Process kinetics of UASB reactors treating non‐inhibitory substrate

The degradation of a non‐inhibitory substrate (sucrose) in upflow anaerobic sludge bed (UASB) reactors with different superficial flow velocites (u_s) was performed to generate experimental data. Additionally, a kinetic model accounting for the mass fraction of methanogens (f) and granule size distribution in UASB reactors is also proposed. At the volumetric loadings of 2.65–21.16 g COD dm^?3 day^?1, both the COD removal efficiency and granule size of the UASB reactors increase with increasing u_s. The f values determined experimentally increase from 0.13–0.24 to 0.27–0.43 if the volumetric loading is increased from 2.65 to 5.29 g COD dm^?3 day^?1. With a further increase in volumetric loading, the f values decline because of the accumulation of volatile fatty acids (VFAs). The predicted residual concentrations of VFAs and COD are in fairly good agreement with the experimental data. From the calculated effectiveness‐factor values, the influence of mass transfer resistance of the substrate sucrose on the overall substrate removal rate should not be neglected. From parametric sensitivity analyses together with the simulated concentration profiles, methanogenesis is the rate‐limiting step. Copyright © 2003 Society of Chemical Industry     

Temperature dependency of granule characteristics and kinetic behavior in UASB reactors

When an inhibitory substrate, phenol, was treated under mesophilic conditions (25, 30, 35, and 40 °C), the upflow anaerobic sludge bed (UASB) reactors at 30 °C resulted in the greatest amount of biomass and the largest granule size, while the UASB reactors at 25 °C resulted in the smallest granule size and the greatest amount of wash‐out of sludge. The granule size tended to be negatively correlated with the amount of wash‐out of sludge. With an increase in temperature, the kinetic constant k for anaerobic phenol degradation increased and the half saturation constant (K_s) decreased. The mass fraction of methanogens (f) increased with increasing operational temperature in the UASB reactors and the activation energy (E_a) for acetate methanogenesis was larger than that for phenol acidogenesis in the batch reactors, indicating that the operational temperature imposes a more influential effect on methanogens than on acidogens. From the results of the activity of acidogens and methanogens (expressed in specific COD utilization rate), the rate‐limiting step is phenol acidogenesis. Copyright © 2004 Society of Chemical Industry     

Determination of potential methane production capacity of a granular sludge from a pilot‐scale upflow anaerobic sludge blanket reactor using a specific methanogenic activity test

A 450 dm³ pilot‐scale upflow anaerobic sludge blanket (UASB) reactor was used for the treatment of a fermentation‐based pharmaceutical wastewater. The UASB reactor performed well up to an organic loading rate (OLR) of 10.7 kg COD m^?3 d^?1 at which point 94% COD removal efficiency was achieved. This high treatment efficiency did not continue, however and the UASB reactor was then operated at lower OLRs for the remainder of the study. Specific methanogenic activity (SMA) tests were, therefore, carried out to determine the potential loading capacity of the UASB reactor. For this purpose, the SMA tests were carried out at four different initial acetate concentrations, namely 500 mg dm^?3, 1000 mg dm^?3, 1500 mg dm^?3 and 2000 mg dm^?3 so that substrate limitation could not occur. The results showed that the sludge sample taken from the UASB reactor (OLR of 6.1 kg COD m^?3 d^?1) had a potential acetoclastic methane production (PMP) rate of 72 cm³ CH₄ g^?1 VSS d^?1. When the PMP rate was compared with the actual methane production rate (AMP) of 67 cm³ CH₄ g^?1 VSS d^?1 obtained from the UASB reactor, the AMP/PMP ratio was found to be 0.94 which ensured that the UASB reactor was operated using its maximum potential acetoclastic methanogenic capacity. In order to achieve higher OLRs with desired COD removal efficiencies it was recommended that the UASB reactor should be loaded with suitable OLRs pre‐determined by SMA tests. © 2001 Society of Chemical Industry     

Performance assessment of a UASB–anoxic–oxic system for the treatment of tomato‐processing wastes

An upflow anaerobic sludge blanket (UASB)–anoxic–oxic system was used to achieve biochemical oxygen demand, NH₄ and total suspended solids (TSS) criteria of 15, 1 and 15 mg dm^?3 at 1.17 days of system hydraulic retention time during treatment of tomato‐processing waste. The incorporation of an anoxic tank was found to affect the improvement in sludge‐settling characteristics, as reflected by about 25–33% reduction in the sludge volume index, along with final effluent TSS and soluble biochemical oxygen demand concentrations of 13 and 9 mg dm^?3, respectively, which met the discharge criteria. Despite incomplete denitrification, sludge settleability was very good (sludge volume index < 60 cm³ g^?1) owing to reduction in volatile suspended solids/TSS ratio from 0.75 to 0.6 as a result of higher alkalinity in the UASB effluent. Also in this study, phosphorus release was observed in the anoxic tank, predominantly due to abundance of acetic acid in the UASB effluent. A phosphate release of 5.4 mg P dm^?3 was observed in the anoxic tank with subsequent P uptake in the following aerobic stage. Copyright © 2006 Society of Chemical Industry     

Effects of cationic polymer on start‐up and granulation in upflow anaerobic sludge blanket reactors

The upflow anaerobic sludge blanket (UASB) has been used successfully to treat a variety of industrial wastewaters. It offers a high degree of organics removal, low sludge production and low energy consumption, along with energy production in the form of biogas. However, two major drawbacks are its long start‐up period and deficiency of active biogranules for proper functioning of the process. In this study, the influence of a coagulant polymer on start‐up, sludge granulation and the associated reactor performance was evaluated in four laboratory‐scale UASB reactors. A control reactor (R1) was operated without added polymer, while the other three reactors, designated R2, R3 and R4, were operated with polymer concentrations of 5 mg dm^?3, 10 mg dm^?3 and 20 mg dm^?3, respectively. Adding the polymer at a concentration of 20 mg dm^?3 markedly reduced the start‐up time. The time required to reach stable treatment at an organic loading rate (OLR) of 4.8 g COD dm^?3 d^?1 was reduced by more than 36% (R4) as compared with both R1 and R3, and by 46% as compared with R2. R4 was able to handle an OLR of 16 g COD dm^?3 d^?1 after 93 days of operation, while R1, R2 and R3 achieved the same loading rate only after 116, 116 and 109 days respectively. Compared with the control reactor, the start‐up time of R4 was shortened by about 20% at this OLR. Granule characterization indicated that the granules developed in R4 with 20 mg dm^?3 polymer exhibited the best settleability and methanogenic activity at all OLRs. The organic loading capacities of the reactors were also increased by the addition of polymer. The maximum organic loading of the control reactor (R1) without added polymer was 19.2 g COD dm^?3 d^?1, while the three polymer‐assisted reactors attained a marked increase in organic loading of 25.6 g COD dm^?3 d^?1. Adding the cationic polymer could result in shortening of start‐up time and enhancement of granulation, which may in turn lead to improvement in the efficiency of organics removal and loading capacity of the UASB system. Copyright © 2004 Society of Chemical Industry     

Evaluation of biosorbents for Cu removal from wastewater in the presence of EDTA

BACKGROUND: This paper evaluates the use of several biosorbents for Cu removal from aqueous solutions in the absence and presence of ethylenediaminetetraacetic acid (EDTA). The objective was to determine the applicability of the sorption process after conventional physicochemical wastewater treatment, or as primary treatment, replacing the physicochemical process. RESULTS: Fixed‐bed experiments were performed at Cu influent concentrations of 2 and 20 mg dm^?3 and EDTA doses between 0 and 10 mg dm^?3. At low Cu concentration without EDTA, Cu uptake capacity followed the order Posidonia oceanica > chitosan > chitin > Scharlau AC > Darco AC, with a maximum, at C/C₀ = 0.2, of 23.2 mg g^?1. In the presence of EDTA, Cu was detected in the effluent from the beginning of the operation, except for the activated carbons and chitosan at low EDTA doses. At higher EDTA doses, the activated carbons showed the best performance. Uptakes at Cu concentration of 20 mg dm^?3 without EDTA were 51.6 (Posidonia oceanica) and 41.4 mg g^?1 (chitosan) at C/C₀ = 0.2. CONCLUSION: A sequence of one fixed bed with Posidonia oceanica followed by another with Scharlau AC should be an alternative to Cu precipitation, with Cu effluent concentration lower than 0.5 mg dm^?3 for more than 350 pore volumes. Copyright © 2007 Society of Chemical Industry     

Comparative evaluation of full‐scale UASB reactors treating alcohol distillery wastewaters in terms of performance and methanogenic activity

In this study, two full‐scale upflow anaerobic sludge blanket (UASB) reactors, namely TUASB and CUASB, at the wastewater treatment plants of the Tekirdaǧ Alcohol (Raki) and Canakkale Alcohol (Cognac) distilleries were investigated in terms of performance, acetoclastic methanogenic capacity and microbial composition. The results were compared with a previously studied other UASB reactor (IUASB) at the wastewater treatment plant of the Istanbul Alcohol (Raki) Distillery from which the two reactors (TUASB and CUASB) were seeded. The IUASB reactor performed well achieving COD removal efficiencies of no lower than 85% at organic logding rates (OLRs) in the range of 6–11 kg COD m⁻³ day⁻¹ between 1996 and 2001. During the last one year of operation, between 2000 and 2001, performance of the CUASB reactor in terms of COD removal efficiency was 70–80% at OLRs in a range of 1–4.5 kg COD m⁻³ day⁻¹ whereas it was 60–80% at OLRs in a range of 2.5–8.5 kg COD m⁻³ day⁻¹ in the TUASB reactor. At the end of year 2000, specific methanogenic activity (SMA) tests were carried out to determine potential loading capacity and optimum operating conditions of the IUASB, CUASB and TUASB reactors. The potential methane production (PMP) rates of the CUASB, IUASB and TUASB reactors were measured as 230 cm³ CH₄ gVSS⁻¹ day⁻¹, 350 cm³ CH₄ gVSS⁻¹ day⁻¹ and 376 cm³ CH₄ gVSS⁻¹ day⁻¹ respectively. When the PMP rates were compared with actual methane production (AMP) rates obtained from the three UASB reactors, AMP/PMP ratios were evaluated to be 0.18, 0.12 and 0.13 for CUASB, TUASB and IUASB reactors respectively. This showed that the CUASB, TUASB and IUASB reactors were using only 18%, 12% and 13% of their potential acetoclastic methanogenic capacity respectively. These results can be interpreted that the three UASB reactors were underloaded compared with their potential acetoclastic methanogenic capacities. It was, therefore, recommended that the three UASB reactors should be loaded at higher organic loading rates or sludge withdrawn in order to maintain an AMP/PMP ratio of 0.6–0.7, which can ensure desired reactor performance with safer operation. Results of epifluoresence microscopic examinations showed that the percentage of total autofluorescent methanogens was approximately 30% of the total population in sludges from the TUASB and IUASB reactors whereas it was 20% in sludge from the CUASB reactor. The two UASB reactors treating raki distillery wastewaters contained sludges having a higher percentage of autofluorescent methanogenic population and higher acetoclastic methanogenic activity. Copyright © 2004 Society of Chemical Industry     

Anaerobic and aerobic treatment of a simulated textile effluent

A simulated textile effluent (STE) was generated for use in laboratory biotreatment studies; this effluent contained one reactive azo dye, PROCION Red H‐E7B (1.5 g dm⁻³); sizing agent, Tissalys 150 (1.9 g dm⁻³); sodium chloride (1.5 g dm⁻³) and acetic acid (0.53 g dm⁻³) together with nutrients and trace elements, giving a mean COD of 3480 mg dm⁻³. An inclined tubular anaerobic digester (ITD) was operated for 9 months on the STE and a UASB reactor for 3 months. For a 57 day period anaerobic effluent from two reactors, a UASB and an ITD, was mixed and treated in an aerobic stage. In days 77–247 68% of the true colour of PROCION Red H‐E7B was removed by anaerobic treatment with no colour removal aerobically and up to 37% COD was removed anaerobically, with a corresponding BOD removal of 71%. For combined anaerobic and aerobic treatment a mean COD removal of 57% and BOD removal of 86% was achieved. Operation of the ITD at a 2.8 day HRT (volumetric loading rate (B _v) 1.24 g COD dm⁻³day⁻¹) and the UASB at a 2 day HRT (B _v 1.74 g COD dm⁻³day⁻¹) gave comparable COD removals but the UASB gave better true colour removal. Effluent from the combined process operating on this simulated waste still contained an average 1500 mg COD dm⁻³, and further treatment would be required to meet consent standards. © 1999 Society of Chemical Industry     

Protein hydrolysis under anaerobic,saline conditions in presence of acetic acid

The hydrolysis of soluble proteins in an anaerobic, saline (24 g dm^?3 NaCl) and mesophilic (37 °C) environment was studied. The inhibitory effect of a volatile fatty acid, acetic acid (HAc), on the hydrolysis rate and hydrolytic biomass activity for a model saline wastewater with a high protein load (total organic carbon, 1153 mg dm^?3 and 1572 mg dm^?3 proteins) was studied. Initial inhibitor concentrations were tested in the range of 0–2000 mg dm^?3 HAc. The microbiological characterization was performed using a total microorganism count by epifluorescence, and hydrolytic bacterial activity was determined by plate count. The protein hydrolysis was modeled according to first order kinetics. The effect of biomass on hydrolysis was analyzed by varying its concentration in the range of 42–210 mg dm^?3 volatile suspended solids. The following apparent hydrolysis kinetic constants (K_h) for proteins at 37 °C were obtained: 1.3, 0.8, 0.6, 0.2 and 0.1 d^?1 for initial concentrations of 250, 500, 750, 880, and 1000 mg dm^?3 HAc, respectively. At concentrations of HAc greater than 1000 mg dm^?3, total inhibition of hydrolysis was observed. The intrinsic hydrolysis constant ( ) at 37 °C, without inhibition, was 2.3 d^?1. The hydrolysis kinetic constant was not affected by the biomass concentration. The hydrolysis kinetics constant was filted to three models: Luong, Levenspiel and non‐competitive inhibition. The model that best represented the experimental data was Luong, obtaining an inhibition constant (K_I) of 1087 mg dm^?3 of HAc and the exponent γ = 0.54. The hydrolysis was inhibited by the presence of HAc, which corresponds to an intermediate compound of the anaerobic process. Copyright © 2004 Society of Chemical Industry     

Anaerobic digestion of alkaline black liquor using an up-flow anaerobic sludge blanket reactor

The anaerobic digestion of alkaline black liquor from a cereal straw pulping mill was studied in batch (serum bottles) and continuous systems (up-flow anaerobic sludge blanket reactor—UASB). The batch digestion studies confirmed that lignin and related compounds (LRC) in the alkaline black liquor were the main inhibitory substances and could not be decomposed by anaerobic bacteria. At organic loading rates of 5–10 kg COD m^?3 day^?1, the UASB reactor achieved 50–60% COD removal efficiencies. Gas production was 2–3 dm³ per dm³ of alkaline black liquor. Two different sludge types were examined in the reactor: granular and cluster-like sludges. Sludge in a cluster, which involved many small granules and flocs, tended to form larger aggregates and possessed good settling ability.     

Kinetics of syntrophic acetogenesis in a saline medium

BACKGROUND: The anaerobic degradation kinetics of volatile fatty acids (VFA) in a saline (24 g NaCl dm^?3) and mesophilic (37 °C) medium was studied under batch test conditions. The acetate production kinetics without inhibition by propionic, butyric and valeric acids was determined. The inhibition of acetate production during syntrophic acetogenesis by VFA and pH was studied. The acetogenesis without inhibition was modelled using a Monod equation. The pH inhibition was represented by a Michaelis pH function, while the inhibition by acetic acid (HAc) was represented by a non‐competitive model. RESULTS: The specific maximum degradation rate and saturation constant (k_{max, VFA}, K_{S, max}) values were (5.89, 15.95), (7.97, 25.99) and (7.75 g VFA g^?1 volatile suspended solids day^?1, 11.52 mg VFA dm^?3) for propionic, butyric and valeric acids respectively, with maximum velocity at pH 7. The inhibition constants (K_{I, HAc}) were 1295, 671 and 572 mg HAc dm^?3 for propionic, butyric and valeric acids respectively. CONCLUSION: VFA and pH can be inhibitory for acetogenesis under these conditions. Copyright © 2008 Society of Chemical Industry     

Effects of Fe(III) on floc characteristics of activated sludge

The effects of Fe(III) on floc characteristics of activated sludge were investigated in nine parallel sequencing batch reactors (SBRs). The results showed that Fe(III) improved the quality of organic matters in the effluent of reactors. Concentrations of Fe(III) up to 23.8 mg dm^?3 decreased suspended solids and turbidity in effluent but overdosage resulted in deterioration of these parameters. Activated sludge floc size measurements indicated that Fe(III) led to a shift in the size distribution from large to small flocs. Concentrations of Fe(III) less than 23.8mg dm^?3 did not significantly change the proportion of larger flocs, but overdosage of Fe(III) markedly decreased the fraction of larger flocs and produced a large number of smaller flocs, which may be responsible for the deterioration of effluent suspended solids and turbidity. Scanning electronic microscopic (SEM) observation suggested high Fe(III) concentrations lead to significant changes in floc morphology and reduction of filamentous microorganisms available for the formation of large aggregates. Copyright © 2005 Society of Chemical Industry     

Methane production from acids in piggery-waste digesters

Results from piggery-waste digestion fit those from a continuous culture of acetate utilising methanogenic bacteria showing that the acid to methane step of this digestion can be regarded as an independent continuous culture behaving as predicted by a simple continuous culture model with a wash-out dilution rate of about 0.4 day^?1 and a K_s value of about 800–900 mg acetic acid dm^?3. However, this was only possible because the waste contained a high concentration of free acid and the application of the results to other digestions is discussed.     

The use of 3,3′,4′,5‐tetrachlorosalicylanilide as a chemical uncoupler to reduce activated sludge yield

To determine whether chemical additions can be used to reduce sludge production in biological wastewater treatment, 3,3′,4′,5‐tetrachlorosalicylanilide (TCS) was added to activated sludge cultures as a metabolic uncoupler. Batch tests confirmed that TCS is an effective chemical uncoupler in reducing the sludge yield at concentrations greater than 1.0 mg dm^?3; a TCS concentration of 1.0 mg dm^?3 reduced sludge yield by approximately 50%. Substrate removal capability and effluent nitrogen concentration were not affected adversely by the presence of TCS when dosed every other day in a range of 2.0–3.6 mg dm^?3 during the 40‐day operation of activated sludge batch cultures. Such sludge growth reduction was associated with the enhancement of microbial activities in terms of the specific oxygen uptake rate and dehydrogenase activity. Sludge settleability of the treated and control samples was qualitatively comparable and not significantly different. Filamentous bacteria continued to grow in sludge flocs only in the control reactor at the end of the 40‐day trial. These results suggest that TCS treatment of activated sludge systems may reduce excess sludge yield. Copyright © 2003 Society of Chemical Industry     

Recycling of FGD gypsum to calcium carbonate and elemental sulfur using mixed sulfate-reducing bacteria with sewage digest as a carbon source

A combined chemical and biological process for the recycling of flue gas desulfurization (FGD) gypsum into calcium carbonate and elemental sulfur is demonstrated. In this process, a mixed culture of sulfate-reducing bacteria (SRB) utilizes sewage digest as its carbon source to reduce FGD gypsum to hydrogen sulfide. The sulfide is then oxidized to elemental sulfur via reaction with ferric sulfate, and accumulating calcium ions are precipitated to calcium carbonate using carbon dioxide. Employing anaerobically digested-municipal sewage sludge (AD-MSS) medium as a carbon source, SRB in serum bottles demonstrated an FGD gypsum reduction rate of 8 mg dm⁻³ h⁻¹ (10⁹ cells)⁻¹. A chemostat with continuous addition of both AD-MSS medium and gypsum exhibited sulfate reduction rates as high as 1·3kg FGD gypsumm⁻³ day⁻¹. The increased biocatalyst density afforded by cell immobilization in a columnar reactor allowed a productivity of 152 mg SO₄ dm⁻³ h⁻¹ or 6·6kg FGD gypsum m⁻³ day⁻¹. Both reactors demonstrated 100% conversion of sulfate, with 75–100% recovery of elemental sulfur and as high as 70% COD utilization. Calcium carbonate was recovered from the reactor effluent upon precipitation using carbon dioxide. The formation of two marketable products—elemental sulfur and calcium carbonate—from FGD gypsum sludge, combined with the use of a low-cost carbon source and further improvements in reactor design, promises to offer an attractive alternative to the landfilling of FGD gypsum.     

Development of the Eco-Cascade- cell reactor

The development of multicompartment rotating cylinder electrode reactors for the removal of metal from aqueous solutions is described. Such reactors approximate to a cascade of continuously stirred tank reactors and the results illustrate that, for electrodeposition of copper powder from acid sulphate solutions, high overall conversions (about 98%) may be realised, with low exit metal concentrations (about 1 mg dm^–3) and reasonable current efficiencies (65–87%).Nomenclature A electroactive surface area (cm²) - C _in inlet concentration of metal (mg dm^–3) - C _out outlet concentration of metal (mg dm^–3) - C _reactor reactor concentration of metal (mg dm^–3) - f _R fractional conversion - (f _R)n overall fractional conversion - F Faraday=96 500 (C mol^–1) - I _L limiting current (A) - k _l mass transfer coefficient (cms^–1) - m weight of metal (g) - M molecular weight of metal - n number of reactor elements in the cascade - N volumetric flow rate (cm³ s^–1) - z electron change - dm/dt rate of removal of metal (gs^–1) This paper was presented, in part, at the Electrochemical Reaction Engineering Symposium, Southampton University, April (1979).     

A kinetic evaluation of the anaerobic digestion of two‐phase olive mill effluent in batch reactors

A comparative kinetic study was carried out on the anaerobic digestion of two‐phase olive mill effluent (TPOME) using three 1‐dm³ volume stirred tank reactors, one with freely suspended biomass (control), and the other two with biomass supported on polyvinyl chloride (PVC) and bentonite (aluminium silicate), respectively. The reactors were batch fed at mesophilic temperature (35 °C) using volumes of TPOME of between 50 and 600 cm³, corresponding to chemical oxygen demand (COD) loadings in the range of 1.02–14.22 g, respectively. The process followed first‐order kinetics and the specific rate constants, K₀, were calculated. The K₀ values decreased considerably from 2.59 to 0.14 d^?1, from 1.93 to 0.23 d^?1 and from 1.52 to 0.17 d^?1 for the reactors with suspended biomass (control) and biomass immobilized on PVC and bentonite, respectively, when the COD loadings increased from 1.02 to 14.22 g; this showed an inhibition phenomenon in the three reactors studied. The values of the critical inhibitory substrate concentration (S*), theoretical kinetic constant without inhibition (K_A) and the inhibition coefficient or inhibitory parameter for each reactor (n) were determined using the Levenspiel model. Copyright © 2004 Society of Chemical Industry     

Effect of loading rate on TOC consumption efficiency in a sulfate reducing process: sulfide effect in batch culture

BACKGROUND: The sulfate reducing process (SRP) was analyzed in order to identify factors that diminish the effectiveness of the SRP during wastewater treatment. The effect of different sulfate loading rates (SLR, 290 to 981 mg SO₄‐S L^?1d^?1) and lactate at a stoichiometric C/S ratio of 0.75 on SRP was studied in an upflow anaerobic sludge blanket (UASB) reactor. The effect of sulfide concentration (0 to 200 mg sulfide‐S L^?1) on SRP in batch culture was evaluated. RESULTS: When the SLR was increased, the total organic carbon (TOC) and sulfate consumption efficiencies decreased from 93% ± 3 to 66% ± 2 and 60% ± 5 to 45% ± 4, respectively. Acetate and propionate were accumulated. Microbial analysis showed the presence of microorganisms related with the SRP, fermentation and methanogenesis. In batch culture, when lactate and sulfate were present, SRP and fermentation were observed. When sulfide was added only SRP was observed. At concentrations higher than 150 mg sulfide‐S L^?1 the efficiencies, yields and specific consumption rates (q) decreased. CONCLUSION: Based on the sulfide‐S/volatile suspended solid ratio, it was found that the decrease in efficiency and accumulation of acetate and propionate in the UASB reactor was not related to sulfide inhibition but to the q of acetate and propionate, which were up to 11 times lower than lactate. Copyright © 2008 Society of Chemical Industry     

Two‐phase anaerobic treatment system for fat‐containing wastewater

This study was conducted to investigate the feasibility of a two‐phase anaerobic treatment system for fat‐containing wastewater. The two‐phase system was composed of a continuously stirred tank reactor for acidogenesis and an upflow anaerobic sludge blanket (UASB) reactor for methanogenesis. Its performance was compared with a conventional single‐phase system of a UASB reactor treating synthetic wastewater containing major long‐chain fatty acids (LCFAs). LCFAs did not cause any significant problem up to the LCFA mixture loading rate of 1.21 kg LCFA‐COD m^?3 day^?1 (3500 mg LCFA‐COD dm^?3) in both systems. However, the efficiency of the single‐phase system deteriorated at loading rates above 1.38 kg LCFA‐COD m^?3 day^?1 (4000 mg LCFA‐COD dm^?3), while that of the two‐phase system was still satisfactory. More than 19.2% of LCFAs were degraded and 11.5% of unsaturated LCFAs were saturated in the acidogenesis of the two‐phase system, which led to the enhanced specific methane production rate and the reduced scum layer of the subsequent UASB reactor. Copyright © 2003 Society of Chemical Industry     

Characteristics of the pH-influenced adaptation of methanogenic sludge to ammonium toxicity

Increasing ammonium-nitrogen concentrations caused failure of methanogenesis at 1900-2000 mg dm^?3. After an adaptation period characterised by an almost nil methane production, methanogenesis appeared to be possible at even higher concentrations. A kinetic analysis of methane production during the adaptation process indicated that the adaptation was the result of a metabolic change in the methanogenic bacteria already present, rather than of growth of new bacteria. A high pH value causing toxic concentrations of un-ionised ammonia during the adaptation period appeared to result in a decreased maximum specific methanogenic activity of the adapted sludge. A low pH value during the adaptation period resulted in a retarded degradation of propionic acid, probably due to inhibition of the hydrogen consuming methanogenic bacteria by undissociated volatile fatty acids, but this did not result in a decreased maximum specific methanogenic activity in the adapted sludge. The maximum specific methanogenic activity at an ammonium-nitrogen concentration of 2315 mg dm^?3 after adaptation as a percentage of that at 1000 mg dm^?3 before adaptation was 31, 65 and 61% for a pH during the adaptation period of 7.6, 7.25 and 7.0 respectively. Except for the sludge which was maintained at pH 7.6 during the adaptation period, after adaptation the maximum specific methanogenic activity at an ammonium-nitrogen concentration of 2315 mg dm^?3 was higher than the maximum specific methanogenic activity at an ammonium nitrogen concentration of 1900 mg dm^?3 before adaptation.