Waste water treatment

VASUKI SILVA

Content • Why we treat or what are the impacts when discharged untreated

• Nature of the pollutants or sewage

• How does a sewage treatment plant look likes and functional units

• Legal frame work

What is waste water?Wastewater

• Also known as sewage• is any water that has been adversely affected in quality by

anthropogenic influence. • originates from a combination of domestic, industrial, commercial or

agricultural activities, surface runoff or storm water, and from sewer inflow or infiltration

Why treat waste water ??• To remove organic and inorganic matter,

which will otherwise cause pollution

• Sedimentation• Eutrophication • High BOD

• To remove pathogenic organisms

• To protect environment and humanhealth

Types of waste water• Domestic Wastewater homes, offices, hotels, institutions comprises sewage (human waste) and greywater from bathrooms,kitchens, laundries

• Industrial Wastewateris the liquid discharge from manufacturing processes; Ex: soft drink and beer companies; sugar processing; metal processing; photo finishing

Do you know ?• From your water supply

Less than 1% is used for drinking purpose

Rest of the 99% is used for cleaning and other activities

• Therefore water contains many suspended and dissolved pollutants

Questions to debate1. What is the quantity of wastewater that your household produces in a single day?

2. Where is your wastewater going? Is it going to a sewer? And where is the rain water going? Does it end up at the sewage treatment plant in your area?

Compare and contrast the difference in your context

Waste water management Generation Collection Treatment Disposal

Treatment plant overview• Functional units

• Physical treatment • Chemical trearment• Biologocal treatment

• Targeting specific groups of pollutants

Largest waste water treatment plant in Netherlands – 1.4 million people

Treatment process overview

Parameters

Stages of waste water treatment

• Preliminary treatment• Primary treatment• Secondary treatment

Preliminary treatment• Removal of coarse solid & other large materials in raw waste water• Preliminary treatment includes;

- Coarse screening – Use bar screens, fine screens- Grit removal – Not include in most small waste water treatment

plants

Primary treatment• Physical process• Settle solids for 2-3 hours in a static, unmixed tank or basin• 75-90% of particles & 50-75% of organics settle out as primary sludge• Enteric microbe levels in primary sludge are 10 times higher than in

raw sewage• Little removal of enteric microbes; typically 50%

Secondary treatment• To remove residual organics & suspended solids• Use a biological process• Removal of biodegradable dissolved & colloidal organic matter by

using aerobic biological treatment processes• Performed in the presence of oxygen by aerobic microorganisms• They metabolize organic matter in waste water & produce inorganic

end products; CO2, NH3, H2O

• Microorganisms must separate from treated waste water by sedimentation to produce clarified secondary effluent• Biological solids removed during secondary treatment – biological

sludge/ secondary sludge• Different approaches;

- Fixed film system- Suspended film system

Fixed film system• Grow microorganisms on substrates such as rocks, sand, or plastic• Waste water is spread over the substrate• Ex: Trickling filters, Rotating biological contactors

Suspended film system• Stir & suspend microorganisms in waste water• Settled out as a sludge• Pumped back into the incoming waste water• Ex: Activated sludge, extended aeration

Chemical treatment• Disinfection is done as a final treatment procedure• Injection of a chorine solution into treated water• Chlorine dosage depends on the strength of waste water & other

factors• Common dosage: 5-15 mg/L• Contact time with waste water: About 15 minutes• Ozone & ultra violet irradiation – not commonly used

Legal frame work- waste water

1980 National Environmental Act ‐ (NEA) No. 47

• 1981 CEA Established‐

• 1988 NEA Amended to include Regulatory Provisions ‐ – Amendment Act No. 56 of1988 Regulatory tools.– Environmental Impact Assessment Procedure(EIA Procedure for major projects)

– Environmental Protection Licencing Procedure (EPL procedure for prescribedIndustries/Activities)

Legal framework cont. • 1990 Regulations gazetted in relation to EPL and Waste Water

Discharge Standards.Gazette Extraordinary No. 595/16 dated 1990 February 02. 2000 NEA Amended to Prescribe the EPL ‐

Activities – Amendment Act No. 53.– Gazette Extraordinary No. 1159/22 dated2000 November 22– Gazette Extraordinary No. 1533/16 dated

Waste Water Discharge StandardsCentral environmental Authority • Tolerance limits for the discharge of Industrial waste into Inland Surface waters.• Tolerance limits for Industrial waste Discharged on land for irrigation Purposes.• Tolerance limits for Industrial and Domestic waste Discharged into Marine Coastal Areas.• Tolerance limits for waste from Rubber Factories being Discharged into Inland Surface waters.• Tolerance limits for waste from Textile Factories being Discharged into Inland Surface Waters.• Tolerance limits for waste from being Discharged from Tanning Industries.• Tolerance limits for discharged of effluents into public Sewers with Central Treatment Plants.