A Study of the Effectiveness of Different Types of Greywater on the Growth of Pisum sativum

On the news we hear about drastic changes in climate, but we have not experienced them full-blown. But what if we did? Imagine living in a world struggling with water, either with too little or too much. It would be difficult to raise crops and livestock, or earn money. This is the society we will be living in once climate change has taken its toll on us.


Background Research

All humans are dependent on water for health, sanitation, and agriculture. Climate change can affect access to fresh water due to sea level rise, flooding, runoff, and drought (“Climate Impacts on Water Resources”). The United Nations expects a decline in water availability in many regions, and it estimates that global agricultural water consumption will increase by 19% by 2050 (“World Water Day 2013”). Water used for food and energy production puts a lot of pressure on the global freshwater supply (Biello). On average, 70% of fresh water is used for agriculture, and up to 90% in fast-growing economies (“World Water Day 2013”). On the other hand, greywater can be used to partially offset the increased demand for freshwater for agricultural purposes. As a result, it reduces the need for water treatment, thus reducing costs and the carbon emitted from water-treatment plants (Biello).

Greywater refers to the wastewater produced in a household, such as the water from washing machines, bathtubs, and bathroom sinks, but excluding toilets and kitchen sinks and appliances (“Overview of Greywater Management”). The quality of greywater differs across different households. It depends on the amount of water used per household and the type of chemicals used for washing and bathing (Boufaroua et al.).

Although greywater contains some nutrients like phosphates and nitrates, it can also contain a variety of chemicals that may be harmful to plant growth (“Overview of Greywater Management”). Greywater can also contain microbes harmful to human health. These chemicals and microbes can be reduced through water filtration methods. There are two major types of greywater filtration methods: primary diversion and secondary treatment methods. Primary diversion systems use coarse screens as filters to remove oil and solids before the greywater is applied on land; they include gravity and pump diversion systems (“Overview of Greywater Management”). Secondary treatment systems further remove oils, solids, and organic materials from greywater. Examples include the slow sand filter, the trickling filter, a constructed wetland, activated sludge, and a rotating biological contactor (“Overview of Greywater Management”).


Question

The question I wanted to answer was as follows: What are the effects of different types of treated greywater on the growth of Pisum sativum (pea plant)?


Hypothesis

I hypothesized that if sand filter-treated shampoo greywater was substituted for tap water, plant growth would be equal to that of tap water. This is because shampoo has milder chemicals and a lower and a more appropriate pH level for plants than laundry detergent. Sand filters are believed to treat greywater better than cloth filters because cloth filters are a primary diversion treatment system, and sand filters are a more effective secondary-treatment system, as described above. Plants watered with the unfiltered, laundry detergent greywater were expected to have the least growth.

 

Materials

The following items are the materials I used to conduct this study:

The seed packets.


  • 21 Green Arrow pea seeds
  • 21 Alaskan pea seeds
  • 4 glass cups
  • 2 small yogurt containers
  • 36-cell plant tray
  • 19 sticks
  • Suave Naturals Daily Clarifying Shampoo
  • Everyday Essential Mountain Stream Detergent
  • Tap water
  • Sand
  • 2 socks
  • 4 yogurt containers (2 small and 2 large)
  • 2 one-liter bottles
  • Gravel
  • 9 cotton balls
  • pH strips
  • Power drill
  • Ruler
  • Pipette
  • 2 beakers
  • Potting soil
  • Lamp
  

Experimental Groups

I used the following seven experimental groups to conduct this study:

  1. Unfiltered detergent water
  2. Unfiltered shampoo water
  3. Detergent water, sand filtered
  4. Shampoo water, sand filtered
  5. Detergent water, cloth filtered
  6. Shampoo water, cloth filtered
  7. Tap water
   

Independent Variables:

My independent variables were as follows:

  1. Type of water: 1) greywater, 2) tap water
  2. Greywater treatment: 1) unfiltered, 2) filtered
  3. Source of greywater: 1) shampoo, 2) detergent
  4. Type of pea plant: 1) Alaskan, 2) Green Arrow
   

Methodology and Procedures

After planting the seeds I waited for them to germinate.


In this experiment, I planted 21 Green Arrow pea seeds and 21 Alaskan pea seeds in Miracle Grow soil. In two cups, I planted three seeds in each. I then labeled the cups Control A (tap water), Alaskan Pea and Control A (tap water), Green Arrow Pea. In a separate tray, I planted one seed in each of 36 small cells. I then sectioned the tray off into six equal parts, each of which was then labeled: Control B (unfiltered detergent), Control B (unfiltered shampoo), Cloth-Filtered Detergent, Cloth-Filtered Shampoo, Sand-Filtered Detergent, and Sand-Filtered Shampoo. Then I broke each of the six parts into two parts of three and labeled them either Green Arrow Pea or Alaskan Pea.

Greywater preparation

Greywater preparation


I made the shampoo greywater using shampoo and tap water, and I made the detergent greywater using detergent and tap water. I mixed one liter of tap water with 5 mL of shampoo to make the shampoo water, and I mixed one liter of tap water with 5 mL of detergent to make the detergent water. I made these solutions to simulate the average ratio of shampoo and detergent in the water used for showers and washing machines, respectively. These became the unfiltered greywater. I made the cloth-filtered and sand-filtered detergent and shampoo samples by filtering the greywater samples through separate cloth or sand filters. I then measured the pH level for each type of water and greywater with pH strips.

I made the sand filters by using a power drill to make 14 filter holes at the bottom of two empty yogurt containers. I placed cotton inside the container, covering the holes to prevent the loose sand from falling through. Then I added a layer of gravel to hold up the sand. Lastly, I added the sand on top of the rocks. I then fastened the filters onto beakers that would collect the filtered water. To make the cloth filters, I used the drill to make 10 filter holes at the bottom of two empty sour cream containers. Then I fitted a clean sock over the top of the opening of each container. I then fastened the cloth filters onto clear glass cups to collect the filtered water.

Anupama drills holes for the sand filters (right). The completed cloth and sand filters (left)

Anupama drills holes for the sand filters (right). The completed cloth and sand filters (left)


I measured plant height every other day.


On the first day, I watered all of the seeds with tap water and then covered them with a small plastic covering to create a greenhouse effect. Every other day after that, I watered the plants using a pipette with the water designated for each plant. After six days, I removed the plastic covering. For the first 12 days, I watered the plants with 2.5 mL with each of their respective types of greywater or tap water. From Day 13, I watered the plants with 5 mL each. For approximately 14 hours per day, the plants grew underneath a lamp. For the first eight days, I measured the plant growth every day, using a ruler in millimeters. After that, I measured plant growth every other day. As soon as plant growth had reached non-self-supporting height, I placed tall sticks into the soil to help stabilize each plant.

I used Microsoft Excel to analyze the results and for recording the raw data, calculating the mean, standard deviation, and coefficient of variation.

 

Results

Figure 1 shows the trends in the average daily growth for the seven sets of Alaskan pea plants. At the end of the study period, it was found that the plants watered by the sand filter-treated detergent greywater grew on average the most; the plants watered by unfiltered shampoo greywater grew the least. The Control A plants, watered by tap water, on average grew higher than all the other plants except for the plants watered with the sand filter-treated detergent greywater.

Figure 1

Figure 1


Figure 2 illustrates the average daily growth of the Green Arrow pea plants. By the end of 20 days, plants watered by sand filter-treated detergent greywater were found to have the most growth on average; plants watered by unfiltered shampoo greywater grew the least. On the other hand, the growth of the Control A plants watered by tap water, on average, was lower than all the other plants except for the plants watered by unfiltered shampoo greywater. 

Figure 2

Figure 2


Figure 3 demonstrates the daily average incremental growth of both Alaskan and Green Arrow pea plants for a period of 20 days. The Green Arrow pea plants germinated later and were significantly smaller than the Alaskan pea plants. For the Alaskan pea plants, Days 10-16 showed the highest rates of growth. For the Green Arrow pea plants, Days 12-16 displayed the highest rates of growth. 

Figure 3

Figure 3


Table 1 shows the relative variability (i.e., the coefficient of variation)in the daily growth of Alaskan pea plants from Day 7 through the end of the study period. For all plants, the relative variability in daily growth during the early part of the study period (soon after germination) was much higher than the growth variability at the end of the study period. Unfiltered shampoo-watered plants had the highest variability in daily growth on most days during the study period.

Table 1. Relative Variability in the Alaskan Pea Plants’ Daily Growth

Day Control A (Tap Water)* Control B1 (Unfiltered L. Detergent) Control B2 (Unfiltered Shampoo) Cloth Filter (L. Detergent) Cloth Filter (Shampoo) Sand Filter (L. Detergent) Sand Filter (Shampoo)

7

8

10

12

14

16

18

20

0%

0%

0%

0%

0%

0%

0%

0%

41%

35%

14%

10%

13%

19%

24%

22%

88%

76%

39%

18%

17%

17%

21%

20%

102%

38%

19%

12%

8%

11%

9%

9%

28%

35%

13%

3%

3%

3%

13%

13%

120%

53%

29%

13%

13%

6%

6%

9%

78%

25%

8%

4%

3%

5%

9%

13%

Note: *Of the three seeds, only one germinated and grew, thus a zero in variability.

Table 2 displays the relative variability in the daily growth of the Green Arrow pea plants across different plant types. Plants watered with the unfiltered shampoo greywater exhibited the greatest variability throughout the study period. Plants watered with the sand-filtered detergent greywater exhibited the least amount of variability.

Table 2. Relative Variability in the Green Arrow Pea Plants’ Daily Growth

Day Control A (Tap Water) Control B1 (Unfiltered L. Detergent) Control B2 (Unfiltered Shampoo) Cloth Filter (L. Detergent) Cloth Filter (Shampoo) Sand Filter (L. Detergent) Sand Filter (Shampoo)

7

8

10

12

14

16

18

20

173

100

55

25

28

19

21

20

173

105

36

16

29

22

8

9

173%

119%

86%

77%

70%

76%

70%

72%

173%

100%

67%

26%

10%

11%

9%

10%

123%

89%

69%

52%

62%

39%

32%

29%

0%

6%

31%

8%

3%

4%

8%

1%

0%

44%

27%

25%

23%

34%

25%

22%

 

 

 

Explanations for Data Trends

For both the Green Arrow and Alaskan pea plants, I found that sand filter-treated greywater had the best impact on growth, and unfiltered shampoo greywater had the worst impact on growth. I thought that the positive impact of sand filter-treated greywater on plants was due to the water containing residues from the sand, which is a natural material, and because detergent contains some nitrates and phosphates, which are plant growth stimulators (Shakhashiri). Although the unfiltered shampoo greywater was pH balanced and had a pH level (6.5) within the range of the desired pH level for pea plant growth, the shampoo greywater may have contained higher amounts of salts (as sodium laureth sulfate). Because it was not filtered, the higher salinity in the greywater could have negatively affected the plant growth.

The higher growth rate between Days 10 through 16 could be partially attributed to fact that they started to receive more water (5 mL) from Day 13. In the earlier part of the study period, the plants germinated between Day 5 and Day 10, thus affecting the average growth for individual plant types. Near the end of the study period, the lateral vines began growing, so the vertical growth became reduced. The high variability in the earlier part of the study period was due to the differences in germination time. For example, the three Green Arrow pea plants watered with unfiltered shampoo greywater had a four-day difference between their germination times. The zero variability for Control A Alaskan pea plants was because only one of three seeds planted germinated and grew. Thus, the differences in germination time could have led to changes in variability through the study period.

   

Conclusion and Importance

The sand filter-treated detergent greywater overall did the best at stimulating plant growth. On the other hand, unfiltered shampoo greywater overall did the worst. This information is significant because these results indicate that even if there are water shortages and water scarcity, people can carry on with their normal lives and still support themselves.  Using simple filtration methods, people in those conditions could filter their greywater with easy and simple household methods, and grow their own food.

   

Additional Research

Although 42 samples were included in the experiment, the study was conducted for only 20 days. If the study had been continued until the plants reached maturity (in 55-65 days), the data might have yielded more conclusive results. Also, exposing the plants to real sunlight and growing them outside in warmer conditions could have made the growing conditions and the results more realistic.

   

Acknowledgements

I would like to thank my science teacher for her feedback, support, and encouragement on this experiment. I would like to thank my mom for teaching me to use Microsoft Excel and helping me set up my experiment. I would like to thank my dad for getting me the materials I needed.

 

Bibliography

Biello, David. “Will There Be Enough Water?” 60-Second Earth, Scientific American, 3 March 2013. Web. 21 Feb. 2014.

Boufaroua, M., A. Albalawneh, and T. Oweis. “Assessing the Efficiency of Greywater Reuse at Household Level and Its Suitability for Sustainable Rural and Human Development.” British Journal of Applied Science & Technology 3.4, 2013: 962-972. Web. 21 Feb. 2014.

“Climate Impacts on Water Resources.” U.S. Environmental Protection Agency, 9 Sept. 2013. Web. 21 Feb. 2014.

“Overview of Greywater Management Health Considerations.” World Health Organization, Regional Office for the Eastern Mediterranean, Amman, Jordan, 2006.PDF. 21 Feb. 2014.

Shakhashiri, Bassam Z. “Chemical of the Week: Agricultural Fertilizers: Nitrogen, Potassium, and Phosphorus.” Science Is Fun, Scifun.org, n.d. Web. 21 Feb. 2014.

“World Water Day 2013: International Year of Water Cooperation.” UN Water, UNESCO, n.d. Web. 21 Feb. 2014.