Accurate detection of sewage flow plays a critical role in industrial production processes. Through precise monitoring of sewage flow, relevant departments can effectively evaluate pollution discharge conditions. When measuring sewage flow, electromagnetic flow meters are the preferred choice for sewage flow measurement. The velocity-area method is a specialized solution for partially filled pipe sewage flow measurement.
This article will detail issues related to sewage flow monitoring.
What is a Sewage Flow Meter?
Sewage flow meters are industrial measuring instruments specifically designed to measure the instantaneous flow rate and cumulative total volume of sewage within various types of sewage pipelines. They are suitable for fluid conditions involving municipal domestic sewage, industrial wastewater, chemical wastewater and sludge-laden sewage—all of which contain impurities, suspended solids and mildly corrosive media.
Unlike standard clear-water flow meters, their structural design takes full account of the tendency of silt, fibres and particulates in sewage to settle and adhere to the meter; most employ obstruction-free, non-clogging measurement structures. Common types include electromagnetic sewage flow meters, ultrasonic sewage flow meters and insertion-type vortex flow meters.
Wastewater VS Sewage
Wastewater refers to the collective term for water discharged from residential activities and stormwater runoff. It includes domestic sewage, industrial wastewater, and other non-reusable water. such as initial rainfall runoff entering drainage pipes. Generally, it denotes water that cannot be recycled. After primary pollution, it cannot meet specific standards through purification treatment.
Sewage refers to contaminated discharge water from domestic and industrial sources. Water that has lost its original functional use is termed sewage. Primarily consisting of post-domestic use water, it contains higher organic matter. And it is relatively easier to treat.
In industrial processing, sewage and wastewater have the following challenges that complicate flow measurement:
1. Large discharge volumes, extensive pollution coverage, and diverse discharge methods;
2. Wide variety of pollutants with significant concentration fluctuations;
3. Corrosive and toxic. Sewage contains highly acidic or highly alkaline pollutants. It is harmful to water quality;
4. Highly variable migration patterns and transformation characteristics after pollutant discharge;
5. Difficulties in restoring water quality.
Types of Sewage Flow Meters
Electromagnetic Flow Meters
Principle of Operation
Based on Faraday’s law of electromagnetic induction, when conductive sewage flows through the instrument’s magnetic field, it cuts across the magnetic field lines.
The electrodes detect the induced electromotive force generated; the magnitude of this electromotive force is directly proportional to the flow velocity of the sewage. Combined with the cross-sectional area of the pipe, this is used to calculate the volumetric flow rate.
There are no throttling elements inside the instrument’s pipe; only the anti-corrosion lining is adapted to the sewage medium. It is unaffected by minor variations in sewage temperature, pressure or density, requiring only that the sewage possesses a certain level of electrical conductivity. It is the mainstream instrument for sewage measurement.
Advantages
1. With no obstructing components inside the pipe, sludge and fibres are unlikely to accumulate and cause blockages, ensuring high long-term operational stability.
2. Fitted with rubber or PTFE linings, it is resistant to corrosion from acidic and alkaline effluent, making it suitable for all types of industrial and domestic wastewater.
3. High measurement accuracy and a wide measurement range ensure stable data collection even at low flow rates.
4. Pressure loss is minimal, placing no additional load on the effluent transfer pumps and offering excellent energy-saving performance.
Applications
Widely used for measuring inflow, outflow and recirculating water in biochemical tanks at sewage treatment works; also suitable for monitoring integrated industrial effluent networks and municipal sewage networks.
It is the most commonly used metering equipment for environmental protection discharge inspections, sewage process control and discharge billing, and can be integrated with central control systems to enable remote, real-time flow monitoring.
Ultrasonic Flow Meter
Principle of Operation
It utilises the time-of-flight measurement principle, with ultrasonic transducers installed on either side of the pipe wall, alternately emitting ultrasonic waves that travel through the wastewater in both the downstream and upstream directions.
The flow of the fluid alters the propagation time of the sound waves; the time difference between the downstream and upstream propagation times is linearly related to the wastewater flow velocity.
By performing calculations and factoring in the pipe cross-sectional area, the volumetric flow rate is determined. There are clamp-on and insertion types; the clamp-on probes do not come into contact with the wastewater, eliminating the risk of medium contamination.
Advantages
1. The clamp-on type requires no pipe cutting or drilling, making retrofitting straightforward; installation can be completed without interrupting operations.
2. As the probes do not come into contact with the sewage, there are no issues with scaling, corrosion or blockages, resulting in low maintenance costs.
3. Suitable for large-diameter municipal sewage pipes; the equipment size is not restricted by pipe diameter.
4. There is no pressure loss, so it does not impose an operational burden on the existing sewage conveyance system.
Applications
Commonly used for monitoring inflow and outflow in ageing municipal sewage trunk networks and large pumping stations, as well as for metering during the retrofitting of large-diameter industrial effluent pipelines.
Suitable for situations where it is impractical to halt operations or excavate pipelines; when used in conjunction with online environmental monitoring systems, it records total sewage discharge in real time.
Vortex Flow Meter
Principle of Operation
A vortex generator is installed within the pipeline; as the sewage flows past, it alternately generates regular vortices behind the generator, with the frequency of vortex release being directly proportional to the flow velocity of the sewage.
The probe detects the vibration signals generated by the vortices, converts them into electrical signals to calculate the flow velocity, and determines the volumetric flow rate by combining this with the cross-sectional area of the pipeline.
Metering is achieved through the Karman vortex street effect in fluid dynamics, and the structure comprises only the vortex generator and the detection element.
Advantages
1. The instrument has a simple structure with few internal components, resulting in a low failure rate and straightforward maintenance.
2. It withstands high-temperature and high-pressure conditions, enabling the measurement of high-temperature cleaning wastewater and heat treatment effluent.
3. It features a wide turndown ratio, allowing stable measurement at both high and low flow rates, whilst the stable output signal facilitates easy integration with control systems.
4. Compact in size, it requires minimal installation space and is suitable for confined pump rooms and small sewage branch pipes.
Applications
Primarily used for measuring cooling wastewater and workshop cleaning effluent with low levels of impurities and fibres, it is suitable for low-pollution drainage pipelines in small processing plants. It is not suitable for effluent with high sludge content or long fibres, and is often paired with a small PLC to enable real-time statistical monitoring and control of drainage flow.
Coriolis Flow Meter
Principle of Operation
Measures mass flow rate utilising the Coriolis force effect. As wastewater enters a pair of vibrating measuring tubes, the fluid flow generates a counter-rotating Coriolis force, causing a phase difference between the two tubes.
By detecting this phase difference, the mass flow rate of the wastewater can be directly calculated; this method is unaffected by changes in wastewater temperature, density or concentration, requires no compensation or conversion, and uses the mass of the medium—rather than its volume—as the measurement basis.
Advantages for Wastewater Measurement
1. Direct measurement of mass flow rate, with no need for density compensation; offers unrivalled measurement accuracy for high-concentration chemical wastewater.
2. Simultaneous output of flow rate and medium density data facilitates the assessment of pollutant concentrations in the wastewater.
3. Measurements are unaffected by fluctuations in temperature, pressure or viscosity, ensuring high measurement stability for complex chemical wastewater.
4. High measurement accuracy meets the requirements for high-precision discharge accounting and material balance statistics.
Applications
Primarily used for the precise measurement of high-concentration corrosive wastewater in the chemical, pharmaceutical and precision manufacturing industries.
Suitable for production workshops requiring accurate accounting of wastewater materials and discharge costs, and can be integrated with online environmental monitoring equipment to achieve high-precision archiving of discharge data.
Sino-Inst Featured Sewage Flow Meter
Why Sewage Flow Monitoring Matters?
Based on our many years of sewage flow measurement experience, sewage flow monitoring is important in multiple aspects.
Environmental Protection and Water Quality Monitoring:
Real-time monitoring of sewage flow and tracking of wastewater discharge lets staff promptly detect abnormal flow and leaks, thereby preventing water pollution incidents.
Optimizing Sewage Treatment Processes:
Flow monitoring precise data provides real-time inflow and outflow of sewage to treatment plants. Help optimize treatment processes, adjust operational parameters, enhance efficiency, and reduce costs.
Environmental Emergency Alerting:
A sewage flow alert system enables early measurement of anomalies. It facilitates a timely emergency response to maximize protection of the aquatic environment.
Sewage Network Management:
Flow monitoring reveals transmission conditions within urban sewage networks. It enables timely monitoring of blockages, leaks, and other issues for maintenance and repairs to ensure unimpeded sewage flow.
Selecting the Most Suitable Sewage Flow Meter
We have extensive experience in sewage measurement, so we concluded the following considerations should be considered when choosing a sewage flow meter:
Sewage Properties: Confirm the element, temperature, pressure, and other properties of the sewage to select the appropriate flow meter.
Flow Range: Select a flow meter with a measurement range that exceeds the actual sewage flow range.
Pipe Diameter Range: Determine the pipe size for the flow meter in advance when measuring sewage flow to ensure accurate results. The suitable pipe diameter is essential for accurate sewage flow measurement.
Measurement Precision: Select the appropriate flow meter accuracy based on your actual requirements. Ensure effective sewage treatment.
Maintenance Costs: Consider maintenance and calibration expenses to select cost-effective products.
Installation Environment: Installation location and flow velocity all influence selection and require a comprehensive evaluation.
FAQ
What Does Sewage Flow Mean?
Sewage flow refers to the volume of sewage passing through a defined cross-sectional area per unit time. Common units: m³/s or m³/h. Based on our many years of sewer flow measurement experience, we summarize two calculation methods for your reference:
Water Level-Flow Relationship Method
This method determines wastewater volume by observing a water level-flow relationship curve. It is suitable for rivers or waterways that require long-term monitoring. By monitoring and measuring the current water level and referencing a pre-set flow-level relationship curve, the current flow rate can be estimated.
Velocity-Area Method
It is the easiest method for calculating sewage flow rate. This method requires measuring the sewage flow velocity and the cross-sectional area of the pipe or channel.
By using this formula, we can calculate the sewer flow rate.
Q = A × v,
where v is the flow velocity, Q is the flow rate, and A is the cross-sectional area. Electromagnetic flow meters can measure sewage flow velocity. And calculate the cross-sectional area based on the shape and size of the pipe.
How to Check If a Flow Meter is Functioning Properly?
The following symptoms indicate a malfunctioning flow meter:
- No flow output or abnormal output.
- Reading deviations.
- Alarm or fault indicator lights are activated.
What are the disadvantages of ultrasonic flow meters?
Temperature Limitations: Ultrasonic flow meters have restrictions on the temperature range of the measured fluid.
Poor Interference Resistance: Ultrasonic flow meters are susceptible to interference from bubbles, scaling, pumps, and other sources of ultrasonic noise, which can affect measurement accuracy.
Strict straight pipe section requirements are essential: 20 pipe diameters upstream and 5 pipe diameters downstream. Failure to meet these specifications results in poor dispersion and reduced measurement accuracy.
Complex Measurement Circuitry: Achieving high-precision results demands exceptional accuracy in sound velocity measurement. This increases the complexity and cost of equipment design and implementation while complicating measurement circuitry.
Expensive: Compared to other alternative flow meters, ultrasonic flow meters are more expensive because of the higher initial purchase cost and the higher maintenance requirements.
In short, electromagnetic flow meters play an important role in sewage flow measurement. Sino-Inst has deep expertise in flow measurement, with numerous successful sewage measurement cases. Our sewage flow meters are highly regarded for their quality and have earned praise from various customers. We can provide customized solutions free of charge. Please contact us immediately.
