2. Water Treatment Activity

Water Treatment Activity.docx  

Background

The standard wastewater treatment options used in rural, urban, and suburban areas are described below. Composting or biological toilets and greywater systems are becoming popular alternatives, predominantly used in rural areas where no centralized wastewater treatment is available. When considering an alternative system such as a composting toilet, a special building or Resource Consent is usually required.

Rural

Septic tanks are predominantly used for the treatment of wastewater on rural properties as central wastewater treatment facilities are impractical and expensive when dwellings are far apart or too difficult to place piping. Septic tanks are large concrete or steel tanks (~4,000L capacity) that are buried beneath the ground, with wastewater flowing into the tank at one end and leaving the tank at the other.

Three layers form in these tanks: a floating ‘scum layer’ at the top, a ‘sludge layer’ of heavier material at the bottom, and in the middle a relatively clear water layer. This body of water contains bacteria and nutrients like nitrogen and phosphorous, but is largely free of solids. As new water enters the tank, the existing water is displaced and flows into a drain field made of perforated pipes buried in trenches filled with gravel. The water is slowly absorbed and filtered through the ground in the drain field. The size of the drain field is determined by the capacity of the ground to absorb water, with larger drain fields required where the ground is hard clay that absorbs water very slowly.

Click to find out more about nutrient overloading (https://www.niwa.co.nz/node/90481/)

Urban and suburban

In urban and suburban areas with high population densities central plants are used to treat wastewater. Most treated wastewater is discharged into rivers, streams out to sea or onto land (some is also discharged to groundwater, estuaries, and wetlands).  Treatment plants commonly use a series of techniques to remove wastes from the water. Sewage generally travels through a series of screens, tanks, bioreactors, clarifiers, and ultraviolet treatments before being discharged into the environment.

The bulk of solids, such as toilet paper, are mechanically removed by screening and settlement in sedimentation tanks (primary treatment). Commonly, this material is washed and compressed and sent to landfills for disposal.

Nutrients and more solids are removed using biological treatments, including activated sludge, aerated systems, trickling filters, biological reactors, and lagoons (secondary treatment). This sludge is dewatered and the solids, which are the remaining organic material and suspended solids, are also disposed of as landfill.

Tertiary treatment is used to remove constituents of wastewater such as organic and inorganic nutrients, dissolved solids, and chemical contaminants like heavy metals. Processes involved in tertiary treatment include percolation, filtration, adsorption, biological and chemically aided removal.

Click to Find out more about nutrient overloading (https://www.niwa.co.nz/node/90481/)

Click to Find out more about chemical contamination (https://www.niwa.co.nz/node/89164/)

Finally, some treatment plants disinfect the remaining wastewater prior to it being discharged, using chlorination, ozonation, ultraviolet radiation, or membrane filtration to kill pathogens.

Click to Find out more about discharges (https://www.niwa.co.nz/node/90511/)

Click to Find out more about infectious substances ( https://www.niwa.co.nz/node/90511/)

Source: https://www.niwa.co.nz/our-science/freshwater/tools/kaitiaki_tools/land-use/waste-water-treatment/activities

Check these for a virtual tour of water treatment plants.

Wastewater Treatment: Sequence of Events

Anything you flush down the toilet will eventually show up at the wastewater treatment plant (albeit not always in its original condition).

1. Place numbers next to each of the steps in the wastewater treatment process listed below to show the order in which they occur.

Wastewater Treatment and Eutrophication

Eutrophication occurs when bodies of water, usually lakes or rivers, experience algal blooms from large inputs of plant nutrients like nitrogen and phosphorus, which leads to low oxygen levels in the water and adverse impacts on aquatic organisms. Both nitrogen and phosphorus can occur in large concentrations in wastewater effluent.

1. Describe the approaches taken at the profiled treatment plant to deal with nitrogen and phosphorus removal prior to the release of the effluent into the environment.
2. Which parts of the nitrogen cycle are utilized during wastewater treatment?
3. Explain why the plant should be (or not) particularly concerned about eutrophication given its release site.

Waste Water Treatment Plant

1. Does both wastewater and storm water come into the plant? If so, why could this be a problem?
2. Preliminary treatment involves _____.
3. What is the purpose of primary clarifiers and/or grit settling tanks?
4. Primary treatment removes _____.
5. What is/can be done with the sludge from primary treatment?
6. Secondary treatment involves _____.
7. How much sludge is produced by annually by the average household?
8. What is B.O.D.? What is the acceptable level for drinking water in ppm?
9. Which microbial species are used in the process? How?
10. How long does the sludge stay in the sludge digesters?
11. What happens to the methane gas that is produced here?
12. How is the sludge disposed of after it is removed from the digester?
13. What are some advantages and disadvantages of using sludge for fertilizer?
14. Advanced (tertiary) water treatment (chlorine, bleach, or ultraviolet light) purpose is _____.
15. List the two advantages of using ozone and two disadvantages.
16. Why do most municipalities not conduct tertiary treatment on effluent?
17. Where does the wastewater go when it leaves the treatment plant?

Septic System

1. Describe how a septic tank works. Highlight how this differs from municipal systems.

Protection: What you can do to protect local waterways; use link below and answer each question. http://esa21.kennesaw.edu/activities/ww-treatment/ww-treat-protecting-waterways-epa.pdf

1. List all of the items you not put down drains. Refer to the Not down My drain
2. What is cheaper to maintain our watersheds: protection and prevention or treatment and restoration? Explain.
3. Explain the regulations placed on wastewater effluent.