Desalination.30(1979)145-153 OElsevierScientifkPublisbkgCompeny, Amstahm-PrWedinTheNetheriends

OPERATING EXPERIRNCRS OF A 15,000 CUBIC METER PER DAY MUNICIPAL

CORFU, GREECE

Dr_ John W. Arnold

IOniCS, Incorporated, 65 Grove Street, Watertown, MA 02172, USA

ABSTRACT

The initial eighteen month period of operation of the 15,000

plant on the Island of Corfu, Greece, is described.

DESALTING PLANT AT

3 m /day municipal

The 15,000 m3/day desalting plant employing the electradialysis reversal process

(EDR) produces potable water (500 ppm) from a blend of brackish sources with sali-

nities up to 2000 ppm TDS. The paper describes the plant and integration of the plant

into the municipdl system. The unique system employed to segregate the treatment of

the different brackish waters employing only the highest salinity water for blowdown

water is also described.

The plant was started up in the fall of 1977 and provided water to the municipal

system during the 1978 season.

The paper presents operating cost data for this period and compares these costs

with projected costs which form part of the contractual agreement with the Muni-

cipality-

The recently approved entry of Greece into the European Economic Community puts

a premium on the development of local industry and, specifically, the continued

development of the tourist industry_ Corfc, an island off the west coast of Greece

in the Ionian Sea. is a major tourist center which is being rapidly developed- This

development has necessitated the improvement and addition of many facilities in-

cluding the improvement in quality and quantity of the water supply system_

Prior to 1978, the water supply system for the Town of Corfu was totally in-

adequate in quantity and the mineral content greatly exceeded the Greek and World

Health Organization Standards for drinking water. The problem was especially criti-

cal during the summer months when low rainfall, coupled with the influx of tourists,

required the use of wells with increasingly higher mineral content and hardness.

The requirement to improve the quality and quantity of the water supply in Corfu,

in order to promote the continued development of tourism, was recognized by the

Greek authorities and resulted in the construction of a 15.000 cubic meter per day

145

146 ARNOLD

desalting plant based on the Ionics Eiectrodialysis Reversal process (EDR)_ The

design of the EDR desalting plant was initiated in late 1974 and the plant was

commissioned in the summer of 1977 with actual plant acceptance performan ce tests

being carried out in October of 1977. The EDR desaltingplantoperateddurinu the

complete 1978 tourist season and has again bean restarted in April. 1979 to meet

the increased water demands of the 1979 tourist season.

The original municipal water system of the Town of Corfu consisted of one well

field and several springs located up to 25 km from the town. The capability of

the original supply was limited to approximately 8,000 m3/d. The original demand 3

ranged from 4.000-5.000 m /d in winter, to the maximum available from the system

(8,000 m3/d) in summer. The geographical location of the sources of raw water

which supply the town are shown in Fig. l_ The well field at Gardiki is approxi-

FIGURE l- Corfu

_mately 25 km from the town reservoir and the Chrysiis spring is closest at approxi-

mately 3 km. The two additional significant springs, St. Nicholas and Karterion

are located approximately midway between the city and the Gardiki wall field. The

quality of the four sources range from the low salinity spring of St. Nicholas

(662 ppm TDS) to the highly mineralized springs of Cbrysiis (2.073 ppm TDS)_ The

better quality sources have limited capacity, whereas the Chrysiis spring has a

capacity in excess of 15,000 m=/d_

Operation of the original municipal system involved the use of water from the

better sources during the winter season, whereas during the summe r season, a blend

of all sources was employed_ This resulted in a poor quality and inadequate supply

during the summer season with frequent service interruptions-

EDR DESALTING PLANT

The EDR desalting plant was constructed for the Municipality of Corfu by a joint

venture company of Ionics. Incorporated Watertown, MA, USA) a;ld Technom S.A.

(Athens, Greece). The "turnkey" contract included the complete study and detailed

mechanical, electrical and civil design which was carried out in Greece by Ionics/

Technom in cooperation with the Kinistry of the Interior in Athens, and the Engi-

neering Department of the Municipality of Corfu. Also included in the contract

ARNOLD 147

were construction of civil works , plant buildings, pipelines, pumping station,

equipment supply and installation, including integrationof the plantwlth the

existing municipal water systen.

Flowsheet and Plant Description

The influent feed water to the EDR desalting plant involves the blending of

waters from the springs of St_ Nicholas and Karterion (2,500 m3/d) with %he high

salinity gypsum water of the Chrysiis sprhg and the supplementary water from the

wells at Gardiki (7.500 m3,d)_ The Chrysiis spring supplies 11,500 m3/d to the EDR

plant and is used as both feed water and concentrate makeup water. Table 1 details

the analysis of these raw water sources together with their volumetric contribution

to the plant capacity. The plant produces 15,000 m3/d of 500 ppm TDs water from a

feed water blend of approximately 1,400 PPm TDS, at a Product recovery rate of 70%.

The waste TDS is approximately 4,000 ppm TDS.

CORN WATER ANALYSES AND FLOWS

~tituent sodium (Na+l

CalCIum Iti-1

Magnesium ww+l

Chlouda (Cl-7

6rcarbaMte (HCO-,I

Sulfate [so=.1

Total Dlssalved Solid3 (lDS)

Daily flow. 641

Total Daily Row. M'

10

100

51

36

261

422

666

7666

St. NiChObS

65

90

31

35

267

244

tcalturlon

21

166

66

36

266

446

2073

11500

21.506

Dlluatu secl

19

26.5

66

36

294

699

1401

165M)

The blended feed water is filtered through 10 micron cartridge filters before

entering a 475 m3 reservoir. The Chrysiis water is divided into two portions, one

is mixed with the feed and the other is added to the recirculated concentrate stream

as makeup water blowdown from the concentrate stream.

The feed water is pumped from the reservoir tank through the membrane stacks and

is desalted and emerges as product water_ The concentrate stream is recirculated

from the concentrate tank through the membrane stacks. The waste water is blowdown

from the concentrate return line from the meznbrane stacks and the makeup water is

added to the concentrate tank. The waste water blowdown, at a pH of 7.6 and approxi-

mately 4000 ppm TDS, is pumped out to the sea.

The membrane stacks of the Corfu EDR plant are arranged in six parallel modules.

Each ioodule contains individual flow controls, DC rectification and instrumentation.

There are ten membrane stacks in each module and each membrane stack contains 380

cell pairs consisting of an anion membrane, cation membrane, concentrate and feed

water flow spacers. The total membrane area in the six plant xmdules is approximately

148 ARNOLD

21,000 square meters.

Each individual module is further divided into four parallel desalting lines.

Two of these lines have two stages of demineralization, and the other two lines

have three stages of demineralization- Approximately 45% of the feed flow passes

through the three stage line and is desalted from 1400 to 462 ppm TDS- The other

55% of the feed passes thrcugh the two stage line and is desalted from 1400 ppm to

532 ppm TDS.

These two product waters are blended in the product line to give a 500 ppm TDS

product water.

The modular plant arrangement provides the flexibility to meet seasonal changes

in the municipal demand and the facility to take care of maintenance requirements

during peak periods of operation.

The plant is installed on a 400 square meter site adjacent to the intersection

of the pipelines from the two raw water sources. The raw waters are pumped to the

Plant site in two pipelines. The first pipeline carries the waters from Gardiki,

St_ Nicholas and Karterion sources_ These combined waters are commonly called the

Perama Water, named after the hill over which the pipeline passes before entering

the plant site. The second pipeline is a 355 mm PVC line bringing water from the

Chrysiis spring.

The main plant building contains the membrane stacks, electrical equipment,

rectifiers, maintenance area, spare parts storage area, and central control room

with adjacent office and personnel facilities. Header piping and controls and

filters are located outside on top of the concrete tanks adjacent to the building.

Process pumps and air compressors for instrument valve air are in a low covered

pump gallery adjacent to the tanks. Fig. 2 illustrates the plant arrangement.

I_ BIIU

FIGURE 2. EDR plant arrangement_

ARNOLD 149

The central control room is situated at the end of the building between the indoor

membrane stack area and the outdoor tank, filter and pump area. This arrangement

permits the operator at the central control panel to observe the indoor and outdoor

equipment through the front and rear control room windows (Fig. 3)_

FIGURE 3. The Corfu EDR control room.

Electrical equipment, the central switch gear , motor controls and DC rectifiers

are in a room located beneath the control room. This central location of the elec-

trical service minimizes the length of power cables and provides the best environmen

for t?le electrical power equipment.

The membrane stack area and the maintenance area are in the main room of the

building. The removal and replacement of membrane stacks from the operating wsitic

to the maintenance area is accomplished by use of an overhead travelling crane which

spans the width of the building. Four spare membrane stacks are located in the

maintenance area and are used to replace operating stacks when required. This per-

mits plant operation to continue at full capacity when the problem stack is serviced

in the maintenance area.

The maintenance area also contains chemical cleaning equipment which can be used

to flush individual membrane stacks or groups of 5 or 10 membrane stacks located in

150 ABmLD

the operating module position.

UNIQUE PROCESS QiARACfERISTICS

The EDR Process

The EDR process is a basic improvement of the classical E-D process. EDR achieves

cleaning and descaling of electrodialysis membrane surfaces several tims per hour

by periodic reversal of the direct current flow through the symmetrical ED membrane

array and by simultaneous interchange of product and concentrate water flow paths

in the membrane stack.

The membrane stack is operated for 18 minutes and then the process is reversed

by an automatic timing circuit in the following sequence.

(i) The direction of the DC field is reversed by reversing the polarity of the electrodes, This polarity reversal immediately begins converting the product compartmants into brine compartments and the brine compart- ments into product compartments, since the direction of the flov of rhe ions is reversed.

(ii) Simultaneously, automatic air operated valves at the module exchange the feed and concentrate stream ffows in the membrane stacks.

(iii) For a period of approximately 1.8 minutes immediately following reversal. the water from both streams is "Off Specification". "Off Specification" water is diverted into the concentrate tank- This 'purge" of the brine and product compartments every 18 minutes breaks up polarization films and flushes away any loose scale,

The automatic in-process self-cleaning results in the prevention of Calcium

carbonate and calcium sulphate scale without the continuous dosage of acid or com-

plexing chemicals. Small quantities of muriatic acid have been used at the Corfu

plant for in-_olace chemical cleaning of the membrane stacks at approximately monthly

intervals. However. no continuous feed of any chemicals has been employed.

Seqregation of Waste Water Feed from Product Water Feed

The design approach employed in the Corfu RDR plant for the segregation of the

various available water sources is unique in the desalination field and is appli-

cable only in the electrodialysis process- The plant design segregates the most

saline water source, the Chrysiis spring, for use as concentrate blcwdown and waste

water. The lower salinity source waters are blended and used as feed water which

passes through the stacks and emerges as product water.

The ability to use a separate source water as concentrate makeup water and,

hence, achieve 100% recovery of the feed supply water is an extramely valuable and

unique characteristic of the electrodialysis process. Specifically. in Corfu, it

permits the further expansion of the municipal capacity by introducing seawater or

diluted seawater for concentrate makeup water to replace blowdown. Thereby, all

existing brackish source waters can be totally recovered as product water. In

general, this unique characteristic provides a desalting process which can be used

to treat and recover 100% of a brackish or waste water source by using a 1eSS

desirable and less valuable saline water as a segregated concentrate and makeup water

ABNOIB 151

OPERATINGEXPERIENCES ANDCOSTS

The Corfu plant was commissioned during the summer of 1977 and actual plant Per-

fonaance tests were carried out in October of 1977. The plant was then shut down

forthreemonths duringthelowdeman d period of the winter of 1977/78. During

this period a complete maintenance overhaul of the plant was carried out.

The plant was restarted in the spring of 1978 and operated duringthe complete

1978 tourist season. The plant was again shut down during the winter of 1978/79

and was restarted in the spring of 1979 to meet the increased demands of the 1979

tourist season-

A number of problems have been experienced during this initial 18 month period

of operation. They may be broadly classified as membrane stack, hardware. and

external factor problems-

The membrane stack problem was identified as an abnormal level of isolated

scaling causing blocked cells in a number of membrane stacks during the intitial

operation. Detailed investigation revealed that these isolated blocked cells

resulted from poor hydraulic flow distribution between the membrane surfaces caused

by intermambrane spacers having too great a thickness variation. These spacers

have subsequently been replaced with spacers of much more uniform thickness. As a

result, the incidence of blocked cells has been reduced to the anticipated design

levels_

The most significant hardware problems experienced during this initial period of

operation have been associated with reversal valves and operators. The problems

were frequent sticking of the valve discs and malfunctioning valve operators. The

The reversal valves employed were tandem coupled pneumatically operated butterfly

valves. The pneumatic operators originally specified by the manufacturer have

proven to be marginally sized. All operators on the inlet side of the module

(higher pressure side) have now been replaced with larger size operators. This

sticking of valves and operators was also aggravated by inadequate and poor quality

air supply. Water in the compressed air supply has been a particular problem during

the cold and rainy days in Corfu. Replacement of these undersized valve operators

by a larger size and installation of additional equipment for drying the air supply

has solved the majority of the valve and operator problems.

The major external factor problem experienced during this period of operation

his been the repeated breaks in one o f the feed water source pipelines. This

pipeline is an old cast iron line installed before plant construction. The frequent

breaks in this line have severely interrupted plant operation and the upset condi-

tions have increased the suspended solids and iron slims material present in this

specific source water. Following the repair of each pipeline break, a slug of

debris is moved down the line. This requires that the pipeline be purged for

some time after each repair and, hence, extends the plant shutdown period. Addi-

tionally, the increase in suspended solids has resulted in an increase in the

152 AFtNOLD

filtercartridge consumption for the filtration of this water source. A new section

of PVC pipeline is presently being installed and is scheduled for completion iu mid

1979_ It is anticipated this new PVC line will solve this troublesome problem-

The water costs based on actual operation during 1977/?8 are presented in Table 2.

The contractual cost data is expressed per unit of production for a 330 day year of

full load operation, whereas the 1977/78 actual cost date reflects the actual load

factor during this period. The difference between the actual and contractual cost

was made up by the equipment manufacturer under warranty.

TADLE 2

CORFU OPERATING AND MAINTENANCE COSTS

Power

EDR & Transfer Pumping

Membrane Replacement

Filter Replacement

Chemicals (acids & soda ash)

Labor Amortization

Insurance

TOTAL

1975 CONTRACTUAL

s/m3

O-048 0,039

0.007 0.009

0.007 0.007

0.003 0.0002

0.009 0.030 D-006 0.018 O-001 0.003

0.081 0.106

1977 ACTUAL

S/m3

The power requirement for the EDR plant comprises the pumping power to transport

the raw water to the plant, the EDR plant power (which includes rectifier power,

all internal pumping power and control power) and power to pump the desalted product

water to the municipal reservoir_ Flow measuring instrumentation was not available

to accurately determine the power to pump the raw water to the plant and, hence, the

power quantities and costs reflect only those associated with the EDR plant and to

transport the desalted water to the reservoir. Table 2 indicates the power consump-

tion over this entire initial operating period is approximately 20% below the con-

tractual values (l-6 76 kwh/m3 at a cost of US dollars 0_048/m3).

The costs for membrane replacement are US SO.O02/m' higher than the contractual

values. This increased cost is due to the relatively high replacement rate of

membranes during the initial period of operation which increased the annual replace-

ment rate from 17% to 25% per year. As detailed above, this was due to the high

incidence of blocked cells caused by non-uniform intermembrane spacers. Following

replacement of these spacers, the membrane replacement rate and cost have reverted

to approximately the contractual value.

The filter cartridge replacement costs were maintained at the contractual value

during this initial period of oPeration despite excessive cartridge use due to the

pipeline breaks noted. The high cartridge replacement caused by repeated pipeline

breaks was more than offset by the extremely low cartridge replacement rate for

AENOLD 1.53

the other pipeline supply , and controlled by repeated purging of the repaired

pipeline before commencing operation_

The only chemical used in the plant is a small quantity of muriatic acid for

chemical flushing of the membrane stacks- The costs in Table 2 correspond to a

once per nmnth flush per membrane stack with 3 to 5% muriatic acid.

The actual labor, amortization and insurance costs are approximately triple the

contractual values $ich reflect the seasonal load factor. Actual load factor

during this initial period of operation has been approximately 30%.

The total water costs over this period of operation confirm the capability of

the EDR plant to produce water for municipal use at realistic load factors at au

attractive economic price.