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Moisture Measurement in Environmental Technology and Biotechnology


Water content is besides temperature one of the most important material properties in commercially used environmental technologies and biotechnological processes. Until today no method was known worldwide useful for fast on line moisture measurement in biomaterials. The moisture meters commercially available suffer from the inhomgenity of such materials, with high effort for taking and handling samples and from a lack of robustness.


The moisture range to be covered in such applications is very broad and reaches from 5% to 80% water content. Most bacteria find their optimal environment at a moisture level between 30% and 60%. This moisture level shall be held permanently in the substrate, which is in applications like biofilters, composting or in applications often difficult. Many real processes are not running optimally due to many or to less water.

Measuring moisture in such materials was a time consuming task. For gravimetric moisture measurement with oven drying samples had to be taken and dried in the laboratory for hours or even days. A real moisture monitoring in the process is not possible this way.

Process methods for moisture measurement in biotechnological applications are commonly based on humidity measurements in air channels. They only work indirectly, and between moisture changes and their measurement often minutes or hours are passing.

Because of the special features of water in the microwave region moisture meters based on microwave principles are a very good choice for moisture measurement in environmental technologies and biotechnology.

Water is a polar substance with very high permittivity compared to dry materials. The close interaction with this property of water at high frequencies makes microwaves the ideal means for getting moisture information.

The microwave moisture meters of the MOIST series are the basis for special microwave sensors developped for environmental technology: MOIST BIO for handheld applications and MOIST BIO P for on line measurements.

The chosen microwave applicator geometry allows a good coupling into the material. Therefore a large material volume (50 to 100 l) can be covered. This leads to some averaging due to the measurement method itself. The radius of interaction around the applicator is between 30 and 50 cm.

Measuring moisture with MOIST BIO microwave applicators gives immediately moisture values of the material. The covered moisture content ranges between 0 and 80%. The accuracy of the moisture measurement can be compared with that of the used reference method.

For all measurements in organic materials it is strongly recommended to take more than one moisture reading and to average the readings. This averaging functionality is already contained in the handheld MOIST 200, which can be combined with MOIST BIO.

There are a lot of examples for the use of microwave moisture meters in environmental technology and biotechnology. Those are

  • moisture measurement in compost
  • moisture monitoring in biofilters
  • moisture measurement in wood chips and wood pellets
  • moisture measurement in biomass
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