My Story With the Use of Micronutrients in Biogas Plants

Schlagwortebiogas yield biological instability biological stability hydrogen sulfide methane bacteria organic loading Promotion propionic acid Wastewater fermentation

Meanwhile, the use of micronutrients or trace elements in biogas plants is a generally acknowledged rule of technology. Till 2007 this was not the case at all. Till 2007 micronutrients were only used in the lab for scientific purposes or sometimes with the fermentation of industrial wastewater.

In 1989 I started using micronutrients in the scope of my dissertation. At my tests to the fermentation of waste water from the production of baking yeast I could not set a stable operation in my lab digesters, not even at a minimum load of the digesters. First I assumed an inhibition due to hydrogen sulfide, as I had between 20,000 and 50,000 ppm hydrogen sulfide in the biogas.

However, a colleague gave me then the idea to check first, if the methane bacteria were supplied with all what they need to grow at all. Thereby we quickly realized that in this waste water elements as selenium, nickel or cobalt could not be found. Already then it was known, that these elements are essential trace elements.

For my luck, the former colleague was well informed about the composition of nutrient media for the culture of methane bacteria and could give me the decisive hints for the dosing of the trace elements. First, the use of the trace element solutions, prepared by a further colleage, were not successful. We first had to learn to add the trace elements in the correct manner and at the right place, also to optimize the composition of the macronutrients.

As we then also created the technical preconditions on the lab digesters, we achieved with our lab digesters loading rates never seen before. Even at middle hydraulic retention times of under one day and COD loading rates of over 20 kg/cbm/d the lab digesters remained biological stable and the COD utilization remained constantly high.

After finalizing the doctorate I focussed more on the practical side of the biogas production. I have faded out the use of micronutrients, as I assumed, that micronutrients are only necessary, if specific substrates as waste water of yeast factories with high hydrogen sulfide concentrations and a lack of micronutrients due to the separated yeasts are fermented. In plants with wastes or liquid manure I saw no necessity for the addition of micronutrients.

Only in 1996 I was again faced with the problem, that in the scope of the commissioning of an anaerobic plant for the fermentation of the waster from a paper factory, a digester could not be brought to performance and remained biological instable. Once again we have analyzed the waste water for selenium, nickel and cobalt and found out, that these elements could not be detected in the waste water, despite of high-quality analysis technique.

Of course I could not start to buy the necessary micronutrients for a big biogas plant in the lab trade and add them. However, I found a manufacturer who produced liquid fertilizers with micronutrients for agricultural purposes. He had a product, which seemed suitable and was available in a sufficiently large quantity.

The use of this product lead to the breakthrough again. Within only three weeks we could operate the waste water fermentation plant at full load. My assumption, micronutrients are only necessary in depleted waste waters, seemed to be confirmed with this second experience in using micronutrients.

As I was mainly concerned with the fermentation of waste in the following time, I forgot the micronutrients again. Even as I had considerable problems with foam formation and increased acid concentrations in the biogas plant Fürstenwald/Spree, which I operated from 1998 to 2007, I rather assumed an inhibition by the high ammonia concentrations than a lack of micronutrients.

Only in 2006, when we inexplicably detected a strong increase of propionic acid in the digester at a fairly moderate loading rate of 3,5 kg oDM/cbm/d in a newly constructed plant processing maize silage, I remembered the successes, which I had with the use of micronutrients and I also remembered the producer of the liquid fertilizers. Together with him we developed a micronutrient solution, adapted to the use in plants processing renewable raw material, which we brought to the market in 2007.

The use of this product was very successful. So we could manage digester loading rates of 10 kg oDM/cbm/d without problems with the fermentation of renewable raw materials. Interestingly, the addition of micronutrients also made an impact in plants with a considerable quantity of liquid manure. The biological process became more stable and the biogas yield increased slightly.

Today, we distribute this further developed product under the brand name Acinor 1000 in Germany, Eastern Europe, South America and South-East Asia. At a correct dosing, in different plant types of various manufacturers with diverse substrates a stable biogas process with a very high biogas yield is achieved, even at a high loading rate.

If you have questions, please leave a comment or contact me. I will collect the questions and answere in a special article.

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Autor/in: Hans Friedmann
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Thema: Biological proc...

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Autor/in: Hans Friedmann
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