FAQ Center

What Types of Wastewater Treatment Facilities Are There?

The two primary methods for handling wastewater are referred to as “centralized” and “decentralized”. Decentralized systems are also referred to as “on-site”.

Centralized treatment facilities are the water treatment facilities that dot the countryside. They collect and treat the water from a municipality. The wastewater is delivered to the facility by an elaborate network of sewer lines. In some cases, storm sewers are also networked with the sanitary sewers.

Decentralized facilities are designed to manage the waste from a household or cluster of households, or a business or another property. In short, it is handling the wastewater at the site rather than transporting it by sewer lines to a centralized plant.

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Isn’t “Centralized” a More Highly Evolved Form of Treatment Than On-Site?

To answer that question we need to look at current methods of wastewater treatment and determine if the minuses associated with them outweigh their positives.

While centralized facilities are viewed by some to be a more evolved form of wastewater treatment than decentralized, that isn’t the case. In fact, the sanitary sewer collection systems used to transport waste to centralized facilities is the main contributor to the migration of pollutants and is the #1 contributor to the pollution of our nation’s waters. How can that be?

Though centralized plants are designed to handle wastewater without the additional load of stormwater also flowing into the network, many cities have combined sewer systems (stormwater & wastewater) that date back to the late 1800’s. Further, it has been a normal and acceptable practice to tie roof down spouts into sewers in many communities. Although this practice is illegal today, millions of these connections still exist.

Anywhere you have high annual rainfall and/or high seasonal groundwater combined with sanitary sewers, you have the potential of overflow. This conceivably includes most of the U.S. east of the Mississippi River and many western states, with Fecal Coliform probably the biggest cause of stream impairment in the country. Most of it is of human origin too, so if you thought the geese were generating it, that isn’t the case.

When systems that are made up of stormwater and sewage collection are collected in the same pipes, and an overflow occurs, often by a heavy rainfall event, it is called a “CSO”, or Combined Sewer Overflow. These CSOs account for about 850 billion gallons of sewage discharged annually from 43,000 combined sewer overflow events. It is estimated that the cost to address these CSOs would approach $90 billion.

There are also about 50,000 sanitary sewer overflows, (SSOs) which annually discharge anywhere from 3-10 billion gallons of sewage. Remedial costs to eliminate these would be in excess of $50 billion. Another big problem with centralized plants is leaking collection pipes, which can contaminate groundwater and surface streams.

These issues take on added significance as a community grows. Local governments have to ask themselves if they are prepared to invest in the building of a centralized system that is expensive to build, expensive to maintain, and prone to serious problems when everything doesn’t go right.

This has caused an increasing number of local officials to look at the benefits offered by decentralized (on-site) wastewater facilities. Another driver has been Clean Water Act ‘antidegradation’ requirements, which mandate maintenance of high water quality unless there are clear economic or social benefits in approving sewage plant discharges to relatively clean surface waters.

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The Charles River Story

In an effort to complete the transformation of the Charles River from one of the nation’s dirtiest urban rivers to one of the cleanest, the federal government reached a landmark settlement with the Massachusetts Water Resources Authority (MWRA). It required that the MWRA implement significant improvements in the Boston sewage collection system.

The agreement finalized a long-term control plan to reduce combined sewer overflows (CSOs) throughout the MWRA system. It is expected to cost MRWA about $20 million and yield sharp reductions in storm overflows containing raw sewage into the Charles River. The settlement is expected to bring CSO discharges to the Charles River down to approximately eight million gallons per year, from a level of 1.7 billion gallons in 1988.

So even aggressive remedial projects do not automatically eliminate the problem, it simply (hopefully?) lessens them.

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How Many On-Site Systems Are There?

The size of the on-site market is very large. Approximately 25% of all new homes built each year have on-site treatment. That equates to over 400,000 new homes annually. This doesn’t include schools, office parks, malls, public entities, etc.

According to a 2003 U.S. census survey there are more than 21 million households using septic tanks or cesspools for treatment. The same survey reports that 339,000 of those systems had reported breakdowns of the system within the prior 3 months.

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What Types of On-Site Wastewater Treatment Are There?

The two primary methods are Septic Tank/Drain Field Systems and ATUs or Aerobic Treatment Units.

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What is a Septic Tank/Drain Field System?

Conventional septic systems have traditionally been the most commonly used technology for treating wastewater. These systems work on demand and gravity to treat and distribute wastewater into the soil.

The systems consist of a septic tank, a distribution box, and a drain field. The system collects all of the household waste into the septic tank, where heavier solids and scum are allowed to separate from the wastewater. This is referred to as “primary treatment”. As additional waste enters the tank, the partially treated wastewater exits the tank, flowing through a distribution box and out into a drain field.

This distribution of wastewater relies on perforated pipe to drain effluent into the soil and is driven by demand. This means that the intake of the system has peaks and lulls depending on activity in the house. As such, wastewater entering the drainfield could exceed the percolation rate of the soil during periods of heavy use, causing surfacing of effluent. Because the system is laid out based on gravity, wastewater flows out of the first holes in the piping network that it can move through. This can lead to overloading of the soil and creating an imbalance. Further, these systems frequently require significant work, including importing rock for trenches and sand, digging extensive trenches, potential changes to site topography, and the need for significant work to ensure that the drain field has the proper soil profile and slope.

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What is Drip Dispersal?

Drip dispersal is the most effective method today of distributing wastewater throughout an area. It begins with wastewater that has gone through a process of treatment to meet local regulations. It is then distributed into the soil through a very sophisticated dripline where the water is further cleaned by the soil and ultimately is either used by the vegetation or the water percolates into the soil to recharge groundwater supplies.

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Why is On-Site Drip Dispersal Such a Good Solution?

When an on-site drip dispersal system is engineered, it is with the needs of the household or building taken into account. The system includes tanks and chambers that capture, hold, settle, frequently aerate, and in general create treated water to a high enough degree that it can be pumped into an area where the soil provides final “polishing”.

Beside the ability of drip dispersal to evenly precisely apply wastewater over a broad area, and the ability to manage the doses as a function of the soil’s absorptive ability, it can also open up sites that until now could not be developed.

Many parts of the country have building sites that are perfect for developing, but there are no sewers to connect to, or the soil conditions do not allow for septic systems to be used. In cases like this, a drip dispersal system for wastewater allows the site to be developed because the wastewater can be effectively managed over the area with very precise dosing. Simply put, you can build where you couldn’t build before.

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What Makes Netafim Dripline Dispersal Products So Good?

Netafim products are used in the most rigorous applications on the planet. Whether it is a farming project in central Africa, or in a silver mine, or on a wastewater project, Netafim products are designed to perform year after year.

The Netafim Bioline dripper traces its beginning to an agricultural dripline that was designed to work with very poor quality water. The dripper inside the tubing is made to emit water at a specific rate based on the type of soil. It is also staged inside the pipe at intervals based on the type of soil that they system is in. With the ability to use a 0.4, 0.6 or 0.9 dripper and to have the drippers staged in the tubing in 12″, 18″ or 24″ intervals, Netafim can perfectly match the flow rate of wastewater onto the site with the percolation rate of the soil. Not too little, not too much. Just right!

The dripper works in a very broad pressure compensating range (the same amount of water being emitted from drippers whether the water pressure is 7 psi or 70 psi). This means that the effluent will be dispersed very evenly across the entire area, not just out of the first holes the water comes into contact with. Bioline drippers also have a built-in “continuous self-flushing feature”. This allows for debris to be purged whenever it threatens to hurt performance and Netafim is the only company to offer this feature. Lastly, the dripper has been treated with the same chemical used to keep mold build-up off commercial shower curtains, thus providing even greater protection against problems.

In short, the Netafim Bioline dripline product line has been used with outstanding success for over 12 years, and takes on-site treatment to a new level of performance.

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Are There Other Reasons Why On-Site Dispersal is a Good Idea?

Yes. In well permitting conditions, a ‘typical’ onsite system is assumed to return 80% – 85% of the water withdrawn from the well via onsite recharge. Once connected to a sewer that takes the water out of the basin of origin, 100% of the water withdrawn is depleted from the aquifer, and thus requires legal augmentation.

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Is Netafim drip dispersal environmentally friendly?

Yes, in a number of ways. When drip dispersal is used in concert with an on site treatment system, no additional strain is placed on the public wastewater infrastructure. This helps reduce the need to build new wastewater treatment facilities and all of the attendant permitting and cost. Further, and especially when an on site system is used in conjunction with a home that has a well, the treated effluent is placed back into nature where it was taken from rather than pumping it miles away and dumping it somewhere after treatment.

The good news keeps on coming. Using Netafim Wastewater Division products like Bioline deliver the effluent in an extremely precise way to the soil. Because of this precision, the effluent is spread across a large area where it is treated and undergoes final purification in a much more environmentally friendly way than older style systems that can overload a specific area, cause surfacing and potential health concerns. This balance of application is good enough to allow this type of system to be used in lieu of or in concert with an irrigation system, and this helps save water for all of us.

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