1. Field of the Invention
The present invention relates to a process t for addressing the problems associated with microbial fouling of surfaces. Of particular interest in this regard is microbial fouling of membrane and heat transfer surfaces.
2. Description of the Related Art
Clean water is often required in many industries, such as the chemical, food and beverage, pharmaceutical, electronics, and power industries. Typically, applications in these industries require treatment of a water source to remove contaminants. Various techniques and chemistries for water treatment are known, including distillation, filtration, ion exchange, reverse osmosis, photo oxidation, and ozonation either alone or in combination with traditional chemical clarification. In many instances, feedwaters containing numerous dissolved solids, organic moieties, and microbially active components will move through a water treatment system or equipment such as a heat exchanger and thereby create a fouling condition that compromises efficiency of said system or equipment.
Membranes are commonly used to remove contaminants contained in process feedwater. Membranes of interest include microfilters, nanofilters, ultrafilters and reverse osmosis membranes. One problem that arises as a natural consequence of the filtration operation is the fouling of membrane surfaces. The fouling material can be broken down into the general classifications of organics, (i.e. humic substances, fats, oils and grease), inorganic, (i.e. clay, silt, calcium carbonate and calcium phosphate), and microbiological. The last group of contaminants (i.e. microbiological) is those to which the currently claimed process is applied.
Chemicals are commonly used to prevent the deposition of contaminants within the membrane. For example, antiscalants are used to remediate inorganic fouling. However, antiscalants have little or no effect on microbial fouling. To control microbial fouling, biocides are often used. However, while biocides kill microorganisms, some microorganisms still exist within the membrane, may feed off the residues of killed organisms and their presence act as a resistance to flow and therefore impede the efficient operation of the membrane system. Exacerbating the situation is the fact that the resultant biofilm that forms on the membrane may provide a protective niche for bio-growth and is difficult to remove. Normal treatments to remove or clean the membrane of microbial contamination requiring the use of chemicals can negatively impact the life of the membrane.
Indeed, the presence of a biofilm not only presents resistance to fluid flow, but when deposited on the surfaces of equipment, such as heat transfer equipment (e.g. heat exchangers used in industrial cooling towers) the biofilm presents a resistance to heat transfer. As in the case of membranes, chemicals known as biocides can be used to alleviate the problem, however these chemicals are costly and represent an environmental hazard. Additionally, the dead microbial materials that remain also hinder heat transfer efficiency. Hence there is a need to remediate biofouling on equipment such as heat transfer surfaces in industrial water processes For instance in a cooling tower the effect of accumulated biomass on the surfaces of the heat transfer equipment is similar to that accumulated on membranes. In one case, a fluid flow restriction results, while in the other a heat transfer flow restriction is the result. In either case, there is a need for a way to prevent microorganisms from entering the equipment, growing and propagating into established biofilms. The presently claimed process addresses this problem by mitigating the effect of microbial matter before it can interact with internal membrane and/or heat transfer surfaces.