Transcript Week 5 : Wastewater Treatment

BCE3403 – Environmental
Engineering
Wastewater Treatment
Mdm Nur Syazwani bt Noor Rodi
Wastewater Treatment
Learning outcome;
1. Be able to describe the sources of wastewater.
2. Be able to explain on the wastewater treatment
process.
3. Be able to differentiate centralized and
decentralized system in water treatment plant.
4. Be able to discuss on the sludge disposal
methods.
Wastewater
What is wastewater?
 Any water that has been used by some human
domestic, agricultural or industrial activity. It
also include storm water runoff.
 All these water go into larger pipes called
sewers.
 The sewers take all the wastewater to the
treatment works.
Municipal sewage system
Wastewater
Sources of wastewater;
1. Domestic : This comes from residential sources
including toilets, sinks, bathing, and laundry. It
can contain body wastes containing intestinal
disease organisms.
2. Non domestic : This is discharged by farms
manufacturing processes, hospitals, restaurants,
commercial enterprises and also stormwater.
Wastewater
What is in the wastewater ? 1. Organisms
 organism is a living thing (such as animal, plant,
fungus, or micro-organism).
 An organism may either be unicellular (single-celled)
or be composed of, as in humans, many billions of cells
grouped into specialized tissues and organs.
 a variety of bacteria, protozoa and works work to
breakdown certain carbon-based (organic) pollution in
wastewater by consuming them.
Wastewater
What is in the wastewater ? 2. Pathogen
 is a biological agent that causes disease or illness to its
host.
 The term pathogen is derived from the Greek "that
which produces suffering.“
 The body contains many natural defenses against some
of the common pathogens in the form of the human
immune system and by some "helpful" bacteria.
Wastewater
What is in the wastewater ? 3. Organic Matter
 Organic matter is matter that has come from a
once-living organism; is capable of decay, or the
product of decay; or is composed of organic
compounds.
 An organic compound is any member of a large
class of chemical compounds whose molecules
contain carbon.
Organic compound e.g.: methane
Wastewater
Objectives of wastewater treatment;
1. One of the principle objectives of wastewater
treatment is to prevent as much of this "oxygendemanding" organic material as possible.
2. Other objectives of wastewater treatment
include, removal of objectionable items,
nutrients and heavy metals.
Conventional Wastewater Treatment Overview
1. Primary Treatment
 Screening
Grit & grease Removal
Sedimentation
Primary
2. Secondary Treatment
 Activated Sludge, Aerated Lagoon, Trickling
Filter etc.
3. Sludge Treatment and Disposal
Conventional Wastewater Treatment Overview
Conventional Wastewater Treatment Overview
Wastewater - Primary Treatment
Primary treatment involves:
1. Screening – to remove large objects
2. Grit chamber – slows down the flow to allow
grit to fall out
3. Primary sedimentation tank – settle able solids
settle out, while oils float to the top and are
skimmed off.
Primary Treatment - Screening
 Screening is the first technique employed in the
wastewater treatment process.
 This step removes all sorts of refuse that has
arrived with the wastewater such as plastic,
branches, rags, and metals.
 The screening process is used primarily to
present the clogging and interference of the
following wastewater treatment processes.
Primary Treatment - Screening
Types of Screens
1. Coarse Screens: Coarse screens also called racks, are usually bar screens,
composed of vertical or inclined bars spaced at equal intervals across a
channel through which sewage flows.
2. Medium Screens: Medium screens have clear openings of 20 to 50 mm.Bar
are usually 10 mm thick on the upstream side and taper slightly to the
downstream side.
3. Fine Screens: Fine screens are mechanically cleaned devices using perforated
plates, woven wire cloth or very closely spaced bars with clear openings of
less than 20 mm. Fine screens are not normally suitable for sewage because of
clogging possibilities.
Primary Treatment - Screening
 This type of screen, called a bar screen, removes
debris from wastewater.
Primary Process – Grit removal
Grit Removal
 The purpose of grit removal is to remove the
heavy inorganic solids, which could cause
excessive mechanical wear.
 Grit includes sand, gravel, clay, egg shells,
coffee grounds, metal filings, seeds and other
similiar materials.
Primary Process – Grit removal
These items settle to the bottom of the grit
channels by gravity
Primary Process – Grit removal
• There are several devices or processes used for
grit removal.
• All of the processes are based on the fact that grit
is heavier than the organic solids that should be
kept in suspension for subsequent treatment.
• Grit removal facilities basically consist of an
enlarged channel area where reduce flow
velocities allow grit to settle out.
Primary Process – Grease removal
• Many oils can be recovered from open water
surfaces by skimming devices - which is
designed to separate the oil and suspended solids
from their wastewater effluents.
• However, hydraulic oils and the majority of oils
that have degraded to any extent will also have a
soluble or emulsified component that will require
further treatment to eliminate.
Primary Process – Grease removal
Primary Process –
Primary Sedimentation (PST)
Primary Process –
Primary Sedimentation (PST)
 Sedimentation simply entails the physical settling
of matter, due to its density, buoyancy, and the
force of gravity.
 Most of the suspended solids in wastewater are
sticky in nature and flocculate naturally – type-2
settling without the addition of coagulants.
Primary Process –
Primary Sedimentation (PST)
 Through sedimentation, the larger solids are
removed in order to facilitate the efficiency of
the following procedures.
 The tank is large enough that fecal solids can
settle.
 Scum removal is accomplished by having sludge
scrappers.
Primary Process
 After primary treatment process, nearly 50-70%
of the solids settle down under influence of
gravity and 25% – 55 % of the incoming BOD
are removed.
 But colloidal and dissolved constitutes are not
affected.
 Continue with the secondary treatment.
Wastewater - Secondary Treatment
 Typically utilize biological treatment processes,
in which microorganisms convert non-settleable
solids to settleable solids.
 Sedimentation typically follows.
 Options include; activated sludge, aerated
lagoon, trickling filters and rotating biological
contactors.