Wastewater Contaminants and Treatment

Abstract

With the utilization of irrigation systems for wastewater treatment and disposal, engineers should be aware of common contaminants, methods of on-farm wastewater treatment, and methods of risk evaluation. The primary concerns with wastewater treatment and reuse are prevention of disease and prevention of nutrient contamination and eutrophication of surface and subsurface water resources. Regulations and treatment processes have been set up as a barrier between contaminants and people. In addition, best management practices have been established for optimal and safe utilization of waste. Epidemiological studies and quantitative risk assessment methods can help to establish the risk to human health of wastewater treatment, containment, and reuse practices. Based on risk assessment, regulators establish rules for wastewater treatment and disposal. The last wall of defense against disease and death is the immune system.

Questions

• 1. What is the fecal-oral pathway of disease transmission?

• 2. Pathogens come from four kingdoms of life: list and describe them.

• 3. List viruses that cause waterborne disease.

• 4. List bacteria that cause waterborne disease.

• 5. List protozoan parasites that cause waterborne disease.

• 6. Look up three of the diseases listed in Table 23.1 on the Internet and describe the symptoms.

• 7. Why are indicator organisms used and how do they distinguish between different sources of disease?

• 8. List the factors that determine wastewater treatment plant discharge pathogen concentration.

• 9. Calculate the required contact time in order to remove 99.9 % of remaining E-coli at a chlorine concentration of 3 mg/L

• 10. What was the key factor that reduced typhoid fever in the United States?

• 11. Why aren’t ozone and chlorine used together?

• 12. What environmental factors influence pathogen fate in the environment?

• 13. Give a brief summary (one paragraph) of how the body fights pathogens.

• 14. How do vaccines help the body fight disease?

• 15. Why must acid be injected at the same time as chlorine during disinfection?

• 16. Redo the risk assessment problem. The expected number of salmonella bacteria in wastewater is 10⁵ MPN/100 ml, and 200 children are expected to play for 16 hours in the landscaped area.

• 17. What are the 3 steps of Risk Analysis?

• 18. What are the 4 steps of Risk Assessment?

• 19. What is BOD and why is high BOD detrimental when wastewater is discharged to streams?

• 20. Describe the difference between oxidation and synthesis and endogenous respiration.

• 21. Calculate the BOD₅ if the dilution factor is 20 to 1, the initial dissolved oxygen concentration is 6 mg/L, and the final dissolved oxygen concentration is 2 mg/L.

• 22. List the steps in the nitrogen cycle in soils.

• 23. How is the nitrogen cycle carried to completion in wetlands with herbaceous aquatic plants?