Effects of nickel, cobalt, and molybdenum on performance of methanogenic fixed-film reactors

Selective trace elements significantly enhanced methane production in coal bed methane systems by stimulating microbial activity

Trace elements are associated with the microbial degradation of organic matter and methanogenesis, as enzymes in metabolic pathways often employ trace elements as essential cofactors. However, only a few studies investigated the effects of trace elements on the metabolic activity of microbial communities associated with biogenic coalbed methane production. We aimed to determine the effects of strategically selected trace elements on structure and function of active bacterial and methanogenic communities to stimulate methane production in subsurface coalbeds. Microcosms were established with produced water and coal from coalbed methane wells located in the Powder River Basin, Wyoming, USA. In initial pilot experiments with eight different trace elements, individual amendments of Co, Cu, and Mo lead to significantly higher methane production. Transcript levels of mcrA, the key marker gene for methanogenesis, positively correlated with increased methane production. Phylogenetic analysis of the mcrA cDNA library demonstrated compositional shifts of the active methanogenic community and increase of their diversity, particularly of hydrogenotrophic methanogens. High-throughput sequencing of cDNA obtained from 16S rRNA demonstrated active and abundant bacterial groups in response to trace element amendments. Active Acetobacterium members increased in response to Co, Cu, and Mo additions. The findings of this study yield new insights into the importance of essential trace elements on the metabolic activity of microbial communities involved in subsurface coalbed methane and provide a better understanding of how microbial community composition is shaped by trace elements.IMPORTANCEMicrobial life in the deep subsurface of coal beds is limited by nutrient replenishment. While coal bed microbial communities are surrounded by carbon sources, we hypothesized that other nutrients such as trace elements needed as cofactors for enzymes are missing. Amendment of selected trace elements resulted in compositional shifts of the active methanogenic and bacterial communities and correlated with higher transcript levels of mcrA. The findings of this study yield new insights to not only identify possible limitations of microbes by replenishment of trace elements within their specific hydrological placement but also into the importance of essential trace elements for the metabolic activity of microbial communities involved in subsurface coalbed methane production and provides a better understanding of how microbial community composition is shaped by trace elements. Furthermore, this finding might help to revive already spent coal bed methane well systems with the ultimate goal to stimulate methane production.

Characteristics of physiology of and genomic mutations in aggregation-enhanced mutants of Methanothermobacter sp. CaT2

The thermophilic hydrogenotrophic methanogen Methanothermobacter sp. CaT2 aggregates by itself. CaT2 is known to have a surface sugar layer and extracellular proteins that may be related to its aggregation. Aggregation-enhanced mutants, CHA001 and CHA002, were isolated after repeated cultivation for more than two years. When treated with proteinase K, CHA001 and CaT2 similarly exhibited a very low degree of aggregation and CHA002 exhibited less aggregation but still retained aggregation, suggesting protein-based aggregation via extracellular proteins in both CHA001 and CHA002, presumably via a putative membrane-bound and extracellularly protruding protein, MTCT_1020, identified previously. Genomic analysis revealed that CHA001 and CHA002 shared a missense mutation of MTCT_1348 and had distinct mutations. These results suggested that the MTCT_1348 mutation provides subsidiary support to the adhesive function of extracellular proteins and that there is an additional mutation(s) in CHA002 for the non-proteinous aggregation capability.

Use of trace elements addition for anaerobic digestion of brewer's spent grains

The brewery industry generates a large amount of by-products and notably Brewer's Spent Grain (BSG) which seems an attractive substrate for anaerobic digestion. Nevertheless, previous studies have shown risk of inhibition in the mono-digestion of lignocellulosic substrates. One way to stabilize the reaction is the addition of trace elements. The current study evaluates and compares the stability of BSG anaerobic mono-digestion with and without addition of trace elements for several BSG samples. Based on the average composition of the BSG, two levels of nutrients addition were defined and tested on 4 different BSG samples. Control reactors, without addition of nutrients, showed signs of instability after 3 months or less of operation, with a decrease in performance and even collapse. On the contrary, supplemented reactors led to a COD removal rate of 60-65% and a methane production ranged between 220 and 350 NL CH₄.kg^-1 VS_added, depending on the sample. According to these results, guidelines for nutrients solution addition adapted to BSG degradation were defined.

Anaerobic digestion of Brewery Spent Grains: Trace elements addition requirement

The current study evaluates and compares the stability of anaerobic digestion of Brewery Spent Grains (BSG) with and without addition of nutrients. Based on the composition of the BSG two levels of nutrients addition were defined. Control reactor, without addition of nutrients, showed signs of instability after 3months of operation and collapsed. On the contrary, supplemented reactors led to a COD removal rate of 60% and a methane production of 280NLCH₄.kg^-1 VS_added. According to these results, it was possible to define an additive solution adapted to BSG degradation.

Increased methane production in cyanobacteria and methanogenic microbe co-cultures

A novel light-to-bioenergy system produced 3.5 times the baseline methane output using a co-culture of cyanobacteria (Oscillatoria sp.) and a methanogenic microbial community. Analysis of micronutrients in the system during the growth phase indicated that cobalt, iron, nickel and zinc were not appreciably consumed. The stable consumption and return of macronutrients calcium and magnesium were also observed. Essential macronutrients nitrogen, in the form of nitrate, and phosphorus showed no cycling during the growth phase and were depleted at rates of 0.35mg/L/day and 0.40µg/L/day, respectively. Biofilm formation increased the resilience of biomass to bacterial degradation in an anaerobic digester, as shown by viability assays of cyanobacterial biofilms in the co-culture.

Optimization of micronutrient supplement for enhancing biogas production from food waste in two-phase thermophilic anaerobic digestion

The aim of this study was to enhance the biogas productivity of two-phase thermophilic anaerobic digestion (AD) using food waste (FW) as the primary substrate. The influence of adding four trace metals (Ca, Mg, Co, and Ni) as micronutrient supplement in the methanogenic phase of the thermophilic system was investigated. Initially, Response Surface Methodology (RSM) was applied to determine the optimal concentration of micronutrients in batch experiments. The results showed that optimal concentrations of 303, 777, 7 and 3mg/L of Ca, Mg, Co and Ni, respectively, increased the biogas productivity as much as 50% and significantly reduced the processing time. The formulated supplement was tested in continuous two-phase thermophilic AD system with regard to process stability and productivity. It was found that a destabilized thermophilic AD process encountering high VFA accumulation recovered in less than two weeks, while the biogas production was improved by 40% yielding 0.46L CH₄/gVS_added/day. There was also a major increase in soluble COD utilization upon the addition of micronutrient supplement. The results of this study indicate that a micronutrient supplement containing Ca, Mg, Co and Ni could probably remedy any type of thermophilic AD process.

Effect of Nickel Levels on Hydrogen Partial Pressure and Methane Production in Methanogens

Hydrogen (H₂) consumption and methane (CH₄) production in pure cultures of three different methanogens were investigated during cultivation with 0, 0.2 and 4.21 μM added nickel (Ni). The results showed that the level of dissolved Ni in the anaerobic growth medium did not notably affect CH₄ production in the cytochrome-free methanogenic species Methanobacterium bryantii and Methanoculleus bourgensis MAB1, but affected CH₄ formation rate in the cytochrome-containing Methanosarcina barkeri grown on H₂and CO₂. Methanosarcina barkeri also had the highest amounts of Ni in its cells, indicating that more Ni is needed by cytochrome-containing than by cytochrome-free methanogenic species. The concentration of Ni affected threshold values of H₂ partial pressure (pH₂) for all three methanogen species studied, with M. bourgensis MAB1 reaching pH₂ values as low as 0.1 Pa when Ni was available in amounts used in normal anaerobic growth medium. To our knowledge, this is the lowest pH₂ threshold recorded to date in pure methanogen culture, which suggests that M.bourgensis MAB1 have a competitive advantage over other species through its ability to grow at low H₂ concentrations. Our study has implications for research on the H₂-driven deep subsurface biosphere and biogas reactor performance.

Methanosarcina Play an Important Role in Anaerobic Co-Digestion of the Seaweed Ulva lactuca: Taxonomy and Predicted Metabolism of Functional Microbial Communities

Macro-algae represent an ideal resource of third generation biofuels, but their use necessitates a refinement of commonly used anaerobic digestion processes. In a previous study, contrasting mixes of dairy slurry and the macro-alga Ulva lactuca were anaerobically digested in mesophilic continuously stirred tank reactors for 40 weeks. Higher proportions of U. lactuca in the feedstock led to inhibited digestion and rapid accumulation of volatile fatty acids, requiring a reduced organic loading rate. In this study, 16S pyrosequencing was employed to characterise the microbial communities of both the weakest (R1) and strongest (R6) performing reactors from the previous work as they developed over a 39 and 27-week period respectively. Comparing the reactor communities revealed clear differences in taxonomy, predicted metabolic orientation and mechanisms of inhibition, while constrained canonical analysis (CCA) showed ammonia and biogas yield to be the strongest factors differentiating the two reactor communities. Significant biomarker taxa and predicted metabolic activities were identified for viable and failing anaerobic digestion of U. lactuca. Acetoclastic methanogens were inhibited early in R1 operation, followed by a gradual decline of hydrogenotrophic methanogens. Near-total loss of methanogens led to an accumulation of acetic acid that reduced performance of R1, while a slow decline in biogas yield in R6 could be attributed to inhibition of acetogenic rather than methanogenic activity. The improved performance of R6 is likely to have been as a result of the large Methanosarcina population, which enabled rapid removal of acetic acid, providing favourable conditions for substrate degradation.

The impact of Ni, Co and Mo supplementation on methane yield from anaerobic mono-digestion of maize silage

The objective of this experimental study was to demonstrate the impact of trace metal supplementation, namely nickel (Ni), cobalt (Co) and molybdenum (Mo), on the methane yields obtained from batch mesophilic anaerobic digestion of maize silage as mono-substrate. The maize silage used in this experimental work initially lacked Ni and Co. Trace metal concentration selected was 0.1 and 0.5 mg/L for Ni and Co, respectively, while it was 0.05 and 0.25 mg/L for Mo. The supplementation by Ni, Co and Mo, individually or in combination at different doses, seemed to improve the methane yields for mono-digestion of maize silage and particularly, the highest methane yield of 0.429 L CH4/g VSadded was obtained, when Ni, Co and Mo were supplemented together at concentrations of 0.5, 0.5 and 0.25 mg/L, respectively.

Long-term anaerobic digestion of food waste stabilized by trace elements

The purpose of this study was to examine if long-term anaerobic digestion of food waste in a semi-continuous single-stage reactor could be stabilized by supplementing trace elements. Contrary to the failure of anaerobic digestion of food waste alone, stable anaerobic digestion of food waste was achieved for 368 days by supplementing trace elements. Under the conditions of OLR (organic loading rates) of 2.19-6.64 g VS (volatile solid)/L day and 20-30 days of HRT (hydraulic retention time), a high methane yield (352-450 mL CH(4)/g VS(added)) was obtained, and no significant accumulation of volatile fatty acids was observed. The subsequent investigation on effects of individual trace elements (Co, Fe, Mo and Ni) showed that iron was essential for maintaining stable methane production. These results proved that the food waste used in this study was deficient in trace elements.

Trace metal requirements for microbial enzymes involved in the production and consumption of methane and nitrous oxide

Fluxes of greenhouse gases to the atmosphere are heavily influenced by microbiological activity. Microbial enzymes involved in the production and consumption of greenhouse gases often contain metal cofactors. While extensive research has examined the influence of Fe bioavailability on microbial CO(2) cycling, fewer studies have explored metal requirements for microbial production and consumption of the second- and third-most abundant greenhouse gases, methane (CH(4)), and nitrous oxide (N(2)O). Here we review the current state of biochemical, physiological, and environmental research on transition metal requirements for microbial CH(4) and N(2)O cycling. Methanogenic archaea require large amounts of Fe, Ni, and Co (and some Mo/W and Zn). Low bioavailability of Fe, Ni, and Co limits methanogenesis in pure and mixed cultures and environmental studies. Anaerobic methane oxidation by anaerobic methanotrophic archaea (ANME) likely occurs via reverse methanogenesis since ANME possess most of the enzymes in the methanogenic pathway. Aerobic CH(4) oxidation uses Cu or Fe for the first step depending on Cu availability, and additional Fe, Cu, and Mo for later steps. N(2)O production via classical anaerobic denitrification is primarily Fe-based, whereas aerobic pathways (nitrifier denitrification and archaeal ammonia oxidation) require Cu in addition to, or possibly in place of, Fe. Genes encoding the Cu-containing N(2)O reductase, the only known enzyme capable of microbial N(2)O conversion to N(2), have only been found in classical denitrifiers. Accumulation of N(2)O due to low Cu has been observed in pure cultures and a lake ecosystem, but not in marine systems. Future research is needed on metalloenzymes involved in the production of N(2)O by enrichment cultures of ammonia oxidizing archaea, biological mechanisms for scavenging scarce metals, and possible links between metal bioavailability and greenhouse gas fluxes in anaerobic environments where metals may be limiting due to sulfide-metal scavenging.

Advances in biogas technology

Biogas technology has been practiced for over a century and is widely used in full-scale facilities in China. However, there are still many technological and economic barriers to be overcomed in its applications. Recent advances and multi-disciplinary cooperations in microbiology, biochemistry, and engineering science are bringing new promises of a better understanding and control of the anaerobic digestion processes, and thus a renaissance of this technology. In particular, great progress in biogas technology has been achieved in China in the approach to larger-scale and more widespread applications. This chapter overviews the recent advances in biogas technology in China, evaluates the current challenges, and discusses the emerging technologies and future perspectives.

Anaerobic digestion of Jatropha curcas L. press cake and effects of an iron-additive

Oil production from Jatropha curcas L. seeds generates large amounts of Jatropha press cake (JPC) which can be utilized as a substrate for biogas production. The objective of this work was to investigate anaerobic mono-digestion of JPC and the effects of an iron additive (IA) on gas quality and process stability during the increase of the organic loading rate (OLR). With the increase of the OLR from 1.3 to 3.2 g(VS) L(-1) day(-1), the biogas yield in the reference reactor (RR) without IA decreased from 512 to 194 L(N) kg(VS) (-1) and the CH₄ concentration decreased from 69.3 to 44.4%. In the iron additive reactor (IAR), the biogas yield decreased from 530 to 462 L(N) kg(VS) (-1) and the CH₄ concentration decreased from 69.4 to 61.1%. The H₂S concentration in the biogas was reduced by addition of the IA to values below 258 ppm in the IAR while H₂S concentration in the RR increased and exceeded the detection limit of 5000 ppm. The acid capacity (AC) in the RR increased to more than 20 g L(-1), indicating an accumulation of organic acids caused by process instability. AC values in the IAR remained stable at values below 5 g L(-1). The results demonstrate that JPC can be used as sole substrate for anaerobic digestion up to an OLR of 2.4 g(VS) l(-1) day(-1). The addition of IA has effectively decreased the H(2)S content in the biogas and has improved the stability of the anaerobic process and the biogas quality.

Anaerobic co-digestion of food waste and piggery wastewater: focusing on the role of trace elements

The objective of this study was to evaluate the feasibility of anaerobic co-digestion of food waste and piggery wastewater, and to identify the key factors governing the co-digestion performance. The analytical results indicated that the food waste contained higher energy potential and lower concentrations of trace elements than the piggery wastewater. Anaerobic co-digestion showed a significantly improved biogas productivity and process stability. The results of co-digestion of the food waste with the different fractions of the piggery wastewater suggested that trace element might be the reason for enhancing the co-digestion performance. By supplementing the trace elements, a long-term anaerobic digestion of the food waste only resulted in a high methane yield of 0.396 m(3)/kg VS(added) and 75.6% of VS destruction with no significant volatile fatty acid accumulation. These results suggested that the typical Korean food waste was deficient with some trace elements required for anaerobic digestion.

Impact of nickel and cobalt on biogas production and process stability during semi-continuous anaerobic fermentation of a model substrate for maize silage

The importance of nickel and cobalt on anaerobic degradation of a defined model substrate for maize was demonstrated. Five semi-continuous reactors were operated for 250 days at 35 °C and a well-defined trace metal solution was added to all reactors. Two reactors each were limited regarding the concentration of Ni(2+) and Co(2+), respectively, for certain time intervals. The required nickel concentration was depending on the organic loading rates (OLR) while, for example, above 2.6 g ODM L(-1) d(-1) nickel concentrations below 0.06 mg kg(-1) FM in the process significantly decreased biogas production by up to 25% compared to a control reactor containing 0.8 mg Ni(2+) kg(-1) FM. Similarly, limitation of cobalt to 0.02 mg kg(-1) FM decreased biogas production by about 10%. Limitations of nickel as well as cobalt lead to process instability. However, after gradual addition of nickel till 0.6 mg and cobalt till 0.05 mg kg(-1) FM the OLR was again increased to 4.3 g ODM L(-1) d(-1) while process stability was recovered and a fast metabolisation of acetic and propionic acid was detected. An increase of nickel to 0.88 mg kg(-1) FM did not enhance biogas performance. Furthermore, the increase of cobalt from 0.05 mg kg(-1) FM up to 0.07 mg kg(-1) FM did not exhibit a change in anaerobic fermentation and biogas production.

Thermophilic anaerobic digestion to increase the net energy balance of corn grain ethanol

U.S. production of fuel ethanol from corn grain has increased considerably over the last 10 years. Intense debate regarding the true environmental impact of the overall production process has been ongoing. The present study evaluated the utilization of thin stillage (a major byproduct of the dry-mill corn grain-to-ethanol process) in laboratory-scale thermophilic anaerobic sequencing batch reactors for conversion to methane. We found that augmentation of cobalt as a growth factor to the thermophilic anaerobic digestion process is required. After reaching sustainable operating performances, the methane potential in the reactors was 0.254 L CH4/g total chemical oxygen demand (TCOD) fed. Together with a reduction in the mass of solids that needs drying, methane generation translates to a 51% reduction of natural gas consumption at a conventional dry mill, which improves the net energy balance ratio from 1.26 to 1.70. At the design hydraulic retention time of 10 days, the digesters achieved TCOD, biodegradable COD, volatile solids, and total solids removal efficiencies of 90%, 75%, 89%, and 81%, respectively. We also found that struvite precipitation occurred in the thermophilic digesters during the course of the study, resulting in possibilities for nutrient recovery.

Effect of cobalt on the anaerobic thermophilic conversion of methanol

The importance of cobalt on the anaerobic conversion of methanol under thermophilic conditions was studied in three parallel lab-scale UASB-reactors and in cobalt-limited enriched cultures. Reactors R1, R2, and R3 were fed with methanol in a bicarbonate-buffered medium, supplied with iron and macronutrients: in R1 all metals were supplied (control), R2 was cobalt deprived, and in R3 all metals were deprived. In the 136 days of continuous experiment, a drop in performance was observed over the last 30 days. Particularly in R3, both methanol removal and methane formation dropped by 7.1% and 13.7%, respectively, compared to the control reactor, R1. When the medium was cobalt-deprived, acetate was not produced and, as a consequence, the enriched consortium lost its capacity to degrade acetate, indicating that the acetotrophic microorganisms were washed out. The addition of 0.5 microM of cobalt to a cobalt-deprived enrichment culture led to acetate accumulation. The results obtained in this study indicate that the mixed consortium requires a proper amount of cobalt, and its addition to a concentration of 0.1 microM leads to the highest methanol conversion rate, with methane as the sole end product from methanol.

Microbial attachment and growth in fixed-film reactors: Process startup considerations

Optimal steady-state performance of any biofilm reactor requires a fully developed and mature biofilm. During fixed-film reactor startup phase, biofilm is in process of development and accordingly, process performance is difficult to quantify. Environmental, cellular and surface factors greatly influence the process of biofilm formation during reactor startup. Improved knowledge of nutritional, toxicological and environmental requirements of wastewater degrading microorganisms has helped define optimal microbial growth conditions. In case of anaerobic fixed film reactors the startup is hindered by low microbial growth rates, strict environmental requirements and limited ability of methanogens to adhere and form fixed biofilms. These obstacles could be overcome by proper support media selection and formulation of appropriate inoculation procedures and startup strategies.

Factors Affecting the Methanogenic Activity of Methanothrix soehngenii VNBF

Methane production by Methanothrix soehngenii VNBF grown on acetate (50 mM) as the sole carbon and energy source was influenced by the addition of Fe, trace elements, and pesticides. The addition of Fe and trace elements significantly enhanced the rate of CH 4 production. The addition of pesticides in the early growth phase caused complete inhibition. However, less inhibition was noted when pesticides were added during early exponential growth phase. Addition to culture tubes of Co, Ni, or Mo at 2 μM produced 64, 41, or 17%, respectively, more CH 4 than that produced in tubes lacking the corresponding trace element. A concentration of more than 5 μM of these trace elements in the medium resulted in decreased CH 4 production, presumably because of toxic effects.

Anaerobic waste stabilization

The present knowledge of the microbiology, physiology and regulation of anaerobic digestion in conventional or advanced processes is reviewed. In all systems the carbon flow from biopolymers to biogas is determined by syntrophic interactions of fermentative or acetogenic bacteria with methanogens at the level of interspecies hydrogen transfer. Inhibitors or heavy metal ions may interfere at different levels. The stabilization of waste at mesophilic and thermophilic temperatures is compared and the process stability as well as the inactivation of pathogens is discussed. Characteristics of conventional digestion systems and of recently developed advanced processes with solids and liquids uncoupling are compared and selection criteria with respect to the type of sludge are outlined. Areas of future research for a better understanding of the biochemistry, the physiology and the regulation of the degradation of pollutants are suggested.