Wastewater TreatmentReview

Combined Sewers 1

Carry both sewage and storm water. During average rainfalls the volume of

water is 5-15 times greater than normal. Sewage treatment plants are not

designed to process this massive volume of water.

During storms, untreated sewage and storm water may flow directly into river.◦ Ex. Potomac River, Washington D.C.

21. Activated sludge process-air is pumped into the tank which supplies bacteria with the oxygen they need to break down the organic matter. Then pumped to a second tank where remaining solids settle out.

The speed that wastewater moves through the soil

Percolation 3

4. Digesters- sludge from the primary and secondary settling tanks is piped to large tanks that re heated to 95F. Sludge held 15-20 days so anaerobic bacteria in waste can digest more organic material. Natural gas or methane is a waste product. Some is burned to provide heat for digesters and also heat for buildings nearby.

Sewage Treatment Plants5. As sewage enters, it flows through a vertical

bar screen that removes rags, sticks, and other large solids. The trash is scraped from bars and taken to a landfill

Sewage Treatment Plants6. Primary Treatment: physical separation of

liquids and solids.1/3rd of the suspended solids (organic matter) settles out to the bottom of the tank and called sludge. Floating grease and oils are skimmed off the surface of the water. The sludge and the effluent, the partially treated wastewater, are piped to separate tanks for further treatment.

7 BIOSOLIDS Sludge = biosolids

WHAT DO WE DO WITH IT?1. EPA approved sites off the coast2. Farmers can use as fertilizers but must be

tested for disease-causing agents and nutrient content (N P K)

3. Used to make compost

8 Sewage Treatment PlantsEffluentPartially treated wastewater that remains after

solids are removed by settlingThe treated wastewater that enters a river through

the outfall pipe at a sewage treatment plant

Holds wastewater before it enters the soil absorption field.

Septic tank 9

10 Chlorination After secondary treatment, wastewater is

disinfected through an outfall pipe into a body of water nearby.

Chlorination – sodium hypochlorite is added to kill any disease-causing bacteria that might remain in the water.

Disadvantage – chlorine reacts with organic compounds to form trihalomethanes, a carcinogenic. Chlorine is also toxic to some aquatic organisms.

11 Sewage Treatment PlantsSame as # 6 - 1/3rd of the suspended solids (organic matter) settles out to the bottom of the tank and called sludge.

SLUDGE = BIOSOLIDS

12 The rivers smelled of sewage and water-

borne diseases: diseases cause by organisms in the water were common

In the mid 1800’s – 25000 people living near the river died of cholera

Caused by Vibrio cholerae bacteria in wastes in the water.

13Primary and Secondary treatment can remove 85% of

the organic matter and nutrients from the sewage.

To reduce the amount of organic matter

14 2. Trickling filters - a tank filled with a rock-like or

grid system that is coated with slime, which contains algae, bacteria, and other pollutant tolerant organisms. The effluent is sprayed over the tank and as it trickles over the organisms, they remove most of the organic matter and nutrients from the wastewater.

15 BIOSOLIDS Sludge = biosolids

WHAT DO WE DO WITH IT?1. EPA approved sites off the coast2. Farmers can use as fertilizers but must be

tested for disease-causing agents and nutrient content (N P K)

3. Used to make compost, landscape plants, fields where corn is grown for farm animals

16Pretreatment Industries must pretreat wastewater before

dumping it into the sewers to reduce the levels of heavy metals.

Required to pretreat wastewater so toxic wastes don’t interfere with the treatment process.

17 Lagoons & Aquaculture Another method for primary and

secondary treatment that requires large amounts of land and less expensive to build/maintain.

A lagoon is a shallow pond where sewage is held for 20-30 days.

In warm climates, algae and bacteria in a series of lagoons provide acceptable primary and secondary sewage treatment.

18. Digesters- sludge from the primary and secondary settling tanks is piped to large tanks that re heated to 95F. Sludge held 15-20 days so anaerobic bacteria in waste can digest more organic material. Natural gas or methane is a waste product. Some is burned to provide heat for digesters and also heat for buildings nearby.

Will pollute nearby streams due to leaching of too much sludge or septage is applied to land nearby.

19. Nitrogen

20 Septic Tanks

Bacteria normally digest about 50% of the solids that remain in the tank. The remainder will accumulated in the bottom as sludge.

The mixture of fluids and solids pumped from the tank is called septage. Septage contains disease-causing organisms. It us usually disposed as spray on farmland.

All cities are required by law to provide both primary and secondary sewage treatment before releasing wastewater into a river.

21 Cities

22 Lagoons

In warmer climates, Hyacinths are added to lagoons to control odors, they use nitrates and phosphates, and roots filter the water.

In cooler climates, duckweed, watercress or cattails are used.

To control mosquitoes, fish that eat the larvae and bats that eat the adults are introduced.

23 Pretreatment Industries must pretreat wastewater before

dumping it into the sewers to reduce the levels of heavy metals.

Required to pretreat wastewater so toxic wastes don’t interfere with the treatment process.

24Primary and Secondary treatment can remove 85% of

the organic matter and nutrients from the sewage.

25The 2000 National Water Quality Inventory

reports that: 40% of streams 45% of lakes 50% of estuaries

were not clean enough to support fishing and swimming.

26. YES Septic Tank – a large tank buried in the

ground to treat sewage from an individual home or business. ◦ Solids settle to the bottom, bacteria break down

organic matter, and the effluent flows through piles into the soil absorption field (drain field).

27 After secondary treatment, wastewater is

disinfected through an outfall pipe into a body of water nearby.

Chlorination – sodium hypochlorite is added to kill any disease-causing bacteria that might remain in the water.

Disadvantage – chlorine reacts with organic compounds to form trihalomethanes, a carcinogenic. Chlorine is also toxic to some aquatic organisms.

28. Combined Sewers Carry both sewage and storm water. During average rainfalls the volume of

water is 5-15 times greater than normal. Sewage treatment plants are not

designed to process this massive volume of water.

During storms, untreated sewage and storm water may flow directly into river.◦ Ex. Potomac River, Washington D.C.

29 For many years our rivers were used to

carry wastewater away from the cities. The industrial revolution and the invention

of the w.c. (water closet) increased the river’s load of wastes(organic matter).

The rivers smelled of sewage and water-borne diseases: diseases cause by organisms in the water were common

The removal of organic matter and nutrients from wastewater is dependent on the length of time the wastewater remains in the treatment tanks or in the lagoon.

30

31 Sludge = biosolids

WHAT DO WE DO WITH IT?1. EPA approved sites off the coast2. Farmers can use as fertilizers but must be

tested for disease-causing agents and nutrient content (N P K)

3. Used to make compost, landscape plants, fields where corn is grown for farm animals

4. Golf course, corn fields

32. Septic Tank – a large tank buried in the

ground to treat sewage from an individual home or business.

Holds wastewater for at least 24 hours before being released into

drainage field