ADVANCED WASTEWATER TREATMENT

• Removal of Nitrogen and Phosphorus

• Removal of Solids

• Removal of Dissolved Solids which constitute the heavy metals, viruses, refractory organics

Applications of tertiary treatment

Centrifugation

suspended solids removal through centrifugal force

air flotation

similar to dissolved air flotation

Ion Exchange

method to remove hardness

Microporous Membrane Filtration

uses membrane as its media

Adsorption

uses activated carbon

Chemical Oxidation

introduce oxidizers to crush a certain compound to form a new compound either solid or gas in order to settle

Disinfection

Water treatment process designed to **destroy disease causing microorganisms.**

Disinfection

The **process of killing (inactivating) harmful and objectionable bacteria**, cysts and other microorganisms (pathogenic) by various **agents such as chemicals, heat, ultraviolet light, ultrasonic waves, or radiation.**

Disinfection

usually **considered a 99+% kill compared to sterilization** that generally attains 100% kill.

Chlorine

is **one of the most widely used disinfectants** and is a **strong oxidant that rapidly kills many harmful micro-organisms.**

Chlorine

is **over three times more effective as a disinfectant against Escherichia coli** than an equivalent concentration of bromine, and o**ver six times more effective than an equivalent concentration of iodine.**

Chlorine

has been **used for applications, such as the deactivation of pathogens include viruses**, **bacteria** including Salmonella, Cholera, Campylobacter and Shigella, and protozoa, including Giardia lamblia and other cryptosporidia in drinking water, swimming pool water and wastewater

• Sodium hypochlorite,

• Calcium hypochlorite,

• Gaseous chlorine, and

• Chlorine dioxide.

Types of Chlorine

Sodium hypochlorite (NaOCl)

a y**ellowish liquid with an active chlorine concentration of 10-15% pH around 13.0**. It is n**ot very stable**, and when it comes in contact with air, light or high temperatures, the chlorine evaporates and therefore its concentration in water decreases. The chemical reaction with water is:

NaOCI + H2O

Calcium Hypochlorite

is **more stable than sodium hypochlorite**, and c**ontains a higher chlorine concentration (30-75%)**. The chemical reaction with water is:

Ca(OCI)2 + 2H20

Gaseous Chlorine (Cl2)

This is **chlorine in its pure form**, which is a very strong oxidizing and disinfecting agent. It is **stored and transported in cylinders, as pressure-liquefied gas**. The chemical reaction with water is:

CI2(g) + H2O

Chlorine dioxide (CIO2)

**very different from the other forms of chlorine** described above as it **cannot be compressed or commercially stored**, because it becomes volatile under pressure. Therefore it is **always produced on site as part of the disinfection process.**

Sodium Chlorite; Hypochlorous Acid

__________ and __________ are s**tored in separate containers and are injected into a chlorine dioxide generator where they react and produce chlorine dioxide.**

chlorine dioxide

The concentrations of ____________ needed to achieve effective disinfection are **lower than the concentrations needed when using other chlorine forms.**

UV Treatment

**leaves no residue in the water due to use of light instead of chemical disinfectants.** However, this method alone (as well as chlorination alone) will not remove toxins from bacteria, pesticides, heavy metals, etc. from water.

Ultraviolet

is **very effective at inactivating cysts, in low turbidity water**. UV light's disinfection effectiveness **decreases as turbidity increases**, a result of the absorption, scattering, and shadowing caused by the suspended solids.

Ozonation

**Formed by passing dry air (or oxygen) through high voltage electrodes t**o produce gaseous ozone that is bubbled into the water to be treated

Treated sewage sludge (Biosolids)

valuable product of the wastewater treatment works.

Sludge

**contains organic material and nutrients** that are important for agriculture or land reclamation.

* Sludge Removal
* Storage
* Conditioning
* Dewatering
* Disposal/Reuse

Sludge Handling and Processes

Primary Sludge

• **3 to 8% solids**

• About 70% organic material

Secondary Sludge

• **Consists of wasted microorganisms and inert materials**

• About 90% organic material

• WAS: 0.5 to 2% solids

• Trickling filter sludge: 2-5% solids

Tertiary Sludge

• If secondary clarifier is used to remove phosphate, t**his sludge will also contain chemical precipitates (more difficult to treat)**

• Denitrification sludges - similar to WAS sludge

Flotation and Gravity Thickening

processes under Thickening

Flotation

• Especially **effective on activated sludge**

• Increases solids content from 0.5 - 1% to 3-6%

Gravity Thickening

• **Best with primary sludge**

• Increases solids content from 1-3% to 10%

Aerobic and Anaerobic Digestion

processes under Stabilization

Aerobic Digestion

• **Extension of activated sludge**

• Accomplished by aeration of sludge then followed by sedimentation

• Supernatant goes back to head of plant (high in BOD, TKN, total-P)

• Treated sludge is 3% solids

Anaerobic Digestion

• 2 stage: **acid fermentation** followed by **methane production**

• Advantages:

• produce methane

• do not add oxygen

• As with aerobic digestion, supernatant goes to headworks

Chemical Conditioning and Heat Treatment

processes under Conditioning

Chemical Conditioning

• Addition of lime, ferric chloride, or alum

Heat Treatment

• High temperature (175-230 °C)

• High pressures (10 to 20 atmospheres)

• Advantages

• bound water is released and sludge is easily dewatered

Disadvantages

• complex process

• highly concentrated liquid stream

Sludge Drying Beds and Filtration

processes under De-watering

Sludge Drying Beds

• Most popular method

• Simple

• Low maintenance

• Effected by climate

Filtration

• Apply vacuum to pull out water

• Force out water by essentially **squeezing water between two moving filter belts**

Incineration and Wet Oxidation

processes under Volume Reduction

Incineration

• **Complete evaporation of water from sludge**

• Requires fuel

• Solid material is inert

• Exhaust air must be treated prior to discharge

Wet Oxidation

• **Treated sludge is wet**

• Requires energy

• Solid material is inert

• Exhaust air must be treated prior to discharge

* Land Spreading
* Municipal Solid Waste Landfill
* Utilization in other materials

methods of Sludge Disposal

Excess Sludge

should be subjected for treatment prior its disposal or reuse.

Biosolids

Treated sludge is called _________ which is **stable material for disposal to landfill or safe for reuse such as land application.**

COD

The **amount of chemically oxidizable materials present in the wastewater**

BOD

The **amount of organic matter that can be biologically oxidized under controlled conditions** (5days @ 20 deg C in dark)

Extended Aeration

a type of **activated sludge process with no primary settling** and **long aerobic detention time** to generate less excess sludge overall

Sequencing Batch Reactor

fill and draw activated system

* Insufficient and Inaccurate Information
* Land Availability
* Uncontrolled Urban Development
* Customer Acceptance

Challenges in Sewerage Service

* Solid Waste
* Uncontrollable Influent Quality
* Hydraulic Shock Loading

Operational Challenges

Lagoon (Oxidation Ponds)

a **man-made lake or body of water** in which organic waste s are consumed or oxidized by bacteria.

Conventional Activated Sludge (CAS)

a continuous flow suspended growth process

Moving Bed Biofilm Reactor (MBBR)

a **hybrid of Suspended growth and Fixed film system**

STM AEROTOR

an activated sludge and fixed film wherein the **media is aerated on the surface**