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Why do so many biogas plants stick to mesophilic temperatures (37-44°C)? Maybe because everyone else does it and it´s known to be safe and investors want to avoid risks.  But what about the biogas yield? My Indian partners were very hesitant to accept my proposal to operate rice straw biogas plants thermophilic (55+ °C). The biogas mainstream in India goes mesophilic . Actually, most of world goes mesophilic when it comes to Biogas. But why?

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5 Reasons for an Investor to Go Thermophilic for Digestion of Rice Straw in India

Investors are cautious people and want to avoid risks. Mesophilic is common and known. The biogas yields are poor. Operating thermophilic saves Capex and Opex and boosts ROI

My Indian partners were very hesitant to accept my proposal to operate rice straw biogas plants thermophilic (55+ °C). The biogas mainstream in India goes mesophilic (37-44 °C). Actually, almost everywhere around the globe plants go mesophilic when it comes to biogas. But why?

A biogas plant is considered to be a technical cow. A cow is a mammal with 37 °C body temperature. Even the German laboratory standard temperature for biogas yield test is 37°C. Therefore, when the biogas business started, people started to operate biogas plants mesophilic.

Times are changing. People learn. More knowledge and experience were gained. Biogas plants started to raise temperature.

When I increased the temperature to 44 °C in my own biogas plant back in 2003, I thought this is the ceiling. I was wrong.

My friend, I built his biogas plant in 2005, increased to 55 °C. Results were better yield, less feedstock needed, lower viscosity, lower parasitic load, lower OPEX, higher profit.

I followed. Other followed to thermophilic. The same success.

2014 – my friend increased the temperature to 62 °C in the hydrolysis tank and kept the temperature in the digester at 55 °C. Even better results.

2022 – another friend, whose biogas plant I built, operates his hydrolysis at 61-62 °C and his digester at 60 °C. (see photo)

Hyper-Thermophilic!!!

SCADA Screenshot May 2022: Tank 1 (Hydrolysis) 61.8 °C, Tank 3 (Digester) 60.0 °C

The results are exceptional. Biogas yield is 35% above the regular biogas yield. There´s only a very low parasitic load because the mixers run only 4 minutes every half an hour, though fibrous material like straw-based manure and others are a big part of the feedstock mix. The solid-liquid screw separator can’t separate any solids because the dry matter is fully digested.

Concerns of investors are beaten by reality

“Maintaining the temperature is difficult.” – In Germany we maintain this temperature even in winter with -20 °C. We insulate the tanks. Maintaining the temperature is much easier in India due to higher ambient temperatures. A proper tank insulation is the key to low heat losses.

“Higher capex with thermophilic installation.” – (Wrong) The capex is lower, because with the higher temperatures the retention time is shorter. So, less digester capacity is needed, shorter pipes, smaller footprint. The slightly higher costs for heating coils and insulation is easily compensated by savings in civil works and piping.

“Using gas for heating purpose” – yes, a bit more gas or heat from the CHP is required to achieve thermophilic temperatures. With 35% more biogas from the same feedstock, you can sacrifice 1% for heating. It still is a huge surplus in energy yield!

“No successful thermophilic biogas plant in India” – No one wants to be the first. No one wants to take the risk. 100 years ago, entrepreneurs, who wanted to stick to horses for transport instead of using a lorry, went bankrupt. Henry Ford became a billionaire.

Why thermophilic beats mesophilic with rice straw!

All the practical experience and observations are backed by science and make sense when you look at the biological processes taking place.

Higher temperatures accelerate the enzyme activity in the biogas plant.

More biogas in shorter time is produced.

This reduces the retention time, the required digester volume and the capex!

Lower viscosity reduces the electricity consumption of mixers and pumps. This is a huge saving in OPEX.

And lower viscosity leads to less wearing of the equipment and therefor lower maintenance cost.

More biogas from the same amount of feedstock.

This reduces the amount of feedstock. Feedstock is the main part of the OPEX. Less costs leads to higher profit.

Lower risk with future price increase for feedstock.

There are additionally many smaller advantages and details, which would fill several pages.

The Killer-Evidence for thermophilic

Most of the German biogas plants were built cheaply for the digestion of maize silage. Maize silage is the main fodder crop in Germany. Easiest to digest.

Prices for maize silage went up and fibrous feedstock is cheaper. But the biogas plants can’t cope with fibre.

With higher ambient temperatures in summer the biogas plants can operate thermophilic. Best results.

Late autumn, winter and early spring the cold ambient temperatures lead to lower temperatures (mesophilic) in the biogas plants, because they are equipped with cheap heating systems.

Performance goes down!

Late spring with higher ambient temperatures and back to thermophilic performance recovers. 

More evidence for thermophilic is not possible!

Germany goes thermophilic

The German biogas plants started mesophilic. But one by one goes thermophilic. Especially, because they replace the now very expensive maize silage with cheap straw-based manure, grass and straw.

If you are interested in this topic, but not fully convinced send me an email (w.danner@snow-leopard-projects.com)

Über den Autor: Walter Danner

Dipl. Ing. agrar.

Walter ist Initiator und Visionär. Und Experte für Biogas und Biomass2Energy. Er hat Biogasanlagen in Europa, Südamerika, Asien und Afrika gebaut. Regionale Wertschöpfung, Ökologie und Biomasse begleiten ihn seit über 30 Jahren. Das wichtigste für ihn: „Derjenige, der ganz unten (oder auch oben) etwas tut, soll was verdienen und nicht nur an ihm verdient werden.“ Das erfordert innovative, out-of-the-box Lösungen. Zum Glück denkt Walter immer zwei Schritte voraus… in alle Richtungen. Er hat die Idee und begeistert jeden dafür.

Walter is an initator and visionary. And expert for biogas and biomass2energy. He built biogas plants all over Europe, South America, Asia and Africa. Regional value addition, sustainability and biomass runs like a central theme for him for over 30 years. Most important for him: “The one taking action on the ground has to benefit, and not the elites benefiting from him.” This needs innovative and out-of-the-box solutions. . Good thing that Walter thinks two steps ahead… in all directions. He comes up with the idea and gets everyone excited about his vision!

Geschäftsführer Walter Danner

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