《 水质工程学 》 Water Quality Engineering Lecturer: Professor Xie Shuibo Lecture 4

1. 《水质工程学》Water Quality EngineeringLecturer: Professor Xie ShuiboLecture 4

2. Water Pollution • I – Oxygen Demanding Wastes • Organic Material, Ammonia • Source • Runoff, Waste discharge, Algae (dead), Leaves / Animal droppings • Measurement • Biological Oxygen Demand (BOD) • Problems • Threatens life, Taste/odour/colour

3. II – Pathogens - Disease Causing Micro-orgs • Bacteria – eg typhoid, cholera • Viruses – hepatitis, poliomyelitis • Protozoa – amebic dysentery • Helminths (parasite worms) Method of dispersal • Waterborne diseases: ingestion • Water contact diseases • Water hygiene diseases: lack of water

4. III – Nutrients • Nutrients enrichment – eutrophication • Nitrites & Nitrates – O2 starvation IV – Other Contaminants (Water) • Salts (salinity) – water use, fresh water orgs • Heavy metals – toxic • Pesticides – toxic • Volatile organics – toxic • Suspended solids – sediments • Thermal pollution – high temp reduces O2 availability, stimulate growth, +ve & -ve impacts

5. Removal of oxygen from rivers 1) By dilution Flow direction Waste discharge (ww) Clean water Contaminated river water Some DO No DO DO reduced DO (Downstream) = (river flow x DOR + ww flow x DOww)/(ww flow + river flow)

6. 2) Microbial consumption of O2 Bacteria + Organic W + O2 CO2 + H2O Waste From water Dilution D.O. Bacteria DISTANCE

7. 3) Re-aeration When O2 drops below value determined by Henry’s Law [O2] = KH PO2  O2 dissolves in water to re-establish equilibirum Waste D.O. Dilution Re-aeration Bacteria consumption DISTANCE

8. 4) Net = Oxygen-sag curve WW discharge D.O DISTANCE Oxygen removal greater than re-aeration Oxygen removal less than re-aeration

9. WQ in lakes Eutrophication • Excessive growth of plants to levels that interfere with water use OR • Input of nutrients (N, P) that stimulate growth of algae and other plants to levels that affect use • Weeds, blue-green algae, tiny plants (phytoplankton)

10. Consequences of eutrophication • Toxicity – blue green algae • Oxygen depletion/severe variations • Creation of septic conditions • Rooted plants impact on navigation, flow • Aesthetic and recreational value degraded

11. Sources of nutrients and sediments • Municipal wastewater discharges • Industrial wastewater discharges • Runoff from agricultural, urban land • Natural sources/decaying vegetation, tributaries Eutrophication status • Oligotrophic – low nutrient content, low productivity • Mesotrophic – medium • Eutrophic – high Oligo Meso Eutr TP < 10micrograms/L 10-20 > 20 Chla < 4 micrograms/L 4-10 > 10

12. Example impacts of a new residential development on water quality and pollution • Consumption of clean water • Generation of wastewater • Wastewater needs treatment/collection • Discharge of wastewater  contamination of receiving waters • Increased runoff, erosion • Pollutants load in runoff  contamination of receiving waters Receiving water bodies can be rivers, lakes, reservoirs, ocean, groundwater, wetlands… Contaminants: oxygen consuming, pathogens, turbidity, sediment, oil and grease, N, P, metals, toxic organics.

13. What can be done? • Reclamation • Processing of wastewater so it can be reused • Recycling • Putting water back into the use scheme which generated wastewater • Reuse • Putting reclaimed water to a beneficial use

14. Sustainable water cycle Objectives • Use of renewable resources (eg rain) • Minimise water use • Minimise water use waste • Maximise reclaimation, recycling and reuse • Maintain feasibility but include social and environmental costs • Minimise adverse effects on human health and environment

15. Domestic water use Water Use % Toilet flushing 40 Hand & body washing 34 Kitchen use 7.5 Drinking 4.5 Washing clothes 7.5 Cleaning House 1.5 Washing Car 1 Watering Garden 4.5

16. Pollution from source Toilet: oxygen consuming, sediments, pathogens, plant nutrients, salts Body washing: foaming, plant nutrients Kitchen: foaming, oxygen consuming, sediments, oil & grease, plant nutrients, salts Washing clothes: foaming, plant nutrients, sediment, chlorinated chemicals Cleaning house: foaming, plant nutrients, chlorinated chemicals, metals, salts Washing car: foaming, hydrocarbons, oil & grease, sediments

17. Plant growth • Nutrients (mainly N, P) • NH4, NO3, N2 • PO4 • Sunlight penetration • Turbidity reduces penetration • Temperature • Higher temp stimulates growth

18. Phosphorus levels in lakes P level Assuming no change with time: Inputs = outputs + sedimentation Inputs = mass/unit time Sedimentation = VSAP mass/unit time Output = mass/unit time Sedimentation Outputs Inputs

19. The limiting nutrient • The nutrient that runs out first limits growth Concentration Concentration N N P P Time Time WHICH IS THE LIMITING NUTRIENT???

20. Estimate impacts of Manly West Development on water quality and pollution • Given: per capita water pollution factors • Runoff pollution loading factors • Runoff estimation factors