Chapters :



Many ocean pollutants are released into the environment far upstream from coastlines. Nutrient-packed fertilizers applied to farmland, for example, often end up in local streams and are eventually deposited into estuaries and bays. These excess nutrients trigger massive blooms of algae that rob the water of oxygen, leaving dead zones where few marine organisms can live. Some chemical pollutants climb high into the food webs—like DDT, the insecticide that placed the bald eagle on the United States Fish and Wildlife’s Endangered Species List. Even pharmaceuticals ingested by humans, but not fully processed by our bodies, end up in aquatic food webs.

Light pollution penetrates under the water, creating a vastly different world for fish living in shallow reefs near urban environments. Light disrupts the normal cues associated with circadian rhythms, to which species have evolved timing of migration, reproducing, and feeding. Artificial light at night can make it easier for predators to find smaller fish prey and can affect breeding in reef fish.  The increased presence of loud or persistent sounds from ships, sonar devices, and oil rigs disrupts natural noises in the marine environment. For many marine mammals, like whales and dolphins, low visibility and large distances make non-visual underwater communication critical. Toothed whales use echolocation—emitting sounds that reflect off surfaces—to help them “see” in the ocean. Unnatural noises interrupt communication, disrupting migration, communication, hunting, and reproduction patterns for many marine animals.


Plastic pollution seeps into the ocean through run-off and even purposeful dumping. The amount of plastic in the Atlantic Ocean has tripled since the 1960s. The garbage patch floating in the Pacific Ocean, almost 620,000 square miles—twice the size of Texas—is a powerful image of our plastic problem. A huge culprit is single-use plastics, used once before tossed into the trash or directly into the ocean. These single-use items are accidentally consumed by many marine mammals. Plastic bags resemble jellyfish, a common food for sea turtles, while some seabirds eat plastic because it releases a chemical that makes it smell like its natural food. Discarded fishing nets drift for years, ensnaring fish and mammals. Bits of plastic swirl throughout the water column, even sinking to the deepest depths of the ocean. Scientists found plastic fibres in corals in the Atlantic Ocean—and more concerning, they found that the corals readily ate plastic over food. Dying marine mammals, washing up on shore, also contain plastic inside their stomachs.


The Agenda 21 adopted by the United Nations Conference on Environment and Development, popularly known as the “Earth Summit” of Rio de Janeiro, 1992, identified protection and management of freshwater resources from contamination as one of the priority issue, that has to be urgently dealt with to achieve global environmentally sustainable development.

Water treatment is a process of making water suitable for its application or converting used water into environmentally acceptable water or even drinking water or to its natural state. Thus, water treatment is required before and after depending on the application. The treatment may include mechanical, physical, biological, and chemical methods and is an integrated comprising of the conventional series of primary and secondary treatment processes, but also includes tertiary treatment and individual treatment of certain streams. All water treatments involve the removal of Solids, Bacteria, Algae, Plants, Inorganic Compounds, And Organic Compounds. The primary and secondary treatment processes handle most of the nontoxic wastewaters while the water having toxic wastes needs to be pre-treated before adding to this flow.

The treatment process is divided into four stages such as:

  • Preliminary treatment
  • Primary treatment
  • Secondary treatment 
  • Tertiary treatment 


In many waste water treatment plants the preliminary treatment is the part of the primary treatment, which includes only the mechanical processes. The pretreatment of the influent involves one or all the following steps depending upon the kind of the waste water to be treated. 

  1. Screening – Screening removes large solid chunks and objects such as rags, paper, plastics, and metals to prevent damage and clogging of downstream equipment, piping etc. 
  2. Comminutors and Grinders: The processing of coarse solids using comminutors and grinders reduces their size of coarser particles so that they can be removed during downstream treatment operations
  3. Grit Removal: Grit includes sand, gravel or other heavy solid materials that are “heavier” (higher specific gravity) than the organic biodegradable solids in the wastewater. The removal of grit prevents unnecessary abrasion and wear of mechanical equipment, grit deposition in pipelines and channels, as well as the accumulation of grit in anaerobic digesters and aeration basins
  4. Fat and grease removal: In some larger waste water treatment plants, fat and grease are removed by passing the wastewater through a small tank where mechanical skimmers collect the fat floating on the surface. Air blowers in the base of the tank may also be used to help the recovery of the fat as froth. 

Primary Treatment:

The equalization tank is followed by neutralization tank where required as streams of different pH partly neutralize each other when mixed. The oils, greases and suspended solids are removed by Floatation, Sedimentation, Filtration or some-times special equipment is also used to remove grit that gets washed into the waste water. The primary treatment prepares the wastewater for the next secondary (biological) treatment. This involves the separation of suspended organic matter (or human waste) from the wastewater. This is done by putting the wastewater into large settlement tanks for the solids to sink or settle down to the bottom of the tank. The settled solids are called ‘Sludge’. At the bottom of these circular tanks, large scrappers continuously scrape the floor of the tank and push the sludge towards the pump away for further treatment. The rest of the water is then moved to the secondary treatment. 

Secondary Treatment:

The secondary treatment is the biological degradation of soluble organic compounds that escapes primary treatment. This process is usually done aerobically in an open, aerated vessel or lagoon where the microorganisms degrade this organic matter, which serve as “food” for them. Microorganisms combine this matter with oxygen from the water to yield the energy they need to thrive and multiply. So, the heavy organic pollution in the river or water bodies can lead to “dead zones”  where no fish can be found and sudden releases of heavy organic loads can lead to DRAMATIC “FISH KILLS”. The water, at this stage, is put into large rectangular tanks. These are called aeration lanes. Air is pumped into the water to encourage bacteria to break down the organic contaminants of sludge that escaped the sludge scrapping process. The biological process is then followed by additional settling tanks (secondary sedimentation) to remove more of the suspended solids and microorganisms called as activated sludge. A fraction of this sludge is recycled in certain processes, but ultimately the excess sludge along with the sediment solids has to be disposed-off. Next, the ‘almost’ treated wastewater is passed through a settlement tank, where, more sludge is formed at the bottom of the tank from the settling of the bacterial action. Again, the sludge is scraped and collected for treatment. The water at this stage is almost free from harmful substances and chemicals. The water is allowed to flow over a wall where it is filtered through a bed of sand to remove any additional particles. The filtered water is then discharged into the water bodies.  

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