Biochemical Oxygen Demand and Sewer Ponds - 1997-98

The Student: Lisa Leaf

The Teacher: Clinton A. Kennedy

How effective are the Cascade sewer ponds?

How effective are the Cascade sewer ponds? I will try to find some answers through the testing of dissolved oxygen and biochemical oxygen demand or (BOD). Each of these tests will allow me to discover if Cascade's sewer ponds are really as effective as we hope they are.

Background Information

Wastewater is defined as liquid wastes collected in a sewer system and conveyed to a treatment plant for processing. Storm runoff is collected in a separate system and then distributed to the nearest watercourse for disposal without treatment. In large cities several of them have a combined wastewater collection system where both storm water and sanitary wastes are collected in the same pipe. There are different types of wastewater and here are a few of them: sanitary or domestic wastewater refers to liquid material collected from residences, business buildings, and institutions; industrial waste refers to wastes from manufacturing plants; municipal wastewater is a general term applied to liquid treated in a municipal treatment plants.
People can generally tell what is the age of wastewater but it depends on the color and odor. Fresh wastewater is usually a light brownish gray color as the anaerobic condition develop the color of wastewater changes sequentially from gray to dark gray and finally black. When the water turns black, it is generally septic and industrial wastes adds color.

Runoff from the watersheds is usually transported in what are called separate system (separate from sewage) or combine (combine with sewage). During and following storms, the storm waters combine with sewer overflows that can contribute to the same constituents as in sewage and in relatively high concentration. The concentration and yield of the total suspended solids from storm water runoff and sewage are similar. Streets and parking lots collect large amount of solid water, that runoff into streams and lakes, and BOD in urban areas in much higher than in areas pristine, but less than raw sewage.

The development of urban areas concentrating people and their waste had to be followed by the development of the waste treatment processes. Some of these are the combined collection of urban runoff from roots and paved areas, and with the collection of water borne human and industrial waste. The advantages of the combined system is that the storm runoff from urban areas flows into sewer treatment plants; the disadvantages is that at times of high flow many sewage treatment plants have storm overflows which discharge directly to watercourses with no treatment or without any settlement.

The principle reasons for sewage treatment plants is to control the capacity of the sewage or pollutes to watercourses by reducing and enabling the bacterial oxidation of organic matter derived from any source. In doing this, the major elements from the waste, carbon, nitrogen, and phosphorus can be oxidized This is why the point source of high concentration of nitrogen and phosphorus is important to identify.
The chemical characteristic of wastewater is present in fours parts: 1) organic matter; 2) the measurement of organic materials; 3) inorganic matter; and 4) gases. I am going to worry about the organic matter and the measurement of organic materials.

In wastewater of medium strength, about 75 percent of suspended solids and 40 percent of filterable solids are organic substances found in nature. The principle groups of organic materials are proteins, carbohydrates, and fats and oils. Along with the others, there are a small number of different synthetic organic molecules ranging from simple to extremely complex in structure, for example surfactants and organic priority pollutants and pesticides.

Each of the carbohydrates found in nature effect the sewage ponds in their own separate ways. Proteins effect on sewage ponds is that there is an extremely foul odor produced by their decomposition. Cellulose is the most important carbohydrate found in wastewater. The destruction of cellulose in the soil goes readily, as result of various fungi. For the most part, these float on top, although a portion is carried into sludge on settling solids. The grease content in wastewater can cause many problems in both sewer and waste treatment plants. If the grease is not removed before the discharge of the waste, it can interfere with biological life in surface waters and create unsightly floating matter and films.

The synthetic carbohydrates effect sewage ponds in their own ways. Surfactants are the safest synthetic carbohydrates. Surfactants, or surface-active agents, are large organic molecules that are slightly soluble in water and cause foaming in wastewater treatment plants and on the surface waters. These priority pollutants are the bad ones, although these priority pollutants may be removed, transformed, generated, or simply transformed in a wastewater collection or treatment system. Volatile organic compounds or VOCs are a great concern because when they are in their vapor state, they spread great harm to the people below and release an increase of reactive hydrocarbon into the atmosphere. Trace organic compounds such as pesticides, herbicides, and other agricultural chemicals are toxic to most life forms and there can be significant contaminants of surface waters.

There have been numbers of tests developed to determine the organic content of wastewater. Laboratory methods commonly used today to measure gross amounts of organic matter include: biochemical oxygen demand, chemical oxygen demand, and total organic carbon. We will only focus on BOD out of these tests to measure the organic matter.

BOD is the most widely used test of organic pollutants applied to both wastewater and surface water. This determination involves the measurement of the dissolved oxygen or DO used by microorganisms in the biochemical oxidation or organic matter. The reasons scientists use BOD results are: 1) how to determine the approximate quantity of oxygen present, 2) to determine the size of the waste treatment facilities, 3) to measure the efficiency of some treatment processes, and the last reason 4) to determine compliance with the wastewater discharge permits.

To test BOD a person needs to do a dissolved oxygen test first and gather BOD samples at the same time. The student or scientist has to wait for fives days for the dissolved oxygen test again in a lab setting. To determine the true BOD, the scientist must subtract the first test, the DO test from the DO test done in the lab. To ensure meaningful results, the sample must be suitably diluted with a special dilution water so that adequate nutrients and oxygen will be available during an incubation period.

A person must wait for five days with the BOD test and not later because within two days after the five carbonaceous oxygen demand starts to occur with the sample prepared, and nitrification starts occurring if the number of the nitrifying bacteria are presented in the sample.

The decrease of BOD and the decline of and rise of DO depict the process known as self-purification, which is dependent on the rate at which oxygen is absorbed back into the stream, which, in turn, is dependent on the turbulence intensity and the water depth.

The number of algae in stream water used for dilution water may produce significant changes in the oxygen content. Short-term BOD determination may show the influence of oxygen production by the algae. After the lack of light, the algae die and algal cells contribute to the total organic content of the sample and the increase of BOD, on the other hand, samples incubated in the light, under the continual photosynthesis, will yield low BOD values.

Dissolved oxygen is the amount of oxygen in any type of water environment whether lake, river, or ocean. There have been set limitations for the standards of DO on the aquatic life and fish , the minimum level of DO for a diverse population of fish is 5 mg/l, the standard for freshwater aquatic life is 5.0 mg/l.

My Project

For my project this year, I wanted to find out if the sewer ponds are really effective. To do this, I had to test the dissolved oxygen below, above, and in the middle of the sewer ponds in the North Fork Payette river. To get really effective results I had to test the BOD levels five later for the dissolved oxygen test.

My hypothesis was that I expected the site with cleanest BOD was the control up stream. I expected the dirtiest site of BOD would be the sewer pond, and the downstream site I expected it to be in the middle between the cleanest and the dirtiest site.

On March 8 I went down to the North Fork of the Payette to gather my samples for the test. In about a 40 minute time frame I took the dissolved oxygen test for the three samples I had. The water was 8 degrees Celsius. First, I tested the water up stream from the sewer ponds as a control for the experiment. The water was taken from the river just below the north bridge, about 5 meters out at the surface of the river. The second one I tested was the downstream site, located just about the south bridge, again surface water about 5 meters out in the river. Third, I tested the stream that was adjacent to the sewer pond, and collected water from the surface about 5 meters out in the river.

For the testing procedure for dissolved oxygen, I filled the bottle with the round stopper with the samples of the North Fork of the Payette river and tried to thrust the stopper in the bottle so no air bubbles would be in the bottle. Then I dumped in the reagents powder Lithium Hydroxide and Potassium Iodine and Maganous Sulfate into the bottle and shook vigorously to mix all these powders together. If oxygen is present there should be a brownish orange color. I let it stand for 2 minutes until the powder settled on the bottom and shook it again, and the powder in the bottle had to settle to the bottom one more time. After the powder settled on the bottom, I put Sulfuric Acid powder in the bottle, and shook it and this time all the powder was dissolved in the bottle; with the bottle turning yellow there is a presence of oxygen. I filled with mixing tube with the water in the bottle and turned it upside down with the square mixing bottle facing face up so the liquid from the mixing tube will be in the square mixing bottle. Then I took the Sodium Thiosulfate Standard Solution that I added in drop by drop into the square mixing bottle and swirled to mix while I counted very drop. Each of the drops I put in, is equal to 1 mg/l of DO. This is also the procedure for the test of the BOD.

The results I came up with are the exact opposite of the results I expected. The control is the measurement that I got up stream, which was 7mg/l, and the other measurements for both mid stream and down stream were 8mg/l. The first time I did the test up stream I got 11 mg/l for the dissolved oxygen reading, but the testing did not go just as it should have, and I thought I might get a wrong reading. So I did it again. The second time, I felt really good with the 7mg/l for the up stream reading. These measurements seem to be accurate with the up stream being the lowest of the three and the two being close together.

Locations: Do test: 2nd Do test: BOD results:
control-up stream 7 5 2
in the river by the sewer pond 8 7 1
down stream 8 8 0

Future Plans

There could be a chance where someone could take this project over next year. Next year there could be more tests done in the beginning of the year and at the end of the year to see the differences in the data between the fall and winter and the spring. Maybe even test in the summer to see the differences between the data collected in the fall or winter and spring with the summer data.


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