Precipitation of heavy metals from coal ash leachate using biogenic hydrogen sulfide | |
| Author | Jayaranjan, Madawala Liyanage Duminda |
| Call Number | AIT Diss. no.EV-12-05 |
| Subject(s) | Leachate Sewage--Purification--Precipitation Sewage--Purification--Heavy metals removal |
| Note | A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Engineering in Environmental Engineering and Management |
| Publisher | Asian Institute of Technology |
| Series Statement | Dissertation ; no. EV-12-05 |
| Abstract | Coal combusted wastes such as coal fly ash, bottom ash and FGD gypsum are pr oduced worldwide in large quantities. However, only up to 30% of fly ash and about 15% of bottom ash are reused and the rest of the coal ash is disposed of in ash dump sites, creating adverse environmental impacts. Therefore, the above scenario was created a need to come up with a solution for safe ash disposal method. In this research, it was focused to develop a biotechnological way of stabilizing heavy metals which could be leach out from the coal bottom ash under various conditions such as natural rains , acid rains and in acid mine drainage conditions. Bench scale investigations for achieving above were consisted of three main steps namely, hydrogen sulphide (H 2 S) production by sulphate reducing bacteria (SRB) using sulphate from solubilized FGD gypsum as the electron acceptor followed by leaching of heavy metals from the coal bottom ash and subsequent precipitation of heavy metals using biologically produced sulphide . Leaching tests of coal bottom ash carried out at acidic pH , revealed the existence of several heavy metals such as Cd , Cr, Hg, Pb, Mn, Cu, Ni and Zn. The concentrations of heavy metals leached out were pH dependent and lowest leaching observed at pH 7.00 while highest at pH 3.00. The highest concentrations reported in these lea ching experiments (in mg/kg dry ash basis) were 1.7, 7.56, 30.76, 669.86, 494.90, 22.44, 342.30 and 709.72 respectively. Molasses was used as an electron donor in the biological sulphate reduction process which produced sulphide rich effluent with concent ration up to 150 mg/L. Sulphide rich effluent from sulphate reduction process was used to precipitate heavy metals as metal sulphides from coal bottom ash leachate . Heavy metal removal efficiencies obtained through sulphide precipitation for Cd, Cr, Hg, Pb , Mn, Cu, Ni and Zn were in the range of 52 - 89%, 50 - 83%, 90 - 100%, 72 - 92%, 52 - 98%, 88 - 100%, 46 - 88% and 43 - 87% respectively for pH range of 3.0 - 7.0. |
| Year | 2012 |
| Corresponding Series Added Entry | Asian Institute of Technology. Dissertation ; no. EV-12-05 |
| 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) | reeda Parkpian ;Bohez, Erik L.J. |
| Scholarship Donor(s) | Asian Institute of Technology Fellowship |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 2012 |