Inhibition Of Methanogens Research Articles

Anaerobic biodegradation of 2,4,6-trichlorophenol by methanogenic granular sludge: role of co-substrates and methanogenic inhibition

The influence of several co-substrates in the anaerobic biodegradation of 2,4,6-trichlorophenol (246TCP) by methanogenic granular sludge as well as in methanogenesis inhibition by 246TCP has been studied. 4 g-COD.L(-1) of lactate, sucrose, volatile fatty acids (VFA) acetate:propionate:butyrate 1:1:1, ethanol, methanol, yeast extract (YE), and 2 g-COD.L(-1) of formate and methylamine were tested. Two concentrations of 246TCP: 80 mg.L(-1) and 113 mg.L(-1) (this last corresponding to the EC(50) for acetotrophic methanogenesis) were tested. Three consecutive co-substrate and nutrient feedings were accomplished. 246TCP was added in the second feed, and the 246TCP removal rate increased considerably after the third feed. Accumulated metabolites after ortho-dechlorination, either 4-chlorophenol (4CP) (when methanol, ethanol or VFA were used as co-substrates) or 2,4-dichlorophenol (24DCP) (with lactate) avoided the complete dechlorination of 246TCP. With methylamine and formate this compound was degraded only partially. Monochlorophenols biodegradation was partially achieved with YE, but both 24DCP and 2,6-dichlorophenol (26DCP) were accumulated. In the presence of sucrose para-dechlorination was observed. 246TCP was better tolerated by methanogens when ethanol and methanol were added because of the highest specific methanogenic activity achieved with these co-substrates. Methanol and ethanol were the best co-substrates in the anaerobic biodegradation of 246TCP.

Deltamethrin Degradation and Soil Microbial Activity in a Riparian Wetland Soil

Abstract The effects of deltamethrin, in the presence and absence of nitrate, on soil microbial activity (as reflected by the rates of soil microbial basal respiration, denitrification, and methanogenesis) were studied in a riparian wetland soil under both aerobic and anaerobic conditions. A microcosm study was carried out with soil collected from the vicinity of a wetland. The soil was then amended with 50, 125, and 250 mg deltamethrin kg−1 dry weight soil, in the presence and absence of 20 mg N-NO3− kg−1 dry weight soil. Half-life values for deltamethrin degradation ranged from 27 to 291 days, depending on experimental conditions. Nitrates had an inhibitory effect on deltamethrin degradation. Deltamethrin, under anaerobiosis, had an inhibitory effect on soil respiration; this effect was reversed in the presence of nitrate. An antagonistic effect between deltamethrin degradation and denitrification activity was observed. In the presence of nitrate, the activation of denitrifying bacteria led to competitive inhibition of methanogens. It was concluded that deltamethrin, designed to affect specific functions of its target organisms, also has an effect on nontarget organisms, that is, the soil microbial community. To our knowledge, this is the first report on the degradation and environmental impact of deltamethrin in a riparian wetland soil.

Characterization of stable isotope fractionation during methane production in the sediment of a eutrophic lake, Lake Dagow, Germany

We measured δ13C of CO2, CH4, and acetate‐methyl in profundal sediment of eutrophic Lake Dagow by incubation experiments in the presence and absence of methanogenic inhibitors chloroform, bromoethane sulfonate (BES), and methyl fluoride, which have different specificities. Methyl fluoride predominantly inhibits acetoclastic methanogenesis and affects hydrogenotrophic methanogenesis relatively little. Optimization of methyl fluoride concentrations resulted in complete inhibition of acetoclastic methanogenesis. Methane was then exclusively produced by hydrogenotrophic methanogenesis and thus allowed determination of the fractionation factors specific for this methanogenic pathway. Acetate, which was then no longer consumed, accumulated and allowed determination of the isotopic signatures of the fermentatively produced acetate. BES and chloroform also inhibited CH4 production and resulted in accumulation of acetate. The fractionation factor for hydrogenotrophic methanogenesis exhibited variability, e.g., it changed with sediment depth. The δ13C of the methyl group of the accumulated acetate was similar to the δ13C of sedimentary organic carbon, while that of the carboxyl group was by about 12% higher. However, the δ13C of the acetate was by about 5% lower in samples with uninhibited compared with inhibited acetoclastic methanogenesis, indicating unusual isotopic fractionation. The isotope data were used for calculation of the relative contribution of hydrogenotrophic vs. acetoclastic methanogenesis to total CH4 production. Contribution of hydrogenotrophic methanogenesis increased with sediment depth from about 35% to 60%, indicating that organic matter was only partially oxidized in deeper sediment layers.

Inhibition of methanogens by bromochloromethane: effects on microbial communities and rumen fermentation using batch and continuous fermentations

Bromochloromethane (BCM), a halogenated methane analogue, was evaluated for its anti-methanogenic activity in both batch and continuous fermentation systems. For batch fermentation, a roughage-based substrate was incubated with mixed rumen microflora for 24 h at two concentrations of BCM (5 and 10 microm). A 89-94 % reduction in methane was obtained in terms of volume and truly degraded substrate (TDS; P < 0.05). The partitioning factor (an index of efficiency of microbial protein production; expressed as mg TDS/ml net gas produced) increased from 3.55 to 3.73 (P < 0.05), while the acetate:propionate proportion decreased from 2.80 to 2.22 (P < 0.05). A complete inhibition of methanogens was associated with a 48 % decrease in Ruminococcus flavefaciens, a 68 % increase in Fibrobacter succinogenes and a 30 % increase in rumen fungi when quantified using qPCR. The continuous fermentation was carried out using the roughage-based substrate in four fermenters, two fermenters being control and the other two fed with BCM (5 microm) once in a day, for nine consecutive days. A persistent effect of BCM on methane reduction (85-90 %) was obtained throughout the study (P < 0.05) with no effect on gas production, SCFA production, acetate:propionate proportion, true degradability and efficiency of microbial mass synthesis (P>0.05). The complete inhibition of methane resulted in a significant decrease in R. flavefaciens and methanogens (P < 0.05) and an increase in fungal population (P < 0.05), while there was no effect on total bacterial and F. succinogenes populations (P>0.05). The batch fermentation confirms the anti-methanogenic activity of BCM, while the continuous fermentation indicates the persistency of this effect under in vitro conditions.

Anaerobic biodegradation of cellulosic material: Batch experiments and modelling based on isotopic data and focusing on aceticlastic and non-aceticlastic methanogenesis

Utilizing stable carbon isotope data to account for aceticlastic and non-aceticlastic pathways of methane generation, a model was created to describe laboratory batch anaerobic decomposition of cellulosic materials (office paper and cardboard). The total organic and inorganic carbon concentrations, methane production volume, and methane and CO(2) partial pressure values were used for the model calibration and validation. According to the fluorescent in situ hybridization observations, three groups of methanogens including strictly hydrogenotrophic methanogens, strictly aceticlastic methanogens (Methanosaeta sp.) and Methanosarcina sp., consuming both acetate and H(2)/H(2)CO(3) as well as acetate-oxidizing syntrophs, were considered. It was shown that temporary inhibition of aceticlastic methanogens by non-ionized volatile fatty acids or acidic pH was responsible for two-step methane production from office paper at 35 degrees C where during the first and second steps methane was generated mostly from H(2)/H(2)CO(3) and acetate, respectively. Water saturated and unsaturated cases were tested. According to the model, at the intermediate moisture (150%), much lower methane production occurred because of full-time inhibition of aceticlastic methanogens. At the lowest moisture, methane production was very low because most likely hydrolysis was seriously inhibited. Simulations showed that during cardboard and office paper biodegradation at 55 degrees C, non-aceticlastic syntrophic oxidation by acetate-oxidizing syntrophs and hydrogenotrophic methanogens were the dominant methanogenic pathways.

Enrichment of a dioxin‐dehalogenating Dehalococcoides species in two‐liquid phase cultures

Enrichment cultures capable of reductively dechlorinating 1,2,4-trichlorodibenzo-p-dioxin (1,2,4-TrCDD) were shown to dechlorinate 1,2,3-trichlorobenzene (1,2,3-TrCB) to 1,3-dichlorobenzene. To test if this activity can be used to enrich for dioxin-dechlorinating bacteria, a two-liquid phase cultivation with 200 mM 1,2,3-TrCB dissolved in hexadecane was established. During the dechlorination of 1,2,3-TrCB, the number of 1,2,4-TrCDD-dechlorinating bacteria increased by four orders of magnitude, eventually accounting for 11% of the total cell number. Characterization of the bacterial communities of the initial dioxin-dechlorinating culture and of the trichlorobenzene enrichments by restriction fragment length polymorphism (RFLP) analysis of cloned 16S rRNA genes revealed a proportional increase of nine different sequence types, one representing a Dehalococcoides strain. Inhibition of methanogens further enhanced the rate of chlorobenzene dehalogenation and also resulted in a rapid dechlorination of 1,2,3,4-tetrachlorodibenzo-p-dioxin that was applied via a hexadecane phase. The further enrichment was monitored by terminal RFLP, quantitative real-time PCR and microscopy, and aimed at the reduction of the accompanying non-dehalogenating populations by using different combinations of electron donors and the application of antibiotics. Hydrogen as the sole electron donor proved to be less efficient due to the co-enrichment of acetogens. The novel Dehalococcoides strain DCMB5 was enriched up to 50% by the cultivation with organic acids, hydrogen and vancomycin, and was finally purified by conventional isolation techniques.

Yellow ginger processing wastewater treatment by a hybrid biological process

With a hybrid wastewater treatment process consisting of neutralization, precipitation, modified two-phase anaerobic digestion, and biological aerated filter (BAF) being developed, the yellow ginger processing wastewater with high COD and high sulphate was treated successfully in the laboratory. With an inserted stripping unit, the modified two-phase anaerobic digestion process eliminated the inhibition of methanogens to the greatest extent, which results in a high-efficiency COD removal. Subsequently, the effluent from the anaerobic units was treated with excellent results in the novel BAF which was equipped with special carriers. This was due to the simultaneous nitrification and denitrification (SND) that occurred there. When the raw water with COD of 18,000–20,000 mg/L, SO 4 2− of 8,500–11,000 mg/L, and NH 4 +-N of 220–300 mg/L was treated by the hybrid process, the concentrations of COD, NH 4 +-N, and total nitrogen (TN) in the effluent were lower than 100, 10 and 15 mg/L, respectively.

Methanogenic toxicity in anaerobic digesters treating municipal wastewater

In upflow anaerobic sludge blanket (UASB) digesters treating raw sewage at low temperatures, the sludge progressively lost methanogenic activity, indicating the possibility of methanogenic activity inhibition caused by wastewater constituents. To check this fact, batch and semi-continuous methanogenic toxicity assays were carried out with raw and centrifuged sewage. Permanent methanogenic toxicity on anaerobic sludge of approximately 50% was found when the sludge exposure to wastewater was renewed in a semi-continuous way. A stronger methanogenic inhibition of about 70–100% was observed when an active anaerobic sludge was exposed to mixed liquor from the UASB digester treating municipal wastewater. Suspended solids removal from sewage slightly reduced methanogenic toxicity. Effective concentration of municipal wastewater that caused a 50% reduction in methanogenic activity was estimated to be in the range of 150–200 mg COD l −1. As methanogenic inhibition appeared to be related to remaining COD, higher methanogenic toxicity in digesters operating with low conversion efficiency will be expected.

Reactive Blue 4 Decolorization under Mesophilic and Thermophilic Anaerobic Treatments

Anaerobic decolorization of anthraquinone dye represented by Reactive Blue 4 (RB4) was studied to evaluate the factors involved in dye-reducing behaviors such as dye concentration, co-substrate, treatment temperature, salt content, and dye-reducing microbial consortia. The experiment was conducted using digested sludge treated under mesophilic (35 degrees C) and thermophilic (55 degrees C) conditions. The results indicated that the thermophilic treatment gave higher potential for this dye decolorization compared with the mesophilic one. A reduced form of RB4 did not show an auto-oxidizing reaction but treated RB4 dye was shown in light yellow color, the intensity of which was related to the initial concentration of the dye used in the treatments. Starch, which showed similar decolorizing efficiency under thermophilic conditions, could be used as a co-substrate instead of glucose for the purpose of operating cost reduction. Due to the high content of salt contained in dye wastewater, the effect of salt (NaCl) was investigated. Results showed that decolorization could be accelerated with a concentration of NaCl lower than 200 mM, but the decolorization was inhibited by high concentrations of salt. The presence of RB4 inhibited methane productivity, while total organic carbon (TOC) reduction was similar to control, without dye addition. Increasing the temperature accelerated the decolorizing potential and TOC reduction. The evaluation of dye-reducing microbial consortia was done with acidogen and methanogen inhibitors which acidogenesis microorganism was dominant in RB4 decolorization.

Investigation of the diversity of homoacetogenic bacteria in mesophilic and thermophilic anaerobic sludges using the formyltetrahydrofolate synthetase gene

Homoacetogenic bacteria are strict anaerobes capable of autotrophic growth on H(2)/CO(2) or CO, and of heterotrophic growth on a wide range of sugars, alcohols, methoxylated aromatic compounds and one carbon compounds, yielding acetate as their sole metabolic end-product. Batch activity tests on anaerobic granular sludge, using H(2)/CO(2) as a substrate and 2-bromoethanesulfonate (BES) as a specific methanogenic inhibitor revealed that H(2)/CO(2) conversion and concomitant acetate production commenced only after a lag period of 60-100 h. This finding suggests that the homoacetogenic population of digester sludge could be maintained by heterotrophic growth on sugars or other organic compounds, rather than by autotrophic growth on H(2)/CO(2). In the present study, two upflow anaerobic sludge bed (UASB) reactors were operated at 37 degrees C and 55 degrees C for two distinct trial periods, each characterised by the application of influents designed to enrich for homoacetogenic bacteria. Specific primers designed for the amplification of the functional gene encoding formyltetrahydrofolate synthetase (FTHFS), a key enzyme in the acetyl-CoA pathway of acetogenesis, were used as a specific probe for acetogenic bacteria. The diversity of acetogens in the granular sludge cultivated in each reactor was revealed by application of FTHFS targeted PCR. Results show that biomass acetogenic composition was dependent upon the operational temperature of the reactor and the substrate supplied as influent.

Anaerobic digestion of secondary residuals from an anaerobic bioreactor at a brewery to enhance bioenergy generation

Many beer breweries use high-rate anaerobic digestion (AD) systems to treat their soluble high-strength wastewater. Biogas from these AD systems is used to offset nonrenewable energy utilization in the brewery. With increasing nonrenewable energy costs, interest has mounted to also digest secondary residuals from the high-rate digester effluent, which consists of yeast cells, bacteria, methanogens, and small (hemi)cellulosic particles. Mesophilic (37 degrees C) and thermophilic (55 degrees C) lab-scale, low-rate continuously-stirred anaerobic digestion (CSAD) bioreactors were operated for 258 days by feeding secondary residuals at a volatile solids (VS) concentration of approximately 40 g l(-1). At a hydraulic retention time (HRT) of 15 days and a VS loading rate of 2.7 g VS l(-1) day(-1), the mesophilic bioreactor showed an average specific volumetric biogas production rate of 0.88 l CH4 l(-1) day(-1) and an effluent VS concentration of 22.2 g VS l(-1) (43.0% VS removal efficiency) while the thermophilic bioreactor displayed similar performances. The overall methane yield for both systems was 0.21 l CH4 g(-1) VS fed and 0.47-0.48 l CH4 g(-1) VS removed. A primary limitation of thermophilic digestion of this protein-rich waste is the inhibition of methanogens due to higher nondissociated (free) ammonia (NH3) concentrations under similar total ammonium (NH4+) concentrations at equilibrium. Since thermophilic AD did not result in advantageous methane production rates or yields, mesophilic AD was, therefore, superior in treating secondary residuals from high-rate AD effluent. An additional digester to convert secondary residuals to methane may increase the total biogas generation at the brewery by 8% compared to just conventional high-rate digestion of brewery wastewater alone.

EFFECT OF METHANOGENIC INHIBITORS, INOCULA TYPE, AND TEMPERATURE ON BIOHYDROGEN PRODUCTION FROM FOOD COMPONENTS

Dark fermentation hydrogen production from a mixture of food components using two different methods of methanogenic inhibition (autoclaving and BES) and three different temperatures (37, 60, and 70 oC) was examined in batch assays for two different mixed anaerobic cultures - one suspended sludge (S) obtained from an anaerobic digester and one granular sludge (G) obtained from a brewery wastewater treatment plant. In general, BES-inhibition of sludge was more robust when compared against heat-treated inoculum. Also, hydrogen, VFA, and sCOD production were affected by increases in temperature although the effects were less severe for G than for S. In addition, differences in individual VFAs were observed between the two inocula. S produced more acetate as a percentage of VFATOTAL compared to G. Conversely, G produced more butyrate compared to S. Differences in the microbial communities were likely responsible for the diverse behaviour of the two inocula.

Evidence for Anaerobic CH 4 Oxidation in Freshwater Peatlands

This study involved in vitro assays of peat soil to investigate the occurrence, importance and potential mechanism(s) of anaerobic methane oxidation (AOM) in several northern peatlands ranging from ombrotrophic bog to minerotrophic fen. Although strong evidence suggests that AOM is linked to sulfate reduction in marine sediments, very little is known about AOM in freshwater systems such as northern peatlands, which have large methane (CH 4 ) production and are a significant source of atmospheric CH 4 . Our results showed a mean net AOM rate of 17 ± 2.6 nmol kg − 1 s − 1 with a maximum rate of 176 nmol kg − 1 s − 1 for a minerotrophic fen in central New York. AOM was demonstrated with three independent methods to verify our results: (a) additions of methanogenic inhibitors, (b) stable isotope enrichment ( 13 C-CH 4 ), and (c) natural abundance stable isotope analysis ( 13 C-CH 4 ). These experiments confirmed that AOM occurs simultaneously with methanogenesis, consumes a significant portion of gross CH 4 production, and significantly fractionates C isotopes (∼ −127‰). Experiments using a variety of potential electron acceptors demonstrated that Fe(III) and SO4 2 − are not quantitatively important, while the role of NO 3 − is uncertain and deserves more attention. The exact mechanism(s) for AOM in peat soils remains unclear; however the AOM rates reported in this study are similar to those reported for CH 4 production and aerobic CH 4 oxidation in northern peatlands, suggesting that AOM may be an important control on CH 4 fluxes in northern peatland ecosystems.

Biohydrogen Production by Mesophilic Anaerobic Fermentation of Glucose in the Presence of Linoleic Acid

In this work, linoleic acid (LA), a long chain fatty acid bearing 18 carbons and two double bonds, inhibited hydrogen consumption in a mixed anaerobic culture acclimated to glucose. At pH=7.6 , a metabolic shift from methane to hydrogen formation was observed in cultures maintained at 37°C and fed 5,000 mg L−1 glucose in the presence of 500–2,000 mg L−1 LA. The hydrogen yield increased with increasing LA levels while the quantity of methane decreased. The major volatile fatty acids produced were acetate and butyrate with greater levels observed in cultures fed with LA. Acetate, butyrate, and hydrogen accumulation suggests inhibition of aceticlastic methanogens, hydrogenotrophic methanogens, and butyrate degrading microorganisms, respectively, in the presence of LA. A maximum hydrogen yield of 1.71±0.22 mole mole−1 glucose was observed only when glucose was reinjected into cultures receiving 2,000 mg L−1 LA plus 5,000 mg L−1 glucose.

Anaerobic biodegradation of biphenyl in various paddy soils and river sediment

The anaerobic degradation of biphenyl was investigated in four uncontaminated Japanese paddy soils and one river sediment sample contaminated with benzene and chlorinated aliphatics. Two of the paddy soils and the sediment were capable of degrading biphenyl anaerobically without any additional medium or electron acceptors. The half-lives of biphenyl biodegradation in the three samples were 212 d in the Kuridashi soil, 327 d in the Kamajima soil, and 429 d in the river sediment. The Kuridashi soil metabolized 1 ± 0.3% of [U- 14C]-biphenyl into CO 2 and 5 ± 2% into water-soluble metabolites after 45 d of incubation. Submerged conditions, which result in lower nitrate and iron oxide contents, and neutral pH, appeared to be the common properties among the samples that influenced their degradation capacities. The addition of 10 mM sulfate and 20 mM Fe(III) as electron acceptors did not enhance the biphenyl degradation rate, whereas 10 mM nitrate completely inhibited biphenyl degradation. The addition of different electron donors (lactate, acetate, or pyruvate) slightly slowed the degradation. Molybdate (an inhibitor of sulfate-reducing bacteria) had an inhibitory effect on biphenyl biodegradation, but bromoethanesulfonic acid (an inhibitor of methanogens) did not. Most biphenyl degradation was observed when only water was added, with no other electron acceptors or donors. These results suggest that sulfate-reducing bacteria and fermentative microbial populations play important roles in anaerobic biphenyl biodegradation in paddy soil.

The Chronic Toxicity of Alcohol Alkoxylate Surfactants on Anaerobic Granular Sludge in the Pulp and Paper Industry

The chronic toxicity of an alcohol alkoxylate surfactant used in the pulp and paper industry was observed in methanogenic consortia under unfed conditions. Methanogenic inhibition was not observed until 250 h of famine conditions while in the presence of the surfactant. The delayed onset of inhibition is likely due to the amount of time necessary for the surfactant to partition into the cellular membrane which uncouples cellular energy conservation mechanisms and exhausts internal energy reserves necessary to maintain homeostasis.

Pretreatment of methanogenic granules for immobilized hydrogen fermentation

Hydrogen can be produced through fermenting sugars in a mixed bacterial culture under anaerobic conditions. Anaerobic granular sludge was proposed as immobilized hydrogen producing bacteria to be used in hydrogen fermentation after methanogenic activity of the granule was eliminated in the pretreatment process. This paper reports an innovative treatment method to directly convert methanogenic granules to hydrogen producing granules using chloroform. Chloroform treatment was compared against acid and heat treatments of sewage sludge and methanogenic granules in terms of effectiveness to eliminate methanogenic activity. The results showed that chloroform treatment was the most effective among the three methods tested. Acid and heat treatments that were effective for sewage sludge treatment were observed not highly effective for application to granules because of the protection from the granular structure. In contrast, methanogens were very sensitive to the chloroform even at very low level. Methane production was almost completely inhibited in both sewage sludge and granules with the treatment with only 0.05% chloroform addition into the culture medium. If the chloroform concentration was controlled at low levels, chloroform selectively inhibited methanogenic activity while did not affect the hydrogen production. At high concentration range, chloroform also inhibited hydrogen production. Chloroform caused irreversible methanogenic activity elimination but hydrogen production recovered to normal after chloroform addition stopped. Chloroform showed desirable selectivity on inhibition of methanogens from hydrogen producing bacteria, nearly permanently eliminated the methane production, postponed the hydrogen consumption to acetic acid, while allowed recovery for normal hydrogen production. Chloroform treated granules were repeatedly cultured for eight time without noticeable damage. Continuous culture with chloroform treated granules showed that the granule structure could be kept for over 15 days and new granules started to form after 10 days operation. The hydrogen productivity reached 11.6 L/L/day at HRT 5.3 h, which all showed potential application of chloroform treatment of methanogenic granules in the immobilized hydrogen fermentation.

Effects of Hydraulic Retention Time (HRT) and Sludge Retention Time (SRT) on the Treatment of Nitrobenzene in AMBR/CSTR Reactor Systems

The effect of hydraulic retention time (HRT) and solid retention time (SRT) on the biodegradation of a synthetic wastewater containing nitrobenzene was investigated in a sequential anaerobic migrating blanket reactor (AMBR) and aerobic completely stirred tank reactor (CSTR) system. Reactor performance was evaluated at six different HRTs (1,1.5,2,2.5,3.5,5.19 and 10.38 days) and at six different SRTs (32,53,76,217,415 and 932 days). The influent COD and nitrobenzene concentration were kept constant at 3000 mg l−1 and 60 mg l−1, respectively, during continuous operation. The maximum COD removal efficiency was found to be 92% at a HRT of 10.38 days and a SRT of 932 days in AMBR reactor. However, nitrobenzene removal efficiencies were found to be 99.9 % through all HRTs and SRTs in AMBR reactor. Most of the influent COD and nitrobenzene concentrations were removed in first compartment of AMBR. The total and methane gas production rates increased from 2760 ml day−1 to 11760 ml day−1 and from 1300 ml day−1 to 3331 ml day−1, respectively, as the HRT was decreased from 10.38 to 1 day in AMBR. However, methane percentage decreased from 47% to 28% with decreased HRTs and SRTs. The methanogens inhibition was observed at lower HRTs. pH values in the compartments and the effluent of AMBR was between optimum values. TVFA concentrations in effluent of AMBR were measured as zero until a HRT of 3.5 days. In the aerobic CSTR reactor, the COD removal efficiency decreased from 79% to 68% with decreased HRT from 6.79 to 0.67 days. It was found that the nitrobenzene transformed to aniline under anaerobic phase, and then the aniline mineralized in the oxidative stage, with efficiencies varying between 79% to 99.9 %, in anaerobic/aerobic reactor system.

Volatile organic sulfur compounds in anaerobic sludge and sediments: Biodegradation and toxicity

A variety of environmental samples was screened for anaerobic degradation of methanethiol, ethanethiol, propanethiol, dimethylsulfide, and dimethyldisulfide. All sludge and sediment samples degraded methanethiol, dimethylsulfide, and dimethyldisulfide anaerobically. In contrast, ethanethiol and propanethiol were not degraded by the samples investigated under any of the conditions tested. Methanethiol, dimethylsulfide, and dimethyldisulfide were mainly degraded by methanogenic archaea. In the presence of sulfate and the methanogenic inhibitor bromoethane sulfonate, degradation of these compounds coupled to sulfate reduction occurred as well, but at much lower rates. Besides their biodegradability, also the toxicity of methanethiol, ethanethiol, and propanethiol to methanogenesis with methanol, acetate, and H2/CO2 as the substrates was assessed. The 50% inhibition concentration of methanethiol on the methane production from these substrates ranged between 7 and 10 mM. The 50% inhibition concentration values of ethanethiol and propanethiol for the degradation of methanol and acetate were between 6 and 8 mM, whereas hydrogen consumers were less affected by ethanethiol and propanethiol, as indicated by their higher 50% inhibition concentration (14 mM). Sulfide inhibited methanethiol degradation already at relatively low concentrations: methanethiol degradation was almost completely inhibited at an initial sulfide concentration of 8 mM. These results define the operational limits of anaerobic technologies for the treatment of volatile organic sulfur compounds in sulfide-containing wastewater streams.

Greenhouse gas mitigation opportunities with immediate application to pastoral grazing for ruminants

Many of the greenhouse gas (GHG) mitigating options proposed by researchers have little immediate application to ruminant production from grazed pastures. Many grazing systems have low inputs and ruminants may have infrequent human intervention, which poses a challenge for mitigating GHG. Farmers must be aware of a need for mitigation, but adoption will only occur if the benefits for profitability exceed the costs of implementation and many potential mitigants are either too expensive (organic acids), have variable responses in vivo (ionophors, oils), are impractical under extensive grazing or are unlikely to be available in the near future (vaccines, methanogen inhibitors). Practical GHG reduction will depend on improvements in animal and dietary management, selection of individuals having low emissions/unit feed eaten, and possible release of mitigants through controlled release intra-ruminal capsules.