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 "oxygen-demanding" 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 Primary

Sedimentation

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 - ScreeningTypes 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.