Removal of toluene from air streams using a gas–liquid–solid three‐phase airlift loop bioreactor containing immobilized cells

Toluene, a kind of volatile organic compound (VOC), is widely used as a solvent (paints and coatings, gums, resins, rubber) as well as a reagent (medicines, dyes, perfumes) and is one of the components of gasoline. Over the more recent decades, many studies have led to the development of biological methods to treat toluene. This paper presents the results of a study on the treatment of airborne toluene using a laboratory‐scale gas–liquid–solid three‐phase airlift loop bioreactor containing immobilized cells. Based on the optimum operating conditions such as the temperature of 28–30 °C, pH of 7.0–7.2, and an empty bed residence time (EBRT) of 39.6 s, a continuous bioprocess showed that this immobilized airlift loop bioreactor had a steady‐state performance within 15 days, the outlet concentrations of toluene were lower than the national emission standard in China (GB 16297‐1996), and the chemical oxygen demand and NH₄⁺‐N of the effluent also satisfied the primary discharge standard in China (GB 8978‐1996). In addition, this immobilized airlift loop bioreactor had a good ability to tolerate shock loads, while the maximum elimination capacity of toluene was 168 g m^?3 h^?1 which was higher than those not only in biofilters and biotrickling filters but also in the airlift bioreactor with free microorganisms. Copyright © 2005 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     

Pretreatment of papermaking‐reconstituted tobacco slice wastewater by coagulation–flocculation

A study using coagulation–flocculation method for the treatment of papermaking‐reconstituted tobacco slice wastewater had been carried out. Polyaluminum chloride (PAC) and polyferric sulfate (PFS) as coagulants, and four kinds of polyacrylamides (PAMs) as flocculants, were employed during the coagulation–flocculation process. The effects of three factors, that is, the dosage of coagulants, the dosage of flocculants and pH on the treatment efficiency of the process were evaluated. The results showed that the efficiencies of PAC and PFS on the reduction of COD, ammonia nitrogen (NH₃‐N) and total suspended solids (TSS) in the treated effluents were equivalent; however, the efficiency of PAC on the color reduction was much higher than that of PFS. In the presence of PAC, a cationic polyacrylamide with very high molecular weight and low charge density (i.e., PAM4) was found to give the highest coagulation–flocculation efficiency. At the optimal conditions, that is, pH of 6.5, PAC dosage of 500 mg/L, and PAM4 dosage of 5 mg/L, the reductions of COD, NH₃‐N, color, and TSS in the process were found to be 70.8, 84.8, 72.3, and 98.5%, respectively. The study also showed that the PAC‐PAM4 scheme can remove the most of aluminum from the raw water. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1092‐1097, 2013     

Pilot‐scale demonstration of pre‐fermentation for enhancement of food‐processing wastewater biodegradability

A pilot‐scale anaerobic/aerobic ultrafiltration system was tested to treat high‐strength tomato‐processing wastewater, to achieve stringent dry‐ditch discharge criteria of soluble biochemical oxygen demand (SBOD) <10 mg dm^?3, total suspended solids <10 mg dm^?3, ammonia nitrogen <3 mg dm^?3 and soluble phosphorus <0.5 mg dm^?3. The anaerobic/aerobic system achieved 99.4% SBOD removal, 91.9% NH₃ N removal and 100% phosphorus removal at an overall hydraulic retention time of 1.5 days and solids retention time of 5 days during the tomato canning season. Respirometric studies confirmed that the pretreatment of tomato‐processing wastewater in the anaerobic reactor increased the readily biodegradable fraction, improved kinetics, and eliminated nutrient deficiency problem. Copyright © 2006 Society of Chemical Industry     

Improvement of the settling properties of Anammox sludge in an SBR

Biological systems for the treatment of wastewater have to provide optimum sludge retention to achieve high removal efficiencies. In the case of slow‐growing micro‐organisms, such as anaerobic ammonia‐oxidizing (Anammox) bacteria, episodes of flotation involving biomass wash‐out are especially critical. In this study a strategy based on the introduction of a mix period in the operational cycle of the Anammox Sequencing Batch Reactor (SBR) was tested for its effects on biomass retention and nitrite removal. Using this new cycle distribution the biomass retention inside the reactor improved as the solids concentration in the effluent of the SBR decreased from 20–45 to 5–10 mg VSS dm^?3 and the biomass concentration inside the reactor increased from 1.30 to 2.53 g VSS dm^?3 in a period of 25 days. A decrease of the sludge volume index (SVI) from 108 to 60 cm³ g VSS^?1 was also observed. Complete depletion of nitrite was achieved in the reactor only with the new cycle distribution treating nitrogen loading rates (g N‐NO₂^? + g N‐NH₄⁺ dm^?3 d^?1) up to 0.60 g N dm^?3 d^?1. Copyright © 2004 Society of Chemical Industry     

Preparation of sorbitol from D‐glucose hydrogenation in gas–liquid–solid three‐phase flow airlift loop reactor

A new process for D ‐glucose hydrogenation in 50 wt% aqueous solution, into sorbitol in a 1.5 m³ gas–liquid–solid three‐phase flow airlift loop reactor (ALR) over Raney Nickel catalysts has been developed. Five main factors affecting the reaction time and molar yield to sorbitol, including reaction temperature (T_R), reaction pressure (P_R), pH, hydrogen gas flowrate (Q_g) and content of active hydrogen, were investigated and optimized. The average reaction time and molar yield were 70 min and 98.6% under the optimum operating conditions, respectively. The efficiencies of preparation of sorbitol between the gas–liquid–solid three‐phase flow ALR and stirred tank reactor (STR) under the same operating conditions were compared. Copyright © 2004 Society of Chemical Industry     

Development of a membrane‐assisted hybrid bioreactor for ammonia and COD removal in wastewaters

A new membrane‐assisted hybrid bioreactor was developed to remove ammonia and organic matter. This system was composed of a hybrid circulating bed reactor (CBR) coupled in series to an ultrafiltration membrane module for biomass separation. The growth of biomass both in suspension and biofilms was promoted in the hybrid reactor. The system was operated for 103 days, during which a constant ammonia loading rate (ALR) was fed to the system. The COD/N‐NH₄⁺ ratio was manipulated between 0 and 4, in order to study the effects of different organic matter concentrations on the nitrification capacity of the system. Experimental results have shown that it was feasible to operate with a membrane hybrid system attaining 99% chemical oxygen demand (COD) removal and ammonia conversion. The ALR was 0.92 kg N‐NH₄⁺ m^?3 d^?1 and the organic loading rate (OLR) achieved up to 3.6 kg COD m^?3 d^?1. Also, the concentration of ammonia in the effluent was low, 1 mg N‐NH₄⁺ dm^?3. Specific activity determinations have shown that there was a certain degree of segregation of nitrifiers and heterotrophs between the two biomass phases in the system. Growth of the slow‐growing nitrifiers took place preferentially in the biofilm and the fast‐growing heterotrophs grew in suspension. This fact allowed the nitrifying activity in the biofilm be maintained around 0.8 g N g^?1 protein d^?1, regardless of the addition of organic matter in the influent. The specific nitrifying activity of suspended biomass varied between 0.3 and 0.4 g N g^?1 VSS d^?1. Copyright © 2004 Society of Chemical Industry     

Phenolic wastewater treatment in a three‐phase fluidised bed bioreactor containing low density particles

The treatment of phenolic wastewater was investigated in a gas–liquid–solid fluidised bed bioreactor containing polypropylene particles of density 910 kg m^?3. Measurements of chemical oxygen demand (COD) versus residence time (t) were performed for various ratios of settled bed volume to bioreactor volume (V_b/V_R) and air velocities (u) to determine the values of (V_b/V_R) and u for which the largest reduction in COD occurred. Optimal operation, corresponding to the largest COD removal, was attained when the bioreactor was controlled at the ratio (V_b/V_R) = 0.55 and an air velocity u = 0.036 m s^?1. Under these conditions, the value of COD was practically at steady state for times greater than 50 h. At this steady state, only about 50% COD removal was achieved in the treatment of a ‘raw’ wastewater (no mineral salts added), whereas in the operation with wastewater enriched in nutrient salts approximately 90% COD removal was attained. The following amount of mineral salts (mg dm^?3): (NH₄)₂SO₄—500; KH₂PO₄—200; MgCl₂—30; NaCl—30; CaCl₂—20; and FeCl₃—7, when added to wastewater before treatment, was sufficient for biomass growth. The application of low density particles (used as biomass support) in a bioreactor allowed the control of biomass loading in the apparatus. In the cultures conducted after change in (V_b/V_R) at a set u, the steady state mass of cells grown on the particles was achieved after approximately 6 days of operation. With change in u at a set (V_b/V_R), the new steady state biomass loading occurred after culturing for about 2 days. Phenolic wastewater was successfully treated in a bioreactor. In the operation conducted in a bioreactor optimally controlled at (V_b/V_R) = 0.55, u = 0.036 m s^?1 and t = 50 h, conversions greater than 99% were achieved for all phenolic constituents of the wastewater. Conversions of about 90% were attained for other hydrocarbons. Copyright © 2005 Society of Chemical Industry     

Fermentation optimization for the production of lovastatin by Aspergillus terreus: use of response surface methodology

A Box–Behnken experimental design was used to investigate the effects of five factors—ie oxygen content in the gas phase; concentrations of C, N and P; and fermentation time—on the concentrations of biomass and lovastatin produced in batch cultures of Aspergillus terreus. The values of the various factors in the experiment ranged widely, as follows: 20–80% (v/v) oxygen in the aeration gas; 8–48 g dm^?3 C‐concentration; 0.2–0.6 g dm^?3 N‐concentration; 0.5–2.5 g dm^?3 phosphate‐concentration; and 7–11 days fermentation time. No previous work has used statistical analysis in documenting the interactions between oxygen supply and nutrient concentrations in lovastatin production. The Box–Behnken design identified the oxygen content in the gas phase as the principal factor influencing the production of lovastatin. Both a limitation and excess of oxygen reduced lovastatin titers. A medium containing 48 g dm^?3 C supplied as lactose, 0.46 g dm^?3 N supplied as soybean meal, and 0.79 g dm^?3 phosphate supplied as KH₂PO₄, was shown to support high titers (～230 mg dm^?3) of lovastatin in a 7‐day fermentation in oxygen‐rich conditions (80% v/v oxygen in the aeration gas). Under these conditions, the culture medium had excess carbon but limiting amounts of nitrogen. The optimized fermentation conditions raised the lovastatin titer by four‐fold compared with the worst‐case scenario within the range of factors investigated. Copyright © 2004 Society of Chemical Industry     

Performance of the hydrolyzation film bed and biological aerated filter (HFB–BAF) combined system for the treatment of low‐concentration domestic sewage in south China

The performance of the hydrolyzation film bed and biological aerated filter (HFB–BAF) combined system in pilot scale (with a daily treatment quantity of 600–1300 m³ d^?1), operated for 234 days, for low‐strength domestic sewage was assessed using different amounts of aeration, reflux ratios and hydraulic loading rates (HLR). In steady state it was found that the average removal efficiency of chemical oxygen demand (COD) and biological oxygen demand at 5 days (BOD₅) were 82.0% and 82.2% and the average effluent concentrations were 15.8 mg L^?1 and 9.4 mg L^?1 respectively as the HFB was running at an HLR of 1.25–1.77 m³ m^?2 h^?1 and the BAF was running at an HLR of 1.56–2.21 m³ m^?2 h^?1. In general, the removal efficiency of total nitrogen (TN) fluctuated with the HLR, gas–water ratio and reflux ratio, so the ratio of gas to water should be controlled from 2:1 to 3:1 and the reflux ratio should be as high as possible. The effluent concentration of TN was 10.4 mg L^?1 and the TN removal averaged 34.3% when the gas–water ratio was greater than 3:1 and the reflux ratio was 0.5. The effluent concentration and removal efficiency of NH₄⁺‐N averaged respectively 2.3 mg L^?1 and 78.5%. The overall reduction of total phosphorus (TP) was 30% and the average effluent concentration was 0.95 mg L^?1. The removal efficiency of linear alkylbenzene sulfonates (LAS) reached 83.8% and the average effluent concentration was almost 0.9 mg L^?1. The effluent concentration and removal efficiency of polychlorinated biphenyls (PCBs) were 0.0654 µ g L^?1 and 37.05% respectively when the influent concentration was 0.1039 µ g L^?1. The excess sludge containing water (volume 15 m³) was discharged once every 3 months. The power consumption of aeration was 0.06–0.09 kWh of sewage treated. The results show that the HFB–BAF combined technology is suitable for the treatment of low‐concentration municipal sewage in south China. Copyright © 2005 Society of Chemical Industry     

Removal of trivalent chromium(III) from solution by biosorption in cork powder

The removal of trivalent chromium from solutions using biosorption in cork powder is described. The adsorption isotherm was determined, along with the effect of different variables, such as biomass particle size, solid–liquid ratio, reaction time, metal concentration and pH, on the efficiency of chromium removal. It was concluded that the adsorption is slow and favoured by an increase in pH. Therefore, using a solid–liquid ratio of 4 g dm^?3 it is possible to reduce the chromium concentration in the solution from 10 mg dm^?3 to less than 1.5 mg dm^?3 in 2 h at 22 °C. The kinetic studies verified that the sorption of chromium by cork was described by a second‐order model. The elution results showed that 50% of the chromium bound to the cork was eluted using 0.5 mol dm^?3 H₂SO₄ and that cork maintains its binding capacity over four cycles of biosorption/elution. © 2002 Society of Chemical Industry     

Application of the Stover–Kincannon kinetic model to nitrogen removal by Chlorella vulgaris in a continuously operated immobilized photobioreactor system

BACKGROUND: The aim of this study was to evaluate the ammonium nitrogen removal performance of algae culture Chlorella vulgaris in a novel immobilized photobioreactor system under different operating conditions and to determine the biokinetic coefficients using the Stover–Kincannon model. RESULTS: The photobioreactor was continuously operated at different initial ammonium nitrogen concentrations (NH₄‐N₀ = 10–48 mg L⁻¹), hydraulic retention times (HRT = 1.7–5.5 days) and nitrogen/phosphorus ratios (N/P = 4/1–13/1). Effluent NH₄‐N concentrations varied between 2.1 ± 0.5 mg L⁻¹ and 26 ± 1.2 mg L⁻¹ with increasing initial NH₄‐N concentrations from 10 ± 0.6 mg L⁻¹ to 48 ± 1.8 mg L⁻¹ at θ_H = 2.7 days. The maximum removal efficiency was obtained as 79 ± 4.5% at 10 mg L⁻¹ NH₄‐N concentration. Operating the system for longer HRT improved the effluent quality, and the percentage removal increased from 35 ± 2.4% to 93 ± 0.2% for 20 mg L⁻¹ initial NH₄‐N concentration. The N/P ratio had a substantial effect on removal and the optimum ratio was determined as N/P = 8/1. Saturation value constant, and maximum substrate utilization rate constant of the Stover–Kincannon model for ammonium nitrogen removal by C. vulgaris were determined as K_B = 10.3 mg L⁻¹ d⁻¹, U_max = 13.0 mg L⁻¹ day⁻¹, respectively. CONCLUSION: Results indicated that the algae‐immobilized photobioreactor system had an effective nitrogen removal capacity when the operating conditions were optimized. The optimal conditions for the immobilized photobioreactor system used in this study can be summarized as HRT = 5.5 days, N/P = 8 and NH₄‐N₀ = 20 mg L⁻¹ initial nitrogen concentration to obtain removal efficiency greater than 90%. Copyright © 2008 Society of Chemical Industry     

Biological Nutrient Removal Using a Novel Laboratory‐Scale Twin Fluidized‐Bed Bioreactor

The capability of biological nutrient removal from wastewater of a novel laboratory‐scale twin fluidized‐bed bioreactor (TFBBR) was studied. The work showed approximately 96 % organic matter, 84 % nitrogen, and 12 % phosphorus removal efficiencies in the first three phases of the study at influent synthetic municipal wastewater (SMW) flow rates of 150, 190, and 240 L/d, with corresponding organic loading rates of 1.3, 1.7, and 2.3 kg COD m^–3 d^–1 and nitrogen loading rates of 0.14, 0.18 and 0.25 kg N m^–3 d^–1. The TFBBR effluent was characterized by <1.0 mg NH₄‐N/L, <4.3 mg NO₃‐N/L, <6 mg TN/L, <6 mg SBOD/L, and 6–10 mg VSS/L. For the three phases, biomass yields of 0.06, 0.066, and 0.071 g VSS/g COD were observed, respectively, which was a significant further reduction in yield compared to the liquid‐solid circulating fluidized‐bed bioreactor technology developed and patented by this research group, of 0.12–0.16 g VSS/g COD. The very low yield was due to a longer solid retention time of 72–108 d.     

An alternative for pre‐treatment of high‐strength raw whey wastewaters: submerged membrane bioreactors

The direct treatment of whey wastewater at various sludge ages (10–75 days) and high biomass concentration (above 50 g mixed liquor suspended solid (MLSS) dm^?3) in a submerged membrane bioreactor (sMBR) is described. The chemical oxygen demand (COD) of raw whey varied in the range of 60 and 90 g dm^?3. After feeding the sMBR with raw whey, effluent COD reduced to about 20 g dm^?3. The effluent was free of suspended solids and total coliform bacteria. Total phosphorus (TP) and orthophosphate (Ortho‐P) in the influent varied between 204 and 880 mg dm^?3 and between 180 and 620 mg dm^?3, and effluent TP and Ortho‐P reduced to 113 and 109 mg dm^?3, respectively. The ammonium and nitrate concentrations in the influent were in the ranges of 3.4 and 120 mg dm^?3 and 10 and 503 mg dm^?3, respectively. The effluent ammonium concentration varied between 17.6 and 198 mg dm^?3 and nitrate concentrations varied between 0.9 and 69 mg dm^?3. Effluent turbidity varied between 23 and 111 FAU (Formazin Attenuation Unit). The results show that sMBR is an effective pre‐treatment system for high‐strength agro‐wastewaters because of its ability to reduce the pollution load. Copyright © 2004 Society of Chemical Industry     

Performance evaluation of the anaerobic fluidised bed system: I. Substrate utilisation and gas production

COD removal efficiencies in the range 75 to 98% were achieved in an anaerobic fluidised bed system designed for the recovery of methane from liquid wastes, when evaluated at COD loadings of between 5.8 to 108 kg m^?3 day^?1, hydraulic retention times of between 4.45 to 8 h, and feed COD concentrations of beween 480 to 9 000 mg dm^?3. More than 90% of feed COD could be removed up to COD loadings of about 40 kg m^?3 day^?1. Up to around 300 dm² of methane were produced per kg COD removed and this methane production rate was independent of the COD loadings applied in this investigation. Volatile acid concentration in the reactor increased sharply at a COD loading of about 40 kg m^?3 day^?1 and therefore, sufficient alkalinity should be provided to prevent pH from dropping to the undesirable level. The anaerobic fluidised bed system can be operated at a significantly higher liquid throughputs while maintaining its excellent efficiency.     

Simultaneous organic carbon and nitrogen removal in an SBR controlled at low dissolved oxygen concentration

Simultaneous organic carbon and nitrogen removal was studied in a sequencing batch reactor (SBR) fed with synthetic municipal wastewater and controlled at a low dissolved oxygen (DO) level (0.8 mg dm^?3). Experimental results over a long time (120 days) showed that the reactor achieved high treatment capacities (organic and nitrogen loading rates reached as high as 2.4 kg COD m^?3 d^?1 and 0.24 kg NH₃‐N m³ d^?1) and efficiencies (COD, NH₃‐N and total nitrogen removal efficiencies were 95%, 99% and 75%). No filamentous bacteria were found in the sludge even though the reactor had been seeded with filamentous bulking sludge. Instead, granular sludge, which possessed high activity and good settleability, was formed. Furthermore, the sludge production rate under low DO was less than that under high DO. Significant benefits, such as low investment and less operating cost, will be obtained from the new process. © 2001 Society of Chemical Industry     

Homogeneous liquid–liquid extraction using perfluorooctanesulfonic acid and calcium and its application to the separation and recovery of vitamin B12

A new phase separation phenomenon was observed in which the perfluorooctanesulfonate ion (PFOS⁻) and calcium ion form an ion‐pair associator and the sedimented liquid phase occurs from the homogeneous aqueous solution. This phenomenon was observed in the neutral pH region at room temperature (25 °C). The optimum concentration conditions for the reagents were [PFOS⁻]_T = 7 × 10⁻³ mol dm^‐3 and [Ca²⁺]_T = 1.1 mol dm^‐3. When these findings were applied to the homogeneous liquid–liquid extraction of vitamin B₁₂, the extraction percentage (E) was 83% and the concentration ratio (ie V_a/V_s, where V_a is the volume of the aqueous phase and V_s is the volume of the sedimented liquid phase) was a maximum of 149. The recovery of vitamin B₁₂ was achieved by adding the propanol–acetone (20 : 80 v/v%) mixed solvent to the sedimented liquid phase; the vitamin B₁₂ precipitated and was filtered. Both the PFOS⁻ and Ca²⁺ were removed by dissolution in the mixed solvent. The recovery percentage of vitamin B₁₂ was 78%. © 1999 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     

Model of simultaneous denitrification and methanogenesis in an Upflow Packed‐Bed Biofilm Reactor: Nitrogen compounds' inhibition and pseudo two‐dimensional biofilm model

BACKGROUND: The modelling of simultaneous denitrification and methanogenesis (DM) in upflow packed‐bed biofilm reactors (UPBR) and the effect of inhibition by nitrogen compounds on methanogenesis has received little attention. This study evaluated the effect using a model that incorporates a pseudo‐two‐dimensional biofilm model. RESULTS: The model was validated through comparison with experimental data, and achieved deviations below 5% for the liquid and gas phases. The model indicated that biomass stratification exists throughout the reactor and within the biofilm interior. At C/N ratios close to the stoichiometric C/N ratio, the process achieves efficiencies greater than 70% for nitrogen load rate (NLR) < 270 mg NO₃^?‐N dm^?3 h^?1. At high C/N ratios (50 mg total organic carbon (TOC) mg^?1 NO₃^?‐N), the process achieves efficiencies greater than 70% for organic load rate (OLR) < 83 mg TOC dm^?3 h^?1. CONCLUSION: The inclusion of the inhibition of methanogenesis by nitrogen compounds did not improve the predictions. Indeed, mass transfer in the biofilm was the phenomenon that most influenced the process. At C/N ratios close to the stoichiometric C/N ratio, process efficiency depends on the NLR; while at high C/N ratios, process efficiency depends on the OLR. Copyright © 2008 Society of Chemical Industry     

Ozone treatment of textile effluents and dyes: effect of applied ozone dose,pH and dye concentration

The ozonation of wastewater supplied from a treatment plant (Samples A and B) and dye‐bath effluent (Sample C) from a dyeing and finishing mill and acid dye solutions in a semi‐batch reactor has been examined to explore the impact of ozone dose, pH, and initial dye concentration. Results revealed that the apparent rate constants were raised with increases in applied ozone dose and pH, and decreases in initial dye concentration. While the color removal efficiencies of both wastewater Samples A and C for 15 min ozonation at high ozone dosage were 95 and 97%, respectively, these were 81 and 87%, respectively at low ozone dosage. The chemical oxygen demand (COD) and dissolved organic carbon (DOC) removal efficiencies at several ozone dose applications for a 15 min ozonation time were in the ranges of 15–46% and 10–20%, respectively for Sample A and 15–33% and 9–19% respectively for Sample C. Ozone consumption per unit color, COD and DOC removal at any time was found to be almost the same while the applied ozone dose was different. Ozonation could improve the BOD₅ (biological oxygen demand) COD ratio of Sample A by 1.6 times with 300 mg dm^?3 ozone consumption. Ozonation of acid dyes was a pseudo‐first order reaction with respect to dye. Increases in dye concentration increased specific ozone consumption. Specific ozone consumption for Acid Red 183 (AR‐183) dye solution with a concentration of 50 mg dm^?3 rose from 0.32 to 0.72 mg‐O₃ per mg dye decomposed as the dye concentration was increased to 500 mg dm^?3. © 2002 Society of Chemical Industry