Water Pollution and Its Prevention Chapter 17
Water Pollution • defined as the presence of a substance in the environment that, because if its chemical composition or quantity, prevent the functioning of natural processes and produces undesirable environmental and health effects.” • almost always the byproducts of worthy and essential activities • producing crops, • creating comfortable home • providing energy and transportation • manufacturing products • removing biological wastes.
. • Many materials used widely are nonbiodegradable • They resist attack and breakdown by detritus feeders and deecomposers. • Examples include plastics. Aluminum cans and synthetic organic chemicals • Any part of the environment may be affected • Our goal should be to manage materials that are man made so that the environment will not be jeopardized for future generations.
Identify the material or • Strategy to avoid or manage pollutants • Identify the sources of the pollutants • Identify the material or materials that are causing the pollution • Develop and implement pollution control strategies to prevent the pollutants from entering the environment’ • Develop and implement alternative means of meeting the need that do not produce the pollution by-product.
Water Pollution: Sources, Type, Criteria • point and nonpoint sources • Point sources discharge pollutants at specific locations through pipes, ditches or sewers into bodies of surface water. • These can include factories, sewage treatment plants and abandoned underground mines. • These are fairly easy to identify. • In developed countries, many industrial discharges are strictly controlled, whereas in most developing countries, this type of discharge is largely uncontrolled.
Nonpoint sources • These are sources that cannot be traced to any single site of discharge. • They are usually large land areas or watersheds that pollute water by runoff, subsurface flow or deposition from the atmosphere. • This could include stormwater, seepage into the ground from croplands, livestock feedlots, logged forests, streets, lawns, and parking lots.
Pathogens • these include bacteria, viruses and other parasitic organisms. • A person or animal may till harbor low populations of a pathogen even after symptoms of the disease disappear. • These are called carriers. • These measures are more important than modern medicine • purification and disinfection of public water supplies with chlorine • sanitary collection and treatment of sewage wastes • maintenance of sanitary standards in food facilities • education in personal and domestic hygiene
Sanitation_ • prevention of disease is good medicine, this has been done through public health measures • over 1 billion people do not have access to safe drinking water • 2.5 billion people live in areas having poor or no sewage collection or treatment • 3 million deaths each year due to waterborne diseases.
Over 1 billion people do not have access to safe drinking water • 2.5 billion people live in areas having poor or no sewage collection or treatment. • Over 3 million deaths each year are traced to waterborne diseases. • One of the Millennium Development Goal (MGD) targets is to reduce by half the number of people without sustainable access to safe drinking water.
Cholera is a disease that is related to unsanitary conditions of areas where there is no sewage treatment. • A cholera outbreak in Peru killed several thousand people in Peru in 1990. • The problems with civil disorder in Liberia led to an outbreak of cholera in 2003. • WHO reports many cholera outbreaks annually and cases number in the thousands with hundreds of deaths.
Organic Wastes – • Human and animal wastes contain organic matter. Other organic matter (leaves, grass clippings, trash) enter bodies of water and can cause excessive aquatic plant growth. • When bacteria and detritus feeders decompose organic matter they consume oxygen gas dissolved in the water. • DO is directly related to temperature. Cold water holds many times more oxygen than warm water.
If there is organic material to consume, bacteria growth will be high and DO kept low. • BOD (biochemical oxygen demand) – a measure of the amount of organic material in water in terms of how much oxygen will be required to break it down biologically, chemically, or both. • The Gulf of Mexico has a region that is larger than the state of Massachusetts. • This is due to organic material washed down the Mississippi from the Midwest.
Chemical Pollutants – because water is an excellent solvent, it is able to hold many chemical substances. • Inorganic chemicals include heavy metals, acids from mine drainage, acid precipitation, road salts, • Organic chemicals include petroleum products, pesticides, polychlorinated biphenyls, cleaning solvents and detergents. • Many of these are toxic at low concentrations • Some may become a part of the food chain and be passed along through biomagnification.
Sediments – • These enter water as natural landforms weather, especially during storms. • Erosion from farmland, construction sites, mining sites, overgrazed rangelands. • When erosion is slight, streams and rivers run clear, supporting aquatic plants. • Sediment entering water in large amounts have a large impact • Silt, sand, clay and organic particles are separated because they are carried at different rates • Clay and humus are carried in suspension- makes the water muddy, reduces the amount of light penetrating the water – reduces photosynthesis
As the material settles, it coats everything, continues to block photosynthesis • Kills animals by clogging their gills and feeding structures • Eggs are particularly vulnerable • Bed load – sand and silt which is not readily carried in suspension but is washed along the bottom. This scours organisms from the rocks, buries and smothers the bottom life, fills in hiding and resting places of fish and crayfish.
Aquatic plants are prevented from reestablishing themselves because the bottom is constantly shifting • Modern storm water management is designed to reduce the bed load. • Many housing developments include storm water retention reservoirs. • This creates a small area of wetland. • Nutrients – phosphorus and nitrogen are the two most important elements for aquatic plant growth. Often they are in low supply in water. • Nutrients become water pollutants when they stimulate undesirable plant growth.
the most serious source of excessive nutrients are sewage outfalls. If the sewage is not treated, high levels of nutrients will enter the water. • Agricultural runoff is the most notorious source of excess nutrients. Runoff from lawns and feedlots are also culprits, • Criteria Pollutants – What concentration is worrisome? • There are standards set by the EPA. There are 158 chemicals identified as pollutants. The list also has recommendations of concentration or freshwater, salt water and human consumption.
Standards for drinking water are much higher • Read in your book on page 472 how the EPA define a potential toxin an responds. • 94% of the US is served with drinking water that meets the drinking water standards
Eutrophication • This term means “well nourished “ • Benthic plants are plants that grow attached to or rooted to the bottom of the water. • Phytoplankton – species of photosynthetic algae. • If phytoplankton grows in the extreme, the water may become pea-soup green and block all light.
Impacts of nutrient enrichment – • Oligotrophic lakes or waters are clear. The lack of nutrients renders the water clear it allows sunlight to pass through the water to support the growth of SAV. • Eutrophication – if an oligotrophic body becomes enriched with nutrients, rapid growth and multiplication of phytoplankton increase the turbidity of the water,
Combating eutrophication – • Attack the symptom • Go to the root cause • Attacking the symptoms include chemical treatments of the weeds, aeration harvesting the weeds, drawing the water down. • Herbicides are used to control the growth of nuisance plants. Copper sulfate and diquat are frequently used. Sometimes glyphosate and 2,4, D are used, • These products are sensitive to fish. • Fish can be killed by the plant material rotting depleting the oxygen supply.
Aeration can be done to increase dissolved oxygen. • Harvesting – where it is possible, bottom rooted vegetation is harvested. • Drawdown - The lake is lowered to kill rooted aquatic plants. They usually grow back over time. • Getting at the root cause • Identify the major point and nonpoint sources of nutrients and sediments.
The EPA has established ecoregional nutrient criteria. • these criteria measures causative factors (nitrogen and phosphorous) and criteria of response factors. These numbers differ for different regions of the country. • Control strategies for Point Sources – • In heavily populated areas the most common source (of phosphate) is sewage treatment plants. • In regions where eutrophication s a problem, detergents containing phosphates have been banned. • Some dishwashing detergents are still high in phosphates.. • Eliminating phosphates from detergents has had a profound impact on waterways that were heavily damaged by effluents.
Control Strategies for Nonpoint Sources – Farm and urban runoff are the culprits here. • The source could be thousands or millions of individual property owners • The EPA has established regulations • Identify the pollutants responsible for degrading the water • Estimate the pollution coming from all sources (point and nonpoint) • Estimate the ability of the body of water to assimilate the pollutants while remaining below the threshold designating poor or inadequate water quality. • Within a margin of safety, allocate the allowable level of pollution among the different sources such that the water quality standards are achieved.
BMP’s • (best management practices) • Reducing or eliminating pollution will require different strategies for different sources. • Farm activities causing erosion due to erosion and leaching and runoff of animal wastes will be different from urban runoff problems. • If standards are not met, the TMDL process must be revisited and new pollution allowances allocated (total maximum daily load).
Recovery • The good news is that water pollution and cultural eutrophication can be reversed. • The Chesapeake Bay suffered from heavy nutrient pollution destroying all but 1/10 of the 600,000 acres of sea grasses. • Lake Washington, east of Seattle, has undergone a great change • In the 1940’s and 50’s sewage effluent was sent into the water at a rate of 20 million gallons per day. • By 1968, the effluent was put into Puget Sound where the effluent was mixed with ocean water. • By 1975, the recovery was complete
Sewage Management and Treatment • Before the late 1800’s, the management of waste was the outdoor privy. • This was a problem where the outdoor privy was close to the well the household used for drinking water • Seepage occurred causing many infectious diseases • The result was the invention of the flush toilet. So then people began draining their wastes into the same place the storm sewers drained - the water ways.
Sewage treatment plants were first built in 1900. • People quickly realized that household waste needed to be treated separately from storm drains. • Even in the US as late as the 1970’s there were still areas in the US that discharged untreated sewage into waterways. • Only about 10%of waste water is collected in developing countries • Even where there are treatment plants, many do not operate effectively.
The pollutants in raw sewage • About 99.9% water since we use so much water to flush • 150 – 200 gallons per person per day • Debris and grit – coarse sand, gravel • Particulate organic materials – fecal matter food from garbage disposals, toilet paper • Colloidal and dissolved organic matter urine, soaps detergents • Dissolved inorganic materials – nutrients from excretory wastes, nitrogen phosphorus. • Some pesticides, heavy metals, etc.
Steps taken to treat the sewage • Preliminary treatment Remove grit and debris – water passes through a series of screens. The water is slowed to allow the grit go settle out. This is taken to a land fill. (you’d be amazed at what goes down a toilet) • Primary treatment – the water goes to a settling basin. The particle matter settles out and is collected as raw sludge. This is treated separately
Secondary treatment • This is also called biological treatment it uses organisms and their metabolism to feed on the colloidal and dissolved organic material and break it down to CO2 and water. The water flows over a series of rocks on which live organisms, detritus feeders, live. Oxygen is provided for the system. • The organisms that live on these rocks represent a food web. The organisms consist of bacteria, rotifers (which feed on protozoans), protozoans, various small worms and other detritus feeders.
The activated sludge is also processed by detritus feeding organisms. The water is aerated (this is the activation part) as it moves through the system. As organisms feed on each other they form clumps called floc, This water goes into another settling tank where the organisms settle out. It is mostly water . 90% of the organic material is removed. The organisms that settle out are put back into the clarifier tank. Surplus amounts of the activated sludge are taken out from time to time and put in with the raw sludge. So the end product is carbon dioxide, water and mineral nutrients that remain in the water solution
After the secondary treatment the resultant mixture is very nutrient rich. Heretofore, this was not considered a problem. Now we know that extra nutrients leads to cultural eutrophication. Today, secondary activated sludge systems have been added to remove nutrients ad oxidize detritus. This is called biological nutrient removal.
Which nutrients are problems? • Nitrogen • phosphorus
BNR, Biological Nutrient Removal • Nitrogen is removed by denitrification. The activated sludge goes into four different zones where denitrifying is controlled • Phosphorus – phosphate is removed as bacteria utilize it in their cells. • Final cleansing and disinfection – wastewater is treated with chlorine, basically Clorox • Another method of disinfecting water is to use ozone. It kills microorganisms and produces oxygen gas. • It can also be passed through an array of UVB lights in the water. UV light kills bacteria.
Now, how is the sludge treated? • Sludge contains lots of bacteria. It is considered a biologically hazardous material. • Anaerobic digestion - Bacteria feed on detritus in the absence of oxygen, The end products are CO2, methane, and water. So one of the products is biogas. This can be used as fuel. • The biogas fuel is commonly used to heat the sludge digesters because the bacteria work best at about 104 degrees F.
After 4-6 weeks, anaerobic digestion is more or less complete • Now it is called treated sludge or biosolids, Most pathogens are gone. • It could be used as a fertilizer for lawns or agricultural fields. Usually it is a liquid, although it can be dehydrated to form sludge cake. • Composting • This can be done where the raw sludge is mixed with wood chips and placed in long narrow piles to break down with bacteria. It can then be used as a soil treatment. • Pasteurization – • after the water is removed from the sludge, it can be put in ovens and pasteurized. The resulting material can be used as fertilizer. Milwaukee uses sludge from the brewing process and sells it as Milorganite
Onsite waste water treatment • Septic tanks – wastewater flows into a tank, The solid material settles to the bottom. Water containing colloidal and dissolved organic material flows into the drain field and percolates into the soil. Accumulated biosolids in the tank must be pumped out every three to five years. • Onsite systems regularly fail. • Some common problems include, grease, cat litter, pesticides, household chemicals being rinsed down drains or flushed down toilets. • Have the septic system inspected frequently • Keep heavy equipment off the drain field • Garbage disposals are not good for septic tanks.
Using effluents for irrigation – • Effluents are used in some towns to irrigate and fertilize residential lawns and open spaces. • Purple pipes in Cary • Reconstructed Wetland systems • Wetlands are good nutrient absorbers • in the 60’s and 70’s some wetlands were converted to pasture • They have now been reclaimed and converted back to wetlands. • These wetlands are being used as a treatment for effluent before it goes back into the James River.
Public Policy • The foundation for public policy and the laws that the EPA can enforce have to come from Congress • The Clean Water Act – required permits for all poi8nt source discharges of pollutants • The Clean Water Act – has funds for building and replacing treatment facilities • Reauthorization of the Clean Water Act is long overdue – it has gotten very political • Nonpoint source pollution is the nation’s number one water pollution problem • New wastewater treatment facilities not far behind