During the washing process of the linen, which chemical substance is the most important? Many people think it is detergents, bleaching agents, and so on. Actually, many laundry factories neglect an important factor in linen washing. That is water.
Advantages and Disadvantages of Water
In linen washing, water runs through the entire washing process.
● Its advantages lie in:
- It has strong dissolving and dispersing power. It has excellent solubility for both inorganic and organic salts and can also dissolve and disperse carbohydrates, proteins, lower fatty acids, and alcohols.
- It is convenient to use and is also non-toxic and odorless. It serves as an extremely safe medium for water-based washing.
- It is cost-effective and abundant. Water is the most economical and fundamental detergent, which is also a readily available source.
● It also has some disadvantages.
- It cannot dissolve grease, so people cannot remove oil-based stains alone with water.
- Its high surface tension makes it difficult for water to penetrate the interior of linen fibers. This results in poor stain removal when fabrics are washed with water alone.
- Generally, water contains metal ions such as calcium and magnesium, which tend to affect the hand feel of linen. Also, iron ions easily make linen yellow. Therefore, to achieve the best linen washing results, water treatment is usually required, and softened water should be used for cleaning.
Concepts of Hard Water and Soft Water
Hard water is water containing a certain amount of impurities such as carbonates, bicarbonates, chlorides, sulfates, and nitrates of calcium, magnesium, iron, aluminum, and manganese. Among these, calcium and magnesium salts are widely distributed in nature, and they are the main components of hard water. In contrast, soft water is the water from which calcium and magnesium salts have been removed.
Hard water and soft water are classified by their hardness levels. There are typically 5 categories.
Extremely soft water: Below 15 PPM
Soft water: 15~50 PPM
Moderately hard water: 50~100 PPM
Hard water: 100~200 PPM
Extremely hard water: Above 200 PPM
The Impact of Hard Water on Linen Washing
The best water quality for washing is soft water. The soft water in nature is extremely scarce. If the hardness of washing water is over the standard, it will affect the washing quality of the linen and cause some harm.
● Impact on Washing Result
Calcium and magnesium ions in hard water deposit on fabrics. This causes white fabrics to become grayish, and has a bad impact on their whiteness and hand feel. Colored fabrics may fade, lose their vibrancy, and become rough to the touch.
The calcium/magnesium deposits on the textiles are firmly adhered to the fabric fibers. As a result, it is a challenge to remove these ions and restore the whiteness of grayed white fabrics. Also, soap scum easily accumulates on the drum walls of industrial washing machines and tunnel washers, which increases the difficulty of equipment maintenance.
Iron ions in water form rust (iron hydroxide) during heated washing, which forms brown spots on fabrics. This also makes white fabrics become yellow overall, and bright-colored fabrics may fade. Removing these rust stains needs rust removers or oxalic acid, but frequent use of such detergents accelerates linen wear and tear.
● Reduce the Effectiveness of Detergents
Calcium and magnesium ions in hard water bind with surfactants in detergents, reducing the surfactants’ activity and preventing detergents from performing as intended. As a result, the same amount of laundry chemicals fails to deliver optimal cleaning results. This forces laundry factories to increase detergent dosage, which leads to higher operational costs.
● Prevent Soil Removal
Calcium and magnesium ions in water can bind with substances in detergents to form precipitates. So some soil particles still adhere to fabrics after washing. These particles penetrate the small pores and capillaries of fibers, lodging in the interstices, and adhere more tenaciously than ordinary soil. It is more difficult to completely remove them.
● Impair Fabric Appearance and Service Life
Hard water dulls the original bright whiteness and luster of linen, and damages fiber color and alters shade. Over time, fibers gradually become stiff, brittle, easily break, and lose strength. Also, linen loses its inherent softness, which ultimately shortens its service life.
● Shorten the Service Life of Laundry Equipment
Under the influence of temperature, deposited limescale corrodes the metal surfaces of industrial washing machines or tunnel washers. Mineral consolidation clogs water pipes, causes severe wear on moving parts, and significantly shortens the equipment’s service life.
The Impact of Hard Water on Linen Ironing
In addition, hard water does harm to the ironing of linen.
● Clog Pipes and Reduce Heat Transfer
During linen ironing, the gradual accumulation of limescale (a deposit from hard water) narrows or even blocks the steam pipes of equipment such as steam generators, flatwork irons, and steam irons. This reduces the heat transfer efficiency of the ironing equipment.
● Corrode Ironing Tools
Limescale formed when hard water is heated is somewhat corrosive. Chloride ions in the limescale erode the pipe walls of containers at high temperatures and form iron salt limescale. This thins the pipe walls of the ironing equipment, which harms heat transfer and leaves potential safety hazards for high-pressure vessels.
Methods of Water Treatment
After understanding the hazards of hard water, laundry factories must do water softening treatment.
There are typically two common water treatment methods in laundry plants: ion exchange and membrane separation.
- The ion exchange method uses resin to replace calcium and magnesium ions in raw water. Once the resin becomes saturated with these ions, it will stop adsorbing them. At this point, industrial-grade pure salt is required to regenerate the resin for reuse. However, resin regeneration takes time and cannot be done indefinitely.
- The membrane separation method uses nanofiltration (NF) membranes or reverse osmosis (RO) membranes to intercept calcium and magnesium ions in water, thereby fundamentally reducing water hardness.
● Advantages
Stable performance, mature technology, large treatment capacity, and low cost.
● Disadvantages
- Relatively cumbersome operation.
- Continuous purchase of industrial salt is required.
- Troublesome resin replacement in the later stage.
❑Membrane Separation Method
● Advantages
Higher-quality effluent, high degree of automation, and simple maintenance.
● Disadvantages
High requirements for inlet water pressure, high initial equipment investment, and high operational costs.
The initial investment cost for resin-based purification is relatively low, and the initial investment cost for reverse osmosis (RO) is higher. However, in long-term operation, RO systems offer simpler maintenance and produce better-quality water.
In addition, laundry factories should also consider the hourly treatment capacity of the water treatment equipment and the size of the soft water tank when making a selection. Different configurations result in significant differences in initial investment costs. To choose the most cost-effective option, a comprehensive analysis and comparison are required based on factors such as the daily linen washing volume, the type of laundry equipment used, and the hourly water inflow of the laundry plants.
Post time: Nov-14-2025