Oxidation of hydrogen sulphide in sour gas by Chlorobium limicola

The aim of this work was to assess the potential for bacterial oxidation of hydrogen sulphide as a purification method of sour gas. Using a continuous culture of Chlorobium limicola, high efficiencies of oxidation of both soluble and gaseous sulphide were achieved, with efficiencies for the latter exceeding 95%. Sulphide added as aqueous sodium sulphide was converted to sulphur and sulphate with almost total removal of the initial 100 mg S l⁻¹ within 24 h. Gaseous sulphide was oxidized at an efficiency of 95% (approximately 3 mmol S h⁻¹ (unit biomass Abs)⁻¹) over 1 h runs at a gas flow rate of 60 ml min⁻¹. With a sulphur recovery system to prevent sulphur accumulation, an efficiency of 70% was maintained. Biological removal of sulphide represents a potentially important biotechnological process, with high potential for viable scale up.     

Effects of nitrobenzene concentration and hydraulic retention time on the treatment of nitrobenzene in sequential anaerobic baffled reactor (ABR)/continuously stirred tank reactor (CSTR) system

The effects of increasing nitrobenzene (NB) concentrations and hydraulic retention times (HRT) on the treatment of NB were investigated in a sequential anaerobic baffled reactor (ABR)/aerobic completely stirred tank reactor (CSTR) system. In the first step of the study, the maximum COD removal efficiencies were found as 88% and 92% at NB concentrations varying between 30 mg L^?1 and 210 mg L^?1 in ABR. The minimum COD removal efficiency was 79% at a NB concentration of 700 mg L^?1. The removal efficiency of NB was nearly 100% for all NB concentrations in the ABR reactor. The methane gas production and the methane gas percentage remained stable (1500 mL day^?1 and 48–50%, respectively) as the NB concentration was increased from 30 to 210 mg L^?1. In the second step of the study it was found that as the HRT decreased from 10.38 days to 2.5 days the COD removal efficiencies decreased slightly from 94% to 92% in the ABR. For maximum COD and NB removal efficiencies the optimum HRT was found as 2.5 days in the ABR. The total COD removal efficiency was 95% in sequential anaerobic (ABR)/aerobic (CSTR) reactor system at a minimum HRT of 1 day. When the HRT was decreased from 10.38 days to 1 day, the methane percentage decreased from 42% to 29% in an ABR reactor treating 100 mg L^?1 NB. Nitrobenzene was reduced to aniline under anaerobic conditions while aniline was mineralized to catechol with meta cleavage under aerobic conditions.     

New integrated bioprocess for the continuous production,extraction and purification of lipopeptides produced by Bacillus subtilis in membrane bioreactor

Recently, a bubbleless membrane bioreactor (BMBR) has been successfully developed for biosurfactant production by Bacillus subtilis [1]. In this study, for the first time, continuous culture were carried out for the production of surfactin in a BMBR, both with or without a coupled microfiltration membrane. Results from continuous culture showed that a significant part of biomass was immobilized onto the air/liquid membrane contactor. Immobilized biomass activity onto the air/liquid membrane contactor was monitored using a respirometric analysis. Kinetics of growth, surfactin and primary metabolites production were investigated. Planktonic biomass, immobilized biomass and surfactin production and productivity obtained in batch culture (3 L) of 1.5 days of culture were 4.5 g DW, 1.3 g DW, 1.8 g and 17.4 mg L^?1 h^?1, respectively. In continuous culture without total cell recycling (TCR), the planktonic biomass was leached, but immobilized biomass reached a steady state at an estimated 6.6 g DW. 11.5 g of surfactin was produced after 3 days of culture, this gave an average surfactin productivity of 54.7 mg L^?1 h^?1 for the continuous culture, which presented a surfactin productivity of 30 mg L^?1 h^?1 at the steady state. TCR was then investigated for the continuous production, extraction and purification of surfactin using a coupled ultrafiltration step. In continuous culture with TCR at a dilution rate of 0.1 h^?1, planktonic biomass, immobilized biomass, surfactin production and productivity reached 7.5 g DW, 5.5 g DW, 7.1 g and 41.6 mg L^?1 h^?1 respectively, after 2 days of culture. After this time, biomass and surfactin productions stopped. Increasing dilution rate to 0.2 h^?1 led to the resumption of biomass and surfactin production and these values reached 11.1 g DW, 10.5 g DW, 7.9 g and 110.1 mg L^?1 h^?1, respectively, after 3 days of culture. This study has therefore shown that with this new integrated bioprocess, it was possible to continuously extract and purify several grams of biosurfactant, with purity up to 95%.     

Poly(3-hydroxybutyrate) production by Cupriavidus necator using waste glycerol

Polyhydroxyalkanoates (PHAs) have been recognized as good substitutes for the non-biodegradable petrochemically produced polymers. However, their high (real or estimated) current production cost limits their industrial applications. This work exploits two strategies to enhance PHAs substitution potential: the increase in PHA volumetric productivity in high density cultures and the use of waste glycerol (GRP), a by-product from the biodiesel industry, as primary carbon source for cell growth and polymer synthesis. Cupriavidus necator DSM 545 was used to accumulate poly(3-hydroxybutyrate) (P(3HB)) from GRP and from commercial glycerol (PG) as control substrate. On PG, productivities between 0.6 g_PHB L^?1 h^?1 and 1.5 g_PHB L^?1 h^?1 were attained. The maximum cell DW was 82.5 g_DW L^?1, the P(3HB) content being 62%. When GRP was used, 68.8 g_DW L^?1 with a P(3HB) accumulation of 38% resulting in a final productivity of 0.84 g_PHB L^?1 h^?1 was obtained. By decreasing the biomass concentration at which accumulation was triggered, a productivity of 1.1 g_PHB L^?1 h^?1 (50% P(3HB), w/w) was attained using GRP. P(3HB) molecular weights (M_w) ranged from 7.9 × 10⁵ to 9.6 × 10⁵ Da.     

Improvement of (R)-carbonyl reductase-mediated biosynthesis of (R)-1-phenyl-1,2-ethanediol by a novel dual-cosubstrate-coupled system for NADH recycling

An NAD(H)-dependent (R)-carbonyl reductase (RCR) from Candida parapsilosis catalyzes the asymmetric reduction of 2-hydroxyacetophenone (2-HAP) to (R)-1-phenyl-1,2-ethanediol ((R)-PED), which is a valuable chiral building block in the pharmaceutical and fine chemical industries. Biosynthesis efficiency of (R)-PED was considerably improved by a novel dual-cosubstrate-coupled system. By simultaneously employing isopropanol (10%, v v^?1) and glycerol (8%, v v^?1) as sacrificial cosubstrates, the (R)-PED product had an excellent optical purity of >99.9% and a conversion of 85.5%, which were nearly 2- and 11-fold higher than those without adding cosubstrate, respectively. Besides, the productivity was dramatically enhanced from 0.02 g L^?1 h^?1 to 5 g L^?1 h^?1, and the maximum acceptable concentration of 2-HAP was elevated to 10 g L^?1. Isopropanol was directly oxidized by RCR in the formation of NADH, while glycerol was metabolized by cellular enzymes to release NADH. Moreover, glycerol prevented cells from losing viability and alleviated the toxicity of isopropanol and acetone for cells. Interestingly, there was a cooperative interaction between isopropanol and glycerol for the improvement of biosynthesis efficiency of (R)-PED.     

Chemoenzymatic synthesis of (S)-duloxetine using carbonyl reductase from Rhodosporidium toruloides

A chemoenzymatic strategy was developed for (S)-duloxetine production employing carbonyl reductases from newly isolated Rhodosporidium toruloides into the enantiodetermining step. Amongst the ten most permissive enzymes identified, cloned, and overexpressed in Escherichia coli, RtSCR9 exhibited excellent activity and enantioselectivity. Using co-expressed E. coli harboring both RtSCR9 and glucose dehydrogenase, (S)-3-(dimethylamino)-1-(2-thienyl)-1-propanol 3a was fabricated with so far the highest substrate loading (1000 mM) in a space-time yield per gram of biomass (DCW) of 22.9 mmol L⁻¹ h⁻¹ g DCW⁻¹ at a 200-g scale. The subsequent synthetic steps from RtSCR9-catalyzed (S)-3a were further performed, affording (S)-duloxetine with 60.2% overall yield from 2-acethylthiophene in >98.5% ee.     

Anammox for ammonia removal from pig manure effluents: Effect of organic matter content on process performance

The anammox process, under different organic loading rates (COD), was evaluated using a semi-continuous UASB reactor at 37 °C. Three different substrates were used: initially, synthetic wastewater, and later, two different pig manure effluents (after UASB-post-digestion and after partial oxidation) diluted with synthetic wastewater. High ammonium removal was achieved, up to 92.1 ± 4.9% for diluted UASB-post-digested effluent (95 mg COD L^?1) and up to 98.5 ± 0.8% for diluted partially oxidized effluent (121 mg COD L^?1). Mass balance clearly showed that an increase in organic loading (from 95 mg COD L^?1 to 237 mg COD L^?1 and from 121 mg COD L^?1 to 290 mg COD L^?1 for the UASB-post-digested effluent and the partially oxidized effluent, respectively) negatively affected the anammox process and facilitated heterotrophic denitrification. Partial oxidation as a pre-treatment method improved ammonium removal at high organic matter concentration. Up to threshold organic load concentration of 142 mg COD L^?1 of UASB-post-digested effluent and 242 mg COD L^?1 of partially oxidized effluent, no effect of organic loading on ammonia removal was registered (ammonium removal was above 80%). However, COD concentrations above 237 mg L^?1 (loading rate of 112 mg COD L^?1 day^?1) for post-digested effluent and above 290 mg L^?1 (loading rate of 136 mg COD L^?1 day^?1) for partially oxidized effluent resulted in complete cease of ammonium removal. Results obtained showed that, denitrification and anammox process were simultaneously occurring in the reactor. Denitrification became the dominant ammonium removal process when the COD loading was increased.     

Hydrogen sulphide removal from air by biotrickling filter using open-pore polyurethane foam as a carrier

A study was conducted on H₂S removal in a biotrickling filter packed with open-pore polyurethane foam. Thiobacillus denitrificans was used as inoculum and a mixed culture population was developed during the process. The inhibitory effect of sulphate concentration (1.8–16.8 g L⁻¹), pH (6.9–8.6), trickling liquid velocity (TLV, 9.1–22.8 m h⁻¹), H₂S inlet concentration (20–157 ppmv) and the empty bed residence time (EBRT, 9–57 s) on the H₂S removal efficiency (RE) were thoroughly investigated. An increase in pH from 6.9 to 8.5 led to a corresponding increase in H₂S removal. In addition, an inhibitory effect of sulphate concentration was observed from 16.8 g L⁻¹ and the maximum elimination capacity was found to be 22 gS m⁻³ h⁻¹ (RE 98%). The RE was constant (98.8 ± 0.30%) for EBRT ≥ 16 s, but a decrease in the EBRT from 16 to 9 s led to a corresponding decrease in RE from 98.2 to 89.6% for a TLV of 9.1 m h⁻¹ and from 97.9 to 94.9% for a TLV of 22.8 m h⁻¹ (inlet load of 11.0 ± 0.2 gS m⁻³ h⁻¹). The sulphur oxidation capacity in the biotrickling filter was not diminished by the presence of other bacteria.     

The investigation of dairy industry wastewater treatment in a biological high performance membrane system

The dairy industry is generally considered to be the largest source of food processing wastewater in many countries. The highly variable nature of dairy wastewaters in terms of volumes and flowrates and in terms of high organic materials contents such as COD 921–9004 mg L⁻¹, BOD 483–6080 mg L⁻¹, TN of 8–230 mg L⁻¹ and SS of 134–804 mg L⁻¹ makes the choice of an effective wastewater treatment regime difficult. A high performance bioreactor, an aerobic jet loop reactor, combined with a ceramic membrane filtration unit, was used to investigate its suitability for the treatment of the dairy processing wastewater. The oxygen transfer rates of the bioreactor were found to be very high (100–285 h⁻¹) on the operating conditions. A loading rate of 53 kg COD m⁻³ d⁻¹ resulted in 97–98% COD removal efficiencies under 3 h hydraulic retention time. The high MLSS concentrations could be retained in the system (up to 38,000 mg L⁻¹) with the contribution of UF (ultrafiltration) unit. During the filtration of activated sludge, the fluxes decreased with increasing MLSS. Cake formation fouling was determined as dominant fouling mechanisms. The results demonstrate that jet loop membrane bioreactor system was a suitable and effective treatment choice for treating dairy industry wastewater.     

Synthesis of S-licarbazepine by asymmetric reduction of oxcarbazepine with Saccharomyces cerevisiae CGMCC No. 2266

S-licarbazepine was synthesized by asymmetric reduction of oxcarbazepine with CGMCC No. 2266. The optimum batch reduction conditions were found to consist of a reaction time of 36 h, temperature of 30 °C, and initial pH value of 7.0. The optimum concentration of the glucose co-substrate was found to be 0.3 mol L⁻¹. The addition of glucose contributed to in situ regeneration of NADPH in cells and improved conversion. Conversion increased with the addition of more biomass and with a decrease in the initial concentration of substrate. Within the membrane reactor, a continuous reduction process was used to improve production efficiency and reduce the inhibition of high-concentration substrate upon reduction. The optimum flux was found to be 20 ml h⁻¹. S-licarbazepine yield was 3.7678 mmol L⁻¹ d⁻¹ in continuous reduction over four days. The enantiometric excess of S-licarbazepine was 100% for both batch and continuous reduction processes.     

Operation of an Anammox SBR in the presence of two broad-spectrum antibiotics

The feasibility of the anaerobic ammonium oxidation (Anammox) process to treat wastewaters containing antibiotics was studied in this work. Concentrations ranging from 100 to 1000 mg L^?1 for tetracycline hydrochloride and from 250 to 1000 mg L^?1 for chloramphenicol were tested in batch assays. A strong inhibitory effect was observed for both antibiotics.A concentration of 20 mg L^?1 of chloramphenicol was continuously added to an Anammox Sequential Batch Reactor (SBR) system, causing a decrease of the nitrogen removal efficiency of 25%. The Specific Anammox Activity (SAA) of the biomass also decreased from 0.25 to 0.05 g N (g VSS d)^?1. Similar effects were observed when 50 mg L^?1 of tetracycline hydrochloride were continuously fed. Both antibiotics did not cause any changes in the physical properties of the biomass. A previous degradation step could be necessary in order to treat wastewaters containing inhibitory concentrations of antibiotics by the Anammox process.     

Nitrogen transformation in the hybrid bioreactor landfill

The hybrid bioreactor landfill was promising in solid waste management. In the work, the nitrogen removal and nitrogen transformation in hybrid bioreactor landfill with sequencing of facultative anaerobic and aerobic conditions was explored. The result showed that the combination of facultative anaerobic and aerobic conditions in the hybrid bioreactor landfill was indeed effective in eliminating ammonia both from the leachate and the refuse thoroughly. About 72% of nitrogen was reduced from the landfilled fresh refuse through the operation of 357 days. At the end of the experiment, the concentrations of COD, ammonia, nitrate and TN in the leachate decreased to 399.2 mg l^?1, 20.6 mg N l^?1, 3.7 mg N l^?1 and 25.3 mg N l^?1, respectively.     

A stable immobilized d-psicose 3-epimerase for the production of d-psicose in the presence of borate

Maximal activity of the immobilized d-psicose 3-epimerase from Agrobacterium tumefaciens on Duolite A568 beads was achieved at pH 9.0 and 55 °C with borate, and at pH 8.5 and 50 °C without borate. The half-lives of the immobilized enzyme at 50 °C with and without borate were increased 4.2- and 128-fold compared to that of the free enzyme without borate, respectively. The immobilized enzyme with borate produced 441 g l^?1 psicose from 700 g l^?1 fructose at pH 9.0 and 55 °C, whereas 193 g l^?1 psicose was produced without borate at pH 8.5 and 50 °C after 120 min in a batch reaction. The immobilized enzyme in a packed-bed bioreactor without borate was produced continuously 325 g l^?1 psicose from 500 g l^?1 fructose at a dilution rate of 1.62 h^?1 over a 236 h period with productivity of 527 g l^?1 h^?1 while that without borate produced 146 g l^?1 psicose at 4.15 h^?1 over a 384-h period with productivity of 606 g l^?1 h^?1. The operational half-lives of the enzyme with and without borate in the bioreactor were 601 and 645 h, respectively. In the present study, psicose was produced stably with high productivity using the immobilized d-psicose 3-epimerase in the presence of borate.     

Nitrate removal and greenhouse gas production in a stream-bed denitrifying bioreactor

Denitrifying bioreactors are currently being tested as an option for treating nitrate (NO₃^?) contamination in groundwater and surface waters. However, a possible side effect of this technology is the production of greenhouse gases (GHG) including nitrous oxide (N₂O) and methane (CH₄). This study examines NO₃^? removal and GHG production in a stream-bed denitrifying bioreactor currently operating in Southern Ontario, Canada. The reactor contains organic carbon material (pine woodchips) intended to promote denitrification. Over a 1 year period, monthly averaged removal of influent (stream water) NO₃^? ranged from 18 to 100% (0.3–2.5 mg N L^?1). Concomitantly, reactor dissolved N₂O and CH₄ production, averaged 6.4 μg N L^?1 (2.4 mg N m^?2 d^?1), and 974 μg C L^?1 (297 mg C m^?2 d^?1) respectively, where production is calculated as the difference between inflow and effluent concentrations. Gas bubbles entrapped in sediments overlying the reactor had a composition ranging from 19 to 64% CH₄, 1 to 6% CO₂, and 0.5 to 2 ppmv N₂O; however, gas bubble emission rates were not quantified in this study. Dissolved N₂O production rates from the bioreactor were similar to emission rates reported for some agricultural croplands (e.g. 0.1–15 mg N m^?2 d^?1) and remained less than the highest rates observed in some N-polluted streams and rivers (e.g. 110 mg N m^?2 d^?1, Grand R., ON). Dissolved N₂O production represented only a small fraction (0.6%) of the observed NO₃^? removal over the monitoring period. Dissolved CH₄ production during summer months (up to 1236 mg C m^?2 d^?1), was higher than reported for some rivers and reservoirs (e.g. 6–66 mg C m^?2 d^?1) but remained lower than rates reported for some wastewater treatment facilities (e.g. sewage treatment plants and constructed wetlands, 19,500–38,000 mg C m^?2 d^?1).     

Nitrogen balance in and export from agricultural fields associated with controlled drainage systems and denitrifying bioreactors

Nitrate loss from drainage tiles across the cornbelt of the upper midwestern US is a result of intensive agriculture with limited crop diversity, extensive periods of fallow soil, and the need for high fertilizer applications to corn, all located on a hydrologically modified landscape. Two methods proposed to reduce tile nitrate export are managed or controlled drainage to limit tile flow and bioreactors to enhance denitrification. Nitrogen budgets and tile flow monitoring were conducted over two- to three-year periods between 2006 and 2009. We estimated N budgets in a seed corn-soybean rotation farming system near DeLand, east-central Illinois, USA, with free (FD) and controlled drainage (CD) patterned tile systems. In addition, wood chip filled trenches (bioreactors) were installed below the CD structures, one lined with plastic and one unlined. We measured daily tile flow and nitrate-N (NO₃-N) concentrations and calculated cumulative N loss from the tile water at both FD and CD areas for a period of three cropping years. We also monitored the tile flow and nitrate concentration in inlet and outlet of the bioreactor associated with a CD system and evaluated the efficiency of the bioreactor for two cropping years. Most components of the N balance were unaffected by CD (yields and therefore N harvested, surface soil denitrification), and there was a negative N balance in the soybean cropping year (?165 and ?163 kg N ha^?1 at FD and CD areas, respectively), whereas seed corn cropping in the following year resulted in positive N balances (29 and 34 kg N ha^?1 at FD and CD areas, respectively). For two years, the overall N balances were ?136 and ?129 kg N ha^?1 at FD and CD areas, respectively, consistent with other recent corn belt studies showing a small net depletion of soil organic N. Controlled drainage greatly reduced tile N export, with a three-year average loss of 57.2 kg N ha^?1 yr^?1 from FD compared to 17 kg N ha^?1 yr^?1 for CD. There was high uncertainty in denitrification measurements and thus the fate of missing N in the CD system remained unknown. Nitrate reduction efficiency of the bioreactor varied greatly, with periods where nearly 100% of the nitrate was denitrified. The overall efficiency of the bioreactor associated with the CD system in reducing the tile N load was 33%. When nitrate was non-limiting, the nitrate removal rate of the bioreactor was 6.4 g N m^?3 d^?1. Little N₂O emission was found from the bioreactor bed and is not thought to be a problem with these systems. Both the tile bioreactor and controlled drainage greatly reduced tile nitrate export in this leaky seed corn and soybean agricultural field.     

Cometabolic degradation of dibenzofuran by Comamonas sp. MQ

In this study, strain MQ belonging to the genera Comamonas was used to cometabolically degrade dibenzofuran (DBF) with naphthalene, phenanthrene, benzene, toluene, biphenyl and nitrobenzene, respectively, for the first time. Strain MQ could cometabolically degrade DBF in the growing system using naphthalene as a substrate and the K_i value of strain MQ on naphthalene and DBF was 90.26 mg L^?1 and 68.34 mg L^?1, respectively. The degradation rate of DBF by naphthalene-cultivated strain MQ cells (0.080 mmol L^?1 h^?1) was 1.05, 1.11, 1.13, 1.18 and 1.27-fold higher than that cultivated by phenanthrene, benzene, toluene, biphenyl and nitrobenzene, respectively. Examination of metabolites indicated that naphthalene-cultivated strain MQ cells degraded DBF to 2-hydroxy-4-(3′-oxo-3′H-benzofuran-2′-yliden)but-2-enoic acid (HOBB) and subsequently to salicylic acid via the lateral dioxygenation and meta cleavage pathway. In contrast, biphenyl-cultivated strain MQ cells degraded DBF to monohydroxydibenzofuran through the lateral dioxygenation without meta cleavage pathway. These results suggested that strain MQ could be useful in the bioremediation of environments contaminated by heterocyclic compounds mixtures with polycyclic aromatic hydrocarbons.     

Efficient synthesis of 5′-O-laurate of 1-β-d-arabinofuranosylcytosine via highly regioselective enzymatic acylation in binary solvent mixtures

Regioselective enzymatic acylations of 1-β-d-arabinofuranosylcytosine (ara-C) with vinyl laurate (VL) in binary organic solvents were explored for the preparation of 5′-O-laurate of ara-C. Among the nine kinds of enzymes, Novozym 435 showed the highest regioselectivity (>99.9%) towards the 5′-OH of ara-C. This lipase showed higher catalytic activity in hexane–pyridine than in other tested solvent mixtures. The most suitable VL to ara-C molar ratio, initial water activity, and reaction temperature were shown to be 15:1, 0.07, and 50 °C, respectively, under which the initial reaction rate and the maximum substrate conversion were as high as 84.0 mmol L^?1 h^?1 and 98.1%, respectively. The product of Novozym 435-catalyzed acylation was characterized by ¹³C NMR and confirmed to be 5′-O-laurate of ara-C.     

CBOD5 treatment using the marshland upwelling system

Five-day carbonaceous biochemical oxygen demand (CBOD₅) removal efficiency was evaluated for the marshland upwelling system (MUS) under both intermediate and saltwater conditions. The MUS treated decentralized wastewater from two private camps and a public restroom in the Grand Bay National Estuarine Research Reserve, Moss Point, Mississippi, and one private camp in the Barataria Terrebonne National Estuary, along Bayou Segnette, Louisiana. Raw wastewater was injected into the surrounding subsurface at a depth of 3.8 or 4.3 m. Various injection flow rates and frequencies were tested in addition to a synthetic wastewater trial. All trials followed a first-order background corrected removal equation, resulting in removal constants ranging from 0.49 to 3.32 m^?1 and predicted surface concentrations from 5.7 to 33.0 mg L^?1. CBOD₅ (unfiltered) influent concentrations of 282 ± 173 mg L^?1 were reduced to an overall effluent mean of 13 ± 13 mg L^?1 by a vector distance of 7 m at Moss Point and from 365 ± 151 mg L^?1 to 3.6 ± 7.6 mg L^?1 by a vector distance of 6 m for Bayou Segnette. Of seven trials, only one failed to achieve effluent CBOD₅ levels below a National Pollutant Discharge Elimination System (NPDES) standard level of 25 mg L^?1.     

Isolation and characterization of Pseudomonas stutzeri QZ1 from an anoxic sulfide-oxidizing bioreactor

Bacterial strain QZ1 was isolated from sludge of anoxic sulfide-oxidizing (ASO) reactor. Based on 16S rDNA sequence analysis and morphological characteristics, the isolate was identified as Pseudomonas stutzeri. The isolate was found to be a facultative chemolithotroph, using sulfide as electron donor and nitrite as electron acceptor. The strain QZ1 produced sulfate as the major product of sulfide oxidation, depending on the initial sulfide and nitrite concentrations. The isolate was capable of growth under strictly autotrophic conditions. The growth and substrate removal of Pseudomonas stutzeri QZ1 were optimal at an initial pH of 7.5–8.0 at 30 °C. The specific growth rate (μ) was found as 0.035 h⁻¹ with a doubling time of 21.5 h. For isolate QZ1, the EC₅₀ values both for sulfide and nitrite were found to be 335.95 mg S L⁻¹ and 512.38 mg N L⁻¹, respectively, showing that the sulfide oxidation into sulfate by Pseudomonas stutzeri QZ1 was badly affected beyond these substrate concentrations.     

Continuous succinic acid fermentation by Actinobacillus succinogenes

Fermentations were performed in an external recycle bioreactor using CO₂ and d-glucose at feed concentrations of 20 and 40 g L⁻¹. Severe biofilm formation prevented kinetic analysis of suspended cell (‘chemostat’) fermentation, while perlite packing enhanced the volumetric productivity by increasing the amount of immobilised cells. The highest productivity of 6.35 g L⁻¹ h⁻¹ was achieved at a dilution rate of 0.56 h⁻¹. A constant succinic acid yield of 0.69 ± 0.02 g/(g of glucose consumed) was obtained and found to be independent of the dilution rate, transient state and extent of biofilm build-up – approximately 56% of the carbon that formed phosphoenolpyruvate ended up as succinate. Byproduct analysis indicated that pyruvate oxidation proceeded solely via the formate-lyase pathway. Cell growth and corresponding biofilm formation were rapid at dilution rates higher than 0.35 h⁻¹ when the product concentrations were low (succinic acid < 10 g L⁻¹), while minimal growth was observed at succinic acid concentrations above this threshold.