Nitrification of fertilizer wastewaters in a biofilm reactor

The nitrification characteristics of fertilizer wastes were investigated in a biofilm system using a submerged aerated filter. The attachment of biomass on packing media was studied. Supplement of organic carbon in the form of glucose and yeast extract enhanced biofilm formation although the nitrifiers did not require organic carbon for growth. After an attachment period, continuous operation of the reactor at different loading rates and dissolved oxygen levels was investigated. The maximum achievable nitrification rate was strongly dependent on the dissolved oxygen. In the dissolved oxygen range of 3·2–3·5 mg dm⁻³, the maximum ammonia removal rate was about 0·17 kg NH₄ N m⁻³ day⁻¹. When the dissolved oxygen was increased to 4·9 mg dm⁻³, removal rates as high as 0·41 kg NH₄ N m⁻³ day⁻¹ could be obtained. Nitrite accumulation depended on the bulk nitrogen and dissolved oxygen concentrations.     

Modelling of simultaneous methanogenesis and denitrification in an upflow packed-bed biofilm reactor

The performance of an upflow packed-bed biofilm reactor was investigated by considering simultaneous methanogenesis and denitrification reactions under step and sinusoidal variations of feed concentration and temperature. For simultaneous step inputs of 20 mg dm⁻³ of NO₃⁻—N and 60 mg dm⁻³ of methanol, the proposed model shows that major conversion of both the substrates takes place in the first half of the reactor. However, when the inlet concentration of methanol is subjected to sinusoidal variation, while that of NO₃⁻—N is maintained stepwise, the exit concentration of both methanol and NO₃⁻—N follow a sinusoidal response. On the other hand, when the inputs are reversed (methanol stepwise and NO₃⁻—N sinusoidal), the response exhibits similar behaviour. For sinusoidal variation of feed temperature the exit concentration profiles of both substrates also follow a sinusoidal pattern. For methanol, the mean steady state conversion under sinusoidal variation is higher than the corresponding steady state concentration when feed temperature is constant at 30°C. The model predictions are in good agreement with the experimental data available in the literature. ©1997 SCI     

Physiology of amidase production by M. methylotrophus: Isolation of hyperactive strains using continuous culture

Penicillium chrysogenum spores were immobilised in K-carrageenan. The effect of the number of viable spores immobilised per bead on the rate of germination and degree of subsequent mycelial growth was investigated. The distribution of active mycelium throughout the bead was determined. At a high spore loading (10³?10⁴ viable spores per bead) the biomass concentration was low and the majority of the actively respiring biomass was located at the bead periphery. Reducing the spore loading (to 50 viable spores per bead) resulted in a fourfold increase in immobilised biomass concentration. At very low spore loadings (5 and 10 viable spores per bead) the concentration of biomass decreased, but mass transfer throughout the bead improved and the uniformity of active immobilised biomass increased. The spore loading also affected the morphology of the growing hyphae and the extent of free cell growth.     

Removal of cadmium from dilute aqueous solutions with a rotating cylinder electrode of expanded metal

The removal of cadmium from dilute solutions using a continuous undivided electrochemical reactor with a rotating cylinder cathode of expanded metal is analysed. The effects of cathodic applied potential, size and orientation of expanded metal meshes and inlet cadmium concentration were ascertained. The results show that cadmium can be removed from dilute solutions (inlet concentration range 5–50 mg dm⁻³) with a high fractional conversion of between 35 and 40% depending on the operating conditions. Thus a minimal residual cadmium concentration of 3 mg dm⁻³ was achieved. The specific energy consumption increases from 0.6 to 2 kWh mol⁻¹ as the cadmium concentration decreases. Copyright © 2003 Society of Chemical Industry     

Comparative bioparticle and hydrodynamic characteristics of conventional and tapered anaerobic fluidized‐bed bioreactors

By maintaining the same operational conditions of one conventional fluidized‐bed bioreactor (CFB) and two tapered fluidized‐bed bioreactors (TFBs), the performance of the TFBs with taper angles of 5 ° and 2.5 ° were found to be superior to that of the CFB with a taper angle of 0 °. Experimental results together with statistical analyses showed that the bioparticle and hydrodynamic characteristics of the TFBs were significantly different from those of the CFB. Also, bioparticle stratification occurred in the three bioreactors. The biofilm thickness (δ) and the specific biomass (β) of the three bioreactors varied in the following decreasing order 5 ° > 2.5 ° > 0 ° under the same volumetric loading. Meanwhile, the specific energy dissipation rate (ω) and the bioparticle washout rates (W = 0.214 ± 0.219; 0.537 ± 0.493 g BAC dm⁻³day⁻¹) of the two TFBs were considerably lower than that of the CFB (W = 1.086 ± 0.916 g BAC dm⁻³ day⁻¹). A lower ω value results in increases in δ and β, and a lower dry density of the biofilm (ρ_d). Accordingly, the performance enhancement with TFBs should be related to their lower ω and W, thicker δ and larger β values. © 2000 Society of Chemical Industry     

Continuous production of thrombomodulin from a Pichia pastoris fermentation

A rotary membrane separation system was used in a continuous fermentation of Pichia pastoris with cell recycling to obtain high cell concentration and high thrombomodulin production. The dilution rates of this continuous fermentation were between 0·25 and 0·35 dm³ day⁻¹, and the production process was maintained for 10 days. Since cells were recycled and only part of liquid broth was taken from the system, a very high cell concentration level (248 g dm⁻³) was obtained. The peak protein expression level was at 72 h after methanol induction, was 300 mg dm⁻³ (3·6 × 10⁵ activity unit cm⁻³) and the total harvested supernatant was three times the working volume.     

Enzymatic Synthesis of Thioesters in Non-conventional Solvents

The feasibility of enzymatic thioesterification between oleic acid and butanethiol in n-hexane, with the immobilised lipase (Lipozyme) from Mucor miehei, has been demonstrated. The immobilised enzyme quantity (100 mg), temperature (40°C), pH range (6–9) and water content (10%) were studied and their optimum values were determined. A preliminary kinetic study indicated a low butanethiol affinity for the enzyme (K_m = 1·85 mol dm⁻³). Even when butanethiol was used without solvent, no substrate inhibition was observed. The possibility of carrying out this reaction in a natural solvent, supercritical carbon dioxide (SCCO₂), was successfully verified. After 8 h reaction, a conversion yield of oleic acid of about 33% was obtained. © 1997 SCI.     

The operational strategy of intermittent cycle extended aeration system in treating sewage

An Intermittent Cycle Extended Aeration System (ICEAS) offers advantages for treating sewage; such as easy operation, process flexibility, and low capital cost. A laboratory‐scale study was made with synthetic‐domestic wastewater (COD = 300 mg dm⁻³; BOD = 210 mg dm⁻³) to investigate appropriate conditions for reduced operating cost. The results from this study indicated that the maximum hydraulic loading and organic loading were 3.5 m³ m⁻³ d⁻¹ and 0.735 kg BOD m⁻³d⁻¹ respectively. The BOD and COD of effluent were 15.5 mg dm⁻³ and 29.6 mg dm⁻³ for the cycle time and aeration time of 3.4 h and 2.65 h. It was not necessary to supply external artificial substrates in the reactor to deal with low wastewater flow that caused the starvation of sludge. Specific oxygen uptake rate (SOUR) was used as the index of microbial activity. The study indicated that the microbial activity could be restored (SOUR = 20.5 mg g⁻¹ MLVSS h⁻¹) after 5–6 days of cultivation when the sludge was deprived of substrate for 17 days. © 1999 Society of Chemical Industry     

Investigation into the viability of a liquid-film three-phase spouted bed biofilter

A variety of technologies exist for the treatment of malodorous air streams, including adsorption, absorption, catalytic combustion, biofiltration and bioscrubbing. Conventional packed bed biofiltration of malodorous substances from waste gas streams has the disadvantages of large unit surface area and relatively uncontrolled design principles. The large bed surface area leads to difficulties in maintaining even moisture and temperature profiles. In addition, the control of such biologically important parameters as pH is difficult. Novel fluidized/spouted beds were studied for biological treatment of gases because of their high specific gas flowrate and vigorous mixing which facilitates enhanced gas–biomass contact. Trials of a range of fluidized and spouted beds, with gas loadings of up to 14000 m³-gas m⁻²-bed h⁻¹, were carried out on various biofilm support media including glass ballotini, rice hulls, plastic discs and granules, silica gel, molecular sieves, vermiculite, perlite, activated carbon, cork, polystyrene and expanded clay. Severe aggregation and wall adhesion restricted the operational range of the reactors. Particle suitability was based on a combination of shape, density, size, porosity and wettability, with large, heavy clay particles performing best. Limited gas-phase bacterial studies on selected media with ammonia- and nitrite-oxidizing bacteria demonstrated the potential of fluidized/spouted beds for efficient biofiltration of ammonia (20–40 mg dm⁻³). © 1998 Society of Chemical Industry     

Reclamation of wastewater from a steel-making plant using an airlift submerged biofilm reactor

A bench-scale airlift submerged biofilm reactor was developed to test the possibility of nitrification of the final effluent discharged from a wastewater treatment process of a steel-making plant with an aim of reusing it as irrigation water. Despite the fluctuation of ammonia concentration in the wastewater (55–90 mg NH₃-N dm⁻³), the ammonia was completely converted to nitrate in the hydraulic retention time of 8 h. When decreasing the hydraulic retention time further down to 4 h, the nitrification efficiency decreased to 67·9%. However, the nitrification efficiency could be significantly enhanced by increasing the airflow rate due to an increase in both of the oxygen transfer rate and liquid circulation rate. At the aeration rate of 4 dm³ min⁻¹ and the hydraulic retention time of 4 h, the nitrification efficiency was as high as 92·6% and the nitrification rate was 34·6 mg NH₃-N dm⁻³ bed h⁻¹. © 1998 Society of Chemical Industry     

Removal of Hydrogen Sulphide by Immobilized Thiobacillus sp. strain CH11 in a Biofilter

An autotropic Thiobacillus sp. CH11 was isolated from piggery wastewater containing hydrogen sulphide. The removal characteristics of hydrogen sulphide by Thiobacillus sp. CH11 were examined in the continuous system. The hydrogen sulphide removal capacity was elevated by the BDST (Bed Depth Service Time) method (physical adsorption) and an immobilized cell biofilter (biological conversion). The optimum pH to remove hydrogen sulphide ranged from 6 to 8. The average specific uptake rate of hydrogen sulphide was as 1·02×10⁻¹³ mol-S cell⁻¹ h⁻¹ in continuous systems. The maximum removal rate and saturation constant for hydrogen sulphide were calculated to be V_m = 30·1 mmol-S day⁻¹ (kg-dry bead)⁻¹ and K_s = 1·28 μmol dm⁻³, respectively. A criterion to design a scale-up biofilter was also studied. The maximum inlet loading in the linear region (95% removal) was 47 mmol-S day⁻¹ (kg-dry bead)⁻¹. Additionally, the biofilter exhibited high efficiency (>98·5%) in the removal of hydrogen sulphide at both low (<0·026 mg dm⁻³) and high (0·078 mg dm⁻³) concentrations. The results suggested that the Thiobacillus sp. CH11 immobilized with Ca-alginate is a potential method for the removal of hydrogen sulphide. © 1997 SCI.     

Technological and kinetic aspects of sublethal acid toxicity in microbial gum production

Chemostat culture of Xanthomonas campestris were obtained at a dilution rate of 0·05 h⁻¹ and the normal feed then supplemented with 0·58 and 1·74 mmol dm⁻³ isobutyric acid (IBA). Data revealed that the organism responded to sublethal acid stress by overproducing xanthan. The acid additions led to transient zones in the continuous cultivation profiles. By adding feed containing 1·74 mmol dm⁻³ IBA, volumetric growth rate immediately decreased from 0·059 to 0·026 g dm⁻³ h⁻¹ whereas the specific xanthan formation rate increased from 0·23 g g⁻¹ biomass h⁻¹ to a maximum 0·65 g g⁻¹ biomass h⁻¹ (with 1·0 mmol dm⁻³ IBA addition), before decreasing as the concentration of acid attained that of the feed. By monitoring the outlet CO₂ in parallel with biomass and polysaccharide levels in the IBA fermentation a 10% diversion of the total carbon flux from biomass synthesis to xanthan biosynthesis was detected. A consistent pattern of variation in activity was detected in enzymes of intermediary metabolism, suggesting an action at the regulatory level. Enhanced activities of carbon catabolism and xanthan anabolic reactions (phosphomannose isomerase) were observed in the presence of the acid. Batch experiments carried out in the pres-ence of IBA gave results which correlated with the undissociated acid form con-centration. An undissociated acid fraction of 6·5×10⁻³ mmol dm⁻³ was calculated in a set of flasks under the same conditions and a statistically vali-dated 12% increase in xanthan production was found. The maximum activation was determined to be below 1·1×10⁻² mmol dm⁻³ when a 58% specific xanthan production rate increase occurred in parallel with a 35% decrease in biomass concentration.     

Factors affecting silver biosorption by an industrial strain of Saccharomyces cerevisiae

Factors affecting silver biosorption by Saccharomyces cerevisiae biomass, obtained as a waste product from industry, were examined. Maximum removal of silver from solution was achieved within 5 min. Increasing the concentration of biomass in experimental flasks from 1 to 8 mg cm⁻³ decreased both silver accumulation, from 224·7 to 89·5 μmol Ag g⁻¹ dry wt, and associated H⁺ ion release, from 109·4 to 31·7 μmol H⁺ g⁻¹ dry wt. The presence of 1·0 mol dm⁻³ cadmium or methionine decreased silver biosorption by 40% and 93% respectively. Boiling in 100 mmol dm⁻³ NaOH or 10 mmol dm⁻³ sodium dodecyl sulphate decreased silver biosorption by 54% and 25% respectively. A temperature increase from 4°C to 55°C decreased silver biosorption by 9%. The metabolic state of the yeast had no effect on silver biosorption. Decreasing the pH of the silver solution caused a reduction in metal removal by the biomass.     

Performance evaluation of the anaerobic fluidised bed system: II. Biomass holdup and characteristics

The biomass holdup and characteristics of the anareobic fluidised bed system for methane recovery from liquid wastes was examined at COD loadings of between 5.8 to 108 kg m^?3 day,^?1 hydraulic retention times of between 0.45 to 8h, and feed COD concentrations of between 480 to 9000 mg dm^?3. Under these operating conditions, the equilibrium biomass holdups increased with increasing COD loadings and varied from 15000 to 32000 mg VSS dm^?3 The distribution of biomass holdup and biofilm thickness in the reactor was relatively uniform, because of the completely mixed conditions maintained and the continuous sloughing of biofilms induced by the effervescence caused by rising methane bubbles. This continuous biofilm sloughing process also eliminated the need for intentional sludge wasting and consequently, the resulting sludge retention time in the reactor decreased with increasing COD loadings. The ability of the anaerobic fluidized bed system to retain a high biomass holdup was clearly demonstrated. As a result this system is ideal for being employed as a high-rate system for methane recovery from liquid wastes, even at low feed COD concentrations.     

The effect of organic loading rate on the anaerobic digestion of two‐phase olive mill solid residue derived from fruits with low ripening index

A study of the effect of organic loading rate on the performance of anaerobic digestion of two‐phase olive mill solid residue (OMSR) was carried out in a laboratory‐scale completely stirred tank reactor. The reactor was operated at an influent substrate concentration of 162 g chemical oxygen demand (COD) dm^?3. The organic loading rate (OLR) varied between 0.8 and 11.0 g COD dm^?3 d^?1. COD removal efficiency decreased from 97.0% to 82.6% when the OLR increased from 0.8 to 8.3 g COD dm^?3 d^?1. It was found that OLRs higher than 9.2 g COD dm^?3 d^?1 favoured process failure, decreasing pH, COD removal efficiency and methane production rates (Q_M). Empirical equations described the effect of OLR on the process stability and the effect of soluble organic matter concentration on the total volatile fatty acids (TVFA)/total alkalinity (TAlk) ratio (ρ). The results obtained demonstrated that rates of substrate uptake were correlated with concentration of biodegradable COD, through an equation of the Michaelis–Menten type. The kinetic equation obtained was used to simulate the anaerobic digestion process of this residue and to obtain the theoretical COD degradation rates in the reactor. The small deviations obtained (equal to or lower than 10%) between values calculated through the model and experimental values suggest that the proposed model predicts the behaviour of the reactor accurately. Copyright © 2007 Society of Chemical Industry     

Biological Removal of Aqueous Hexavalent Chromium

The conventional chemical reduction of Cr(VI) to Cr(III) and subsequent Cr(OH)₃ precipitation are expensive due to the use of large amounts of chemicals and the generation of chemical sludges. An attempt was carried out for microbial Cr(VI) removal in an anaerobic chemostat fed with an acetate-containing synthetic medium. With 26 mg Cr(VI) dm⁻³ in the influent, almost complete removal of Cr(VI) was achieved at dilution rates of 0·15 and 0·32 day⁻¹ at 20°C and at 35°C, respectively. The optimum Cr(VI) mass loading and the specific Cr(VI) applied rates were found to be 5 mg Cr(VI) dm⁻³ day⁻¹ and 0·02 mg Cr(VI) mg⁻¹ VSS day⁻¹, respectively. Either the influent Cr(VI) concentration or the dilution rate could be adjusted to maintain an efficient removal of Cr(VI) in a continuous operation. Since the Cr(VI)-reducing activity is associated with the biomass concentration in the system, recycling the effluent solids is essential for practical application. In a batch reactor with the biomass collected from the chemostat, NaAc degradation appeared to be proportional to Cr(VI) reduction with the ratio of 9 mg C mg⁻¹ Cr(VI) at 35°C. As reactions proceeded, the oxidation–reduction potential correspondingly decreased and both pH and alkalinity increased. © 1997 SCI.     

Improved modelling of the unsteady‐state behaviour of an immobilized‐cell,fluidized‐bed bioreactor for phenol biodegradation

The dynamic response of an immobilized‐cell, fluidized‐bed reactor (ICFBR) to step changes in phenol loading was investigated at 10°C for a pure culture of Pseudomonas putida Q5, a psychrotrophic bacterium. A novel dynamic model was developed and tested to simulate the response of all four key process variables: the bulk phenol concentration, the suspended biomass concentration, the concentration profile of the substrate in the biofilm and the biofilm thickness. Accurate model predictions required the use of kinetics, determined using cells which were not acclimated to the post‐shock reactor conditions (‘unacclimated’ cells) and the implementation of a specific‐growth‐rate suppression factor to account for the unbalanced growth situations experienced during the transient response periods.     

Production of Hexanoic Acid by Free and Immobilised Cells of Megasphaera elsdenii: Influence of in-situ Product Removal Using Ion Exchange Resin

The objective of this work was to improve the production of hexanoic acid by the anaerobic rumen bacterium, Megasphaera elsdenii, using product removal and immobilised cell approaches. Hexanoic acid, the major product of glucose metabolism by M. elsdenii strain ATCC25940, was produced at concentrations of 2–3 g dm⁻³ in stirred batch cultures. With pH controlled manually at 7, maximum concentrations of hexanoic acid increased to 6–8 g dm⁻³ with yields (g product per g glucose used) of approximately 30%. When an anion exchange resin, Amberlite IRA 400, was added during early stages of culture to minimise product inhibition, growth was not impaired and cell lysis, which was commonly seen during the stationary phase in control fermentations, was prevented. The presence of resin in pH-controlled, stirred batch fermentations increased the rate of glucose consumption and doubled hexanoic acid productivity: the equivalent of 11 g dm⁻³ of hexanoic acid was made with an estimated yield of up to 39%. Cells were immobilised successfully in κ-carrageenan and, when cell densities in inocula were sufficiently high, rates of glucose consumption and product formation were similar to free cells. Including resin in cultures of immobilised cells had effects similar to those above. Using a fed-batch mode with immobilised cells cultured in the presence of resin further increased final concentrations of hexanoic acid (up to 19 g dm⁻³) but yields were lower (20–30%) and productivity did not increase. These results show that production of volatile fatty acids can be improved significantly by product stripping onto an anion exchange resin. © 1997 SCI.     

Zinc uptake by Streptomyces rimosus biomass using a packed‐bed column

The ability of Streptomyces rimosus biomass to bind zinc ions in batch mode was shown recently. The aim of this study was to determine the zinc uptake capacity by Streptomyces rimosus biomass in continuous mode. Bacterial biomass was able to bind more Zn(II) after pretreatment with sodium hydroxide (1 mol dm⁻³) than without treatment. The maximum adsorption capacity and the adsorption capacity at the saturation point calculated by means of both the exchange zone model and the Thomas model were practically identical of about 2.9 mg_Zn(II) g⁻¹_biomass. This result was lower than the batch adsorption capacity of Streptomyces rimosus, indicating that the packed‐bed is not the most appropriate process to exploit the bacterial biomass adsorption capacity. The effect of zinc concentration in the range of 10 to 200 mg_Zn(II) dm⁻³ on the biosorption capacity of the packed‐bed was not significant. Biomass regeneration with 0.1 mol dm⁻³ HCl gave a 90% recovery of the adsorbed Zn(II). © 1999 Society of Chemical Industry     

Selection and isolation of glucose-tolerant amylolytic Aspergillus by cyclic fed batch culture process

A simple cyclic fed batch culture system was developed for selection and subsequent isolation of glucose-tolerant Aspergillus niger strain. A culture medium which contained 1.2 g dm⁻³ of glucose was inoculated with a non-glucose-tolerant A. niger (K_i =20.25 g dm⁻³). A culture medium of higher glucose concentration (100 g dm⁻³ and 200 g dm⁻³) was fed at a rate equal to the rate of HN₄⁺ consumption by means of a pH control system. The maximum and minimum liquid levels in the fed batch culture vessel were determined by two liquid level detectors which activated and deactivated a harvest pump. The novelty of the selection system is that the frequency and pressure of selection increase gradually but continuously, and they are determined by the intrinsic potential of the culture. The process was fully automatic. An Aspergillus mutant which had a glucose inhibition constant of 3200 g dm⁻³ was isolated after six generations. The process should be particularly useful for screening filamentous microorganisms growing on novel substrates or tolerating inhibitors.