Download Water supply and treatment

Water and Soil Pollution
Objectives
w To identify main types, sources and effects of water pollutants
w To understand the relationship between water and soil pollution
w To review water pollution avoidance and mitigation measures
Three “Media”
w Air
w Water
w Ground
w Important to understand interactions
w Important to identify tradeoffs
Types of Water Pollution
w Sewage
w Infectious agents
w Sedimentation
w Organic compounds
w Inorganic compounds (minerals)
w Radioactive isotopes
w Thermal pollution
Water Pollution Interactions
w
Warm water holds less O2
w BOD
n
n
Requires O2
Contains and promotes disease
Domestic Sewage
w Hazardous materials
w BOD (Biochemical oxygen demand)
w Disease (especially fecal coliform)
n
Cholera in London
w Dissolved solids (minerals)
w Suspended solids
w Oil and Grease
BOD
w Biochemical oxygen demand
w Fecal matter, food production
w Carbon, hydrogen and oxygen
w Requires O2 to decompose
w
Excess BOD exhausts available O2
Agriculture
w Mostly “nonpoint” sources
w Sediment (erosion)
w Persistent pesticides
w BOD from fertilizers and wastes
w Nutrients from fertilizers
Industry
w Mostly “point” sources
w Oil and grease, BOD (oil refineries)
w BOD, dioxin (bleach paper mills)
w “Specialty” effluents
w BOD, coliform (hog farms)
Mining
w Arsenic (Nevada problem)
w Can contaminate groundwater or surface water
w Copper
w Uranium tailings
w Acidity
Las Vegas Wash
w All Las Vegas and Henderson treated sewage (point sources)
w Storm runoff (non-point sources)
w Extremely high periodic storm runoff
w Las Vegas Bay: swimming
w Water intake: chlorinated
Map of LV Wash
Eutrophication
w Oligotrophic lakes
n
n
Low levels of minerals, low BOD
Slow-moving, shallow lakes undergo eutrophication
w Artificial eutrophication speeds this process
n
n
Dissolved O2 drops
Species change
Wastewater treatment
w Three stages
w Primary treatment
w Secondary treatment
w Tertiary treatment
Primary treatment
w Physical removal
w Settling ponds
w Clarifiers
w Bottoms removed to landfill
w Occasionally useful as fertilizer
w Standard in much of the world
Secondary Treatment
w Biological removal of organic material
w C6H12O6 + 6O2 à 6CO2 and 6H2O
w “Bugs”
w Oxygen is added (aerators)
w Another set of clarifiers
w Standard in most of US, Japan
Tertiary Treatment
w Chemical removal of materials
w Can be extremely expensive
w Rare
Figure 21-13
Wetlands
w Wetlands can serve a wastewater treatment function
w Some plants absorb minerals very quickly
w These can be used as mulch, or even fuel
w Increased interest lately
Wastewater Control Options
w “Mitigation”
w Change process
n
n
Recycled paper
Non-chlorine bleaching
w Reduce waste
n
Reuse water
w Remove pollutants
n
“end of pipe” solution
Groundwater Contamination
w Can be a problem around mines, old industrial sites, landfills
w Laws restricting land use are recent
w Love Canal: legally filled with toxic chemicals
w Seeped into basements
Soil Salinization
w All water contains some minerals
w Water is used by plants or evaporates
w Leaves minerals behind
w Repeated
w Plants can’t live when salts are too high
w Civilization
n Fertile Crescent
n California?