In today’s highly competitive markets, many industries and organizations have already taken initiatives to implement new technology and wise use of all available natural resources of water and energy. They make plans with local utilities to reduce their demands for energy and water to save costs and improve the long-term sustainability of their business.
For potable water we don’t compromise. But for many routine industrial and commercial applications, treated recycled water is the effective way to reduce the demand for valuable fresh water resources. It is also a recognized green building practice.
In ground water, river, deep wells, tap water where oxygen content is low, the iron or manganese-bearing water is clear and colorless. Iron and manganese are in dissolved form. When exposed to air, iron and manganese are oxidized and change from colorless dissolved forms to colored solid forms.
Due to oxidation of softened iron grains in water convert iron particles into white, then yellow and finally convert it into red brown solid particles that settle down in water and remaining suspended iron particles leave the water with a red color. Manganese, generally, is dissolved in water, although some shallow wells contain colloidal manganese (black color). These sediments are responsible for the discoloration properties of water containing high concentrations of iron and manganese. These residues may be severe enough to block water pipes hence try to solve problems from its grass root level. Therefore, understanding of various parameters that play direct or indirect vital role in water is necessary.
Various Parameters
Iron and manganese can disturb flavor and color of food and water. They may react with coffee, tea and some alcoholic beverages to produce a black sludge, which affects both taste and appearance.
Manganese is intolerable in water even when present in smaller concentrations than iron. Iron will cause reddish-brown stain of dirty washing, ceramic tiles and floor and dishes, utensils and even glassware.
Manganese acts in a similar way but causes a brownish black stain. Soaps and detergents do not remove these stains, and use of chlorine bleach and alkaline builders (such as sodium and carbonate) may intensify the stains.
Iron and manganese deposits will form step by step layers in pipelines, pressure tanks, water heaters and water softeners. This reduces available quantity and pressure of the water supply. Iron and manganese accumulations become an economic problem when water supply or water softening equipment must be replaced. It also leads to increase in energy costs from pumping water through constricted pipes or heating water with heating rods coated with iron or manganese mineral deposits. Due to these reasons, some water softeners plants and RO plants do not prevent blocking of pipes and equipment. But it only removes few minerals and gets effect of soft water. That means water softener may control total dissolved solid particles. But, it is less effective in controlling hardness due to calcium and magnesium. It is all due to iron or manganese. These non-pathogenic (not health threatening) bacteria occur in soil, shallow storage tank, and some surface waters. The bacteria feed on iron and manganese in water. These bacteria form red-brown (iron) or black-brown (manganese) fungus or slime in toilet tanks and can clog water systems.
Various Parameters with reference to industrial applications (Cooling Towers)
Cooling towers are widely used in all industries, hotels and commercial buildings for dissipating heat in open recirculating cooling systems. They are designed to provide close air or water contact. Heat removal is mainly by evaporation of part of cooling water. Some sensible heat loss (direct cooling of water by air) also occurs. But, it is only a minor portion of total heat rejection.
An open recirculating cooling system uses same water again and again to cool process equipment. Heat absorbed from the process must be dissipated to allow reuse of water. Cooling towers spray ponds, and evaporative condensers are used for this purpose.
Open recirculating cooling systems save a lot of make up or fresh water as compared to the unconventional method, once through cooling. The quantity of water discharged to waste is greatly reduced in the open recirculating method, and advance E water Descaling treatment is more economical.
In open recirculating cooling systems, it needs more treatment with respect to problems:
- Due to cooling by evaporation increases the soften solids absorption in water, raising corrosion and deposition tendencies the relatively higher temperatures significantly increase corrosion potential.
- Long preservation time and boiling water in an open recirculating system increase tendency for natural growth of ground gases such as sulfur dioxide, ammonia or hydrogen sulfide that can be absorbed from air, causing higher corrosion rates.
- Germs, nutrients, and possible foulants can also be absorbed into water across tower.
Hardness
Combination of calcium and magnesium deposition, calcium and magnesium both can lead to scale formation.
- Calcium is the most difficult as certain calcium salts does not soluble in water.•Magnesium does not create much problem unless silica levels are also high. This could result in magnesium silicate scale in heat exchangers. Most salts are easily soluble with increasing temperature, but calcium carbonate becomes less soluble with increasing temperature. So, the best way is to break the bonding of calcium and carbonate and also magnesium and carbonate to reduce hardness.• Advance E-water Descaler treats above processes conveniently with energy efficient and eco-friendly manner without adding any chemical. This reduces maintenance cycle up to 80 % and saves lots of money, machine and manpower.
pH Alkalinity (Water’s ability to neutralize acids)
- Bicarbonates generally represent main part of measured alkalinity, amounts of carbonate and hydroxide alkalinity.
- Alkalinity is an important mean of predicting probable. Calcium carbonate scale. High alkalinity means acidic water has a pH < 7; alkaline water has > 7.•Health effect of pH on drinking water depends upon where pH falls within its range. The US Environmental Protection Agency recommends a pH between 6.5 and 8.5 for drinking water.
- A high pH leads to excessive calcium and other ceramic like deposits.
- pH of cooling water becomes acidic because of atmospheric elements or infiltration of process elements, a pH lower than six will destroy this protective coating in a few months. Engineers and manufacturers then have to apply expensive coatings and repair damage that may have occurred. If the repair process is extensive, costly process interruptions may be required.
- Silica
Silica is difficult to remove scale deposits. Pre-treatment like silica filter or side stream filtration is often required if the silica levels are above 120 ppm (as SiO2).
TSS Total Suspended Solids (undissolved material such as sludge, sand, fine clay, and vegetation.)
• Unlike (TDS) Total dissolved solids, not all suspended solids enter the cooling system with make up water. Some might be generated as corrosion and scale by-products or from air or water contact. Suspended solids can transform to biofilm and cause under deposit corrosion. TSS can be controlled through pretreatment, filtration etc.
Ammonia
- Provides platforms, an ideal nutrient for many bacteria. It can promote biofilm development and growth in heat exchangers and cooling tower block up. It is also tremendously corrosive to copper alloy, you can find lot of case study. Ammonia can reduce or deny some non-oxidizing biocides such as glutaraldehyde. (Bromine is a more cost-effective biocide than chlorine if ammonia is present.)
Phosphate
- At higher concentrations (calcium greater than 1,000 mg/l and phosphate greater than 20 mg/l) there is a potential for calcium phosphate scaling in heat exchangers, especially, at high heat loads and low cooling water flow rates. Therefore, close monitoring of blow down is required. Phosphate can also act as a nutrient for biofilms.
Chloride
- It can be corrosive to most metals, especially, mild steel. A chloride limit of 300 ppm is often used for stainless steel, but limits for other metals may go as high as 1,000 ppm.
Iron
If it combines with phosphate to form undesirable foulants, it may also deactivate specialised polymers used to inhibit calcium phosphate scaling. Recycled water may have a high concentration at 0.12 to 0.32 of iron. Specialised treatment of iron is expected to be required for this concentration.
Biological Oxygen Demand (BOD)
It reflects the organic content for biological organisms and the associated demand for oxidizing biocide in addition to the amount used for bio fouling control.
Nitrates and Nitrites
Nitrates and Nitrites can provide additional mild steel corrosion control at levels above 300 mg/l in the concentrated cooling water. It can contribute to reductions in stainless steel cracking and pitting erosion. Nitrates do not attack copper alloys or protect them from corrosion.
Zinc
Zinc can assist phosphates and nitrates in reducing mild steel corrosion rates and pitting tendencies. Levels in cooling water above 0.5 mg/l are beneficial, but levels above 3.0 mg/l can contribute to deposits.
Organics
Organics can act literally as fertilizer for micro-organisms. Water-soluble cationic polymers can react with some anionic treatment biocides, as well as some scale and corrosion inhibitors.
Fluoride
At 10 ppm or more can combine with calcium to cause scale formation.
Heavy Metals (e.g. Cu, Ni, and Pb)
Copper and nickel can plate out on steel, causing localized galvanic corrosion that can rapidly penetrate thin steel heat exchanger tubes.
For Validation and improving make up water quality initiative taken by Chief engineers of world’s state of art “Akshardham” Temple Gandhinagar, they are using ample recycled water successfully with this advance E-water technology.
India’s State of art Biggest Luxuries Resort –Madhubhan Resorts and Spa is using heavy recycled good quality E-water for makeup/ Feed water in cooling tower and swimming pool.
Conductivity (A measure of dissolved solids)
Conductivity is an approximate measure of ionic concentration. As water quality constituents contributing ions change, conductivity settings used for system control have to be adjusted.
Calcium Hardness pH (as CaCO3)
The concentration of calcium increases, so does its probability of precipitating out of solution. Potential scaling can be controlled through the use of pretreatment, scale inhibitors or deposit control agents.
Partial Softening of Makeup Water
Partial softening of the makeup water prior to its introduction to the cooling tower is an effective pre-treatment method to increase cooling tower efficiency. Partial softening reduces water hardness, alkalinity and silica. In this method the water is treated with lime or a combination of lime and soda ash to precipitate the ions contributing to hardness and alkalinity. The precipitate is treated physically which saves lots of chemical treatment. Partial softening is used to treat water with moderate to high hardness and alkalinity in the range of 150 to 500 ppm as CaCO3.
Conclusion
Water treatment technologies are really endless.
- RO plant and softener plant have their own advantages. But limitations are wastage of lots of water in which we cannot debate. However, if you prefer cost-effective solution with aim to save water and environment, then usage of recycled water reduce wastage of water. Reusing water is possible with some advance E-water technology.
- Rinse water continuously as per desired applications and check its parameter and replace it with fresh water after one week, two week or as per usage containing nearly no detectable levels of ions. However, with low in TDS may be corrosive and may need corrosion inhibitors. This water source can be used by itself or can be mixed together with water that has a high TDS concentration to give up an intermediate TDS concentration.•Adequate testing, control, and performance monitoring must be maintained in order to assure good system operation and protection. The use of recycled water depends on the final water quality in the cooling system, the systems metallurgy, the levels of nutrients present, and the operating conditions in the cooling components. Recycled water can contribute to corrosion, but the presence of phosphates and nitrates can provide mild steel corrosion control. All increased corrosives, except ammonia, can be reduced or eliminated with water treatment chemicals under good control.
AUTHORS CREDIT & PHOTOGRAPH
Prof Gaurang Sharma
Professor,
BVM Engineering
College, V V Nagar,
Anand, Gujarat
