82 MANUFACTURING
RO uses a semi-permeable membrane to separate and capture the vast majority of impurities. As the feed water enters the semi-permeable membrane under pressure, the water molecules pass through, while the contaminants are held back and discharged through a reject stream. The reject stream can be fed through a secondary RO unit to reduce water rejected to drain, while the permeate from this RO can be recycled back to the feed water of the main system. RO can remove up to 99% of the dissolved solids, particles, colloids, organics, bacteria and pyrogens from the feed water. This can be coupled with a continuous electro-deionisation (CEDI) unit that uses a combination of resin and semi- permeable membranes to separate dissolved impurities (ions) from water and achieve the required conductivity standard. These systems use an electric current to continuously regenerate the resin mass and so do not require the use of chemicals.
Maintaining quality and ensuring compliance However, achieving the defined standard of water quality is not always straightforward. Poor system design can cause contamination. It is also important to consider the monitoring and testing regime, as required by the GMP guidelines, as well as the ongoing maintenance and servicing of the system. Eliminating other sources of contamination is also crucial. The International Society of Pharmaceutical Engineers (ISPE) provides guidance on the design of purified water systems in its Baseline Pharmaceutical Engineering Guide on Water and Steam Systems. Its recommendations include minimising deadlegs in pipework and maximising flow velocities to prevent stagnation. The guide also recommends the use of hygienic, zero deadleg valves to maintain microbiologically compliant water. Leading water treatment specialists such as Veolia Water Technologies can provide advice and guidance on the design of the system to ensure best practice is applied. In addition to the design of the system, the materials used also need to be considered carefully. Many water distribution systems, including those in cosmetics manufacturing facilities, are constructed using ABS (Acrylonitrile Butadiene Styrene) or PVCU (Poly Vinyl Chloride Unplasticised) pipework. Both materials can leach plasticisers and adhesive residues into the water, which can impact the quality of the water. The alternative to this is stainless steel, which has been used extensively in pharmaceutical and healthcare water systems and has proved to be far superior in terms of minimising contamination. The
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highly corrosion resistant 316L grade stainless steel has long been used in pharmaceutical and medical applications to ensure a high level of hygiene and low contamination. For smaller systems up to 25 mmNB, crosslinked polyethylene (PEX) is a cost effective and safe alternative to stainless steel. Importantly for purified water installations, both materials can be hot water sanitised.
Regular sanitisation is an integral part of
GMP protocols and essential for the control of microbial contamination. Chemical sanitisation requires the introduction of potentially hazardous chemicals, like sodium hypochlorite, ozone, hydrogen peroxide or peracetic acid, into the system. Once introduced, it is necessary to ensure that the sanitising solution reaches all the points of use on the system and remains in contact for a predetermined time. After the sanitising contact period, the solution has to be completely flushed from the system to prevent chemical contamination. Also, because RO systems operate at room temperature and the water is not
heated during the process, there is a risk of biofilms developing. Biofilms form inside the equipment, are difficult to remove and protect microorganisms from disinfection chemicals, potentially leading to increased levels of microbial contamination. Heat sanitisation can provide an effective solution to protecting the system against the formation of biofilms. Hot water sanitisation uses no chemicals and the heat is transferred by the movement of hot water through the system and aided by natural convection in the water and heat conduction along the pipework. This means that the downstream side of closed valves will usually reach sanitisation temperature without the valves needing to be opened.
Also, heat sanitisable membranes are now widely available for reverse osmosis, CEDI and ultrafiltration units. This means that the treatment equipment, storage vessels and distribution pipework can be sanitised as a whole system. The temperature is easily monitored by reliable, non-intrusive sensors mounted on the outside surface of the pipework. The relatively low cost of the
April 2020
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