Chapter 22.6 – 22.10 (Wastewater)

Why is wastewater treated

To remove disease-causing microorganisms, To remove harmful chemicals and toxins, To remove particles and impurities, To make water safe and pleasant to drink.

How is drinking water treated

Sedimentation, Coagulation, Filtration, Chlorination and Storage and distribution

6 Main goals of wastewater treatment

1. Remove organic matter

2. eliminate pathogens,

3. remove solids and suspended materials,

4. reduce nutrients (nitrogen and phosphorus),

5. remove toxic chemicals and heavy metals,

6. protect the environment and public health

Wastewater

Water that has been used in homes, industries, or businesses and contains dissolved or suspended waste materials.

Primary Treatment

The first stage of wastewater treatment that uses physical processes (like screening and sedimentation) to remove large solids and settleable materials.

Secondary Treatment

The biological stage where microorganisms break down organic matter (measured as BOD) in aeration tanks or biofilters.

Tertiary Treatment

Advanced treatment that removes nutrients (nitrogen, phosphorus), chemicals, and pathogens to produce high-quality effluent.

BOD (Biochemical Oxygen Demand)

A measure of how much oxygen microorganisms need to break down organic matter in water; high BOD indicates high organic material

Clarifier

A settling tank where solids settle to the bottom (as sludge) and clear water rises to the top; used in both primary and secondary stages.

Sludge

The solid material that settles out of wastewater during treatment; can be further treated and used as fertilizer or disposed of safely.

Floc

Clumps of particles formed when coagulants are added during treatment; these heavier particles settle out during sedimentation.

Aeration

The process of adding air or oxygen to wastewater to help aerobic bacteria break down organic matter during secondary treatment.

Activated Sludge

A mixture of aerated wastewater and microorganisms that consume organic matter; the microorganisms form flocs that settle out in the secondary clarifier.

Effluent

The treated water that leaves a wastewater treatment plant and is released into rivers, lakes, or reused.

Influent

The untreated wastewater that enters a treatment facility.

Disinfection

The final step, where chlorine, ozone, or UV light is used to kill remaining pathogens before discharge.

Digestion

The biological decomposition of organic solids (sludge) by bacteria under anaerobic or aerobic conditions to reduce volume and odor.

Grit Chamber

A tank that slows water flow so that sand, gravel, and other heavy particles settle out before primary treatment.

Scum

The floatable materials (like oils, fats, and grease) that rise to the surface of clarifiers and are skimmed off.

Primary Treatment (from slides)

Uses physical processes such as grates and screens. Allowed to settle om tanks (clarifiers), separation of solids and effluent still has a substantial BOD.

Secondary treatment (from slides)

Uses an aeration basin and mixers that sorts the sludge to the bottom of the inal clarifier and allows treated water to be released. Uses floc

Terirary Treatment Nitrogen removal 1st step

Turms Ammonia to Nitrate. Nitrogen present in sewage as NH3 and Nitrosomonas and Nitrobacter convert ammonia to No3 in aeration basins, called nitrification and costumes a great deal of oxygen

Tertiary Treatment Nitrogen removal 2nd step

Nitrate to Nitrogen gas. Nitrate is converted to N2 gas (denitrification by bacteria. Nitrogen gas bubbles out of waste water. Beneficial because reduces energy required for wastewater treatment

Tertiary Treatment Phosphorous removal

A group of bacteria called PAO’s will remove P under the appropriate conditions. Involves cycling bacteria between anaerobic and aerobic conditions

Chlorine in wastewater disinfection

Gaseous chlorine is dangerous. Forms carciongenic chlorinated organics THM’s

Ultravoielt light for wastewater disinfection

UV light damages bacterial DNA and prevent bacteria from reproducing. If bacteria dont reproduce, they will not be detected n the MPN test

How are indicator organisms (coliforms detected

Standard method - Macconkey broth and water, EMB agar, Gram stain, Membrane Filter

Anaerobic digestion

Bacteria start eating eachother as solids as they are in there for 30 days. Used for high BOD industrial wastewater. Reduces amount of sludge for disposal. Produced methane