Water and Life and environment, 2021-02-21.pptx

Water and Life and environment, 2021-02-21.pptx

1. Water Quality and Life

2. Water Quality and Life

3. Criteria for Aquatic Life DO The water quality criterion for dissolved oxygen, therefore, takes these factors into account. Depending on the water temperature requirements for particular aquatic species at various life stages, the criteria values range from 5 to 9.5 mg/l, i.e. a minimum dissolved oxygen concentration of 5-6 mg/l for warm-water biota and 6.5-9.5 mg/l for cold-water biota. Higher oxygen concentrations are also relevant for early life stages. More details are given in Alabaster and Lloyd (1982) and the EPA (1976, 1986).

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5. Irrigation Even when the presence of pesticides or pathogenic organisms in irrigation water does not directly affect plant growth, it may potentially affect the acceptability of the agricultural product for sale or consumption . Criteria have been published by a number of countries as well as by the Food and Agriculture Organization of the United Nations (FAO)

6. Irrigation Criteria Takes into Account Water quality criteria for irrigation water generally take into account, amongst other factors, such characteristics as crop tolerance to salinity, sodium concentration and phytotoxic trace elements. The effect of salinity on the osmotic pressure in the unsaturated soil zone is one of the most important water quality considerations because this has an influence on the availability of water for plant consumption . Sodium in irrigation waters can adversely affect soil structure and reduce the rate at which water moves into and through soils. Sodium is also a specific source of damage to fruits. Phytotoxic trace elements such as boron, heavy metals and pesticides may stunt the growth of plants or render the crop unfit for human consumption or other intended uses .

7. Livestock watering Livestock may be affected by poor quality water causing death, sickness or impaired growth. Variables of concern include nitrates, sulphates, total dissolved solids (salinity), a number of metals and organic micropollutants such as pesticides . In addition, bluegreen algae and pathogens in water can present problems. Some substances, or their degradation products, present in water used for livestock may occasionally be transmitted to humans . The purpose of quality criteria for water used for livestock watering is, therefore, to protect both the livestock and the consumer.

8. Livestock Water Standard Criteria for livestock watering usually take into account the type of livestock, the daily water requirements of each species, the chemicals added to the feed of the livestock to enhance the growth and to reduce the risk of disease, as well as information on the toxicity of specific substances to the different species

9. Recreational use Recreational water quality criteria are used to assess the safety of water to be used for swimming and other water-sport activities. The primary concern is to protect human health by preventing water pollution from faecal material or from contamination by microorganisms that could cause gastro-intestinal illness, ear, eye or skin infections. Criteria are therefore usually set for indicators of faecal pollution, such as faecal coliforms and pathogens. There has been a considerable amount of research in recent years into the development of other indicators of microbiological pollution including viruses that could affect swimmers. As a rule, recreational water quality criteria are established by government health agencies.

10. Amenity use Criteria have been established in some countries aimed at the protection of the aesthetic properties of water. These criteria are primarily orientated towards visual aspects. They are usually narrative in nature and may specify, for example, that waters must be free of floating oil or other immiscible liquids, floating debris, excessive turbidity, and objectionable odours. The criteria are mostly non-quantifiable because of the different sensory perception of individuals and because of the variability of local conditions.

11. Commercial and sports fishing Water quality criteria for commercial and sports fishing take into account, in particular, the bioaccumulation of contaminants through successive levels of the food chain and their possible biomagnification in higher trophic levels, which can make fish unsuitable for human consumption.

12. In India, the Central Pollution Control Board (CPCB) has developed a concept of designated best use. Designated Best Use Class Criteria Drinking Water Source without conventional treatment but after disinfection A 1.Total Coliforms Organism MPN/100ml shall be 50 or less 2. pH between 6.5 and 8.5 3. Dissolved Oxygen 6mg/l or more 4. Biochemical Oxygen Demand 5 days 20  C, 2mg/l or less Outdoor bathing (Organised) B 1.Total Coliforms Organism MPN/100ml shall be 500 or less 2. pH between 6.5 and 8.5 3. Dissolved Oxygen 5mg/l or more 4. Biochemical Oxygen Demand 5 days 20  C, 3mg/l or less Drinking water source after conventional treatment and disinfection C 1. Total Coliforms Organism MPN/100ml shall be 5000 or less 2. pH between 6 and 9 3. Dissolved Oxygen 4mg/l or more 4. Biochemical Oxygen Demand 5 days 20  C, 3mg/l or less Propagation of Wild life and Fisheries D 1. pH between 6.5 and 8.5 2. Dissolved Oxygen 4mg/l or more 3. Free Ammonia (as N) 4. Biochemical Oxygen Demand 5 days 20  C, 2mg/l or less Irrigation, Industrial Cooling, Controlled Waste disposal E 1. pH between 6.0 and 8.5 2. Electrical Conductivity at 25  C micro mhos/cm, maximum 2250 3. Sodium absorption Ratio Max. 26 4. Boron Max. 2mg/l Below-E Not meeting any of the A, B, C, D & E criteria

13. A colour coding frequently used to depict the quality of water on maps Blue water This water can be directly used for drinking, industrial use, etc. Green water Water contained in soil and plants is termed as green water White water Atmospheric moisture is white water Brown or grey water Various grades of wastewater are shown by brown or grey colour

14. Water Quality Criteria Characteristics Designated best use A B C D E Dissolved Oxygen (DO)mg/l, min 6 5 4 4 - Biochemical Oxygen demand (BOD)mg/l, max 2 3 3 - - Total coliform organisms MPN/100ml, max 50 500 5,000 - - pH value 6.5-8.5 6.5-8.5 6.0-9.0 6.5-8.5 6.0-8.5 Colour, Hazen units, max. 10 300 300 - - Odour Un-objectionable - - Taste Tasteless - - - - Total dissolved solids, mg/l, max. 500 - 1,500 - 2,100 Total hardness (as CaCO 3 ), mg/l, max. 200 - - - - Calcium hardness (as CaCO 3 ), mg/l, max. 200 - - - - Magnesium hardness (as CaCO 3 ), mg/l, max. 200 - - - - Copper (as Cu), mg/l, max. 1.5 - 1.5 - - Iron (as Fe), mg/l, max. 0.3 - 0.5 - - Manganese (as Mn), mg/l, max. 0.5 - - - - Cholorides (as Cu), mg/l, max. 250 - 600 - 600 Sulphates (as SO 4 ), mg/l, max. 400 - 400 - 1,000 Nitrates (as NO 3 ), mg/l, max. 20 - 50 - - Fluorides (as F), mg/l, max. 1.5 1.5 1.5 - - Phenolic compounds (as C 2 H 5 OH), mg/l, max. 0.002 0.005 0.005 - - Mercury (as Hg), mg/l, max. 0.001 - - - - Cadmium (as Cd), mg/l, max. 0.01 - 0.01 - - Salenium (as Se), mg/l, max. 0.01 - 0.05 - - Arsenic (as As), mg/l, max. 0.05 0.2 0.2 - - Cyanide (as Pb), mg/l, max. 0.05 0.05 0.05 - - Lead (as Pb), mg/l, max. 0.1 - 0.1 - - Zinc (as Zn), mg/l, max. 15 - 15 - - Chromium (as Cr 6+ ), mg/l, max. 0.05 - 0.05 - - Anionic detergents (as MBAS), mg/l, max. 0.2 1 1 - - Barium (as Ba), mg/l, max. 1 - - - - Free Ammonia (as N), mg/l, max - - - 1.2 - Electrical conductivity, micromhos/cm, max - - - - 2,250 Sodium absorption ratio, max - - - - 26 Boron, mg/l, max - - - - 2

15. Suspended particulate matter and sediment The attempts in some countries to develop quality criteria for suspended particulate matter and sediment aim at achieving a water quality, such that any sediment dredged from the water body could be used for soil improvement and for application to farmland. Another goal of these quality criteria is to protect organisms living on, or in, sediment, and the related food chain. Persistent pollutants in sediments have been shown to be accumulated and biomagnified through aquatic food chains leading to unacceptable concentrations in fish and fish-eating birds. NOTE: SEE VARIOUS TABLE FOR DATA

16. WATER QUALITY ASSESSMENT AND POLLUTION CONTROL WMA 318 PART 3

17. TYPES OF WATER Water is commonly described either in terms of its nature, usage, or origin . The implications in these descriptions range from being highly specific to so general as to be non-definitive . Ground waters originate in subterranean locations such as wells, while surface waters comprise the lakes, rivers, and seas.

18. TYPES OF WATER (Cont) Fresh Water (precisely less than 0.5%) Fresh water may come from either a surface or ground source, and typically contains less than 1% sodium chloride . It may be either " hard " or " soft ," i.e., either rich in calcium and magnesium salts and thus possibly forming insoluble curds with ordinary soap. Actually, there are gradations of hardness, which can be estimated from the Langelier or Ryznar indexes or accurately determined by titration with standardized chelating agent solutions such as versenates.

19. TYPES OF WATER (Cont) Brackish Water Brackish water contains between 0.5 or 1 and 2.5% sodium chloride, either from natural sources around otherwise fresh water or by dilution of seawater. Brackish water differs from open seawater in certain other respects. The biological activity, for example, can be significantly modified by higher concentrations of nutrients. Fouling is also likely to be more severe as a consequence of the greater availability of nutrients. The main environmental factors responsible, singly or in combination, for these differences are the salinity , the degree of pollution , and the prevalence of silt .

20. TYPES OF WATER (Cont) Seawater Seawater typically contains about 3.5% sodium chloride, although the salinity may be weakened in some areas by dilution with fresh water or concentrated by solar evaporation in others . Seawater is normally more corrosive than fresh water because of the higher conductivity and the penetrating power of the chloride ion through surface films on a metal. The rate of corrosion is controlled by the chloride content, oxygen availability, and the temperature.

21. Saline Water is classified as "saline" when it becomes a risk for growth and yield of crops. Saline water has a relatively high concentration of dissolved salts (cations and anions). Salt is not just "salt" as we know it - sodium chloride (NaCl) - but can be dissolved calcium (Ca 2+ ), magnesium (Mg 2+ ), sulfate (SO 4 2 -), bicarbonate (HCO 3- ), Boron (B), and other compounds. Water can be both saline and sodic, or saline-sodic. If water has an EC greater than 4 (2 for horticulture) and a Sodium Adsorption Ration (SAR) greater than 12, it is considered saline-sodic The concentration is usually expressed in parts per million (ppm) of salt. If water has a concentration of 10,000 ppm of dissolved salts, then one percent (10,000 divided by 1,000,000) of the weight of the water comes from dissolved salts.

22. Classification of Salinity Slightly saline water contains around 1,000 to 3,000 ppm. 0.1-0.3% Moderately saline water contains roughly 3,000 to 10,000 ppm. 0.3-1% Highly saline water has around 10,000 to 35,000 ppm of salt. 1-3.5% Seawater has a salinity of roughly 35,000 ppm, equivalent to 35 g/L. 3.5-5.0% Brine Greater 50,000 ppm. 5.0% above

23. Salinity in Different Water Bodies Water salinity based on dissolved salts in parts per thousand (ppt) Fresh water Brackish water Saline water Brine < 0.5 0.5 – 30 30 – 50 > 50

24. Relationship between Tidal and Salinity Salinity variations of the tidal water irrigating the rice fields at Warri mangrove swamp were studied for one calendar year. It was found that the mean pH is 7.24 for low tides and 7.14 for high tides, and pH is highest in July for both high and low tides. Sodium, calcium and magnesium, the major cationic constituents of the soluble salts in the saline tidal irrigation water, as well as potassium a minor ionic constituent were all found to be highest in June at both low and high tides. Also, both the Electrical Conductivity (EC) and the derived Sodium Adsorption Ration (SAR) were highest in June. Salinity at both high and low tides is highest in June but lowest in September for high tides and in October for low tides. The indications are that the adverse effects of salinity are largely responsible for the poor initial growth and survival of the rice variety during early seedling stage. From salinity point of view, it would appear that October is the most favourable month to transplant rice at the Warri mangrove swamp.

25. Effects of Salinity Saline water reduces plant growth to varying degrees, with grass and grain crops generally showing less sensitivity and field crops being most sensitive. Aside from biomass reduction, salinity can have additional effects on plants. For example, in a study by Bauder et al., both inoculated and non-inoculated alfalfa were grown with irrigation waters of progressively higher salinity levels Correction of Salinity There are no amendments, chemicals, or additives available commercially that can be added to saline water to make the salt go away. Dilution with a non-saline water or salt precipitation with an evaporation process which leaves the salt behind and traps the evaporated water can be used. Dilution of saline irrigation water is only possible if there is a source of non-saline water with which to dilute the saline water

26. TYPES OF WATER (Cont) The combination of high conductivity and oxygen solubility is at a maximum at this point (oxygen solubility is reduced in more concentrated salt solutions). The corrosion of numerous metals in a wide range of saline waters is reported in the following Table . Effect of velocity on the corrosion of metals in seawater

27. TYPES OF WATER (Cont) Distilled or Demineralized Water The total mineral content of water can be removed by either distillation or mixed-bed ion exchange. In the first case, purity is described qualitatively in some cases (e.g., triple-distilled water), but is best expressed, for both distilled and demineralized water, in terms of specific conductivity. Water also can be demineralized by reverse osmosis or electrodialysis.

28. TYPES OF WATER (Cont) Steam Condensate Water condensed from industrial steam is called steam condensate. It approaches distilled water in purity, except for contamination (as by DO or carbon dioxide) and the effect of deliberate additives (e.g., neutralizing or filming amines).

29. TYPES OF WATER (Cont) Boiler Feedwater Make-up The feedwater make-up for boilers is always softened and subsequently deaerated. It may vary in quality from fairly high dissolved solids (e.g., Zeolite-Treated), to very pure demineralized feed for high-pressure boilers. It tends to be highly corrosive, because of its softness, until thoroughly deaerated. This term is more precise than “ boiler feedwater ” , which may include recirculated steam condensate in various ratios to fresh make-up water.

30. TYPES OF WATER (Cont) Potable Water Potable water is fresh water that is sanitized with oxidizing biocides such as chlorine or ozone to kill bacteria and make it safe for drinking purposes. By definition, certain mineral constituents are also restricted. For example, the chlorinity will be not more than 250 ppm chloride ion in the United States or 400 ppm on an international basis.

31. TYPES OF WATER (Cont) Process or Hydrotest Water/Firewater These terms are essentially non-definitive, since the water employed may be of almost any chemistry, ranging from demineralized water to quite saline fresh water or even seawater in some cases. “ Produced water ” is that which originates in oil and gas production, emanating from geological sources with the hydrocarbons.

32. TYPES OF WATER (Cont) Cooling Water Cooling water is another undefined term, although it implies that any necessary treatment against excessive scaling or corrosion has been applied, or corrosion-resistant material selected . This may include anything from fresh water to seawater, and may comprise either an open- or closed-loop system, or a once-through system.

33. TYPES OF WATER (Cont) Waste Water By definition, waste water is any water that is discarded after use. Sanitary waste from private or industrial applications is contaminated with fecal matter, soaps, detergents, etc., but is quite readily handled from a corrosion standpoint. Industrial wastes from chemical or petrochemical sources can contain strange and specific contaminants which greatly complicate materials selection, especially in the uses of plastics and elastomers.

34. WATER QUALITY ASSESSMENT AND POLLUTION CONTROL WMA 318 PART 4

35. SOURCES OF WATER POLLUTION The surface water and groundwater systems Surface water is the water we see in streams, rivers, wetlands, and lakes across the country. Every square mile of ground drains into one of these bodies of water. The area drained is known as a watershed. As smaller creeks and rivers feed into larger ones, the size of the watershed increases.

36. SOURCES OF WATER POLLUTION (Cont) While surface water is found in the form of rivers and lakes, groundwater is stored in aquifers . Aquifers are formations of cracked rock, sand, or gravel that hold water and yield enough water to supply wells or springs. More than 95 percent of the world ’ s usable water resources are stored in its groundwater. Approximately third-quarter of all Nigerians depends on groundwater for their drinking water. In most times, 80 percent of all Nigerians depend on groundwater for their drinking water, and more than 97 percent of all rural Nigerians, depend on groundwater for their drinking water supplies.

37. SOURCES OF WATER POLLUTION (Cont) As people pump and use water from these underground aquifers, the water must be replaced. Aquifers are replenished or recharged by water seeping down through the soil from surface water supplies. In some parts of the country, groundwater supplies are very deep, and pollutants may be filtered out by layers of soil, sand, and gravel. In parts of Nigeria, there are more direct links to the groundwater. In some parts of north-central and south of Nigeria, the groundwater supply may come within a few meters of the soil surface. That ’ s why this area of south is covered with wetlands and prairie potholes. In these areas, there is much less filtration by the soil and a greater risk of contamination by animal wastes, pesticides, and other pollutants. In other parts of the country, like the east and some part of the south west corner, limestone sits just below the soil surface. This limestone layer, or karst, can crack, erode, and form caverns that allow water and any pollutants to travel with little filtering from the soil.

38. SOURCES OF WATER POLLUTION (Cont) Non-point source pollution refers to pollutants that come from a widespread area and cannot be tracked to a single point or source. Soil erosion, chemical runoff, and animal waste pollution are all examples of non-point source pollution. Non-point source pollution is major water quality problem by sheer volume and in terms of current and future economic costs to the nation.

39. SOURCES OF WATER POLLUTION (Cont) Point source pollution – also known as “ the end of the pipe pollution ”– can be traced to a specific source, such as a leaking chemical tank, effluents coming from a waste treatment or industrial plant, or a manure spill from a hog confinement lagoon. Although this may seem easy to control, there are economic, political, and other factors involved. For known point source pollution threats, households, communities, industry, and agribusiness must deal with the problem of disposing of wastes and by-products.

40. TREATMENT OF POLLUTANTS TREATMENT METHODS There are various levels of treatment that prevent dumping raw waste products from being dumped into surface waters. Industrial wastes may require special treatment to remove harmful chemicals before reentering the water system. For the more common problem of organic wastes, the three main treatment methods for treating waste water are septic systems, lagoons, and sewage treatment plants. Each method must be properly sized so that the treatment system is able to handle the volume of waste entering it. Septic systems are designed for individual households, lagoons may meet the needs of small towns, and sewage treatment facilities are necessary for controlling pollution.

41. TREATMENT OF POLLUTANTS (Cont) Septic systems Septic systems are generally used in rural areas to handle household wastes. They usually use a large tank buried in the ground to contain and break down household sewage. Attached to the tank is a series of perforated pipes that are buried in a drain field and are usually surrounded by crushed rock or gravel to facilitate drainage. Fats, oils, and grease, as well as large waste particles, are stored and later pumped out of the holding tank, while the water and suspended solids in the water flow into the soil through the perforated pipes. The soil around the septic system filters many harmful compounds, and bacteria break down organic matter.

42. TREATMENT OF POLLUTANTS (Cont) STANDARD: Septic systems are most popular in rural and suburban areas and must be located in soils that meet standards for percolation or the ability to drain away water. standards require a maximum percolation rate of one inch of water in 60 minutes. A slow percolation rate allows soil bacteria to break down wastes as they move into soil layers. CONCERN: Septic systems are generally a greater source of concern for groundwater pollution than for surface water pollution. However, septic systems are a real concern for surface water pollution when they are located near lakes, rivers, and streams. Of particular concern are lakes with high concentrations of tourist homes. Note: 1 Cube Inch is equal 16.34 cm 3, Multiple inch by 2.54 to get Centimetre

43. TREATMENT OF POLLUTANTS (Cont) Lagoons Many communities, feedlot operators, and industries use lagoons to control wastes. A lagoon is simply one or a series of shallow holding pits into which wastes are pumped and treated. In a well-designed lagoon system, the material is aerated so bacteria can break down the organic matter. STANDARD: In municipal lagoons, the water generally stays in the lagoon for at least 30 days for this process to be completed. Then the water is removed and treated with chlorine as needed to destroy remaining bacteria. The remaining solids must be disposed of by spreading on farm fields or burying. CONCERN: Lagoons are inexpensive to construct and operate compared to other systems. However, poorly constructed lagoons and lagoons built where the water table is very high have been found to leak. The most often found contaminant tends to be nitrates.

44. TREATMENT OF POLLUTANTS (Cont) Treatment plants We require two levels of sewage treatment. Primary sewage treatment simply filters out unwanted items such as sticks, stones, garbage, and other debris that arrive at the treatment plant and allows time for the solid materials to settle out. Secondary treatment uses aeration and aerobic , or oxygen-using, bacteria to break down organic wastes. The water is then treated with chlorine to kill bacteria and discharged into adjacent rivers and streams. Treatment plants remove approximately 90 percent of the organic waste and suspended solids, less than 70 percent of the toxic metals and synthetic organic chemicals, 50 percent of the nitrogen in the form of nitrates, and 30 percent of the phosphorus in the form of phosphates . CONCERN: This remaining discharge is still high in nutrients and is not pure water entering the surface water. More advanced treatment systems are available, but they are rarely used due to their high cost. The remaining sludge is sent to a landfill as waste or applied to the land as a soil additive.

45. Wastewater Treatment Process

46. TREATMENT OF POLLUTANTS SUMMARY Runoff pollution is difficult to control. The best method of control is limited use of chemical pesticides. The speed and amount of movement depends on whether the pesticide is water-soluble, the soil type, the amount of rain, and the proximity of the water table to the surface . Over time, nearly all pesticides break down to other chemicals as they are exposed to sunlight and air. Generally, it is these base chemicals that are detected in groundwater. Some agricultural drainage wells provide direct pathways for pollutants to enter groundwater. The forms of nitrogen that cause problems as pollutants are the nitrate and ammonium forms. The nitrate form is water-soluble and moves with the water into surface water or groundwater. The ammonium form attaches to soil particles.

47. MAINTAINING AND IMPROVING WATER QUALITY Cultural, Mechanical, Biological and Chemical Control

48. The best solution is prevention Just as there is no single source of water pollution, there is no single answer to solve the problem. Once water has become contaminated, it is very difficult, if not impossible, to clean. Surface water flows quickly, and a pollutant will generally be diluted as it enters larger bodies of water. However, even large bodies of water, such as the Gulf of Mexico near the mouth of the Mississippi River, cannot tolerate many years of eroded soils, increased nutrients, and chemical pollution. Groundwater, however, moves very slowly. In heavy clay layers or in bedrock, water might only move several inches per year. Even in gravel and sand aquifers, groundwater may move only several hundred to a thousand feet per year. Once the water is polluted, it will spread out slowly over a period of many years . Some problems, such as hazardous waste sites, require massive, expensive clean-up procedures. With other problems, such as large manure spills, little can be done but let the wastes become diluted as they reach larger bodies of water. However, there are steps to take to reduce some of the most serious problems such as siltation from erosion is passed legislative law to warn deterrent

49. Other Methods Are No-till and minimum-till farming: Most of the crop residues - the stalks and leaves of the harvested crop - are left on the surface of the field with no-till and minimum-till farming. Crops are planted into the crop residue the next year. This may reduce soil loss by up to 90 percent. The residue helps keep raindrops from directly hitting the soil and breaking it into small erodible particles. With no-till or minimum-till farming, crop residue remains to protect the soil from rain or wind. Contour farming: Contour farming involves planting crops in rows that circle around a hill in contours rather than in straight rows that go up and down the hill. These contours help break the water flow. With conventional farming methods, straight rows encourage the water to run down the row and wash along soil.

50. Other Methods Are (Cont) Terraces: For very steep hillsides, terraces may be required. Terraces are constructed by planting a short slope with grass or other cover crops and then planting the level area with crops. This pattern of short slopes and planting areas follows the hillsides. This practice breaks up the steep hill into a series of shorter slopes and level areas and slows down the water flow. Since the terraces are planted in grass, they hold the slope in place and reduce erosion. Terracing provides good protection for steeper slopes, especially if combined with low-till or no-till farming. Grassed waterways: Where concentrated water runoff occurs due to the sloping of several hills or along bottom slopes, planting grass or hay is recommended. As water collects and runs along these erosion-prone areas, the denser root systems of the grasses help hold the soil in place to prevent these areas from washing out and forming gullies.

51. Other Methods Are (Cont) Grasses and filterstrips: Stream banks and road ditches also need to be protected. Plants growing on banks and slopes help hold the soil. Along stream and river banks, filter-strips of grasses and trees help slow down water run-off and help prevent soil from washing into waterways. Filter strips help reduce erosion along stream and river banks.

52. Good pest management depends Since polluted groundwater is nearly impossible to clean, prevention is the only solution. For pesticides, this means reducing the use of chemicals and focusing on an integrated pest management program that controls weeds and insects by more natural means whenever possible and resorting to pesticides only as a last resort. Good pest management depends on four methods of s control: cultural, mechanical, biological, and chemical.

53. CULTURAL CONTROL Cultural control relies on planting factors such as crop rotation and planting after weeds have been killed following germination. Good management starts with scouting fields on a regular basis . Keeping records of past problem areas helps control pests, as well as the need for chemical means of controlling pests. The first step is to determine the seriousness of the infestation of weeds or insects. This is where trade-offs take place. Will the potential loss of crop yield be greater than the cost of chemical treatment? Are there other options that might be cheaper and less environmentally dangerous? There are no set answers since each farm is different and each year brings new challenges.

54. MECHANICAL CONTROL Mechanical weed control or cultivation is one of the oldest forms of control. Tools like the rotary hoe are used when plants are small, while a cultivator is used on larger plants. Although mechanical control requires the use of fuel to pull the implement across the fields, it results in reduced chemical control. Most farmers substituting mechanical control for herbicides estimate that it costs them about half of what their neighbors spend on chemical control.

55. BIOLOGICAL CONTROL Biological control introduces insects and plant diseases that target specific weed or other pest populations. One example in the Midwest is the introduction of the musk thistle weevil which feeds on musk thistles. Thistles are tough weeds to control, and the weevil appears promising in controlling pest populations. Insect control is best suited for pasture land rather than crop land Cultivation tends to disrupt the life cycle of the insects. Researchers are also developing microbial controls. These microbes are essentially plant diseases that occur naturally. The microbes are cultured in labs and sprayed on fields where they select the weeds but not the crops. One major advantage of biological control is that the diseases can adapt to changing weeds so they can ’ t build up resistance or tolerances, which has occurred with herbicides and insects. Musk thistle weevils are used as a biological control on thistles.

56. CHEMICAL CONTROL Farmers using other controls methods must occasionally resort to chemical control for tough cases. However, even when chemical control is required, it ’ s possible to reduce the amounts of chemicals used. Careful calibration or setting of the sprayer is essential to not over-apply chemicals. In addition, many farmers use banding techniques that spray chemicals in a narrow band over the crop row and rely on cultivation for the weeds between rows. An Iowa State University research study shows that this method reduces the amount of chemicals used by 50 to 67 percent, while maintaining the corn yield on 99 percent of the fields tested.

57. Controlling nitrate pollution General management practices may help ease the problem of nitrate pollution, but they also rely on trade-offs that protect both the economic interests of the farmer and the natural environment. The bottom line is not to apply more nitrogen based fertilizers, either artificial or natural animal byproducts, than the crops need for that growing season. Since ammonia may be lost to the air and nitrates may be moved with the water, it is economical for the farmer to apply only the amount of nitrogen needed and only at the time it is needed by the plants.

58. SUMMARY Storm water, drainage systems in town and city are also considered to be dispersed sources of many pollutant, because, even though the pollutant are often convene into streams or lakes in drainages pipes or storm sewer, they are usually many of these discharges scattered over a large area.

59. SUMMARY (Cont) Pollutants from dispersed sources are much more difficult to control. Many people think that sewage is the primary culprit in water pollution problems, but dispersed sources cause a significant fraction of the water pollution in Nigeria. The most effective way to control the dispersed sources is to set appropriate restriction on land use.

60. SUMMARY (Cont) In addition to being classified by there origin, water pollutant can be classified into group of substances base primarily on there environmental or health effect. E.g., the following lists identify 9 specific types of pollutants. Pathogenic organism Oxygen-demanding substances Plant nutrients Toxic organics Inorganic chemicals Sediments Radioactive substances Heat Oil

61. SUMMARY (Cont) Domestic Sewage is a primary source of the first three types of pollutant. Pathogen or diseases causing micro-organism are excreted in the feaces of infected person and may be carried into water receiving sewage discharges. Sewage from communities with large population is very likely to contained pathogen of some type. Sewage also carries oxygen demanding substance — the organism waste that exert a biochemical oxygen demand as they are decomposed by microbes. BOD changes the ecological balance in a body of water by depleting the Dissolved Oxygen DO content. Nitrogen and phosphorus, the major plant nutrients are in sewage, too, as well as in runoff from farm and from suburban lawns.

62. SUMMARY (Cont) SOLUTION Conventional Sewage treatment processes significantly reduce the amount of pathogens and BOD in sewage, but do not eliminate them completely. Certain virus, in particular, may be somewhat resistant to the sewage disinfection processes. (A virus is an extremely small pathogenic organism that can only be seen with electron microscopes). To decrease the amount of Nitrogen and Phosphorus in sewage, usually some form of advanced sewage treatment must be applied.

63. Toxic Chemical Toxic organic chemical, primary pesticide may be carry into the water in the surface runoff from agricultural areas. Perhaps the most dangerous type is the family of chemical called Chlorinated hydrocarbons. Common examples are known by there common chemical names as chlordane, Dieldrin, Heptachlor, and the famous DDT., which has been banned all over the world. They are very effective poison against insect that demand agriculture crops. Unfortunately, they can kill fish, birds, and animals, including humans. And they are not very biodegradable, taking more than 30 years in some cases to dissipate from the environment.

64. Inorganic and Oil Poisonous inorganic chemical, specifically those of the heavy metal group, such as lead, mercury, and chromium, also usually originate from industrial activities and are considered hazardous waste. Oil is washed into surface water in ruoff from road and parking lot, and groundwater can be polluted from leaking underground tanks, accidental oil spills from large transport tankers at a sea occasional occur, causing significant environmental damage. Blow out accident at offshore oil wells can release many thousand of tonnes of oil in a short period of time. Oil spills at sea may eventually move towards shore, affecting aquatic life and damaging recreational areas.

65. CALCULATIONS

66. EXPRESSING CONCENTRATION The properties of solutions, suspensions and colloids depend to large extent on their concentrations. A dilute or weak solution has a relatively small amount of solute dissolved in the solvent. It has a characteristic different from those concentrated or strong solution of the same substances, in which a relatively large amount of solute is present. Since concentrations need to be expressed quantitatively, instead of qualitatively terms like dilute or strong, concentration are usually expressed in terms of mass per unit volume, part per million or billion, or percent. MASS PER UNIT VOLUME: One of the common types of concentration is milligram per liter (mg/L). For example, if a mass of 10 mg of oxygen is dissolved in a volume of 1 L of water, the concentration of that solution is expressed simply as 10mg/L. If 0.3g of salt is dissolved in 1500mL of water, then the concentration is expressed as 300mg/1.5L=200mg/L, where 0.3g = 300mg and 1500mL = 1.5L (1g=1000mg/L; 1L=1000mL). Very dilute solutions are more conveniently expressed in term of micrograms per liter (g/L). For example, a concentration of 0.004mg/L is preferably written as its equivalent 4g/L. Since 1000g=1mg, e.g., a concentration of 1250g/L is equivalent to 1.25mg/L. In air, concentrations of particulate matter of gases are commonly expressed in terms of micrograms per cubic meter (g/m3).

67. PART PER MILLION: One liter of water has a mass of 1kg. But 1kg is equivalent to 1000g or 1 million mg. therefore, if 1 mg of a substance is dissolved in 1 L of water, we can say that there is 1 mg of solute per million mg of water. In other words, there is one part per million (1 ppm) Neglecting the small changes in the density of water as substances are dissolved in it, we can say that, in general, a concentration of 1 mg per liter is equivalent to one part per million: 1mg/L=1ppm. Conversion is very simple; for example, a concentration of 17.5 mg/L is identical to 17.5ppm The expression mg/L is preferred over ppm just as the expression g/L is preferred over its equivalent of ppb. But both types of units are still used and the student should be familiar with each.

68. PERCENTAGE CONCENTRATION: Concentrations in excess of 10000mg/L are generally expressed in terms of percent, for conveniences. For practical purposes, the conversion of 1 percent = 10000 mg/L be used even though the density of the solutions are slightly more than that of pure water (10000mg/L = 10000mg/1000000mg = 1 mg/100 mg = 1 percent). The concentration of salts in seawater is about 35000mg/L. To convert to percent salts, divide by 10,000 obtaining 3.5 percent. The concentration of wastewater sludge may be about 3 percent solids. To convert this to mg/L, multiply by 10,000 getting 30000mg/L solids. A concentration expressed in terms of percent may be also computed using the following expression. Percent = (Mass of Solute (mg)/ Mass of Solvent (mg)) X 100

69. U.S CUSTOMARY UNITS: The expression grains per gallon (gpg) are sometimes used for concentrations of certain substances in water. One grain per gallon is equivalent to a concentration of 17.1 milligrams per liter: 1gpg=17.1mg/L The expression pounds per million gallon is also used in US customary unit of concentration for water treatment applications. Since 1 gallon of water weighs 8.34lb, 1 gal/mil gal is the same as 8.34 lb/mil gal. Or we can say that 1mg/L = 8.34 mil gal to convert from mg/L to lb/mil gal, multiply by 8.34; to go from lb/mil gal to mg/L. divide by 8.34

70. EXAMPLE: A 500-mL aqueous solution has 125mg of salt dissolved in it. Express the concentration of this solution in terms of (a) mg/L, (b)ppm, (c)gpg (d) Percent and (e) lb/mil gal Solution (125mg/500mL)X1000mL/L = 250mg/L 250mg/L = 250 ppm (250 mg/L X 1gpg)/17.1 mg/L = 14.6 gpg Applying this equation Percent = (Mass of Solute (mg)/ Mass of Solvent (mg))X 100 Percent = 0.125g/500g X 100 = 0.025 percent Or divide 250mg/L by 10,000 to get 0.025 percent 250 mg/L X 8.34 = 2090 lb/mil gal EXAMPLE: How many pounds of chlorine gas should be dissolved in 8 mil gal of water to result in a concentration of 0.2 mg/L Solution 0.2 mg/L X 8.34 = 1.67 lb/mil gal And 1.67 lb/mil gal X 8 mil gal = 13 lb

71. BIOCHEMICAL OXYGEN DEMAND: Bacteria and other microorganisms use organic substance for food. As they metabolize organics are broken down into simpler compounds, such as CO2 and H2O, and the microbes use the energy released fro growth and reproduction. When this process occurs in water, the oxygen consumed is the DO. If oxygen is not continually replaced in the water by artificial or natural means, then the DO level will decrease as the organic are decomposed by the microbes. This need for oxygen is called Biological Oxygen Demand . In effect, the microbes “ demand ” the oxygen for use in the biochemical reactions that sustain them. Organic waste in sewage is one of the major types of water pollutants. It is impractical to isolate and identify each specific organic chemical in these wastes and to determine its concentration. Instead, the BOD is used as an indirect measure of the total amount of biodegradable organics in the water. The more organic material there is in the water; the higher the BOD exerted by the microbes will be.

72. In addition to being used as a measure of the amount of organic pollutant in streams or lakes, the BOD is used as a measure of the strength of sewage. This is the most important parameters for design and operation of water pollution control plant. A strong sewage has a high concentration of organic material and a correspondingly high BOD. The complete decomposition of organic material by microorganisms takes time, usually 20d or more under ordinary circumstances. The amount of oxygen used to completely decompose or stabilize all the biodegradable organics in a given volume of water is called Ultimate BOD , or BODL for example, if a 1-L volume of municipal waste requires 300 mg of oxygen for complete decomposition of the organics, the BODL would be expressed as 300mg/L. One liter of waste from an industrial or food processing plant may require as much as 1500 mg of oxygen for complete stabilization of the waste. In this case, the BODL would be 1500mg/L, indicating a much stronger waste than ordinary municipal or domestic sewage. In general, then, the BOD is expressed in terms of mg/L of oxygen. The BOD is a function of time. At the very beginning of a BOD test, or time = 0, no oxygen will have been consumed and the BOD = 0. As each day goes by oxygen is used by the microbes and the BOD increase. Ultimately, the BODL is reached and the organics are completely decomposed. A graph of the BOD versus time has the characteristic shape called the BOD Curve.

73. The BOD curve can be expressed mathematically by the following equation: BODt = BODL X (1 – 10-kt) Where BODt = BOD at any time t. mg/L BODL = Ultimate BOD, mg/L k = constant representing the rate of BOD reaction t = time, d The rate at which oxygen is consumed is expressed by the constant k. the value of this rate constant depend on the temperature, the type of organic material, and the types of microbes exerting the BOD. For the ordinary domestic sewage at a temperature of 20oC, the value of k is usually about 0.15/d

74. Example: A sample of sewage from a town is found to have a BOD after 5 d (BOD 5 ) of 180mg/L. Estimate the Ultimate BOD (the BOD L ) of the sewage assuming that k = 0.1/d for this waste water. Solution BODt = BODL X (1 – 10 -kt ) 180 = BODt = BODL X (1 – 10 -kt ) , It implies that 180 = BODL X (1-10 -0.1X5 ) Therefore 180 = BODL X (1- 0.316) ; 180 = BODL X 0.684 Rearranging terms to solve for BODL gives BODL = 180/0.684 = 260 mg/L Rounded off. This is particularly true when the BOD data are used to monitor the efficiency of a water pollution control plant. It has been found that more than two-third of the BODL is usually exerted within the first 5d of decomposition. For instance, in the preceding example, the 5d BOD is 180/260 = 0.69, or 69% of the ultimate BOD. For practical purposes, the 5d BOD, or BOD5, has been chosen as a representation of the organic content of water or waste water. For standardization of results, the test must be conducted at a temperature of 20 o C. In summary, the parameter of BOD 5 is the amount of dissolved oxygen used by microbes in the 5 d to decompose organic substances in water at 20oC.

75. Measurement of BOD5 The traditional BOD test is conducted in the standard 300-mL glass BOD bottles . The test for 5-d BOD of water sample involves taking two DO measurements: an initial measurement when the test begins, at time t = 0, and a second measurement, at t = 5, after the sample has been incubated in the dark for 5 d at 20oC. The BOD5 is simply the difference between the two measurements. For example consider that a sample of water from a stream is found to have an initial DO of 8.0 mg/L. It is placed directly into a BOD bottle and incubated for 5 d at 20oC. After the 5 d, the DO is determined to be 4.5mg/L.The BOD is the amount of oxygen consumed, or the difference between the two DO readings. That is, BOD5 = 8.0 – 4.5 = 3.5mg/L. Very clean bodies of surface water usually have a BOD5 of about 1 mg/L due to the presence of naturally occurring from decaying leaves and animal wastes. BOD5 values in excess of 10 mg/L, however usually indicate the presence of sewage pollution.

76. EXPERIMENTATION: When measuring the BOD5 of sewage, it is necessary to first dilute the sample in the BOD bottle. Domestic sewage usually has a general BOD value of 200 mg/L. If the sample were not diluted, the entire DO will be completely depleted and it would not be possible to get a DO reading on the fifth day. Computation of the BOD5, using this dilution method in a 300-ml BOD bottle, is done by using the following equation: Where DO0 = Initial DO at t = 0 D05 = DO at t = 5d V = Sample volume, mL

77. EXAMPLE : A 6.0-ml sample of wastewater is diluted to 300 mL with distilled water in a standard BOD bottle. The initial DO in the bottle is determined to be 8.5 mg/L, and the DO after 5d at 20 o C is found to be 5.0 mg/L. Determine the BOD 5 of the wastewater and compute its BOD L . Assume that k = 0.1/d SOLUTION: BOD5 = ((8.5-5.0) X 300)/ 6.0 = 3.5 X 300/6.0 = 180 mg/L Now applying BODt = BODL X (1 – 10 -kt ) 180 = BODL X (1 – 10 -0.1X5 ) and BODL = 180/0.684 = 260mg/L

78. CHEMICAL OXYGEN DEMAND The BOD test provides a measure of the biodegradable organic material in water, i.e., of the substance that microbe can readily use for food. There might also be non biodegradable or slowly biodegradable substance that will not detected by the convectional BOD test. The Chemical Oxygen Demand, COD is another parameter of water quality which measures all organics, including the non biodegradable substances. It is a chemical test using a strong oxidizing agent (Potassium Dichromate), sulphuric acid and heat. The result of the COD test can be available in just 2hours, a definite advantage over the 5d required for the standard BOD test. COD values are always higher than BOD values for the same sample, but there is generally no consistent correlation between the two tests for different wastewater. In other word, it is not feasible to simply measure the COD and then predict the BOD. Because most waste water treatment plant are biological in their mode of operation, the BOD is more representative of the treatment process and remains a more commonly used parameter than the COD.

79. SOLIDS: Solids occurs in water either in solution or in suspension. These 2 types of solid are distinguish by passing the water sample through a glass-fibre filter. By definition, the Suspended Solid are retain on top of the filter and the Dissolved Solid pass through the filter with the water. If the filtered portion of the water sample is placed in a small dish and then evaporated, the solid in the water remain as a residue in the evaporating dish. This material is usually called Total Dissolved Solid TDS . The concentration of TDS is expressed in term of mg/L. it can be calculated as follows. Where A = equal to weigh of dish plus residue. Mg B = Weight of empty dish C = Volume of sample filtered mL.

80. Example: The weight of an empty evaporating dish is determined to be 40.525g. After a water sample is filtered, 100mL of the sample is evaporated from the dish. The weight of the dish plus dried residue is found to be 40.545g. Compute the TDS concentration = 200mg/L In drinking water, dissolved liquid may caused taste problems. Hardness, corrosion, or aesthetic problem may also accompany excessive TDS concentration. In wastewater analysis and water pollution control, the suspended retained on the filtered are of primary importance and are referred to as TOTAL SUSPENDED SOLID TSS. The TSS concentration can be computed using the TDS equation, where A represent the weight of the filtered plus retained solid B represent the weight of the clean filter C represent the volume of the sample filtered