Water Treatment

Chapter 11

Sewage Treatment• Rationale• More than 500 pathogenic bacteria, viruses, and

parasites can travel from human or animal excrement through water.

• Natural Processes• In many areas, outdoor urination and defecation is

the norm.• When population densities are low, natural processes can

quickly eliminate waste.

• Artificial Wetlands Are a Low Cost Method • Natural water purification

• Effluent can be used to irrigate crops or raise fish for human consumption.

Lincoln Wastewater FacilitiesUnderneath and throughout Lincoln are over 1,000 miles of sanitary sewer lines and 16 pumping stations

114 employees at solid waste and wastewater facilities

Theresa Street Facility

27th & Cornhusker

20 million gallons of water daily

Northeast Facility

5 million gallons of water daily

Combined this would fill Holmes Lake in 3.5 days

Lincoln Northeast Treatment Facility

3. aeration basin

1. screening and grit basin

2. primary clarifiers

4. secondary clarifiers

5. disinfection

6. solids digestion7. solids dewatering

Municipal Sewage Treatment

1. Primary Treatment - Physical separation of large solids from the waste stream

• screening, pumping, grit removal• get the big stuff out• material collected hauled to

landfill

• primary clarification• removes settleable solids• removes floatable

materials like grease• 2-4 hrs

primary clarifier

2. Secondary Treatment - Biological degradation of dissolved organic compounds

• Biological Treatment• Aeration basin• removes pollutants with

bacteria and protozoans• must be aerated• 8 hrs

• Secondary clarification• separates treated

wastewater from microorganism (from aeration basin)

• Disinfection• chlorination or UV light

Municipal Sewage Treatment

2. Solids processing - Biological degradation of dissolved organic compounds

• solids digestion• anaerobic digesters to

stabilize organic solids• produce methane gas

(CH4) which can power turbine to generate electricity

• 18-20 days• solids dewatering

• removes excess water• solids (organ rich

material)

Municipal Sewage Treatment

Belt Filter Press Dewatering

Anaerobic Digesters

2. Solids processing - Biological degradation of dissolved organic compounds

• land application• soil amendment and

fertilizer• alternatively dewatering is

replaced by collecting liquid and using it as fertilizer on city owned land

Municipal Sewage Treatment Subsurface Biosolids Injection

Municipal Sewage Treatment

3. Tertiary Treatment - Removal of plant nutrients (nitrates and phosphates) from secondary effluent.

• Chemicals, or natural wetlands

• Lincoln does not have tertiary treatment

• In many US cities, sanitary sewers are connected to storm sewers.• Heavy storms can overload

the system, causing by-pass dumping of raw sewage and toxic runoff directly into watercourses

Unusual Pollutants are Now Being Detected in Surface Waters