Optimal design of membrane processes. A problem of choices between process layout, operating conditions and adopted control system

The development of membrane processes as a technology for environmental treatment applications and in particular for the purification of wastewater streams has significantly increased in the last decades. Fouling on membranes appears to be one of the main technical limit of this technology. This phenomenon causes the unavoidable deposition of particles on the membrane surface, building a resistive growing layer to permeability. Sensible fouling of the membrane leads to a significant reduction of the performances, a decrease of the operating life and, as a consequence, the increase of the operational costs due to the replacement or cleaning of the exhausted membrane modules. The presence of the fouling phenomena makes the proper design and control of membrane systems a difficult task. Optimal design of the membrane processes will be here discussed. The procedure requires to determine the optimal process layout given the input data and target requirements. At the end, the required membrane area is calculated. This latter property is strictly dependant of the adopted operating conditions, most importantly by the adopted value of transmembrane pressure (TMP). Moreover, it depends if the value of TMP remain fixed as a function of time or is variable (as in case of fixed permeate flow rates). Therefore, the optimal design of the system may occur only if the adopted control strategy is defined a priori. As a consequence, design choices of the membrane process layout, operating condition and adopted control system are strictly dependant, and connections between these different aspects should not be neglected during the engineering and P & I development stage of membrane systems. This paper will start from the theory of the boundary flux, in order to describe a novel design approach to membrane systems. Parallel to this, the development of an advanced control system, that allows to limit fouling formation during operation, is presented. The advanced control system relies on a suitable simulation software capable to predict the boundary flux, that changes the controller's set-points accordingly. Finally, the paper will merge all elements together, and report about the optimal design of membrane processes equipped with the advanced membrane process control system; validation of the proposed approach will be based on the use of a custom simulation model in ASPEN HYSYS and by experiments on lab scale

Optimization study of the fouling build-up on a RO membrane for pretrated olive mill wastewater purification

Even though membranes are considered in many aspects a mature technology, a range of features are still in development and under investigation. Regarding this, the main handicap of this technology is inevitably membrane fouling. Fouling issues have investigated by many research groups in the last years to convince investors to implement membranes as substitutes of a range of unit operations at industrial scale. In the wastewater treatment field, this is especially problematic, given the low economic value of the product, that is, treated water. On another hand, the management of the effluents generated by olive oil industries, olive mill wastewaters (OMW), is a task of global concern not anymore constrained to a specific region. These wastewaters represent an ever-increasing problem still unresolved. The present work was aimed for the modelling and optimization of a reverse osmosis (RO) membrane operation for the purification of pretreated olive mill wastewater, with a focus on the dynamic fouling development minimization on the selected membrane as a function of the set-up of the operating conditions. For this goal, beforehand a factorial design was implemented for the optimization of the RO treatment of the OMW stream. The results gathered were thereafter interpreted by means of the response surface methodology. A significant impact was noted to be driven by the operating pressure and the tangential velocity on the fouling rate on the RO membrane. The response surfaces withdrawn from the experimental data support the previous results, and the optimised parameters - ambient temperature range (24 - 25 °C), moderate operating pressure (25 - 30 bar) and turbulent tangential flow (3.1 - 3.5 m s -1 ) - were found to provide a stable permeate flux of 32.3 - 38.5 L h -1 m -2 . These results reveal the proposed process could be operated successfully at ambient temperature conditions and medium operating pressure, boosting the economic efficiency of the RO purification of this effluent. Finally, the parametric quality standards stablished to reuse the purified effluent for irrigation purposes were checked and found to be satisfactory

Optimal design of membrane processes. A problem of choices between process layout, operating conditions and adopted control system

The development of membrane processes as a technology for environmental treatment applications and in particular for the purification of wastewater streams has significantly increased in the last decades. Fouling on membranes appears to be one of the main technical limit of this technology. This phenomenon causes the unavoidable deposition of particles on the membrane surface, building a resistive growing layer to permeability. Sensible fouling of the membrane leads to a significant reduction of the performances, a decrease of the operating life and, as a consequence, the increase of the operational costs due to the replacement or cleaning of the exhausted membrane modules. The presence of the fouling phenomena makes the proper design and control of membrane systems a difficult task. Optimal design of the membrane processes will be here discussed. The procedure requires to determine the optimal process layout given the input data and target requirements. At the end, the required membrane area is calculated. This latter property is strictly dependant of the adopted operating conditions, most importantly by the adopted value of transmembrane pressure (TMP). Moreover, it depends if the value of TMP remain fixed as a function of time or is variable (as in case of fixed permeate flow rates). Therefore, the optimal design of the system may occur only if the adopted control strategy is defined a priori. As a consequence, design choices of the membrane process layout, operating condition and adopted control system are strictly dependant, and connections between these different aspects should not be neglected during the engineering and P & I development stage of membrane systems. This paper will start from the theory of the boundary flux, in order to describe a novel design approach to membrane systems. Parallel to this, the development of an advanced control system, that allows to limit fouling formation during operation, is presented. The advanced control system relies on a suitable simulation software capable to predict the boundary flux, that changes the controller's set-points accordingly. Finally, the paper will merge all elements together, and report about the optimal design of membrane processes equipped with the advanced membrane process control system; validation of the proposed approach will be based on the use of a custom simulation model in ASPEN HYSYS and by experiments on lab scale

In vitro ion chelating, antioxidative mechanism of extracts from fruits and barks of tetrapleura tetraptera and their protective effects against fenton mediated toxicity of metal ions on liver homogenates

The aim of the present study was to investigate the antioxidant activity and protective potential of T. tetraptera extracts against ion toxicity. The antioxidant activity of the extracts was investigated spectrophotometrically against several radicals (1,1-diphenyl-2-picrylhydrazyl (DPPH•), 2,2′-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS•), hydroxyl radical (HO•), and nitric oxide (NO•)), followed by the ferric reducing power, total phenols, flavonoid, and flavonol contents. The effects of the extracts on catalase (CAT), superoxide dismutase (SOD), and peroxidase activities were also determined using the standard methods as well as the polyphenol profile using HPLC. The results showed that the hydroethanolic extract of T. tetraptera (CFH) has the lowest ICvalue with the DPPH, ABTS, OH, and NO radicals. The same extract also exhibited the significantly higher level of total phenols (37.24 ± 2.00 CAE/g dried extract); flavonoids (11.36 ± 1.88 QE/g dried extract); and flavonols contents (3.95 ± 0.39 QE/g dried extract). The HPLC profile of T. tetraptera revealed that eugenol (958.81 ± 00 mg/g DW), quercetin (353.78 ± 00 mg/g DW), and rutin (210.54 ± 00 mg/g DW) were higher in the fruit than the bark extracts. In conclusion, extracts from T. tetraptera may act as a protector against oxidative mediated ion toxicity. © 2015 Bruno Moukette Moukette et al

Kinetics and boundary flux optimization of integrated photocatalysis and ultrafiltration process for two-phase vegetation and olive washing wastewaters treatment

In many of the studies available on the treatment or fractionation by membrane technology of the effluents by-produced by olive oil factories, the problem of fouling is not correctly approached or not even addressed. In the present study, the operating framework of a spiral wound polymeric ultrafiltration (UF) membrane module was optimized by the boundary flux theory, which merges both the critical and threshold flux theories for simplification purpose and was formerly validated by the Authors. The raw wastewater, a mixture of olive washing and olive vegetation wastewaters, was pretreated by two processes developed in prior research: pH-temperature flocculation (pH-T F) and photocatalysis with lab-made ferromagnetic-core titanium dioxide nanoparticles under ultraviolet light (UV/TiO2 PC). The organic matter removal during UV/TiO2 PC fitted accurately a two-step first-order kinetic model. Also, the proposed boundary model fits the membrane experimental data with accuracy. Higher boundary flux values were confirmed for batch UF when the feedstream is further pretreated by UV/TiO2 PC (23.3-23.6% increment), and also slightly higher feed recovery and significant minor sub-boundary fouling index a. Moreover, the higher rejection of the organic pollutants (53.3%) permits achieving the standard limits to reutilize the purified effluent for irrigation purposes

Boundary flux optimization of a nanofiltration membrane module used for the treatment of olive mill wastewater from a two-phase extraction process

The boundary flux theory was used to modelize the performance of a nanofiltration (NF) membrane in the treatment of the effluents exiting a two-phase olive oil extraction process, in particular olive mill (OMW) and olives washing (OWW) wastewater streams. The results obtained from the pressure-cycling experiments exhibit a boundary flux pattern with very low long-term fouling for all analyzed feedstocks. This observation is confirmed by the low values of the sub-boundary fouling parameter (α) obtained by the fitting of the experimental flux data measured during batch-run operation to the boundary flux model. Reduced long-term fouling (28.6-33.3%) occurred during NF operation of the effluents after the proposed secondary treatment, which comprised pH-temperature flocculation followed by ultraviolet (UV) photocatalysis with ferromagnetic-core nanocatalyst and an ultrafiltration separation step (UF). Otherwise, a decrease of long-term fouling in the range of 57.1-60% was observed by using the secondary-treated 1:1 (v/v) mixture of OMW and OWW as feedstock. Moreover, processing both feedstocks to the complete secondary treatment led to increased feed recovery rates (85-90%) and boundary flux values (12.3-19.6 L h-1 m-2). Finally, the standard limits to reuse the purified effluents for irrigation were successfully achieved. © 2014 Published by Elsevier B.V

Going from a Critical Flux Concept to a Threshold Flux Concept on Membrane Processes Treating Olive Mill Wastewater Streams

No abstract available. Paper available online at http://ac.els-cdn.com/S1877705812035126/1-s2.0-S1877705812035126-main.pdf?_tid=51cf2262-123a-11e4-8c55-00000aacb35f&acdnat=1406100421_d16cee368259594a68b1c05bc1019a4

Photocatalytic treatment of olive mill waste water by n-doped titanium dioxide nanoparticles under visible light

In this work N-doped TiO2 sol-gel material was successfully synthesized and used for coating on glass spheres of 1 mm in diameter. The composite material was characterized by dynamic light scattering (DLS) and X-ray diffraction (XRD).The catalytic activity of the obtained photocatalyst was investigated in terms of degradation of organic compounds in diluted and undiluted olive mill wastewater (OMWW) samples. The tests were performed in a batch photoreactor, irradiated by a 150W visible light lamp. The reduction of chemical oxygen demand (COD) was chosen as key parameter of the organic matter degradation. The obtained results showed that the adopted doping and the number of coating layers influences the outcome. Copyright © 2013, AIDIC Servizi S.r.l

Batch membrane treatment of olive vegetation wastewater from two-phase olive oil production process by threshold flux based methods

The more efficient continuous centrifugation-based olive oil extraction processes brought as drawback a significant increment of the generated effluents, highlighting olive vegetation wastewater (OVW) as the most polluted. In this work, OVW from a two-phase olive oil extraction process (OVW-2) was treated by means of batch membrane operations in sequence comprising UF, NF and RO. This treatment is capable of successfully removing the organic matter and other pollutants from the wastewater, but membrane fouling can limit drastically membranes operation and longevity. Threshold flux-based methods represent a reliable tool to avoid fouling problems and were formerly applied to treat OVW streams coming from a three-phase production line (OVW-3). Below threshold flux conditions, no relevant rates of fouling are observed, thus making the treatment process technically and economically feasible. In order to increase the threshold flux values, some pretreatment processes were conducted on the feedstock, such as pH-T flocculation and successively photocatalysis by novel lab-made titanium dioxide nanoparticles. The latter provided 22.3%, 17.6% and 20.4% further threshold flux increase to UF, NF and RO, respectively. At the end, a permeate with COD equal to 121 mg/L was successfully obtained, respecting both Italian and Spanish standards for discharging purified OVW-2 in municipal sewers. (c) 2012 Elsevier B.V. All rights reserved