Monitoring of wastewater quality in the outlet of a grease separator

Application Report | Water & Wastewater

  • Proof of compliance with limit values and full transparency over sewage quantities discharged
  • Automated process monitoring by way of combined measurement of pH, conductivity and flow rate


Kesselhut Entsorgungs GmbH specialises in the inspection and cleaning of pipe and sewer systems, roads and industrial plants. The range of services offered by the municipal service provider also includes the disposal of faeces, oil and grease separation. In the German federal state of Saxony-Anhalt, the company operates a plant for the separation of grease. The site is fed with industrial wastewater.

Measurement requirements

The operation of grease separators is subject to strict technical and environmental regulations. As the wastewater downstream of the grease separator is discharged into the municipal sewage network, the customer must report to the local wastewater association. The authority monitors compliance with the permissible limit values mainly by way of pH and conductivity. Kesselhut is legally required to submit these parameters to the wastewater association on a regular basis. This implies continuous monitoring of the effluent downstream of the grease separator using suitable process instrumentation. In order to be able to further automate the process and increase process reliability, the customer was looking for a partner who could provide both the measurement technology as well as the technical consulting and service needed.

KROHNE Solution

For limit value monitoring, KROHNE supplied analytical sensors and flowmeters tailored to the customer's needs. For pH measurement, the OPTISENS PH 8300 is used. Designed for wastewater applications, this glass sensor features a robust, dirt-repellent PTFE ring diaphragm as well as an integrated temperature sensor. The pH sensor was installed into a U section using the SENSOFIT IMM 1000 immersion assembly.

For inductive conductivity measurement, the customer uses the OPTISENS IND 1000 with polypropylene (PP) sensor body. The compact inductive conductivity sensor for industrial wastewater also has a non-wetted Pt1000 for temperature compensation. For this application the OPTISENS IND 1000 was supplied with an immersion holder it is firmly attached to.

Both analytical sensors are equipped with the 2-channel MAC 100 analytical transmitter. In this way, only one single transmitter is required to transmit both the pH and the conductivity readings to the control room. The MAC 100 was provided as a panel-mount version, allowing for a flexible installation on the wall regardless of the transmitter’s dimensions. To accurately monitor the sewage quantity, the client also installed the OPTIFLUX  4300. Thanks to its PU liner, the electromagnetic flowmeter is ideally suited for measuring even heavily contaminated wastewater. Given the patented "virtual reference" of the device, there was no need to apply a conventional grounding method using additional grounding rings. The flowmeter was supplied as a remote version with field-mounted (F) signal converter.

Customer benefits

The customer benefits from a bespoke solution which in addition to pH and conductivity also automate the recording and evaluation of data on wastewater quantities in the control room. This enables Kesselhut to provide evidence on precisely the wastewater quantities that have been discharged to the sewer system. The customer can use the balancing in their billing practice with the wastewater association. The process instrumentation also provides complete proof that all limit values are being adhered to. In case of strongly deviating readings, the disposal company can take countermeasures in time. In this way, the company avoids contamination of the sewage system and unnecessary surcharges from the water authority.

Products used


Electromagnetic flowmeter for advanced process and custody transfer (CT) applications

  • High accuracy (±0.2%), certified for custody transfer
  • For low conductivity media (>1 μS/cm) and high solid contents (≤70%)
  • Flange: DN2.5…3000 / ⅒…120", max. PN40 / ASME Cl 600 (higher on request)
  • 3 x 4…20 mA, HART®,Modbus, FF, Profibus-PA/DP, PROFINET


Potentiometric pH sensor for wastewater, surface and process water applications

  • For use with analytical transmitter
  • Process connection: PG13.5
  • 0…14 pH; Max. +70°C / +158°F; 10 bar / 145 psi
  • Glass sensor with PTFE diaphragm and optional Pt100 for temperature compensation


Inductive conductivity sensor for water, wastewater and chemical applications

  • For use with analytical transmitter
  • Process connection: G1½ union nut and immersion versions
  • 1…2000 mS/cm; Max. +100°C / +212°F
  • Electrodeless conductivity sensor with Pt1000 for temperature compensation


Immersion assembly for general water and wastewater treatment applications

  • For use with OPTISENS COND 1200 or ∅12 / 120 mm and ∅0.47 / 4.7" sensors
  • Sensor connection: PG13.5 or G½ (female); Process connection: immersion
  • Immersion length: 1 m / 39.37"
  • Max. +80°C / +176°F, pressureless

MAC 100

Liquid analytical transmitter for measurements with sensors of the OPTISENS portfolio

  • Output: 3 x 4…20 mA, 3 relays (mechanical)
  • Input: max. 2 x sensor, 2 x temperature
  • -15…+55°C / +5…+131°F (ambient)
  • Robust housing for wall-mount installation