WASTEWATER ENGINEERING TREATMENT SYSTEMS (PART 2)

raw sludge or primary sludge

the mass of settled solids

90 - 95%

Primary Treatment Removal Efficiency of Settleable Solids

50 - 65%

Primary Treatment Removal Efficiency of Suspended Solids

20 - 35%

Primary Treatment Removal Efficiency of BOD

sedimentation tank

After preliminary treatment, the WW still contains light organic suspended solids, some of which can be removed from the sewage by gravity in a __________.

Settling and Clarification/Clarifier

other terms for sedimentation

sedimentation; suspended solids

The objective of treatment by ______ is to remove readily available settleable solids and floating materials and thus reduce the ______ content.

sludge

suspended solids

scum

floating materials

Primary Tanks or Clarifiers

Settling tanks that receive raw wastewater **prior to biological and/or chemical treatment** are called _____________ where sedimentation or settling predominates.

Primary Clarifier

its purpose is to remove suspended solids from wastewater

1 to 2 hours

Primary Tank’s Detention Time

* **D**iscrete Particle Settling
* **F**locculent Settling
* **H**indered (or zone) Settling
* **C**ompression

Types of Settling Phenomena in WW

* Zeta Potential
* Van der Waals

Natural Forces involved in Settling

Zeta Potential

natural repelling force that **holds particles in suspension**

Van der Waals

natural attracting forces that **we want to enhance**

Coagulation

refers to the series of chemical and mechanical operations by which coagulants are applied and made effective.

rapid mixing

_______ to disperse coagulant chemicals by violent agitation into the water being treated

flocculation

_______ to agglomerate small particles into well-defined floc by gentle agitation for a much longer time

* Alum - aluminum sulfate
* Sodium aluminate
* Ferric sulfate
* Ferrous sulfate
* Ferric chloride
* Polymers

coagulants

Flocculation

it follows coagulation in the conventional water treatment process

Flocculation

the physical process of slowly mixing the coagulated water to increase the probability of particle collision.

effective mixing

Through experience, we see that __________ reduces the required amount of chemicals and greatly improves the sedimentation process, which results in longer filter runs and higher quality finished water.

Polymers

To increase the speed of floc formation and the strength and weight of the floc, _______ are often added

Jar Test

simulation of coagulation or flocculation process

Jar Test

determine the optimum dosage of coagulant

Dissolved Air Flotation

**injection of air while the liquid is under pressure** of several atmospheres, followed by the release of pressure to the atmospheric level.

Dispersed Air Flotation

air bubbles are formed by introducing the gas phase directly into the liquid phase through a reducing impeller or thru diffuser

Vacuum Air Flotation

saturation with air at atmospheric pressure, followed by application of a vacuum to the liquid.

* Aluminum and ferric salts
* Activated silica

chemical additives

Secondary/Biological Treatment

it is biological in nature and aims to remove oxygen demanding pollutants

1. **S**uspended Growth Biological Treatment
2. **A**ttached Growth Biological Treatment
3. **C**ombined Processes
4. **L**agoon Processes

Types of Secondary Treatment

* **C**arbonaceous BOD and Suspended Solids Removal
* **N**itrification
* **D**enitrification
* **B**iological Nutrients Removal
* **B**iological Phosphorus Removal
* **S**olid Destruction/Stabilization

Objectives of Secondary Treatment

Homogeneous Reactions

reactants are distributed uniformly throughout the fluid so that the potential for reaction at any point within the fluid is the same. It can either be ***irreversible or reversible.***

Heterogeneous Reactions

occur between one or more constituents that can be identified with specific sites, such as those on an ion-exchange resin and those that require the presence of a solid-phase catalyst.

Batch

flow is **neither entering nor leaving the reactor.** The liquid contents are mixed thoroughly.

Plug-Flow or Tubular Flow

fluid particles pass through the tank and are **discharged in the same sequence in which they enter**. The particles retain their identity and remain in the tank for a time equal to the theoretical detention time. This type of flow is **approximated in long tanks** with a long tanks with a high length-to-width ratio in which longitudinal dispersion is minimal or absent.

Continuous-Flow Stirred Tank Reactor (CFSTR)

Completely-Mix Reactor

Continuous-Flow Stirred Tank Reactor (CFSTR)

The reactants entering the reactor (which are dispersed immediately) and the **products flowing out from the reactor are considered as continuou**s.

Arbitrary Flow Reactor

any degree of **partial mixing** between plug-flow and complete-mix.

Packed Bed Reactor

Are **filled with inert packing media** for the growth of biomass

Fluidized Bed Reactor

filled with the p**acking material that expands and gets fluidized** when wastewater moves upward in the reactor.

Trickling Filter

It consists of a fixed bed of rocks, gravel, slag, polyurethane foam, sphagnum peat moss, ceramic, or plastic media over which sewage or other wastewater flows downward and causes (biofilm) to grow, covering the bed of media.

Aerobic conditions

_______________ are maintained by splashing, diffusion, and either by forced-air flowing through the bed or natural convection of air if the filter medium is porous.

Rotating Biological Contactor (RBC)

allows the wastewater to come in contact with a biological medium in order to remove pollutants in the wastewater before discharge of the treated wastewater to the environment, usually a body of water (river, lake or ocean).

Rotating Biological Contactor (RBC)

It consists of a series of closely spaced, parallel discs mounted on a rotating shaft which is supported just above the surface of the waste water.

Microorganisms

________________ grow on the surface of the discs where biological degradation of the ww pollutants takes place

Activated Sludge Process

The _______________ consists of the oxidation of organic wastes by bacteria followed by the separation of the suspended solids from the treated wastewater.

* **I**nfluent
* **A**eration Tank
* **C**larifier
* **R**eturn Sludge
* **W**aste Sludge Removal

The activated sludge process consists of :

settling of the sludge

Following ______________, a portion of the organism mass is rećycled to repeát the treatment process. The overall result is a clear supernatant and a well-managed activated sludge biomass, which is the sum of all biological materials in the secondary treatment system.

2 to 8 days

retention time for young sludge

>8 days

retention time for old sludge

Mixed Liquor Suspended Solids (MLSS)

the ratio of waste streams and microorganism

Activated Sludge

a biological process where microorganisms are mixed with screened influent and grown in an aeration tank.

Settling Tank

where mixed liquor is conveyed after a few hours of detention in the aeration tank

RAS Pump; WAS Pump

The settled mixed liquor is returned by _______ to the aeration tank for another cycle of contact. The excess microorganisms are removed from the process by _______

Microorganisms

**Bacteria, prótozoa, viruses, fungi and algae** are among the various life forms one can expect to find in the activated sludge system.

Bacteria

the most numeroús and the most important to the biological treatment process

ROTATORIA

rotifers

NEMATODA

roundworms

Virus and Fungi

Little importance as far as removing food material from the wastewater

Sarcodina

amoeboids forms

Mastigophora

flagellates

Ciliata

free swimming ciliates and stalked ciliates

Suctoreans

suctoria

Operator

Normally it is the _________ that **created the conditions favorable to the microorganism.**

* Food
* Hydraulic Load
* Oxygen
* Temperature
* pH
* Toxicity
* Trace Nutrients

Environmental Factors for Healthy Microorganisms Growth

organic

The food consumed by microorganisms is mostly _______ materials in wastewater.

greater; more food; faster

The ______ the organic load into the biological system, the ______ there is available and the ______ the microorganisms will grow.

Hydraulic Load

refers to the amount of water entering the aeration tank

increases; decreases; food supply; slowing

As the hydraulic load ______, the concentration of organics may ______ that would have the effect of decreasing the ______ and ______ the growth rate

Aerobic Respiration

it is the process where most aquatic microorganisms, including protozoa, fungi and most bacteria use free DO in the **process of converting food to energy and raw materials for growth**

Aerobes

organisms that function in aerobic respiration is called

Facultative Respiration

process where a few bacteria obtain the oxygen they need from chemically bound oxygen compounds such as **nitrate and sulfate**

Facultative Aerobes

organisms that function Facultative Respiration is called

aerobic respiration process

The ____________ is more efficient at oxidizing organics than the anaerobic respiration process. Thus, to keep the microorganism working at high efficiency, it is desirable to provide sufficient DO levels within the aeration tank.

temperature; rate of reaction

When the _________ increases, the _________ increases; thus the rate of cellular growth or the microorganism population increases.

doubles

The rate of microorganism growth _____ every 10 °C increase in temperature up to a limiting temperature.

slow

at low temp. the growth is _____

moderate

Most microorganisms do best at _______ temperatures

Psychrophilic

cold-loving

Mesophilic

mid-range temp.

Thermophiles

can survive in extreme temp.

Acid conditions (low pH)

__________ can destroy the ability to convert food to energy and raw materials

6\.5 to 8.5

Most microorganisms do well at a pH of ________

toxic materials; smaller amounts

If _______ enter the system in **large amounts**, they could **destroy all the microorganisms**. In _______, they could **decrease the growth rate** or **selectively destroy the more susceptible microorganism.**

BOD5:N:P:Fe = 100:5:1:0.5

weight ratio for industrial WTP

* **C**omplete Mix Activated Sludge Process
* **C**onventional (Plug Flow)
* **C**ontact Stabilization
* **S**tep Feed
* **E**xtended Aeration
* **O**xidation Ditch
* **H**igh Purity Oxygen
* **S**equential Batch Reactor (SBR)

Activated Sludge Modes

Acidophiles

can survive in acid pH level

Alkalinophiles

can survive in alkaline pH level

Neutrophiles

can survive in neutral or mid-range pH

Anaerobic Pond

* 2-5 m deep
* Receive high organic loading (usually >100g BOD/m3 d)
* contain **no DO and no algae**
* Primary function is **BOD Removal**
* Retention time is **1 day**

Facultative Pond

"Biological bacteria digest the organic wastes in the wastewater.” The process is improved and prolonged with the use or baffle walls to avoid the short-circuiting of the flow of the wastewater. "

Facultative Pond

1-2 m deep

Primary function is **removal of BOD**

Area: **2 ha**

Depth: **1.85 m**

Retention Time: **5 Days**

Primary Facultative Pond

type of Facultative Pond that receive raw ww

Secondary Facultative Pond

type of Facultative Pond that receive settled ww

Maturation Pond

**Odor, settleable solids and fecal bacteria** are further reduced in this pond due to the ultraviolet 1ight disinfection from the sunlight and can now serve as a breeding ground for fish culture. "

Maturation Pond

1-1.5 m deep

**Receive the effluent from the Facultative Pond**

Primary function is **removal of pathogens**

Area: **1.5 ha**

Depth: **1.85 m**

Retention Time: **6 Days**

Constructed Wetlands

engineered systems that **use natural functions of vegetation, soil, and organisms to treat different water streams**. Depending on the type of wastewater that has to be treated the system has to be adjusted accordingly which means that pre- or post-treatments might be necessary

Constructed Wetlands

can be **designed to emulate the features of natural wetlands**, such as acting as a biofilter or removing sediments and pollutants such as heavy metals from the water. Some constructed wetlands **may also serve as a habitat for native and migratory wildlife**, although that is usually not their main purpose.