The anaerobic treatment of sulfate containing wastewater

A. Visser

Research output: Thesisinternal PhD, WU

Abstract

<br/> <p>In the anaerobic treatment of sulfate containing wastewater sulfate reducing bacteria (SRB) will compete with methanogenic- (MB) and acetogenic bacteria (AB) for the available substrates such as hydrogen, acetate, propionate and butyrate. The outcome of this competition will determine the endproduct of the anaerobic mineralisation proces: methane or sulfide.<p>The occurrence of the sulfate reduction proces is often considered unwanted due to the problems associated with the sulfide formed in the proces. These problems are: malodour, corrosion, toxicity, reduced removal of COD, reduced methane formation and higher levels of H <sub>2</sub> S in the biogas. More recently the sulfate reduction proces is used in biological processes that aim at the removal of oxidised sulfur compounds from different waste streams.<br/> <p>In the competition between the SRB and AB this study shows that butyrate degrading AB can effectively compete with the SRB. The growth rates of both bacteria was found in the same range. On the contrary, propionate degrading AB are outcompeted by the SRB due to the better growth kinetic properties of the latter.<p>Concerning the competition between the SRB and MB for hydrogen the present study clearly shows that in anaerobic reactors hydrogenotrophic MB are outcompeted by the SRB. This apply both for mesophilic (30 °C) as for thermophilic (55 °C) conditions. However, the hydrogenotrophic MB are not expelled from the biomass but remain present in relative high number.<p>The competition between the acetotrophic MB (AMB) and acetotrophic SRB (ASRB) depends on several conditions. In this research the following items were investigated:<br/>* The kinetic growth properties of AMB and ASRB under different conditions with respect to the pH and sulfide concentration.<br/>* The ability of the ASRB and AMB to attach to granular sludge or a biofilm.<br/>* The competition between the bacteria at higher temperatures (55 °C)<br/>The results of these studies are:<br/>* At neutral or acidic pH values the AMB can compete with the ASRB. The growth rates and acetate affinities for both bacteria are than in the same range. Moreover, at these pH values the AMB and ASRB are more or less equally inhibited by the toxic sulfide. At more alkalic pH values (PH>7.5) the ASRB likely will outcompete the AMB. At these pH values the growth rates of the ASRB are significant higher then for the AMB and the ASRB are much less inhibited by the produced sulfide.<br/>* Granulation experiments shows that the ASRB can maintain in granular sludge, resulting in the formation of sulfidogenic granular sludge. They are also effectively able to form a biofilm on pumice as a carrier. No significant difference between the attachment capacity of AMB or ASRB could be detected.<br/>* Under thermophilic (55 °C) conditions the ASRB can compete with the AMB. At higher pH values than 7.5 the ASRB even become predominant. At more neutral pH values there exist an equilibrium between the ASRB and AMB.
Original languageEnglish
QualificationDoctor of Philosophy
Awarding Institution
Supervisors/Advisors
  • Lettinga, G., Promotor, External person
  • Hulshoff-Pol, L.W., Promotor, External person
Award date12 Sep 1995
Place of PublicationS.l.
Publisher
Publication statusPublished - 1995

Keywords

  • waste water treatment
  • water treatment
  • anaerobic treatment
  • sulfates
  • waste treatment
  • purification plants

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