Denitrification and desulfurization with elemental sulfur and hydrogen sulfide
Date
2012-06-14
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Degree Level
Masters
Abstract
Compared with conventional heterotrophic denitrification, sulfur-based autotrophic denitrification offers several advantages for the treatment of waters contaminated with nitrite or nitrate. First, it eliminates the needs for adding of organic carbons in the case of organic deficient wastewaters. Furthermore, the quantity of sludge produced under autotrophic conditions is substantially lower than that in a heterotrophic process which in turn reduces the cost associated with the treatment and digestion of the sludge.
Desulfurization under denitrifying conditions is a suitable alternative for removal of H2S from contaminated gaseous streams because it eliminates the need of light energy input required for photoautotrophic desulfurization, and the supply of oxygen in aerobic chemolithotrophic desulfurization, in which simultaneous presence of both hydrocarbon gas and oxygen imposes a serious safety issue.
In this work sulfur-based autotrophic denitrification and denitritation were studied in batch system using freely suspended cells and in a continuous biofilm reactor. Desulfurization of a H2S-containing gaseous stream under denitrifying conditions was studied in a semi-continuous packed bed reactor. Coleville enrichment, a mixed culture originated from a Canadian oil reservoir, which has the ability to function under both heterotrophic and autotrophic conditions, was used as the bacterial culture.
The order of preference for electron donors used by the Coleville enrichment during the denitrification was established as: sulfide > biologically produced sulfur > acetate > elemental sulfur. Sulfate productions closely matched with theoretical values expected from stoichiometry in the batch experiments. Sodium bicarbonate functioned as an effective buffering agent and an inorganic carbon source during sulfur-based autotrophic denitrification. Strong inhibitory effect of nitrite on bacterial activity was observed.
In the continuous biofilm reactor, sulfur-based nitrate removal rate increased linearly with the increase of nitrate loading rate through either an increase of feed flow rate or a variation of feed concentration. Similar trends were observed in the nitrite removal experiment. The highest nitrate removal rate (17.3 mM h-1) was obtained at a nitrate loading rate of 24.2 mM h-1 (corresponding residence time: 0.4 h) with a nitrate removal efficiency of 71.3% and a total nitrogen removal efficiency of 9.5%. The highest nitrite removal rate (13.2 mM h-1) was achieved at a nitrite loading rate of 18.0 mM h-1 (corresponding residence time: 0.6 h) with a nitrite removal percentage of 73.6%. The removal rates obtained in the present work were much higher than those reported in the literature.
In the semi-continuous desulfurization experiments, the removal efficiency of H2S remained greater than 98.6% and 99.4% with nitrate and nitrite as the electron acceptor, respectively. The reduction rates of nitrate and nitrite increased with the increase of H2S loading rate through a variation of feed gas flow rate. The observed denitrification and denitritation rates were much higher than those obtained in the batch denitrification experiments with elemental sulfur and acetate.
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Keywords
denitrification, desulfurization, elemental sulfur, hydrogen sulfide, Coleville enrichment, anaerobic
Citation
Degree
Master of Environment and Sustainability (M.E.S.)
Department
School of Environment and Sustainability
Program
Environment and Sustainability