Effect of co‐contaminant phenol on performance of a laboratory‐scale RBC with algal‐bacterial biofilm treating petroleum hydrocarbon‐rich wastewater

BACKGROUND: Hydrocarbon degradation by algal‐bacterial systems has advantages over degradation by conventional heterotrophic systems. However, oily wastewaters often contain co‐contaminants that may inhibit the degradation of total petroleum hydrocarbons (TPH), leading to system failure. RESULTS: This paper reports the effect of phenol on treatment of wastewater containing petroleum hydrocarbons, i.e. diesel oil in a lab‐scale rotating biological contactor with biofilm consisting predominantly of Burkholderia cepacia and a freshwater algal culture. The effect of phenol loading from 0.11–0.69 g phenol m^?2 d^?1 on diesel degradation was studied with 21 h hydraulic retention time and TPH loading of 27.33 g TPH m^?2 d^?1. With increase in phenol loading, complete removal of phenol was observed. However, TPH removal decreased from 99% to 94% and significant decrease in TCOD removal was observed possibly due to biomass growth in suspension. Presence of algal culture in the biofilm made it feasible to operate the RBC at a high organic loading. The benefits included better immobilization of the bacterial culture, release of oxygen and generation of alkalinity. Lowering in pH due to accumulation of acidic intermediates formed during oil biodegradation was not observed in this study. CONCLUSION: This system can be recommended for treatment of industrial wastewaters containing TPH and phenols, with proper handling of biosolids. Copyright © 2010 Society of Chemical Industry     

Study of saline wastewater influence on activated sludge flocs through automated image analysis

BACKGROUND: In activated sludge systems, sludge settling ability is considered a critical step in effluent quality and determinant of solid–liquid separation processes. However, few studies have reported the influence of saline wastewater on activated sludge. This work aims the evaluation of settling ability properties of microbial aggregates in a sequencing batch reactor treating saline wastewaters of up to 60 g L^?1 NaCl, by image analysis procedures. RESULTS: It was found that the sludge volume index (SVI) decreased with salt content up to 20 g L^?1, remaining somewhat stable above this value. Furthermore, it was found that between the first salt concentration (5 g L^?1) and 20 g L^?1 aggregates suffered a strong deflocculation phenomenon, leading to a heavy loss of aggregated biomass. Regarding SVI prediction ability, a good correlation coefficient of 0.991 between observed and predicted SVI values was attained. CONCLUSION: From this work the deflocculation of aggregated biomass with salt addition due to pinpoint floc formation, dispersed bacteria growth and protozoa absence could be established. With respect to SVI estimation, and despite the good correlation obtained, caution is advisable given the low number of SVI data points. Copyright © 2008 Society of Chemical Industry     

Anaerobic digestion of olive mill wastewater in a periodic anaerobic baffled reactor (PABR) followed by further effluent purification via membrane separation technologies

BACKGROUND: The combined treatment of olive mill wastewater (OMWW) by applying the anaerobic digestion process and further treatment in a system consisting of filters and membranes is presented. The anaerobic digestion of the OMWW took place in a high rate system, the periodic anaerobic baffled reactor (PABR). Application of the membrane system aimed at purifying the anaerobic effluent. RESULTS: An increase in the organic loading rate was achieved by increasing the influent chemical oxygen demand (COD) and alternatively by decreasing the hydraulic retention time (HRT). The first option caused process failure, since the volatile fatty acids accumulation resulted in negligible biogas production. In contrast, the second change (decrease in HRT) led to stable operation that permitted the reduction of the HRT to 3.75 d and increase of the organic loading rate to 8.9 g tCOD L^?1 d^?1 with satisfactory total COD removal (72%). Higher total COD removal (up to 80%) was observed at lower organic loading rates (<3.5 g tCOD L^?1 d^?1). Further purification in the membrane units resulted in a final permeate of less than 0.1 g tCOD L^?1. The membrane systems proved to be more efficient on the anaerobic effluent than on the raw OMWW (the final permeate in that case contained 1g tCOD L^?1). CONCLUSIONS: The anaerobic digestion of OMWW in a PABR was stable even at high organic loading rates. Filtering and membrane fractionation of the PABR effluent resulted in a final permeate stream of high quality, suitable for irrigation and/or reuse in the proposed operating scheme for diluting the OMWW prior to anaerobic digestion. Copyright © 2009 Society of Chemical Industry     

厌氧膜生物反应器及其膜污染探析

厌氧膜生物反应器(anaerobic membrane bioreactor,AnMBR)集厌氧生物技术和膜分离技术于一体,具有高负荷、低能耗、可回收沼气和高效截留等优点,在高浓度有机废水治理领域潜力巨大。然而,国内外关于AnMBR的工程运行参数较为欠缺。此外,膜污染问题是阻碍该工艺应用推广的重要致因,故其一直是AnMBR的研究热点。本文概述了AnMBR的工艺特征以及AnMBR的结构、组合方式及其特点,指出当前外置式应用较多,内置式因其特点也逐渐引起关注;综述了AnMBR及其组合工艺在国内外的工程应用现状,指出该技术多在实验室阶段,且于工程化方面国内落后于国外;探析了膜污染机理及其影响因素(膜组件、污泥特性和操作条件等影响因素)关于膜污染的作用机制;并总结了一些控制膜污染的典型预防和控制措施,以期为相关研究应用提供参考。     

Start‐up and enrichment of a granular anammox SBR to treat high nitrogen load wastewaters

BACKGROUND: Landfill leachate is characterized by low biodegradable organic matter that presents difficulties for the complete biological nitrogen removal usually performed by conventional biological nitrification/denitrification processes. To achieve this, the anaerobic ammonium oxidation (anammox) process is a promising biological treatment. This paper presents an anammox start‐up and enrichment methodology for treating high nitrogen load wastewaters using sequencing batch reactor (SBR) technology. RESULTS: The methodology is based on the gradual increase of the nitrite‐to‐ammonium molar ratio in the influent (from 0.76 to 1.32 mole NO₂^?‐N mole^?1NH₄⁺‐N) and on the exponential increase of the nitrogen loading rate (NLR, from 0.01 to 1.60 kg N m^?3 d^?1). 60 days after start‐up, anammox organisms were identified by polymerase chain reaction (PCR) technique as Candidatus Brocadia anammoxidans. After one year of operation, NLR had reached a value of 1.60 kg N m^?3 d^?1 with a nitrogen (ammonium plus nitrite) removal efficiency of 99.7%. The anammox biomass activity was verified by nitrogen mass balances with 1.32 ± 0.05 mole of nitrite removed per mole of ammonium removed and 0.23 ± 0.05 mole of nitrate produced per mole of ammonium removed. Also, enrichment of anammox bacteria was quantified by fluorescence in situ hybridization (FISH) analysis as 85.0 ± 1.8%. CONCLUSIONS: This paper provides a methodology for the enrichment of the anammox biomass in a SBR to treat high nitrogen loaded wastewaters. Copyright © 2007 Society of Chemical Industry     

Sustained nitrite accumulation in a membrane‐assisted bioreactor (MBR) for the treatment of ammonium‐rich wastewater

A membrane‐assisted bioreactor (MBR) for sustained nitrite accumulation is presented, treating a synthetic wastewater with total ammonium nitrogen (TAN) concentrations of 1 kg N m^?3 at a hydraulic retention time down to 1 day. Complete biomass retention was obtained by microfiltration with submerged hollow fibre membranes. A membrane flux up to 189.5 dm³ day^?1 m^?2 could be maintained at a suction pressure below 100 kPa. Nitrification was effectively blocked at the nitrite stage (nitritation), and nitrate concentration was less than 29 g N m^?3. The rate of aeration was reduced to obtain a mixture of ammonium and nitrite, and after adjusting this rate the TAN/NO₂‐N ratio in the reactor effluent was kept around unity, making it suitable for further treatment by anaerobic oxidation of ammonium with nitrite. After increasing again the rate of aeration, complete nitrification to nitrate recovered after 11 days. It is suggested that nitrite accumulation resulted from a combination of factors. First, the dissolved oxygen (DO) concentration in the reactor was always limited with concentrations below 0.1 g DO m^?3, thereby limiting nitrification and preventing significant nitrate formation. The latter is attributed to the fact that ammonium‐oxidising bacteria cope better with low DO concentrations than nitrite oxidisers. Second, the MBR was operated at a high ammonia concentration of 7–54 g N m^?3, resulting in ammonia inhibition of the nitrite‐oxidising microorganisms. Third, a temperature of 35 °C was reported to yield a higher maximum growth rate for ammonium‐oxidising bacteria than for nitrite‐oxidising bacteria. Nitrite oxidisers were always present in the MBR but were out‐competed under the indicated process conditions, which is reflected in low concentrations of nitrate. Oxygen limitation was shown to be the most important factor to sustain nitrite accumulation. Nevertheless, nitritation was possible at ambient temperature (22–24 °C), lower ammonia concentration (<7 g N m^?3) and when using raw nitrogenous wastewater containing some biodegradable carbon. Overall, application of the MBR for nitritation was shown to be a reliable technology. © 2003 Society of Chemical Industry     

Cleaning secondary effluents with organoclays and activated carbon

BACKGROUND: Flocculation, adsorption and ultrafiltration, alone and in combination, were tested for tertiary treatment of Beer Sheva (southern Israel) municipal wastewater. The focus was on the adsorption of soluble organics with powdered activated carbon (PAC) and with organoclays. RESULTS: Adsorption on 0.6 g L^?1 octadecyltrimethylammonium bromide (ODTMA) ‐ bentonite and flocculation with 130 mg L^?1 FeCl₃ reduced the dissolved organic carbon (DOC) level by 46%, and that was the highest DOC retention obtained with the organoclays. Retention achieved with 0.6 g L^?1 PAC and 130 mg L^?1 FeCl₃ was 65%. Filtration through a more hydrophobic PVDF‐30 membrane for 30 min resulted in 35–40% flux drop. A reasonable 6–7% flux reduction was obtained with filtration through a more hydrophilic PS‐50 membrane. CONCLUSION: Oganoclays at low doses are a good target adsorbent for single low molecular weight molecules. On average, higher TOC retention was achieved with PAC. Introduction of adsorption as a pre‐treatment step can lead to minimization of flux losses, reduced demand for flocculation and improved economics of the entire treatment. Copyright © 2011 Society of Chemical Industry     

Electrolytic reduction improves treatability of humic acids containing water streams

BACKGROUND: An understanding of the structure of humic acids is essential for their degradation or physical removal from wastewaters. This work aims at targeting the reactivity of these molecules by modifying their properties. Structural alterations were carried out by electrolytically reducing the solution containing humic acid in an electrolytic cell to convert them into less polar structures. RESULTS: Overall it was observed that electrolytic reduction of humic acids strongly facilitated their further treatability. First, the reduced forms of humic acids exhibited improved adsorption on activated carbon. For 1 kW h of electrical energy consumed during electrolytic reduction, the additional chemical oxygen demand (COD) adsorbed was 60 g for a synthetic humic acid solution. Similarly, the additional COD adsorbed (kW h)^?1 was found to be 35 g and 112 g for humic acid‐rich effluent and landfill leachate, respectively. In comparison with non‐reduced control samples, a 200‐fold decrease in the chloroform formation was observed when electrolytically reduced drinking water samples were supplemented with a chlorine dosage of 150 mg L^?1. Moreover, an enhanced membrane flux was obtained with electrically reduced samples, indicating their improved membrane filterability. CONCLUSION: The electrolyzed humus species were characterized by analyzing their surface tension and particle size. This work addresses an alternative technology for the treatment of water streams containing humic acids. Copyright © 2007 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     

Filtration process cost in submerged anaerobic membrane bioreactors (AnMBRs) for urban wastewater treatment

The objective of this study was to evaluate the effect of the main factors affecting the cost of the filtration process in submerged anaerobic membrane bioreactors (AnMBRs) for urban wastewater (UWW) treatment. Experimental data for CAPEX/OPEX calculations was obtained in an AnMBR system featuring industrial-scale hollow-fiber (HF) membranes. Results showed that operating at J₂₀ slightly higher than the critical flux results in minimum CAPEX/OPEX. The minimum filtration process cost ranged from €0.03 to €0.12 per m³, mainly depending on SGD_m (from 0.05 to 0.3 m³·m^?2·h^?1) and MLSS (from 5 to 25 g·L^?1). The optimal SGD_m resulted in approx. 0.1 m³·m^?2·h^?1.     

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.     

Synthesis,characterization and performance evaluation of an optimized ceramic membrane with physical separation and photocatalytic degradation capabilities

The main goal of the present study is synthesis, characterization and performance evaluation of an optimized photocatalytic ceramic membrane for wastewater treatment. It consists of three layers including alumina (Al₂O₃) macroporous support, colloidal titania (TiO₂) mesoporous intermediate layer and polymeric TiO₂ mesoporous top layer in order to obtain a pore gradient from the support through the top layer of membrane. The colloidal and polymeric TiO₂ layers were prepared via the sol-gel method and coated using sol dip-coating approach. In order to optimize the membrane, physical separation and photocatalytic degradation capabilities of each colloidal and polymeric layer as a function of time were evaluated using Rhodamine B (RhB) aqueous solution. Thus, optimum coating number of intermediate layer and top layer were determined. Also, the performance of the optimized membrane was investigated via oily wastewater treatment using crude oil and water emulsion. Based on the performance results, two consequence colloidal layers and one polymeric layer were considered as the optimum layer number. Also, RhB photocatalytic degradation was 24.7% and RhB physical separation and permeation flux were 40.4% and 25.7?kg?m^?2 h^?1, respectively. Furthermore, based on the oily wastewater treatment experiments, permeation flux and chemical oxygen demand (COD) rejection at the best-operating conditions (pressure of 5?bar, the temperature of 30?°C and cross flow of 600?l?h^?1) were 29.1?kg?m^?2 h^?1 and 78.4%, respectively. The prepared membrane was found efficient and exhibited high industrial potential due to its multifunctional capability and thus can be employed as an advanced material for wastewater treatment applications.     

Removal of oxytetracycline (OTC) in a synthetic pharmaceutical wastewater by sequential anaerobic multichamber bed reactor (AMCBR)/completely stirred tank reactor (CSTR) system: biodegradation and inhibition kinetics

BACKGROUND: The antibiotics in industrial and munipical wastewaters could not be removed effectively in conventional anaerobic and aerobic biological treatment plants. Few studies have been performed to investigate the biodegradation and inhibition kinetics of oxytetracycline (OTC) on methanogens and total volatile fatty acids (TVFA). RESULTS: A high rate anaerobic multichamber bed reactor (AMCBR) was effective in removing the molasses‐chemical oxygen demand (COD), and the OTC antibiotic with yields as high as 96% at an influent OTC loading rate of 133.33 gOTC m^?3 day^?1 at a hydraulic retention time (HRT) of 2.25 days. Increasing the OTC loading rates from 22.22 gOTC m^?3 day^?1 to 133.33 gOTC m^?3 day^?1 improved both hydrolysis and specific utilization of molasses‐COD. The inhibition constants of TVFA (K_I?TVFA?meth) and OTC (K_I?OTC?meth) on methanogens decreased at OTC loadings > 133.33 gOTC m^?3 day^?1. The direct effect of OTC loadings > 133.3 gOTC m^?3 day^?1 on acidogens and methanogens was evaluated using the Haldane inhibition kinetic. CONCLUSION: OTC antibiotic was effectively removed in a sequential AMCBR/completely stirred tank reactor (CSTR). The Haldane inhibition constant (K_ID) decreased significantly at high OTC loads indicating the increase in toxicity. Copyright © 2012 Society of Chemical Industry     

Removal of phosphorus from anaerobic membrane bioreactor effluent by ion exchange resin

The adsorption and regeneration mechanisms of phosphorus in anaerobic membrane bioreactor (AnMBR) effluent by anion exchange resins were investigated in this study. A strongly basic anion exchange resin (Amberlite IRA958) was selected due to its higher exchange capacity and antifouling performance. The effects of wastewater compounds, flow rate, and bed height of dynamic ion exchange column were determined. The dynamic ion exchange column exhibited stable treatment capacity and high exchange/regeneration capacity for phosphorus for long-term operation. However, humic acid could not be entirely regenerated by NaCl solution and the optimal regeneration protocol needs further investigations.     

Carbon credit and emission trading: Anaerobic wastewater treatment

The concept of carbon credit arose out of increasing awareness of the need to reduce emissions of greenhouse gases to combat global warming which was formalized in the Kyoto Protocol. In addition to contribution to sustainable development with energy recovery in the form of methane, carbon credits can be claimed by application of advanced anaerobic processes in wastewater treatment for reducing emissions of greenhouse gases. As anaerobic granular systems are capable of handling high organic loadings concomitant with high strength wastewater and short hydraulic retention time, they could render much more carbon credits than other conventional anaerobic systems. Granular anaerobic processes have become an attractive choice of treatment technology especially for high strength wastewaters, considering the fact that in addition to efficient waste degradation, the carbon credits can be used to generate revenue and to finance the project. This paper presents a scenario on emission reduction based on a methane recovery and utilisation project. An example analysis on emission reduction and the future trend is also outlined.     

Effect of oxygen transfer rates on alcohols production by Candida guilliermondii cultivated on soybean hull hydrolysate

BACKGROUND: In this research the use of soybean hull hydrolysate (SHH) as substrate for xylitol and ethanol production using an osmotolerant strain of Candida guilliermondii was studied. The production of alcohols was investigated in batch cultivations in which the variable parameter was the volumetric oxygen mass transfer coefficient (k_La) obtained from three different conditions of air supply: anaerobic (150 rpm, no aeration); microaerobic (300 rpm, 1 vvm), and aerobic (600 rpm, 2 vvm), corresponding to k_La values of 0; 8; and 46 h^?1, respectively. RESULTS: SHH, although presenting a very high osmotic pressure (1413 mOsm kg^?1), was completely metabolized under aerobic conditions with high biomass productivities of 0.49 g cells (L h)^?1, with little formation of ethanol. Xylitol was produced under microaeration, with product yield of 0.22 g g^?1 xylose, with the formation of glycerol as a by‐product. No xylose was metabolized under anaerobic conditions, but ethanol was produced from hexoses with high product yields of 0.5 g g^?1. CONCLUSION: These results suggest that the hydrolysis of soybean hull and its conversion to ethanol and other alcohols could be an important use of this agro‐industrial waste, which could be used for biofuel, xylitol or biomass production, depending on the aeration conditions of the cultures. Copyright © 2008 Society of Chemical Industry     

Effect of inhibitory compounds on the anaerobic digestion performance of diluted wastewaters from the alimentary industry

BACKGROUND: Up to now the effect of inhibitory compounds on the anaerobic digestion performance of urban and industrial wastewaters has been mostly studied in fluidized bed and upflowing anaerobic sludge blanket (UASB) bioreactors but not in upflow packed‐bed biodigesters. RESULTS: In this paper, response surface methodology (RSM) was used to quantify the effect of various inhibitory compounds (olive oil, ethanol and phenol) on chemical oxygen demand (COD) removal and biogas production rate from synthetic solutions and real industrial wastewaters by anaerobic digestion. The synthetic solutions possessed the same composition in these inhibitory compounds as diluted effluents from olive oil mill and winery industries. The process was performed in a laboratory scale digester containing anaerobic sludge from the Urban Reclamation Station of Toledo (Spain). The comparison of both individual factors and interactions between factors showed that the addition of olive oil at moderate concentrations (up to 0.5% w/w) did not change the performance of the process in comparison with that observed when feeding to the system a model solution (51.5% COD removal, 0.65 L biogas day^?1). However, low concentrations of ethanol or phenol (250 and 150 mg L^?1, respectively) almost completely inhibited the methanogenic phase. Moreover, a strong interaction between ethanol and phenol concentrations on COD removal was observed. CONCLUSION: The experimental results showed quantitatively the importance of some inhibitory compounds on anaerobic treatment of both synthetic solutions and real wastewaters from olive oil mill and winery industries. Inhibitory effects are closely related to both the organic loads and the anaerobic bioreactor used. Copyright © 2009 Society of Chemical Industry     

Strategies to optimize phosphate removal from industrial anaerobic effluents by magnesium ammonium phosphate (MAP) production

BACKGROUND: Owing to more stringent phosphate discharge requirements and the increasing prices of fertilizers, beneficial recovery and reuse of phosphate from industrial anaerobic effluents is becoming an important issue. Phosphate recovery by struvite or magnesium ammonium phosphate (MAP) permits its recycling in the fertilizer industry because struvite is a valuable slow release fertilizer. Two different approaches to MAP crystallization depending on initial levels of phosphate in the wastewaters were tested and compared. RESULTS: For low‐phosphate‐containing anaerobic effluents (<30 mg PO₄^3?‐P L^?1), a novel approach using ureolytic induced MAP formation with MgO addition appeared to be suitable. The residual phosphate concentrations in the effluent ranged from 5 to 7 mg PO₄^3?‐P L^?1 and the separated matter contained residual amounts of Mg(OH)₂. High‐phosphate‐containing anaerobic effluents (100 to 120 mg PO₄^3?‐P L^?1) were treated efficiently using air stripping combined with MgCl₂ and NaOH reagents, yielding residual phosphate levels of 8 to 15 mg PO₄^3?‐P L^?1 and spherical pure MAP crystals of 0.5 to 2 mm. CONCLUSION: Results show that depending on the initial phosphate concentrations in the wastewaters and the ammonium and magnesium levels, the strategy selected for struvite crystallization is a determinative factor in achieving a cost effective technology. Copyright © 2008 Society of Chemical Industry     

Kinetic Modeling of Styrene Biodegradation by Rhodococcus erythropolis PTCC 1767: Effect of Adaptation to Styrene and Initial Biomass Concentration

Styrene is found at high concentrations in many petrochemical wastewaters and, due to its toxicity, has to be removed from these wastewaters before their discharge. Biological treatment of these wastewaters using pure or mixed microbial cultures that remove styrene through biodegradation has many advantages compared to physic-chemical processes. However, the growth of most of pure or mixed microbial cultures used previously for biodegradation of styrene is retarded at relatively low styrene concentration. In this study, the biodegradation of styrene by Rhodococcus erythropolis PTCC 1767 was considered. The effect of initial biomass concentrations (X), in the range 0.31 gL^?1 and 2.2 gL^?1, and exposure of R. erythropolis to styrene-containing media–on the kinetics of styrene biodegradation was studied.

The results of kinetic showed that, for runs at X?=?2.2 gL^?1, the kinetic data were satisfactorily fitted to the Monod model although the Haldane model gave a better fit of the kinetic data at all initial values of X. The results of kinetic modeling also showed that, with increase in X, the maximum specific removal rate (q_m) decreased whereas the threshold styrene concentration S_threshold increased. On the other hand, the exposure of the bacterial population to successive media in which styrene concentration was increased in a stepwise manner resulted in increase in the values of both q_m and S_threshold. The results of the present study showed the good potential of R. erythropolis for biodegradation of styrene in petrochemical wastewaters, although studies with real petrochemical wastewaters are needed to confirm this potential.     

Design and performance characterization of a new shear enhanced module with inbuilt cleaning arrangement

BACKGROUND: Shear enhanced membrane modules are becoming popular as they enable high permeate flux in almost all membrane filtration processes due to the high shear rate they generate at the membrane surface. In this article, the design of a new shear enhanced module with unique hydrodynamic cleaning facility is proposed. The device, presently at laboratory scale was named the Spinning Basket Membrane (SBM) module because of its inherent structural similarity with the well known Spinning Basket Reactor. An aqueous solution of polyethylene glycol was chosen as test fluid for the present study. RESULTS: The module was characterized under different parametric conditions of transmembrane pressure (TMP), feed concentration (C₀) and rotational speed of the basket (Ω). It was observed that with its inbuilt cleaning facility the module was able to restrict the flux decline to within 15% of its start up value, even after 21 h of continuous running, with a maximum initial flux as high as 612 L m^?2 h^?1. CONCLUSION: Based on the performance of the module, it may be concluded that this module could be scaled up for nearly uninterrupted industrial operation with reduced requirement for chemical cleaning, which is rare in the membrane industry to date. Copyright © 2012 Society of Chemical Industry