Process Engineering for Pollution Control and Waste Minimization_8 pot

A summary of opportunities for membrane technologies in the treatment ofmining and mineral process streams was presented by Awadalla and Kumar 4.This study indicated a variety of applica

cells in a rectangular reaction tank A high-voltage electrode coated with ethylene is wound on the perforated baffle plate separating the extraction andstripping cell When a high-voltage electrostatic field is applied to the reactiontank, the aqueous drops in the organic continuous phase disintegrate into numer-ous smaller droplets under the action of the electrostatic field This provides agreat deal of surface area for separation The extractant dissolved in the continu-ous organic phase acts as a shuttle to transport metal ions from the extraction cell

poly-to the stripping cell

A summary of opportunities for membrane technologies in the treatment ofmining and mineral process streams was presented by Awadalla and Kumar (4).This study indicated a variety of applications including acid mine drainage(AMD), treatment of flotation water, copper smelting and refining wastewater,mill wastewater, removal of ammonium and nitrate ions, membranes in thealuminum industry, treatment of groundwater, treatment of uranium wastewater,treatment of dilute gold cyanide solutions, recovery of zinc from pond water, rareearth (RE) concentration, and separation of selenium from barren solution.AMD contains pollutants such as iron, manganese, calcium, magnesium,and sulfate ions Although lime neutralization is considered the “best availabletechnology economically achievable,” it is no longer considered environmentallyacceptable because of the low-level contamination of heavy metals which cannot

be removed Alternatively, almost complete removal of dissolved solids can beachieved by the use of ion exchange, distillation, and reverse osmosis (RO) toproduce high-quality water which can be used by municipalities or industry Theuse of RO is best implemented as a supplement to neutralization processes.The RO concentrate stream is neutralized and clarified prior to discharge orrecycled Coupled RO/ion exchange can be used when high concentration ofcalcium sulfate and/or iron fouling is a problem For the case of water reuse inwhich completely demineralized water is not essential, a charged ultrafiltrationprocess using negatively charged noncellulosic membranes was utilized For thecase of AMD for coal conversion processes, high-ultrafiltration recovery withhigh removal of calcium sulfate and iron and good flux are required Recovery

of up to 97% is achievable by introducing an interstage settling step cially available charged ultrafiltration membranes by PSAL (millipore type ofnoncellulosic skin on cellulosic backing) were used in this study Cost fortreatment using UF with interstage settling are $1.33/1000 gal of AMD, includingmembrane replacement cost, pumping cost, and lime cost

Commer-In order to avoid problems with recycling wastewater from flotation millswhich contain the breakdown products of collector-frother reagents, the watermust be purified before recycling to the mining operation The traditional methodfor treatment of flotation water involves lime precipitation, ozonation, adsorption

on activated carbon, and biological treatment (4) Biological treatment requiresexcessive holdup and is dependent on the climate, the presence of toxic heavy

metals, and sensitive control of the microorganisms Reverse osmosis has beenused for the recovery of flotation reagents Commercial RO membranes havebeen used to remove 95% of organic carbon, calcium, and magnesium from theflotation feed stream.

Scrubber blowdown from a primary copper smelting plant and acid ing water from a selenium-tellurium plant have been treated using negativelycharged noncellulosic ultrafiltration membranes (4) Removal of over 85% of Asand Se from the acid processing water was made possible when the pH wasadjusted to 10 and the solids were settled prior to ultrafiltration Scrubberblowdown was effectively treated without pH adjustment to a pH of 4.5 Arsenic-containing wastewater was also pretreated with UF and polished using RO Thismethod produced a permeate stream containing less than 50 ppb arsenic.Alkaline solutions of NaCN are used to leach gold-containing ores, produc-ing dilute gold cyanide solutions (4) The two conventional methods of recoveringgold from these solutions include the Merill-Crowc process of cementation usingzinc powder and adsorption using activated carbon Concentrated gold solutionsare formed by elution Reverse osmosis has been investigated as a means toconcentrate the dilute gold solutions In the case of metal finishing operationsusing gold and cyanide solutions, FilmTec FT-30 membranes have been used toprovide rejections in the range of 91–99% for free and combined cyanides (withcopper and zinc) Membrane performance was strongly pH dependent Reverseosmosis has also been used for silver and copper cyanide concentration (Os-monics, Inc) This study utilized a nitrogen-containing aromatic condensationpolymer Experiments indicated that the feed could be concentrated three timeswith 70% removal of permeate, resulting in low gold content in the permeate.Nanofiltration (NF) and RO have been used for removal of ammonium andnitrate ions from synthetic and actual mine effluents (5) In mine and mill water,ammonium and nitrate ions are generated from the degradation of cyanide fromgold mill effluents and ammonium nitrate-fuel oil (ANFO) blasting agents inmines Nitrogen-containing reagents are also used in ore processing and extrac-tive metallurgy The results of experiments using NF and RO membranes werereported for testing and actual mill effluent The results of the testing were thatgood removal of ammonium (>99%) and nitrate ions (>97%) were achieved using

process-RO, while NF was less effective Lower effectiveness of the NF membrane wasbelieved to be caused by ammonium being present in the sulfate form and not thelarger ammonium iron sulfate complex which does not form because there is noiron in the mining effluent No scaling or fouling problems were observed inthese studies

Cross-flow membrane technolgies have also been applied to mineral pensions (6) In this study, using microporous filtration (0.1-µm membranes)suspensions of CaCO3 were investigated using an intermittent cleaning approach

sus-in order to sus-increase the permeate flux

A thorough review of membrane technology for applications to industrialwastewater treatment has been made by Caetano (7) In this review, E Drioliprovides a broad overview in the areas of desalination, gas separation, pervapora-tion, membrane bioreactors, enzyme membrane reactors, and hybrid systemsbased on pervaporation and distillation.

In the more general area of environmental applications, significant workhas been done on the treatment of streams containing metals There has been agreat deal of interest in the use of ion-exchange membranes in this area Sengupta(8) has investigated electromembrane partitioning as a means for heavy metaldecontamination This is a unique and rather interesting new approach for thein-situ removal of metals from contaminated soils

A low-level direct current (DC), less than 1 V/cm, is applied to the soilwhile a composite ion-exchange membrane is wrapped around the cathode Uponimposition of the DC potential, the cations move toward the cathode, where theyare captured by the composite membrane By the design of the ion-exchangemembrane, the nonselective ions should pass freely through the membrane Themembrane utilized for this work is a thin sheet prepared by grinding a cross-linked polymer ion exchanger and suspending the ion exchanger in a PTFEporous matrix These membranes are 90% ion exchanger, 10% PTFE, and aremicroporous with >40% voids with a pore size distribution below 0.5 µm Onepotential problem with this process is that periodically these membranes must beremoved and chemically regenerated with strong (3–5%) mineral acid solution.Electrodialytic decontamination of soil polluted with heavy metals has beeninvestigated using ion-exchange membranes by Hansen et al (9) The process forremoval of metal ions from soils using electric current and passive membranes isknown as electrokinetic soil remediation This method involves the use of passivemembranes to separate the polluted soil from the electrodes There are severalshortcomings to this approach, including addition of acid counterions into the soil,return of heavy metals back into the soil, and heavy-metal precipitation at the H+and OH– front By introduction of ion-exchange membranes into the electro-kinetic soil remediation process, an electrodialytic soil remediation processresults The ion-exchange membranes are oriented in certain directions Thisorientation, with pairs of anion- and cation-exchange membranes placed on bothsides of the polluted soil, eliminates all three of the problems mentioned above.This configuration also provides two compartments containing liquid solutionsand the heavy metals, which can be withdrawn as needed In this situation,heavy-metal ions pass through the cation-exchange membrane in the direction ofthe cathode and are prevented from passing through the anion-exchange mem-brane and never reach the cathode They end up in the compartment between thetwo ion-exchange membranes

Li et al (10) have investigated the use of a cation-selective membrane forremoval of heavy metals from soils An improvement in the traditional elec-

troremediation approach is described In this work a cation membrane is placedaround the cathode to prevent hydroxyl species moving toward the anode Thisprevents precipitation of metals in the soil, and the metals precipitate in thecolumn of water around the cathode.

Membranes are also used for removal of metals for industrial applications(11) Bulk liquid membranes are used for facilitated transport of silver using arotating film pertraction device In this process two aqueous solutions areseparated by an organic liquid The membrane liquid is in contact with the donorand acceptor liquids adhering to the surfaces of the rotating disks Transport ofthe solvent involves extraction from one solution and stripping in the other Thispaper describes the recovery of silver from nitrate solutions using the rotating film

pertraction method using tri-isobutylphosphine sulfide (TIBPS) in n-octane as the

liquid membrane Aqueous silver nitrate was the donor phase and the acceptorphase was aqueous ammonia The results of the study indicated that because oflow rates of transport of other metals, including copper, zinc, and nickel, rotatingfilm pertraction can be used effectively to separate silver from solution

Yang et al (2) describe a unique metal extraction method using two sets ofhydrophobic microporous hollow fiber membranes for separation of metals insolution One set of hollow fibers carries an acidic organic extractant (LIX 84,anti-2-hydroxy-5-nonylacetophenone oxime) in a diluent The other set of hollow

fibers carries a basic organic extractant (TOA, tri-n-octylamine) The aqueous,

metal-containing stream is carried on the shell side of the membrane system.Cations, including copper, zinc, and nickel, are transported into the acidicextractant Anions, including chromium(VI), mercury, and cadmium, are ex-tracted into the basic stream

Palladium has also been separated from silver in a nitric acid solution usingliquid surfactant membranes (12) The organic carrier used in these studies is LIX

860, which is a β-hydroxyoxime The liquid surfactant membrane is Span 80, a

commercially available surfactant, and the solvent is n-heptane The aqueous

donor phase contains silver and palladium and is acidified using nitric acid Thereceiving phase contains thiourea and is tested in hydrochloric, perchloric, nitric,and sulfuric acids Under optimal conditions, palladium was separated from silverrecovered in entirety

Another liquid membrane, investigated by Fu et al (13), is trioctylamine(TOA) as a mobile carrier in kerosene Precious metals, including gold,palladium, platinum, iridium, and ruthenium in hydrochloric acid, were ex-tracted using this membrane system The metals were extracted into perchlorateand nitric acid solutions An inert PTFE polymer 80 µm thick, 74% porous,and 0.45 µm in average pore diameter was used as a support for the liquidmembrane

Low-pressure reverse osmosis (RO) was used by Ujang and Anderson (14)for separation of mono- and divalent ions Sulfonated polysulfone membranes are

used as a low-pressure reverse osmosis process for separation of mono- anddivalent zinc ions It was observed that the higher the operating pressure, thegreater was the permeate flux for both species At lower operating pressure,higher permeate fluxes were observed using divalent ions Metal removal ofdivalent ions was greater for divalent ions than for monovalent ions for allconcentrations.

2 ADSORPTION MATERIALS AND PROCESSES

Recovery of gold from cyanide has been evaluated using many different sorbent materials Petersen and Van Deventer (15) investigated the competitiverole of gold and organics on adsorption by a variety of adsorbents, includingactivated carbon, ion-exchange resin, ion-exchange fibers, and membranes Avariety of adsorbents were investigated, including coconut shell activated carbon,macroporous ion-exchange resin, ion-exchange membrane, and ion-exchangefibers (polypropylene-based strong-base and weak-base fibers) Adsorbents wereevaluated after being exposed to the organic compound, sodium ethyl xanthate,for 6 h The absorbents were challenged with a variety of organic compounds,including ethanol, sodium ethyl xanthate, potassium amyl xanthate, and phenol.The two mechanisms investigated to explain the reduced adsorption of gold inthe presence of the organics were (a) blockage of the carbon pores by the organic,and (b) competition between gold cyanide and organics for the active sites on thecarbon surface The results of the study indicated that both the rate of adsorptionand the equilibrium loading were affected by the organic on the adsorption ofgold cyanide onto activated carbon The resin particles were only effected by therate of adsorption, while the membranes and fibers experienced both kinetic andequilibrium changes The results of this study indicated that the long-chainorganics (xanthates) have a higher degree of inhibition of mass transfer of goldcyanide compared to the low-molecular-weight substance (ethanol) The aromaticsubstances did not affect the performance of the fibers or membrane This isbecause the small pore diameters did not permit the large aromatics to penetrate.The results indicated that the second mechanism, a competitive effect betweengold cyanide and the organic compounds, was responsible for the results observedfor the gold-equilibrated absorbents

ad-Klein et al (16) have investigated polymeric resins as adsorbents forindustrial applications The motivation for investigation of polymeric resinsversus activated carbon is their ease of regeneration Activated carbon systemsare typically regenerated using steam or thermal methods, while polymeric resinscan be regenerated using simple solvents such as aliphatic alcohols The resinsused were methylene-bridged styrene divinylbenzene-based co-polymer (DowChemical, Midland, MI) Some of the characteristics of these polymeric resinswhich may be controlled are hydrophobicity, pore size, and surface area These

resins were challenged with benzoic acid and chlorobenzene, and adsorptionisotherms and bed regeneration curves were generated The results of this studyindicated that with only few bed volumes (15–25), using methanol as regenerant,90–95% of the adsorbed solute could be recovered The polymeric resins main-tained good adsorptive capacity after repeated cycling.

3 ION-EXCHANGE MATERIALS AND PROCESSES

Applications of ion exchange to leaching solutions of an Algerian gold ore havebeen investigated by Akretche et al (17) In the cyanide medium, the gold andother metals such as silver, copper, and iron attach to the anion-exchange resin.These metals are later eluted with acid thiourea to yield a concentrated solutionwhich is treated by cementation or an electrolytic method This work describesthe use of electrodialysis of copper(I), which is normally not feasible due to thepresence of formamidine disulfide This is accomplished when the solutions areobtained by elution of cuprocyanides by thiourea

4 CONCLUSIONS

There have been great strides in the development of new technologies forpollution control in the mining industry during the past five years, many in thedevelopment of new materials and processes Many of these developments are inthe areas of membranes, adsorbents, and ion exchange In the area of membranes,

a great of work has been done using liquid membranes These are generallysupported synthetic membrane systems with a variety of liquids to facilitatetransport Electroremediation and electrodialytic membrane approaches have alsoseen a great deal of attention Activated carbon-based and other organic ab-sorbents have been used for treatment of mining wastes Polymeric resins havealso been used as adsorbents for industrial applications Anionic ion-exchangeresins have also been used for treatment of leaching solutions

6 D Si-Hassen, A Ould-Dris, M Y Jaffrin, and Y K Benkahla, J Membrane Sci.,vol.

VA, Lancaster, PA: Technomic Publishing Co Inc., pp 174–182.

9 H K Hansen, L M Ottosen, S Laursen, and A Villumsen, Separation Sci Technol.,

vol 32, no 15, pp 2425–2444, 1997.

10 Z Li, J Yu, and I Neretnieks, Environ Sci Technol., vol 32, pp 394–397, 1998.

11 L Boyadzhiev and K Dimitrov, J Membrane Sci., vol 68, p 137–143, 1994.

12 T Kakoi, M Goto, and F Nakashioo, Separation Sci Technol., vol 32, no 8,

16 J Klein, G M Gusler, and Y Cohen, Removal of Organics from Aqueous Systems:

Dynamic Sorption/Regeneration Studies with Polymeric Resins In Novel Absorbents and Their Environmental Applications, Y Cohen and R W Peters (eds.), AIChE

Symp Ser., vol 91, pp 72–78.

17 D E Akretche, A Gherrou, and H Kerdjoudj, Hydrometallurgy, vol 46, pp 287–

301, 1997.

The present chapter reviews recent efforts at the author’s laboratory, aimed

at in-situ monitoring of priority pollutants Continuous monitoring, effected in thenatural environment, offers a rapid return of the chemical information (with aproper alarm in case of a sudden discharge), avoids costs and errors associatedwith the collection of discrete samples, while maintaining the sample integrity.The use of remote sensors thus has significant technical and cost benefits over

traditional sampling and analysis Our latest developments of remote chemical probes will be covered in the following sections.

electro-2 REMOTELY DEPLOYED ELECTROCHEMICAL SENSORS

Remotely deployable submersible sensors capable of monitoring contaminants inboth time and location are advantageous in a variety of applications These rangefrom shipboard marine surveys, downhole monitoring of groundwater contami-nation, to real-time analysis of industrial streams The development of sub-mersible electrochemical probes requires proper attention to various challenges,including the effect of sample pH, ionic strength, dissolved oxygen, or naturalconvection, specificity and sensitivity, surface fouling, in-situ calibration, andminiaturization By addressing these and other obstacles, we were able to developremote sensors for a wide range of inorganic and organic contaminants

2.1 Remote Monitoring of Metal Contaminants

Metal pollution has received enormous attention due to its detrimental impact onthe environment The need for continuous monitoring of trace metals in a variety

of matrices has led to the development of submersible sensors based on chemical stripping analysis (1,2) Stripping analysis has been established as apowerful technique for determining toxic metals in environmental samples (3,4).The remarkable sensitivity of stripping analysis is attributed to its unique “built-in” preconcentration step, during which the target metals are electroplated ontothe surface Both electrolytic and nonelectrolytic (adsorptive) accumulationschemes have thus been employed to achieve sub-parts-per-billion detection

electro-limits The analytical current signal (i), obtained during the subsequent stripping (potential scanning) step is proportional to the metal concentration (C) and accumulation time (tacc):

Remote metal monitoring has been realized by eliminating the needs formercury surfaces, oxygen removal, forced convection, or supporting electrolyte(which previously prevented the direct immersion of stripping electrodes intosample streams) This was accomplished through the development of nonmercuryelectrodes, judicious coupling of potentiometric stripping operation, and the use

of advanced ultramicroelectrode technology (1) Compatibility with field tions was achieved by connecting the three-electrode housing [including a goldfiber working electrode, in the polyvinyl chloride (PVC) tube], via environmen-tally sealed three-pin connectors, to a 25-m-long shielded cable Convenient andsimultaneous quantitation of several trace metal levels (e.g., Pb, Cu, Ag, Hg) has

opera-thus been realized in connection to measurement frequencies of 20–30/h (based

on deposition periods of 1–2 min)

The in-situ monitoring capability of the remote metal sensor was strated in studies of the distribution of labile copper in San Diego Bay (CA) (5).For this purpose, the probe was floating on the side of a small U.S Navy vessel.The resulting map of copper distribution reflected the metal discharge andcirculation pattern in the bay We are currently collaborating with Prof Daniele’sgroup in using the remote probes for assessing the distribution of metal contam-inants in the canals and lagoon of Venice, Italy (6)

demon-The extension of remote stripping electrodes to additional metals thatcannot be electroplated relies on the adaptation of adsorptive stripping protocolfor a submersible operation (7) Such procedures rely on the formation andadsorptive accumulation of complexes of the target metals Accordingly, remoteadsorptive stripping sensors require a new probe design based on an internalsolution chemistry Such a renewable-reagent adsorptive stripping sensor relies

on the continuous delivery of the ligand, its complexation reaction with the metal

“collected” in a semipermeable microdialysis sampling tube, and transport of thecomplex to the working electrode compartment Such dialysis sampling alsooffers extension of the linear range and protection against surface fouling (due toits dilution and filtration actions)

The new flow-probe format was employed for monitoring trace metals such

as nickel, uranium, or chromium As desired for effective in-situ monitoring, suchadsorptive stripping probes have the capability to detect rapidly fluctuations inthe analyte concentration continuously Such ability is indicated from Figure 1,

which displays the response of a chromium probe (8) upon switching from the

5-to 25 µg/l chromium solutions Such behavior is attributed to the reversibility ofthe accumulation/stripping cycle, with the stripping and subsequent 10-s “clean-ing” steps completely removing the accumulated complex In addition, the

F IGURE 1 Response of the remote chromium(VI) probe to alternate sures to (a) “low” (5 µg/l) and (b) “high” (25 µg/l) chromium(VI) levels Accumulation for 30 s at –0.9 V; square-wave voltammetric stripping scan.

expo-reagent flow continuously replenishes the solution, to “erase” an internal buildup

of chromium

Other groups have also been involved in the development of remote metalsensors For example, Kounaves’s team reported on probes based on mercury-plated iridium-based microelectrode arrays and square-wave voltammetric strip-ping detection (9) A solid-state reference electrode that eliminates leakage ofelectrolyte to the surrounding low-ionic-strength aquatic environment was em-ployed The device developed by Buffle’s group (4,10) has been coupled to athick agarose-gel antifouling membrane that facilitates measurements in complexmedia There is no doubt that these and similar developments of submersiblestripping sensors will have a major impact on the surveillance of our waterresources

2.2 Remote Modified Electrodes and Biosensors

Chemically and biologically modified electrodes (CMEs) have greatly enhancedthe power of electrochemical detectors and devices (11) The ability to deliber-ately control and manipulate surface properties can lead to a variety of attractiveeffects Electrochemical sensors based on modified electrodes combine the re-markable sensitivity of amperometry with new chemistries and biochemistries.Such manipulation of the molecular architecture of the detector surface offers newlevels of reactivity that greatly expand the scope of electrochemical devices, andenhance the power of in-situ electrochemical probes

2.3 Biosensors

Biosensors are small devices employing biochemical molecular recognition erties as the basis for a selective analysis The major processes involved in anybiosensor system are analyte recognition, signal transduction, and readout Theremarkable specificity of biological recognition processes has led to the develop-ment of highly selective electrochemical biosensors In particular, enzyme elec-trodes, based on amperometric or potentiometric monitoring of changes occurring

prop-as a result of the biocatalytic process, have the longest tradition in the field ofbiosensors Such devices are usually prepared by immobilizing an enzyme ontothe electrode surface The integration of these devices with remotely deployedprobes should add new dimensions of specificity to in-situ electrochemicalmonitoring of pollutants In the adaptation of enzyme electrodes to a submersibleoperation, one must consider the influence of actual field conditions (pH, salinity,temperature) on the biocatalytic activity

The first remotely deployed biosensor targeted phenolic contaminants

in connection to a submersible tyrosinase enzyme electrode (12) The enzyme,immobilized within a stabilizing carbon paste matrix, converted its phenolicsubstrates to easily reducible quinone products The sensor responded rapidly

to micromolar levels of various phenol contaminants, with no carryover ory) effects.

(mem-We also developed a remote biosensor for field monitoring of phosphate nerve agents (13) The device relied on the coupling the enzymaticactivity of organophosphate hydrolase (OPH) with the submersible amperometricprobe configuration Low (micromolar) levels of paraxon or parathion have thusbeen measured directly in untreated natural water matrices The OPH enzymeobviates the need for lengthy and irreversible enzyme inhibition protocols com-mon to inhibition-based biosensors

organo-Finally, hydrogen peroxide and organic peroxides have been monitored atlarge instrument–sample distances by incorporating a reagentless peroxidasebioelectrode into the remote probe assembly (14) A low detection potential(~0.0 V) accrued from the use (co-immobilization) of a ferrocene co-substrateallowed convenient monitoring of micromolar peroxide concentrations in un-treated samples

2.4 Modified Electrodes

Chemical layers can also be used to enhance the performance of electrochemicaldevices The use of electrocatalytic surfaces can expand the scope of remoteelectrodes to pollutants possessing slow electron-transfer kinetics One example

of the adaptation of modified electrodes for a submersible operation is a remotesensor for toxic hydrazine compounds, based an electropolymerized films of3,4-dihydroxybenzadehyde (15) The low-potential detection accrued from thiscatalytic action offers convenient measurements of micromolar hydrazine con-centrations in untreated groundwater or river water samples

We also developed a submersible probe based on a carbon-fiber workingelectrode assembly, connected to a 50 ft-long shielded cable, for the continuousmonitoring of the 2,4,6-trinitortoluene (TNT) explosive in environmental matri-ces (16) The facile reduction of the nitro moiety allowed convenient andfast (1–2 s) square-wave voltammetric measurements of parts-per-million levels

of TNT

The ability to perform metal–ligand complexation reactions on a cable platform,

in connection to adsorptive stripping measurements, has led to the development

of submersible electrochemical analyzers (17) As opposed to current in-situsensors (which lack sample preparatory steps, essential for optimal analyticalperformance), the new on-cable automated microanalyzer will eventually incor-porate all the steps of the analytical protocol into the submersible device The new

“lab-on-cable” concept thus involves the combination of sampling, sample

pre-treatment, separation of components, and detection step (along with self-calibration)into a single sealed submersible package The first generation of this submersiblemicrolaboratory integrates microdialysis sampling, with reservoirs for the re-agent, waste, and calibration/standard solution, along with the micromump andnecessary fluidic network on a cable platform (Figure 2) The sample and reagentare thus brought together, mixed, and allowed to react in a reproducible manner.Future generations will accommodate additional functions (e.g., preconcentration,filtration, extraction) for addressing the needs of complex environmental samples.Micromachining technology is being explored for further miniaturization and forfacilitating these in-situ sample manipulations Proper attention is also beinggiven to the design of compact, low-powered, automated instrumentation forunattended operation, “smart” data processing, and signal transmission (viasatellite links) Such a standalone “microlaboratory” can be submersed directly

in the environmental sample, to provide real-time continuous information on awide range of priority pollutants The ability to perform in-situ all the necessary

F IGURE 2 Schematic diagram of the electrochemical “lab-on-cable” system: (A) cable connection; (B) micropump; (C) reservoirs for reagent and waste solutions; (D) microdialysis sampling tube and an electrochemical flow detector.