Michele Christian explains the synergy of membrane cleaners
Membrane cleaning often challenges water treatment facilities across a variety of industries. As membranes become fouled from use they become less effective. Clean membranes allow for the proper flow of water. Keeping membranes clean is key to maintaining an optimal flux rate and helps to ensure that the treatment facility is operating effectively.
The economics of maintenance Treatment facility operators realise the importance of implementing a regular membrane cleaning regime, but are often challenged to find the right cleaning products. Ideally they will want to find a cleaner that will restore membrane flux (which will in turn prolong the life of the membrane), reduce the cleaning frequency needed, be safe for both the membranes and the environment, and prove easy to use. Using the right membrane cleaner is a good economic decision as it minimises downtime and prolongs membrane life. Since membranes are extremely expensive, most facilities try their best to keep them operational for as long as possible.
Many membranes are sensitive to harsh chemicals and extreme pH levels. It is important for treatment plant and laboratory operators to choose cleaners that will not be harmful to the membranes. Many speciality cleaners with mild pH ranges and safe ingredients are formulated to be effective, non-harmful cleaning agents for membranes.
The correct chemical is key
Another consideration in choosing the proper membrane cleaner is the type of soil found in the water that is being treated. Alkaline cleaners dissolve oils and greases; some also contain chelants that can suspend metals and minerals. Citric acid cleaners are excellent at dissolving scale, such as calcium carbonate or iron oxide. Hazardous acid cleaners, such as sulphuric, hydrochloric and phosphoric, will serve the same purpose, but citric acid is much safer and has a broader range of filter compatibilities. A citricacid cleaner that also contains surfactants can go after many oils and greases that might be present in addition to the scale. In the food processing industry, soils can contain proteins and starches; in this case enzymatic cleaners might be needed. Most foulants are combinations of various soils; therefore choosing a formulated cleaning product with multifunctional ingredients is usually best.
One US wastewater treatment plant has an auxiliary effluent re-use facility constructed specifically to produce reverse osmosis quality water destined for ethanol production. The plant requires approximately 1,000,000 gallons (3.8 million litres) of reverse osmosis water per day above its normal processing volumes. The wastewater control systems manager manages the effluent re-use facility to ensure this additional volume is met on a daily basis. A key component of the effluent re-use facility is the ultra-filtration process, which uses 0.4μ polyvinylidene difluoride (PVDF) membranes with an upper pH limit of 10.0. These membranes are fouled primarily with petroleum sulphonates and bacterial secretions. Particularly in cold weather, the upstream BOD step has frequent “upsets,” where the bacteria die and secrete a water- soluble foulant that adheres strongly to the PVDF polymer and significantly increases the trans-membrane pressure (TMP). These “upsets” must be resolved quickly to ensure a plentiful supply of pure water.
Passing the test
To determine the optimal cleaning regime, the plant manager systematically evaluated the performance of 20 different cleaners and hundreds of different combinations and concentrations, including commonly used commodities and many formulated membrane cleaners. The results found International Products Corporation’s Micro-90 was one of the top performing cleaners in the study. Micro-90 stood out because the product performed better than all of the commodities and other formulated membrane cleaners, particularly on the bacterial secretions. It worked effectively without the use of phosphates, silicates, and strong alkalis, at a membrane-compatible pH of only 9.5, and at a 0.3% concentration.
The synergy
Micro-90 is a mild yet powerful, multipurpose, alkaline cleaning concentrate that has long been used in laboratories, industrial applications and critical cleaning processes. It is a chelating detergent that contains ionic and non-ionic ingredients, which combine to produce a variety of cleaning actions. It lifts, disperses, emulsifies, sequesters, suspends, and decomposes soils, then rinses away leaving the surface absolutely clean.
Micro-90’s target soils include oil, grease, wax, tar, flux, particulates, hard water stains, and biological debris. It is highly effective at defouling filter membranes and can be validated in critical cleaning applications.
A model for the future
Micro-90 has been in use at the effluent re-use facility since October 2010. Some of the original PVDF membranes are still used and continue to see considerable TMP drops after cleaning with Micro-90. Although the bacterial upsets cannot be prevented, their fouling can be resolved in a predictable manner with the use of Micro-90. Since the initial use of the cleaner, the effluent re-use facility design engineers have recommended it to other similarly designed effluent re-use facilities because of the product’s effectiveness, safe profile, compatibility and economical cost per use.
Because so many variables can exist in choosing the right cleaning product for each facility, it is important for treatment plant and laboratory operators to work with cleaner manufacturers that can offer them technical guidance and a variety of products to best meet their needs.
Match cleaner to industrial soil
IPC cleaners Cleaner pH Typical soils removed
Micro-90 9.5 Greases, oils, metals
Micro Green Clean 9.8 Greases, oils
Micro A07 3.0 Hard water salts, scales
Zymit Pro 7.5 Biological, protein, polysaccharides
For more information, visit www.scientistlive.com/eurolab
Michele Christian is with International Products Corp.
