WASTE WATER TREATMENT

INTRODUCTION

•     Waters often contain high levels of organic matters from industrial and agricultural wastes and human wastes.

•     It is necessary to remove organic matter by the process of waste water treatment.

•     It produce water containing nutrients and some micro organisms which can be released to river and stream.

•     Probably the most important role is in the treatment of solid and liquid wastes from domestic, municipal, agricultural and industrial sources.

•     A major aspect of this is the degradation or elimination of xenobiotic compounds within industrial waste streams and the necessary bioremediation of contaminated land or bodies of water.

•     This technology also reduces our reliance on synthetic chemical pesticides by allowing the implementation of biological control measures using bioinsecticides, biofungicides.

METHODS OF WASTE WATER TREATMENT

     There are 3 types of treatment:

•     Primary Treatment

•     Secondary Treatment

•     Teritary Treatment

Primary Treatment

Preliminary treatment and primary sedimentation.

 

Secondary Treatment:

•     In waste water treatment the microorganism are usually in the form of aggregates or supported biofilms.

•     Aerobic Biological Treatment

•     An aerobic Biological Treatment

 

Aerobic Biological Treatment

•     The basic principle of aerobic treatment is that waste water is bought into contact with a mixed microbial population of aerobic organisms and oxygen. Soluble, suspended and colloidal biodegradable materials that contributes to the BOD are then metabolized.

•     During process, part of biodegradable material is converted into CO₂ and a proportion becomes new biomass.

 

Homogeneous Activated Sludge Process

•     The basic principles of process are that waste water is bought into contact with a mixed microbial population, in the form of flocculated suspension, within a continuously aerated and agigated tank.

 

 

     Modes of Operation of Activated Sludge Plants

     The percentage BOD removal, HRT, biomass yield and sludge age vary depending on the nature of waste being treated.

 

     There are 3 main modes of operation for activated sludge plants:

•     Conventional

•     Executed Aeration

•     High Rate Treatment

 

Conventional Processing:

•     It is used for complete treatment of waste waters such as domestic sewage.

 

Extended Aeration:

•     Operates at a lower SLR than conventional plants and achieves approximately the same degree of purification, but the operating HRT is significantly longer.

 

High Rate Treatment:

•     Mostly used for partial processing of strong industrial waste water and designed to remove only 60-80% of BOD

 

 

Dissolved Oxygen in activated Sludge Plans:

•     The DO concentration required within the aeration basic can be determined by either mathematically modelling the system to predict oxygen demand at difficult times of the day.

 

There are three types filters:

•     Trickle Filter

•     Low Rate Filter

•     High Rate Trickle Filter

 

Trickle Filter

•     The basic principles of aerobic trickle filters is that a microbial population is allowed to develop as a biofilm on an inert support material within a biological reactor.

Low Rate Filter

•     As used in sewage works are usually designed to produce effluents of high quality.

High Rate Trickle Filter

•     Are often used for treating concentrated industrial waste waters as roughing process rather than complete treatment.

 

Anaerobic Waste Water Treatment

•     Anaerobic treatment is often performed on sludge and high strength industrial waste water.

•     They biograde polluting waste water or sludge to generate methane, CO₂ and biomass.

 

There are three trophic groups:

•     Fermentative Hydrolytic Bacteria

•     Acetogenic Bacteria

•     Methogenic Bacteria

 

Fermentative Hydrolytic Bacteria

•     A group of facultative and obligate bacteria able to secrete extra cellular enzymes that hydrolyse complex polymers. Such as proteins, lipids and poly sacchrides.

 

Acetogenic Bacteria

•     The metabolize end products from group-1 micro organism primary forming acetic acid, CO₂ and hydrogen.

 

Methogenic Bacteria

•     Selection of strict obligate anaerobes associated with methane production.

 

•     Sludge Treatment and Disposal

•     During primary sedimentation and biological treatment stages vast quantities of sludges can be generated.

•     These primary and secondary on sludges are highly polluting and depending on final method of disposal.

 

Sludge Thickening

•     The aim of sludge thickening is to significantly reduce the volume of sludge before further treatment while retaining solids content.

 

Sludge Stabilization

•     The main aim of sludge stabilization are to reduce the solids content of sludges, to destroy pathogenes.

 

Sludge Watering

•     Sludges are dewatered to further increase the solids content to 50% (W/v).

 

 

Disposal of Sludges and other Solid Wastes:

•    Methods routinely used for the disposal of final sludges and other solid wastes.

 

a) Land Filling:

•    Which is also used for the other agricultural, industrial and urban wastes.

 

b) Incineration:

•    Incineration is routinely used for solids and well dewatered sludges with solids contents in excess of 30% (w/v).

 

c) Biologically Stabilized Dewatered Sludge:

•    May be used as a low cost fertilizer and soil conditioner on agricultural land.

TERITARY WASTE WATER TREATMENT

•     Is any physiochemical or biological process employing bioreactors, precipitation, filteration, or chlorination procedures similar to those employed for drinking water purification.

 

•     Tertiary treatment sharply reduces the levels of inorganic nutrients, especially phosphate, nutrite and nitrate from final effluent.

 

•     Waste water receiving tertiary treatment essentially contains no nutrients and cannot support extensive microbial growth.

 

•     Tertiary treatment is the most complete method of treating sewage but has not been widely adopted due to the costs associated with such complete nutrient removal.

 

 

Waste Water Microbiology and Water Purification

•     Water is the most important potential common source of infectious diseases and can also be a source for chemically induced intoxications.

•     Water purity is most important single factor for ensuring public health.

•     The methods commonly used to assess water quality depend on standard microbiological and chemical technique.

 

Coliforms and Water Quality

•     Califorms are useful indicators of water contaminations because many of them inhabit the intestinal tract of humans and other animals in large numbers.

•     Califorms are defined as facultatively aerobic, gram negative, non spore-forming, rod shaped bacteria that ferment lactose with gas formation within 48 hours at 30⁰C

 

     Waste Water Commonly contains potentially harmful inorganic and organic compounds as well as pathogenic microorganisms.

•     Waste water collected from every day form washing, cooking activities must be treated to remove contaminants before it can be released into surface waters.

 

Waste Water Treatment  & Biochemical Oxygen Demand

 

•     The goal of a waste water treatment facility is to reduce organic and microorganic material in waste water to a level that no longer support microbial growth and to eliminat other potentially toxic materials.

•     The relative amount of dissolved oxygen consumed by micro organisms to completely oxidize all organic and inorganic matter is a water sample.

•     Typical values for domestic waste water including sewage are approximately 200 BOD units for industrial waste water for example from sources such as diary plants, the values can be high as 1500 BOD units.

•     Waste water facilities designed to treat both low BOD, sewage and high BOD industrial waste.

 

 

Water Borne Microbial Disease

•     Cholera is a severe diarrheal disease chlorea is caused by vibrio cholerae, a gram negative, curved, rod shaped. Protobacterium typically transmitted through ingestion of contaminated water.

 

Giardiasis and Cryptosporidiosis

•     Giardiasis and Cryptosporidiosis are diseases caused by protista Giardia intestinals and cryptosporidiam parvtan respectively. These organisms continue to be problematic even in well regulated water supplies.

REFERENCES

•     Brock Biology of Microorganisms, Madigan, Martinco, Dunlap, 12^th Edition, Pearson Benjamin Cummings.

 

•     Microbiology, Prescott, Harley, Klein, 7^th Edition, McGraw Hill International

 

•     Industrial Microbiology. Waites, Morgan, Rockey and Higton. Blackwell Publishing.