Measurement technology in pressure sewage system

Melbourne’s sewerage system is a system of over 3,000km of pipes and pumps that are managed by various agencies. These systems safely transfer sewage from homes and businesses to treatment plants for processing, and they are important to the health of the city. The sewage strategy explores how this system is managed to protect the environment as well as safeguard essential rainwater-treatment systems across Melbourne’s metropolitan area.

Victoria’s sewer and sewerage treatment facilities have had to adapt and change to keep up with the city’s increasing population which is set to double by 2050. Rapid growth is expected in the north and west of Melbourne. The increased population will also mean increased demand for pressure sewage services. However, as the city becomes more populated and hotter, with rainfall expected to go down, intense storms are more than likely to be frequent, and warmer sewage temperatures will increase the rates of odour, corrosion and clogging of pipes.

Treatment and management of municipal wastewater have shifted towards pressure sewage systems from the conventional gravity sewage system. Wastewater management through pressure sewage systems offer lower installation charges, minimise the infiltration of groundwater, and mitigate the environmental and health hazards associated with gravity sewers. However, there are challenges in the control and monitoring of the amount of wastewater to be processed in the plant. Pressure sensors are used to capture the real-time data, but they must be able to reliably measure in this corrosive environment.

Reliable monitoring of the wastewater level not only ensures timely processing of waste without stressing the process, but also prevents the sewage overspill which is environmentally hazardous. Therefore, monitoring systems must be installed at strategic locations such as having the right kind of pressure sensors linked up with real-time alarms on the system. This enables operation teams to remotely monitor the process in real-time and be alerted if anomalies occur. The team will be able to investigate the problems and issue advanced warnings to the maintenance team if they need to fix the system. Pressure monitoring systems play an integral role in ensuring high deliverability in the pressure sewer systems.

General pressure sensors can be used to design systems for real-time control and monitoring in the pressure sewage system, as long as the sensors can measure the required level. However, users should also ensure that the sensors can return reliable measurements continuously. As the process media in the sewer systems contains many types of aggressive materials, users need to ensure that the sensors can be used for long-term operation in this challenging environment as regularly replacing broken sensors costs a lot of investment.

Controlling Volume of Treated Wastewater

In the pressure sewer system, municipal wastewater is collected in the local collection / holding tanks. Pump is installed to periodically transfer the wastewater to the processing plant.

The sewage level in the holding tank must be controlled to ensure that the tank contents do not overspill which will cause environmental hazards. Pressure sensors are used to monitor the level of wastewater in the sewage holding tanks. The sensors are installed in all sewage tanks in the municipality. This gives the operators real-time information about the sewage levels. The sensors form part of the chain in the measurement system to control the volume of wastewater to be treated.

An example of real-time applications would be the system pump from the tank that is almost filling. This can be done automatically or remotely controlled by the operator from the main control room. For this system to be successful and reliable, the engineering of this measurement system must utilize pressure sensors that can reliably measure in a sewage environment continuously.

Selecting Pressure Sensors for Sewage Monitoring

While there are several types of pressure sensors, each engineered for a specific function, you can make the selection on the basis of whether or not the sensor is subject to extreme conditions, whether or not chemical substances directly interacting with the sensor may affect its functionality, and whether sensor construction is ideal for the specific application.

1. Compatibility with Process Media
   A pressure sensor is lowered to the bottom of the sewage tank and connected to a control system at the top of the tank. Its job is to continuously monitor the level of the wastewater in the well and provide accurate data. It continuously monitors the pressure of wastewater during the pumping process and the pump automatically turns off when the pressure sensor indicates that the level has reached the pre-set low or high level.
   
   During its service life in the sewage system, a pressure sensor will come in contact with several kinds of media such as grease, suspended particles, mineral build-up, tree roots, fats, carbohydrates, a mixture of gases such as hydrogen sulphide, ammonia, methane, esters, carbon monoxide, sulphur dioxide and nitrogen oxides.
   
   Therefore, when choosing a pressure sensor for a pressure sewage system, it is essential to check whether or not the product has been designed and manufactured with materials that can withstand harsh process media. Also, ensure that the diaphragms and welds should be strong enough to hold on under pressure and different process media, while fittings must have excellent resistance to leakages of any kind.

 

2. Environmental Conditions
   The environment in a pressure sewage system is highly corrosive with biological contaminants such as sulphate reducing bacteria which significantly reduces the pH of the wastewater. Considering a pressure sensor for a sewage system is in constant contact with the corrosive wastewater, it raises the concern of decreasing the effectiveness of the sensor, even to the point where it will fail over time.
   
   Therefore, a measurement system which can withstand the harsh conditions specific to sewage must especially be used in the pressure sewage system. Considering it will act as the control parameter across the process, sensors that can withstand low pH levels should be used.
   
   To perform optimally while dealing with outside pressure in these environmentally-challenging conditions, it is important that the pressure sensor is constructed from a durable material that can withstand corrosion and other atmospheric uncertainties of pressure sewage systems. For such applications, choose the ones with pressure fittings made from highly corrosion-resistant stainless-steel materials.

 

3. Process isolating diaphragm
   A pressure-sensing diaphragm is a circular piece of material that is positioned around the edge and exposed to the pressure media on one side. When pressure is applied to one side, such as by a gas or fluid, the diaphragm will flex and give way to the force. This movement of the diaphragm depends on the magnitude of the applied pressure.
   
   Since the pressure sensor diaphragm is constantly exposed to process media, it can clog or cause the sensing element to become highly contaminated, leading to inaccurate results. This eventually causes the operation to fail, causing the surrounding environment to overflow with hazardous contaminants.
   
   A process isolating the diaphragm addresses this problem of the clogged or contaminated sensor, by separating. It enables the pressure to come in contact with a flat membrane by leaving no pressure hole in the test head. This eliminates clogging or contamination of sensor elements by the process media. The flush membrane structure is adopted in such applications that have excellent media compatibility. In a flush mount, there is no recess that can become clogged, causing process failure.

 

Apart from the above-mentioned considerations, you must also address hazardous area certifications of the pressure sensor before making a decision. Relevant approvals for hazardous media sensors can include IECEx, ATEX, CSA etc.

Not considering the vital elements that can affect the performance of a pressure sensor is the reason why incompatibilities occur and the problems that stem from them. Selecting the right pressure sensors requires an understanding of the system requirements while considering the aforementioned points. It helps to narrow down the ideal sensor for the pressure sewage system that will give accurate results.

Combining more than 40 years of industrial experience, engineers at Bestech Australia provide rich expertise in modifying and customizing sensors for tailor-made high-precision testing applications. Modifying the pressure sensor for the pressure sewage system, incorporating design and material that can withstand the pressure and corrosive nature of process media are employed in the sensor manufacturing stage to optimise the operation.

Bestech Australia has established successful partnerships with researchers and local manufacturers to support all their testing and measurement needs. The company provides full local technical support from system design, testing and commissioning. We established a long-standing collaborative relationship with all our suppliers and combined this partnership with its local expertise to back local manufacturing and testing capability.

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