Slurry density meter · PS7000

Sludge Thickening / Digestion / Dewatering / Alum Flower Online Monitoring Solution

Municipal sludge treatment

In the sludge thickening, digestion, and dewatering processes of municipal wastewater treatment plants, conventional gamma-ray density meters pose radiation safety risks, while insertion-type instruments are prone to clogging from hair and fibers. This results in PAM flocculant dosing being based on empirical estimates, leading to chemical waste and fluctuating cake moisture content. The PS7000 series ultrasonic acoustic impedance slurry concentration meter employs a non-contact ceramic probe installed at the thickener underflow, the digester recirculation line, and the dewaterer feed pipe, enabling online density monitoring that is radiation-free, clog-free, and responsive within seconds, thereby supporting precise closed-loop PAM dosing.

Applicable industries
Water & Wastewater
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Sludge Thickening / Digestion / Dewatering / Alum Flower Online Monitoring Solution

PISONICS· Xi’an Pisonics

PS7000 Series

Ultrasonic Acoustic Impedance Slurry Density Meter

Water Treatment / Municipal Sludge Industry Application Case

—— Sludge Thickening / Digestion / Dewatering / Alum Flower Online Monitoring Solution ——

Non‑Nuclear · Optimized PAM Dosage · Reduced Sludge Disposal Costs

Water Treatment / Municipal Sludge · PS7000 Application Solution

1. Process Background

The sludge treatment section of municipal wastewater treatment plants is a key application area for density measurement. The excess sludge produced in the primary and secondary clarifiers (with a solids content of approximately 0.5%–1.0%) is first concentrated to 3%–6% in the thickening tank, then fed into the anaerobic digester (at 35°C, with a retention time of 20–30 days) for stabilization and volume reduction. Finally, mechanical dewatering equipment (centrifuges or belt presses), in conjunction with the flocculant PAM, reduces the moisture content to ≤80%, yielding a sludge cake suitable for incineration, landfilling, or resource recovery.

In addition, measuring “alum flower concentration” during the coagulation and sedimentation stage at water treatment plants helps optimize the automated dosing of coagulants such as PAC and PAM; similarly, monitoring sludge concentration in neutralization, sedimentation, and flocculation tanks in industrial wastewater treatment is critical for ensuring stable equipment operation and compliance with discharge standards. The core control variable throughout the sludge process—the density of the sludge entering the dewatering machine—directly determines the amount of PAM flocculant added and the final moisture content of the sludge cake, thereby influencing sludge disposal costs and overall operating expenses.

2. Pain Points of Traditional Density/Concentration Measurement Solutions

• The densely populated environment of municipal wastewater treatment plants (with operators, maintenance staff, visitors, and others) places significant pressure on radiation safety management when using gamma‑ray density meters; several new projects have already banned the use of radioactive sources.

• The complex composition of sludge (containing organic matter, hair, fibers, plastic fragments, and other foreign materials) causes frequent wrapping and clogging of insertion‑type tuning fork and rotary instruments, requiring weekly shutdowns for cleaning.

• Differential pressure diaphragms have a short service life when exposed to corrosive anaerobic digestion sludge (containing hydrogen sulfide and organic acids), with severe zero‑point drift.

• PAM dosage has long been estimated “by experience,” leading to overuse that wastes the costly reagent (PAM costs 15,000–30,000 yuan per ton) while simultaneously degrading dewatering performance.

3. PS7000 Solution

The PS7000 is deployed at three critical points in the sludge treatment process: the underflow outlet of the thickening tank (PS7000 #1), the digestor recirculation line (PS7000 #2), and the feed line to the dewatering machine (PS7000 #3—the key measurement point). The density of the sludge entering the dewatering machine serves as the core input signal for the automated PAM dosing control system, enabling precise, on‑demand addition of the flocculant.

Sludge Thickening / Digestion / Dewatering / Alum Flower Online Monitoring Solution

Figure 1 Schematic Layout of Density Measurement in the Sludge Treatment Process at a Municipal Wastewater Plant

Core Technical Advantages of the PS7000 in Water Treatment and Municipal Sludge Applications

▶ Completely non-nuclear—aligns with the “zero-radiation” management philosophy for municipal public utilities, posing no approval hurdles for either new installations or retrofits;

▶ Non-contact ceramic probe—hair, fibers, and foreign objects in the sludge do not interfere with measurements at all; zero wrapping and zero clogging;

▶ Response time < 1 second—abrupt changes in sludge concentration can be instantly fed back to the PAM dosing pump, avoiding the waste of chemicals caused by traditional “lagged dosing”;

▶ 316L + PTFE lining—resistant to sulfur-induced corrosion in digested sludge, with a service life ≥ 5 years;

▶ Optional 4G module—automatically uploads municipal plant operation and maintenance data to the cloud, enabling integration with smart water‑management platforms;

▶ When paired with DCS/PLC, it enables closed-loop control of PAM dosing, reducing PAM consumption by an average of 10%–20%.

4. Customer Value

Comparison Dimensions

Original Conventional Solution

PS7000 Solution

Radiation Compliance

γ-ray measurements require a license

Intrinsically safe · Radiation-free

Sludge Foreign-Object Interference

Frequent entanglement with insertion-type density meters

Non-contact · Zero interference

Instrument service life

Diaphragm/tuning fork wears out within half a year

Ceramic probe ≥ 5 years

PAM Dosage

Empirical estimation · High waste

Density feedback · Reduces reagent consumption by 10%–20%

Mud cake moisture content

Fluctuation · Instability

Stable feed · Increased rate of meeting moisture content standards

In a technical upgrade project at a municipal wastewater treatment plant in eastern China, with a capacity of 300,000 cubic meters per day, three PS7000 units replaced the original nuclear‑based density meters and differential pressure instruments, installed at the thickener underflow, the digestor recirculation loop, and the dewaterer feed line. After eight months of operation, statistical data show that PAM usage decreased by 18% year‑on‑year (saving nearly 2 million yuan in chemical costs annually), the average moisture content of the sludge cake dropped from 82.3% to 78.5%, and external sludge disposal costs fell by approximately 6%. This project has become a model case for non‑nuclear density measurement, promoted by the local housing and urban‑rural development authorities.

Conclusion

Based on the four ultrasonic measurement principles of the PS70 series (acoustic impedance, acoustic attenuation, sound velocity, and sonar frequency modulation), Xi’an Pisonics’ PS7000 covers the full range of online density/concentration measurement needs, from two‑phase solid–liquid slurries to clean, homogeneous liquids. Tailored to the process characteristics of the water treatment and municipal sludge sectors, the PS7000 ultrasonic acoustic impedance slurry density meter provides end‑to‑end technical support—from instrument selection and installation/commissioning to long‑term operation and maintenance.

For an in‑depth discussion of your project’s specific conditions, customized selection recommendations, or on‑site technical consultation, please feel free to contact the Xi’an Pisonics engineering team at any time.

More applications for Slurry density meter

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Online Measurement of Gypsum Slurry Density in Absorption Towers

In the wet flue-gas desulfurization process, real-time monitoring of gypsum slurry concentration is crucial for ensuring the quality of the by-product gypsum and the proper operation of equipment. However, conventional concentration meters—such as mass flow meters, tuning fork sensors, and differential pressure concentration meters—suffer from issues like radiation safety concerns, bubble interference, and scaling. Pisonics’ PS7000 employs ultrasonic technology for non-contact measurement, can penetrate bubble layers to deliver stable and reliable concentration data, and requires no maintenance, with a service life exceeding five years.

Online Density Measurement for Limestone Slurry Preparation

During the preparation of limestone slurry, conventional density-measurement solutions suffer from issues such as wear and scaling, leading to inaccurate data and compromising flue-gas desulfurization efficiency. The PS7000 acoustic impedance concentration meter overcomes these challenges through non-contact ultrasonic measurement, delivering stable, high-precision online density monitoring and ensuring consistent control of slurry concentration.

Online Measurement of Desulfurization Wastewater Density

In the flue-gas desulfurization process at power plants, online monitoring of the slurry density in the underflow from the thickener is critical. Conventional contact-type instruments are prone to scaling and corrosion, making it difficult to meet the demands of long-term, stable operation. Pisonics’ PS7000 acoustic impedance concentration meter employs a non-contact ceramic probe and a corrosion-resistant lining, effectively addressing severe corrosion and fouling while ensuring the accuracy and stability of the measurement data.

Online Density Measurement for the AFT Tower (High-Concentration Desulfurization Slurry Processing Tower)

In the AFT tower, measuring the density of high-concentration, high-viscosity, and easily crystallizing slurries has long been a challenge. The PS7000 acoustic impedance concentration meter, employing non-contact measurement, overcomes the failures of conventional instruments caused by clogging, wear, and crystallization, enabling real-time, continuous monitoring of slurry density and automated control of the discharge process, thereby ensuring stable system operation.

Selection support

Guides

Comparisons

Voices from users of this product

"Our original tuning fork and differential pressure meters on the absorber gypsum discharge main had recurring problems with bubbles and scaling — we had to shut down weekly to clean them. After switching to PS7000, both problems disappeared. Basically maintenance-free now, accuracy is stable, and it fully meets our FGD process control needs."

Thermal Control Foreman Wang
Thermal Control Specialist
A certain thermal power plant in Inner Mongolia

"After switching to the PS7000, our overflow density readings finally stabilized — we stopped tuning reagent dosing by feel. The unexpected win was not having to clean the sensor weekly; our previous radiometric meter needed window-wiping almost daily in the scaling slurry."

Director Li
Mineral Processing Workshop Director
A certain copper mining enterprise

"Our potash blending tank is a harsh environment — KCl near saturation, 30~40% crystal content, temperature swinging 5~20°C. Traditional density meters can't hold up here. After two weeks of PS7000 service, the deviation from manual lab samples stayed in the 0.5~0.8% range, even during concentration peaks. No anomalies."

Director Xie
Process Engineer
A potash fertilizer plant in Qinghai

FAQ

Is the PS7000 ultrasonic density meter a radiometric device? Does it need a radiation license?

The PS7000 is an acoustic-impedance ultrasonic density meter with no radioactive source whatsoever. No radiation license is required. It uses only piezoelectric transducers to send and receive ultrasonic signals — the same physical principle as medical and NDT ultrasound.

If you're currently using a Cs-137 / Co-60 source-based meter and want to remove the regulatory burden, PS7000 is a drop-in alternative. We also offer the PS7500 gamma meter, which uses an exempt-activity Na-22 source (< 1000 KBq) — also requires no radiation license.

Can PS7000 really measure stably in bubbly mining slurries?

Yes.

The PS7000 employs a linear frequency-modulated (Chirp) acoustic impedance algorithm—after transmitting a broadband ultrasonic pulse, the host unit analyzes the echo signal in the frequency domain, and multiple-reflection interference caused by bubbles is identified and eliminated by the algorithm. This is the core difference between the PS7000 and conventional reflective ultrasonic density meters: traditional single-frequency reflection is highly sensitive to bubbles, whereas the PS7000’s Chirp algorithm is virtually immune to them.

At the gypsum discharge line of an absorption tower in a thermal power plant in Inner Mongolia (under conditions of continuous air oxidation that generate dense bubbles), the PS7000 has been operating stably for several years after replacing the original tuning fork concentration meter.

What installation requirements does the PS7000 have?

The installation requirements for the PS7000 flanged direct-insertion type are as follows:

  1. Straight-run pipe sections: ≥5D (upstream) + 2D (downstream), where D is the nominal pipe diameter;
  2. The installation point must operate with a full pipe to avoid stratification of gas and liquid phases;
  3. The applicable pipe sizes range from DN50 to DN1000 (larger sizes can be customized);
  4. The flanges are compatible with ANSI/DIN/JIS standards;
  5. In highly abrasive conditions, it is recommended to use a 316L probe with special ceramics or a 2205 duplex stainless steel probe;
  6. In strongly corrosive environments, a PTFE-lined option is available.

If the pipeline does not allow for tapping, please consider the PS7010 clamp-on type instead.

PS7000 vs nuclear density gauges: which costs less over the life cycle?

On purchase price alone, ultrasonic and nuclear gauges sit in a similar bracket. The gap opens over 5 to 10 years of ownership.

Hidden cost list of a Cs-137 / Co-60 nuclear gauge:

  • Radiation safety licensing and annual reviews, plus operator training and certification;
  • Licensed transport and installation filing for the source;
  • Dose monitoring and record keeping during service;
  • Source replacement as activity decays (purchase, transport, commissioning, return of the old source);
  • End-of-life disposal of the spent source — often the single largest bill.

PS7000 acoustic-impedance ultrasonic gauge: no radioactive source and no permits of any kind; non-contact sensor with zero wear and zero clogging, sensor life of 5 years or more, virtually maintenance free with no consumables. Power plant, potash and iron ore sites have run 2+ years at near zero maintenance.

Bottom line: on a 5-year basis the total cost of ownership of the PS7000 is typically far below a nuclear gauge. Where a nuclear principle is genuinely required (such as dense-medium coal washing), the PS7500 with an exempt-activity Na-22 source needs no license, though the roughly 2.6-year half-life still implies periodic source renewal.