A Comparison Of Wastewater Treatment Methods Environmental Sciences Essay

Water constitutes over 70 % of the Earths surface and is a really of import resource for all people and the environment. If H2O gets polluted it cant be the elixr of life any longer to aquatic and to the wild life that depend on it. Rivers and watercourses polluted with chemical contaminations account as one of the most important environmental jobs. Water pollution is fundamentally a human fallacy.This used H2O is called “ effluent ” . Turning population and rapid industrialization has increased the volume of effluent manifold finally deteriorating the fresh H2O resources and environing environment due to inappropriate management.It is 99.94 per centum H2O, with merely 0.06 per centum of the effluent being dissolved and suspended solid stuff.

Infiltration/inflow: immaterial H2O that enters the cloaca system through indirect and direct agencies such as through leaking articulations, clefts, or porous walls.Inflow is storm H2O that enters the cloaca system from storm drain connexions, roof headings, foundation and cellar drains or through manhole screens ;

Features: Fresh, aerophilic, domestic H2O has been said to hold the smell of kerosine or newly turned Earth. Aged, infected sewerage is well more violative to the olfactory nerves.The characteristic rotten-egg smell of H sulphide and the mercaptans is declarative of infected sewage.Fresh sewerage is typically gray in colour.septic sewerage is black.The category of chemical compounds found in effluent are illimitable and so they are better known by the name of the trial used to mensurate them which are BOD5 and COD test.Industrial procedures generate a broad assortment of effluent pollutants.The features and degrees of pollutants vary significantly from industry to industry.

Waste-water quality is assessed based on physical, chemical, and biological features. Physical parametric quantities include coloring materials, smell, temperature, and turbidness. Insoluble contents such as solids, oil and lubricating oil, are to be considered under this category.. Solids may be farther subdivided into suspended and dissolved solids every bit good as organic ( volatile ) and inorganic ( fixed ) fractions. Chemical factors to be considered are: biochemical O demand ( BOD ) , chemical O demand ( COD ) , entire organic C ( TOC ) , and entire O demand ( TOD ) . Inorganic chemical parametric quantities include salt, hardness, pH, sourness and alkalinity, every bit good as concentrations of ionised metals such as Fe and manganese, and anionic entities such as chlorides, sulphates, sulphides, nitrates and phosphates. Bacteriological parametric quantities include coliforms, fecal coliforms, specific pathogens, and viruses. Both components and concentrations vary with clip and local conditions.


Waste-water flow fluctuates with fluctuations in H2O use, which is affected by a battalion of factors including clime, community size, life criterions, dependableness and quality of H2O supply, H2O preservation demands or patterns, and the extent of metre services, in add-on to the grade of industrialization, cost of H2O and supply force per unit area. Wide fluctuations in effluent flow rates may therefore be expected to happen within a community

Effluent does non flux into a municipal effluent intervention works at a changeless rate. The flow rate varies from hr to hr. In most metropoliss, the form of day-to-day activities sets the form of sewerage flow and strength. Above-average sewerage flows and strength occur in mid-morning.The invariably altering sum and strength of effluent to be treated makes efficient procedure operation difficult.Also, many intervention units must be designed for the maximal flow conditions encountered which really consequences in their being oversized for mean conditions.Flow equalisation is non a intervention procedure in itself, but a technique that can be used to better the effectivity of both secondary and advanced effluent intervention processes.The intent of flow equalisation is to stifle the fluctuations so that the effluent can be treated at a about changeless flow rate.Flow equalisation can significantly better the public presentation of an bing works and increase its utile capacity.In new workss, flow equalisation can cut down the size and cost of the intervention units.

Wastewater intervention options may be classified into groups of procedures harmonizing to the map they perform and their complexness:

The basic methods of handling municipal effluent autumn into the undermentioned phases, which is shown in the signifier of block flow:

The procedure flow diagram of a basic effluent intervention procedure is as follows:


General footings used to depict different grades of intervention in order of increasing intervention degree are preliminary, primary, secondary and third and/or advanced effluent intervention.

Preliminary intervention:

Preliminary intervention prepares waste-water influent for farther intervention by cut downing or extinguishing non-favourable waste-water features that might otherwise impede operation or overly increase care of downstream procedures and equipment. These features include big solids and shreds, scratchy grit, smells, and, in certain instances, intolerably high extremum hydraulic or organic burdens. Preliminary intervention processes consist of physical unit operations, viz. testing and comminution for the remotion of dust and shreds, grit remotion for the riddance of coarse suspended affair, and floatation for the remotion of oil and lubricating oil. Other preliminary intervention operations include flow equalization, septage handling, and odour control methods.

Primary Treatment:

Primary intervention is designed to take organic and inorganic solids by the physical procedures of deposit and flotation. About 30 – 40 % of the pollutants are removed from the waste Waterss. Primary intervention acts as a precursor for secondary intervention.

Secondary intervention:

The intent of secondary intervention is the remotion of soluble and colloidal organics and suspended solids that have escaped the primary intervention. This is typically done through biological procedures, viz. intervention by activated sludge, fixed-film reactors, or laguna systems and deposit.

Chemical intervention utilizes a coagulator such as Fe or aluminium.Then solid organic affair and P are precipitated into larger pieces which are separated as sludge. Suspended solids removal through chemical intervention involves a series of three unit operations: rapid commixture, flocculation and settling..A once-through chemical intervention system is shown below the tabular array.

Advantage: greater remotion efficiency, the feasibleness of utilizing higher overflow rates, and more consistent public presentation. On the other manus, curdling consequences in a larger mass of primary sludge that is frequently more hard to inspissate and dewater. It besides entails higher operational costs and demands greater attending on the portion of the operator.


Adsorption is the procedure of roll uping soluble substances within a solution on a suited interface. In waste-water intervention, surface assimilation with activated carbon-a solid interface-usually follows normal biological intervention, and is aimed at taking a part of the staying dissolved organic matter.Particulate affair nowadays in the H2O may besides be removed.. The two most common types of activated C are farinaceous activated C ( GAC ) , which has a diameter greater than 0.1 millimeter, and powdered activated C ( PAC ) , which has a diameter of less than 200 mesh. A schematic of an activated C contactor is shown below the tabular array.

Advantage: Exploitation powdered activated C in concurrence with traditional biological intervention provides first-class outflowing bio-assay consequences, provides for toxicity control within the bioreactor, and proA­motes higher nitrification efficiency than that of a conventional activated-sludge system.


Oxidation is a procedure widely used for effluent intervention by which the pollutants are removed or converted into more biodegradable substances. Catalytic moisture air oxidization ( CWAO ) is a liquid stage reaction between organic stuff in H2O and O. CWAO is an attractive intervention for waste watercourses, which are excessively dilute to incinerate and excessively concentrated for biological intervention. It can be defined as the oxidization of organic and inorganic substances in an aqueous solution or suspension by agencies of O or air at elevated temperatures and force per unit areas. It is besides called flameless burning Typical conditions for CWAO scope from 125 to 300a-¦C and at force per unit areas from 0.5 to 20 MPa. Residence times may alter from 15 to 120 min, and the chemical O demand ( COD ) remotion may typically be about 75-90 % .


Dechlorination is the remotion of free and entire combined Cl residue from chlorinated effluent wastewater before its reuse or discharge to having Waterss. Chlorine compounds react with many organic compounds in the wastewater to bring forth unsought toxic compounds that cause long-run inauspicious impacts on the H2O environment and potentially toxic effects on aquatic microorganisms.

Beginning: Adapted from Liu and Liptak, Wastewater Treatment

ACTIVATED CARBON CONTACTOR: Beginning: Metcalf and Eddy, Wastewater Engineering, 3rd edition.






Biological P remotion was observed to make a lower limit of 0.4mg/l in the wastewater

Chemical P remotion was observed to make whatever outflowing quality demand as more and more chemicals are dosed

SLUDGE PRODUCTION ( The production of sludge is considered as a really of import factor in the pick of a effluent intervention method presents )

Sludge production is less compared to chemical method.

Chemical P remotion produces more sludge, approximately 25 % more sludge than by biological agencies.


As the volume of the anaerobiotic zone of the Bio -P procedure is reduced, there are alterations in the outflowing quality and the efficiency of P remotion is reduced

The decrease of the volume of the anaerobiotic zone has no effects on the chemical P remotion

Consumption OF ENERGY

It was possible to cut down the capacity of the aeration device down to 1000kg O2/hr and still hold good intervention consequences in footings of COD and nitrogen remotion in the Bio-P process.Beyond this bound ( less than 100kg O2/hr ) COD and the Nitrogen in the wastewater are excessively high.

Same sum of COD and Nitrogen in the wastewater is observed at 500kgO2/hr.So chemical method is more immune to decrease in aeration capacity than the Bio-P procedure by atleast 500kgO2/hr aeration capacity.


Annual cost for sludge disposal is saved by Bio-P compared to chemical method.

The cost of buying chemicals is high and no nest eggs with respect to sludge disposal compared to Bio-P remotion.

The economic cost of intervention has been evaluated based on a summing up of the single costs associated with sludge production, cost of chemicals, energy cost and costs associated to volume nest eggs. The purpose of an economic cost is non to reflect the exact fiscal cost but an estimation that could be used as a guideline for the building of a new works or for comparing of the two procedures.



Biological procedure removes solid organic affair and dissolved organic affair. The chemical procedure removes solid organic affair and phosphorus.Chemical precipitation cleans the H2O really quickly, say in less than 15mins after the induction of the procedure, we have clean H2O, whereas with biological intervention it will take 3 hour to accomplish the same.Biological procedure stopping points relatively long clip and is dependent on the effectivity of the microorganisms.Chemical and Biological interventions work in different ways and accomplish different results.We have to find the major causes of O lack in Waterss and choose the intervention in conformity with local environmental requirements.Purification in itself demands resources.Biological intervention requires a long abode clip and energy is consumed when air is blown into the sewerage water.Consequently the Biological works is large and more complex.The micro-organisms have to be adapted to the pollution which sensitises the whole system.Chemical purification requires add-on of coagulators which is done in a little pool and at lower energy consumption.The entire energy used for chemical intervention is merely 15 % of that required for biological intervention, even if the energy used for production and distribution of coagulators is included.In footings of the entire ecological emphasis, the chemical procedure is favoured.Life rhythm appraisals show the biological procedure to be a larger consumer of resources and therefore it is more negative interms of its full environmental impact.If there is no demand to take dissolved organic affair a biological procedure could make greater ecological harm than chemical procedure due to the entire energy ingestion and the natural stuffs used when building the works. The environment makes demands on the purification procedure and if advanced purification is necessary both biological and chemical methods must be used..In Norway, the bing chemical works built wholly within bedrock was extended with the N remotion system due to the increased food load.With the alone combination of chemical and biological procedures this works occupies less than half the volume of the conventional biological procedure.


Effective effluent aggregation and intervention are of great importance from the point of view of both environmental and public wellness. Any effluent intervention works needs important investing and Operation Maintenance and control, and hence any determination to implement such a installation should be carefully considered. It is non a good thought to reason that any intervention method is better than the other.Each one has its ain advantages and disadvantages.The pick of which method is to be used will depend on the society, the discharge demands and the costs they are ready to incur.As a concluding decision, the winning construct these yearss should non be based on which procedure should be used in isolation to the other, but instead utilizing the advantages of both processes together to obtain best consequences, while at the same clip understating their disadvantages. Extensive research activity in this field has led to important betterment and variegation in the procedures and methods used for waste-water intervention and sludge direction. Public wellness jeopardies are frequently associated with waste-water reuse, and accordingly it is indispensable to circulate cognition and information about the danger of natural waste-water reuse and issue safe reuse guidelines.