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Controlling Moisture In Digestate

Controlling Moisture In Digestate
2 Nov 2022  |
With the ever-increasing effects of global warming on the environment, governments have agreed to reduce the carbon released into the atmosphere. A major contributor to global carbon emissions is the use of fossil fuels. As a result, the use of renewable fuel sources has become a major new industry.

The utilization of Anaerobic Digesters (AD) is now becoming a major source of renewable gas (Biomethane). AD is a naturally occurring process using microorganisms in the absence of air in which animal and plant materials, known as biomass, are broken down. The process is performed in sealed tanks or digesters. The main output of the process is biogas which can be used to generate electricity or directly fed into the existing gas network. The by-products of AD are residual heat and digestate. Digestate is a nutrient-rich matter that can be used as fuel, fertilizer, or animal bedding.

The need to measure the moisture content of digestate

The digestate that is produced in the AD process needs to be dried for several reasons:

  • Reduced handling and spreading costs
  • Reduced transport costs on and off-site
  • An additional blending of the digestate can be performed to produce fertilizer or create a fuel source
  • Control of the final product for use in animal bedding
  • Utilizing the waste heat energy produced in the AD process

Therefore, the control of moisture, during the drying process, is vital to produce a final product that is suitable for its intended market.

The benefits of installing Hydronix microwave moisture measurement sensors

  • Dryers can be used more efficiently thereby reducing energy costs
  • Improved and consistent product
  • Reduction of spoilt/wasted material
  • Not affected by dust or color
  • Automation of the drying process, reducing the need for manual intervention

Recommended Installation

The installation method is dependent on the application and the dryer type. The majority of digestate dryers are of the horizontal bed design. The material is moved along the dryer and heat is passed through the bed and the material. The dwell time and temperature are controlled to ensure the product is at the correct moisture when it exits the dryer.

Hydro-Mix XT Dryer Installation Method

We recommended that you install the sensor in the cool zone, using a skid, so it is positioned on top of the flowing material coming out of the dryer.

Hydro-Mix XT Installed

You can also install the sensor after the dryer in the material transport system, either in a screw or chain conveyor.

Hydro-Mix XT Screw Conveyor Installation

Result after installing the sensors

A well-implemented installation will measure the moisture levels of the materials exiting the dryer to an accuracy of +/- 0.5% enabling the dryer to be controlled more precisely.

Real-time control of the dryer (as opposed to waiting for oven tests) ensures that the dryer is controlled instantaneously resulting in increased energy efficiency. There is also a reduction in the amount of substandard or wasted product caused by the time delay between periodic sampling and subsequent dryer adjustment.

Hydro-Mix XT sensors

Hydro-Mix XT sensors are constructed of stainless steel and have an abrasion-proof ceramic measuring faceplate. The sensor is designed to be installed flush-mounted with the surface of a skid or mechanical material transport system, allowing the material to flow freely over the measuring faceplate without causing any build-up.

The Hydro-Mix XT has configurable parameters such as signal filtering and smoothing designed to eliminate noise created by the metal screw and air voids. The sensor also features a choice of output options such as 0-20mA (0-10V), 4-20mA, USB, Ethernet and RS485/232 and may be configured to output a moisture percentage value directly from the sensor. The Hydronix Hydro-Com software enables simple set-up and configuration of the sensor using a PC or laptop and USB connection.


The inclusion of a microwave moisture measurement system into the existing process will help you to:

  • achieve consistent quality products
  • reduce the number of spoilt materials
  • provide instant savings
  • repay its capital expenditure in a very short time.

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Hydronix is the world’s leading manufacturer of digital microwave sensors for online moisture measurement. Hydronix was established in 1982 and pioneered the digital microwave moisture measurement technique. Hydronix has a global presence, selling to over...

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