Sewage Treatment

1

IntroductionIntroduction

The bulk of the biodegradable pollutants that can be released into the environment is made up of:1. Domestic wastes2. Institutional liquid waste3. Industrial wastes 4. Agricultural wastes

2

Two Phases Of Water Pollution

•Chemical pollution

•Physical pollution

3

4

Chemicals Pollution

Pesticides and fertilizers that contain nitrates and phosphates are a source of chemicals that cause water pollution. These chemicals seep into the groundwater and mix with runoff moving to lakes and rivers.

Chemical pollution is mainly industrial, with the release of acids, alkali and toxic compounds, which can poison the living organism in the waterways.

5

Physical Pollution

Physical pollution is the release of contaminants into the waterway of materials that can change the water’s physical conditions, as the warm water which it is used for cooling in the industries.

6

There are two forms:1.liquid ,2. solid.

Their sources: 1.private houses.2.commercial buildings, 3.institutions like schools and hospitals.

7

Domestic wastes

Composition:

• 99.9% of water by weight, • Dissolved organic material• Suspended solids• Micro-organisms (pathogens) and other components.

8

Organic materials Inorganic materials

Sodium Fats

Calcium Proteins

Magnesium Carbohydrates

Chlorine Detergents

Sulphates

Bicarbonates

Nitrates

Ammonia

Traces of heavy metals

9

75% of solids and 40% of the dissolved material are organic.

Two methods to detect the quality of the sewage:

BOD5: biological oxygen demand in five days (expressed by mg/L or g/m³ at 25 c for 5 days). �

COD: chemical oxygen demand using an oxidizing agent.

10

Its objective is to produce an environmentally-safe fluid waste stream (or treated effluent) and a solid waste (or treated sludge) suitable for disposal or reuse (usually as farm fertilizer).

11

The quality of the treated waste released from the treatment system depends on:

the volume and condition of the receiving water ,its ability to dilute the waste.

12

Sewage collection and treatment is typically subject to local, state and federal regulations and standards. Industrial sources of wastewater often require specialized treatment processes.

13

Sewage treatment generally involves four stages:

1. primary treatment2. secondary treatment and 3. tertiary treatment.

In addition to these three, some scientists adds the preliminary stage to them obtaining by this four stages.

14

Sewage treatment stages

The preliminary stagePreliminary stage removes materials that can be easily collected like large debris by using screens and grit channels.

15

The influent sewage water is screened to remove all large objects like cans, rags, sticks, plastic packets etc. carried in the sewage stream.

Pre-treatment may include a sand or grit channel where the velocity of the incoming wastewater is adjusted to allow the settlement of large debris. For small sanitary sewer systems, the grit chambers may not be necessary, but grit removal is desirable at larger plants

16

17

Primary treatment stagePrimary treatment consists of temporarily holding the sewage in a quiescent basin where heavy solids can settle to the bottom while oil, grease and lighter solids float to the surface.

The settled and floating materials are removed and the remaining liquid may be discharged or subjected to secondary treatment.

18

Secondary treatment stage

Secondary treatment removes dissolved and suspended biological matter.

Secondary treatment is typically performed by micro-organisms in a managed habitat.

19

Secondary treatment stage

Secondary treatment may require a separation process to remove the micro-organisms from the treated water prior to discharge or tertiary treatment.

Secondary treatment systems are classified as fixed-film or suspended-growth systems or ponds and lagoons .

20

1. Fixed-film or attached growth systems include trickling filters, Moving Bed Biofilm Reactors (MBBR), or rotating biological contactors, where the biomass grows on media and the sewage passes over its surface.

21

It is used in the secondary treatment. A trickling filter consists of a fixed bed of rocks, lava, gravel, polyurethane foam, sphagnum peat moss, ceramic, or plastic media over which sewage or other wastewater flows downward and causes a layer of microbial slime (biofilm) to grow, covering the bed of media.

22

Trickling Filters

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.

23

Trickling Filters

Trickling Filters

24

25

26

27

28

Rotating biological contactors

2. Suspended-growth systems include activated sludge, where the biomass is mixed with the sewage and can be operated in a smaller space than fixed-film systems that treat the same amount of water.

However, fixed-film systems are more able to cope with drastic changes in the amount of biological material and can provide higher removal rates for organic material and suspended solids than suspended growth systems.

29

Suspended Film Systems:– Stir and suspend microorganisms in

wastewater – Settled out as a sludge – Pumped back into the incoming

wastewater – Ex: Activated sludge

Settle sewage from primary sedimentation

Waste Sludge

Air

Settlement

Effluent

Flow

Sludge Sludge

recycled

31

Aeration and

rapid mixing

Settlingcollects sludge

on bottom

Secondary process

airdiffuser

From

pri

mary

pro

cess

To te

rtiary

pro

cess

33

• In general, activated sludge like plants encompass a variety of mechanisms and processes that offer dissolved oxygen to promote the growth of microorganisms that substantially removes organic material.

34

Activated sludge:•mixed community of microorganisms,•Both aerobic and anaerobic bacteria may exist,•Biological floc is formed,

• The basic process is given below: sewage + microorganisms + oxygen = growth of

microorganisms (biomass) + Carbon dioxide.

36

The result will be

A nearly solid free water that can be

discharged back into the river

It can undergo further treatment (tertiary

treatment) if the pollution level in it

can still causes some risks.

Or

Settle sewage from primary sedimentation

Waste Sludge

Air

Settlement

Effluent

Flow

Sludge Sludge

recycled

37

Physical components of activated sludge process

• Aeration tank – oxygen is introduced into the system

• Aeration source – ensure that adequate oxygen is fed into the tank – provided pure oxygen or compressed air

• Secondary clarifiers Activated-sludge solids separate from the surrounding wastewater

• Activated sludge outflow line– Pump activated sludge

back to the aeration tank • Effluent outflow line

– discharged effluent into bay or tertiary treatment plant

Sludge treatment and disposal

This treatment and disposal are applied by several ways that include:

43

Disposal of excess sludge

Reduction in sludge

production

Disposal of the excess sludge can be applied by:

44

3. Composting

3. Ponds And Lagoons

A pond is a body of standing water, either natural or man-made, that is usually smaller than a lake.

45

The enclosed body of water behind a barrier reef or barrier

islands or enclosed by an atoll reef is called a lagoon.

46

Ponds And Lagoons

Stabilization ponds or lagoons are also known as Oxidation Ponds.

They are used for simple secondary treatment of sewage effluents.

Within an oxidation pond, heterotrophic bacteria degrade organic matter in the sewage which results in production of cellular material and minerals.

47

The production of these minerals supports the growth of algae in the oxidation pond. Growth of algal populations allows further decomposition of the organic matter by producing oxygen. The production of this oxygen replenishes the oxygen used by the heterotrophic bacteria.

48

Disadvantages of Oxidation ponds

Oxidation ponds tend to be inefficient Require large holding capacities The degradation is relatively slow The effluents containing the oxidized products need to be periodically removed from the ponds.

49

50

Tertiary treatment: removing of phosphate, nitrate, and pathogenic micro-organisms to produce potable water and to prevent eutrophication.

Involving chemical precipitation, disinfection with chlorine, filtration through sand filters, and the use of maturation ponds.

N.B: The purpose of disinfection in the treatment of waste water is to substantially reduce the number of microorganisms in the water to be discharged back into the environment.

51

Tertiary treatment stage

Tertiary treatment stage

52

53

Preliminary treatment Primary treatment Secondary

treatment Tertiary treatment

54

55

56