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Chapter: Civil : Water Resources and Irrigation Engineering : Irrigation Water Requirements

Water characteristics and quality

Physical characteristics, Chemical characteristics, Biological characteristics

Water characteristics and quality:

ü        Physical  characteristics

 

ü        Chemical characteristics

 

ü        Biological characteristics

 

 

 

Physical  characteristics

 

Turbidity

 

ü      the clarity of water Transparency of natural water bodies is affected by human activity, decaying plant matter, algal blooms, suspended sediments, and plant nutrients

 

ü      Turbidity provides an inexpensive estimate of total suspended solids

 

ü      TSS concentration Turbidity has little meaning except in relatively clear waters but is useful in defining drinking-water quality in water treatment measures how deep a person can see into the water

 

Total Solids (TS) - the total of all solids in a water sample

 

Total Suspended Solids (TSS) - the amount of filterable solids in a water sample, filters are dried and weighed

Total Dissolved Solids (TDS) - Non filterable solids that pass through a filter with a pore size of 2.0 micron, after filtration the liquid is dried and residue is weighed EPA Secondary Drinking Water Recommendation is for TDS of less than 500mg/L Volatile Solids (VS) - Volatile solids are those solids lost on heating to 500 degrees C - rough approximation of the amount of organic matter present in the solid fraction of wastewater

 

 

 

Chemical Characteristics

 

Commonly measured chemical parameters are:

 

'pH

 

'Alkalinity

 

'Hardness

 

'Nitrates, Nitrites, & Ammonia

 

'Phosphates

 

'Dissolved Oxygen & Biochemical Oxygen Demand

 

pH:

 

The pH of water determines the solubility of many ions and biological availability of chemical constituents such as nutrients (phosphorus, nitrogen, and carbon) an heavy metals (lead, copper, cadmium)

 

Hardness

ü        Hard water is found in about 85% of USA.

 

ü        Prevents lathering/sudsing - hotter water and extra rinse cycles may be required

 

ü        Fabric appearance declines & life may be reduced

 

ü        Minerals may clog pipes & cause excessive wear on moving parts

 

Solutions:

'Distill water to remove the calcium and magnesium

 

'Soften the Water - Replaces calcium and magnesium ions with sodium or potassium ions

 

Cation exchange

Strong adsorption » » » Weak adsorption

Al+3 > Ca+2 > Mg+2 > K + = NH4+ > Na + >H +

Nitrogen

Nitrogen   gas   (N2)   makes   up   78.1%   of   the

 

ü        An essential nutrient required by all plants and animals for formation of amino acids (the molecular units that make up protein) N must be "fixed" (combined) in the form of ammonia (NH3) or nitrate (NO3) to be used for growth

 

'N2 + 8H+ + bacteria = 2NH3 + H2

'NH3 + O2 + bacteria = NO2- + 3H+ + 2e-

'NO2- + H2O + bacteria = NO3- + 2H+ +2e-

 

ü        Ammonia NH3 (extremely toxic) continually changes to ammonium NH4 + (relatively harmless) and vice versa, relative concentration depends on temperature & pH At higher temperatures and pH, more N is in the ammonia form

 

Maximum Contaminant Level (MCL): nitrite-N : 1 mg/L nitrate-N : 10 mg/L

nitrite + nitrate (as N) : 10 mg/L

Sources:

Fertilized areas; Sewage disposal; Feed lots; N cycle

 

PHOSPHATES

 

ü        Secondary Drinking Water Standard EPA recommendation'total phosphate should be <0.05 mg/L (as phosphorus) in a stream where it enters a lake or reservoir

 

ü        total phosphate should not exceed 0.1 mg/L in streams that do not discharge directly into lakes or reservoirs

 

Sources:

 Erosion; Fertilizer; Sewage; Feed lots; Detergents

 

Dissolved Oxygen

 

ü        Dissolved Oxygen DO mg/L 'only gas routinely measured in water samples (depends on temperature, salinity, and pressure)

 

ü          Analysis should be performed on site immediately after sampling

 

ü        Oxygen enters the water by photosynthesis of aquatic biota transfer across the air-water interface

 

ü        DO < 5mg/L stresses aquatic life (the lower the concentration, the greater the stress)

 

 

 

Biological Characteristics

Harmless bacteria ~ present in large numbers

ü        in feces and intestinal tracts of humans and

 

ü                    other warm-blooded animals Environmental Impact

 

ü          indicator of contamination with human or animal fecal material

 

may indicate contamination by pathogens or disease producing

 

ü        bacteria or viruses Criteria

 

ü        Swimming ~ fewer than 200 colonies/100 mL

 

ü          Fishing and boating ~ fewer than 1000 colonies/100 mL

 

ü        Domestic water supply ~ fewer than 2000 colonies/100 mL

 

ü        Drinking water 0 colonies/100mL

 

Biological Oxygen Demand

 

ü        Biological Oxygen Demand is a measure of oxygen used by microorganisms to decompose organic waste (add a microorganism seed to all samples seal sample dead plants, leaves, samples, from air, store in dark to prevent photosynthesis, subtract seeded control, measure decrease in DO)

ü        Nitrates & phosphates are plant

 

ü        nutrients so may contribute to high

 

ü        BOD levels When BOD levels are high, dissolved

 

ü        oxygen decreases ' fish and other grass clippings, manure, sewage, or food waste aquatic organisms may not survive


An index of the degree of organic pollution in water

BOD level of 1-2 ppm - very good

BOD level of 3-5 ppm - moderately clean BOD level of 6-9 ppm - somewhat polluted

 

 

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Civil : Water Resources and Irrigation Engineering : Irrigation Water Requirements : Water characteristics and quality |


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