Water Pollution and its Prevention
Develop and implement pollution control strategies to prevent the pollutants from entering the environment 5. Develop and implement alternative means of meeting the need that do not produce the polluting by product II. Water Pollution: Sources, Types, Criteria For purposes of regulation, it is customary to distinguish between point sources and nonpoint sources of pollutants ·Point sources involve the discharge of substances from factories, sewage systems, power plants, coal mines, and oil wells ·Two basic strategies are employed in attempting to bring water pollution under control: 1) reduce or remove the sources and 2) treat the water before it is released so as to remove pollutants or convert them to harmless forms A.
Pathogens ·Most serious water pollutants are the infectious agents that cause sickness and death ·Pathogens – disease causing bacteria, viruses and other parasitic organisms ·The following measures were important in controlling waterbourne diseases: 1. Purification and disinfection of public water supplies with chlorine or other agents 2. Sanitary collection and treatment of human and animal wastes 3.
Maintenance of sanitary standards in all facilities in which food is processed or prepared for public consumption 4. Instruction in personal and domestic hygiene practices ·Largely because of poor sanitation regarding water and sewage, a significant portion of the world’s population is chronically infected with various pathogens B. Organic Waste When bacteria and detritus feeders decompose organic matter in water, they consume oxygen gas dissolved in the water ·Bacteria keep the water depleted in DO as long as there is dead organic matter to support their growth and oxygen replenishment is inadequate ·Biochemical oxygen demand is a measure of the amount of organicmaterial in water, in terms of how much oxygen will be required to break it down biologically, chemically, or both ·If the system goes anaerobic, only bacteria can survive, using their abilities to switch to fermentation or anaerobic respiration C.
Chemical Pollutants ·The organic chemicals are another group of substances found in polluted waters ·Many of these pollutants are toxic even at low concentrations ·At higher concentrations, they can change the properties of bodies of water so as to prevent them from serving any useful purpose except navigation D. Sediments ·Sediments have direct and extreme physical impacts on streams and rivers ·Sediment entering waterways in large amounts has an array of impacts ·Modern storm-water management is designed to reduce the bed load E. Nutrients More nutrients mean more plant growth, so nutrients become water pollutants when they are added from point or nonpoint sources and stimulate undesirable plant growth in bodies of water F. Water Quality Standards ·The EPA has listed 167 chemicals and substances as criteria pollutants ·Two important applications of water quality criteria are the National Pollution Discharge Elimination System and Total Maximum Daily Load programs 17. 2 Wastewater Management and Treatment ·Sewage borne bacteria were responsible to infectious diseases I.
Development of Wastewater Collection and Treatment System ·To alleviate the problem of sewage-polluted waterways, facilities were designed and constructed to treat the outflow before it entered the receiving waterway ·Gradually, regulations were passed requiring municipalities to install separate systems—storm drains for collecting and draining runoff from precipitation and sanitary sewers to receive all wastewater II. The Pollutants in Raw Wastewater ·The total mixture of water collected from all drains is called raw sewage.
It mostly consists of water ·The pollutants in raw sewage are usually divided into four categories which correspond to the techniques used to remove them: 1. Debris and grit: bags, course sand, gravel, other objects 2. Particulate organic material: fecal matter, food wastes, toilet paper 3. Colloidal and dissolved organic material: very fine particles of particulate organic material, bacteria, urine, soap, detergent 4. Dissolved inorganic material: nitrogen, phosphorous, nutrients III. Removing the Pollutants from Wastewater ·The challenge of treating wastewater is more than installing a technology A.
Preliminary ·Removing debris and grit is called preliminary treatment ·Debris is removed by letting raw sewage flow through a bar screen B. Primary Treatment (Removal of Particular Organic Material) ·After preliminary treatment, the water moves onto primary treatment, where it flows very slowly through large tanks called primary clarifiers ·At the same time, fatty or oily material floats to the top, where it is skimmed from the surface ·All the material that is removed is combined into raw sludge which is treated separately C.
Secondary Treatment (Removal of colloidal and Dissolved Organic Materials) ·Secondary treatment uses natural decomposers and detritus feeders ·The wastewater from primary treatment is a food- and water-rich medium for the decomposers and detritus feeders ·As the organisms feed on each other, they tend to form into clumps, called floc D. Biological Nutrient Removal ( Removal of Dissolved Inorganic Material) ·In the natural nitrogen cycle, various bacteria convert nutrient forms of nitrogen back to nonnutritive nitrogen gas in the atmosphere through denitrification ·Phosphate is removed as excess rganisms are removed from the system E. Final Cleansing and Disinfection ·With or without BNR, wastewater is subjected to a final clarification and disinfection IV. Treatment of Sludge ·Pathogens are certain to be present in raw sludge because it includes material direct ·The commonly used methods for treating sludge and converting it into organic fertilizer are anaerobic digestion A. Anaerobic Digestion ·Anaerobic digestion is a process of allowing bacteria to feed on the detritus in the absence of oxygen ·Because of its methane content, biogas is flammable and can be burned for fuel B.
Compositing ·Raw sludge is mixed with wood chips to reduce the water content ·Bacteria and other decomposers break down the organic material to rich humus like material that makes an excellent treatment for poor soil C. Pasteurization ·After the raw sludge is dewatered, the resulting sludge cake may be put through ovens that operate like oversized laundry dryers. In the dryers, the sludge is pasteurized ·The product is dry, odorless organic pellets V. Alternative Treatment Systems
A. On-site Wastewater Treatment Systems ·Wastewater flows into the tank, where particulate organic matter settles to the bottom ·Soil bacteria decompose the colloidal and dissolved organic material that comes through the leaching field B. Using Effluents for Irrigation ·The nutrient-rich water coming from the standard secondary-treatment process is beneficial for growing plants ·It can be used for irrigation. However, it is important to ensure that it has been properly treated C.