Ch 22 Flashcards
Hydrologic cycle definition
the cyclic exchange of water between the atmosphere and biosphere
steps of hydrologic cycle
-water precipitates as rain; falls to earth
-water is returned to air by evaporation
water passing through the ground picks up ______
nutrients;
carbon runoff accelerates microbial respiration
O2 becomes depleted
water carrying nutrients into the river _______ BOD
increases
BOD stands for
biochemical oxygen demand: the amoung of O2 removed from the environment by aerobic respiration
high BOD can threaten
viability of fish & other aquatic animals when O2 levels are low
cutoff of acceptable O2 levels
< 5 mg/L
-air saturated water = 8mg/L
-sewage = >600mg/L
how is O2 measured
dissolved oxygen probe
eutrophication definition
process occurring due to influx of excess nutrients that triggers hypoxic zones in water
steps of eutrophication
-influx of N, P boosts levels of phototrophs, ; a mat of growth occurs
-once excess N, P is used uspm the algal mass dies and falls to the bottom
-heterotrophic bacteria in the sediment feat on organic matter
-aerobic respiration depletes oxygen from the water - fish killed
how does wastewater treatment affect BOD
it decreases BOD and the level of human pathogens before water is returned to local rivers
Preliminary treatment
removes solid debris
primary treatment
fine screens and sedimentation tanks remove in soluble particles
secondary treatment
microbial decomposition of organic content
tertiary treatnent
chlorination or other chemicals applications to eliminante pathogens
