However, this is also a gaseous component of the atmosphere that is creating the “greenhouse effect” and thus should be used, not released to air.

What are BOD and COD?

 WW do not contain a single organic compound; it is a mixture of organic compounds, each in various oxidation state – that is why a non specific test must be used
 to determine the concentration of organic carbon, the collective parameters are needed: BOD5 a COD.  COD – chemical oxygen demand – it is the quantity of the biodegradable (biomass + consumed oxygen) and non-biodegradable organic carbon.  BOD5 – biochemical oxygen demand – the concept of BOD depend on assessing the potential of a WW that contains an available organic carbon as a source for aerobic organisms by measuring the amount of oxygen utilized during growth of the microorganisms. There’s difference between COD and BOD that BOD indicates just the quantity of biodegradable organic carbon in WW. BOD5 is then the difference in oxygen content at the beginning of the experiment and at its end after five days.  Very important parameter is then ratio BOD5 / COD, this is the indicator of convenience of biological WWT. For the utilization of this method the ratio has to be higher than 0,5.

Physical and chemical methods for WWT

 Equalization or homogenization
 Sieving and micro-sieving
 Sedimentation
 Filtration
 Flotation
 Clearing and coagulation
 Adsorption
 Extraction
 Deaeration
 Distillation
 Gamma radiation
 Oxidation and reduction
























































In biological WWT we use 2 basic methods:
 Activation pools
 Biological filters












WATER RESOURCES

Water is the driving force of all nature.
(Leonardo da Vinci)

In an animal or a plant, 99 molecules in 100 are water… An organism is a pool in a stream of water along with metabolites and energy move through ecosystems.
(W.V. Macfarlane)

 At any single moment, 94% of the earth’s water is found in the oceans, 4% is in inaccessible aquifers, and 1,5% is locked up in polar ice and glaciers. This leaves about 0,5% of the earth’s water available for human use, but most of this water is hard to reach and much too costly to be of any practical value.
 Three out of every five people in the developing nations do not have access to clean, disease-free drinking water. According to the World Health Organization, 80% of all disease in these countries results from the contaminated water that people drink and bath in.
 Water shortage arises from two principal problems: First, water is not evenly distributed across the face of the earth.