Environmental Biotechnology and Bioremediation
This section covers environmental biotechnology, especially sewage treatment, bioremediation, and biogas. The exam tests BOD and COD, treatment stages, and the difference between bioaccumulation and biosorption.
Core rules
BOD is the oxygen consumed by microorganisms while oxidizing biodegradable organic matter; COD is the oxygen equivalent of chemical oxidation and includes non-biodegradable matter, so COD is generally greater than or equal to BOD. Sewage treatment has primary physical removal, secondary biological treatment such as activated sludge, and tertiary polishing. Aerobic treatment uses oxygen and produces carbon dioxide and sludge; anaerobic digestion produces biogas, mainly methane and carbon dioxide. Bioremediation uses organisms to degrade or detoxify pollutants. Bioaugmentation adds specific degraders. Phytoremediation uses plants. Biosorption is passive binding to dead or living biomass; bioaccumulation is active uptake. Composting is aerobic.
Worked example
A BOD test uses a dilution factor of 5. Initial dissolved oxygen is 8.0 mg/L and final dissolved oxygen is 2.0 mg/L. BOD5 = (8.0 - 2.0) x 5 = 30 mg/L. The dilution factor corrects for the sample being diluted with oxygen-saturated water. If no dilution were used, the factor would be 1.
Traps that cost marks
BOD is not the same as COD. Anaerobic digestion is not an aerobic process. Biosorption is not the same as bioaccumulation. Coliforms indicate faecal contamination but are not necessarily pathogens. Do not ignore the dilution factor in BOD calculations.