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The Process Of Waste Water Treatment

Every minute of the day, we have wastewater that goes down toilets and drains in our homes, schools and factories which ends up in water treatment plants. A waste water treatment plant is a plant where contaminants from waste water are removed before it is released to local water sheds. The process used by wastewater treatment plant is similar to how wetlands, streams and lakes naturally purify water. The processes used to purify the water produces solid material called bio solids, which is used by farmers as fertilizer.

Once the wastewater leaves a house, school or any other institution or place it ends up in the sewer system. The sewer system is made up of several thousand miles of sewer pipes that carry the water to a pumping station. These pumping stations then transport the wastewater to the wastewater treatment plant.

Water Treatment Plants

Once the wastewater reaches the plant, the  wastewater treatment process starts. The first process in the primary treatment stage is called influent. The incoming of water is called the influent. Here, every drop of water passes through fine screens. This removes rags and other large material such as: paper towels, feminine hygiene products and flushable wipes. Then the water goes to the Grit Chambers. Now here, we know that wastewater is nothing but 99.9% water. Therefore, a vortex action is used in the grit chambers to allow sand, gravel, and other inorganic solids to accumulate in the bottom of the Grit Chamber Tanks.

The next stop for this wastewater is primary settling tank. These primary tanks, are also referred to as sedimentation tanks, they are slowed down to allow heavier solids to settle to the bottom of the tanks. The settled solids are called primary sludge. Here the primary treatment ends and the water goes to secondary treatment.

In secondary treatment process, the wastewater goes to aeration tank. Here, the biological treatment begins. Air is pumped into large mixing tanks that mix the wastewater with bacteria and microorganisms that will consume the organic matter and nutrients that contaminate the water as food. The next stop are those final clarifying tanks. Here in these finds you might even find ducks, geese and other birds.

Waste Water Treatment Process

The aerated wastewater with the bacteria and microorganisms, called “mixed liquor”, flows to the final clarifying tanks. This four hour process allows the microorganisms to be separated from the clean water by settling to the bottom of the tanks. Ninety percent of these microorganisms are sent back to the aeration tank to clean more water. The other ten percent of the microorganisms are pumped to the solids handling process to be made into fertilizer. The water finally leaves the final clarifiers completing the secondary treatment.

The next and final step of the wastewater treatment is called effluent where it passes through UV Light Chambers or let’s say disinfection chambers designed to kill disease-causing bacteria with ultraviolet light. The treated wastewater finally returns back to the environment where the recycling process can begin all over again.

We need to remember that earth has a limited amount of water. Through the water cycle, Earth naturally cleans dirty water so that water can be used by plants, animals, and humans. Therefore, it is very important that we protect this natural resource!

Purified Water

What Is The Differenece Between RO and DI Water Purification?

Today, people look for different water purification systems and then often ask the difference between RO and DI water purifications. Both the water purifications are different from each other and we need to understand each technology individually.

Reverse Osmosis or commonly known as RO is the opposite of a natural process simply called osmosis. Osmosis is the natural movement of water molecules across a semipermeable membrane. The process naturally moves water from a low ion concentration to a higher ion concentration across a semipermeable membrane. This natural process is used by our bodies to get water to our individual cells.

Reverse Osmosis semipermeable membrane

By applying pressure to the more concentrated (dirtier) side of a semipermeable membrane, water molecules are pushed back across the membrane to the less concentrated (cleaner) side, resulting in more purified water. This process is called Reverse Osmosis and can typically remove 90-99% of most contaminants. Though this technique or method may not be 100% perfect, it is extremely cost effective as the RO Membrane can last for quite some times or let’s say few years if used properly and with care. Reverse Osmosis is often used to partially clean-up tap water before any other purification technology is used to remove the remaining 1-10% of contaminants.

Coming to DI water purification system or better known as Deionization has many names like Ion Exchange, Strong Acid/Strong Base, Polishing, Nuclear Grade and so on. Nuclear grade DI filters can remove inorganic chemicals down to very low parts per billon (PPB) levels. This makes them excellent for producing Ultra-Purified (Type I, 18.2 Megohm) water. Water of this quality is used with the most sensitive laboratory analytical instruments, which are designed to detect chemicals at extremely low concentration levels.

water purification system

The Deionization filters function by exchanging positive hydrogen and negative hydroxyl molecules for the positive and negative contaminant molecules in the water. Positive chemicals, like calcium, exchange places with the hydrogen molecules and negative chemicals, like iodine, exchange places with the hydroxyl molecules. Over a period of time, positive and negative contaminants in the water displace all the active hydrogen and hydroxyl molecules on the DI resin and then the filter needs replacement. Regeneration of the deionization filter is possible, but only in an industrial environment setting.

Deionization is an on-demand process supplying purified water when needed. This is important because water at this extreme purity level degrades quickly. The nuclear grade deionization resin or polishing mixed bed resin removes almost all the inorganic contaminants in the water increasing the resistivity of the water to a maximum of 18.2 megohm-cm. However, deionization alone does not remove all types of contaminants like dissolved organic chemicals. Deionization filters are not physical filters with a pore size and cannot remove bacteria or particulates.

Here, compared to RO purification system DI treatment can be expensive. In other words quickly using up the purification capacity of deionization filters can be an expensive option for labs that choose to supply tap water to UltraPure (Type I) Polishing Systems.

Today there are several tests for identifying the purity level of water. The simplest test is a direct measurement of electrical conductivity or resistivity. Most inorganic chemicals are either negatively charged (anions) or positively charged (cations), and therefore transmit an electrical current when electrodes are inserted in the water. The more ions present, the greater the conductivity, or the lower the resistivity of the sample water.

Conductivity is expressed in microsiemens/cm and is used to measure water with a large number of ions present. Resistivity is expressed in megohms-cm and is used in the measurement of water with few ions. Conductivity and resistivity are mathematical reciprocals of each other. Therefore, at 25° C, 18.2 megohm water, which is the highest purity water obtainable also, has a conductivity of 0.055 microsiemen/cm.

Remember, both RO and DI purification systems are excellent in their own ways and it solely depends on what purpose we need the purified water for.