Effects of hydraulic retention time and sulfide toxicity on ethanol and acetate oxidation in sulfate-reducing metal-precipitating fluidized-bed reactor

The effects of hydraulic retention time (HRT) and sulfide toxicity on ethanol and acetate utilization were studied in a sulfate-reducing fluidized-bed reactor (FBR) treating acidic metal-containing wastewater. The effects of HRT were determined with continuous flow FBR experiments. The percentage of ethanol oxidation was 99.9% even at a HRT of 6.5 h (loading of 2.6 g ethanol L(-1) d(-1)), while acetate accumulated in the FBR with HRTs below 12 h (loading of 1.4 g ethanol L(-1) d(-1)). Partial acetate utilization was accompanied by decreased concentrations of dissolved sulfide (DS) and alkalinity in the effluent, and eventually resulted in process failure when HRT was decreased to 6.1 h (loading of 2.7 g ethanol L(-1) d(-1)). Zinc and iron precipitation rates increased to over 600 mg L(-1) d(-1) and 300 mg L(-1) d(-1), respectively, with decreasing HRT. At HRT of 6.5 h, percent metal precipitation was over 99.9%, and effluent metal concentrations remained below 0.08 mg L(-1). Under these conditions, the alkalinity produced by substrate utilization increased the wastewater pH from 3 to 7.9-8.0. The percentage of electron flow from ethanol to sulfate reduction averaged 76 +/- 10% and was not affected by the HRT. The lowest HRT did not result in significant biomass washout from the FBR. The effect of sulfide toxicity on the sulfate-reducing culture was studied with batch kinetic experiments in the FBR. Noncompetitive inhibition model described well the sulfide inhibition of the sulfate-reducing culture. (DS) inhibition constants (K(i)) for ethanol and acetate oxidation were 248 mg S L(-1) and 356 mg S L(-1), respectively, and the corresponding K(i) values for H(2)S were 84 mg S L(-1) and 124 mg S L(-1). In conclusion, ethanol oxidation was more inhibited by sulfide toxicity than the acetate oxidation.     

The oxidation,fate and effects of iron during on-site bioremediation of groundwater contaminated by a mixture of polychlorophenols

Kinetics of simultaneous iron and polychlorophenol (CP) oxidation by groundwater enriched cultures were studied in laboratory and during actual remediation in orderto reveal the fate and effects of iron on aerobic on-site bioremediation of boreal groundwater. 2,4,6-tri- (TCP), 2,3,4,6-tetra- (TeCP) and pentachlorophenol (PCP)were degraded in fluidized-bed bioreactor (FBR) by over 99%, over 99%, and over96%, respectively. The oxygen consumption rate for CP-biodegradation was 1.31mol DO L^-1 min^-1 and 0.29 mol DO L^-1 min^-1 for iron oxidation, i.e. approximately 12% of the oxygen was consumed by iron oxidation during normal FBR operation. Mineralization of CPs was confirmed by DOC removal and chloride release of 158% and 78%, respectively. Excess DOC removal was due to partial degradation of the natural organic matter (NOM) (1.1 mg L^-1 or 24% DOC removal) in the groundwater. Removal of NOM consumed 0.91 mol DO L^-1min^-1. Iron oxidation in the FBR was over 94% of which chemical Fe(II) oxidation accounted for up to 10%. Fe(III) partially accumulated (58 to 69%) in the system. The TCP- and CP-biodegradation consumed DO at two times higher rates than the Fe(II)-oxidation in both, laboratory and full-scale, respectively. The batch assays atvarious TCP and Fe(II) ratios and DO concentrations showed simultaneous oxygenconsumption by TCP and Fe-oxidizers and that increased Fe concentrations do notoutcompete the bioremediation of CP's for available oxygen. Abbreviations: DAPI: 4',6'-Diamidino-phenylindole; DO:Dissolved oxygen; DOC: Dissolved organic carbon; FBR: Fluidized-bed bioreactor;HRT: Hydraulic retention time; NOM: Natural organic matter; PCP: Pentachlorophenol; SEM: Scanning-electron microscopy, TeCP: 2,3,4,6-Tetrachlorophenol; TCP: 2,4,6-Trichlorophenol     

The isolation and use of iron-oxidizing,moderately thermophilic acidophiles from the Collie coal mine for the generation of ferric iron leaching solution

Moderately thermophilic, iron-oxidizing acidophiles were enriched from coal collected from an open-cut mine in Collie, Western Australia. Iron-oxidizers were enriched in fluidized-bed reactors (FBR) at 60 degrees C and 70 degrees C; and iron-oxidation rates were determined. Ferrous iron oxidation by the microbiota in the original coal material was inhibited above 63;C. In addition to four iron-oxidizers, closely related to Sulfobacillus spp that had been earlier isolated from the 60 degrees C FBR, one heterotroph closely related to Alicyclobacillus spp was isolated. The Alicyclobacillus sp. isolated from the Collie coal mine tolerated a lower pH than known Alicyclobacillus spp and therefore may represent a new species. The optimum temperature for growth of the iron-oxidizing strains was approximately 50 degrees C and their maximum temperatures were approximately 60 degrees C. The FBR was adjusted to operate at 50 degrees C and was inoculated with all of the isolated iron-oxidizing strains. At 60 degrees C, an iron-oxidation rate of 0.5 g Fe(2+) l(-1) x h(-1) was obtained. At 50 degrees C, the iron-oxidation rate was only 0.3 g Fe(2+) l(-1) x h(-1). These rates compare favourably with the iron-oxidation rate of Acidianus brierleyi in shake-flasks, but are considerably lower than mesophilic iron-oxidation rates.     

Process for biological oxidation and control of dissolved iron in bioleach liquors

Iron has a central role in bioleaching and biooxidation processes. Fe²⁺ produced in the dissolution of sulfidic minerals is re-oxidized to Fe³⁺ mostly by biological action in acid bioleaching processes. To control the concentration of iron in solution, it is important to precipitate the excess as part of the process circuit. In this study, a bioprocess was developed based on a fluidized-bed reactor (FBR) for Fe²⁺ oxidation coupled with a gravity settler for precipitative removal of ferric iron. Biological iron oxidation and partial removal of iron by precipitation from a barren heap leaching solution was optimized in relation to the performance and retention time (τ_FBR) of the FBR. The biofilm in the FBR was dominated by Leptospirillum ferriphilum and “Ferromicrobium acidiphilum.” The FBR was operated at pH 2.0 ± 0.2 and at 37 °C. The feed was a barren leach solution following metal recovery, with all iron in the ferrous form. 98–99% of the Fe²⁺ in the barren heap leaching solution was oxidized in the FBR at loading rates below 10 g Fe²⁺/L h (τ_FBR of 1 h). The optimal performance with the oxidation rate of 8.2 g Fe²⁺/L h was achieved at τ_FBR of 1 h. Below the τ_FBR of 1 h the oxygen mass transfer from air to liquid limited the iron oxidation rate. The precipitation of ferric iron ranged from 5% to 40%. The concurrent Fe²⁺ oxidation and partial precipitative iron removal was maximized at τ_FBR of 1.5 h, with Fe²⁺ oxidation rate of 5.1 g Fe²⁺/L h and Fe³⁺ precipitation rate of 25 mg Fe³⁺/L h, which corresponded to 37% iron removal. The precipitates had good settling properties as indicated by the sludge volume indices of 3–15 mL/g but this step needs additional characterization of the properties of the solids and optimization to maximize the precipitation and to manage sludge disposal.     

氧化亚铁硫杆菌分离复壮及固定化的研究

用稀释涂布平板法从已退化的氧化亚铁硫杆菌（Thiobacillus ferrooxidans）菌液中分离出氧化活性较高、生命力强的氧化亚铁硫杆菌T1。以H2软性填料作为氧化亚铁硫杆菌的固定化载体,构建了固定床生物反应器。考察了固定床生物反应器氧化Fe2+的情况：Fe2+最大氧化速率达7.67g/(L·h)。并对固定床生物反应器运行过程中在载体表面形成的沉淀物进行了研究,通过X衍射证明此沉淀物为黄钾铁矾［Kfe3(SO4)2(OH)6］。     

Modeling of ferrous iron oxidation by a Leptospirillum ferrooxidans-dominated chemostat culture

The objective of this study was to evaluate a direct classical bioengineering approach to model data generated from continuous bio-oxidation of Fe(2+) by a Leptospirillum ferrooxidans-dominated culture fed with either 9 g or 18 g Fe(2+) L(-1) under chemostat conditions (dilution rates were between 0.051 and 0.094 h(-1)). The basic Monod and Pirt equations have successfully been integrated in an overall mass balance procedure, which has not been previously presented in this detail for Fe(2+) oxidation. To ensure chemostat conditions, it was found that the range of the dilution rates had to be limited. A too long retention time might cause starvation or non-negligible death rate whereas, a too short retention time may cause a significant alteration in solution chemistry and culture composition. Modeling of the experimental data suggested that the kinetic- and yield parameters changed with the overall solution composition. However, for respective feed solutions only minor changes of ionic strength and chemical speciation can be expected within the studied range of dilution rates, which was confirmed by thermodynamic calculations and conductivity measurements. The presented model also suggests that the apparent Fe(3+) inhibition on specific Fe(2+) utilization rate was a direct consequence of the declining biomass yield on Fe(2+) due to growth uncoupled Fe(2+) oxidation when the dilution rate was decreased. The model suggested that the maintenance activities contributed up to 90% of the maximum specific Fe(2+) utilization rate, which appears close to the critical dilution rate. Biotechnol. Bioeng. 2008;99: 378-389. (c) 2007 Wiley Periodicals, Inc.     

Bacterial oxidation of ferrous iron at low temperatures

This study comprises the first report of ferrous iron oxidation by psychrotolerant, acidophilic iron-oxidizing bacteria capable of growing at 5 degrees C. Samples of mine drainage-impacted surface soils and sediments from the Norilsk mining region (Taimyr, Siberia) and Kristineberg (Skellefte district, Sweden) were inoculated into acidic ferrous sulfate media and incubated at 5 degrees C. Iron oxidation was preceded by an approximately 3-month lag period that was reduced in subsequent cultures. Three enrichment cultures were chosen for further work and one culture designated as isolate SS3 was purified by colony isolation from a Norilsk enrichment culture for determining the kinetics of iron oxidation. The 16S rRNA based phylogeny of SS3 and two other psychrotolerant cultures, SS5 from Norilsk and SK5 from Northern Sweden, was determined. Comparative analysis of amplified 16S rRNA gene sequences showed that the psychrotolerant cultures aligned within Acidithiobacillus ferrooxidans. The rate constant of iron oxidation by growing cultures of SS3 was in the range of 0.0162-0.0104 h(-1) depending on the initial pH. The oxidation kinetics followed an exponential pattern, consistent with a first order rate expression. Parallel iron oxidation by a mesophilic reference culture of Acidithiobacillus ferrooxidans was extremely slow and linear. Precipitates harvested from the 5 degrees C culture were identified by X-ray diffraction as mixtures of schwertmannite (ideal formula Fe(8)O(8)(OH)(6)SO(4)) and jarosite (KFe(3)(SO(4))(2)(OH)(6)). Jarosite was much more dominant in precipitates produced at 30 degrees C.     

固定化氧化亚铁硫杆菌培养条件对黄铁矾沉淀的影响

以聚乙烯醇-海藻酸钠复合材料为载体,Ca(NO3)2为交联剂对氧化亚铁硫杆菌进行包埋固定化。该固定化细胞的连续培养技术可以用于处理H2S、SO2,为了减少减少固定化细胞培养过程中带来许多不利效应的黄铁矾沉淀 (NH4Fe3(SO4)2(OH)6）,采取了改变初始pH值和目前普遍采用的9K培养基中的(NH4)2SO4浓度,K2HPO4浓度三种方法。结果显示：在三种方法中,降低(NH4)2SO4浓度是比较可行的一种方法,当(NH4)2SO4从3.0 g/L降低到0.5g/L,Fe2+氧化速率几乎没有受到影响,沉淀形成速率却减少了45%。在固定化细胞连续运行时,降低9K培养基中(NH4)2SO4的含量,当稀释率为0.4 h-1,运行时间为96 h,Fe2+氧化速率高达3.75 g/L.H,结果显示反应柱内沉淀明显减少,同时Fe2+氧化速率并没有明显变化。     

Performance and ethanol oxidation kinetics of a sulfate-reducing fluidized-bed reactor treating acidic metal-containing wastewater

The treatment of simulated acidic wastewater (pH 2.5–5)containing sulfate (1.0–2.2 g l^-1), zinc (15–340 mg l ^-1) and iron (57 mg l ^-1) was studied in a sulfate-reducing fluidized-bed reactor (FBR) at 35 °C.The original lactate feed for enrichment and maintenance of the FBRculture was replaced stepwise with ethanol over 50 days. The robustnessof the process was studied by increasing stepwise the Zn, sulfate andethanol feed concentrations and decreasing the feed pH. The following precipitation rates were obtained: 360 mg l ^-1 d ^-1 for Zn and 86 mg l ^-1 d ^-1 for Fe, with over 99.8% Zn and Fe removal, with a hydraulic retention time of 16 h. Under these conditions, 77–95% of the electrons were accepted by sulfate reduction. The alkalinity produced from ethanol oxidation increased the wastewater pH from 2.5 to 7.5–8.5. Michaelis–Menten constants (K_m) determined in batch FBR experiments, were 4.3–7.1 mg l ^-1 and 2.7–3.5 mg l ^-1 for ethanol and acetateoxidation, respectively. The maximum oxidation velocities (V_max)were 0.19–0.22 mg gVS ^-1 min ^-1 and0.033–0.035 mg gVS ^-1 min ^-1, for ethanol and acetate, respectively. In summary, the FBR process produced a good quality effluent as indicated by its low organic content and Zn and Fe concentrations below0.1 mg l ^-1.     

Flocculants effect in biomass retention in a UASB reactor treating dairy manure

The performance and biomass retention of an upflow anaerobic sludge bed (UASB) reactor treating liquid fraction of dairy manure has been investigated at several organic loading rates. Two identical UASB reactors were employed. The biomass of one UASB reactor (FBR) had previously been treated with a cationic polyacrylamide, the other reactor was operated as a control reactor (CR). At 3 and 2 days of HRT both reactors functioned similarly, but at 1.5 days HRT some differences were observed between both effluents. Mean COD(T) removal percentages were 83.4% and 76.5%; COD(VFA) values in effluents were 977 and 2682 mg l(-1) for the FBR and the CR respectively. The VSS initial value in both reactors was 25.66 g VSS, whereas after the experiment the quantities were 31.83 g VSS in the FBR and 23.18 g VSS in the CR reactors. Polymer addition resulted in a higher degree of biomass retention and better performance in the FBR reactor.     

Preparation of metal ion buffers for biological experimentation: a methods approach with emphasis on iron and zinc

Transition metal ions are a challenge to study in physiology because of problems associated with solubility, oxidation, binding, and attaining appropriate free activities in solution. This review discusses these problems and potential ways of accommodating them. Special attention is given to iron and zinc ions, but many of the concepts can be applied for studying other transition metals. Selection of reagents appropriate for metal work (including water, salts, noncomplexing pH buffers) is briefly discussed. Calculation of the solubility product (K(sp)) for common iron and zinc precipitates is covered, as well as techniques used to solubilize Fe(3+) with organic chelates. Factors that affect Fe(2+) oxidation are mentioned, and the use of ascorbate as a reducing agent is considered. Measurement of the rate of Fe(2+) oxidation (or Fe(3+) reduction) with the Fe(2+) chromophores ferrozine and BPS is also discussed. Generation of a free metal ion activity through use of metal buffers (chelators) is discussed. Theoretical problems associated with this technique are explored, and selected shareware metal ion buffer calculators are described. Finally, techniques for measuring and minimizing nonspecific binding of iron and zinc ions to biological membranes are considered.     

Kinetics of iron oxidation by Leptospirillum ferriphilum dominated culture at pH below one

The kinetics of ferrous iron oxidation by Leptospirillum ferriphilum (L. ferriphilum) dominated culture was studied in the concentration range of 0.1-20 g Fe(2+)/L and the effect of ferric iron (0-60 g Fe(3+)/L) on Fe(2+) oxidation was investigated at pH below one. Denaturing gradient gel electrophoresis of PCR amplified 16S rRNA genes followed by partial sequencing confirmed that the bacterial community was dominated by L. ferriphilum. In batch assays, Fe(2+) oxidation started without lag phase and the oxidation was completed within 1 to 60 h depending on the initial Fe(2+) concentration. The specific Fe(2+) oxidation rates increased up to around 4 g/L and started to decrease at above 4 g/L. This implies substrate inhibition of Fe(2+) oxidation at higher concentrations. Haldane equation fitted the experimental data reasonably well (R(2) = 0.90). The maximum specific oxidation rate (q(m)) was 2.4 mg/mg VS . h, and the values of the half saturation (K(s)) and self inhibition constants (K(i)) were 413 and 8,650 mg/L, respectively. Fe(2+) oxidation was competitively inhibited by Fe(3+) and the competitive inhibition constant (K(ii)) was 830 mg/L. The time required to reach threshold Fe(2+) concentration was around 1 day and 2.3 days with initial Fe(3+) concentration of 5 and 60 g/L, respectively. The threshold Fe(2+) concentration, below which no further Fe(2+) oxidation occurred, linearly increased with increasing initial Fe(2+) and Fe(3+) concentrations. Fe(2+) oxidation proceeds by L. ferriphilum dominated culture at pH below 1 even in the presence of 60 g Fe(3+)/L. This indicates potential of using and biologically regenerating concentrated Fe(3+) sulfate solutions required, for example, in indirect tank leaching of ore concentrates.     

Chalcopyrite concentrate leaching with biologically produced ferric sulphate

Biological ferric iron production was combined with ferric sulphate leaching of chalcopyrite concentrate and the effects of pH, Fe3+, temperature and solids concentration on the leaching were studied. The copper leaching rates were similar at pH of 1.0-1.8 and in the presence of 7-90 g L-1 Fe3+ despite massive iron precipitation with 90 g L-1 Fe3+. Increase of the leaching temperature from 50 degrees C to 86 degrees C and solids concentration from 1% to 10% increased the copper leaching rate. Increase in solids concentration from 1% to 10% decreased the copper yields from 80% to 40%. Stepwise addition of ferric iron did not improve the copper yields. CuFeS2, Ag and Cu1.96S potentials indicated the formation of a passivating layer, which consisted of jarosite and sulphur precipitates and which was responsible for the decreased leaching rates.     

High-rate acidophilic ferrous iron oxidation in a biofilm airlift reactor and the role of the carrier material

In this study, the feasibility and engineering aspects of acidophilic ferrous iron oxidation in a continuous biofilm airlift reactor inoculated with a mixed culture of Acidithiobacillus ferrooxidans and Leptospirillum ferrooxidans bacteria were investigated. Specific attention was paid to biofilm formation, competition between both types of bacteria, ferrous iron oxidation rate, and gas liquid mass transfer limitations. The reactor was operated at a constant temperature of 30 degrees C and at pH values of 0-1.8. Startup of the reactor was performed with basalt carrier material. During the experiments the basalt was slowly removed and the ferric iron precipitates formed served as a biofilm carrier. These precipitates have highly suitable characteristics as a carrier material for the immobilization of ferrous iron-oxidizing bacteria and dense conglomerates were observed. Lowering the pH (0.6-1) resulted in dissolution of the ferric precipitates and induced granular sludge formation. The maximum ferrous iron oxidation rate achieved in this study was about 145 molFe(2+)/m(3).h at a hydraulic residence time of 0.25 h. Optimal treatment performance was obtained at a loading rate of 100 mol/m(3).h at a conversion efficiency as high as 98%. Fluorescent in situ hybridization (FISH) studies showed that when the reactor was operated at high ferrous iron conversion (>85%) for 1 month, the desirable L. ferrooxidans species could out-compete A. ferrooxidans due to the low Fe(2+) and high Fe(3+) concentrations.     

Fast kinetics of fe oxidation in packed-bed reactors

Thiobacillus ferrooxidans was used in fixed-film bioreactors to oxidize ferrous sulfate to ferric sulfate. Glass beads, ion-exchange resin, and activated-carbon particles were tested as support matrix materials. Activated carbon was tested in both a packed-bed bioreactor and a fluidized-bed bioreactor; the other matrix materials were used in packed-bed reactors. Activated carbon displayed the most suitable characteristics for use as a support matrix of T. ferrooxidans fixed-film formation. The reactors were operated within a pH range of 1.35 to 1.5, which effectively reduced the amount of ferric iron precipitation and eliminated diffusion control of mass transfer due to precipitation. The activated-carbon packed-bed reactor displayed the most favorable biomass holdup and kinetic performance related to ferrous sulfate oxidation. The fastest kinetic performance achieved with the activated-carbon packed-bed bioreactor was 78 g of Fe oxidized per liter per h (1,400 mmol of Fe oxidized per liter per h) at a true dilution rate of 40/h, which represents a hydraulic retention time of 1.5 min.     

Neural network prediction of thermophilic (65 degrees C) sulfidogenic fluidized-bed reactor performance for the treatment of metal-containing wastewater

The performance of a fluidized-bed reactor (FBR) based sulfate reducing bioprocess was predicted using artificial neural network (ANN). The FBR was operated at high (65 degrees C) temperature and it was fed with iron (40-90 mg/L) and sulfate (1,000-1,500 mg/L) containing acidic (pH = 3.5-6) synthetic wastewater. Ethanol was supplemented as carbon and electron source for sulfate reducing bacteria (SRB). The wastewater pH of 4.3-4.4 was neutralized by the alkalinity produced in acetate oxidation and the average effluent pH was 7.8 +/- 0.8. The oxidation of acetate is the rate-limiting step in the sulfidogenic ethanol oxidation by thermophilic SRB, which resulted in acetate accumulation. Sulfate reduction and acetate oxidation rates showed variation depending on the operational conditions with the maximum rates of 1 g/L/d (0.2 g/g volatile solids (VS)/d) and 0.3 g/L/d (0.06 g/g VS/d), respectively. This study presents an ANN model predicting the performance of the reactor and determining the optimal architecture of this model; such as best back-propagation (BP) algorithm and neuron numbers. The Levenberg-Marquardt algorithm was selected as the best of 12 BP algorithms and optimal neuron number was determined as 20. The developed ANN model predicted acetate (R=0.91), sulfate (R=0.95), sulfide (R=0.97), and alkalinity (R=0.94) in the FBR effluent. Hence, the ANN based model can be used to predict the FBR performance, to control the operational conditions for improved process performance.     

Kinetic studies of iron deposition in horse spleen ferritin using O2 as oxidant

An optical flow cell provided a means to conveniently measure the rate of successive Fe(2+) oxidation reactions catalyzed by horse spleen ferritin (HoSF) to determine if both ferroxidase and mineral core Fe(2+) oxidation reactions occur. The oxygen concentration and pH were held constant and multiple additions of Fe(2+)/HoSF ratios of 1, 10, 100, 150, 250 and 400 were conducted, creating core sizes ranging from 12 to 2800. During these oxidations, the absence of nonspecific Fe(OH)(3) formation and the presence (>95%) of Fe(OH)(3) deposited within the core of HoSF demonstrated the validity of monitoring iron deposition into HoSF by this procedure. Initial rates for oxidation of 5-50 Fe(2+)/HoSF established that the reaction is overall first order in Fe(2+) concentration. However, when full progress curves were analyzed at a variety of Fe(2+)/HoSF ratios, two first-order reactions (k(1) approximately 0.035 s(-1) and k(2) approximately 0.007 s(-1)) were found to contribute to the overall Fe(2+) oxidation reaction. The proportion of the fast reaction increased with increasing Fe(2+)/HoSF ratio until at approximately 400, it was the dominant reaction. For the Fe(2+)/HoSF ratios examined, the overall rate of iron deposition is independent of the size of the mineral core, a result suggesting that an increasing mineral core size does not enhance the rate of Fe(2+) oxidation. Comparison of successive additions of 1.0 Fe(2+)/HoSF showed that oxidation of the first 8-10 Fe(2+) produced a Fe(III) species with a lower molar absorptivity per Fe(III) than that of the bulk core. Measurement of the H(+)/Fe(2+) ratio confirmed this difference in behavior by giving an H(+)/Fe(2+) ratio of approximately 1.0 below and 2.0 for ratios >30 Fe(2+)/HoSF. The faster reaction was attributed to ferroxidase catalysis and the slow reaction to nonspecific ferroxidase activity of the HoSF protein shell.     

A continuous lactic acid production system using an immobilized packed bed of Lactobacillus helveticus

A 5 l packed bed bioreactor was used to study the effect of initial lactose concentration and hydraulic retention time (HRT) on cell growth, lactose utilization and lactic acid production. Up to 95% of the initial lactose concentration was utilized at longer HRTs (30-36 h). The study showed that lactic acid production increased with increases in HRT (12-36 h) and initial lactose concentrations. The highest lactic acid production rate (3.90 g l(-1) h(-1)) was obtained with an initial lactose concentration of 100 g/l and an HRT of 18 h, whereas the lowest lactic acid production rate (1.35 g l(-1) h(-1)) was obtained with an initial lactose concentration of 50 g/l and an HRT of 36 h. This suggested that optimal lactic acid production can be achieved at an HRT of 18 h and initial lactose concentration of 100 g/l.     

Development of an optimal medium for continuous ferrous iron oxidation by immobilized Acidothiobacillus ferrooxidans cells

This study was aimed at developing an immobilized bioreactor system in which long-term continuous ferrous iron oxidation can be realized with no formation of jarosite, which causes clogging of support pores and reactor lines. For this purpose, a medium with no jarosite formation was developed first by selecting optimal nitrogen and phosphate sources and their concentrations. Then with the developed medium containing ammonium phosphate instead of ammonium sulfate and potassium phosphate, repeated batch and continuous operations of ferrous iron oxidation by Acidothiobacillus ferrooxidans cells immobilized in a depth filter were successfully performed for an extended period of time. For about 510 h of operation including 450 h of continuous operation at dilution rates of 0.1, 0.2, and 0.3 h(-)(1), no formation of jarosite and thus no clogging of the reactor system were observed. The maximum ferrous iron oxidation rate was as high as 2.6 g/(L.h) at a dilution rate of 0.3 h(-)(1).     

Packed- and fluidized-bed biofilm reactor performance for anaerobic wastewater treatment

Anaerobic degradation performance of a laboratory-scale packed-bed reactor (PBR) was compared with two fluidized-bed biofilm reactors (FBRs) on molasses and whey feeds. The reactors were operated under constant pH (7) and temperature (35 degrees C) conditions and were well mixed with high recirculation rates. The measured variables were chemical oxygen demand (COD), individual organic acids, gas composition, and gas rates. As carrier, sand of 0.3-0.5 mm diameter was used in the FBR, and porous clay spheres of 6 mm diameter were used in the PBR. Startup of the PBR was achieved with 1-5 day residence times. Start-up of the FBR was only successful if liquid residence times were held low at 2-3 h. COD degradations of 86% with molasses (90% was biodegradable) were reached in both the FBR and PBR at 6 h residence time and loadings of 10 g COD/L day. At higher loadings the FBR gave the best performance; even at 40-45 g COD/L day, with 6 h residence times, 70% COD was degraded. The PBR could not be operated above 20 g COD/L day without clogging. A comparison of the reaction rates show that the PBR and FBR per formed similarly at low concentrations in the reactors up to 1 g COD/L, while above 3 g COD/L the rates were 17.4 g COD/L day for the PBR and 38.4 g COD/L day for the FBR. This difference is probably due to diffusion limitations and a less active biomass content of the PBR compared with the fluidized bed.The results of dynamic step change experiments, in which residence times and feed concentrations were changed hanged at constant loading, demonstrated the rapid response of the reactors. Thus, the response times for an increase in gas rate or an increase in organic acids due to an increase in feed concentration were less than 1 day and could be explained by substrate limitation. Other slower responses were observed in which the reactor culture adapted over periods of 5-10 days; these were apparently growth related. An increase in loading of over 100% always resulted in large increases inorganic acids, especially acetic and propionic, as well as large increases in the CO(2) gas content. In general, the CO(2) content of the gas was very low, due to the large amount of dissolved CO(2) that exited with the liquid phase at low residence times. The performance of the FBR with whey was comparable to its performance with molasses, and switching of molasses to whey feed resulted in immediate good performance without adaptation.