World Water Issues

Contaminant Removal at a Wastewater Treatment Plant

A typical wastewater treatment plant aims to remove various contaminants. Inert solids are removed through clarification, where suspended particles settle out and are removed. Treatment relies on aeration to encourage bacteria to metabolize organic contaminants. To encourage a healthy biological system, some of the water being treated is recycled from the end of the system to the front. Some contaminants, however, are too small or have other chemical properties that do not allow them to be treated conventionally. Those compounds are not removed in a conventional treatment plant.

Identify the part of the plant in which each of the following contaminants will be removed, and explain why (i.e. Where do you expect the contaminant to go? Will it be removed physically or through biological conversion?). Use the process flow diagrams on the following pages, and remember that all wastewater treatment relies on solid-liquid separation.

1.  Toilet Paper

2.  Sand

3.  Simple Sugars

4.  Salt

5.  Grease & Oil

6.  Coffee Grinds

World Water Issues

World Water Issues

Contaminant Removal at a Wastewater Treatment Plant

Answer Key

1.  Toilet paper is removed physically in screens.

2.  Sand is removed physically in settling tanks.

3.  Simple sugars are consumed by bacteria.

4.  Salt is not removed in a typical WWTP.

5.  Grease floats to the top of the water (it is less dense), and is taken out with skimmers.

6.  Removed biologically, as coffee acts as food for the bacteria; Removed physically through settling (for bigger grinds); Caffeine diffuses from the coffee grinds and is not removed in the WWTP.


Water Reuse

Orange County, California has had a major population boom in the last few decades, though the drinking water resources are limited. In the Orange County Water District, water has traditionally come from three sources: a 600 mile aqueduct carrying water from Northern California and the Sacramento-San Joaquin Delta, a 240 mile aqueduct carrying water from the already severely burdened Colorado River, and an underground aquifer replenished by the Santa Ana River, local rainfall, and surplus water from the aqueducts (this last one counts for only 55% of the total). In order to alleviate some of the water scarcity concerns in this area, the Orange County Water District has adopted a new form of recycling: wastewater recycling for drinking water. The program was originally proposed in the early ‘90s and was rejected after negative reactions from the public after the program was labeled “toilet-to-tap” by the media. After ten years, the program was restarted and is now being implemented. Similar wastewater reuse systems are in place in Singapore and near Washington, D.C.

The Chicago-land area is very fortunate to be located on one of the largest freshwater ecosystems in the world. While the resources seem vast to us, it is important to remember that we must protect the resources that we have by reducing the burden we put on the ecosystem (i.e. the amount of water we withdraw). Some creative ways to reduce water consumption are below. Please describe in 3-4 sentences what each system is and does.

1.  Rain barrels

2.  Graywater systems

3.  Low-flow fixtures

What are other things you can do around the house to limit your water consumption?


Water Reuse

Answer Key

  1. Rain barrels – are designed to collect rain water. There are two purposes for this. The water can be reused as water for irrigation or use for non-potable applications in the home (toilet water) so that potable treated water is not used unnecessarily. Rain barrels also remove a fraction of the water that enters your sewers. This lowers the burden on the wastewater treatment plant in places like Chicago that have combined sanitary and storm sewers.
  2. Graywater systems – separate treated potable water from “lightly used” (gray) water. Potable water is used at faucets, in the shower, and for dishwashers and clothes washers. The water from these places is stored and used, in lieu of potable water, in your toilet or for irrigation around the house.
  3. Low-flow fixtures – limit the flow of water over a given period of time. At maximum opening, low-flow fixtures will use less water than average fixtures. This limits the water consumed (and associated energy) and wastewater requiring treatment.

What are other things you can do around the house to limit your water consumption?

·  Turn off the faucet when you brush your teeth.

·  Take shorter showers or, if you really want to soak, take a bath instead.

·  Water your lawn with gray water or rain water. Otherwise only water plants late at night or early in the morning, so that the water can soak into the roots before it is evaporated by the sun.

·  Use biodegradable soaps, toilet paper, and other materials. Limit (and avoid wherever possible) disposal of inorganic materials down the drain.

·  Never dispose of pharmaceuticals (i.e. old medicines, aspirin) down the drain.

Resources:

http://www.ocwd.com/Programs---Projects/ca-17.aspx

http://www.uswaternews.com/archives/arcconserv/8oracou3.html


Embedded Water Content

Embedded water content (also known as virtual water and embodied water) refers to the amount of water required in total to produce a product. The embedded water content of several items is listed below. (Note: 3.875 Liters equal 1 gallon; 2.2 pounds equal 1 kilogram.)

Food Product Embedded Water Content

1 sheet of paper 10 L

1 cup of tea 30 L

1 apple 70 L

1 cup of coffee 140 L

1 bottle of beer 150 L

1 loaf of bread 440 L

1 filet of chicken 683 L

1 kg wheat 1,300 L

1 bag of sugar 1,500 L

500 g cheese 2,500 L

1 kg eggs 3,300 L

1 kg broken rice 3,400 L

1 kg beef 3,875 L

Textile Product Embedded Water Content

1 cotton shirt 4,100 L (medium, 500 grams)

1 pair of jeans 10,850 L (1 kg of denim)

1 bed sheet 9,750 L (900 g)

What is in your lunch today? How much water (embedded) in total did it take to produce your lunch?

According to “Importance of Energy Efficiency to the Water and Wastewater Sector” by Matthew Yonkin, Katherine Clubine, and Kathleen O’Connor (NYWEA, 2008), “New York’s drinking water sector consumes an average of 580 kWh/MG, which is nearly 70 percent less energy than the national average of 1,400 kWh/MG.” Assume that on average it takes 1,400 kilowatt-hours (kWh) per million gallons (MG) of water treated. How much energy was required to make your lunch?

Find the embedded water content of three other household products.

Resources:

http://news.bbc.co.uk/2/hi/science/nature/8628832.stm

http://en.wikipedia.org/wiki/Virtual_water