Seawater Pretreatment Research Articles

An Improved Configuration of Vertical-Flow Mesh Tube Filters for Seawater Pretreatment: Performance, Cleaning, and Energy Consumption

Roughing filters are types of porous media filter used in pretreatment systems where the raw water contains a large amount of suspended particles (SPs) and organic matter. Mesh tube filtration (MTF) media are roughing-filter media composed of low-density polyethylene used for SP removal during wastewater treatment. In this study, we present an improved MTF design—a porous filter bed (PFB), which exhibits superior SP removal performance compared to conventional MTF media. We then compare the applicability of MTF and PFB to both the primary pretreatment process for seawater desalination and the water reuse process. In bench-scale SP removal experiments, PFB shows removal rates of 46.7%, 68.0%, 67.6%, and 68.4% at hydraulic retention times of 15, 20, 30, and 60 min, respectively, which are better than those of MTF. The specific energy consumption (SEC) of batch dissolved air flotation (DAF) was known to range from 0.035 to 0.047 kWh/m3, whereas the SEC calculated for pilot-scale MTF and PFB is 0.027 kWh/m3 and minimum energy for influent supply, respectively. This suggests that PFB can compete with DAF as a primary pretreatment process. MTF predominantly removes SPs by sedimentation, whereas SP removal in PFB typically occurs via deposition of SPs on the mesh tube media.

Solar nano-photocatalytic pretreatment of seawater: process optimization and performance evaluation using response surface methodology

Solar nano-photocatalytic pretreatment of seawater: process optimization and performance evaluation using response surface methodology

Solar nano-photocatalytic pretreatment of seawater: process optimization and performance evaluation using response surface methodology

Solar nano-photocatalytic pretreatment of seawater: process optimization and performance evaluation using response surface methodology

TiO2/photo-Fenton process for seawater pretreatment: Modeling and optimization using response surface methodology (RSM) and artificial neural networks (ANN) coupled genetic algorithm (GA)

TiO2/photo-Fenton process for seawater pretreatment: Modeling and optimization using response surface methodology (RSM) and artificial neural networks (ANN) coupled genetic algorithm (GA)

TiO2/photo-Fenton process for seawater pretreatment: Modeling and optimization using response surface methodology (RSM) and artificial neural networks (ANN) coupled genetic algorithm (GA)

TiO2/photo-Fenton process for seawater pretreatment: Modeling and optimization using response surface methodology (RSM) and artificial neural networks (ANN) coupled genetic algorithm (GA)

Low-cost ceramic microfiltration membrane made from natural phosphate for pretreatment of raw seawater for desalination

A novel ceramic microfiltration (MF) membrane was prepared from natural phosphate and its properties were thoroughly characterized. An investigation of the effect of sintering temperature on the features of phosphate membrane was carried out in the range from 900 to 1100 °C. The optimized membrane sintered at 1000 °C exhibits 697 L h−1 m-2 bar−1 of permeability, 25.6 % of porosity, 0.26 μm of average pore size and 19.7 MPa of flexural strength. When evaluated for filtration of raw seawater as a potential pretreatment for reverse osmosis desalination, the prepared membrane reduced total organic carbon (TOC) and turbidity by 73 and 98 %, respectively, as well as reducing silt density index (SDI) from 5.41 to 3.25. Furthermore, the fouling mechanism and the flux recovery were also studied. Finally, simple cleaning of the prepared membrane performed after the MF experiment led to recover 74 % of its original water flux.

Synthesis and characterization of TiO2 and palm oil fiber ash hybrid photocatalysts for seawater pretreatment

Titanium dioxide (TiO2) has been used in various applications such as air purification, water purification, and photoelectrochemical conversion systems. However, developing advanced materials with enhanced performance for catalytic applications, especially water treatment, is highly required. This work aims to study the effect of (TiO2) photocatalyst in pretreatment seawater desalination. The catalyst with a mass ratio of TiO2: palm oil fibre ash (POFA) at 0:100, 40:60, 60:40, and 100:0 was synthesized via wet impregnation. The catalyst was calcined at 500 ℃ for four hours. The mixture of artificial seawater and catalyst at a mass ratio of photocatalyst: artificial seawater at 1:300 was put in a one-litre borosilicate photo-reactor fixed with mercury light of 350 nm for two hours with stirring at 1000 rpm. In this investigation, an evaporator was used to collect the freshwater. The fresh and spent catalysts were characterized via X-Ray Diffractogram (XRD), Nitrogen physisorption analysis, Diffuse Reflectance Spectrometer (DRS), Scanning Electron Microscopy (SEM), and Energy Dispersive X-Ray Spectroscopy (EDX). The catalyst with Ti: palm oil fibre ash (POFA) at 40:60 and 60:40 can reduce the COD at 45 % and 41%, respectively. As more OPFA was added into the hybrid TiO2 catalyst, there has been a change in the properties of seawater due to the use of special evaporators, especially EC and TDS. It can be deduced that the hybrid TiO2 photocatalyst synthesized with OPFA has vast potential to treat seawater.

Numerical Modeling of Beach Well Intake as Pre-Treatment for a Desalination Plant

Pre-treatment of seawater plays a critical role in removing colloidal particles, algae, sediment, and microbes, which could adversely affect the desalination process. This study focused on the utilization of the natural process of infiltration by beach wells to pre-treat the intake water for the desalination process. The scope of the study was achieved by drilling two beach wells at Al-Khobar and Jubail sites at the Arabian Gulf of Saudi Arabia at 50 m depth each. In addition to that, a total of eight monitoring wells were drilled for pump testing. Numerical modeling was conducted using SEEP/W to investigate the properties of well water flux at the beach wells. The comprehensive physio-chemical parameters such as cation, silt density index (SDI), total dissolved solids (TDS), total suspended solids (TSS), chemical oxygen demand (COD), total organic carbon (TOC), salinity, and alkalinity were analyzed for a quality assessment concerning the actual seawater. Preliminary experimental results show a reduction of the targeted parameters and indicate that beach well sand filtration in the Eastern Province would be a valuable pre-filtration step in reverse osmosis (RO)-based drinking water production systems. The water flux values for both sites were 0.0197 and 0.0208 m3/s/m2, respectively, which corresponds to 72 m3/h/m2 and 1356.48 m3/h/m2. In terms of the rate of pumping flow, the model suggests production can be increased by 20 and 53 times the measured production of the Jubail and Al-Khobar sites, respectively. The experimental results of water parameters, such as cation, SDI, TDS, TSS, etc., indicate that beach well sand filtration in the Eastern Province would be a valuable pre-filtration step in reverse osmosis drinking water production systems.

The decline of scale-forming ions from R.O feed water using kaolinite/nano-sized iron oxide composite

The study was designed to synthesize iron oxide-kaolinite composite to apply as a sorbent for a pre-treatment of seawater used as feed water in reverse osmosis units. Herein, we present kaolinite/Nano-sized iron oxide composite through the impregnation process. The morphologies of synthesized iron oxide and kaolinite-iron oxide nanocomposites were characterized by thermal gravimetric analysis (TGA), transmission electron microscopy (TEM), zeta potential measurement (ZPM), scanning electron microscope (SEM) and X-ray diffraction as well as FTIR. The results indicated iron oxide was well dispersed on the surface of kaolinite. Kaolinite/iron oxide composite has been found particularly useful for adsorption of scale-forming ions from seawater. The parameters controlling the uptake of the scales ions from seawater are contact time, initial ions concentration, adsorption dose, temperature, and pH. The removal efficiency reached 84% for barium under certain conditions. The adsorption follows Pseudo 2nd order with a maximum adsorbent capacity of 2.2 mg g−1. The pseudo-second order kinetic model was found to be the best model describing the process.

Surface modification of anti‐fouling novel cellulose/graphene oxide (GO) nanosheets (NS) microfiltration membranes for seawater desalination applications

AbstractBACKGROUNDReverse osmosis (RO) is becoming the predominant technology for the future of desalinated of seawater. Nonetheless, operational challenges such as membrane biofouling in RO desalination plants result in membrane deterioration and high energy costs. In this regard, pre‐treatment technologies, such as microfiltration (MF) membranes, are proven to reduce the impact of membrane biofouling in RO systems. Hence, surface modifications of commercial cellulose MF membranes with graphene oxide nanosheets (GONSs) at different concentrations were carried out in this research study. The new membranes were characterized by scanning electron microscopy (SEM) and Raman spectroscopy amongst other methods of analysis. A continuous cross‐flow MF system was used to investigate the performance of the new cellulose/GONS membranes with regards to total bacteria count (TBC) removal, water flux, and biofouling resistance.RESULTSTBC removal efficiency of 93.6 ± 2.4% and 27.4 ± 12.5% was achieved using the new cellulose/GONS membranes and control pristine cellulose membranes, respectively. This higher removal efficiency was achieved at a water flux of 334.7 ± 10.4 L/(m2 h). Furthermore, a dramatic 55% increase in the transmembrane pressure (TMP) of the pristine cellulose membrane was observed after 24 h operation compared to only a 6% increase in the newly fabricated cellulose/GONS membranes, reflecting their strong anti‐fouling properties.CONCLUSIONSurface modification of MF membranes with anti‐fouling nanomaterials such as GONS has the potential to be implemented in the pretreatment of seawater to improve the RO performance and lower the energy consumption. © 2020 Society of Chemical Industry

New insights into membrane fouling by alginate: Impacts of ionic strength in presence of calcium ions.

While water chemistry (e.g., ionic strength, calcium concentration and organic foulants) is the primary property of surface water, its effects on membrane fouling in process of membrane-based water production and seawater pretreatment have not well investigated. In this study, fouling behaviors of alginate solutions in presence of different calcium ion concentration and ionic strength levels were investigated. It was found that alginate solutions complexing with 1.5mM calcium possessed a remarkably high specific filtration resistance (SFR) (above 3.596×1015mkg-1), and the SFR descended with calcium concentration and increased with ionic strength. A series of characterizations suggested that zeta potential, particle size, viscosity and morphology of alginate solutions were close related with foulant layer microstructure and these fouling behaviors. Based on these characterizations, the thermodynamics described by Flory-Huggins lattice theory was proposed to explain the remarkably high SFR of alginate gel for 1.5mM calcium level. Meanwhile, preferential intermolecular coordination combined with Flory-Huggins lattice theory was suggested to be responsible for the descend trend of SFR with calcium concentration. Furthermore, electrostatic double layer compression effect together with Flory-Huggins lattice theory could well interpret the increase trend of SFR with ionic strength. This study provided the essential mechanisms underlying effects of ionic strength on alginate fouling in presence of calcium ions, and thus deepened understanding of membrane fouling.

Development of carbon nanotube membranes for dissolved gases removal as seawater pretreatment

Development of carbon nanotube membranes for dissolved gases removal as seawater pretreatment

Emerging investigator series: control of membrane fouling by dissolved algal organic matter using pre-oxidation with coagulation as seawater pretreatment

High AOM removal achieved by pre-oxidation with coagulation–flocculation-dissolved air flotation. In situ ferrate was formed by wet chemical oxidation of NaOCl-Fe3+. Membrane fouling was significantly alleviated and assessed by OCT technique.

Fabrication of flat ceramic microfiltration membrane from natural kaolinite for seawater pretreatment for desalination and wastewater clarification

The aim of this work is the manufacturing of flat microfiltration membrane made from Moroccan natural kaolinite clay and corn starch as porosity agent. The membrane was prepared by uniaxial pressing technique and sintering at 1,100 degrees C. The effect of starch on membrane features was investigated from 0 to 15 wt.%. The membrane has a diameter of 37.8 mm and a thickness of 2.3 mm. In order to optimize its properties, prepared membrane was characterized in terms of apparent porosity, water absorption, apparent density, mechanical strength, pore size, microstructure, and water permeability measurements. Experimental results showed that the membrane prepared with 10 wt.% of starch is considered as an optimized membrane which has an average pore size of 2.3 mu m, the mechanical strength of 20.2 MPa, and permeability of 2,129 L h(-1)m(-2) bar(-1). The optimized membrane was applied for pretreatment of raw seawater for desalination and clarification of agro-food effluent using dead-end filtration under pressure of 0.12 bar. Filtration results showed that turbidity rejection achieves 73% and 99%, respectively for raw seawater and agro-food model effluent.

Energy-efficient seawater softening and power generation using a microbial electrolysis cell-reverse electrodialysis hybrid system

Here we describe the development and testing of a hybrid system that combines microbial electrolysis and reverse electrodialysis (RED) to benefit energy production from seawater. A tubular, continuous-flow, microbial electrolysis cell (MEC) was used prior to RED to remove multivalent ions (Ca2+ and Mg2+) that are known to decrease RED power generation due to high electric membrane resistance. When a membrane electrode assembly was applied to reduce external resistance in the MEC, Ca2+ and Mg2+ were effectively removed with efficiencies of 84 ± 5% and 99 ± 5% (current density of 4.0 ± 0.2 A/m2), respectively, and H2 was simultaneously generated. A high H2 (purity > 99.5%) production rate (2.00 ± 0.09 m3/m3·d) at an applied voltage of 1.5 V, and maximum electrical energy efficiency (169 ± 4%) was accomplished at an applied voltage of 0.9 V and with an anode hydraulic retention time of 6 h. Effluent (47 mS/cm) from the MEC was fed to the RED stack as a high-concentration solution and the conductivity of treated seawater was lower than untreated seawater (53.7 mS/cm) due to Ca2+ and Mg2+ elimination from the seawater. Despite its lower conductivity, treated seawater produced higher power (0.29 W/m2, 26% increase) compared to untreated seawater due to the removal of Ca2+ and Mg2+. Therefore, the MEC is superior to other energy-consuming seawater pretreatment system as it produces energy during seawater pretreatment and successfully integrates with RED to enhance power generation.

Impact of isolated dissolved organic fractions from seawater on biofouling in reverse osmosis (RO) desalination process

The biofouling potential of three isolated dissolved organic fractions from seawater according to their molecular weights (MWs), namely, fractions of biopolymers (F.BP, MW > 1000 Da), humic substances and building blocks (F.HS&BB, MW 350–1000 Da), and low molecular weight compounds (F.LMW, MW < 350 Da) were characterized by assimilable organic carbon (AOC) content. The AOC/DOC ratio was in the order of F.LMW (∼35%) > F.BP (∼19%) > F.HS&BB (∼8%); AOC/DOC of seawater was ∼20%; organic compositions of seawater were BP ∼6%, HS&BB ∼52% and LMW ∼42%; LMW accounted for >70% of AOC in seawater. Their impact on SWRO biofouling in term of flux decline rate was in the order of F. LMW (∼30%) > F.BP (∼20%) > F.HS&BB (<10%). Despite being the major organic compound in seawater, HS&BB showed marginal effect on biofouling. The role of indigenous BP was less critical owing to its relatively low concentration. LMW, which was the major AOC contributor, played a significant role in biofouling by promoting microbial growth that contributed to the build-up of soluble microbial products and exopolymeric substances (i.e., in particular BP). Therefore, seawater pretreatment shall focus on the removal of AOC (i.e., LMW) rather than the removal of biopolymer.

Seawater pretreatment with an NF-like forward osmotic membrane: Membrane preparation, characterization and performance comparison with RO-like membranes

A nanofiltration-like (NF-like) forward osmosis (FO) membrane was prepared by interfacial polymerization and applied for seawater pretreatment. The prepared NF-like FO membrane shows much higher water permeability and higher divalent salt to monovalent salt selectivity compared to a commercial reverse-osmotic-like (RO-like) FO membrane. The comparison between NF-like FO membrane and RO-like FO membrane in FO process was systematically investigated by using an antiscalent (sodium polyacrylate, PAANa) solution as draw solution. Both NF-like and RO-like FO process showed high rejection of alginate and sulfate. However, the water flux and monovalent salt (NaCl) passage in NF-like FO process were much higher, which enables the NF-like FO membrane to be a better candidate for pretreating seawater. The findings provide new insights on the design and preparation of FO membranes for seawater pretreatment.

Flotation behavior of enargite in the process of flotation using seawater

The presence of enargite (Cu3AsS4) in porphyry copper deposits is an important matter as this mineral shows good flotability in the presence of the thiol collectors used in the flotation copper sulfides thus contaminating the final concentrate. Besides a relevant problem in Chilean mining is the scarcity of water resources so the use of seawater has become a feasible solution. The flotation behavior of copper sulfides and molybdenite in seawater was previously studied but there are no systematic studies related to the flotation of enargite using seawater. The objective of this work is to study the behavior of enargite in the process of flotation using seawater and to compare the flotation of enargite and chalcopyrite in this aqueous medium. The results indicate that the recovery of enargite is strongly depressed at pH > 9 in the process of flotation using seawater, behavior that can be explained in the first place by the adhesion of the hydrolysis products of magnesium on the surfaces of the enargite particles. The analyses of the Pourbaix diagrams for the As-Ca and As-Mg systems also suggest that the enargite depression in seawater observed at pH > 9 can not only be related to the adsorption of hydroxo complexes of magnesium and calcium, but also to the interaction of these metals with oxidized arsenic species such as arsenate and arsenite. As these compounds are hydrophilic in nature they reduce enargite recovery. Pre-treatment of seawater before flotation to remove most of the calcium and magnesium present through the precipitation of hydrolyzed complexes of these cations is a suitable way to improve enargite recovery at pH > 9.

Fenton oxidation-based cleaning technology for powdered activated carbon-precoated dynamic membranes used in microfiltration seawater pretreatment systems

In this study, we investigated the performance of powdered activated carbon dynamic membranes (PAC DMs) in fouling mitigation strategies during cross-flow microfiltration for high-efficiency seawater pretreatment. By altering the fouling mechanism and water molecule pathway, PAC DMs successfully enhanced the pseudo-steady-state filtration flux and rejection of cross-flow microfiltration by 53% and 29%, respectively, compared to filtration without a PAC DM. Moreover, Fenton oxidation processes (FOPs) application in the DMs’ cross-flow cleaning was studied and showed promising results, recovering up to 28% of the initial filtration flux when used alone and 52% when combined with alkaline cleaning. This study provides insight into the utilization FOPs cleaning technology for PAC DMs cross-flow cleaning, allowing the automation and optimization of DMs operation.

Advanced coagulation using in-situ generated liquid ferrate, Fe (VI), for enhanced pretreatment in seawater RO desalination during algal blooms

Harmful algal blooms (HABs) are considered a major threat for seawater reverse osmosis (SWRO) plants. The presence of HABs in the raw feed water can cause increase of chemical consumption within the desalination plant, increase membrane fouling rate and might lead to plant shutdown. The removal of Algal Organic Matters (AOMs) during the pretreatment will help in increasing the membrane lifetime, reduce operation cost and increase the plant reliability. In this study, the efficiency of liquid ferrate and ferric chloride during coagulation on the removal of AOMs was investigated. The liquid ferrate was generated in-situ by wet oxidation of ferric iron using hypochlorite in a caustic medium. Two seawater models were employed, the first one contains 10 mg c/L of sodium alginate and the second one contains also 10 mg c/L of Chaetoceros affinis algae (CA). During the advanced coagulation, liquid ferrate proved to be more effective in removing AOM than ferric chloride, with an overall DOC removal of 90%, enabling 100% algal removal and the inactivation of 99.99% of the microorganisms. The results presented in this study highlights the efficiency of liquid ferrate as seawater pretreatment during the HABs events.