| Author | Saovapak Suktrakoolvait |
| Call Number | AIT Diss. no.EV-00-1 |
| Subject(s) | Sewage--Purification--Biological treatment
|
| Note | A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Technical Science |
| Publisher | Asian Institute of Technology |
| Abstract | Biological sulfate removal can be accomplished through series of reactions viz.: anaerobic sulfate reduction to sulfide followed by aerobic sulfide oxidation to elemental sulfur. In this research, the feasibility of these processes for sulfate and sulfide removal were investigated under laboratory conditions. The experimental studies were conducted in two separate phases. Biological sulfate reduction to sulfide by sulfate reducing bacteria (SRB) using molasses as an electron donor and carbon source was accomplished in Phase I, while, Phase [I focused on biological sulfide oxidation to elemental sulfur by bacteria of the Thiobacillus genus and the formation of well-settleable sulfir sludge. Phase I : Biological Sulfate Reduction. Feasibility of a laboratory scale UASB process for sulfate reduction with molasses as an electron donor and carbon source is demonstrated. Competition between MPB and SRB was influenced by COD/S ratio in the feed. Sulfate removal over 80% could be achieved at COD/S ratio higher than 10 when MPB predominated. Activity of MPB and SRB was inhibited at dissolved sulfide concentration of about 200 mgS/L. Competition between MPB and SRB was intense as COD/S ratio was reduced from 5 to 2. Further reduction in COD/S ratio to 0.? led to formation of sulfidogenic granules. COD removal reduced to about 30% at COD/S ratios less than 2 due to accumulation of sulfurous precipitates and non-biodegradable portion from molasses in the sludge. Reduced gas production rates further imposed limitations on diffusion of organic substrate into granule. Sulfidogenic process operation yielded sulfate removal up to 70% at COD/S ratio of about 3.5. Phase I] : Biological Sulfide Oxidation. Feasibility of a laboratory scale fluidized bed process for biological sulfide oxidation to elemental sulfir and the formation of well-settleable SUlfiJl' sludge is demonstrated. Sulfide oxidation strongly depends upon oxygen concentration, sulfide loading rate and upflow velocity. At DOr higher than 0.1 mg/L, sulfate was the main production of sulfide oxidation. Upon increasing the sulfide loading rate, the sulfate production rate decreased as sulfide oxidation to sulfur showed marked increase. Low formation of sulfate could mean that sulfide was inhibitory to sulfate producing bacteria. Sulfide conversion higher than 90% was obtained at sulfide loading rate of 0.13- 1.6 kgS/m,3d. At DOr less than 0.1 rug/L, sulfur was the major end product of the sulfide oxidation. Upflow velocity in the range of 16 -26 m/h and sulfide loading rate of 0.9-1.6 kgS/mr3d was necessary for generation of biogranules containing 65 -76% of elemental sulfur. The elemental sulfur production of 76% was obtained at upfiow velocity of 17 m/h with sulfide loading rate upto 1.6 kgS/mr3d. Morphological examination of the sulfur sludge showed elemental sulfur deposition in the sludge granule outside the cell. |
| Year | 2000 |
| Type | Dissertation |
| School | School of Environment, Resources, and Development (SERD) |
| Department | Department of Energy and Climate Change (Former title: Department of Energy, Environment, and Climate Change (DEECC)) |
| Academic Program/FoS | Environmental Engineering (EV) |
| Chairperson(s) | Annachhatre, Ajit P. ; |
| Examination Committee(s) | Lin, C. Kwei ;Preeda Parkpian ; |
| Scholarship Donor(s) | Government of Austria; |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology |