Membrane sanitisation

Higher temperature possible for "heat sanitisable" membranes. Check with manufacturer. 

Preventive sanitisation is much more effective than corrective disinfection because a single attached bacteria is easier to kill and remove than a biofilm. Membrane life is shortened by extensive sanitisation. 

Sanitisation means disinfection for reducing microbial contamination down to an acceptable level, whereas sterilisation implies the inactivation of all microorganisms. Cleaning always precedes sanitisation. When a membrane system (membrane elements, pressure vessels and piping) has been infected by bacteria or mould, the system requires chemical sanitisation. Hot water sanitisation is used in pharmaceutical membrane systems. 

If an alkaline cleaning has preceded sanitisation, alkalinity must be carefully rinsed out of the membrane vessels, and the pH checked before hydrogen peroxide or hydrogen peroxide/peracetic acid solution is applied. The rinse must include the permeate side. If the alkahnity is not rinsed out, the membranes may get oxidised. 

HWS is commonly used to kill microorganisms. RO membranes reject bacteria and other microbes. However, due to defects in the membrane surface, the rejection is not 100% or absolute so that microorganisms can pass through the membrane into the permeate side of the membrane where they can multiply. Hence, sanitisation of a membrane system is essential for the production of US Pharmacopeia (USP) water and water for injection to meet the very low bacterial limits [57-59]. HWS of RO membrane (and EDI) systems is a relatively recent development made possible by the development of TFC membranes and membrane equipment capable of handling hot water at 85° C for a short time membrane elements are manufactured with special adhesives, permeate tubes and connectors to withstand elevated temperatures. These membranes also make it possible to sanitise and protect the RO membranes from bio-fouling especially when the use ofbiocides is not acceptable. Typical membrane manufacturers specifications of hot water sanitisable TFC membranes are given in Table 2.14. 

Table 2.14 Hot water sanitisable operating conditions for a TFC-SW-RO membrane eiement ...

Clean-in-place (CIP) — the membranes are cleaned with acid followed by sanitising with sodium hypochlorite solution when the TMP exceeds 1 bar, typically 4— 6 weeks. Only one membrane unit is cleaned at a time. A combination of citric acid and sulphuric acid is inj ected by the dosing pump in the filtered water transferred from the CIP tank. The solution is circulated for 30 min followed by soak and aeration steps that last 90 min. Next, a dilute sodium hypochlorite solution is injected by the dosing pump in the filtered water transferred from the CIP tank. The solution is circulated for f SO min followed by soak and recirculation steps that last 90 min. 

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