Chloride Level: Anaerobic Digestion
The question of chloride level and anaerobic digestion arises in a number of ways, and we will endeavour to discuss some of them here. If you arrived at this page after searching on the term “chloride level anaerobic digestion” and this page does not answer your question, then please do Contact Us, or join our Forum and post a question.
Chloride Concentration as an Inhibitor of Fermentation
Some otherwise high calorie feedstocks are available, which have high chloride concentrations and the question that then arises is whether these will harm the fermentation process during anaerobic digestion.
It is well known that the presence of the chloride radical is likely at some point, as concentration rises, become inhibitory on digestion.
The simple answer would seem to be that fermentation processes do proceed very well in nature within marine environments, with sea water chloride concentrations in the tens of thousands of milligrams per litre, and a combination of chlorides in the sea water mix, including sodium and magnesium present.
Inhibition will vary with pH as well, and tends to increase as pH increases (check this ? - this may be the wrong way around!).
As in all biological, processes the point at which inhibition occurs will always vary with the particular mix of organisms in your digester. Also, with biological systems it is usually possible by running the digester for long periods under certain conditions, to acclimatise the organisms present by self selection so that they achieve better than initial results would suggest. It may even be worthwhile hunting out a similar Anaerobic Digestion plant to obtain a few loads of seeding sludge from that plant in order to start up a new plant.
For high chloride wastewater treatment in UASB designs elevated chlorine will not improve stability.
It would probably be advisable to undertake a pilot treatability trial on all high chloride concentration wastes at laboratory scale before embarking on a full plant design.
Chloride Concentrations in the Liquid Digestate
If the feedstock contains a high chloride concentration or the AD process itself tends to concentrate chlorides in the reactor, the liquid digestate will also show high chloride content.
This is not a concern in the wetter temperate climates where regular rainfall will serve to wash out substances as highly soluble as the chlorides.
However, the continued use of a saline digestate as a fertiliser on arid and irrigated land should be considered, as there may be a marginal effect on increased saline build-up in soils and possibly also, in some circumstances, of groundwater.
Chloride Impact Anaerobic Digestion
Finally, there is clearly, looking at various technical research paper abstracts available through web searches, but only purchased at a price a body of work which has been devoted to weed seed viability after anaerobic digestion, and whether elevated chloride concentrations present during fermentation reduces seed survival rates.
We would imagine that this will be an important point for many considering use of agricultural Anaerobic Digestion. If the solid digestate was to actively spread persistent weed species, then this could be a major problem.
(If anyone has obtained a definitive paper on this, it would be most appreciated if you were to join our Forum and post a review of it there, or email it to the web master via the email address given on the About Us/Contact page. Then the community would know where to obtain this information. I am sure that we are happy to pay for technical research papers if we know in advance that they will contain authoritative answers to our questions. However, few can afford to purchase in the mere hope that a paper will prove to contain the nugget we are after!)
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