Project topics and materials
Get Complete Project Material File(s) Now! »
Chromium
Chromium (a Greek word meaning colour) is also a chemical element (represented as Cr) and was discovered in the 17th century as a red crystalline mineral crocoite and formally used as pigment (Wikipdia.org; Jefferson, 2018). Chromium compounds are found in the environment from natural sources in the form of ore, in the hexavalent state. Free chromium in the form of chromate mainly originated from industrial activities (WHO, 1988; Merian, 1984). Naturally, chromite is the most prevalent form in the environment. It consists of two main refined products, which are: ferrochromium and metallic chromium (Westbrook, 1983; Hartford, 1983). Second, lead chromate (as crocoite) and potassium dichromate (as lopezite) are known to occur naturally in the environment (IARC, 1990). Industrial activities such as mining and smelting, industrial wastewater and leaching of soluble Cr(VI) compounds from wastes such as mine tailings, waste rock, dust and slag piles are the major source of chromium in the environment (Barceloux, 1999). Figure 2.4 indicates the total input of chromium in the environment; where metal use is the highest chromium input, followed by rock weathering and coal combustion (Merian, 1984).
Chromium is found in all matters, such as: rock, air, water and soil (Kimbrough, et al., 1999). In rocks, the most important mineral deposit of chromium is chromite (Mg, Fe2+) (Cr, Al, Fe3+)2O4, which, however, is rarely pure (Kimbrough et al., 1999). The concentration of chromium in rocks varies from an average of 5 mg/kg (range of 2-60 mg/kg) in granitic rocks, to an average of 1800 mg/kg (range, 1100-3400 mg/kg) in ultrabasic and serpentine rocks (US NAS, 1974b). Chromium is present in most soils in its trivalent form, although Cr(VI) can occur under oxidizing conditions (ATSDR, 2008a). In the USA, the geometric mean concentration of total chromium was 37.0 mg/kg (range, 1.0-2000 mg/kg) based on 1319 samples collected in contaminated soils (ATSDR, 2000), whereas at 173 Canadian sites, chromium soil concentration ranged from 10-100 mg/kg (d.w.) (CEPA, 1994c).
The concentration of chromium in uncontaminated waters is extremely low (< 1 μg/L or < 0.02 μmol/L) (CEPA, 1994c). Anthropogenic activities (e.g. electroplating, leather tanning) and leaching of wastewater (e.g. from sites such as landfills) may cause contamination of the drinking water (EVM, 2002). In the air, chromium is usually introduced through forest fires, volcanic eruptions, combustion and industrial emissions. Cr(VI) is reported to account for approximately one third of the 2700-2900 tons of chromium emitted into the atmosphere annually in the USA (ATSDR, 2008a). Based on USA data collected from 2106 monitoring stations from 1977 to 1984, the arithmetic mean concentrations of total chromium in the ambient air (urban, suburban, and rural) were in the range of 0.005-0.525 μg/m3 (ATSDR, 2000).
CHAPTER 1: INTRODUCTION:
1.1 Background
1.2 Aim and objectives
1.3 Methodology
CHAPTER 2: LITERATURE REVIEW
2.1 Chemistry and toxicity of arsenic (As) and chromium (Cr)
2.2 Occurrence and sources of arsenic and chromium
2.3 Environmental interaction of arsenic and chromium
2.4 Health impacts of arsenic and chromium
2.5 Arsenic and chromium production and industrial uses
2.6 Arsenic and chromium removal techniques and limitations
2.7 Microbial metabolism and metal resistance
2.8 Microbial oxidation of As(III) to As(V)
2.9 Microbial reduction of Cr(VI) to Cr(III)
2.10 Cr(VI) reduction linked to As(III) oxidation
2.11 Bioremediation applications.
2.12 Biofilm theory and structure
2.13 Summary
CHAPTER 3: MATERIALS AND METHOD
3.1 Source of microorganism
3.2 Culture enrichment
3.3 Culture isolation
3.4 Culture storage and sub-culturing
3.5 Culture characterization
3.6 Microbial analysis
3.7 Cr(VI) reducing potential experimental plan
3.8 As(III) oxidation potential experimental plan.
3.9 Batch experimental plan
3.10 Analytical methods
3.11 Reagents
3.12 Growth media
3.13 Continuous-flow reactor experiment
3.14 Scanning electron microscopy
3.15 Routine monitoring parameters
CHAPTER 4: EXPERIMENTAL RESULT AND DISUCSSION
4.1 Microbial analysis
4.2 Threshold limit analysis
4.3 Batch experiment
CHAPTER 5: CONTINIOUS-FLOW REACTOR RESULT AND DISCUSSION
5.1 Biomass characteristic
5.2 Reactor start-up
5.3 Glass bead packed-bed PFR with anaerobic CSTR retrofit
5.4 Ceramic bead packed-bed PFR with anaerobic CSTR retrofit
5.5 Glass bead versus ceramic bead packed-bed reactor
CHAPTER 6: BIOFILM KINETIC MODEL
CHAPTER 7: CONTINIOUS-FLOW MODELLING
CHAPTER 8: CONCLUSION AND RECOMMENDATIONS
BIBLIOGRAPHY
APPENDICES
