Maria Diná Afonso

Streaming potential measurements to assess the variation of nanofiltration membranes surface charge with the concentration of salt solutions

Abstract The main objective of this work is the determination of the effective surface charge of commercial nanofiltration (NF) membranes through streaming potential measurements in order to prove the existence of a relationship between the membrane surface charge, CM, and the feed solution concentration, Cf, of the type of a Freundlich isotherm: ln C M =a+b ln C f . This relationship was an important finding of a model developed previously, which describes the NF mass transfer mechanisms and predicts the NF performance of single salt solutions. Two loose NF membranes, Desal G-10 and Desal G-20, are characterised as for the hydraulic permeability, molecular weight cut-off (MWCO), and ion exchange capacity (IEC). Permeation experiments of NaCl, Na2SO4, MgCl2 and MgSO4 solutions, in the range of concentrations 0.0002–0.02 N, are carried out in a DOW pilot unit with a plate-and-frame module, the permeate fluxes and the salt rejections being measured for pressures between 2.5 and 12.5 bar, at constant flow rate, pH, and temperature. The streaming potential developed in the salt solutions flowing parallel to the membranes is measured by an electro-kinetic-analyser (EKA, Anton Paar). This equipment automatically calculates the zeta potential and corrects it for the membrane surface conductance. The membrane surface charge is determined by using the Gouy–Chapman equation. The membrane Desal G-20, the one bearing a higher surface charge, appears to display a logarithmic relationship for NaCl: ln C M ( mol/m 3 )=3.57+0.475 ln C f ( mol/m 3 ) , though in a smaller concentration range than intended to be checked, due to the scattering of zeta potential data above 0.005 N. Furthermore, the surface charge of Desal G-20 is likely to be partially due to adsorption of ions since its IEC is lower than the surface charge determined by electrokinetic measurements at some experimental conditions.

Review of the treatment of seafood processing wastewaters and recovery of proteins therein by membrane separation processes: prospects of the ultrafiltration of wastewaters from the fish meal industry

Abstract The wastewaters generated in fish meal production (average flow rates of 1100 m3/h for a plant capacity of 100 ton fish/h) contain a high organic load, and therefore they should not be discharged directly into the sea without effective treatment in order to prevent a negative impact on the environment. On the other hand, these effluents contain a large amount of potentially valuable proteins. These proteins can be concentrated by means of ultrafiltration (UF) and recycled into the fish meal process, improving its quality and the economic benefits from the raw material, whereas the treated water can be discharged into the sea or reused in the plant. Due to the high concentration of suspended matter in these effluents, microfiltration (MF) pre-treatment is required. An extensive review of the application of pressure-driven membrane separation processes in the treatment of seafood processing effluents and recovery of proteins therein is presented. Two effluents from a fish meal plant located in Talcahuano, Chile, were characterised and microfiltrated with a Whatman filter No. 1. A mineral tubular membrane, Carbosep M2 (MWCO = 15 kDa, ID = 6 mm and L = 1.2 m) was used in the UF experiments. The operating conditions were optimised in total recirculation mode, and the subsequent concentration experiments were carried out at 4 bar, 4 m/s, ambient temperature and natural pH. The results show that UF reduces the organic load from the fish meal wastewaters and allows the recovery of valuable raw materials comprising proteins. Moreover, they point out that further investigation should be dedicated to the use of UF membranes of lower molecular weight cut-off — or even NF membranes — in order to achieve complete recovery of the proteins contained in these effluents. Although the membrane undergoes severe fouling, it can easily be cleaned through a caustic washing.

Brackish groundwater treatment by reverse osmosis in Jordan

Jordan is characterised by an arid to semi-arid climate and its population is increasing at an annual rate of 3.6%. With such a high population growth rate and fast social-economical development, water demand and wastewater production are steeply increasing, and the gap between water supply and demand is getting wider. Furthermore, the constraints for water resources development are also rising due to high investment costs and water quality degradation due to over-exploitation of aquifers. Desalination of Red Sea water by reverse osmosis (RO) and/or brackish groundwater desalination by nanofiltration or RO might be technically and economically viable to cope with water scarcity and overcome the water deficit in Jordan. The technical-economical feasibility of brackish groundwater treatment by RO for potable water production was investigated in this work. Brackish groundwater samples were collected from the Zarqa basin, Jordan, and characterised in terms of pH, conductivity, total solids, total dissolved solids, total suspended solids, and volatile solids. The water samples were pre-treated through a microfiltration cartridge (5 μm pore diameter) in order to eliminate the suspended matter. A pilot plant equipped with a FilmTec RO membrane (SW30-2521) was operated at 20–30 bar, 40°C, natural pH and up to a water recovery ratio of 77.5%. The results showed that RO is actually efficient since it highly reduced the content of organic and inorganic matters present in raw waters (rejections >98.5%) at a relatively affordable price (0.26 €/m3). This study contributes to the development of efficient technologies to produce affordable potable water in Mediterranean countries where the threat of water shortages is a severe problem.

Desalination of brackish water by nanofiltration and reverse osmosis

Abstract Jordan is characterised by an arid climate and its population is increasing at an annual rate of about 3.6%. The annual consumption of fresh water per capita is less than 200 m3 compared to the international average of 7500 m3. Jordans water resources comprise surface water (41%), ground water (54%) and treated wastewater (5%). With such a high population growth rate and fast socio-economic development, water demand and wastewater production is steeply increasing and the gap between water supply and demand is getting wider. On the other hand, the constraints for water resources development are also increasing due to high investment costs and water quality degradation caused by over exploitation of aquifers. Jordan is likely to face a potable water crisis by 2010, by depleting the fresh water sources. Desalination of water from the Red Sea by reverse osmosis (R0) and/or desalination of brackish water from some basins by nanofiltration (NF) or RO might be technically and economically viable to cope with water scarcity and overcome water deficit in Jordan. In this work, treatment of brackish water by RO and NF into potable water is investigated. Brackish water samples were collected from Zarqa basin, Jordan, and characterised in terms of pH, conductivity, total solids (TS), total suspended solids (TSS) and total organic carbon (TOC). The brackish water samples were pre-treated through microfiltration (MF) cartridges in order to get rid of the suspended matter. A pilot plant equipped with composite RO and NF membranes was operated at 20 bar, ambient temperature, natural pH and up to water recovery rates of 95%. The results show that both processes are efficient, as they highly reduce the organic and inorganic contents present in the raw waters. The technical and economical feasibilities of NF and RO processes for the production of potable water from brackish water were compared. This study contributes for the development of efficient technologies for the production of affordable potable water in Mediterranean countries where the threat of water shortages is a serious problem, especially in summer.

Nanofiltration of wastewaters from the fish meal industry

The wastewaters generated in the fish meal industry, a water-intensive industry, contain a high organic load comprising a significant amount of proteins. Therefore, they should not be discharged without a suitable treatment in order to prevent negative impacts in the environment, and allow the recovery of high added value products. The effluent generated in a fish meal plant located in Talcahuano, Chile, was characterized, and pre-treated by microfiltration (MF) cartridges in series (80, 20 and 5 μm). A multi-channel ceramic membrane of 1 kDa MWCO, Kerasep NanoN01A, was used in the nanofiltration (NF) experiments. The operating conditions were optimised in total recycling mode, and the subsequent concentration experiment was carried out at 4 bar, 4 m/s, ambient temperature and natural pH. The results from this work clearly show that NF is an efficient and ecologically suited environmental technology for decontamination and recycling of the wastewaters generated during the fish meal production, as it allows both the recycle of water (permeate stream) and proteins (concentrate stream) into the fish meal process, besides environmental pollution abatement. Although the membrane undergoes severe fouling, it can be effectively cleaned through a basic-acid washing cycle.

Membrane separation processes in the pulp and paper industry

Abstract A study has been made on the utilization of inorganic membranes for the removal of colour from effluents of the first caustic extraction in the pulp and paper production. Experiments have been performed for ultrafiltration alone and, for this operation, in series with a microfiltration pretreatment. In both operations CARBOSEP tubular membranes were used with a microfiltration membrane of pore diameter equal to 0.14 μ and an ultrafiltration membrane with a cut-off of 10,000. The pressure ranged from one to five bar and feed circulation velocities of 0.7, 1.3 and 1.8 m/s were investigated. The introduction of microfiltration brings about no significant improvement of the quality and quantity of the permeates.

Nanofiltration removal of chlorinated organic compounds from alkaline bleaching effluents in a pulp and paper plant

Three commercial nanofiltration membranes were used for the removal of chlorinated organic compounds from the first alkaline extraction effluent originated from a kraft mill, using eucalyptus wood as raw material. The assays were carried out at the following operating conditions: pressure = 20 bar, temperature = 20°C and circulation velocity = 2 m/s. The results show the nanofiltration feasibility. For the three membranes the rejection factors of chlorinated organic compounds are greater than 95% and two of them present permeate fluxes of approx. 42 kg/hm2. Several reference solutes with a wide range of molecular weights and functional groups were also permeated. Their results compared with those of mill effluent allow us to conclude that the effluent tannic compounds are not in a fouling form and that the majority of the organochlorinated matter has a molecular weight greater than 500 Da.

Ultrafiltration of bleach effluents in cellulose production

Abstract Ultrafiltration performance for colour removal in the effluents of the first caustic extraction stage in cellulose production has been investigated. The pH of the effluents is adjusted to 8.65. The operation is optimized with respect to polysulfone membrane cut-off, operating pressure and feed circulation rate. The dependence of product rate with pressure and of colour rejection with feed circulation rate is quantified. For a membrane of 10,000 cut-off, the colour removal is maximal and nearly independent of the feed circulation rate.

Membrane separation processes in pulp and paper production

Abstract In cellulose production utilising the kraft process the bleaching plant is the major factor responsible for pollution problems. In fact, the strongly coloured compounds are mainly concentrated in the effluents of the first alkali extraction stage (E1). The large amount of work devoted to the utilisation of ultrafiltration (UF) for colour removal from these effluents is mostly relative to ultrafiltration using organic membranes and more specifically polysulphone membranes. Due to the fouling problems posed in previous work(1,2) with polysulphone membranes, the present work addresses the utilisation of mineral membranes for microfiltration and ultrafiltration of bleach plant effluents. Investigated is the advantage of a sequence of microfiltration and ultrafiltration steps with respect to the direct use of ultrafiltration.

Crossflow microfiltration of marble processing wastewaters

The wastewaters generated during the marble processing (cutting and grinding operations), the average flow rates of which are ca. 15 m3/h for a plant producing 45 m2 of polished marble/h, contain a high load of particulate matter. Furthermore, crushed stone operations sometimes use flotation agents, such as organic amines, fatty acids, and pine oils, in order to remove impurities from the marble. Therefore, the marble processing wastewaters should not be disposed directly into the environment without a suitable treatment in order to prevent negative impacts and comply with the national legislations currently in force. On the other hand, bearing in mind the severe water shortage in Mediterranean countries, which are intensive producers of carbonaceous rock and stone, it would be of utmost importance to recover and reuse the processing wastewaters generated in these plants. In this work, the treatment of marble processing wastewaters by microfiltration (MF) was investigated. Wastewaters from a marble processing plant located in Pero Pinheiro, Portugal, were characterised in terms of pH, conductivity, total solids (TS), and total suspended solids (TSS). A Micro Carbosep 60 module equipped with a mono-tubular mineral MF membrane, Carbosep M45 (nominal pore size = 0.45 μm, ID = 6 mm, L = 0.60 m), was tested at ambient temperature, natural effluent pH, a broad range of transmembrane pressures and crossflow velocities, and up to a 9-fold concentration. MF eliminated the suspended matter from marble wastewaters, allowing the treated water to be recycled into the process, whereas the concentrated stream (rich in particulate matter) can be used elsewhere, e.g. in the ceramic industry. The results from this work clearly show that MF is an efficient and ecologically suited environmental technology for decontamination and recycling of the wastewaters generated by marble processing plants, besides the environmental pollution abatement involved.