A simple elemental balance for the anaerobic sulfate removal by De sulfovibrio alaskensis 6SR

Abstract

Sulfate-reducing bacteria(SRB)are currently important for the design of new technologies for bioremediation of water contaminated with heavy metals.The papercovers two areas investigated in the project for the basic design ofbatch bioreactors using sulfate-reducingbacterium Desulfovibrioalaskensis6SR: 1) a simple theoretical and experimental study of sulfate removal in the presence and absence of chromium VI(Cr(VI))incultures using Postgate medium (with 30 g/L of NaCl) and the development of a simulation model to predict the dynamics of D. alaskensis6SRand 2)black box stoichiometrieswerestudied.Bacterial growth and product formation were monitored at 37 °C and pH7.0-7.5by measuring the time courses of the concentrations of free cells(biomass=X), substrates (lactate= Land sulfate=S), and products (acetate=Aand total sulfide=H,namely, biogenic𝐻!𝑆) in liquid mediumunder anaerobic conditions.The results can be summarized as follows. The dynamics of bioprocess variables for D. alaskensis 6SR on modified Postgate C medium showed a sulfate removal of 80-85% for a fermentation time of 30hours. The maximum specific growth rate was markedly dependent on the medium Cr(VI).Itsmaximum growth rate was 0.55 1/h averaged over three experimental runs(n=3). In the bioprocesses without and with hexavalent chromium, a negative effect on cell growth rate of 21.6% was observed in contrast to the control. The dynamics of the bioprocess state was also affected by decreasing rates of substrate consumption and product generation observed during the exponential growth phase.The stoichiometric of the sulfate-reducing process considered the elemental balance of carbon(C), hydrogen(H), oxygen(O), nitrogen(N), and sulfur(S), and was proposed as a function of reaction rates 𝑟", 𝑟#, and 𝑟$and expressed as a function of yield coefficientsas a function of carbon energy source 𝑌"%(i=A, H,N, W,D: A=acetate, H=sulfide, N=NH3, W=water, D=CO2). Predictions based on the analysis of black box stoichiometries indicatedthat overall stoichiometryfor sulfate-reducing process was