Water Quality Considerations for

TreatmentWater sources

PollutionTreatment needs

Hydrological cycle

Water retention in aquifers

Volume of water in the atmosphere (if condensed) ~ 3,100 mi3 or 12,900 km3 = 0.001 % of Earth's total water volume= 0.035% of all fresh water = 4.5% of all surface water= 1 inch to cover all of Earth’s surface

Atmosphere: superhighway for fresh water cycle around the globe

Atmospheric water

Rainfall distribution on Earth

World climatic areas

World climatic areas

Safe and reliable supplies of water

Not without environmental consequences

Ensuring supplies

Alternative water sources

Promising, yet elusive

Water pollution

Hypoxia

Hypoxia Mississippi Delta

Fertilizer and nitrogen cycle

Effect of Salinity on SoilsSalinity: Sodium and ChlorideGood Salts: Calcium, Magnesium Hold soil particles togetherProblem Salts: Sodium – soil dispersion Chloride - toxicity

Ca++

Mg++

Na+

Sodium Absorption Ratio (SAR)

Consequences of Soil DispersionPoor DrainageLess infiltration of waterIncreased water runoffLess efficient leaching of salt

Loss of Soil StructureLoss of soil pore spaceDecreased oxygenIncreased soil erosion

Plant EffectsHigh soil bulk densityDecreased root growthAnoxia and root death

Poor water infiltration leads to soil ponding: poor leaching,salt accumulation, low soil oxygen, root death fromanoxia, and increased Phytophthora root rot.

The effect of salinity on plants

Chloride 0.61%

Chloride 0.58% Sodium 0.35%

Environmental protection

Typical water treatment process with lime softening

Water reclamation

Process units in water treatmentPre-chlorination – for algae control and arresting any biological growthAeration – along with pre-chlorination for removal of dissolved iron and manganese and stripping volatilesCoagulation – for flocculationCoagulant aids, such as polyelectrolytes – to improve coagulation and for denser floc formationSedimentation – for initial solids separation, that is, removal of suspended solids trapped in the flocFiltration – removing additional solids from waterDesalination – removing soluble inorganics from waterSoftening – removing calcium from waterDisinfection – inactivating microbesAdsorption – removing undesirable organic compounds

Reflection The general technologies are well developed and generalized designs are available which are used by many water utilities (public or private)

No unique solution (selection of unit processes) for any type of water New technologies are still developedDifficult to standardize unit processes for different water sources. Treatability studies for each source of water in different seasons required for appropriate processes.