Other than ammonia, sulphides are known to inhibit methane generation.  In cow manure inhibitory levels of sulphides are not common.  However, in some Western European countries acidification of animal manure using sulphuric acid is a well-known technology that is being used to reduce ammonia emissions from manure.  In such conditions inhibitory levels of sulphides can be found in dairy manure and can adversely affect the anaerobic digestion.  There is some research indicating close to 50% reduction in CH4 generation due the presence of inhibitory levels of sulphides in previously acidified manure.

Another potential factor that can inhibit CH4 generation from dairy cow manure may be residuals of antibiotic agents such as ionophores.  One of the most common ionophore added to dairy feed formulations are Monensin.  In North America the use of monensin is common. (Its benefits include improvements in milk production, antiketogenic effects, and reduced risk of acidosis). Monensin has indicated an antimethanogenic effect in the rumen and being suggested as a strategy to mitigate enteric CH4 emissions from cows.

There are some limited research that indicate up to 40% of dietary supplemented monensin may be found in feces in its active form, suggesting potential inhibitory effect on CH4 generation from manure. However, not sufficient research evidence has accumulated to confirm or disprove this effect.

These are few factors that can potentially affect CH4 generation from cow manure, at least in North American and Western European context.

Dear Chengming, 

Fermentable organic mass should not contain such substances (antibiotics, solvents, detergents), which affects the activity of microorganisms. Does not contribute to "work" of microorganisms and some inorganic matter. Water is used for diluting the manure must be clean. Excessive concentration of the individual substances in the water or the salts can inhibit the growth of bacteria and hence the production of biogas. The upper limit of some common inorganic compounds shown in the table (see File).

Sincerely,

Zenon

There is a useful chapter (17) on Toxicity in Michael H Gerardi's book ' The microbiology of Anaerobic Digesters, Wastewater Microbiology Series of Wiley- Interscience (2003) in print.  Biogas production on continuous digesters relies on a simple idea, the rate of growth of the Methanogenic bacteria exceeds the rate of death + washout.   A little bit of inhibition that slows the rate of growth has little practical effect as long as the retention time is sufficient.   Acidification of manures can cut the rate of net growth by a factor of 2 so the retention time has to double.  For pig slurry from 12 days to 24 or more.  For cattle slurry it depends on the diet but aim to double from say 20 days to say 40 days if you are recycling more than a third of the digestate back to the beginning of the process.  It can take a year to achieve acclimatisation to ammonium at high levels so do not expect ultimate performance from a digester that is started in a month, and run for a month.  The best results in toxicity/VOC/VFA/Odour experiments have come from digesters operated continuously for several years.

https://www.researchgate.net/post/What_are_the_scopes_for_ammonia_recovery_and_removal_from_animal_manure