Last Updated on 23/08/2020 by Piero Mattirolo
Re-publication of an article by Mario A. Rosé on Agronotizie
Optimally manage a biogas plant it means becoming a "breeder of bacteria".
Like farm animals, i battery they do their best if they are kept in conditions that are optimal for them, it is therefore essential to monitor the various aspects that affect the functioning of the entire anaerobic system. It is known to all that the different manufacturers and some independent workshops, offer biological care service.
Typically all of these services have a weakness: the results are not provided in real time. Moreover, the analyzes provided, generally they only concern the dynamics of the anaerobic degradation process, but not the verification of the biomass quality – silage or by-products that are – with which the system is powered.
Some plant managers have equipped themselves with simple tools such as the pHmetro or the automatic titrator (called FOS / TAC in the lingo) and the results are often disappointing e, in some cases, even disastrous.
This table clarifies why:
| Parameter | Utility | Necessary tool |
| pH | Almost nothing. When there are significant changes in pH, it is generally too late and the plant is collapsing. | pHmetro |
| FOS / TAC | Poor. The guidelines apply to single tank systems fed with cow manure and corn. If other matrices or their mixtures are used, the "canonical" values are no longer valid. In plants a 2 or more tanks, it would take a specific FOS / TAC table for each stage of digestion. The tool does not provide any a priori assessment on the quality of biomass or manure, only an indirect indication of the state of the bacterial system (when it can sometimes be too late). | Automatic titrator or pH meter and burettes for manual titration |
| Biomethanization efficiency of the plant | High, as it indicates the % of degradation of the silage achieved by the process | Muffle furnace and thermobalance or precision balance |
| Dry matter of biomass | Media. By only detecting the dry matter, only a rough indication of the biomass quality is obtained. Two different batches of biomass, the parity of SS, they can make more or less methane. | Thermobalance or precision scale and oven |
| Volatile solids of biomass | High. SV content provides a’ more reliable indication of the methanogenic potential of a biomass, however, it is not a definitive figure. | Muffle furnace and thermobalance or precision balance |
| Residual methane potential of the digestate | Very high. Provides an indication of the unused fraction of the silage or feed biomass. | Laboratory batch reactor and measurement system for the volumes of gas produced by fermentation |
| BMP (Methanigen potential) of biomass | Very high. Provides an indisputable indication of the actual yield that can be expected from a batch of silage or other biomass, allowing to evaluate if the price of the same is appropriate. When using biomass mixtures, the BMP test allows to evaluate any inhibitory or synergistic effects. | Laboratory batch reactor and measurement system for the volumes of gas produced by fermentation |
| Complete degradation curve of biomass | Very high. Allows you to program the digester feeding and establish the optimal retention time of solids for each substrate or mixture of them. The ultimate value of the curve, For definition, is the BMP. | Laboratory batch reactor and measurement system for the volumes of gas produced by fermentation |
| Hydrolytic activity of the inoculum | Very high. It allows you to predict biological problems in time, or diagnose them more accurately when they happen. | Laboratory batch reactor and measurement system for the volumes of gases produced by fermentation and reference matrices. |
| Substrate inhibition | Very high. It allows you to measure the maximum amount of a given substrate that can be fed into the digester without causing problems. This test is particularly suitable when using "problematic" substrates (manure of animals treated with antibiotics, pollina, likely, remains of slaughter…) | Laboratory batch reactor and measurement system for the volumes of gas produced by fermentation |
| High school (specific methane activity) | Very high. Together with the hydrolytic activity test, allows you to measure the actual bacterial activity of the inoculum and therefore the health of the digester. | Batch laboratory batch reactor and measurement system for the volumes of gas produced by fermentation |
| Effectiveness of additives (probiotics, enzymes, etc.) | Very high. Additives are usually expensive, but their effectiveness is more often than not magnified by the sellers. Some even have unwanted effects: increase the amount of gas produced, but they lower the methane content. | At least 2 laboratory batch reactors with relative system for measuring the volumes of gas produced by fermentation |
| Small-scale simulation of the process, accelerated start-up strategies of the plant | Very high. During the start-up phase of the system, it allows you to save over 50% of the diesel fuel required for initial heating. In operation, allows you to optimize feeding strategies, of agitation, of recirculation between tanks, optimal working temperature, etc. | Continuous laboratory reactor kit, gas flow measurement system and data logging system with specific software |
How can we see, the minimum tools to be equipped in order to preventively monitor the biogas plant without leaving anything to chance, I'm a termobilancia The precision balance, a muffle furnace it's a reactor system(i) batch and meter(i) of the volume of gas produced over time.
A mini-laboratory configured in this way, it allows to carry out tests on a small scale, so as not to risk productivity losses caused by the "table" management of the plant.
Like all techniques, the measurement of the various parameters useful for managing a biogas plant requires a minimum of learning and a little’ of attention following the procedures correctly.
Generally, with 8 hours of theoretical training and some’ of practice, more than satisfactory results can be obtained.
Investments in equipment fluctuate from 3.200 € for a basic kit with good precision but manual reading, up to 16.000 € for a mini-workshop with 6 batch reactors, gas volume measurement with ± 1% margin of error and automatic data management.
There are even more powerful systems, but generally exceed the actual needs of the biogas plant manager, as they are designed for academic research or for the development or improvement of technologies by plant manufacturers.
Good morning,
the article does not mention the amount of ammoniacal N which is “poison” of bacteria. What do you propose to control it e, in case of necessity, contain it?
That of the ammoniacal N that poisons the plants is one of many “half truths” that run in the Italian biogas folklore. The fact is that the concentration of ammoniacal N affects the process or not, depending on a number of factors: temperature, simultaneous concentration of SH2, concentration of volatile fatty acids , C / N ratio… Unfortunately in Italy it is full of self-proclaimed people “biology” who have never done a biological test and speak by extrapolating data from the “literature”, which among other things is full of wrong generalizations or even flaws in logic (see that of the FOS / TAC and that of electrical conductivity).
If a plant is suspected of having NH4 excess problems- , it is mandatory to carry out biological tests with inoculum taken from the same plant, and test what happens with different hypotheses. For example, I did some tests for a client to whom the “biologist” on duty had said to reduce the percentage of droppings because “NH3 inhibits the process”. The tests showed that the system could work better even by increasing the droppings and changing the proportions of the other substrates. In another case, a “discoverer” claimed that adding a powder made from a zeolite had to improve performance because “neutralizes the NH4-“. Laboratory tests showed that the addition of the product changed only a little’ the shape of the curve, but the final BMP of the droppings was the same with or without product. Furthermore, the dust tended to precipitate, which is something that must always be avoided in built plants “to the German”, with low and wide ballasts. The answer to your question is therefore that there is no single answer that works for everyone, must be verified on a case by case basis.