Efficiency of the anaerobic digestion of amine wastes

Laboratory-scale anaerobic degradation of monoethanolamine waste (MEAw) with co-substrate organics was conducted at room temperature and organic loading rates from 0.19 to 5.03 kg COD/m³ day for 486 days in a hybrid digester. 90 % feed COD conversion to methane was obtained at the lower loads and only 45 % at the highest MEA waste/COD ratio (MEAwr) of 0.62 due to inhibition of methanogenesis. Inhibition at comparable loads decreased with time, implying that the culture adapted to the challenging feed. Methane yield was negatively correlated to MEAwr applied and inhibition avoided at MEAwr <0.5. Acetate accumulation implies inhibition of acetoclastic methanogenesis that can be caused by ammonia, a product of MEAw degradation. Moderate total ammonia nitrogen and free ammonia nitrogen accumulation, maximum 2.2 g N/l and 90 mg N/l, respectively suggests, however, that other components of MEAw, and/or degradation products of such, also inhibit methanogenesis, disturbing the digester performance.     

Influence of phenol additions on the efficiency of an anaerobic hybrid digester treating landfill leachate

Summary A hybrid digester with leachate as substrate was used to determine the influence of the addition of phenol. The phenol was increased stepwise from 2 to 25 mg/l and then to 30, 40, 50 and 60 mg/l leachate. Within 24 h the addition caused a significant decrease in the COD removal and biogas production while the methane content increased. Phenol loading was characterised by the accumulation of volatile fatty acids. With the continuous addition of phenol, a recovery time of 28 d was required for the performance to reach the control values. As the concentration was increased, the recovery time shortened to 8 d at 20 mg/l. At higher concentrations (>50 mg/l) the recovery time was found to increase to >60 d.     

Microbial Ecology in Anaerobic Digestion at Agitated and Non-Agitated Conditions

To investigate the distribution and dynamics of microbial community in anaerobic digestion at agitated and non-agitated condition, 454 pyrosequencing of 16s rRNA was conducted. It revealed the distinct community compositions between the two digesters and their progressive shifting over time. Methanogens and syntrophic bacteria were found much less abundant in the agitated digester, which was mainly attributed to the presence of bacterial genera Acetanaerobacterium and Ruminococcus with relatively high abundance. The characterization of the microbial community corroborated the digestion performance affected at the agitated condition, where lower methane yield and delayed methane production rate were observed. This was further verified by the accumulation of propionic acid in the agitated digester.     

A comparison of the performance of mesophilic and thermophilic anaerobic filters treating papermill wastewater

Two anaerobic filters, one mesophilic (35 degrees C) and one thermophilic (55 degrees C), were operated with a papermill wastewater at a series of organic loadings. The hydraulic retention time (HRT) ranged from 6 to 24 h with organic loading rates (OLR) 1.07-12.25 g/l per day. At loading rates up to 8.4 g COD/l d, there was no difference in terms of the removal of soluble COD (SCOD) and gas production. At the higher organic loading rate, the SCOD removal performance of thermophilic digester was slightly better compare to mesophilic digester. Similar trend was also observed in terms of the daily methane production. The stability of thermophilic digester was also better than mesophilic digester particularly for the higher organic loadings. Volatile fatty acid accumulation was observed in the effluent of the mesophilic filter at the higher organic loading rates. The Stover-Kincannon model was applied to both digesters and it was found that model was applicable to both digesters for papermill wastewater. K(B) and U(max) constants from the Stover-Kincannon model were also derived.     

Inhibition of a methanogenic population by thioglycollate

Thioglycollate added at 3.2 mM inhibited methane (CH₄) production from propionate by a methanogenic bacterial population obtained from an anaerobic digester. Gas production from acetate was not inhibited at this concentration. Glucose added in a semi-synthetic medium was degraded in the presence of 3.2 mM thioglycollate but propionate accumulated in the medium and the methanol yield was reduced. The severity of inhibition of propionate degradation increased with further incubation.     

New data on temperature optimum and temperature changes in energy crop digesters

As a result of self-heating in anaerobic digesters when using energy crops in the feedstock, the influence of temperature on the digestion process came back into focus. The aim of this study was to investigate the impact of such temperature increases on process stability. Furthermore, different strategies for the transition from mesophilic to thermophilic conditions and the resulting methane yields at different temperature levels were evaluated. Two main effects were identified with different bio-slurries from agricultural biogas plants: (1) a failure of methane production connected to changes in the microbial community; and (2), a slow but continuous accumulation of propionic acid, though without an immediate effect on methane production. All strategies for increasing the operating temperature showed negative effects on digester performance, some with serious economic consequences for the operator. It was shown that methane yields at different temperature levels in the mesophilic and sub-thermophilic ranges are similar.     

Anaerobic treatment of baker's yeast effluent using a hybrid digester with polyurethane as support material

Summary A high-strength baker's yeast effluent was anaerobically treated using a hybrid digester under mesophilic conditions. The digester was subjected to a substrate COD concentration of 21 767 mg/I at three different HRTs. At HRTs of 3.0, 2.0 and 1.0 d, the digester reduced the substrate COD by 76, 61 and 33%, respectively. Although the best COD removal was obtained at an OLR of 7.30 kg COD/m³.d, the highest COD removal rate (6.51 kg COD/M³-d) was found at 10.65 kg COD/m³.d at an HRT of 2.0 d. The low methane yield and VFA accumulation found in the digester effluent, indicated inhibition on methanogenic level and this was considered to be the rate-limiting step during the anaerobic treatment process. The overall efficiency of the digester indicated that this digester design and support medium was suitable for the treatment of a high-strength, sulfate-rich baker's yeast effluent.     

Toxic effects of thiol-reactive compounds on anaerobic biomass

The objective of this study was to characterize the toxic effects of three well known thiol-reactive electrophilic compounds, N-ethylmaleimide (NEM), pentachlorophenol (PCP) and 1-chloro-2,4-dinitrobenzene (CDNB) on anaerobic biotransformation process. The work was part of a larger investigation on potassium efflux as a possible response mechanism of anaerobic microorganisms to the presence of thiol-reactive organic compounds and the interference of such compounds on the reductive dehalogenation process. Using anaerobic toxicity assay (ATA) and granular anaerobic biomass from a full-scale upflow anaerobic sludge blanket (UASB) reactor, inhibitory concentrations of these compounds that reduced the microbial activity of granular biomass to 50% of a control (IC50) were determined to be 592, 0.97, and 450 mg/l for NEM, PCP, and CDNB, respectively. Toxicity of NEM was also tested on anaerobic biomass from a municipal wastewater treatment plant digester and slightly lower IC50 of 532 mg/l was obtained. The results presented here indicate that anaerobic biomass can acclimate to the three thiol-reactive compounds studied and recover from inhibition as long as the toxicant concentration is below a threshold level. That threshold concentration was found to be 500 mg/l for NEM on biomass from the municipal digester, 1 mg/l for PCP, and 500 mg/l for CDNB, both on granular biomass. Granular anaerobic biomass showed recovery even at NEM concentrations of 1000 mg/l.     

Effects of ammonia nitrogen of H2 and CH4 production during anaerobic digestion of dairy cattle manure

A number of researchers have verified the inhibitory effects of elevated H2 concentrations on various anaerobic fermentation processes. The objective of this work was to investigate the potential for using hydrogen gas production to predict upsets in anaerobic digesters operating on dairy cattle manure. In an ammonia nitrogen overload experiment, urea was added to the experimental digesters to obtain increased ammonia concentrations (600, 1,500, or 3,000 mg N/l). An increase in urea concentration resulted in an initial cessation of H2 production followed by an increase in H2 formation. Additions of 600, 1,500, or 3,000 mg N/l initially resulted in the reduction of biogas H2 concentrations. After 24 h, the H2 concentration increased in the 600 and 1,500 mg N/l digesters, but production remained inhibited in the 3,000 mg N/l digesters. Both methane and total biogas production decreased following urea addition. Volatile solids reduction also decreased during these periods. The digester effluent pH and alkalinity increased due to the increased NH4 formed with added urea. Based on these results, changes in H2 concentration could be a useful parameter for monitoring changes due to increased NH3 in dairy cattle manure anaerobic digesters.     

Mesophilic anaerobic treatment of sludge from saline fish farm effluents with biogas production

The mesophilic anaerobic treatment of sludge from saline fish farm effluents (total solids (TS): 8.2-10.2 wt%, chemical oxygen demand (COD): 60-74 g/l, sodium (Na): 10-10.5 g/l) was carried out in continuously stirred tank reactors (CSTRs) at 35 degrees C. COD stabilization between 36% and 55% and methane yields between 0.114 and 0.184 l/g COD added were achieved. However, the process was strongly inhibited, presumably by sodium, and unstable, with propionic acid being the main compound of the volatile fatty acids (VFA). When diluting the sludge 1:1 with tap water (Na: 5.3 g/l), the inhibition could be overcome and a stable process with low VFA concentrations was achieved. The results of the study are used to make recommendations for the configuration of full-scale treatment plants for the collected sludge from one salmon farming licence and to estimate the energy production from these plants.     

Inhibitory effect of chlorinated guaiacols on methanogenic activity of anaerobic digester sludge

Of four chlorinated guaiacols, tetrachloroguaiacol at 62 M inhibited acetate methanogenesis, the strongest decreasing activity by 50%. 4,5,6-Trichloroguaiacol, 4,5-dichloroguaiacol, and 4-chloroguaiacol showed 50% inhibition at 0.13, 0.32, and 1.50 mM, respectively. Degradation test results of volatile fatty acids (acetic, propionic, and butyric acid) by anaerobic digester sludge (stored 5 weeks) indicated that syntrophic butyrate degraders of this sludge were more sensitive to tetrachloroguaiacol than acetoclastic methanogens and syntrophic propionate degraders.     

Inhibitory effects of the macrolide antimicrobial tylosin on anaerobic treatment

A laboratory-scale anaerobic sequencing batch reactor (ASBR) was operated using a glucose-based synthetic wastewater to study the effects of tylosin, a macrolide antimicrobial commonly used in swine production, on treatment performance. The experimental period was divided into three consecutive phases with different influent tylosin concentrations (0, 1.67, and 167 mg/L). The addition of 1.67 mg/L tylosin to the reactor had negligible effects on the overall treatment performance, that is, total methane production and effluent chemical oxygen demand did not change significantly (P < 0.05), yet analyses of individual ASBR cycles revealed a decrease in the rates of both methane production and propionate uptake after tylosin was added. The addition of 167 mg/L tylosin to the reactor resulted in a gradual decrease in methane production and the accumulation of propionate and acetate. Subsequent inhibition of methanogenesis was attributed to a decrease in the pH of the reactor. After the addition of 167 mg/L tylosin to the reactor, an initial decrease in the rate of glucose uptake during the ASBR cycle followed by a gradual recovery was observed. In batch tests, the specific biogas production with the substrate butyrate was completely inhibited in the presence of tylosin. This study indicated that tylosin inhibited propionate- and butyrate-oxidizing syntrophic bacteria and fermenting bacteria resulting in unfavorable effects on methanogenesis.     

Digestion of sand-laden manure slurry in an upflow anaerobic solids removal (UASR) digester

Studies on the performance of a laboratory scale upflow anaerobic solids removal (UASR) digester were carried out using sand-laden cow manure slurries having total solids (TS) concentration as 50 and 100 g/l. Hydraulic retention time (HRT) was maintained as 32.4 days, which resulted in the volatile solids (VS) loading rates of 1 and 1.64 g/l d. The UASR system was designed to remove sand from the manure slurry, while anaerobically digesting biodegradable solids inside a single reactor. To enhance the contact of microorganisms and substrate, the liquor from the top of the digester was recirculated through the bed of settled solids at its bottom. Volatile solids reduction through this process was observed to be 62% and 68% in the case of feed slurries having TS concentration as 50 and 100 g/l (referred in the text as 5% and 10% feed slurries), respectively. The methane production rates were observed to be 0.22 and 0.38 l/l d, while methane yield was 0.21 and 0.27 l CH₄/g VS loaded, for 5% and 10% feed slurries, respectively. This indicates that the increase in the VS loading had a positive impact on methane production rate and methane yield. It would be of interest to study the performance of a UASR digester at higher solids loadings and with longer solids retention times. Nonetheless, the presented study showed that sand-laden manure slurries can be successfully digested in a UASR digester producing methane energy equivalent to 4 kW h per m³ of digester volume per day.     

The effect of concentration of phenols on their batch methanogenesis

The biodegradability of phenol and six other phenolic compounds (o-, m-, and p-cresol, 2-, 3-, and 4-ethylphenol) was examined in batch methanogenic cultures. The effect of concentration of these alkyl phenols on the anaerobic biodegradation of phenol was also evaluated. The inoculum used in this study was cultivated in a continuous flow laboratory fermenter with phenol as the primary substrate. Phenol, at initial concentrations as high to 1400 mg/L was completely degraded to methane and carbondioxide after 350 hours incubation. Complete degradation of m- and p-cresol was also observed while the ethylphenols and o-cresol were not significantly degraded.At initial concentrations exceeding 600 mg/L, phenol inhibited the phenol-degrading microorganisms but not the methanogens. At about 600 mg/L, cresols reduced the rate of phenol degradation to 50% of that observed in a control culture containing only 200 mg/L phenol. Ethylphenols were more inhibitory than cresols. Phenol degrading microorganisms were more susceptible to inhibition by cresols and ethylphenols than were the methanogens. The inhibitory effects of the three isomers of cresol and ethylphenol did not vary with the isomer but rather with the substituted functional group.     

Inhibition of methanogenesis and its reversal during biogas formation from cattle manure

The composition of volatile fatty acids in the biogas digester based on cattle manure as substrate and stabilised at 25°C showed that it contained 87–88% branched chain fatty acids, comprising of isobutyric and isovaleric acids, in comparison to 38 % observed in the digester operating at 35°C. Mixed cellulolytic cultures equilibrated at 25°C (C-25) and 35‡C (C-35) showed similar properties, but rates of hydrolysis were three times higher than that observed in a standard biogas digester. The proportion of isobutyric and isovaleric were drastically reduced when C-25 was grown with glucose or filter paper as substrates. The volatile fatty acids recovered from C-25 (at 25°C) inhibited growth of methanogens on acetate, whereas that from C-35 was not inhibitory. The inhibitory effects were due to the branched chain fatty acids and were observed with isobutyric acid at concentrations as low as 50 ppm. Addition of another micro-organismRhodotorula selected for growth on isobutyric completely reversed this inhibition. Results indicate that the aceticlastic methanogens are very sensitive to inhibition by branched chain fatty acids and reduction in methane formation in biogas digester at lower temperature may be due to this effect.     

The effect of propionic to acetic acid ratio on anaerobic-aerobic (low dissolved oxygen) biological phosphorus and nitrogen removal

In this paper, three lab-scale sequencing batch reactors (SBR-A, B, and C) operated with anaerobic/aerobic (low dissolved oxygen, 0.15-0.45 mg L(-1)) configuration were long-term cultured, respectively with single acetic acid and propionic/acetic acid of 1/1 and 2/1 (carbon molar ratio), and the comparisons of anaerobic and aerobic transformations of phosphorus and nitrogen among them were made. With the increase of propionic/acetic acid, lower anaerobic phosphorus release and higher phosphorus release to short-chain fatty acids uptake ratio were observed, and less anaerobic and aerobic transformations of glycogen and poly-3-hydroxybutyrate as well as total polyhydroxyalkanoates occurred, but the transformations of poly-3-hydroxyvalerate and poly-3-hydroxy-2-methyvalerate increased. The phosphorus removal efficiency was respectively 81, 94 and 97% in SBR-A, B and C. Almost all ammonium was removed and no significant nitrite was accumulated at different propionic/acetic acid ratios. However, the nitrate accumulation and total nitrogen removal were observed to be affected by propionic/acetic acid ratio. The total nitrogen removal efficiency was 61, 68 and 82%, and the aerobic end nitrate concentration was 8.05, 6.40 and 3.54 mg L(-1) in three SBRs, respectively. All the above studies indicated that the sole acetic acid caused more nitrate accumulation than propionic and acetic acids mixture, and a pertinent increase of wastewater propionic/acetic acid ratio was of benefit to both nitrogen and phosphorus removal in an anaerobic/aerobic (low dissolved oxygen) biological wastewater treatment process.     

Isolation from a Shea Cake Digester of a Tannin-Tolerant Escherichia coli Strain Decarboxylating p-Hydroxybenzoic and Vanillic Acids

A facultatively anaerobic, mesophilic, Gram-negative, non-motile, non-sporulated bacterium, designated strain C2, was isolated from an anaerobic digester fed with shea cake rich in tannins and aromatic compounds and previously inoculated with anaerobic sludge from the pit of a slaughterhouse, after enrichment on tannic acid. The straight rods occurred singly or in pairs. Strain C2 fermented numerous carbohydrates (fructose, galactose, glucose, lactose, mannose, maltose, melibiose, raffinose, rhamnose, ribose, saccharose, sorbitol, trehalose, and xylose) and peptides (Biotrypcase, Casamino acids, and yeast extract), producing acid and gas, and had a G + C content of 51.6 ± 0.1 mol %. Strain C2 was very closely related to Escherichia coli (= DSM 30083^T) phylogenetically (similarity of 99%), genotypically (DNA homology of 79%), and phenotypically. The isolate tolerated tannic acid (hydrolyzable tannin) and decarboxylated by non-oxidative decarboxylation only p-hydroxybenzoic and vanillic acids to their corresponding phenol and guaicol, under anaerobic and aerobic conditions without further degradation. Adding glucose increased growth and the rate of conversion. High concentrations of p-hydroxybenzoic acid or vanillic acid inhibited growth, and decarboxylation could not occur completely, suggesting phenol toxicity. In contrast, the type strain of E. coli cannot metabolize p-hydroxybenzoic and vanillic acids, anaerobically or aerobically, with or without glucose added. Received: 30 July 2001 / Accepted: 17 August 2001     

Effect of molybdate ions on methanation of simulated and natural waste-waters

Summary Sulphate in concentrations of 500 and 1000 mg SO₄-S/l did not inhibit methanation of synthetic waste-water (acetate + methanol + glucose) by sludge from a digester treating neutral spent sulphite process effluents. The role of sulphate reducers in the conversion of those substrates was minor although sulphate-reducing bacteria were present with a viable count similar to that of methane-producing bacteria in the sludge. Neutral spent sulphite liquor was partially converted to methane (40% of chemical oxygen demand) under these conditions.Molybdate (20 mM) inhibited methanation of both synthetic waste-water and neutral spent sulphite liquor. Acetate accumulated in glucose plus molybdate media. Molybdate had a direct inhibitory effect on enriched acetoclastic methane-producing bacteria. Molybdate was bacteriocidic to sulphate-reducing bacteria and bacteriostatic to methane-producing bacteria.     

Performance evaluation of a mesophilic anaerobic fluidized-bed reactor treating wastewater derived from the production of proteins from extracted sunflower flour

A study of the anaerobic digestion of wastewater derived from the production of protein isolates from extracted sunflower flour was carried out in a laboratory-scale, mesophilic (35 degrees C) fluidized-bed reactor with saponite as bacterial support. Chemical oxygen demand (COD) removal efficiencies in the range of 98.3-80.0% were achieved in the reactor at organic loading rates (OLR) of between 0.6 and 9.3 g COD/I d, hydraulic retention times (HRT) of between 20.0 and 1.1 d and average feed COD concentration of 10.6 g/l. Eighty percent of feed COD could be removed up to OLR of 9.3 g COD/l d. The yield coefficient of methane production was 0.33 l of methane (at STP) per gram of COD removed and was virtually independent of the OLR applied. Because the buffering capacity of the experimental system was maintained at favorable levels with excess total alkalinity present at all loadings, the rate of methanogenesis was not affected by loading. The experimental data indicated that a total alkalinity in the range of 2,000-2,460 mg/l as CaCO3 was sufficient to prevent the pH from dropping to below 7.0 for OLR of up to 9.3 g COD/l d. The volatile fatty acid (VFA) levels and the VFA/alkalinity ratio were lower than the suggested limits for digester failure (0.3-0.4) for OLR and HRT up to 9.3 g COD/l d and 1.1 d, respectively. For a HRT of 0.87 d (OLR of 12.1 g COD/l d) the start of acidification was observed in the reactor.     

Enhancing the anaerobic digestion of corn stalks using composite microbial pretreatment

A composite microbial system (XDC-2) was used to pretreat and hydrolyze corn stalk to enhance anaerobic digestion. The results of pretreatment indicated that sCOD concentrations of hydrolysate were highest (8,233 mg/l) at the fifth day. XDC-2 efficiently degraded the corn stalk by nearly 45%, decreasing the cellulose content by 22.7% and the hemicellulose content by 74.1%. Total levels of volatile products peaked on the fifth day. The six major compounds present were ethanol (0.29 g/l), acetic acid (0.55 g/l), 1,2-ethanediol (0.49 g/l), propionic acid (0.15 g/l), butyric acid (0.22 g/l), and glycerine (2.48 g/l). The results of anaerobic digestion showed that corn stalks treated by XDC-2 produced 68.3% more total biogas and 87.9% more total methane than untreated controls. The technical digestion time for the treated corn stalks was 35.7% shorter than without treatment. The composite microbial system pretreatment could be a cost-effective and environmentally friendly microbial method for efficient biological conversion of corn stalk into bioenergy.