MCB of Sewage Treatment & Disposal

8/2/2019 MCB of Sewage Treatment & Disposal

1/22

By

Dr Emmanuel Odjadjare


2/22

MICROBIOLOGY OF SEWAGE

TREATMENT & DISPOSAL


3/22

Introduction Industrial revolution and population growth has resulted

in the generation of increasingly large volume of wastes

These wastes contain pollutants which may be harmful tothe environment and public health

Hence the essence of treating waste is to eliminate ordrastically reduce pollutant content before discharge

Our focus in this class shall be on treatment and disposalof sewage/wastewater

Sewage is used interchangeably with wastewaster incourse of this presentation


4/22

Outline

Types of sewage treatment facilities

Activated sludge system

Microbiology of activated sludge

Stages of treatment of wastewater

Regulatory standards for wastewater effluent qualityEffectiveness of wastewater treatment

Consequences of inadequate wastewater treatment

Microbial pathogens in wastewater


5/22

Types of Sewage Treatment

Facilities

Sewage treatment facilities vary from country to countryand from community to community within the samecountry

It also varies with social status

The degree of treatment vary with the end use orapplication of the sewage


6/22

Oxidation ponds They are effective, low-cost, and simple technology for

reducing the BOD of a wastewater before it is discharged toan aquatic ecosystem It consists of ring or oval shaped channel equipped with

mechanical aeration devices

Screened sewage entering the pond, is aerated by

mechanical devices

Oxidation ponds typically operate in an extended aerationmode with long detention and solids retention times

b d


7/22

Anaerobic pond Consists of a relatively deep (3-4 m) pond which ensures

anaerobiosis

The process is mediated by anaerobic bacteria; producingCH4 & CO2,

Used prior to aerobic treatment, an anaerobic system can bevery effective and economical for removing highconcentrations of BOD5 and COD

Works well in warm climates

Can remove up to 60% BOD @ 20

o

C & as much as 75% at25oC


8/22

Aerobic ponds

This wastewater treatment facility contains bacteria andalgae in suspension

maintains aerobic conditions throughout its depth

There are two types of aerobic ponds:

shallow ponds

aerated ponds


9/22

Shallow pond Shallow aerobic ponds obtain their dissolved oxygen via two

processes:

oxygen transfer between air and water surface, and

oxygen produced by photosynthetic algae

Can remove up 95% soluble BOD

effluent contains large amount of algae


10/22

Aerated ponds

It is similar to an oxidation pond except that it is deeperand mechanical aeration devices are used to transfer oxygeninto the deeper portions of the pond

The aeration device also facilitates a proper mix of thewastewater and bacteria

The main advantage of the aerated pond is that theyrequire less area than oxidation ponds

The disadvantage is that the mechanical aeration devices

require maintenance and external energy source


11/22

Facultative ponds Ponds operate in a facultative manner having aerobic and

anaerobic zones

Solids from the incoming waste settle into the anaerobicsludge near the bottom of the pond and are degradedanaerobically

releasing soluble degradable organic material andnutrients which diffuse upwards in the pond

oxygen is supplied by algal photosynthesis and to a limitedextent by diffusion from the air

bacterial respiration is "facultative at middle zone


12/22

Trickling filter Consists of a bed of porous material (rocks, slag, plastic)

Microbes in the wastewater attach themselves to the bed orfilter media

Microbial degradation (aerobic) takes place as wastewaterflows through the media

The wastewater is then collected at the bottom through anunder drain system

The effluent is settled by gravity to remove biological solids

prior to being discharged


13/22

Rotating Biological Contractors (RBCs) A number of circular plastic disc are mounted on a central

shaft

These discs are submerged and rotated in a tank containingthe wastewater to be treated

Microorganisms responsible for treatment becomeattached to the disc and rotate into and out of thewastewater

RBCs have also been developed for the biological treatmentof odours

The RBCs have been used in treating winery wastewater andother domestic and industrial effluents


14/22

The Activated Sludge System The most widely applied Biological treatment of sewage

The primary objective of the system is the removal ofsoluble biodegradable compounds

It also removes pathogens from the water supply

removal efficiency of pathogens and indicator microbes

vary with the treatment process, type, retention time,other biological flora present in activated sludge, oxygenconcentration, pH, temperature and the efficiency inremoving suspended solids

f f


15/22

Stages of treatment of sewage:

The Activated Sludge Process


16/22

Microbiology of activated sludge

A mixed microbial community is involved

Aerobic condition ensures aerobic biological degradation

The microbes employ the organic matter in the sewage assource of carbon and energy to develop their biomass

In the process organic matter is degraded & BOD reduced

Other microbes are involved in mineralization of inorganiccompounds such as N, P, etc


17/22

The entire microbial community is collectively called theactivated sludge

Members of this community include: bacteria, fungi,viruses, protozoa, and helminths

The make up of the community depends on factors such as:

the physical & chemical nature of the sewage and

specific characteristics of individual members of thebiological community

R l t t d d f


18/22

Regulatory standards for

wastewater effluent quality To Protect the environment and public health

Regulatory agencies are usually set up to formulateguidelines & regulations necessary to ensure good sewageeffluent quality for various purposes

Regulatory guidelines vary from country to country and

some cases among states within a country

These guidelines normally sets allowable limits for variouspollutants contributable by sewage


19/22

Effectiveness of wastewater

treatment

effectiveness of conventional wastewater treatmentprocesses is increasingly becoming due to new challenges:

increased knowledge about the consequences of waterpollution resulting in stricter regulations

Industrial growth and increasing population coupled withdiminishing water resources


20/22

Other challenges affecting effective sewage treatmentinclude:

old and worn-out collection facilities requiring

the character and quantity of contaminants are more

complex in relation to the original design of plants

farm runoff and increasing urbanization provide additionalsources of pollution not controlled by conventional

wastewater treatment

The inadequacy of conventional disinfectant to removesome resistant pathogens like viruses and protozoa

C f i d t


21/22

Consequences of inadequate

wastewater treatment

The consequences of discharging untreated or inadequatelytreated wastewater into the environment are as diverse asthey are many

These include:

Eutrophication

DO depletion

Sedimentation may result in destruction of aquatic habitats


22/22

Acute and chronic toxicity to aquatic life from chemicalcontaminants

Bioaccumulation and biomagnification of chemicals inthe food chain

Release of pathogens of public health significancethrough consumption of contaminated drinking water orwater used in food processing

Carcinogenic and endocrine disrupting substances aswell as pharmaceuticals can pass through even the mostadvanced wastewater treatment systems

Socio-economic impact

Documents

MCB of Sewage Treatment & Disposal