SEWAGE AND WASTE DISPOSAL

Wastes are

“substances or objects which are disposed off or are required to be disposed off by the provisions of the law.  

Disposal is   “any operation which may lead to resource recovery, recycling, reclamation, direct re-use or alternative uses   

 CLASSIFICATION OF WASTES 

Wastes in Liquid Form

(Sewage)

Example: domestic washing, chemicals, oils, waste water from ponds, manufacturing industries and other sources

Solid Wastes

Domestic, Commercial & Industrial wastes

Example: plastics, styrofoam containers, bottles, cans, papers, scrap iron and other trash

Bio-degradable 

Can naturally degrade 

Paper, wood, fruits and others

Non-biodegradable

Cannot be degraded 

Plastics, bottles, old machines,cans, styrofoam containers, etc  

THREE BASIC APPROACHES TO TREATMENT

•Dilute and Disperse

• Concentrate and Contain

• Reduce, Recycle and Reuse 

WASTEWATER TREATMENT

Mimics natural processes in wetlands

• Remove solids

• Digest organic matter through

•Aerobic bacteria

•Anaerobic bacteria

• Wetland plants trap and concentrate pollutants

• Sediment provides natural filters

• Also provides a habitat

PRIMARY WASTEWATER TREATMENT

Removes about 30-40% of

pollutants

• Screening

Removes grit

(stones, sand, large particles)

• Sedimentation

Remaining particulate matter settles out to form a mud called “sludge”

• Discharge or go on to                             next stage of treatment 

SECONDARY TREATMENT

Removes 90% of pollutants

• Waste water pumped  through an Aeration tank

•Aerobic bacteria digest more organics

• Sedimentation Tank

•More sludge settles out

•Sludge sent to a digester

•Anerobic bacteria digest more organics

•Methane produced

SECONDARY TREATMENT

•Disinfection of wastewater

Chlorine

Ozone

• Discharge into surface waters or disposal wells or on to Advanced Treatment

Note: Secondary Treatment does NOT remove all nutrients, heavy metals, solvents and pesticides

•ADVANCED TREATMENT

• Removes 95% of the pollutants

•Targets nutrients, heavy metals, and synthetic chemicals

•Treated wastewater can be used as reclaimed water

•Techniques vary:

•Filters

•Chemical treatment

•SLUDGE DISPOSAL

•Further treatment required

• Sludges are thickened (dewatered) to reduce the volumes transported off-site for disposal.

• Some cities superheat the wastewater sludge and convert it into small pelletized granules that are high in nitrogen and other organic materials.

•Example: In New York City, several sewage treatment plants have dewatering facilities that use large centrifuges along with the addition of chemicals such as polymer to further remove liquid from the sludge. The removed fluid, called centrate, is typically reintroduced into the wastewater process. The product which is left is called "cake" and that is picked up by companies which turn it into fertilizer pellets. This product is then sold to local farmers and turf farms as a soil amendment or fertilizer, reducing the amount of space required to dispose of sludge in land

SEWAGE TREATMENT IN DEVELOPING COUNTRIES

In many developing countries the bulk of domestic and industrial wastewater is discharged without any treatment or after primary treatment only.

     Examples:

–In a country such as Iran, Tehran's majority of population has totally untreated sewage injected to the city’s groundwater.

–In Israel, about 50 percent of agricultural water usage (total use was 1 billion cubic meters in 2008) is provided through reclaimed sewer water. Future plans call for increased use of treated sewer water.

–Most of sub-Saharan Africa is without wastewater treatment.

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