In scenarios such as sewage treatment, municipal pipeline network operation and maintenance, and wastewater discharge in various industries, flow data is the core basic data for process control, energy consumption statistics, sewage charging, and environmental protection online monitoring, and is an important basis for water management and environmental protection compliance. Different from clean media such as clean water and pure water, sewage has a harsh overall working condition environment, with characteristics such as a large amount of impurities, easy corrosion, unstable water quality, and irregular flow patterns. Most traditional flow meters on the market are developed specifically for clean fluids, and after being put into sewage working conditions, they are prone to problems such as data drift, measurement failure, and frequent equipment malfunctions. Not only does it increase the costs of spare parts procurement and manual operation and maintenance, but it also gives rise to multiple potential hazards such as process allocation imbalance, inaccurate sewage discharge metering, and environmental protection audit violations. Xingao has been deeply involved in the flow metering industry for many years, innovatively researching and developing solutions to address the pain points of full-category sewage measurement, and has become a reliable partner in the field of wastewater metering by using professional technical solutions to solve industry metering problems.
Domestic sewage and wastewater
Reference for domestic sewage and wastewater:wikipedia
Supplement: Basic Definitions and Differences between Sewage and Wastewater
In the environmental protection and water services industry, wastewater and sewage are frequently used technical terms. Their concepts are similar, but their defined scopes differ. Meanwhile, they are often used interchangeably in daily industry applications. The specific definitions are as follows:
Wastewater
Wastewater is a broad concept, generally referring to all water bodies that have undergone changes in water quality, lost their original usability, and been discharged after being used in human production and living activities. It has the most comprehensive coverage, generally including three major categories: urban domestic wastewater, industrial production wastewater, and agricultural wastewater, encompassing all waste water bodies generated by household, commercial, industrial, and agricultural activities.
sewage
Sewage belongs to the narrow concept and usually specifically refers to urban sewage , which is also the main treatment object of current municipal sewage treatment and pipeline network metering projects. At present, in industry textbooks, policy documents, and environmental monitoring literature, sewage and domestic wastewater can basically be used interchangeably. According to the treatment stage, sewage can be divided into two categories:
- Raw sewage: The original sewage without any purification treatment, directly collected by the pipeline network and channeled into the sewage treatment station;
- Treated wastewater : After multiple processes such as grit removal, biochemical treatment, and filtration, the effluent that meets the standards and is discharged externally, also known as treatment plant effluent.
- Domestic sewage : Generated from residents’ daily life, mainly including human excreta, bathing wastewater, laundry wastewater, kitchen wastewater, etc.;
- Urban public sewage: Derived from urban commercial and public institutions, it encompasses the comprehensive wastewater discharged from places such as restaurants, laundries, hospitals, schools, office buildings, shopping malls, etc.
Summary of the Subordination Relationship between the Two
Wastewater > Sewage: Wastewater is a general term for all types; sewage specifically refers to domestic and commercial wastewater at the urban level; domestic sewage only focuses on wastewater generated by residents’ daily lives and urban supporting public facilities, excluding industrial and agricultural wastewater. In the context of municipal flow measurement, the sewage mentioned in this article uniformly refers to urban domestic sewage and comprehensive public wastewater.
Common Problems in the Wastewater Flow Measurement Industry: Dissecting the Four Core Pain Points of Traditional Instrument Malfunctions
Sewage includes types such as municipal domestic sewage, industrial production wastewater, and comprehensive pipeline network sewage. The water quality components and operating conditions vary greatly, imposing strict requirements on the anti-clogging, corrosion-resistant, and flow state adaptability capabilities of flow meters. The fundamental reason why traditional meters cannot adapt to the complex working conditions of sewage is mainly concentrated in four dimensions: impurity clogging, dual losses of the medium, conductivity fluctuations, and non-full pipe flow state:
Impurities entangle and accumulate, prone to blockage and high failure rate
Core Issue: Sewage is a complex fluid, with a wide variety of impurities that cannot be completely avoided, which is the primary factor leading to malfunctions in traditional instruments. Domestic sewage contains soft impurities such as hair, fibers, tissues, and kitchen waste; industrial and comprehensive sewage from industrial parks is mixed with hard and soft impurities such as solid particles, colloidal precipitates, and woven waste.
Disadvantages of Traditional Meters: Traditional meters such as impeller, throttling, and turbine types have precise internal structures. Small components such as impeller shafts, throttling orifices, and detection probes are extremely vulnerable to being entangled by flexible impurities and blocked by the accumulation of solid residues, directly impeding the normal operation of the equipment.
Negative Impact : Clogging failures can directly lead to smaller metering values, chaotic data fluctuations, and in severe cases, directly jam the impeller, causing the meter to be scrapped. Meanwhile, the equipment requires frequent disassembly for cleaning and replacement of parts, resulting in high labor and spare parts costs. In severe cases, it can also cause pipeline network blockages, impeding the normal conveyance of sewage, and affecting sewage treatment and enterprise production progress.
Double erosion of corrosion and wear, resulting in short equipment lifespan and frequent replacement
Core Issue: Sewage meters are in long-term contact with complex media, simultaneously subjected to chemical corrosion and physical erosion and wear. The dual erosion accelerates equipment aging, which is the key pain point for the high-frequency replacement of meters in the industry.
Instrument Disadvantages
Chemical corrosion: Wastewater from chemical engineering, electroplating, and pharmaceutical industries contains corrosive components such as acids, alkalis, and chloride ions. The anaerobic environment in closed pipe networks breeds hydrogen sulfide gas, which continuously corrodes electrodes, casings, and seals made of carbon steel and ordinary stainless steel, leading to electrode failure, casing rusting, and seal leakage;
Physical wear: During the flood season, sewage, sand washing water, and mine wastewater carry a large amount of hard sediment particles, and the high-velocity fluid continuously scours the inner wall of the instrument and the probe, causing wear and deformation of components.
Negative Impact : After the superposition of double losses, the measurement accuracy of traditional instruments experiences a cliff-like decline, the service life of equipment is significantly shortened, requiring replacement in just a few months under harsh operating conditions, and only 1-2 years under normal operating conditions. The long-term superposition of equipment procurement costs increases the burden on project operation.
Conductivity fluctuates, water quality is sensitive, and measurement deviation is large
Core Issue: Electromagnetic flow meters are currently the mainstream equipment for sewage metering. Their working principle relies on the conductivity of water bodies, but the conductivity of sewage is greatly affected by sewage sources, seasonal temperatures, treatment processes, and time-period loads, with values spanning a wide range and having no fixed standard.
Instrument Drawbacks : Conventional general-purpose electromagnetic flowmeters have fixed thresholds and cannot achieve Self-Adaptation to the dynamically changing conductivity of water quality. The conductivity of domestic sewage, high-salt industrial wastewater, and diluted discharged sewage varies significantly, making it difficult for a single model of instrument to cover all scenarios.
Negative Impact : When the conductivity of the medium is lower than the device threshold, the meter directly disconnects and the data returns to zero; when the conductivity suddenly rises or falls, the signal becomes disordered, resulting in non-linear errors. Blind selection not only fails to achieve accurate measurement but also leads to waste of equipment investment and increases the trial-and-error cost of project selection.
Non-full pipe normalization, complex flow regime, and metering error exceeding the standard
Core Issue: The vast majority of sewage collection pipe networks worldwide operate in a gravity flow mode, without constant pressure, and the pipes are typically in a semi-full or non-full state; meanwhile, sewage discharge is affected by work and rest schedules, shifts, and flood seasons, with flow fluctuations reaching up to dozens of times, resulting in extremely unstable flow patterns.
Instrument Drawbacks : More than 90% of traditional flow meters on the market have factory calibration algorithms that are only suitable for full-pipe flow conditions in pressure pipelines, unable to intelligently recognize dynamic liquid levels, and unable to correct cross-sectional area and flow velocity data in real time under non-full-pipe conditions; moreover, they cannot adapt to special flow conditions such as low flow velocity, turbulent flow, and vortices.
Negative Impact : In gravity flow pipe networks, the measurement error of traditional instruments generally exceeds 30%, which not only fails to meet the industry’s rigid standards for environmental protection online monitoring and sewage discharge metering settlement, but also cannot provide effective reference data for sewage treatment process control.
Measurement Challenges
- Sewage impurities easily clog the internal precision structure of the instrument, resulting in frequent malfunctions and high operation and maintenance costs;
- Sewage combines chemical corrosion and physical abrasion from sediment, resulting in rapid equipment aging and frequent replacement;
- Ordinary electromagnetic flowmeters cannot adapt to fluctuating water conductivity, resulting in large measurement deviations;
- Sewage gravity flow pipes are often non-full and have unstable flow patterns, resulting in the measurement error of traditional instruments exceeding the standard;
Advantages of the Solution
- Handling fluid media with complex properties
- The product features high precision, good stability, and low power consumption.
- It has various installation forms and can record historical data.
- Products can be customized according to actual working conditions.
Electromagnetic Flowmeter
Electromagnetic flow meters adopt a non-invasive and non-blocking design, are developed based on Faraday’s law of electromagnetic induction, are only suitable for conductive liquids, and are widely used in flow measurement of sewage, wastewater, and various complex industrial fluids.
Advantages:
- can accurately measure wastewater content
- Simple structure, no moving parts, almost no wear, low maintenance cost; no flow-blocking structure, no pressure loss during operation.
- It has strong adaptability and can measure corrosive liquids, dirty media, and oily liquids containing suspended solids.
- Measurement accuracy can reach ±0.5% or higher, with stable and reliable performance, and is less prone to deviation during long-term use; measurement data is not affected by fluid density, viscosity, temperature, or pressure.
- Supports high-pressure customization, with optional specifications of 10MPa, 16MPa, 25MPa, and 42MPa, meeting the usage requirements of high-pressure pipelines.
- Supports 4-20mA, pulse dual signals, and RS485 output
- Complete functional configuration: Equipped with a digital display for viewing instantaneous flow and cumulative total; compatible with multiple power supply modes including 220V AC, 24V DC, and battery.
Disadvantages:
- The device must be powered on to operate properly;
- Only conductive liquids are applicable; gases and non-conductive media cannot be detected.
- The measuring pipeline must be full and the medium flow must be stable to ensure accurate data;
- When the medium contains bubbles or gas, it is prone to causing errors in measurement data.
Ultrasonic Flowmeter
Ultrasonic flow meters measure fluid flow based on the principle of acoustic wave induction, and are mainly divided into two major categories: transit time type and Doppler type; among them, the Doppler model is more suitable for sewage media containing suspended solids.
Advantages:
- It uses an external clamp-type non-invasive installation method, eliminating the need for pipe cutting;
- No flow-blocking components, no pressure loss during the measurement process;
- Easy to install, suitable for renovation projects of old pipelines.
Disadvantages:
- Measurement data is susceptible to interference from internal bubbles in the medium and fluctuations in flow velocity;
- Measurement accuracy depends on installation workmanship and is significantly affected by on-site conditions.
Installation and Maintenance Tips
- Follow Manufacturer Guidelines: Always adhere to straight tube requirements, grounding requirements, and sensor alignment requirements.
- Avoid bubbles: Bubbles can affect readings. Ensure the pipeline is always filled with water or install an exhaust valve.
- Regular Calibration: Although many instruments have low maintenance costs, regular calibration checks ensure long-term accuracy.
- Sensor Cleaning: In sewage applications, inspect and clean sensors to prevent accumulation or dirt.
- Monitoring Output: Use remote monitoring or SCADA systems to track performance and detect abnormal situations in real time.
