Environmental pollution-Water pollution sources-Impacts on the environment –Waste water treatments-physical, chemical and biological treatments

Environmental pollution consists of five basic types of pollution, namely, air, water, soil, noise and light.

Air pollution is by far the most harmful form of pollution in our environment. Air pollution is cause by the injurious smoke emitted by cars, buses, trucks, and factories, namely sulphur dioxide, carbon monoxide and nitrogen oxides. Even smoke from burning leaves and cigarettes are harmful to the environment causing a lot of damage to man and the atmosphere. Evidence of increasing air pollution is seen in lung cancer, asthma, allergies, and various breathing problems along with severe and irreparable damage to flora and fauna. Even the most natural phenomenon of migratory birds has been hampered, with severe air pollution preventing them from reaching their seasonal metropolitan destinations of centuries.

Chlorofluorocarbons (CFC),  released from refrigerators, air-conditioners, deodorants and insect repellents cause severe damage to the Earth’s environment.  This gas has slowly damaged the atmosphere and depleted the ozone layer leading to global warming.

Water pollution caused industrial waste products released into lakes, rivers, and other water bodies, has made marine life no longer hospitable. Humans pollute water with large scale disposal of garbage, flowers, ashes and other household waste. Acid rain further adds to water pollution in the water. In addition to these, thermal pollution and the depletion of dissolved oxygen aggravate the already worsened condition of the water bodies. Water pollution can also indirectly occur as an offshoot of soil pollution – through surface runoff and leaching to groundwater.

Noise pollution, soil pollution and light pollution too are the damaging the environment at an alarming rate. Noise pollution include aircraft noise, noise of cars, buses, and trucks, vehicle horns, loudspeakers, and industry noise, as well as high-intensity sonar effects which are extremely harmful for the environment.

Soil pollution, which can also be called soil contamination, is a result of acid rain, polluted water, fertilizers etc., which leads to bad crops. Soil contamination occurs when chemicals are released by spill or underground storage tank leakage which releases heavy contaminants into the soil. These may include hydrocarbons, heavy metals, MTBE, herbicides, pesticides and chlorinated hydrocarbons.

Water pollution

Sources of surface water pollution are generally grouped into two categories based on their origin. Point sources:- (contaminants that enter a waterway from a single, identifiable source, such as a pipe or ditch) . Ex. discharge from a sewage treatment plant, a factory, or a city storm drain.  Non–point sources (NPS) :- (diffuse contamination that does not originate from a single discrete source). NPS pollution is often the cumulative effect of small amounts of contaminants gathered from a large area. Ex. leaching out of N compounds from fertilized agricultural lands. Contaminated storm water washed off of parking lots, roads and highways, called urban runoff.

Impact on the environment

1. Bio accumulation

Fish and shellfish kills have been reported, because toxins climb the food chain after small fish consume copepods, then large fish eat smaller fish, etc. Each successive step up the food chain causes a stepwise concentration of pollutants such as heavy metals (e.g. mercury) and persistent organic pollutants such as DDT. This is known as biomagnification, which is occasionally used interchangeably with bioaccumulation.

2. Spread of infectious disease

Infectious diseases such as cholera and typhoid can be contracted from drinking contaminated water.

3. Health disorders

Our whole body system can have a lot of harm if polluted water is consumed regularly. Other health problems associated with polluted water are poor blood pressure, vomiting, skin lesions and damage to the nervous system. In fact the evil effects of water pollution are said to be the leading cause of death of humans across the globe.

4. Alteration of chemistry of river and water course

Pollutants in the water alter the overall chemistry of water, causing a lot of changes in temperature. These factors overall have had an adverse effect on marine life and pollutes and kills marine life. Marine life gets affected by the ecological balance in bodies of water, especially the rivers and the lakes.

5. Eutrophication of water bodies

Nitrates and phosphates from waste water will increase the growth of algal bloom there by creating anoxic zone leading to killing of fishes called eutrophication  

6. Damages to food chain

The water pollution has damaged the food chain and is very important for the food preparation of plants through photosynthesis. When Filth is thrown in water the toxins travel from the water and when the animals drink that water they get contaminated and when humans tend to eat the meat of the animals is infected by toxins it causes further damage to the humans.

 Waste water treatment – Physical, chemical and biological treatments

Wastewater treatment is the process of removing contaminants from wastewater and household sewage, both runoff (effluents) and domestic. It includes physical, chemical, and biological processes to remove physical, chemical and biological contaminants. 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).

Wastewater Treatment Methods

Physical: Sedimentation (Clarification), Screening, Aeration, Filtration, Flotation and Skimming, Degassification, Equalization etc.,

Chemical: Chlorination, Ozonation, Neutralization, Coagulation, Adsorption, Ion Exchange

Biological: 1) Aerobic :Activated Sludge Treatment Methods, Trickling Filtration, Oxidation Ponds, Lagoons, Aerobic Digestion                                        

               2) Anaerobic  : Anaerobic Digestion, Septic Tanks, Lagoons 

Physical methods include processes where no gross chemical or biological changes are carried out and strictly physical phenomena are used to improve or treat the wastewater.  

Examples would be coarse screening to remove larger entrained objects and sedimentation (or clarification). In the process of sedimentation, physical phenomena relating to the settling of solids by gravity are allowed to operate.  Usually this consists of simply holding a wastewater for a short period of time in a tank under quiescent conditions, allowing the heavier solids to settle, and removing the "clarified" effluent.  Sedimentation for solids separation is a very common process operation and is routinely employed at the beginning and end of wastewater treatment operations. While sedimentation is one of the most common physical treatment processes that is used to achieve treatment, another physical treatment process consists of aeration -- that is, physically adding air, usually to provide oxygen to the wastewater.  Still other physical phenomena used in treatment consists of filtration.  Here wastewater is passed through a filter medium to separate solids.  An example would be the use of sand filters to further remove entrained solids from a treated wastewater.  Certain phenomena will occur during the sedimentation process and can be advantageously used to further improve water quality.  Permitting greases or oils, for example, to float to the surface and skimming or physically removing them from the wastewaters is often carried out as part of the overall treatment process. 

In certain industrial wastewater treatment processes strong or undesirable wastes are sometimes produced over short periods of time.  Since such "slugs" or periodic inputs of such wastes would damage a biological treatment process, these wastes are sometimes held, mixed with other wastewaters, and gradually released, thus eliminating "shocks" to the treatment plant.  This is call equalization.  Another type of "equalization" can be used to even out wide variations in flow rates.  For example, the wet well of a pump station can receive widely varying amounts of wastewater and, in turn, pump the wastes onward at more uniform rates. 

Chemical treatment consists of using some chemical reaction or reactions to improve the water quality.  Probably the most commonly used chemical process is chlorination.  Chlorine, a strong oxidizing chemical, is used to kill bacteria and to slow down the rate of decomposition of the wastewater.  Bacterial kill is achieved when vital biological processes are affected by the chlorine.  Another strong oxidizing agent that has also been used as an oxidizing disinfectant is ozone. 

A chemical process commonly used in many industrial wastewater treatment operations is neutralization.  Neutralization consists of the addition of acid or base to adjust pH levels back to neutrality.  Since lime is a base it is sometimes used in the neutralization of acid wastes. 

Coagulation consists of the addition of a chemical that, through a chemical reaction, forms an insoluble end product that serves to remove substances from the wastewater.  Polyvalent metals are commonly used as coagulating chemicals in wastewater treatment and typical coagulants would include lime (that can also be used in neutralization), certain iron containing compounds (such as ferric chloride or ferric sulfate) and alum (aluminum sulfate). 

Certain processes may actually be physical and chemical in nature.  The use of activated carbon to "adsorb" or remove organics, for example, involves both chemical and physical processes.  Processes such as ion exchange, which involves exchanging certain ions for others, are not used to any great extent in wastewater treatment. 

Biological treatment methods use microorganisms, mostly bacteria, in the biochemical decomposition of wastewaters to stable end products.  More microorganisms, or sludges, are formed and a portion of the waste is converted to carbon dioxide, water and other end products.  Generally, biological treatment methods can be divided into aerobic and anaerobic methods, based on availability of dissolved oxygen. 

Combination of waste water treatments

Preliminary Treatment

At most plants preliminary treatment is used to protect pumping equipment and facilitate subsequent treatment processes.  Preliminary devices are designed to remove or cut up the larger suspended and floating solids, to remove the heavy inorganic solids, and to remove excessive amounts of oils or greases. 

Primary Treatment

In this treatment, most of the settleable solids are separated or removed from the wastewater by the physical process of sedimentation. The purpose of primary treatment is to reduce the velocity of the wastewater sufficiently to permit solids to settle and floatable material to surface.  Therefore, primary devices may consist of settling tanks, clarifiers or sedimentation tanks. 

 Secondary Treatment

Secondary treatment depends primarily upon aerobic organisms which biochemically decompose the organic solids to inorganic or stable organic solids.  This treatment is a biological treatment

  Tertiary and Advanced Wastewater Treatment

The tertiary treatment has been used to describe processes which remove plant nutrients, primarily nitrogen and phosphorous, from wastewater. Improvement and upgrading of wastewater treatment units as well as the need to minimize environmental effects has led to the increased use of tertiary treatment.