Chlorinationplantdischargeintosea

MohamedZiaudeenShahulHameedA0066188U

User

7/19/2015

Abstract:

The aim of this report is to look on the problems related to the dosing of sodium hypochlorite

which should be contained only for the usage in sea water chamber of a typical power plant or

any other process plants that uses sea water for cooling purposes and to ensure that it will not

affect the marine organism’s growth and their life cycle in the sea.

If chlorinated water reaches an aquatic system, it has the potential to kill fish and other aquatic

organisms because of the chlorine concentration. One mode of action is likely through damaging

the gills, thus preventing the fish from breathing. Therefore, in many instances, it will be

necessary to dechlorinate the water in order to make it safe for discharge to the environment.

This report analyzes on various dechlorination techniques as well as methods for monitoring

chlorine levels in the sea water.

The clorine dosing not only affects the marine organisms but a number of studies have been

undertaken to identify the health effect of chlorinated water and DBPs on humans, but the

findings do not yield a conclusive result . Nonetheless, concerns have led to the regulation of

DBP formation, through suggestions such as the adoption of stringent maximum contaminant

levels (MCLs) and the use of other disinfectants such as chlorine or chlorine related compounds.

The mass transfer analysis on how it is effectively dechlorinated has also been evaluated in this

work. The objectives are to determine the how to efficiently transport waste chlorine by adding

dechlorinating agents and also to find the best and safe operational conditions.

This report basically analyzes the sea water intake chamber which is taken as control volume

and how diffusion and dispersion affects the hypochlorite dissolution into the sea water.

Initially the report focus will be on electrochemical reaction and mass balance analysis around

the sea water intake chamber, sodium hypochlorite dosing point into the chamber. Finally the

critical operating parameters will be discussed on how effective the electrochemical plant can be

operated without affecting the marine eco systems.

Objectives:

The objectives for this work are:

1)To analyze various physical and chemical processes involved in the production of chlorine.

2)Effective treatment of the waste water discharge of electro chlorination plant into the sea

3)Reduce the flow and pressure of sodium hypochlorite into the intake of sea water, so that it

reduces the mass transfer effect by diffusion outside the sea water chamber.

4)Mechanical means of control in the sea water chamber so that reduces the loss of hypochlorite

by means of dispersion mass transfer.

5)To produce the required concentration of sodium hypochlorite for dosage and analyze the

optimum control parameters.

Need for hypochlorite dosing :

To prevent biofouing in exchangers and equipments. It affects heat exchangers, water-

cooling pipes, propellers, Heating and cooling systems. Biofouling might also be found in power

stations or factories. Just like a clogged drain in the kitchen or bathroom, buildup of matter

inside cooling system pipes decreases performance. Again, fouling causes a domino effect.

Equipment must be cleaned frequently, at times with harsh chemicals, and the obstruction of

piping can lead to a shutdown of plants and economic losses.

To prevent this Biofouling and to increase the efficiency of equipments in power plant or

water treatment plant, sodium hypochlorite dosing is essential.

Figure 1: Typical Bio fouling in exchangers

Process description:

Sea water is used in power plants for condensing the massive amount of steam exhaust which

exits the end stage of steam turbine. Installation of cooling tower in Singapore terms is not

practical because of space constraint, spread of legionella bacteria and operational and

mechanical cost involved.

Chlorine is produced by passing an electric current through a solution of brine (common salt

dissolved in water). This process is called electrolysis. The production of chlorine is performed

by means of three existing technologies, according to the cell type used:

• Membrane cell.

• Mercury cells.

• Diaphragm cells.

In this report we will discuss about membrane cell process.

There are two types of reactions which takes place at anode and cathode. Potential difference is

applied between the anode and cathode on the sea water, as shown in the equation and there is

no separation between the products obtained by electrolysis .sodium hypochlorite is produced

directly and hydrogen is one of the by product which is to be avoided, according to the equations

described below, This hypochlorite produced tends to have lower concentrations than that

obtained in the cell membrane and has poorer quality, to introduce higher concentrations of

NaCl.

Reaction at anode: - equation I

2Cl→Cl! + 2e"

Reaction at cathode: equation II

2H!O + 2e" → H! + 2OH"

Sodium hypochlorite generation in electrolyzer: equation III

Cl! + 2OH" → Cl" + ClO + H!O

NaCl+H! →NaOCl +H!

The chlorine gas and sodium hypochlorite produced are commonly used for chlorination process

and for reducing or limiting the marine growth in the sea water pipeline. Chlorine gas hydrolyzes

in the water as shown in the equation. This is a reversible reaction and K1 represents forward

reaction and K-1 represents reverse reaction.

equation IV

Cl! + H!O ⇌ HOCl + Cl" + H#, KCl! =K$ K"$-

According to the literature the K1 and K-1values are calculated and these values essentially help

us to operate the electrolyzer – rectifier at an optimum temperature and at an optimum flow rate .

They are 22.3s-1 and 4.3 x104M-2s-1, respectively. For the production of chlorine it is given as

KCl2 =.3x10-4M2.Hypochlorous acid resulting from reaction as given in the next equation , is a

weak acid which dissociates in aqueous solution.

The rate equation can be given as

equation V

HOCl ⇌ ClO" + H#, K%&'(

As per the literature values , KHOCl reported to lie in between 1.5 x10-8 (KHOCl, at 0 °C=7.82)

for temperatures between 0 and 25°C.As we can note that it’s not practical to get the sea water

temperature typically below 29°C and average temperature of operation will always be at 32°C.

So options are considered to operate the rectifier –transformer at 25 °C - 26 °C, so that the

production of HOCl can be controlled without compromising the flow rate.

Advantages of electro chlorination process:

Most power plants find this process as the most economical way as the raw material used will

be sea water which is the source already available and the operation and maintenance cost

involved will be less as there are only few equipments involved in the operation.

Figure 2: Electrochllorination process

How chlorine disinfection works:

Chlorine kills pathogens such as bacteria and viruses by breaking the chemical bonds in their

molecules. Disinfectants that are used for this purpose consist of chlorine compounds which can

exchange atoms with other compounds, such as enzymes in bacteria and other cells. When

enzymes come in contact with chlorine, one or more of the hydrogen atoms in the molecule are

replaced by chlorine. This causes the entire molecule to change shape or fall apart. When

enzymes do not function properly, a cell or bacterium will die.

When chlorine is added to water, underchloric acids form:

Cl2 + H2O -> HOCl + H+ + Cl-

Depending on the pH value, underchloric acid partly expires to hypochlorite ions:

Cl2 + 2H2O -> HOCl + H3O + Cl-

HOCl + H2O -> H3O+ + OCl-

This falls apart to chlorine and oxygen atoms:

OCl- -> Cl- + O

Underchloric acid (HOCl, which is electrically neutral) and hypochlorite ions (OCl-, electrically

negative) will form free chlorine when bound together. This results in disinfection. Both

substances have very distinctive behaviour. Underchloric acid is more reactive and is a stronger

disinfectant than hypochlorite. Underchloric acid is split into hydrochloric acid (HCl) and

atomair oxygen (O). The oxygen atom is a powerful disinfectant.

The disinfecting properties of chlorine in water are based on the oxidising power of the free

oxygen atoms and on chlorine substitution reactions

Chlorination by-products

The major environmental concern of chlorination is the persistent by-products formed during the

chlorination process between chlorine and mineral or organic constituents of natural waters. It is

collectively describes as chlorination by-products (CBPs).

Chemical species generated by reactions of oxidation, addition and substitution with organic

matters are called CBPs. The formation of CBPs is found to be influenced by chlorine dose,

water quality, and local environmental conditions. However, it is not linearly related to the initial

hypochlorite and/or final total residual oxidant (TRO) concentrations. Furthermore, many CBPs

had proved to be toxic and carcinogenic for animals and humans when subject to long-term

exposure.

When applied to sea water chlorination, it refers to chlorinated and brominated compounds.

There are four major groups of CBPs, namely,

• Trihalomethanes

• Haloacetic acids

• Haloacetonitriles

• Halophenols (1)

Mass balance in the control volume:

In cases where we are dealing with rates of change, and where the hypochlorite, which is the

chemical of interest (i) enters the control volume only in water (not as an addition of dry

materials), the mass balance can be expressed in a form of equation as shown below:

.

𝐑𝐚𝐭𝐞𝐨𝐟𝐢𝐧𝐜𝐫𝐞𝐚𝐬𝐞𝐨𝐟𝐬𝐭𝐨𝐫𝐚𝐠𝐞𝐨𝐟𝐢𝐢𝐧𝐭𝐡𝐞𝐜𝐨𝐧𝐭𝐫𝐨𝐥

𝐯𝐨𝐥𝐮𝐦𝐞

@ = .

𝐍𝐞𝐭𝐫𝐚𝐭𝐞𝐨𝐟𝐚𝐝𝐯𝐞𝐜𝐭𝐢𝐨𝐧𝐨𝐟𝐢𝐢𝐧𝐭𝐨𝐭𝐡𝐞𝐜𝐨𝐧𝐭𝐫𝐨𝐥

𝐯𝐨𝐥𝐮𝐦𝐞

@ ± .

𝐍𝐞𝐭𝐫𝐚𝐭𝐞𝐨𝐟𝐟𝐨𝐫𝐦𝐚𝐭𝐢𝐨𝐧𝐨𝐟𝐢

𝐛𝐲𝐫𝐞𝐚𝐜𝐭𝐢𝐨𝐧𝐢𝐧𝐬𝐢𝐝𝐞𝐭𝐡𝐞𝐜𝐨𝐧𝐭𝐫𝐨𝐥𝐯𝐨𝐥𝐮𝐦𝐞

@

Because we will be dealing mostly with substances dissolved or dispersed in sea water and

Hypochlorite, it will be convenient for us to express the storage and transport terms in the above

equation based on concentrations. Doing that, and translating the word equation into symbols

yields an equation in the following form:

𝐝𝐝𝐭(∫ cdv)+, = ∑ QiCi-./(01 -∑ QiCi023/(01 ± ∫ rdv+,

In some cases, like low tides and high tides we need to consider varying flow rates and

concentration in the chamber often we deal with system that have stable conditions of sodium

hypochlorite and that is called steady state.

First case, we can consider the sea water as intake chamber as a batch reactor i.e, Q = 0. Batch

reactor as in our case assumed to be well mixed.

Disinfecting the sea water intake flowing at 20 m3 /hr x 1hr/60 sec x 1min/60sec

=20 x 1/3600 = 0.005m3/sec.

Water chamber assumed to be approx 5000m3. The influent (i.e,) sea water contains 104 sea

water creature per litre and chlorine dosage 2000 ppm (i.e,) 2000mg/l and the concentration in

the sea water chamber will be 2000 mg in (5000 x 1000)l =4 x 10-4mg/l.

The chlorine reacts with water in such a way that is depleted at a rate

𝒓𝒄𝒍 = R"𝟎.𝟐𝟎𝒉𝒓

S 𝑪𝒄𝒍*

When chlorine is exposed the organisms disappear at a rate of

𝑟;<= = −>!.!## ?@$%&'(% #@$%

𝑐;<=

Figure 3:Control volume for this process

X𝑑𝑑𝑡 [X 𝐶AB

AC𝑑𝑣^ =_ 𝑄D

DEFB;G𝐶AB,I −_ 𝑄D

;KL𝐶AB,I +X 𝑟AB

AC𝑑𝑣

Here each j represents a different inflow and outflow of sea water in and out of the

chamber.

Sodium Hypochlorite dosing tank

Sea water intake

Q1 = Sea water flow in to the chamber

Q2 , C2 = hypo in

Q3 = sea water inlet to the condenser

As the system is operating at steady rate, the reaction rate will be same throughout the

tank. There are two inflows the (hypochlorite dosing) chlorine in hypo and sea water flow (main

flow) in and out of the chamber and the main flow stream contains no chlorine.

𝑄DE𝐶ABMNO + 𝑄PQR;FB;G𝐶AB,PQR; − a𝑄DE + 𝑄PQR;b𝐶S+ 𝑟AB𝑉= 0

𝑄PQR;FB;Ga𝐶AB,PQR; −𝐶ABb − 𝑄DE𝐶AB+𝑟AB𝑉 = 0

𝑄PQR;FB;G =𝑄DE𝐶AB − 𝑟AB𝑉𝐶AB,ML;AT − 𝐶AB

Substitution of rate equation in the above form

𝑄PQR; =𝑄DE𝐶AB − dR−0.2 ℎ- S𝐶ABh 𝑉

𝐶AB,ML;AT − 𝐶AB

=S)*@$%#UVW.! PX Y@$%Z[

@$%,-./$0–@$% =

1!'2

3 #UVW.! PX Y]WWW^2Z[1!!!'(

% "_`&!45'(%

(4𝑥10"_𝑚𝑔/𝑙)

𝑄PQR; = 4.08𝑥10"_𝑚a

ℎ

The hypo dosing will dissipate from the chamber outlet when there is a turbulent flow or

high tide in the sea. This process can be assumed that the sea water chamber behaves like CSTR.

Method I:

Optimum residence time of chlorine in the chamber:

By reducing the residence time in the system, the amount of chlorine escape from the chamber

can be reduced.

Residence time is the average amount of time that a particle spends in a particular system. This

measurement varies directly with the amount of substance that is present in the system. Over

here the system we have taken is the ocean and we assume our control volume lies within the

part of ocean. The residence time is a representation of how long it takes for the concentration to

significantly change in the sediment or the concentration of sea water which is negligible.

The base definition for residence time also has a universal mathematical equation that can be

added to and adapted for different disciplines. This is as follows:

𝑟 =𝑠𝑦𝑠𝑡𝑒𝑚𝑐𝑎𝑝𝑎𝑐𝑖𝑡𝑦𝑡𝑜ℎ𝑜𝑙𝑑𝑎𝑠𝑢𝑏𝑠𝑡𝑎𝑛𝑐𝑒

𝑓𝑙𝑜𝑤𝑟𝑎𝑡𝑒𝑜𝑓𝑡ℎ𝑒𝑠𝑢𝑠𝑡𝑎𝑛𝑐𝑒𝑡ℎ𝑟𝑜𝑢𝑔ℎ𝑡ℎ𝑒𝑠𝑦𝑠𝑡𝑒𝑚

The generic variable form of this equation is as follows:

𝑟 =𝑉𝑞

In environmental terms, the residence time definition is adapted to fit with oceans. More

specifically it is the time during which water remains within an ocean and around the

hydrological cycle. The time involved may vary from days for shallow gravel aquifers to

millions of years for deep aquifers with very low values for hydraulic conductivity. Residence

times of water in rivers are a few days, while in large lakes residence time ranges up to several

decades. Residence times of continental ice sheets are hundreds of thousands of years, of small

glaciers a few decades.

In order to get a more clear understanding of the residence time, mass transfer by advection,

diffusion and dispersion must be considered.

Mass transfer by advection:

Mass transfer by dosing hypochlorite in the sea water intake chamber

𝜕𝑀D

𝜕𝑡 = 𝑄$𝐶$D + 𝑄!𝐶!D − 𝑄a𝐶aD

Mass transfer by diffusion

Sea water mixes with sodium hypochlorite.

Equation: 2 𝑗b,c = 𝑗dDFF,` +𝑗dDMR,`

eeL(𝐶𝑉) = (𝑄DE𝐶DE − 𝑄;KL𝐶;KL)+ (𝑟C + 𝑟f𝑎)𝑉

Mass transfer by dispersion:

Sea water intake creates turbulence inside the chamber and it leads to mass transfer by

dispersion.

Equation:3 𝑉 dAdL= 𝑄(𝐶DE − 𝐶;KL) +(𝑟C + 𝑟f𝑎)𝑉

Combining all the equations advection + diffusion + dispersion:

Equation:4 𝑄(𝐶DE − 𝐶;KL) +(𝑟C + 𝑟f𝑎)𝑉 = 0

dAdL=(𝑟C + 𝑟f𝑎)

Now we consider the evaporation of chlorine and take this into the account in our calculation so

that it will determine whether the hypochlorite closing into the chamber leaks out of the chamber

and how fast it evaporates.

Chlorine evaporates at a rate of 0.75gm active chlorine per day from the solution.

The evaporation rate of chlorine can be increased by bubbling air through the solution at the

outlet of the chamber. The rate of loss of chlorine from the sea water can be characterized by the

equation

𝐫 = −R𝟎. 𝟕𝟓 𝐦𝐢𝐧- S𝐜

Where c is the concentration of hypochlorite in the chamber .therefore, the removal of

hypochlorite can be characterized by a I order equation. Since we assume the sea water chamber

to be a steady state batch mixed reactor under normal conditions such as low tides.

𝐶𝐶𝑖𝑛

=1

1 +𝐾1𝑡𝑑

Where td is the detention time and to find td ,the below equation can be used.

V = Qtd

5000m3 = 20m3/h x td

5000=20m3/60min x td

Td=15000 min

C=4 X 10-4 mg/l

C-. = 2000mg/l

𝐶4X10!"mg/l

=1

1 + (0.75)(15000)

Concentration of chlorine at this rate using an additional mechanical means of evaporation will be 3.555 x 10-8 mg/l

If we use air bubble to help the mass transfer rate the amount of chlorine remains in the solution

will be 8.888 x 10-6 %.

Method – II:

Reducing the flow rate of chlorine:

Chlorine dosage can be controlled, so that the dispersion rate is lesser than the inlet flow to

the sea water condenser. But this raises a concern on dependability of operations and it has to be

monitored closely and also adjusted very often.

Excessive closing particularly hyperchlorination (use of high levels of chlorine) has several

known and potential negative effects on product sensor quality. Water treatment should be

managed with the goal of minimizing excessive closes. A term “disinfection hurdle” can be used

to help guide water quality management. The disinfection hurdle is the minimum point at which

there is enough free active disinfectant available to neutralize microbial activity to an acceptable

level.

(mg/l Cl2) (mgd flow) (8.34lbs/gal)=lbs/day Cl2

Figure 4: Chlorine dosing and point source

For example if the pipe line flow is approximated to 20,000m3/day, chlorine dosing can be

calculated and compared with the break point chlorination chart as below.

Flow rate of stream=20,000m3/day

If dosage would be 90.0ks of chorine/day

Conc. Of chlorine dosage

90kg/day $dOQ!WWWW^2 𝑥

$W6^=T=

𝑥 $^2

$WWWB =0.45mg/l

Figure 5:Break point chlorination

The amount of chlorine dosing added to the

pipe system is reffered to as break point

chlorination.Sufficient chlorine is added to

satisfy the chlorine demand and excess chlorine

is used as disinfectant.

According to the graph , The dosing should

not exceed 7 mg/l to avoid free chlorine

residual.

Calculating Flow (Q) of Discharge Water : Flow rates are required in order to calculate the

corresponding dosing rate of dechlorinating

solution required to neutralize the discharge

water. Two ways to determine the flow rate (Q)

of discharge water are by calculations or by

measurement as shown aove. A third way

would be to estimate flow by experience,

however, this is obviously not as accurate.

It is possible to calculate the flow rate (Q)

of water by knowing the velocity of water

being

discharged, and the cross-sectional area of the source of discharge, eg., a discharge pipe. The

following steps outline how to calculate the flow rate knowing the velocity of water exiting the

pipe:

i) Cross Sectional Area of Pipe

𝐶𝐴 = 1/4πd2

where p = 3.14... and

d = diameter in metres

ii) Calculate flow in cubic metres/second

𝑚#

𝑠𝑒𝑐= 𝐶𝐴 ∗ 𝑣𝑒𝑙𝑜𝑐𝑖𝑡𝑦𝑜𝑓𝑤𝑎𝑡𝑒𝑟𝑖𝑛𝑚/𝑠

iii) Calculate the flow in

𝑙/𝑚𝑖𝑛 =𝑚#

𝑠𝑒𝑐∗ 1000

𝑙𝑚# ∗ 60𝑠/𝑚𝑖𝑛

The value for Q will be in L/min (litres per minute). (2)

Analysis using tracer study :

On doing a tracer study on how chlorine dosing affects the surrounding other than the control

volume , the graph from literature study on chlorine dosing as a disinfectant can be used. Figure

6 is a comparison amongst normalised tracer curves, including results for idealised flow patterns

Plug Flow and Complete Mixing, as well as the Plug Flow with Dispersion condition estimated

for a contact tank in which chlorine is dosed periodically. experimentally by Rauen (2005) and

results of tests obtained in that study for distinct prototypeconfigurations. The plots show: a)

Residence Time Distribution (RTD) curves; and b) F-curves.

E(θ) is the normalized tracer concentration, F(θ ) is the accumulated tracer mass and θ is the

normalized time. The plotting area has been restricted where necessary to allow for a better

visualisation of the central part of the curves, noting that for the PlugFlow RTD curve E(θ )àα

for θ = 1.0 , while the Complete Mixing RTD curve is described by E(θ) =e"k, so that E (θ) à

0 as θ = α (3).

To prevent short circuiting the chamber :

This shows if the chlorine chamber should act as a completely mixed reactor , so that it will

have a characteristic similar to that of graph 2 and also a phenomenon called short circuiting can

be prevented. It is not practical to place any mixing devices in the giant chamber but when the

dosing line is placed in tangential direction it will create a spiral flow which will ensure the

dispersion in the chamber and the chances of short circuiting can be minimized. The advective

flow also usually creates and drives the flow recirculation zones by way of flow

separation,adverse pressure gradients, shear and viscous effects. It follows that the degree of

occurrence of short circuiting and enhanced mixing is proportional to the level of

longitudinal dispersion observed in the chamber.

Method III:

Dechlorinate the effluent:

Though Chlorination has been used widely to disinfect the sea water or waste water prior to

using in equipments like heat exchangers & reactors, dechlorination is an essential finishing

treatment process prior to the discharge.

Previously disinfected wastewater with significant levels of residual chlorine was routinely

discharged into the drainages and sewers. However it is clear that residual chlorine is toxic to

many kinds of aquatic life. Moreover, when chlorine reacts with organic materials in water it

forms carcinogenic trihalomethanes. As a result, dechlorination was instituted to remove residual

chlorine from wastewater prior to discharge into sensitive aquatic waters.

1. Sulfur Dioxide:

The least expensive and most effective way to dechlorinate is by the use of sulfur dioxide as a

reducing agent. It reacts with the hypochlorite ion to break the bond between the oxygen and

chlorine. The use of free residual chlorination followed by dechlorination with sulfur dioxide to

control the residual of potable water entering a distribution system is now an accepted modern

water treatment process.

Stoichometrically, 0.9 parts of sulfur dioxide are required to remove one part chlorine. In actual

practice, at least 10% excess may be required for complete dechlorination. Sulfur dioxide in

water dissolved rapidly to form sulfurous acid as shown in the equation below:

Equation 1: SO2 + H2O à H2SO3

The sulfite ion (SO3 -2), reacts with both free and combined forms of chlorine, as illustrated in equations as follows : Equation 2: H2SO3 + HOCl à H2SO4 + HCl (Free Chlorine) Equation 3 : H2SO3 + H2O + NH2Cl à NH2HSO4 + HCl (Combined Chlorine) As an alternative to sulfur dioxide gas, various dry chemicals are available which form sulfur

dioxide in solution. These include sodium sulfite (Na2 SO3 ), sodium metabisulfite (Na2 S2 O5

), sodium bisulfite (NaHSO3 ). However, Sodium metabisulfite and sodium bisulfite are mainly

used in small facilities because these materials are more difficult to control compared to sulfur

dioxide. The main disadvantage of this technique is an excess of sulfur dioxide must be present

to destroy all the chlorine. This excess sulfur dioxide not only creates an oxygen demand and,

but it also threatens aquatic life.

2. Activated Carbon:

Carbon adsorption is also an effective dechlorination method. The process of chlorine removal

by activated carbon is not a pure adsorption process. It also involves a chemical reaction

between the chlorine and the water where carbon acts as the catalyst. The reaction is believed to

be as follow:

a. With free chlorine residual:

C + HOCI à C(O) + HCI

b. With monochloramine (Two parallel reactions):

NH2CI + H2O + C à NH3 + HCI +C(O)

2NH2CI + C(O) à N2 + 2HCI + H2O + C

c. With dichloramine

2NHCI2 + H2O + C à N2 + 4HCI + C(O)

Where C is the carbon surface and C(O) is the surface oxide. Carbon adsorption is usually

implemented when total dechlorination is desired. But this technique has high equipment cost

compare to other methods. Regular backwashing of carbon beds is also necessary to restore

dechlorination efficiency.

3. Hydrogen Peroxide:

Hydrogen peroxide has found increasing use as an effective dechlorination agent for free

chlorine (HOCl and –OCl). It has been effectively used both for municipal and industrial

wastewater dechlorination. It reduces free chlorine, producing water and oxygen according to the

following equation:

OCI- + H2O2 à CI- + H2O + O2

Hydrogen peroxide reacts with free available chlorine in solutions with pH > 7. While there is no

upper limit to the pH, as a practical matter, pH 8.5 is preferred in order to provide an

instantaneous reaction. However, hydrogen peroxide reacts very slowly with combined available

chlorine. Consequently, solutions which contain ammonia (e.g., most municipal wastewater

effluents) cannot be dechlorinated with H2O2. When used on a large scale, dechlorination with

peroxide can be expensive and pose certain health risks.

Summary :

Despite the various methods of chlorine reduction or prevention in the ocean water or in the

drinking water, there are even alternatives which were tried in places like Italian Lagoon of

Venice. Chlorine dioxide, Peracetic acid (as anti-slime) and ammonium quaternary salts (as

molluschicide) are used as an alternative for sodium hypochlorite. The dosage of these

alternative products, now in use, has been optimised by a new method of electrochemical

monitoring system BIOX.

If there are effective cleaning systems or mechanical raking systems in the upstream the dosage

of chemicals can be much reduced in percentage when compared to those of the ineffective

mechanical cleaning systems.

Table of Figures:

Figure 1: Typical Bio fouling in exchangers ................................................................................................. 3 Figure 2: Electrochllorination process ......................................................................................................... 5 Figure 3:Control volume for this process .................................................................................................... 8 Figure 4: Chlorine dosing and point source ............................................................................................... 13 Figure 5:Break point chlorination .............................................................................................................. 13

Bibliography 1. Jenner, Henk and Wither, Andrew. Chlorination by-products in power station cooling water. s.l. : EDF Energy, 2011.

2. ENKON Environmental Limited, E. Chlorine Monitoring and Dechlorination Techniques Handbook.

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