How do Variable Flow Rates Affect Your Design

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Vacuum Systems operate on a ratio between air and water, either too much air or too much water can negatively impact on the system which could lead to failures or higher operating costs.

Systems are designed and built for an average flow rate but in many of the communities where vacuum systems are built they never perform at the average flow.

To look at a couple of examples

  • A Coastal Holiday Town that during the winter has 500 people but in the height of summer has 5,000 people. During the winter more air is required to keep sewage flowing. Less air is required in summer when valves are all operating frequently.
  • A wealthy community where residents are building 10 bedroom mansions. For most of the year only 2 people live in the house, but at Thanksgiving and Christmas twenty people are living in the house. Can the system cope with a large increase in flows.
  • A community that has a section with a caravan park (RV Park) and a camping ground area. During certain holiday periods massive flows occur at these locations.
  • A system which on one line has a large secondary school and a primary school. During the summer holidays no flow enters the system along this stretch. Will that impact on collection pits further upstream?

One of the unique features of the Flovac Monitoring System (FMS) is its ability to communicate two ways. We have developed controllers for our valves that can receive messages to open for a period of time.

The smart controller can open for longer during extreme wet weather events or during quiet winter off season periods or less air during very busy periods. It can be programmed to only admit more air when it senses flooding is occurring in the vacuum main which more air would help.

If the client would like to, they can remotely fire the controller to assist the system.

One client is programming a number of valves to open at 5 am prior to peak so that the vacuum mains can be emptied prior to the large peak flows and this reduces the peak impact on the system. This system is also being operated prior to large wet weather events.

Imagine if the weather forecast suggested a large storm would occur in the afternoon. The operator could fire a few valves injecting air into the system which could empty the vacuum mains completely prior to the wet weather occurring. Not only would the vacuum system handle the storm better but so would the treatment plant which would have received excess flows prior to the start of the storm.

Eco Resort, affected by seasonal flows

To read more about this Click Here

Why is a Vacuum Sewer the Best Collection System for the Environment

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Gravity/Low-Pressure/Vacuum – which has the Greenest Credentials

It is very clear that septic tanks and cesspools are a disaster for the environment for a number of reasons. Leaking into waterways, poisoning fish and water birds, creating algae blooms. Affecting the overall health of the community.

The choice of a gravity sewer, low pressure sewer (grinder pump) or vacuum system is not as clear in many peoples minds. In many communities the health of the

Clean waterways are essential

community is important, but even more so, the health of the environment. Many people move to coastal communities because of their love of the natural environment. Maybe the beautiful lake, their favorite beach or special fishing spot. If the area is being affected by sewage spills or sewage smells on a regular basis, closing beaches or impacting local shellfish, how will that affect their property prices and quality of life.

Naturally, the cost of sewerage infrastructure is a critical factor, lets take that as a given, if costs are close to equal, what type of system would be best for the environment?

When clients have done carbon footprint studies in the past, the main areas they look at are in construction, materials and whole of life operational costs which include product replacements and energy use.

Construction

Gravity sewers tend to be either laid deep in the ground or have multiple pump stations. Deep sewers can mean pipes laid at 5-10 metres (15-30 feet deep trenches), we have seen deeper. In coastal areas this can mean dewatering which can impact the water table. If a contractor is dewatering the trench, that water goes somewhere else. This can impact the overall watertable which can kill off vegetation or impact the aquifer. Whole eco systems can be affected.

Both vacuum and low pressure systems tend to have shallow pipework and construction time is short. That means that equipment at site is much shorter. A project might be installed in a matter of months rather than years. A major carbon impact.

 

Construction Environmental Impact

Materials

Coastal area’s gravity sewers need either large diameter pipes or multiple pump stations. One of our earlier costal communities we used one vacuum pump station to replace 17 gravity pump stations. The amount of equipment required in 17 stations would be tremendous.

Low pressure systems it’s even worse. In a community of 1,000 houses, you would need 1,000 pumps and pump chambers. In a vacuum system you would require only 200-250 chambers. Vacuum collection pits are not filled with metal pumps and electrical components. They house vacuum valves which have a 50-year design life with minor parts changes every 10 years. The valves bodies from Flovac have a recycle stamp on them as the PP and GP can be recycled.

Whole of Life Operational Costs

Energy costs are the largest component of operational costs in sewer systems.

In cases such as the one in the section above where one vacuum pump station replaced 17 gravity stations, you can be sure that the energy costs of 17 stations were a lot more than a single vacuum station. That system looked after 1,800 houses. A low pressure pump system would require 1,800 pumps, each one requiring electricity.

Due to the low energy requirements, some vacuum systems are now being powered by solar.

The Bigger Risks

Sewerage leaking into the waterways.

In gravity sewers, you could have leaks for months before someone reports a bad smell or something nasty floating in the lake.

Low pressure sewers use a positive pressure and if there is a pipe break sewage can be squirt meters into the air and can be very hard to contain. Contamination of waterways can occur quickly.

Vacuum sewers cannot leak. They operate under a negative pressure and in some projects you will see water and vacuum sewer pipes in the same trench as you cannot get sewage leaking out of the pipe. This video shows how that is possible.

Other benefits

When we installed the vacuum system at the Eco Resort Couran Cove south of the Great Barrier Reef in Australia there were a number of reasons why a vacuum sewer was chosen – You can read about the project here. 

The environmental benefits that they looked at were:

  • Ability to handle low flush toilets thus reducing the ultimate treated water disposal problem
  • Minimal impact on the landscape during construction with shallow trenches
  • Maximum water recovery for reuse in the re-vegetation irrigation system
  • Construction route flexibility thus minimizing the damage to vegetation
  • Ability to transport grey and black water in the one small bore pipe
  • Ability to safely lay all services in the one trench with minimal spacing
  • Zero infiltration and exfiltration
  • Ability of the system to service the entire site with one centralized pump station
  • Ability of the scheme to service the Boardwalk accommodation and even the boat sullage

Flovac vacuum systems are referenced as The Green Future of Sewerage. It is easy to see why. What outcome do you want for your community, lets hope its the Green one.

Wet Wipes Blocking Sewers? Not in Vacuum Sewers

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As we all know homeowners will put almost anything down their sewer line. Phones, balls, plastic, pegs, cups and the bane of sewer operators around the world, WET WIPES.

Flovac recently created a new video showing what items can go through the Flovac vacuum valve. We asked operators around the world to suggest items that had been causing them problems in their gravity sewers and in their low pressure pumping systems. Operators have learnt that putting a sign above someones toilet listing what not to flush unfortunately becomes more of a challenge for many people with a broad range of items ending up in the sewer causing blockages and potentially damage to pumps.

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In more recent times the biggest problems in sewers have been caused by wet wipes and fatbergs. With both products it has been widely reported that there has been no evidence of damage or failure in a vacuum system.

The valve standards in many countries including Australia and Europe demand that the vacuum valve can handle a number of items like plastic bags, nappies, condoms and sanitary pads. Operators also suggested cigarette packets, phones and golf balls.

We have posted the video onto the front page of the Flovac web page.