Inhibition Of Methanogenic Activity Research Articles

Excessive Ethanol Oxidation Versus Efficient Chain Elongation Processes

PurposeChain elongation is a metabolic feature that consists of the elongation of short-chain fatty acids to longer and more valuable acids when ethanol is available. To lower the operational costs, the process can also be performed using mixed microbial cultures. However, certain microorganisms in the mixed cultures can use the ethanol provided in competing reactions, which is usually termed excessive ethanol oxidation (EEO). Although minimizing ethanol use is essential, there is a lack of studies analyzing the extent, causes, and solutions to excessive ethanol oxidation processes.MethodsTo address this knowledge gap, ethanol, and acetic acid mixtures, at a molar ratio of 5 to 2, were fermented, and the following were analyzed: the fermentation profile at different (1) pH and (2) headspace gas compositions, (3) a 16S analysis of the headspace gas composition fermentations, and (4) a thermodynamic analysis of the reactions involved.Results and Conclusions: All fermentations, except the ones at the lowest pH (5.3), exhibited a significant EEO activity that reduced the yield of chain-elongated products. It was demonstrated that neither the inhibition of methanogenic activity nor the increased H2 partial pressure is an efficient method to inhibit EEO. It was also shown that CO2 can act as an electron acceptor for EEO, promoting the growth of acetogenic bacteria. In the absence of CO2, sulfate was used as an electron acceptor by sulfate-reducing bacteria to facilitate EEO. Methods such as low pH operation with in-line extraction, and the use of alternative sulfur salts, are proposed to increase the ethanol use efficiency in chain elongation processes.Graphical

Multifaceted roles of methylisothiazolinone intervention in sludge disintegration and acidogenic and methanogenic pathways for efficient carboxylate production during anaerobic fermentation

Anaerobic fermentation is a promising approach for sludge treatment, although it is frequently hindered by the tight structure of extracellular polymeric substances (EPS) and limited metabolic activities. This work firstly discovered that methylisothiazolinone (MIT, a commonly used antimicrobial agent in water treatment) effectively disintegrated the sludge structure and stimulated metabolic pathways, leading to efficient volatile fatty acids (VFAs) production. The presence of MIT (ranging from 10 to 40 mg/g TSS) contributed to the acidogenic process but strongly restrained the methanogenesis, and the distinct interfering effect is highly associated with the MIT dose. The VFAs accumulation reached a maximum of 1776.7 mg COD/L (5.2 times of control) but faced a complete inhibition of methanogenic activity at 40 mg/g TSS. Spectroscopic and molecular docking analysis revealed that MIT interacted with and disrupted the EPS (mainly proteins) structure by forming hydrogen bonds with N-H groups. This disruption facilitated the release of biodegradable organics, which served as fermentation substrates. Furthermore, the MIT-mediated improvement selectively enriched the hydrolytic-acidifying bacteria (i.e., Clostridium and Caloramator) and stimulated the associated metabolic functions, particularly in the uptake, hydrolysis, and metabolism of amino acids considering the high expressions of encoding genes (e.g., oppA, pepP, gdhA). However, methanogens' reproductive and metabolic abilities were suppressed due to their inefficient response and adaptation to MIT. This suppression was evident through downregulated genetic expressions involved in DNA replication and aminoacyl-tRNA synthesis. Consequently, a decline in methanogens abundance (e.g., Methanothrix, and Methanosarcina) and methanogenic activity occurred, impeding the consumption of VFAs. This work provided an innovative niche to promote resource recovery in the sludge anaerobic system and deciphered the underlying mechanisms at both biochemical interactive steps and microbial genetic traits.

The effect of organics transformation and migration on pore structure of bituminous coal and lignite during biomethane production.

Biomethane generation by coal degradation not only can increase coalbed methane (CBM) reserves, namely, microbially enhanced coalbed methane (MECBM), but also has a significant effect on the pore structure of coal which is the key factor in CBM extraction. The transformation and migration of organics in coal are essential to pore development under the action of microorganisms. Here, the biodegradation of bituminous coal and lignite to produce methane and the cultivation with inhibition of methanogenic activity by 2-bromoethanesulfonate (BES) were performed to analyze the effect of biodegradation on coal pore development by determining the changes of the pore structure and the organics in culture solution and coal. The results showed that the maximum methane productions from bituminous coal and lignite were 117.69μmol/g and 166.55μmol/g, respectively. Biodegradation mainly affected the development of micropore whose specific surface area (SSA) and pore volume (PV) decreased while the fractal dimension increased. After biodegradation, various organics were generated which were partly released into culture solution while a large number of them remained in residual coal. The content of newly generated heterocyclic organics and oxygen-containing aromatics in bituminous coal was 11.21% and 20.21%. And the content of heterocyclic organics in bituminous coal was negatively correlated with SSA and PV but positively correlated with the fractal dimension which suggested that the retention of organics contributed greatly to the decrease of pore development. But the retention effect on pore structure was relatively poor in lignite. Besides, microorganisms were observed around fissures in both coal samples after biodegradation which would not be conducive to the porosity of coal on the micron scale. These results revealed that the effect of biodegradation on pore development of coal was governed by the combined action of organics degradation to produce methane and organics retention in coal whose contributions were antagonistic and determined by coal rank and pore aperture. The better development of MECBM needs to enhance organics biodegradation and reduce organics retention in coal.

Anaerobic digestion of mixed urban biowaste: The microbial community shift towards stability

Anaerobic digestion is applied worldwide to treat food waste (FW) with the aim of obtaining renewable bioenergy by exploiting the methane gas produced. However, there are several problems in practical applications, primarily due to system instability. Although exhaustive knowledge regarding anaerobic microbial community composition has been established, few studies have investigated long-term correlations between microbial consortia, operative conditions and feedstock characteristics. Here, microbial community shifts as a response to feedstock variations were investigated in long-term semi-continuous systems, which were evaluated by an in situ cell detection method and 16S rRNA gene amplicon sequencing. FW digestion showed progressive system instability caused by the inhibition of methanogens, which resulted in volatile fatty acid accumulation and process failure at the low organic loading rate (OLR). Conversely, by co-digesting FW with waste-activated sludge (WAS), a stable process with methane yields of up to 0.27 Nm3 kg−1VSfed for OLR = 1.7 gVS L−1d−1 was achieved. This stabilizing effect was not related to the buffering capacity of WAS, but to its capacity to avoid volatile fatty acid accumulation and falls in pH by overcoming methanogenic activity inhibition. WAS addition promoted the establishment of a stable and active archaeal population in anaerobic co-digestion (AcoD) reactors. The continuous supply of trace elements together with the seeding of microbial functional groups were the main drivers that positively affected process stability.

Carbonaceous Greenhouse Gases and Microbial Abundance in Paddy Soil under Combined Biochar and Rice Straw Amendment

Little is known about the carbonaceous greenhouse gases and soil microbial community linked to the combination of biochar (BC) and rice straw (RS) in paddy soils. The objectives of this research were to evaluate the effects of combining BC and RS on (1) CH4 and CO2 production from paddy soil, (2) archaeal and bacterial abundance, and (3) rice grain yield. The experiments consisted of a pot trial and an incubation trial, which had a completely randomized design. The experiments included five treatments with three replications: (a) the control (without BC, RS, and chemical fertilizer (CF)); (b) CF; (c) BC 12.50 t ha−1; (d) RS 12.50 t ha−1; and (e) combined BC 6.25 t ha−1 + RS 6.25 t ha−1 + CF. In the sole RS treatment, CH4 production (0.0347 mg m−2 season−1) and the archaeal and bacterial abundance (5.81 × 108 and 4.94 × 1010 copies g−1 soil dry weight (DW)) were higher than outcomes in the sole BC treatment (i.e., 0.0233 mg m−2 season−1 for CH4 production, and 8.51 × 107 and 1.76 × 1010 copies g−1 soil DW for archaeal and bacterial abundance, respectively). CH4 production (0.0235 mg m−2 season−1) decreased significantly in the combined BC + RS + CF treated soil compared to the soil treated with RS alone, indicating that BC lessened CH4 production via CH4 adsorption, methanogenic activity inhibition, and microbial CH4 oxidation through bacterial methanotrophs. However, the archaeal abundance (3.79–5.81 × 108 copies g−1 soil DW) and bacterial abundance (4.94–5.82 × 1010 copies g−1 soil DW) in the combined BC+ RS + CF treated soil and the RS treated soil were found to increase relative to the treatments without RS. The increase was due to the easily decomposable RS and the volatile matter (VM) constituent of the BC. Nevertheless, the resultant CO2 production was relatively similar amongst the BC, RS, and BC + RS treated soils, which was indicative of several processes, e.g., the CO2 production and reduction that occurred simultaneously but in different directions. Moreover, the highest yield of rice grains was obtained from a combined BC + RS + CF treated soil and it was 53.47 g pot−1 (8.48 t ha−1). Over time, the addition of BC to RS soil enhanced the archaeal and bacterial abundance, thereby improving yields and reducing CH4 emissions.

In situ biogas stripping of ammonia from a digester using a gas mixing system

ABSTRACTPrevious studies have suggested the use of digester biogas mixing systems for in situ ammonia removal from anaerobic digestates. The feasibility of this was tested at moderate and complete gas mixing rates at mesophilic and thermophilic temperatures in a 75-L digester. Experimental results showed that at gas mixing rates typical of full-scale commercial digesters the reduction in total ammonia nitrogen concentrations would be insufficient to allow stable acetoclastic methanogenesis in mesophilic conditions, or to prevent total inhibition of methanogenic activity in thermophilic food waste digestion. Simulation based on batch column stripping experiments at 55°C at gas violent flow rates of 0.032 m3 m−2 min−1 indicated that ammonia concentrations could be reduced below inhibitory values in thermophilic food waste digestion for organic loading rates of up to 6 kg VS m−3 day−1. These mixing rates are far in excess of those used in full-scale gas-mixed digesters and may not be operationally or commercially feasible.

Methanogenic activity inhibition by increasing the linear alkylbenzene sulfonate (LAS) concentration

ABSTRACTThe effect of the initial concentration of linear alkylbenzene sulfonate (LAS) on specific methanogenic activity (SMA) was investigated in this work. Six anaerobic flasks reactors with 1 L of total volume were inoculated with anaerobic sludge (2 g VSS L−1). The reactors were assayed for 42 days, and fed with volatile fatty acids, nutrients, and LAS. The initial LAS concentrations were 0, 10, 30, 50, 75, and 100 mg L−1 for the treatment flasks T1 (control), T2, T3, T4, T5, and T6, respectively. When compared with T1, T2 exhibited a 30% reduction in maximum SMA and total methane production (TMP). In treatment T3 through T6, the reductions were 44–97% (T3–T6) for SMA, and 30–90% (T3–T6) for TMP. Total LAS removal increased following the increase in the initial LAS concentration (from 36% at T1 to 76% at T6), primarily due to the high degree of sludge adsorption. LAS biodegradation also occurred (32% in all treatments), although this was most likely associated with the formation of non-methane intermediates. Greater removal by adsorption was observed in long-chain homologues, when compared to short-chain homologues (C13 > C10), whereas the opposite occurred for biodegradation (C10 > C13). The C13 homologue was adsorbed to a great extent (in mass) in T4, T5 and T6, and may also have inhibited methane formation in these treatments.

Inhibitory effect of clay mineral on methanogenesis by Methanosarcina mazei and Methanothermobacter thermautotrophicus

With increased concentration of methane in the atmosphere and its impact on climate, effective mitigation of methane emission is of global importance. Recent studies have shown the inhibition of microbial methanogenesis upon addition of ferruginous clay minerals. To better elucidate the mechanism of the inhibitory effect of clay minerals on methanogenesis, laboratory experiments with Methanosarcina mazei and Methanothermobacter thermautotrophicus were performed in batch systems in which pristine kaolinite or iron-coated kaolinite were added as representative clay minerals. Soluble Al in solution and production of Fe(II) and methane gas were monitored over the course of the experiments. The mineralogical changes in the kaolinites were characterized with scanning electron microscopy. The results confirmed that both Ms. mazei and Mt. thermautotrophicus were capable of reducing ferric iron with H2/CO2 as methanogenic reactants. Both pristine and iron-coated kaolinites could act as effective inhibitors of methanogenesis. The overall methane production was similar with pristine kaolinite and iron-coated kaolinite, although at the beginning of the experiment less CH4 was observed in iron-coated kaolinite system. The inhibition of methanogenic activity observed in pristine kaolinite was primarily ascribed to the toxicity effect of aluminum. A more effective inhibition of methanogenesis in iron-coated kaolinite during the first several days could be explained by the combined effects of aluminum toxicity and diversion of electron flow from CO2 to Fe(III). Our results have important implications for mitigating methane emission in natural or anthropogenic settings.

Sulfidogenesis interference on methane production from carbohydrate-rich wastewater.

Two anaerobic fixed-structured bed reactors were fed with synthetic wastewater simulating the soluble fraction of sugarcane vinasse to evaluate the interference of sulfidogenesis on methanogenesis. The reactors running in parallel were subjected to the same operating conditions. The influent organic matter concentration (in term of chemical oxygen demand (COD)) remained close to 4,000 mgCOD L(-1) and the hydraulic retention time was 24 hours. One reactor, the methanogenic (control reactor), received sulfate only to provide the sulfur required as a nutrient to the methanogenic biomass. The other one, the sulfidogenic/methanogenic reactor (SMR), received sulfate concentration corresponding to COD/sulfate ratios of 4, 5 and 3. In the last phase, the COD removal efficiencies were higher than 96% in both reactors and the SMR achieved 97% of sulfate removal efficiency (COD/sulfate ratio of 3 and influent sulfate concentration close to 1,300 mgSO4(2-) L(-1)). Both reactors also had similar methane yields in this phase, close to 350 mLCH4 gCODremoved(-1) at standard temperature and pressure. These results indicated no significant inhibition of methanogenic activity under the sulfidogenic conditions assessed.

Acid Endurance and Sorption of Zn<sup>2+</sup> of Anaerobic Granular Sludge Acclimated by Flue Gas Pretreatment Wastewater

With the aim to use anaerobic granular sludge, the methanogenic activity inhibition and recovery of anaerobic granular sludge from an industrial anaerobic reactor (s1) were investigated by measuring the methane volume at low pH. A lab-scale upflow anaerobic sludge blanket (UASB) reactor was inoculated with s1.s1 was used to remove Zn2+ in wastewater. The results show that activity of s1 is similar when the pH value is 6.5 to 7.0. The methane volume is obviously decreased when the pH value is 6.0. The activity is completely inhibited when the pH value is 4.5. The activity is fully recovered when the pH is above 6.5 and hardly recovers when the pH fell to 4.5. The main Zn2+ removal mechanism is chemical adsorption.

Adaptation of Methanogenic Communities to the Cofermentation of Cattle Excreta and Olive Mill Wastes at 37°C and 55°C

The acclimatization of methanogens to two-phase olive mill wastes (TPOMW) was investigated in pilot fermenters started up with cattle excreta (37°C) and after changing their feed to excreta plus TPOMW (37°C or 55°C) or TPOMW alone (37°C) until a steady state was reached (28 days). Methanogenic diversity was screened using a phylogenetic microarray (AnaeroChip), and positive targets were quantified by real-time PCR. Results revealed high phylogenetic richness, with representatives of three out of the four taxonomic orders found in digesters. Methanosarcina dominated in the starting excreta (>96% of total 16S rRNA gene copies; over 45 times more abundant than any other methanogen) at high acetate (0.21 g liter(-1)) and ammonia N concentrations (1.3 g liter(-1)). Codigestion at 37°C induced a 6-fold increase of Methanosarcina numbers, correlated with CH(4) production (r(Pearson) = 0.94; P = 0.02). At 55°C, the rise in temperature and H(2) partial pressure induced a burst of Methanobacterium, Methanoculleus, Methanothermobacter, and a group of uncultured archaea. The digestion of excreta alone resulted in low but constant biogas production despite certain oscillations in the methanogenic biomass. Unsuccessful digestion of TPOMW alone was attributed to high Cu levels inducing inhibition of methanogenic activity. In conclusion, the versatile Methanosarcina immediately adapted to the shift from excreta to excreta plus TPOMW and was responsible for the stimulated CH(4) production at 37°C. Higher temperatures (55°C) fostered methanogenic diversity by promoting some H(2) scavengers while yielding the highest CH(4) production. Further testing is needed to find out whether there is a link between increased methanogenic diversity and reactor productivity.

Cobalt toxicity in anaerobic granular sludge: influence of chemical speciation

The influence of cobalt speciation on the toxicity of cobalt to methylotrophic methanogenesis in anaerobic granular sludge was investigated. The cobalt speciation was studied with three different media that contained varying concentrations of complexing ligands [carbonates, phosphates and ethylenediaminetetraacetic acid (EDTA)]. Three fractions (nominal added, dissolved and free) of cobalt were determined in the liquid media and were correlated with data from batch toxicity experiments. The average concentration of cobalt that was required for 50% inhibition of methanogenic activity (IC50) for free Co2+ in the three sets of measurements was 13 micromol/L with a standard deviation of 22% and a similarity of 72% between the data obtained in the three different media for the range of cobalt concentrations investigated. The standard deviation of the IC50 for the other two fractions was much higher, i.e. 85 and 144% for the added cobalt and dissolved cobalt, respectively, and the similarity was almost 0% for both fractions. Complexation (and precipitation) with EDTA, phosphates and carbonates was shown to decrease the toxicity of cobalt on methylotrophic methanogenesis. The free cobalt concentration is proposed to be the key parameter to correlate with cobalt toxicity. Thus, the toxicity of cobalt to granular sludge can be estimated based on the equilibrium-free cobalt concentration.

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.

Anaerobic Biodegradation of Sterols Contained in Kraft Mill Effluents

Bleached kraft mill requires large quantities of water and chemicals reactives and generates effluents containing active organic compounds. Specifically, hormonal changes in fish and their communities have been demonstrated, which could be attributed to endocrine-disrupting chemicals (EDCs) contained in kraft mill effluents. This chronic toxicity is attributable to extractive compounds, such as resin acids, sterols, and fatty acids. The goal of this work is to evaluate the methanogenic toxicity and anaerobic biodegradation of stigmasterol and beta-sitosterol. A continuously anaerobic filter (AF) was used for the anaerobic biodegradation of stigmasterol and beta-sitosterol. Three phases were evaluated. In phase I, an elementary chlorine-free bleached kraft mill effluent was fed to the reactor whereas in phases II and III, the effluent was supplemented with increasing stigmasterol and beta-sitosterol concentrations. The AF displays high performance in biological oxygen demand (BOD5) removal (up to 94%); however, only 50% of the chemical oxygen demand (COD) was removed. Simultaneously, the AF system shows a great ability to remove beta-sitosterols (77-100%) and stigmasterols (87-95%). No negative effect on the methanogenic activity inhibition was shown by beta-sitoesterols and stigmasterol. However, a mixture of beta-sitosterols and stigmasterols (ratio 1:1) caused a less than 10% reduction in methanogenic activity.

Methanogenic toxicity and continuous anaerobic treatment of wood processing effluents

Wood processing effluents contain different types of phenolic compounds, from simple monomers to high molecular weight (MW) polyphenolic polymers, that can inhibit wastewater treatment. This work presents a comparative study of the methanogenic toxicity produced by three wood processing effluents (hardboard, fiberboard and BKME (kraft mill effluent)) using Pinus radiata, Eucalyptus and Tepa as feedstock (the last one being a native Chilean tree species). This study evaluates the influence of non-adapted granular and adapted flocculent sludge on forest industrial wastewater treatment as well as continuous anaerobic biodegradation of hardboard processing effluent using the upflow anaerobic sludge blanket (UASB). The adapted biomass (flocculent sludge) did not show any lag-phase signs. The 50% IC (the concentration causing 50% inhibition of methanogenic activity) was 4.3 g COD-effluent (chemical oxygen demand (COD)-of the effluent)/l and 2.8 g COD-effluent/l for the flocculent sludge and the granular sludge, respectively. The UASB system worked at low organic load rates (0.1–0.4 g COD/l d) with the COD removal ranging between 10 and 30%, and color removal did not occur under anaerobic conditions due to high MW. Indeed, the MW analysis indicates the presence of phenolic compounds over 25,000 Da in the anaerobic effluent.

Effect of ammonia on the methanogenic activity of methylaminotrophic methane producing Archaea enriched biofilm

Ammonia is a metabolic product in the decomposition of protein wastes, and has a recognized inhibitory effect on methanogenesis; this effect has been slightly quantified on methanogenic biofilms and particularly those populated by methanogenic Archaea which produce ammonia as a catabolic product from methylated amines. This paper presents studies on the effect of ammonia on maximum methanogenic activity of anaerobic biofilms enriched by methylaminotrophic methane producing Archaea (mMPA). The effect of unionized free ammonia on the specific maximum methanogenic activity of a mMPA enriched biofilm was studied, using 250 mL flasks containing ceramic rings colonized by 30 day-old experimental biofilm and adding 48.8 (control system), 73.8, 98.8, 148.8, 248.8, 448.8 and 848.8 mg NH 3-N/L. The systems were maintained for ten days at a pH of 7.5 and temperature of 37°C. The results showed that at 848.8 mg NH 3-N/L, biofilm methane production required 36 h adaptation period, prior to entering into maximum production phase. The highest maximum methanogenic activity reached a value of 2.337±0.213 g COD methane/g VSS∗day when 48.8 mg NH 3-N/L was added, and inhibition was clearly observed in those systems above 148.8 mg NH 3-N/L, producing under 1.658±0.185 g COD methane/g VSS∗day. The lowest methanogenic activity reached was 0.639±0.162 g COD methane/g VSS∗day at the system added with 848.8 mg NH 3-N/L. When applying the Luong and non-competitive inhibition models, the best fit was obtained with the non-competitive model, which predicted 50% inhibition of methanogenic activity at 365.288 mg NH 3-N/L.

Influence of Flow Regime on the Concentration of Cyanide Producing Anaerobic Process Inhibition

A study was conducted to analyze the effects of cyanide on methanogenic bacterial populations in both continuous and batch reactors. The appropriate toxicity assays were divided into two parts, i.e. 1) batch assays, and 2) continuous flow assays, using a 6.5-litre up-stream anaerobic sludge blanket reactor (UASB). A synthetic substrate was used as feed for both assays using 99% sucrose as a carbon source, and potassium cyanide (KCN) as a free cyanide source. In the first part, the treatments with the lowest and highest percentages of Specific Methanogenic Activity (SMA %) were 3 and 10 mg CN−/l. A 0.96 mg/l concentration of cyanide caused methanogenic activity inhibition by 50% during the exposure stage. During the recovery stage, Methanogenic Activity of treatments had a considerable increase compared to the results from direct cyanide exposure, except for treatments of 7 and 10 mg CN−/l. The concentration of cyanide that inhibits Specific Methanogenic Activity by 50% was 6.1 mg CN−/l during this stage. In the second part, the reactor was continuously fed with a synthetic substrate (COD≈ 1500 mg/l). After the anaerobic sludge became acclimated, cyanide concentrations from 0.5 and 130 mg CN−/l were progressively added. The hydraulic retention time remained constant at 12 hours throughout the entire experiment. Results indicated that while partial inhibition occurred for concentrations of 3, 20 and 100 mg CN−/l, severe inhibition occurred for 130 mg CN−/l.

Influence of flow regime on the concentration of cyanide producing anaerobic process inhibition

A study was conducted to analyze the effects of cyanide on methanogenic bacterial populations in both continuous and batch reactors. The appropriate toxicity assays were divided into two parts, i.e. 1) batch assays, and 2) continuous flow assays, using a 6.5-litre up-stream anaerobic sludge blanket reactor (UASB). A synthetic substrate was used as feed for both assays using 99% sucrose as a carbon source, and potassium cyanide (KCN) as a free cyanide source. In the first part, the treatments with the lowest and highest percentages of Specific Methanogenic Activity (SMA %) were 3 and 10 mg CN − /l. A 0.96 mg/l concentration of cyanide caused methanogenic activity inhibition by 50% during the exposure stage. During the recovery stage, Methanogenic Activity of treatments had a considerable increase compared to the results from direct cyanide exposure, except for treatments of 7 and 10 mg CN − /l. The concentration of cyanide that inhibits Specific Methanogenic Activity by 50% was 6.1 mg CN − /l during this stage. In the second part, the reactor was continuously fed with a synthetic substrate (COD≈ 1500 mg/l). After the anaerobic sludge became acclimated, cyanide concentrations from 0.5 and 130 mg CN − /l were progressively added. The hydraulic retention time remained constant at 12 hours throughout the entire experiment. Results indicated that while partial inhibition occurred for concentrations of 3, 20 and 100 mg CN − /l, severe inhibition occurred for 130 mg CN − /l.

Inhibition of anaerobic digestion by terephthalic acid and its aromatic by products

With 14.4 million tons produced in 1993, purified terephthalic acid (PTA) and dimethylterephthalate (DMT) are the main monomers used in the world polyester production. Even though there are ten industrial digestors treating the effluents of both products, little is known about the influence of their organic components, terephthalic (TA), p-toluic (p-tol), benzoic (BA) and phthalic (PA) acids as well as 4-carboxybenzaldehyde (4-CBA) on methanogenesis. This study shows that the concentrations of 4-CBA, p-tol and TA required to inhibit by 50% the hydrogenotrophic methanogenic activity are respectively 5.4, 34 and more than 100 mM. At the maximum concentration tested (10 mM), the inhibition of the acetoclastic methanogenic activity by the same compounds was less than 12%. The results indicate that at the concentration of TA, p-tol and 4-CBA found in PTA and DMT wastewater, no significant inhibition of the methanogenic activity should be observed for PTA but that the hydrogenotrophic activity could be reduced by as much as 30% in the case of DMT. The degradation of TA was completely inhibited by the presence of BA and glucose while the presence of phthalate had no effect. According to these results, it is concluded that it is at least possible to anaerobically treat the easily biodegradable compounds of these effluents (acetic, benzoic and formic acid) as they would not be significantly inhibited by TA, p-tol or 4-CBA.

Inhibition of methanogenic activity of starch-degrading granules by aromatic pollutants

The effects of nine common aromatic pollutants from chemical industry on the bioactivity of anaerobic granules were examined. The granules were obtained from an upflow anaerobic sludge blanket (UASB) reactor treating wastewater containing colloidal starch. The specific methanogenic activities (SMA) of granules were measured at 37°C in serum vials using 3000 mg/l of colloidal starch as substrate, plus individual pollutants at various concentrations. The toxicity was expressed by the IR50 and IC50 values, i.e. the toxicant/biomass ratio and concentration at which levels the granules exhibited only 50% of their original bioactivities. Results showed that in general the granules exhibited mild resistance to toxicity of aromatic pollutants, probably due to the granules' layered microstructure. The toxicities, which were dependent on the nature of chemical functional group, of the aromatic pollutants were in the following descending order: cresols > phenol > hydroxyphenols/phthalate > benzoate. There was only marginal difference between the toxicity of the steric isomers. For the seven phenolic pollutants, the more hydrophobic the functional group the higher the toxicity. The granules' resistance to toxicity suggested the plausibility of anaerobic treatment of wastewater from the chemical industry.