CLEAN IN PLACE CLEANERS
Osmosis is a process found in all biological systems and results in water from a diluted solution passing spontaneously through a semi-permeable membrane onto a more concentrated solution on the other side, releasing energy in the process. This is counter productive to the requirements of desalination where in fact, we require the reverse to occur, i.e. we need fresh water to pass out of the concentrated solution to accumulate on the other side of the membrane where we collect and utilize it. A reversed process of this type requires the input of energy. One such mechanism is called, for obvious reasons, Reverse Osmosis, commonly abbreviated to R.O.
From the outset of an RO systems functional life, the membranes which are a vital aspect of the plants performance are subject to fouling; both of an organic and inorganic nature. Organic fouling relates mostly to bio fouling of the membranes; caused by organic matter such as bacteria; virus or phytoplankton material in the feed water. Inorganic fouling relates to inorganic matter such as heavy metals and concentrated salt compounds attaching themselves to the membrane wall forming scale crystals.
Membranes in an RO system become fouled by mineral scale, biological matter, colloidal particles and insoluble organic constituents. Deposits build up on the membrane surfaces during operation until they cause loss in normalized permeate flow, loss of normalized salt rejection, or both. Elements should be cleaned when one or more of the below mentioned parameters are applicable:
• The normalized permeate flow drops 10%
• The normalized salt passage increases 5 - 10%
• The normalized pressure drop (feed pressure minus concentrate pressure) increases 10 - 15%
If you wait too long, cleaning may not restore the membrane element performance successfully. In addition, the time between cleanings becomes shorter as the membrane elements will foul or scale more rapidly.
Clean in Place (CIP) Cleaning utilises chemicals circulated through the RO system to remove fouling off the membranes. Some RO Plants have a CIP cleaner installed with the plant. Most do not and it is left to the operator to instigate and arrange the membrane clean. If membrane cleaning is not instigated; irreparable damage can occur to the membrane wall and permanently affect the performance of the membrane.
A CIP plant consists primarily of a storage tank; sediment filter; heater element; pH monitor; temperature Monitor; flow meter; pump with VSD. Water in the storage tank is preheated to a maximum of 38 degrees Celsius. A specific alkaline cleaner is added to the tank filled with permeate water until
The pH reaches 11+. The alkaline solution is then slowly pumped through the membrane housings as a low flow; then allowed to sit and soak the membranes; then after a prescribed time; fast flow flushed from the membranes. The same process occurs with an acid cleaner of pH < 3. A good CIP clean will remove the foulant material on the membranes and restore the membranes to original performance.
Due to most existing RO plants not having their own built in CIP cleaners; AWS has designed 3 specific CIP
Plants. These stand alone CIP skids vary in size and can be purchased or rented. For existing plants with no CIP cleaners; AWS makes available its small and large CIP skid units to all prospective clients at a minimal rental providing they use AWS range of Genesys Chemicals with the clean. Assistance for the first clean is provided and the CIP units left with the customer for subsequent cleans. Both CIP units are skid mounted with independent heaters; electrical panels; storage tanks; pH and temperature monitors; VSD Pumps; flow meter and hoses. Alternatively; AWS can build to purpose your own tried and proven performance CIP unit.