Wastewater TreatmentCity of London

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What is Wastewater?• Water used in our communities and businesses leaves as

wastewater to be treated and returned to the environment.• All water that is used within the house and goes down a drain.

– Toilets, showers, washing machines, sinks, dishwashers, etc.– Industrial, commercial, and institutional waste– What should not be included in wastewater?

• There is on average 180 ML/day of wastewater treated.

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Why do we need to treat it?• Wastewater can contain a variety of contaminants that

can be harmful to the environment, humans and animals.

• By treating wastewater we can control the spread of water borne diseases.

• It also keeps our rivers, lakes and ground water clean and healthy.

• The City of London monitors Thames River health to ensure effluent does not have negative impacts.

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Greenway Lab• Greenway Lab does the tests for all 6 Pollution Control Plants (PCPs)• Test are done at varying intervals at Influent, Effluent and Sludge

• Tests Include:– Biochemical Oxygen Demand– Heavy Metal Testing– Ammonia– Total Phosphorus– Total Kjeldahl Nitrogen (TKN)– Cations– Chloride Nitrate/Nitrite, Sulphate– Oil and Grease– Solids (Volatile Suspended Solids, VSS and Volatile Total Solids, VTS)– Total Coliforms and E. coli– pH

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Wastewater Operations: Background

• The City of London has 6 Pollution Control Plants (PCP’s):– Greenway: 1901– Vauxhall: 1916– Pottersburg: 1956– Adelaide: 1958– Oxford: 1960– Lambeth: 1963– Future: Southside

Pollution Control Plant

Capacity (Cubic Metres per Day)

Actual Flow 2012 (Cubic Metres per day)

Adelaide 36,400 23,400

Greenway 152,175 115,200

Oxford 17,250 9,000

Pottersburg 39,100 23,500

Southland 564 258

Vauxhall 20,900 14,900

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Regulations• The Ontario Ministry of the Environment regulates more than 470

wastewater treatment plants owned my municipal governments.

• Wastewater Treatment is regulated under the Ontario Water Resources Act (OWRA) which falls under the Ministry of the Environment.

• What does it regulate?– Effluent Quality– Reporting Requirements– Effluent sampling and monitoring

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The System

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Step 1: Moving Wastewater to a PCP

Raw sewage (seen above) is usually >95% water.

Pumping stations and gravity sewers move wastewater to PCPs around the City.

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As the wastewater enters the PCP it flows through steel screens with 25 mm openings. This removes larger material including:- Paper- Plastic- Leaves- Sticks

Step 2: Inlet Works and Coarse Screens

The solids removed in the screening process are collected and sent to the landfill.

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Step 3: Grit RemovalHeavier inorganic solids are removed using the vortex system.

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Step 4: Primary Clarifier

Larger organic solids are settling out of the wastewater.

These units are designed to allow organic solids to settle out by gravity.

The grease forms a scum which is skimmed from the surface of the tanks.

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Step 5: Aeration Tanks

The wastewater is now treated through a biological process to stabilize the dissolved and finely suspended impurities.

This is an activated sludge processes and involves the use of bacteria and microscopic organisms.

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Wastewater during Aeration

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Step 6: Secondary Treatment (Final Clarifiers)

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Sludge Collected from Secondary Treatment

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Step 7: Disinfection

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Final Effluent

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Step 8: Sludge Disposal

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Raw SludgeSludge from the primary settling tank

Centrifuges

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The Final Effluent• Technology is excellent in allowing only minute traces of many

substances to be found in the final effluent.• We need to be aware that what we put down the drain may make

its way back into the environment and possible back into our drinking water.

• Research shows that these products can remain in wastewater effluent:– Personal Care Products– Estrogen– Sugars– Pharmaceuticals

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Link to Population

• Wastewater generation will increase as population increases.

• In London, the surcharge for wastewater is based on water consumption.