How To Extend Wastewater Pipe Life With Integrated Water Management
Written by AOS Treatment Solutions on January 11, 2017
Wastewater treatment is one of the most utilized methods for pollution control in the United States. Almost all treatment plants function similarly and use a two- stage process.
What Are the Two Stages of Wastewater Treatment?
Stage One, or primary treatment, consists of wastewater flowing through large screens to remove floating items such as sticks and rags, that have a good chance of harming treatment equipment or clogging pipes if allowed to flow further into the system.
After the screening, wastewater moves into a grit chamber. This is where sediment such as small stones, sand and gravel settle to the chamber’s bottom.
Following screening and grit chamber treatment, Stage One concludes with a stop in the sedimentation tank. The wastewater then moves to the final part of treatment.
Stage Two, or secondary treatment, takes out around 85 percent of the organic material remaining in wastewater by using bacteria to destroy it. There are two sub-stages in Stage Two, they are the trickling filter or the activated sludge process.
The trickling filter is a technique for wastewater treatment that is made up of a bed of stones between three to six feet deep. Sewage passes through the stone bed where bacteria accumulates and consumes most organic matter. The cleaned water then trickles out through a network of pipes, where it is sent for further treatment in a sedimentation tank.
The second and more widely used process today is the activated sludge process. This process works by having sewage come into close contact with bacteria and sludge, which helps speed up how quickly the sewage is consumed.
No matter which technique is used, they both end the same way: disinfection using chlorine and then discharge into receiving waters. Often, the water is treated so well consumers and businesses will go onto reuse it. However, sometimes other chemicals are also added to the cleaned water, such as aluminum sulfate.
Aluminum sulfate serves as a coagulation agent that causes sediment to become sludge. It is made up of positively charged aluminum molecules that attract the organic and solid particles found in wastewater. When the aluminum sulfate molecules combine with these contaminants, they become heavy and settle to the bottom for easier removal.
Due to lack of oxygen, however, aluminum sulfate can also turn into a toxic gas known as hydrogen sulfide. When this chemical is exposed to oxygen, it turns into sulfuric acid, a highly toxic and corrosive compound. It is so corrosive, in fact, that it can shorten the life of concrete water pipes by 90 percent.
Pipe life can be extended by simply using a coagulant that is sulfate-free. So, why doesn’t this happen?
Why Should There Be Integration of Water Treatment and Water Supply Agencies?
Changing the coagulating agent to a non-sulfate chemical is simple, yet occurs infrequently. This is because most areas have separate water supply and water treatment agencies. Aluminum sulfate is the cheapest coagulation substance on the market and fits well with the water treatment goal of giving residential and business consumers potable water at the lowest cost.
Water supply agencies are charged with maintaining the pipes through which cleaned wastewater flows, but has no say in the chemicals used to treat the water. Integrating the two agencies will give them a common purpose in recognizing that it is worth sacrificing small increases in water treatment costs to avoid early destruction of water supply concrete pipes. It seems senseless that one end of the wastewater treatment process is so out of touch with the other end of the process.