Biological Impurities (OD), Nitrogen Cycle

Theoretical Oxygen Demand (ThOD)

Calculated via chemistry balance equation

Biological Oxygen Demand (BOD)

Tested in a BOD bottle. Put seed bacteria from the water & a water sample and see how much oxygen remains after a certain period of time → creates exponential graphs; only measures biodegradable oxygen matter (will always be less than or equal to theoretical oxygen demand)

Chemical Oxygen Demand (COD)

Use a strong oxidant to experimentally determine OD; accounts for non-biodegradable organics as well; If ideal/performed correctly, COD = ThOD

Major Stages (4) in the Oxygen Sag Curve?

Clean Zone, Decomposition Zone, Septic Zone, Recovery Zone

(Oxygen Sag Curve) Clean Zone characteristics

Non-problematic oxygen levels

(Oxygen Sag Curve) Decomposition zone characteristics

ideal for the rapid growth of plants, algae and other organisms. This rapid growth quickly depletes the level of dissolved oxygen preventing continued aerobic respiration.

(Oxygen Sag Curve) Septic zone characteristics

level of oxygen is too low to support organisms that live by aerobic respiration. In this region anaerobic organisms (especially bacteria) flourish and produce noxious waste products such as methane (CH4) and hydrogen sulfide (H2S).

How to calculate Oxygen Deficit (D)?

Deficit = Saturation level of oxygen in water/max dissolved oxygen in water, mg/L - Concentration of dissolved oxygen in water, mg/L

Eutrophication

excessive richness of nutrients in a lake or other body of water, frequently due to runoff from the land, which causes a dense growth of plant life and death of animal life from lack of oxygen.

What is cultural eutrophication?

When human water pollution speeds up the aging process of a body of water due to excessive nutrient runoff.

From N/P critical and N/P water determine whether N or P is the limiting nutrient

If N/P water > N/P critical, P is limiting; vice versa for Nitrogen

Describe the stages of the Nitrogen Cycle

Nitrogen Fixation: Nitrogen gas → Ammonia via lightning/bacteria; Nitrification: Ammonia → Nitrates/Nitrites via oxidation or nitrogen fixing bacteria; Assimilation: Plants and animals incorporate nitrates as plant proteins and nucleic acids; Ammonification: Process of dead organisms breaking down into ammonia; Denitrification: Nitrates/Nitrites → Nitrogen gas (O2 must be absent)

Human activity impacts on Nitrogen Cycle?

We make fertilizer (Synthetic Nitrogen Fixation)

NITROGEN FIXATION

The process of nitrogen gas is converted into ammonia by lightning or bacteria.

NITRIFICATION

The process of ammonia being converted into nitrates and nitrites (via oxidation/nitrogen fixing bacteria)

ASSIMILATION

plants and animals incorporate the nitrates and ammonia formed from nitrogen fixation/nitrification → turns into plant proteins and nucleic acids

AMMONIFICATION

The process of dead organisms breaking down into ammonia.

DENITRIFICATION

The process of nitrates and nitrites being converted into nitrogen gas or gaseous nitrogen. (reduction of NO3- to N2 (O2 must be absent!))