SO4 and NO3 are electron acceptors like oxygen. In the absence of oxygen, bacterial will use NO3 as electron acceptor and glycerol will be oxidized and produce nitrogen gas. This process is called denitrification.

When all NO3 is used up, bacterial will use SO4 as the next electron acceptor. In this reaction H2S is produced which causes odor and reduce pH in anaerobic bioreactors.

Decease in pH will reduce the activity of methanogenesis bacteria, methane production and COD removal.

Hi Mustapha,

Sulfur is an essential element for all organisms. Almost all proteins have sulfur in their structures. For anaerobic bacteria sulfur is available mostly in form of sulfide (S-2), sulfur (S0), Thiosulfate (S2O3), sulfite (SO3) and sulfur ammino acid. The existence of SO4 in anaerobic systems provides a suitable conditions for SRBs (sulfur reducing bacteria) to compete with MPB (methane production bacteria) to degrade available substrates. Also, SO4 is a strong electron acceptor where organic materials (substrates) are electron donor. So, it is not true that having more SO4 improves the COD removal in anaerobic systems. There is a ratio of COD/SO4 in anaerobic systems that needs to be controled for the prevention of inhibition. Generally, for the acetate uptake, which is a critical compound for acetogenotrophic methanogens, if this ratio is between 1.7 and 2.7, there is always a competition between SRBs and MPBs. For the COD/SO4

sulfur is needed as growth nutrient (approx 1% of dry weight biomass), so in high rate bioreactors it is not a trace element, it must be present at concentrations >> 1 mg/l while trace elements like copper, zinc etc are mostly less than 1 mg/l.except perhaps for iron. Sulfate is a good sulfur source for many anaerobes, sulfate will be reduced to sulfide under anaeobic conditions and that also may act as sulfur source.

For many wastewater sulfur limitation is not a concerns because ist is present already. Even in drinking water usually there is sufficient sulfate.

Sulfate which is added above the nutrient requirements ends up as sulfide. This consumes COD so this does not end up in methane (biogas).So it decreases biogas yield, and sulfide will distribute among liquid and gas and thereby deteriorates biogas quality. On the other hand, this may be used benficially to remove sulafte from wastewaters

In addition to what others have said, I am currently working on removal of toxic elements from aqueous solution under sulfidic-anoxic conditions. you may need to test for the presence of hydrogen sulfide as a product of sulfate and sulfide reduction. I guess you may observe significant variation in your results when KH2PO4 is used as electrolyte as opposed to NaNO3. The presence or absence of sulfate in your batch experiments is a function of how tight your reducing environment is.

Hi Mustapha

When there isn't oxygen and NO3 as an electron acceptor in waste-water, bacteria consume SO4 as an electron acceptor that with its low concentration oxidize organic matter and in anaerobic condition remove COD. I working on treatment of organic matter in anoxic environment and my biomass use SO4 when there isn't no NO3 in bioreactor even in trace element of SO4, so that effluent has a odor and be black, but still COD removed, though at a slower rate.

Dear Davidson!

KH2PO4 is strong buffer and will most likely cause coagulation and subsequent precipitation of various organic matter instead of biodegradation and probably methane generation. Is this your aim?

Sulphates behaves as an electron acceptor in anaerobic processs. The sulphate reducing bacteria utilize the electron donor organic subtrate for the reduction of sulphates. Organic matter will be removed with sulphate reduction (and sulfides are produced). Trere is a COD/sulphade ratio for the succesful procedure of the anaerobic treatment. Biogenic sulfide formation can remove heavy metals (S-2 +M+2 produced MS, insoluble), but reduse pH and inhibits methane production.

Hello Mustapha

I agree with the above discussed suggestion by Jan Weijma about your question