Biological sulfuric acid transformation: Reactor design and process optimization

Abstract

As an alternative to the current disposal technologies for waste sulfuric acid, a new combination of recycling processes was developed. The strong acid (H(2)SO(4)) is biologically converted with the weak acid (CH(3)COOH) into two volatile weak acids (H(2)S, H(2)CO(3)) by sulfate-reducing bacteria. The transformation is possible without prior neutralization of the sulfuric acid. The microbially mediated transformation can be followed by physiochemical processes for the further conversion of the H(2)S.The reduction of sulfate to H(2)S is carried out under carbon-limited conditions at pH 7.5 to 8.5. A fixed-bed biofilm column reactor is used in conjunction with a separate gas-stripping column which was installed in the recycle stream. Sulfate, total sulfide, and the carbon substrate (in most cases acetate) were determined quantitatively. H(2)S and CO(2) are continually removed by stripping with N(2). Optimal removal is achieved under pH conditions which are adjusted to values below the pK(a)-values of the acids. The H(2)S concentration in the stripped gas was 2% to 8% (v/v) if H(2)SO(4) and CH(3)COOH are fed to the recycle stream just before the stripping column.Microbiol conversion rates of 65 g of sulfate reduced per liter of bioreactor volume per day are achieved and bacterial conversion efficiencies for sulfate of more than 95% can be maintained if the concentration of undissociated H(2)S is kept below 40 to 50 mg/L. Porous glass spheres, lava beads, and polyurethane pellets are useful matrices for the attachment of the bacterial biomass. Theoretical aspects and the dependence of the overall conversion performance on selected process parameters are illustrated in the Appendix to this article.

Biological sulphate reduction using gas‐lift reactors fed with hydrogen and carbon dioxide as energy and carbon source

“…Except for the results of Isa et al ,7 who found only 50% inhibition at concentrations exceeding 1000 mg free H,S/L, total inhibition of growth is generally obtained at concentrations below 550 mg free H2S/L. 10913*15, 19 Our experiments demonstrate that effluent concentrations of 450 mg free H,S/L can be obtained at neutral pH, which facilitate the biological sulphide oxidation stage of the sulphate recycling process.…”

Effects of hydraulic retention time and sulfide toxicity on ethanol and acetate oxidation in sulfate‐reducing metal‐precipitating fluidized‐bed reactor

“…On the other hand, dissolved sulfide is toxic to SRB, and therefore, sulfide product inhibition may be expected in these single-stage processes. The overall effect of sulfide on the SRB growth and activity has been described qualitatively by many authors (Choi and Rim, 1991;Hiligsmann et al, 1998;Kalyuzhnyi et al, 1997;Kolmert et al, 1997;Oleszkiewicz, 1991, 1993;O'Flaherty et al, 1998;Reis et al, 1992;Stucki et al, 1993;Visser et al, 1996;Yamaguchi et al, 1999). However, there are only a few studies that quantitatively report the sulfide inhibition kinetics (Maillacheruvu and Parkin, 1996;Okabe et al, 1995).…”

Long-term competition between sulfate reducing and methanogenic bacteria in UASB reactors treating volatile fatty acids

“…The expected predominance of acetate-utilising SRB (ASRB) over acetateutilizing MB (AMB) in excess of sulfate has been confirmed in continuously stirred tank reactors and in the contact process (Middleton and Lawrence, 1977;Gupta et al, 1994). However, the outcome of the competition is less predictable in modern high-rate anaerobic reactors based on sludge immobilization, as both ASRB (Choi and Rim, 1991;Stucki et al, 1993) and AMB (Hoeks et al, 1984;Mulder, 1984) can be predominant in these reactors. The presence of AMB in excess of sulfate was found to be influenced by the reactor pH (Visser et al, 1996) and temperature (Visser et al, 1992), bacterial immobilization properties (Isa et al, 1986), and the acetate (Yoda et al, 1987) or sulfate (Overmeire et al, 1994) concentration.…”