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Operational Costs for Vacuum Sewer Systems

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How much does it cost to operate and maintain your vacuum sewer system? Is that high and what is normal? Lets also talk about the best way to reduce your maintenance costs.

Critical Factors

Flovac’s operations group has completed audits of systems in many locations and through our benchmarking process we have determined a number of common factors involved.

Before we dig deeper there are two important statements we can make.

  1. You need to know how much your vacuum systems costs to operate. Most utilities, do not know. Once you understand what the main costs are, you can do something about them
  2. All systems which have monitoring systems installed have significantly lower operational costs as well as reduced risks.

The overall cost varies, smaller versus larger, country to country, so its probably best to focus on what makes up the cost. Try and find what was in the whole of life costs when this system was first being suggested. How accurate was that. If it is different, why is it different and if more expensive, what can be done about it.

Vacuum systems should always be cheaper to operate than a low pressure pump system and in a similar difficult location should have cheaper operations costs than a gravity system with multiple pump stations.

Cost Breakdown

  1. Energy Costs (30{f2ac4d1e1d40dc2e2d9280a1dfa90d854b2d8c80eba743affa37fc4ce2e16def}). For many utilities this is one of the easiest things to focus on and also easiest to get accurate data on.  It could be that your pumps are just old and it’s time for a rebuild/service or replacement. With vacuum systems, energy costs are highly correlated with the air/liquid ratio of the system. That’s our first design principal and our first operational health check. Air transports the sewage to the station. The amount of air is measured by the vacuum pump run times and the size of the pumps. If there is too much air, either due to leaks in the system, old valves or badly tuned valves then your vacuum pumps will run longer than needed. In most systems vacuum pumps should run approximately 6 hours per day. Sewage pump run times are determined by the amount of sewage in the system. If you have infiltration or a user dumping in more than they should, then your pump run time will increase. In most vacuum systems the sewage pumps should run about 2-3 hours per day. You need to check what the optimal air to liquid ratio is for your system. When it is at its optimal level your energy costs should be at their lowest possible point.
  2. Consumables (20{f2ac4d1e1d40dc2e2d9280a1dfa90d854b2d8c80eba743affa37fc4ce2e16def}) In vacuum systems consumables can either be related to parts for the vacuum valves and controllers, or related to pump station equipment. This is different to long term capital replacements, pump and valve replacements, this is covering annual spending on oil and filters and valve/controller parts. In our experience of sales of parts to systems, valve and controller parts should only be required every ten years. It is highly unusual for sales to be any more frequent than this. In most pump stations the main cost is oil and filters for rotary vane vacuum pumps. Liquid ring pumps and claw vacuum pumps require a lot less maintenance but might not handle the required duty for your system. The best way to reduce your oil costs is to reduce the run time on your pumps. See the above section on energy costs. If you are watching the air/liquid ratio and keeping your pump run times at optimal levels then your oil requirements will be minimal.
  3. Preventative Maintenance (30{f2ac4d1e1d40dc2e2d9280a1dfa90d854b2d8c80eba743affa37fc4ce2e16def}) A number of systems do no preventative maintenance at all and so this 30{f2ac4d1e1d40dc2e2d9280a1dfa90d854b2d8c80eba743affa37fc4ce2e16def} cost will be lumped in with call-outs. We would tend to visit each pit once a year to check the pit condition, valve condition and controller timing. At every ten years we replace the required parts in the valve and controller. With monitoring a lot of our preventative maintenance time is spent at the computer. Analysing data to show infiltration, air/liquid ratio, changes to end of line pressure, failing components and remotely adjusting the timing of certain controllers to take into account seasonal flows as required.
  4. Call-Outs (20{f2ac4d1e1d40dc2e2d9280a1dfa90d854b2d8c80eba743affa37fc4ce2e16def}) If preventative maintenance is done correctly then this number should remain low.  We have outline in the following graph the breakdown of callouts to a vacuum system. A system with 200 vacuum valves should have a 5{f2ac4d1e1d40dc2e2d9280a1dfa90d854b2d8c80eba743affa37fc4ce2e16def} call-out rate, meaning that there should be 10 callouts in the year.  The biggest cost here is time spent in the field finding the fault. In many projects we have found that a refresher training program for the operators can help reduce time in the field a lot. The other biggest cost reduction comes from installing a monitoring system. Have the operator being directed directly to a problem or being told ahead of time when a controller is going to fail can save significant money and resources.

    Follow Up

    If you would like to follow up on any of these points please contact your closest Flovac office.  You can contact our Operations group about audits or training courses, or just some advice about your system. If you would like to see some more information about monitoring systems you can Click Here

Sheltering Sewers from the Rain

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Pacific Northwest community optimizes its vacuum sewer system with cutting-edge telemetry monitoring

Full Article Click here

Making the switch from a purely septic-based wastewater handling model to a publicly owned and operated vacuum sewer system solved problems for the small community of Miles Crossing, Oregon. It also brought unforeseen inflow and infiltration issues.

Rain events revealed the need for tracking down operational overload issues in the system, which could only effectively be accomplished via automation tools. Retrofitting a monitoring system has given the district’s operators a real-time view of their system, potential sources of I&I, and a means to protect the mechanical health of this key community infrastructure investment.

Below sea level

The Miles Crossing Sanitary District is fairly new, incorporated when the community decided to shift from private septic systems to a public sewer system. The decision to convert the community — home to a population of approximately 800 — was based upon several factors:

• The town’s topography — situated on Youngs Bay, between the Youngs River and the Lewis and Clark River, is completely flat with elevation from 1 to 10 feet below sea level.

• Dikes are situated between properties to prevent them from going underwater during high tide or rain events.

• The high-water table was causing the area to experience a rapidly rising number of septic system failures, affecting groundwater quality.

The district opted for an vacuum sewer system versus a traditional gravity system. The latter would not have been feasible due to the depths required for installation combined with high-water table levels. The vacuum system implementation process, which cost the community approximately $4 million, began in 2000 and was fully in service by 2010. It comprises 372 gravity pit connections (323 of these being residential), and a single pump station that receives the entire flow from 7.25 miles of vacuum mainline. From the pump station, two 75 hp pumps move the effluent 1.75 miles under Youngs Bay to the town of  Astoria, Oregon, for treatment.

Not quite right

On normal, dry days, Miles Crossing would pump an average of 36,000 gallons per day; but during rain events, that would jump dramatically, sometimes by more than 150,000 gallons. Unlike a traditional system where I&I can exist between joints, cracks in manholes or other conveyance structures, a vacuum system is closed. Brandon Smith, pump station operator, and Carl Gifford, superintendent for the Miles Crossing Sanitary Sewer District, suspected stormwater was entering the system.

“One of the biggest challenges with a system like this is that not only do we not want the stormwater — the system simply cannot handle it indefinitely — but since we don’t handle our own treatment, we were sending extra effluent to Astoria that created extra costs,” Smith says. “Our job became finding out where that excess water was entering the system, and then correcting it.”

Gifford and Smith learned that when the system was put in place, contractors had taken each line that was tied into the property’s existing septic, severed it, and then tied it into the new vacuum system. On many properties, storm drains and gutters, as well as other forms of outside drainage, had been run into the septic system. The impact of bringing all these lines into the new vacuum system — instead of just the sanitary line — was unknown to the contractors.

These extra tie-ins created an unnecessary burden on the system and the pump station operations, so they needed to be located and removed. The task of finding the sources of these I&I culprits was labor-intensive and slow, so the district began looking for a technology solution that would assist in this discovery process.

Trial and error

As a first attempt, Gifford and Smith utilized individual pit-fire counters. Each time an individual property’s vacuum pit fired, it would trigger an analog or digital display to track the number of firings. This method proved expensive and unreliable as a measurement or pinpointing technique. As they continued to research other solutions, they were contacted by FLOVAC.

FLOVAC had been well established globally in the field of successful vacuum sewer system installations and was seeking connections in the North American market. It was able to offer Miles Crossing a telemetry system that could be connected to each vacuum pit and would deliver the detailed data the district needed to help pinpoint and mitigate its I&I issue.

Each vacuum interface valve or connection has a magnet located inside of the top section of the valve body. The FLOVAC monitoring system works by attaching a special sensor to the valve body to detect the movement of this magnet. It detects each time the valve opens and closes, as well as how long each valve stays open.

Numbers tell all

As vacuum valves tend to fire when 10 gallons of effluent have entered the sump, the volume of flows can be calculated from the number of activations. When an unusually high volume of water enters the sump, the valve will take in a larger quantity of fluid during that one cycle. The district could detect such occurrences by how long the valve stayed open. Depending on how many properties are connected to a single collection pit, they would be able to narrow down the point of infiltration to a small area.

Related: Flood Affected Sewer Systems

With the installation of the FMS, monitoring and telemetry data now lets operators see what the entire system is doing in real time. It allows them to view individual homes and their pits, and provides information on how many times it has fired, and when.

“This is especially helpful during a rain event,” Smith says. “We can see average trends for a property. For example, if a home that normally fires 30 times a day during a weather event starts showing 5,000 fires instead, we know there’s a problem and can deploy immediately to the property while the rain event is still happening to see exactly what’s taking place.”

One big discovery uncovered by monitoring involved a property with a partially collapsed lateral. Although it was functioning sufficiently to serve the home, it had been crushed in some areas. Where it ran from the home under the rock driveway, it was acting like a natural storm drain, pulling water straight from the surface into the sewer system pit. Using CCTV push cameras to inspect and document the line’s condition, the utility team was able to show the property owner the extent of the damage, its effects, and then work with them to develop a plan of action to resolve it.

Subtle adjustments

Normally, the monitoring units are connected to a transmitting antenna that sends data to the central monitoring system wirelessly. Due to the flat terrain and steel manhole covers on the pits, Miles Crossing ran conduit pipe out to a utility pedestal at the roadsides and installed the wireless telemetry equipment there. Everything works wirelessly through the latest Gateway, Bluetooth and LoRaWAN technology and is tied into the district’s SCADA system.

“We can set parameters as far as what we are asking it for, and to send us text messages when there are different alarms. This extra information is especially helpful when we are experiencing a lot of rainfall,” Smith says.

Since its installation, the system has required minimal maintenance. A yearly visual inspection of each valve pit is typically all that has been needed. Rare mishaps can occur, but — due to the very nature of the sealed system’s construction — if things happen, the pumping equipment operation and vacuum attributes make pinpointing issues quick.

Moving forward

Nearly 60{f2ac4d1e1d40dc2e2d9280a1dfa90d854b2d8c80eba743affa37fc4ce2e16def} of the system has been fitted with the telemetry monitoring system, and phase two of the project, a complete system rollout, is commencing shortly.

“By retrofitting the entire system with the FMS, we will know when there’s a problem before the homeowner does,” Gifford says. The monitoring system also provides a high-level float that can alert the operators when a pit begins to have an issue. Now Gifford and Smith can be more proactive versus reactive in keeping the system in peak operating status, while cutting down on field time and hunting down overflows.

With just a little more than half the system being monitored, the district has already seen significant savings in treatment costs, Gifford says.

“The vacuum system was a great solution for this community and now with the telemetry tools, we will have a sustainable, high-performing and affordable sanitary system for our district for generations to come.”

Related: Information about Flovacs Monitoring System

Is Infiltration Causing Problems in Your Sewerage System?

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Not long after Miles Crossing Sanitary Sewer District in Oregon installed a new vacuum sewer system they realized they had an issue that needed an immediate fix. According to the superintendent, Carl Gifford, “Our flows exceed 180,000 gallons [on heavy rain days] due to a massive I/I issue that we grew to have”.  This excess can put a strain on the system which can increase utility bills, not to mention, Miles Crossing is a collection system only.  They have to work with a neighboring system for treatment and have a limit on max flow that can be sent.

Flovac and Miles Crossing were able to meet and come up with a  plan to utilize Flovac Monitoring System to overcome these issues.

“With this system, we can monitor the fires from each individual pit. During a rain event, it is really simple to tell which ones contribute to the massive I/I we are dealing with. During the last winter, we were able to identify 9 sources of I/I that we were able to repair”.

Gifford also mentions how the system allows for the sewer district to know about problems before customers do. “An additional benefit that we observed with this system is the alarms that it provided. Numerous times we were called out for a high-level at a residence and were able to make the repair and get it back online before the customer knew there was a problem. This helps greatly with the risk management of possible failures and the following lawsuits that have happened in the past”.

Due to less load on the system, Miles Crossing have been able to add residential connections creating revenue.

To find out more about the Flovac Monitoring System – Click Here

Image on Front Cover Torsten Blackwood—AFP/Getty Images

Growing Pains or Growing Old Pains – What best describes your old gravity sewer?

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What happens when your sewerage network gets too old? Your old clay pipes have cracked or are filled with roots, every time it rains it seems like its a direct line from the clouds to the Treatment Plant. People in the community start asking why you are spending a load of money on treating rainwater instead of just sewerage.

If you are part of a coastal community it could be worse, your old broken  pipes could be letting seawater into the system every time there is a high tide or major storm. Salt water can cause major problems at the Treatment Plant. For communities like Miami Beach who get storm surges flooding their sewers and closing their beach on an increasingly regular basis it can cause major economic and health risks. Santa Pola in the Alicante area of Spain found that the impact of global warming and rising sea levels caused a complete failure of their old sewer system.

The town of Santa Pola with over 10,000 homes replaced their whole gravity sewer system with a Flovac vacuum sewerage system. As vacuum mains are laid in shallow trenches it was possible to skirt around, above and below exiting infrastructure and eventually replace the network. You can read more about that project here.

It could be that the old gravity sewer system with large heavy pipes just wasn’t suited to the ground conditions that are often found near the coast or in swampy area’s and that over time they no longer have the correct grade to remove the sewage or have pipes that continually break allowing ground water into the system as well as blockages. This occurred at Hope Island on Queensland’s famous Gold Coast.  Gold Coast Council have developed a Master Plan and slowly replaced a number of area’s with vacuum sewers. When the original gravity sewer was laid, there was no choice, developers were racing to put up houses and council at that stage had no experience with vacuum sewers and so deep gravity mains were installed. Almost immediately problems were noticed as the ground subsided in different area’s. Sewage backed up in pipes and was unable to flow as the grades first allowed for in the networks were no longer the same.

When looking at upgrading a gravity sewer, pipe relining can be an option, but in many cases this becomes an ongoing expensive option and be too difficult in a large network. Some utilities just look to replace the old pipework, but in most communities this is just not practical. This could mean uprooted gardens, roads out of use for a number of months, noise, dust and a huge cost.

For many communities it is the size of the town that has changed dramatically over the years. In most cases this has meant an increase in the population as people move from the city to the coast. Developers move into the fringes of the town. Planning regulations change allowing for sub dividing of the old large land blocks or height and density changes. This puts pressure on existing sewers that are already not coping due to age and lack of maintenance. This has happened, not only in small coastal towns but in larger developed cities like Abu Dhabi and New Delhi. Vacuum sewers can be used to supplement the towns aging sewer system, loads can be taken off the main system by a series of collection pits and shallow pipework.

Flovac vacuum sewers have shown time and again, their versatility. This means either their ability to handle density changes or climate changes. It might even mean changes in ground conditions as happened in Christchurch New Zealand when they suffered from a terrible earthquake. The old gravity sewers in the city and surrounding suburbs broke and left residents with no service for months. Vacuum sewers have now replaced a large portion of the gravity sewers in Christchurch and although difficult has proved to be a better long term  solution for the residents and operators. Christchurch systems

Vacuum sewers should not be looked at as the only solution in many of these towns. In some cases a combination of grinder pumps, gravity and vacuum is going to be the better result for the community. Whether the problem is growing pains, or growing old pains a vacuum solution might offer the versatility that you need.

Flood Affected Sewer Systems

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Vacuum sewerage systems are ideal in areas that are subject to flooding

Nearly all vacuum sewerage systems are found in coastal area’s many of which are subject to flooding from rain/storms or rising sea levels. We all understand the problems that occur if I&I is present, we all know what causes it to occur.

We have operated a number of systems during major floods without the system going down. In one Sydney system major floods occurred every two years (see photo above), our operations contract stated that if any homeowner could not continue to use their plumbing they would be put up at a hotel at our cost. Happily we did not spend a cent on hotel costs.

For the vacuum valve to meet the European standard it must be able to operate under a full 10 inches of water. To meet the Australian standard it must operate without problem under 18 inches of water. By ensuring all hose clips are properly in place and the controller breather is clear of any water , the system will continue to operate.

In area’s where flooding is common we tend to put the controller and controller breather in a pillar besides the pit to ensure that the operator can still fire the valve without trying to access the pit through the flood water which might not always be possible.

Water infiltration from the homeowners property.

We have found that the main source of stormwater entering a system comes from the homeowners property. In some flood areas we have seen that certain sections of the town will regularly go under water. This usually means that residents have to be evacuated and in the past the water inundation from that area could risk the whole system. In this case we would install a remotely controlled division valve that would cut off that section of the town from the vacuum system. It is controlled from the operations base so that operators are not put at risk trying to isolate the area.

In some older towns we find that some houses, or more often camping grounds or caravan parks are set at ground levels

that are blow the legislated 100 year old flood levels that people can build at. If we find houses affected in this way, they must pump into the vacuum system rather than drain into it so that the system is not put at risk.

Candycanes/Gooseneck house breather vents when placed on properties will often be a source of infiltration, usually due them either being cut down by homeowners who object to them being in the middle of their yard or by gardeners knocking them over with their lawn mowers. At times they are placed too low to the ground, under the flood level. In these cases we would install a  Dedicated Pillar or think carefully about where the gooseneck vent is placed. Putting it in the middle of the yard risks it being cut down allowing water to enter the system. Putting it at the roof or garage top or against the house wall will limit water entering the system.

Smart Monitoring

As technology has improved, many asset managers have embraced the ability to locate exactly where and when I&I may be occurring. A sensor on a vacuum valve giving the open/close status will also be able to tell the operator the number of activations in a day. It is very easy for the operator to set up an alert to advise if any particular valve is operating more frequently than the general average, especially during wet weather events.

Once the operator has established which collection pit is activating more frequently than the other valves in the area, they can then troubleshoot the problem. The likely problems are that the homeowner has cut their house vent or inspection point to allow rainwater to enter the system or may have connected up their stormwater system to the sewer system or have a cracked gravity line feeding from the house to the pit. A letter to the homeowner to make the necessary rectifications is required.

There may also be groundwater or stormwater entering the collection pit due to incorrect pipework entering the pit allowing for water to enter. This is usually picked up at commissioning, if not should now be rectified.

You should also make sure that the pit lid is made for area’s that have flooding and has a seal and no holes to allow water to enter. the pit should not be located at a low point in the street.

The monitoring system makes it possible to identify these problems and fix them. this is not possible in a gravity system.

System Design

When designing a gravity sewer consideration must be made for Infiltration and Inflow on the pipes, the pump stations and the treatment plant.

Stormwater cannot enter the vacuum system via the vacuum pipework as it must remain tight for the vacuum pressure to hold tight. If a break occurs in a main it is immediately noticed and repaired.

An allowance is made for I&I but only for a small amount of the network, that being the homeowner gravity lines. So the system is not designed for infiltration and all steps must be taken to ensure that it does not occur. Luckily in a vacuum system the source of any I&I can be located.

If you have any leaks into your system, contact an expert for advice.

Exfiltration – Why Can’t Vacuum Sewers Leak?

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Gravity sewers have been used for hundreds of years, but they come at a much higher cost than many options reports accurately record. When selecting what type of sewerage system to use, take into account the risks associated with the solution. What happens if a sewer overflows? What happens if a storm or large wet weather event occurs. What will happen if a pipe breaks. What will be the cost and what will be the risk? A vacuum sewer could be far cheaper than you realise.

When you reflect on the damage and the cost of exfiltration from sewer networks the statement that we often hear ‘gravity sewers require no maintenance – we just put them in and leave them be” is wrong and does not reflect the true risks of not only gravity systems, but also low pressure systems as well as old septic tanks and combined sewers.

Sewage leaks can occur for a number of reasons. the most common is leaking sewer pipes (this may be caused by tree roots or ground movement). A break in a gravity line  can remain undetected for months or even years. In a Low Pressure Pump system a break will lead to a surcharging sewer which will be difficult to repair and costly.

With Low pressure systems a pipe break is easier to detect as some local TV news anchor is excitedly showing the 50 foot geyser in the middle of main street.

Overflows can also be caused by the system being inundated with stormwater which overwhelms the entire system allowing polluted stormwater to enter waterways.

A vacuum sewer piping network is leak tight, as it operates under a negative pressure any break cannot allow exfiltration to occur and as the pipe is less than 1/3 full at any time there is no surcharge.

What are the main problems if exfiltration occurs?

Health Issue’s

In the USA the Centres for Disease Control and Prevention (CDC) and the US EPA regularly report on annual deaths due to sanitary sewer overflows.  Sickness is widespread with the most common symptoms being diarrhea and nausea. This can be caused not only by drinking the water but also by swimming and eating shellfish and fish.

Of greatest concern is infectious disease, such as the contamination of Wallis Lake oysters in Australia with the sewage-derived virus hepatitis.

In Baradine a small town in Australia The Department of Health reported a 30{f2ac4d1e1d40dc2e2d9280a1dfa90d854b2d8c80eba743affa37fc4ce2e16def} reduction in student sick days at the local school once a new vacuum system was installed. In far north tropical Queensland the introduction of a vacuum system led to a reduction is diseases caused  by mosquitoes.

Not only is the health of the broader community at risk, there is also a risk for sewer operators needing to deal with overflows and backed up sewers.

Environmental Issue’s

In the nineties nearly 20{f2ac4d1e1d40dc2e2d9280a1dfa90d854b2d8c80eba743affa37fc4ce2e16def} of Florida’s manatee population died due to an algae bloom which had intensified due to sewer overflows.

On average 140 beaches in the US are closed or have warnings due to sewage contamination. KawaKawa Bay in New Zealand which had been a source of shellfish and a place to swim for the indigenous Maori population for hundreds of years was completely closed for ten years due to sewer overflows from a growing seaside community. It was only after a vacuum system was installed that the bay was reopened.

Sewage contamination readily degrades in the environment, but in water it can soak up oxygen from the waterway. Low oxygen levels can kill large numbers of fish and other aquatic life. Sewage also has toxic levels of ammonia that can poison aquatic life, along with many other contaminants.

Overflows contribute nutrients and sediment that encourage the vigorous growth of invasive weeds, such as willows, blackberries and privet, which often choke native species along stream channels and banks.

Aquaculture and Tourism Impact

Owners of Marina’s know the impact of attracting houseboats and tourists if sewage is contaminating the marina area, with bad smells putting off people going to local restaurants.

Dal Lake, one of the most scenic tourist spots in Kashmir has suffered terribly from sewage overflows from nearby towns but even worse from raw sewage entering the lake from houseboats on the lake.

Tourists going to Brazil for the Olympics and the World Cup were told not to go near the beaches. Dr Daniel Becker, founder of the nonprofit Center for Health Promotion in Rio, said: ‘In Rio, if you’re going to the beach, you’re going to sewage.’

“A sewer line clogged with grease caused raw sewage to spill into the Five Mile River , forcing the closure of shellfish beds from Darien’s Long Neck Point to Wilson Point in Norwalk.”  This is a common story, found around the world where sewage overflows can affect not only health but the livelihood of businesses.

Financial and Reputational

In many countries fines are being issued to water authorities if sewage overflows occur. The Environmental Protection Agencies must report any overflows and state and federal reporting is mandatory. If there is a death related to a sewage overflow that could of been prevented then lawsuits and possibly prison could affect senior people within the wastewater industry.

Newport Bay in California had to close its beach to swimmers and divers on one of its busiest weekends due to a large sewage spill that was caused by a sewage pump stopping, flooding the streets and beach. Not only was the beach closed for 4 days, ruining many tourists holidays, it also financially hurt local small businesses including restaurants who are talking about legal action against the Costa Mesa Sanitary District. The District has now been fined $503,000 by the regulators of  The Santa Ana Regional Water Quality Control Board. Sadly it didn’t end there with a smaller spill caused by tree roots blocking a sewer main causing beaches to close for three days the following year.

There are always lots of big fish down at the lake because.

The first problem, is how do you know that you have a leak or overflow.Usually it is because sewage has been spotted at the local playground/beach/street. Or because you know from flow meters at the Treatment Plant that not all the flow is reaching it. In New Delhi it is estimated that only 60{f2ac4d1e1d40dc2e2d9280a1dfa90d854b2d8c80eba743affa37fc4ce2e16def} of all sewage collected is actually reaching the treatment plant.

Even with new technologies it is difficult to find leaks when the pipes are buried 10 metres (40 feet) underground. It is also very expensive to fix that leak. Not only is there potentially a disruption to service, a closing of roads the restoration of the surface, you need to find an allocation in the budget to make those repairs.

Why doesn’t all this happen with a vacuum sewer?

Well admittedly, homeowners can still create overflows at the home and badly maintained systems will always have problems. Modern wireless and cable monitoring systems reduce this risk considerably and is a game changer.

Firstly though, all vacuum mains are fairly small diameter, 125, 160, 200 dia (6,8,10 inches) and laid at a very shallow depth (Under 1.5m or 6 feet) So if there is ever a break it can be reached quickly and repaired without loss of service or expensive restoration. All pipework has to be pressure rated so it is a lot thicker than traditional sewer pipe.

Sewage is transported quickly in the pipe by air. The pipe is full mainly of air and not sewage. Large sections of the pipe are empty with sewage only collecting at lifts in the system. All pipework is under a negative pressure created at the pump station. If a pipe breaks, it sucks in and does not let any water leak out.

Once there is a leak or break in a pipe, the vacuum pump at the vacuum pump station must run longer. This creates an alarm which is transmitted to the operator. He is made aware that a leak is occurring in the system, this may be at the vacuum pump station, at a valve pit or in the pipework. A reticulation monitoring system will automatically notify the operator if there is something blocked in a valve or there is a break in the line. When pressure is monitored at each pit it is easy to detect in which section between two pits a break has occurred.

If a break has occurred, it would usually be due to an outside contractor breaking the pipe, tree roots rarely get into vacuum mains as they are pressure pipes. As a break is at minimum depth it is easy to locate and repair and no sewage would have leaked out.

If a blockage has occurred and sewage is backing up in the pit it cannot overflow through the manhole cover as there is a partition between the sump and cover preventing sewage from flooding at this point. If it starts to back up towards the house a high level alarm in the pit sends an urgent alarm to an operator who attends to the problem. If the problem is hard to solve or an experienced operator is not available a suction truck can be used at this point.

At the Eco Resort near the Barrier Reef in Australia a vacuum system was chosen to ensure that no sewage could affect the local ecology nor leak into the swimming lagoons which would have closed the resort.

As any leak in the pipework, must be repaired immediately, no stormwater can enter the system during wet weather events. This is common in gravity systems where breaks may go unnoticed. This means that the vacuum system can never be inundated with stormwater and wet weather infiltration is not included in design parameters.

Due to the velocity of water in the pipes there is not build up of fats or grease and wet wipes or other objects do not cause blockages at the vacuum valve nor in the pit. See Video for information.

Vacuum Sewers are considered to be the Low Cost of Sewage collection, both in capital costs and also in maintenance costs. Risk is a very important consideration.