂₄) value of 72% ± 0.23 on Day 10 of incubation. The partially purified biosurfactant showed zero tolerance for salinity and had its optimal activity at 27°C and pH 2.0.     

Integrating sugarcane molasses into sequential cellulosic biofuel production based on SSF process of high solid loading

Background

Sugarcane bagasse (SCB) is one of the most promising lignocellulosic biomasses for use in the production of biofuels. However, bioethanol production from pure SCB fermentation is still limited by its high process cost and low fermentation efficiency. Sugarcane molasses, as a carbohydrate-rich biomass, can provide fermentable sugars for ethanol production. Herein, to reduce high processing costs, molasses was integrated into lignocellulosic ethanol production in batch modes to improve the fermentation system and to boost the final ethanol concentration and yield.

Results

The co-fermentation of pretreated SCB and molasses at ratios of 3:1 (mixture A) and 1:1 (mixture B) were conducted at solid loadings of 12% to 32%, and the fermentation of pretreated SCB alone at the same solid loading was also compared. At a solid loading of 32%, the ethanol concentrations of 64.10 g/L, 74.69 g/L, and 75.64 g/L were obtained from pure SCB, mixture A, and mixture B, respectively. To further boost the ethanol concentration, the fermentation of mixture B (1:1), with higher solid loading from 36 to 48%, was also implemented. The highest ethanol concentration of 94.20 g/L was generated at a high solid loading of 44%, with an ethanol yield of 72.37%. In addition, after evaporation, the wastewater could be converted to biogas by anaerobic digestion. The final methane production of 312.14 mL/g volatile solids (VS) was obtained, and the final chemical oxygen demand removal and VS degradation efficiency was 85.9% and 95.9%, respectively.

Conclusions

Molasses could provide a good environment for the growth of yeast and inoculum. Integrating sugarcane molasses into sequential cellulosic biofuel production could improve the utilization of biomass resources.