MID MIX technique

VSGM is currently in the process of obtaining BAT (Best Available Technology) for MID MIX.

Sustainable solution

VSGM wants to contribute to a circular, environmentally friendly society. We do so with our MID MIX technique. Due to natural chemical reactions in the processing unit, the MID MIX is a system that consumes little energy. It has a very low CO₂ footprint and emits no NOx. Based on the results as described in the mLCA, it can be concluded that the MID MIX + carbonating (capturing CO₂) route has a lower environmental impact (better score) than sludge incineration. We can even guarantee a negative environmental impact! This makes the route environmentally superior to sludge incineration. The use of CaO in the MID MIX process causes environmental impact, but this is more than compensated for by the absorption of CO₂ and the conversion of the Neutral into a hybrid/synthetic limestone flour that can be used as a cement substitute.

Another interesting route with a low environmental impact for MID MIX is so-called dehydration. Using our own green energy, secondary CaO is produced from Neutral without any CO₂ emissions occurring in this process.

Click here to request the full mLCA from CE Delft.


The MID MIX technology was developed in Croatia almost 13 years ago. Since then, Astra Engineering has further developed the technology. Since then, more than 130 types of material (sludge and waste) have been successfully processed with the MID MIX technology. Probably the most unique MID MIX operation is being managed and run by Yunirisk in Belgrade, Serbia.
The MID MIX technique has been patented worldwide. VSGM markets the MID MIX in large parts of Europe.

Application and capacity

The basic single line MID MIX installation processes between 4 and 8 tonnes of sludge per hour. The installations can be permanently installed at locations where sludge is collected. In addition, there are semi-mobile installations that can be used flexibly at locations where sludge is produced. In principle, two operators are needed to operate the production line. The system can be controlled to a specific required output. For larger volumes, tailor-made installations are designed. Depending on the demand, several installations can be used in parallel. Different configurations, scalable up to very large volumes, can be set up according to the needs of a customer or the emergence of a new demand.

The basic process

The processing sludge is converted to the product Neutral in a reactor by adding CaO. The installation consists of various components. From the supply buffer, dewatered sludge is pre-treated and then processed in two reactors. Here, CaO is added. Moisture is extracted through an exothermic reaction and various chemical and physical processes take place. The core processes that take place in the plant are soldigation and molecular encapsulation of heavy metals. The end product, Neutral, is cooled. The ventilation air from the process is treated in a bag filter and a scrubber. About 65% of the total input mass is converted into the final Neutral product. There is no residual product during the process that needs to be disposed of as waste.

End product Neutral

After processing sludge in the MID MIX, the circular building material Neutral is created. It consists of 80%-90% Calcium Hydroxide (Ca(OH)2) and 20%-10% Calcium Carbonate (CaCO3). Neutral can be used as an aggregate in construction, as a soil improver and as a substitute for primary building materials. However, there are two routes, using primary Neutral as a base, that have a very beneficial impact on the environmental score of the MID MIX process. The routes are Carbonation and Dehydration.
With Carbonation, primary Neutral is reacted with CO2 whereby the CO2 is permanently stored. Between 500 kg and 700 kg of CO₂ can be captured in 1,000 kg of Neutral. This CO₂ can be captured elsewhere and transported to a CO₂ conversion box. When installed next to a flue gas duct, CO₂ can be led directly to the box where the process takes place. In both cases, a hybrid/synthetic limestone flour is the end product. Carmeuse can apply the end product and therefore gives a 100% off-take guarantee of the carbonated Neutral.
In dehydration, primary Neutral is heated to 600˚C and CaO is recovered. This secondary and circular CaO can be re-used. The CaO then has no CO2 footprint.