Text 5. Wastewater Treatment.

 

Domestic sewage treatment. Domestic sewage is 99.9% pure water, the other 1% are pollutants. These pollutants although small, pose risk on a large scale. In urban areas, domestic sewage is typically treated by centralized sewage treatment plants. Municipal treatment plants are designed to control conventional pollutants: BOD and suspended solids. Well-designed and operated systems (i.e., secondary treatment or better) can remove 90 percent or more of these pollutants. Some plants have additional sub-systems to treat nutrients and pathogens. Most municipal plants are not designed to treat toxic pollutants found in industrial wastewater.

Cities with sanitary sewer overflows or combined sewer overflows employ one or more engineering approaches to reduce discharges of untreated sewage, including: utilizing a green infrastructure approach to improve stormwater management capacity throughout the system; repair and replacement of leaking and malfunctioning equipment; increasing overall hydraulic capacity of the sewage collection system (often a very expensive option).

A household or business not served by a municipal treatment plant may have an individual septic tank, which treats the wastewater on site and discharges into the soil. Alternatively, domestic wastewater may be sent to a nearby privately-owned treatment system (e.g. in a rural community).

Industrial wastewater treatment. Some industrial facilities generate ordinary domestic sewage that can be treated by municipal facilities. Industries that generate wastewater with high concentrations of conventional pollutants (e.g. oil and grease), toxic pollutants (e.g. heavy metals, volatile organic compounds) or other non-conventional pollutants such as ammonia, need specialized treatment systems. Some of these facilities can install a pre-treatment system to remove the toxic components, and then send the partially-treated wastewater to the municipal system. Industries generating large volumes of wastewater typically operate their own complete on-site treatment systems.

Some industries have been successful at redesigning their manufacturing processes to reduce or eliminate pollutants, through a process called pollution prevention.

Heated water generated by power plants or manufacturing plants may be controlled with: cooling ponds, man-made bodies of water designed for cooling by evaporation, convection, and radiation; cooling towers, which transfer waste heat to the atmosphere through evaporation and/or heat transfer; cogeneration, a process where waste heat is recycled for domestic and/or industrial heating purposes.

Agricultural wastewater treatment.

Non-point source controls. Sediment (loose soil) washed off fields is usually the largest source of agricultural pollution. Farmers may utilize erosion controls to reduce runoff flows and retain soil on their fields. Common techniques include contour plowing, crop mulching, crop rotation, planting perennial crops and installing riparian buffers.

Nutrients (nitrogen and phosphorus) are typically applied to farmland as commercial fertilizer; animal manure; or spraying of municipal or industrial wastewater (effluent) or sludge. Nutrients may also enter runoff from crop residues, irrigation water, wildlife, and atmospheric deposition. Farmers can develop and implement nutrient management plans to reduce excess application of nutrients.

To minimize pesticide impacts, farmers may use Integrated Pest Management (IPM) techniques (which can include biological pest control) to maintain control over pests, reduce reliance on chemical pesticides, and protect water quality.

 

 

Point source wastewater treatment.

Farms with large livestock and poultry operations, such as factory farms, are called concentrated animal feeding operations or confined animal feeding operations and are being subject to increasing government regulation. Animal slurries are usually treated by containment in lagoons before disposal by spray or trickle application to grassland. Constructed wetlands are sometimes used to facilitate treatment of animal wastes, as are anaerobic lagoons. Some animal slurries are treated by mixing with straw and composted at high temperature to produce a bacteriologically sterile and friable manure for soil improvement.

Urban runoff. Retention basin for controlling urban runoff.

Effective control of urban runoff involves reducing the velocity and flow of storm-water, as well as reducing pollutant discharges. Local governments use a variety of storm-water management techniques to reduce the effects of urban runoff. These techniques, called best management practices (BMPs) in the U.S., may focus on water quantity control, while others focus on improving water quality, and some perform both functions.

Pollution prevention practices include low impact development techniques, installation of green roofs and improved chemical handling (e.g. management of motor fuels & oil, fertilizers and pesticides). Runoff mitigation systems include infiltration basins, bioretention systems, constructed wetlands, retention basins and similar devices.

Thermal pollution from runoff can be controlled by storm-water management facilities that absorb the runoff or direct it into groundwater, such as bioretention systems and infiltration basins. Retention basins tend to be less effective at reducing temperature, as the water may be heated by the sun before being discharged to a receiving stream.

 

After you read Text 4 and 5

· Complete the following sentences according to the context:

1. The impact of industrial discharges depends not only on biochemical oxygen demand and the amount of suspended solids, but also on ……………………

2. Commercial livestock and poultry farming are the source of ………………..

3. ………………... includes waste from sinks, toilets, and industrial processes.

4. Well-designed municipal treatment plants can remove ….…. % of …………… pollutants.

5. To minimize pesticide impacts, ………………………………………………

6. Some industrial specialized treatment systems can install …………………... and then send …………………………………………………………………

7. ……………………….. can be controlled by storm-water management facilities that ………………………………………………………………….

8. ……………………………….. is usually the largest source of agricultural pollution.

9. A household not served by a municipal treatment plant may have ………………..…..., which ………………………………………………….

 

Agencies and organizations

that work to prevent water pollution and provide relevant information:

 

· Advisory Committee on Protection of the Sea (ACOPS) - www.acops.org

· Clean Ocean Action - www.cleanoceanaction.org

· Friends of the Earth - www.foe.co.uk

· Greenpeace - www.greenpeace.org/oceans

· International Water Association - www.iwahq.org.uk

· Marine Conservation Society - www.mcsuk.org

· Save Our Seas - www.saveourseas.org

· Wetlands International - www.wetlands.org

· WWF - www.panda.org

 

 

Fast Facts

 

· Earth is 2/3 water, but all the fresh water only represents one hundredth of one percent.

· You use about 12,000 gallons of water every year.

· One gallon of motor oil can contaminate up to 2 million gallons of water.

· Nearly 1.5 billion people lack safe drinking water and at least 5 million deaths per year can be attributed to waterborne diseases.

· With over 70 percent of the planet covered by oceans, people have long acted as if these very bodies of water could serve as a limitless dumping ground for wastes.

· Beaches around the world are closed regularly, often because of high amounts of bacteria from sewage disposal, and marine wildlife is beginning to suffer.

· Ninety-five percent of all fresh water on earth is ground water. Ground water is found in natural rock formations. These formations, called aquifers, are a vital natural resource with many uses.

· Different items take different lengths of time to degrade in water:

Cardboard – Takes 2 weeks to degrade.

Newspaper – Takes 6 weeks to degrade.

Photodegradable packaging – Takes 6 weeks to degrade.

Foam – Takes 50 years to degrade.

Styrofoam – Takes 80 years to degrade.

Aluminium – Takes 200 years to degrade.

Plastic packaging – Takes 400 years to degrade.

Glass – It takes so long to degrade that we don’t know the exact time.

Important Terms

 

A quifers – natural rock formations, which contain ground water.

B ase flow – The portion of stream flow that is not runoff and results from seepage of water from the ground into a channel slowly over time. The primary source of running water in a stream during dry weather.

B est Management Practice (BMP), nonstructural – Strategies implemented to control stormwater runoff that focus on pollution prevention such as alternative site design, zoning and ordinances, education, and good housekeeping measures.

B est Management Practice (BMP), structural - Engineered devices implemented to control, treat, or prevent stormwater runoff pollution.

B iochemical Oxygen Demand (BOD) – The amount of oxygen used by microorganisms in the breakdown or decay of organic matter in a waterbody.

B ioengineering – Restoration and stabilization techniques that use plants, often native species, to mimic natural functions and benefits.

B iofiltration – The use of vegetation (usually grasses or wetland plants) to filter and treat stormwater runoff as it is conveyed through an open channel or swale.

B iological diversity – The concept of multiple species of organisms living together in balance with their environment and each other.

B iological monitoring and biological indicators – Surveys of aquatic biota in a waterbody where the organisms (plants, macro-invertebrates, and fish) serve as indicators of the quality and characteristics of that waterbody.

B ioretention – The use of vegetation in retention areas designed to allow infiltration of runoff into the ground. The plants provide additional pollutant removal and filtering functions while infiltration allows the temperature of the runoff to be cooled.

B rownfields – Abandoned or underutilized properties where development is complicated by real or perceived contamination.

B uffer zone – A designated transitional area around a stream, lake, or wetland left in a natural, usually vegetated state so as to protect the waterbody from runoff pollution. Development is often restricted or prohibited in a buffer zone.

C hemical water quality – The quality of a waterbody determined using chemical rather than physical or biological parameters and methods.

C ombined sewer overflow (CSO) – During rainfall events, the volume of stormwater entering a combined sewer system often is far greater than the capacity of the interceptor (large collector pipe) and sewage treatment plant and, as a result, the untreated sewage and stormwater mixture empties directly into receiving waters through designated overflow points.

C ombined sewer system – A sewer system that conveys stormwater runoff along with sanitary sewage and industrial waste.

D etention – The storage and slow release of stormwater following a precipitation event by means of an excavated pond, enclosed depression, or tank. Detention is used for both pollutant removal, stormwater storage, and peak flow reduction. Both wet and dry detention methods can be applied.

E utrophication - The process of slowly filling in a water body with sediments and organic matter.

E stuary – A semi-enclosed coastal waterbody such as a bay, mouth of a river, salt marsh, or lagoon, where freshwater and saltwater mix. These waters support a rich and diverse ecology.

E vapotranspiration – The loss of water to the atmosphere through the combined processes of evaporation and transpiration, the process by which plants release water they have absorbed into the atmosphere.

F ilter Strip – Grassed strips situated along roads or parking areas that remove pollutants from runoff as it passes through, allowing some infiltration, and reductions of velocity.

F lashy stream – A stream or river that is characterized by dramatic fluctuations in flow, in which sharply higher flows in wet weather can be followed by very low flows in dry weather.

F loatables – Materials found in runoff that are buoyant, such as polystyrene, plastic, some organic material, or cigarette butts.

F loodplain – Can be either a natural feature or statistically derived area adjacent to a stream or river where water from the stream or river overflows its banks at some frequency during extreme storm events.

G eographic Information System (GIS) – A database of digital information and data on land-use, land cover, ecology, and other geographic attributes that can be overlaid, statistically analyzed, mathematically manipulated, and graphically displayed using maps, charts, and graphs.

G roundwater – Water that flows below the ground surface through saturated soil, glacial deposits, or rock.

H ydrology – The science addressing the properties, distribution, and circulation of water across the landscape, through the ground, and in the atmosphere.

I mpervious surface – A surface that cannot be penetrated by water such as pavement, rock, or a rooftop and thereby prevents infiltration and generates runoff.

I mperviousness – The percentage of impervious cover within a defined area.

I nfiltration – The process or rate at which water percolates from the land surface into the ground. Infiltration is also a general category of BMP designed to collect runoff and allow it to flow through the ground for treatment.

N ational Pollutant Discharge Elimination System (NPDES) – A provision of the Clean Water Act that prohibits discharge of pollutants into waters of the United States unless a special permit is issued by the EPA, a state, or (where delegated) a tribal government or and Indian reservation.

N atural buffer – A variable width area maintained with natural vegetation between a pollutant source and a waterbody that provides natural filtration and other forms of protection.

N on point source - delivers pollutants indirectly through environmental changes. One way in, which this occurs, is through run-off.

O utfall – The point of discharge from a river, pipe, drain, etc. to a receiving body of water.

 

O verburden – Material overlying a deposit of useful geologic materials or bedrock.

P athogens - or disease producing organism.

P eak discharge – The greatest volume of stream flow occurring during a storm event.

P erformance standard – An established amount or limit of a specified pollutant that can be discharged from a land-use activity or BMP.

P oint source - occurs when harmful substances are emitted directly into a body of water. One way in which this occurs, is when someone throws a coke can into a body of water.

P ollution - to make foul or unclean; dirty.

P olluted runoff – Rainwater or snowmelt that picks up pollutants and sediments as it runs off roads, highways, parking lots, lawns, agricultural lands, logging areas, mining sites, septic systems, and other land-use activities that can generate pollutants.

R etrofit – The creation or modification of a stormwater management practice, usually in a developed area, that improves or combines treatment with existing stormwater infrastructure.

R unoff – Water from rainfall, snowmelt, or otherwise discharged that flows across the ground surface instead of infiltrating the ground.

S anitary sewer system – Underground pipes that carry only domestic or industrial wastewater to a sewage treatment plant or receiving water.

S ediments - minerals or organic matter deposited by water, air, or ice...matter which settles to the bottom a liquid.

S edimentation – A solid-liquid separation process utilizing gravitational settling to remove soil or rock particles from the water column.

S iltation – A solid-liquid separation process utilizing gravitational settling to remove fine-grained soil or rock particles from the water column.

S SO (separate sewer overflow) – Wastewater entering sanitary sewers may be so great, because of blockage, a lack of capacity, inflow and infiltration, or other reasons, that the collection system or sewage treatment plant cannot handle the increased flow. As a result, untreated sewage empties directly into receiving waters, often from manholes or up through sewer connections.

S torm sewer system – A system of pipes and channels that carry stormwater runoff from the surfaces of building, paved surfaces, and the land to discharge areas.

S tormwater – Water derived from a storm event or conveyed through a storm sewer system.

S tormwater utility – A utility established to generate a dedicated source of funding for stormwater pollution prevention activities where users pay a fee based on land-use and contribution of runoff to the stormwater system.

S urface water – Water that flows across the land surface, in channels, or is contained in depressions on the land surface (e.g. runoff, ponds, lakes, rivers, and streams).

S wale – A natural or human-made open depression or wide, shallow ditch that intermittently contains or conveys runoff. Can be used as a BMP to detain and filter runoff.

U rban (metropolitan) runoff – Runoff derived from urban or suburban land-uses that is distinguished from agricultural or industrial runoff sources.

W ater (hydrologic) cycle – The flow and distribution of water from the sky, to the Earth's surface, through various routes on or in the Earth, and back to the atmosphere. The main components are precipitation, infiltration, surface runoff, evapotranspiration, channel and depression storage, and groundwater.

W atershed – The land area, or catchment, that contributes water to a specific waterbody. All the rain or snow that falls within this area flows to the waterbodies as surface runoff, in tributary streams, or as groundwater.

Acronyms

 

BMP - Best Management Practice

BOD - Biochemical Oxygen Demand

CSO - Combined Sewer Overflow

EPA - United States Environmental Protection Agency

ESC - Erosion and Sediment Control

GIS - Geographic Information System

MS4 - Municipal Separate Storm Sewer System

NAFSMA - National Association of Flood and Stormwater Management Agencies

NPDES - National Pollutant Discharge Elimination System

NRDC - Natural Resources Defense Council

SSO - Separate Sewer Overflow