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High purity water is water
which has been treated and modified to rigorous specifications. These specifications
include the removal of all contaminants (including organic compounds like
bacteria and non-organic compounds like ions), total organic carbon (TOC) and dissolved
gases. This creates water with very low conductivity and high resistance and
safe for injections into the bloodstream. Whilst there are many uses for high
purity water in Industry, including semiconductors, power generation (turbines
and super critical boilers) and solar photovoltaics, this report will focus on
the manufacture and application of high purity water in the pharmaceutical
industry. High purity water is commonly a diluent for many pharmaceutical
products. This include high purity water that is bacteriostatic for injections,
sterile water for inhalation of therapy products and sterile water for internal
irrigation therapy products (Rowe et al., 2014)


In this report I will discuss
the process by which high purity water is manufactured including the main
process overview, the reactants, and products and by products. I will also
discuss criticisms of the process and new manufacture designs being developedS1 .

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Process overview

The production of high purity
water is a multi- step process that differs due to the application of the product
and the start materials used.


Pre treatment

Large solid particulates are first to be removed
from the water using filtration. Clarifiers remove these particles; the number
of clarifiers in a system is dependent on the state of the raw water. Generally,
the raw water used to make ultrapure water for pharmaceutical use is of a sufficient
quality that only one or two clarifiers are required in pre-treatment. Large
grit is removed before entering the primary clarifier which produces a
homogenous liquid. This can then be biologically treated in the secondary clarifier
using coagulation and flocculation reagents (Mykolaiovch, 2005). This causes any suspended
solids to clump together and settle at the bottom of the clarifier which are
the removed. At this stage lime softening may also occur to reduce the alkalinity
of the water which reduces the probability of scale formation at later stages
of purification, particularly reverse osmosisS2 .


Capacitive deionisation (CDI)

This is the process by which
the removal of salt ions from water occurs resulting in water which is
deionised. This is achieved by applying an electrical potential difference across
two electrodes. Anions in the water are stored in the anode; likewise cations
are stored at the cathode.

Porous carbon is normally the
preferred material for the electrodes as it has a high surface area, good
conductivity, and high capacitance. (Anderson, 2010)

Commonly used porous carbons
in industry include carbon aerogel, carbon nanotube, graphene (Porada, 2013). In scale up,
100,000 tonnes of water can go through a CDI plant daily, with water recovery
at 75%. Whilst CDI is effective at removing large ions in the water, it does
not necessarily capture smaller ions so further deionisation processes have to
occur down the system line to counter this.

This process is advantageous
as it has a low level of energy consumption and is environmentally friendly. (Laxman, 2015). The raw material
for this process is brackish water, which has lower salinity than seawater. It
is favourable to use this start product as it responds well to treatment via
capacitive deionisation and it a waste product from the semi-conductor industry
so can be acquired at a relatively low cost. (Chong, 2017)





Reverse Osmosis (RO)

This is another process in the
production of high purity water involved in removing ions from water. In RO
water is forced from high solute concentration to low solute concentration by
applying a pressure that is in excess of the osmotic pressure. (He, 2016)

The start, raw water is
injected with sulphuric acid to lower the Ph then fed into production
trains. These contain membranes made up of a dense layer or polymer matrix which allow water
to pass through but prevent other solutes from entering. This system produces two
flow streams, one containing the water (permeate stream) and one containing reject
material (concentrate stream) (Yokogawa, 2015). The movement of the water is
controlled by high pressure pumps; for brackish water these pumps generally
operate between 15.5 and 26 bar (Lachish, 2002).

The water is then passed
through cartridge filters which remove sand and silt. All liquid by-products at
this stage are removed via a pipeline into a deep injection well. (Lachish,
The minimal energy requirements to complete RO is 0.75 kw/m3 of
water however, normally industry it is around 2 kw/m3 (Lachish,
The efficiency of the RO system in removing particles is determined by
conductivity measurements at the inlet and outlet of the tank.



Electrodeionisation (EDI)

EDI was developed as process,
that, coupled with reverse osmosis, in order to achieve maximum purity of
water. The main function of EDI is to remove ions using anion exchange resin,
which is commonly made from a styrene-divinylbenzene copolymer (Szilagyi, 1999). The resin bed is continuously
regenerated using a electrical current which eliminates the need for chemical
regeneration which reduces potential hazards and costs due to regulatory compliance
i.e. the disposal of waste products.

The water is fed
through a two-chamber system; the first is where the water is fed into to, and
the second is where the ions are removed. Due to the current flowing through
chambers the bonds in the water molecule break forming a hydrogen and hydroxyl

H2O                 H+
+ OH-                 

This occurs with
the contaminant ions also which exchange in the resin bed onto the second
chamber and are trapped into the contaminant stream (Szilagyi, 1999). Commonly, a pump is placed in the chambers
to increase mixing in the chambers and reduce the formation of scale so less maintenance
is required for the chambers.


UV sterilisation

UV radiation is
used to sterilise the water of bacteria. This the most favourable method as UV
does not remain in the water supply, does not produce drug resistant bacteria
and does not have a large impact on the environment. (Mori, 2007) The water is passed
through a dual wavelength UV steriliser (185-nm and 254-nm­) (Witham, 2007), this generates
hydroxyl radicals which, in turn oxidise organic matter and destroy bacteria.
The oxidation of the organic matter produces carbon dioxide which is removed
through an outlet and into the atmosphere. The remnants of the destroyed bacteria
are then removed by a submicron filter (Yokokgawa 2015).

UV radiation is instrumental
in the removal of TOC in the water. The level of TOC in the water is crucial in
determining whether the water fits the specifications for high purity water;
since the TOC cannot be measured directly, it is determined by the conductivity
of the final product.



is a process utilised to remove the gases which have dissolved, like carbon
dioxide and oxygen from the water. (Bhaumik, 2004). 
These gases are present in the water due to natural dissolution from the
air and due advanced oxidation processes performed by bacteria in the water
stream. Vacuum degasification is a method that is often used to remove oxygen from
water despite its shortcomings due to high operational costs (Tai, 1994). Another method to
remove oxygen is catalytic reduction which involves utilisation of a reducing
agent, namely H2 and N2H4. Both these methods
use membrane modules which provide a stable interface for gas transfer to
occur. A advantage of the use of membrane modules is that they can be operated
and a range of flow rates.


Process considerations

When designing a
system to produce high purity water many factors have to be considered. The
velocity of the flow rates need to have Reynolds of around 3000to ensure
turbulent flow. This is to ensure microbial attachment to pipe surfaces is not
likely and reduce the probability of a biofilm in tanks. (Soini, 2002). The production of
high purity water is not produced by batch and is continuous, with steady state
flow to avoid particle bursts which can increase stress on the pipes that they
are flowing through. High purity systems are commonly designed with reverse
return piping incorporated which helps prevent back flow (Siegenthaler, 2016). In the pharmaceutical industry, pipes
are primarily made from stainless steel, which contributes a small amount of metallic
substances to the water but was deemed low risk in this industry.

The membranes and
filters used in the process have to be ultra clean and non-corrosive. Most
filters are made from a mixture of polymers including polyethylene, nylon and polysulfoneS3 .
Membranes and filters are normally welded to their point of action; adhesives
are avoided at all costs as they break down and contaminate the water supply

Another factor to be
considered is process size. Typically, larger water production plants are favourable
than smaller lab sized purifications units. This is because larger systems tend
to have well trained operators running the plant at all times which allows for
the use of chemical treatments thus increasing efficiency.



The continued production
of high purity water is vital for the pharmaceutical industry. Not only does it
serve medical purposes in the industry, for example acting as a diluent for
injections and inhalation therapies, but it is also important in the continued
research in the biological field. High purity water is used as basis in growing
cell cultures as it provides a good control because it is basically free from
contaminants (Rathod, 2013). High purity water
also has applications in Mass Spectroscopy, again providing a contaminant free
liquid so that analysis remain uncompromised (Worley, 2012). The market for high purity water is expected
grow to a worth of $7.15 billion by the year 2020 (Markets, 2016)


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