Quick Biogas Inhibition Tests to identify inhibitors in Biogas Substrates are badly needed by the commercial biogas plant industry. Traditional methods such as the Diary Farmer's “Aerobic Plate Count” inhibitor test are not directly applicable to anaerobic biogas conditions, so a New Biogas Substrate Inhibition Test Method has been badly needed. Read on to find out what tests are now available
What is Ammonia Inhibition During Anaerobic Digestion?
In anaerobic digestion, ammonia inhibition is a major cause of reactor failures and economic losses. due to digester gas output which slows down. Often operators are unable to see any apparent reason when inhibition occurs. However, it can be that the ammonia concentration has risen and/ or that the pH has changed to cause biogas output inhibition.
Even though ammonia is an important ingredient for bacterial development, large quantities of ammonia may hinder methanogenesis during the anaerobic digestion process. As a result, ammonia is viewed as a possible inhibitor during anaerobic digestion, especially when dealing with complex substrates such as manure or the organic percentage of municipal solid waste (OFMSW). Some may contain elevated ammonia concentrations on entry to the digester.
Both ammonium ion (NH4+) and free ammonia (NH3) are inhibitory, both directly and indirectly. Both NH3 and NH4+ contribute to inhibition in normal AD circumstances.
Ammonia exists in two forms in aqueous solutions: the protonated cation NH4+ (ammonium) and the gaseous form NH4 (free ammonia or FA). The pH of the solution determines the balance between these two types.
Process inhibition is also affected by pH, temperature, and ammonium and ammonia concentrations so comprehensive monitoring is needed in combination with biogas inhibition tests.
Recovery of Anaerobic Digestion Systems Following Ammonia Inhibition
It is feasible to recover anaerobic digestion systems following ammonia inhibition. But it requires either ceasing or significantly reducing feed rates, or adding chemicals to the digester vessel until the methanogenic organisms that produce the methane return to health.
Ammonia is created through the biological breakdown of nitrogenous materials. The two main forms of inorganic ammonia nitrogen are ammonium ion (NH4+) and free ammonia (NH3).
The inhibition of anaerobic digestion by ammoniacal nitrogen has received a lot of research attention. But despite many studies, ammoniacal nitrogen inhibition continues to pose a hazard to many anaerobic digesters and drives the need for Biogas Inhibition Tests.
The Role of pH (Acidity to Alkalinity Balance) in Ammonia Inhibition
The unionised form of ammonia nitrogen contains both the ionised form (ammonium, NH4+) and the unionised form (ammonia, NH3).
A rise in pH promotes the development of the more hazardous unionised form (NH3), whereas a drop promotes the creation of the ionised (NH4+) form.
The toxicity of ammonia is also affected by temperature.
Characteristics of Ammonia
Ammonia gas has a distinctively strong odour (think of window and floor cleaners). Ammonia concentrations in streams are rarely high enough to produce this stench, but water with a foul, septic, or organic-waste odour may have rather high ammonia concentrations.
The major products of anaerobic digestion of organic waste are methane and carbon dioxide, while elevated ammonia concentrations may be present in the digestate.
Accumulation of Ammonia During the AD Process
As a result, during the breakdown of the feedstock, ammonia tends to accumulate and the effluent would be recirculated in the digester (Sheng et al).
A high ammonia concentration can disrupt the methanogenesis process and reduce the amount of methane generated during anaerobic digestion.
During the anaerobic digestion process, the recommended amount of total ammonia nitrogen (TAN) in the reactor for a favourable and hospitable environment for methanogens is less than 200 mg/L. (Liu & Sung 2002).
To understand the biochemistry of each digester at any time the ammonia level needs to be monitored for use in Biogas Inhibition Tests
The Biogas Inhibition Test
A Biogas Inhibition Test is a test technique used to measure free ammonia and ammonium inhibition on acetoclastic methanogens.
A method for characterising ammoniacal nitrogen inhibition which would be very useful in the prevention of biogas production slowdowns is needed that is:
- reliable, as well as
- a robust inhibition modelling methodology.
Research results have demonstrated that NH3 and NH4+ inhibition must be measured together. This can only be done by conducting inhibition experiments at different total ammoniacal nitrogen (TAN) concentrations and pH values.
Ammonia Concentration Test Kits
Ammonia concentration test kits are available from Hach at the ranges of ammonia expected in a biogas digester from 100 to 3,000mg/l of ammoniacal-N.
There are many fish tank and pond ammonia test kits available online but these are not usually suitable for the much higher ammonia values in a digester.
Ammonia Inhibition Test
Amur, an AD operator and services provider, has introduced what it claims is the industry's first fast inhibition test.
Biogas Inhibition Tests, about which information provided online suggest runs alongside Amur's unique Bullet BMP test, yields findings in just 24 hours. That's as opposed to the 30 days necessary for previous AD industry analyses.
The straightforward test is said to be based on highly sensitive microorganisms that respond fast when exposed to inhibitor-causing toxins.
Previous industry inhibitory analysis was restricted. It could only be accomplished using biological BMP testing, which evaluates biogas potential. The addition of a second test for inhibition provides operators with greater flexibility.
Amur's Bullet BMP technology seems to be cutting-edge technology and uses near-infrared spectrum analysis to identify the components of a sample during a biogas inhibition test.
The results are described as being calibrated and benchmarked against known biomethane potential from a variety of waste sources before being quantitatively computed and transformed into BMP.
Archive Post from July 2017:
A major biogas plant systems provider WELTEC BIOPOWER, has now recognised the need for a quick Biogas Inhibition Test and has set about developing a solution. Read our 2017 article on the state-of-the-art at that time:
The Problem Which Needs Solving by a New Biogas Inhibition Test for Anaerobic Digestion Plants
Anaerobic digestion plant operators are regularly faced with a dilemma whether or not to accept a feedstock as a biogas plant substrate. To be told the source of the material in detail is generally not enough to base a reasoned judgement on the applicability of adding that feedstock to an existing or new AD plant.
A knowledge of such information about a feedstock such as its pH, calorific value, alkalinity, heavy metals content, and ammonia concentration, will be useful. But, it won't inform the plant operator of possible negative inhibitory effects which in extreme cases might possibly occur to the extent that introducing a new feedstock could jeopardise the entire gas production of the digester.
For this to be made possible, a quick test needs to be developed by experienced water chemistry and biochemistry specialists. This test needs to provide controlled conditions under which anaerobic biochemical activity can be measured, including biogas yield so that inhibitory factors due to chemicals and even some moulds in a feedstock, can be predicted in advance.
This is no easy task to accomplish, so watch this space and we will provide further information as more results of the research described below become available.
Now we suggest that you read the following WELTEC BIOPOWER PRESS RELEASE ON THIS SUBJECT WHICH WAS RELEASED IN MARCH 2017:
WELTEC BIOPOWER Develops Innovative Analysis Procedure for Biogas Substrate Inhibition Tests
Together with renowned partners, the biological department of biogas specialist WELTEC BIOPOWER in Vechta, Germany, is developing a quick test for identifying inhibitors in biogas substrates.
Input mass may contain substances that prevent efficient biogas production.
For example, a small amount of mould is sufficient to cause such an adverse effect in silage. Ammonium, copper, zinc, drugs and disinfectants are often identified as inhibitors in slurry and manure.
Even traces of these substances are detrimental to the bacteria in the digester and thus counterproductive to the digestion process.
Therefore, it is absolutely necessary to identify such inhibitors before transferring the substances into the digester.
Since December 2016, WELTEC is involved in a research project to establish a new procedure that will solve this problem.
The project is subsidised by the German Federal Ministry of Food and Agriculture (BMEL) via Fachagentur Nachwachsende Rohstoffe e.V. (Agency for renewable resources).
In collaboration with HAWK, the Göttingen University of Applied Sciences and Art, WELTEC is developing a quick, reliable and inexpensive procedure for identifying inhibitors in input substances.
For this, various feedstocks are first examined in the WELTEC lab in Vechta and at HAWK in Göttingen with the help of the Ankom system. This system delivers precise information on the gas production.
Moreover, the change of the acid spectrum is monitored while deliberately adding inhibitors.
The resulting target curves will henceforth be compared with the gas production curves of substrates.
This comparison is to reveal whether the substrate contains any inhibitors.
Previously, the aerobic four-plate inhibitor test used to be employed for identifying inhibitors.
Actually, this test is designed for the dairy industry and does not reflect the conditions in the digester.
Therefore, the test results are not as authoritative as required.
With the new anaerobic procedure, results are to be available after three days.
In this way, biogas plant operators will be able to determine the quality of their input materials precisely, speedily and inexpensively.
“The need and demand are on hand. Currently, there is no quick and reliable way to identify such potential process disruptions, though this would be vital to avoid unscheduled downtimes of biogas plants”,
explains Sabine Lampe, graduate biologist and supervisor of the research project at WELTEC BIOPOWER.
This is what made WELTEC and HAWK initiate the project, in which the Fraunhofer UMSICHT Institute in Oberhausen and Berlin-based analytics specialist Aokin are also involved.
“Based on this innovative procedure, biogas plant operators will be able to decide faster whether to buy offered silage or liquid manure or whether to use a certain batch of their own slurry”,
explains Sabine Lampe.
She added that it would also be possible for substrate providers to use quick biogas inhibition tests to diagnose digester problems.
WELTEC BIOPOWER GmbH · Zum Langenberg 2 · 49377 Vechta · Germany Phone: +49 4441 99978-0 · Fax: +49 4441 99978-8 ·
WELTEC Company Profile:
WELTEC BIOPOWER has run its lab in Vechta since 2009. In Vechta, the biologists and lab team can conduct all-important analyses and regularly examine samples from more than 300 digesters. The biogas plant manufacturer is thus well equipped to assist plant operators in their daily operations, making sure that the biogas production remains on the success track. via www.weltec-biopower.de
[Article first published in July 2017. Updated December 2021.]