The importance of pretreatment tailoring on the performance of ultrafiltration membranes to treat two-phase olive mill wastewater

In this work, the performance of an ultrafiltration (UF) membrane in the treatment of the effluents by-produced by olive mills is addressed by applying different pretreatments on the raw effluents. By conducting a photo-catalytic process (UV/TiO2 PC) after pH-temperature flocculation (pH-T F) higher threshold flux values were observed for all feed stocks than by applying solely the pH-T F process, with an 18.8–34.2% increment. In addition, the performance of the UF membrane was also improved in terms of rejection efficiency, such that higher rejection values were yielded by the membrane for the organic pollutants (RCOD) by 48.5 vs. 39.9% and 53.4 vs. 42.0%. The UF membrane performance was also improved in terms of the volume feed recovery factor (VFR), achieving up to 88.2 vs. 87.2% and 90.7 vs. 89.3%. Results in the same line were also observed when the highly polluted olives oil washing wastewater raw stream was previously mixed with the effluent stream coming from the washing of the olives. This permits the UF to permeate, achieving the standard limits to reuse the purified effluent for irrigation purposes (COD values below 1000 mg·L−1), which makes the treatment process cost-effective and results in making the olive oil production process environmentally friendly.En este estudio se aborda el rendimiento de una membrana de ultrafiltración (UF) para el tratamiento de los efluentes generados por la industria oleícola, mediante la aplicación de distintos pretratamientos. Tras aplicar un proceso fotocatalítico (UV/TiO2 PC) después de una floculación pH-temperatura (pH-T F) se observaron flujos límite para todos los efluentes mayores que tras la aplicación únicamente del proceso pH-T F, con incrementos del 18.8–34.2 %. Además, el rendimiento de la membrana de UF mejoró en términos de eficiencia de rechazo, con mayores valores de rechazo respecto de los contaminantes orgánicos (RCOD), 48.5 vs. 39.9 % y 53.4 vs. 42.0 %. El rendimiento de la membrana mejoró también en términos de recuperación de volumen de alimentación (VRF), alcanzando hasta un 88.2 vs. 87.2 % y 90.7 vs. 89.3 %. Se observaron resultados en la misma línea cuando las aguas residuales del lavado del aceite, altamente contaminadas, fueron previamente mezcladas con el efluente generado en el lavado de las aceitunas. Esto permite que el permeado de la UF cumpla con los límites estándar para la utilización del efluente para riego (valores de la DQO inferiores a 1000 mg L−1), favoreciendo la eficiencia económica del proceso de tratamiento y permitiendo que el proceso de producción del aceite de oliva pueda ser respetuoso con el medio ambiente.The membrane pilot plant was constructed in the framework of the European project PHOTOMEM (contract no.FP7-SME-2011, grant 262470) and revamped under the European project ETOILE (contract no. FP7-SME-2007-1, grant 222331). Funding by the EC is gratefully acknowledged. The Spanish Ministry of Science and Innovation is also gratefully acknowledged for having funded the projects CTQ2007-66178 and CTQ2010-21411, as well as the University of Granada

About the limits of microfiltration for the purification of wastewaters

In the past, microfiltration was widely used as a pretreatment step for wastewater stream purification purposes. Experiences performed during the last years shows that microfiltration fails to maintain its performances for longer period of times. Many case studies demonstrate that the adoption of microfiltration leads to the failure of the overall process; the severe fouling of the microfiltration membranes leads to high operating costs with the consequence to make the treatment of the wastewater economically unfeasible. The boundary flux concept is a profitable tool to analyze fouling issues in membrane processes. The boundary flux value separates an operating region characterized by reversible fouling formation from irreversible one. Boundary flux values are not content, but function of time, as calculated by the subboundary fouling rate value. The knowledge of both parameters may fully describe the membrane performances in sub-boundary operating regimes. Many times, for wastewater purification purposes, ultrafiltration membranes appear to be suits better to the needs, even they exhibit lower permeate fluxes compared to microfiltration. Key to this choice is that ultrafiltration appears to resist better to fouling issues, with a limited reduction of the performances as a function of time. In other words, it appears that ultrafiltration exhibit higher boundary flux values and lower sub-boundary fouling rates. In this work, after a brief introduction to the boundary flux concept, for many different wastewater streams (more than 20, produced by the most relevant industries in food, agriculture, manufacture, pharmaceutics), the boundary flux and sub-boundary fouling rate values of different microfiltration and ultrafiltration membranes will be discussed and compared. The possibility to successfully use microfiltration as a pretreatment step strongly depends on the feedstock characteristics and, in detail, on the particle size of the suspended matter. In most cases, microfiltration demonstrates to be technically unsuitable for pretreatment purposes of many wastewater streams; as a consequence, the adoption of microfiltration pushes operators to exceed boundary flux conditions, therefore triggering severe fouling, that leads to economic unfeasibility of the process in long terms

Chromium recovery by membranes for process reuse in the tannery industry

Leather tanning is a wide common industry all over the world. In leather processing, water is one of the most important medium, almost 40-45 L water kg-1 raw-hide or skin is used by tanneries for processing finished leathers. The composition of tannery wastewater presents considerable dissimilarities in the concentration range of pollutants both of inorganic (chlorides, with concentration ranging from several hundred to over 10,000 mg L-1 Cl–; sulphate (VI), ammonium ions and sulphide ions, exhibiting concentration that ranges from tens to several hundred mg L-1) and organic (the COD value is usually several thousand mg L-1 O2). Throughout the years, many conventional processes have been carried out to treat wastewater from tannery industry: unfortunately, in this case, biological treatment methods give rise to an excessive production of sludge, whereas physical and chemical methods are too expensive in terms of energy and reagent costs. In this work, a membrane process based on NF membrane modules was adopted to treat the tannery feedstock after primary conventional treatment. In a first step, the determination of all boundary flux parameters, in order to inhibit severe fouling formation during operation, were performed. After this, experimental work was carried out to validate the approach. The target of water purification was reached, that is the legal discharge to municipal sewer system in Italy of 90% of the initial wastewater stream volume. This allows having an immediate cost saving of 21%. Moreover, the developed process leads to a second benefit, that is the production of 5% of the initial volume as a highly chromium-rich concentrate at no cost suitable to tannery process recycle and reuse. In this case, cost saving rates exceeds 40%. At the end, scale-up of the investigated process will be discussed from technical and economic point of view

Regarding the rejection performance of a polymeric reverse osmosis membrane for the final purification of two-phase olive mill effluents previously treated by an advanced oxidation process

In previous works on olive mill wastewater (OMW), secondary advanced oxidation treatment solved the problem related to the presence of phenolic compounds and considerable chemical oxygen demand. However, the effluent presented a significant salinity after this treatment. In this work, an adequate operation of a reverse osmosis (RO) membrane is addressed to ensure constant performance over a long period of time. In this paper, the effect of the operating parameters on the dynamic membrane rejection performance towards the target species was examined and discussed. Rejection efficiencies of all species were observed to follow a similar pattern, which consisted of slight initial improvement that further decreased over time. Rejection of both divalent ions remained constant at over 99% regardless of the operating conditions. Rejections were noticed to follow the order SO42- > Cl- > NO3- and Ca2+ > Mg2+> K+> Na+, as a rule. Divalent species were moderately more highly rejected than monovalent ones, in accordance with their higher charge and molecular size, and sulfate anions were consistently rejected by over 99%. Finally, the RO membrane exiting treated effluent was depleted of the high electro conductivity initially present (above 97% rejection), permitting its re-use as good quality irrigation water (below 1 mS/cm)

Sobre la eficiencia del rechazo de una membrana polimérica de ósmosis inversa para la purificación del agua residual de almazara de dos fases, previamente tratada mediante un proceso avanzado de oxidación

In previous works on olive mill wastewater (OMW), secondary advanced oxidation treatment solved the problem related to the presence of phenolic compounds and considerable chemical oxygen demand. However, the effluent presented a significant salinity after this treatment. In this work, an adequate operation of a reverse osmosis (RO) membrane is addressed to ensure constant performance over a long period of time. In this paper, the effect of the operating parameters on the dynamic membrane rejection performance towards the target species was examined and discussed. Rejection efficiencies of all species were observed to follow a similar pattern, which consisted of slight initial improvement that further decreased over time. Rejection of both divalent ions remained constant at over 99% regardless of the operating conditions. Rejections were noticed to follow the order SO42- > Cl- > NO3- and Ca2+ > Mg2+> K+> Na+, as a rule. Divalent species were moderately more highly rejected than monovalent ones, in accordance with their higher charge and molecular size, and sulfate anions were consistently rejected by over 99%. Finally, the RO membrane exiting treated effluent was depleted of the high electro conductivity initially present (above 97% rejection), permitting its re-use as good quality irrigation water (below 1 mS/cm).En trabajos previos con agua residual de almazara, se solucionó el problema en relación a la presencia de compuestos fenólicos y la considerable concentración de material orgánico. Sin embargo, el efluente presentaba una salinidad significativa tras éste. Este trabajo tiene por objetivo estudiar la adecuada operación de una membrana de ósmosis inversa (OI) para asegurar rendimientos constantes por largos períodos de tiempo de operación. Se examina y discute el efecto de los parámetros de operación en el rendimiento dinámico del rechazo de especies diana. Se observó que la eficiencia de rechazo de todas las especies siguió un patrón similar, consistente en una mejora inicial que posteriormente minoró con el tiempo de operación. El rechazo de iones divalentes se mantuvo constante sobre 99% independientemente de las condiciones de operación. La selectividad del rechazo siguió el orden SO42- > Cl- > NO3- y Ca2+ > Mg2+ > K+> Na+ en general. Las especies divalentes fueron moderadamente más rechazadas que las monovalentes, en concordancia con su mayor carga y tamaño molecular, y los iones sulfato fueron consistentemente rechazados al 99%. Finalmente, el efluente a la salida de la membrana de OI se encontraba exento de los altos valores de conductividad inicialmente presentes (rechazo superior al 97%), permitiendo su reutilización como agua de regadío de buena calidad (inferior a 1 mS/cm)

Comparación entre métodos de extracción líquido-líquido y en fase sólida previos a la identificación de la fracción fenólica presente en las aguas residuales procedentes del lavado del aceite de oliva obtenido mediante el sistema de extracción de aceite de oliva en dos fases

Phenolic compounds from olive mill wastewater (OMW), are characterized by a strong antioxidant activity. At the same time, they represent an environmental problem because they are difficult to degrade. The purpose of this work was to identify these biologically active compounds in the OMW from two-phase olive oil production in order to convert a polluting residue into a source of natural antioxidants. After optimizing the extraction process of phenolic compounds using liquid-liquid extraction (LLE) and solid phase extraction (SPE) methods, it was determined that the most appropriate sequence comprised a previous centrifugation to remove the lipid fraction, followed by liquid extraction with ethyl acetate or SPE. The most important compounds identified in olive oil washing wastewater (OOWW) were tyrosol, hydroxytyrosol and succinic acid; whereas the ones in the wastewater derived from the washing of the olives (OWW) were cresol, catechol, 4-methylcatechol, hydrocinnamic acid and p-hydroxy-hydrocinnamic acid.Los compuestos fenólicos presentes en las aguas residuales de la industria oleícola (OMW) se caracterizan por una gran actividad antioxidante. Por otra parte, suponen un problema medioambiental debido a que son difíciles de degradar. El objetivo de este trabajo fue la identificación de estos compuestos biológicamente activos que se encuentran en las OMW generadas del proceso de obtención del aceite de oliva por el sistema de dos fases, para así convertir un residuo contaminante en una fuente de antioxidantes naturales. Tras optimizar el proceso de extracción de los compuestos fenólicos utilizando extracción líquido-líquido (LLE) y extracción en fase sólida (SPE), se obtuvo que la secuencia más apropiada comprendió una centrifugación previa para eliminar la fracción lipídica, seguida de una extracción líquida con acetato de etilo o una SPE. Los compuestos más importantes identificados en las aguas residuales del lavado del aceite de oliva (OOWW) fueron tirosol, hidroxitirosol y el ácido succínico, mientras que los de las aguas residuales derivadas del lavado de las aceitunas (OWW) fueron cresol, catecol, 4-metilcatecol, ácido hidrocinámico y ácido p-hidroxi-hidrocinámico

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

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