The Isolation of Bacteria from Sewage water


The Isolation of Bacteria from Sewage water for the decomposition of HDPE (High Density Polyethylene) plastic films

Chapter I- Introduction


Plastic is lightweight, durable and impermeable. These qualities have made plastic a preferable material for society. But the abundant production of plastic due to the great demand of society means an excessive deal of disposal as well. The use of these lightweight, inexpensive materials are as single-use items that will go to the garbage dump within a year, where they’ll persist for centuries. This imposes a threat to the health of people, animals, and the environment.

Most plastic bags are made from polyethylene (PE) which is a polymer consisting of long chains of the monomer ethylene (Burd, 2008). A molecule of Polyethylene is made up of a long chain of carbon atoms with one hydrogen atom attached to each carbon atom.

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High Density Polyethylene (HDPE) is one kind of Polyethylene material that is used for making plastic products such as shopping bags, shampoo bottles, etc. (Freudenrich, Ph.D, 2011). HDPE plastic bags have a high melting point and tensile strength, making it difficult to be decomposed, which is a problem in maintaining the cleanliness of the environment.

Wastewater comes from two major sources: human sewage and process waste from manufacturing industries. Waste water treatment involves containing naturally occurring bacteria and microbes at a high concentration in tanks to form active sludge. The bacteria in the sludge feed on the carbon molecules from the waste in order to grow, thus, cleansing the waste water (Davies B.Sc, Ph.D, 2005)

Previous studies have also shown that plastics that end up in landfills degrade due to certain types of carbon-thriving bacterium that break down the plastic into simpler and safer forms such as water and alcohol.

Since High Density Polyethylene plastic is basically made up of carbon molecules, and sewage water contains various bacterium that are used for wastewater treatments it can be concluded that certain bacterium in sewage water can be utilized in degrading HDPE plastic bags.


What is the effect of the isolated bacteria from the sewage water to the HDPE plastic in terms of weight?


1. How many types of decomposing bacteria can be found in the sewage water?

2. What would be the most effective decomposing bacteria for HDPE plastic that may be found in sewage water?

3. How much weight loss will HDPE plastic have with the help of these decomposing bacteria?


1. To identify and isolate the PE- degrading bacteria in sewage water.

2. To discover a way to utilize bacteria in decomposing plastic waste.

3. To identify strains of bacteria that is not considered as PE degrading bacteria


This study shows the importance of the presence of bacteria in sewage water. It may not be the reason for people to avoid the contamination of bodies of water but it may be an assurance that HDPE (High Density Polyethylene) plastic films will degrade through the existence and exposure of cultured bacteria in sewage water. The strains of bacteria will be isolated and identified then will be used to decompose plastic and make sure that the strain of bacteria is the main cause for its degradation and weight loss. It is common knowledge to know that PE degrading bacteria are present in landfill but there are questions to people if PE degrading bacteria are consistently present in bodies of water, and if the strains of bacteria that inhabit water largely affect the decomposition of plastic films, these questions will be answered after the experimentation. The study can be more interesting if the resulting isolated bacteria are not described as PE degrading bacteria. It will be a new discovery because the identified bacteria will be considered as a new medium for decomposition.


In the said study, the researchers are focused in isolating bacteria and using it as a decomposer of HDPE (High Density Polyethylene) plastic bags. They are limited to utilizing samples from sewage water, with the assumption that it contains various kinds of microorganisms, as a source of the bacteria that they will need in decomposing the said plastic. The researchers are also limited to using High-density Polyethylene bags which is known for its high density and strong tensile strength. Furthermore, due to its high density, this kind of plastic is not easily decomposed making it as a problem in maintaining the cleanliness of the environment.

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Chapter II- Review of Related Literature

  1. Plastic

Plastic is a lightweight, impermeable and durable material. It has many uses to society most commonly for packaging and storage. It is presented in a variety of ways depending on the mixture and the chemical bonds. The chemical bonds of plastic make it slow down the degrading process making the high production of this material harmful to the environment. It is harmful especially when it is not disposed properly. Most plastics have organic polymers. Most of these polymers have either chains of carbon dioxide alone or with oxygen, sulphur and or nitrogen.

  1. Polyethylene

Polyethylene is the most common plastic used today. Approximately 80 million tons of it is produced yearly. Its main use is for packaging. It commonly has a long carbon chain with two hydrogen atoms attached to each carbon atom in the chain. It is chemically synthesized from ethylene, which is a compound usually made from petroleum or natural gas.

  1. HDPE

When there are no long chains of polyethylene branching from the carbon atoms the polyethylene is now classified as linear polyethylene. It is more costly than LDPE but even though it is costly it is sturdier. Linear polyethylene is made by a procedure called Ziegler-Natta Polymerization.

  1. Water

Water has the chemical equation H2O. It covers 71% of the earth’s surface. It is in liquid form at standard pressure and temperature. Water is also a necessity of all biotic forms in the earth. Water moves continually through the water cycle.

  1. Sewage Water

Sewage water is carried waste in the form of solution or suspension. It is from man’s waste from his daily activities. Classes of sewage include sanitary, commercial, industrial, agricultural and surface runoff. The wastewater from residences and institutions, carrying body wastes (primarily feces, urine and semen), washing water, food preparation wastes, laundry wastes, and other waste products of normal living, are classed as domestic or sanitary sewage. Liquid-carried wastes from stores and service establishments serving the immediate community, termed commercial wastes, are included in the sanitary or domestic sewage category if their characteristics are similar to household flows. Wastes that result from an industrial process or the production or manufacture of goods are classed as industrial wastewater. Their flows and strengths are usually more varied, intense, and concentrated than those of sanitary sewage. Surface runoff, also known as storm flow or overland flow, is that portion of precipitation that runs rapidly over the ground surface to a defined channel. Precipitation absorbs gases and particulates from the atmosphere, dissolves and leaches materials from vegetation and soil, suspends matter from the land, washes spills and debris from urban streets and highways, and carries all these pollutants as wastes in its flow to a collection point.

  1. Bacteria

Bacteria are from the Kingdom of Prokaryotes. They are very abundant in the earth and are one of the very first life forms to exist. Usually a few millimetres long and are spherical, rod or spiral in form. They may be found in almost every habitat. They play a big role in recycling nutrients like in the conversion of compounds and in the fixation of nitrogen. These bacteria can adapt to environmental conditions very well and survive wherever they are placed.


In making this experiment, the researchers must prepare the following materials - the sample bottle must be prepared for the collection of sewage water. It has to be properly labeled to avoid misuse/confusion. The researchers will get the plastic films from a plastic processor and distributor. The next steps would be with a help of a certified scientist. In the isolation of the bacteria, either way for a dilute sample such as water you would probably have to concentrate the sample. It is best to have a few liters of sample. First filter out the particulate matter with a 20 uM filter, then you can use water sampling nitrocellulose filter disc of 0.2 um. This probably needs a vacuum pump to draw the water through.

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You can then rinse this disc or swab it with a moist swab and use a series of dilutions to inoculate agar plates. Take a 10 ul drop and spread it out over the agar plate using a sterilized spreader. The agar i use for water samples is mostly very dilute in nutrients so that I do not have an overgrowth of one type of bacteria. I have used 1/5th strength nutrient agar, that is the nutrients do not dilute the agar strength. There are a whole variety of water based agars but the ISP2 media diluted to 1/4 strength was one of the best.. You can also take some of the waste water and filter it and use it for making wastewater agar to see if this will produce any colonies or try adding a very small amount of diluted nutrients. As above you can also use a host of diagnostic agars to see if there are any particular groups of organisms in the water. Another factor is the temperature of incubation. This is probably the best temperature to isolate the most organisms. Use room temperature incubation or 10C incubation to isolate the widest variety of organisms. If you use 37C you will probably only select out a few organisms. The researchers may try some under anaerobic conditions also if they have anaerobic jars. Generally at low temperatures colonies might not develop for a few weeks, so after a day you might have to wrap your plates with parafilm or keep them in moist conditions to prevent them drying out.