The WaterCAMPWS Center for Advanced Materials for Purification of Water with Systems University of Illinois at Urbana-Champaign
Curriculum Connection: Chemistry, Biology, Environmental Science
Grade Level: 9-12
Topic: Bioreactors, DO, pH, metabolism
Lesson Duration: Approximately 60 minutes
This W.E.T. is centered on principles aerobic and anaerobic metabolism of microorganisms. Water and waste water treatment plants microorganisms to degrade organic wastes during the treatment process.
This lab demonstrates change of DO and pH relative to the biodegradation of sugar by yeast paralleling microorganism activity in an actual treatment plant.
1. Students will learn key vocabulary associated with aerobic and anaerobic metabolism.
2. Have a basic understanding of aerobic and anaerobic metabolism, and be able to it to real
3. Recognize differences between aerobic and anaerobic metabolism and the uses of each
during water treatment.
4. Understand how aerobic and anaerobic metabolism are used in water purification techniques.
Illinois State Learning Standards:
; 11.A.4a Formulate hypotheses referencing prior research and knowledge.
; 11.A.4b Conduct controlled experiments or simulations to test hypotheses. ; 11.A.4c Collect, organize and analyze data accurately and precisely. ; 11.A.4d Apply statistical methods to the data to reach and support conclusions. ; 11.A.4e Formulate alternative hypotheses to explain unexpected results. ; 13.A.3a Identify and reduce potential hazards in science activities.
NSES Standards: In grades 9-12, students will learn:
; Content A Abilities necessary to do scientific inquiry & understandings about scientific inquiry. ; Content B Structure and properties of matter, motions and forces, and interactions of energy and matter ; Content E Abilities of technical design and understandings about science and technology ; Content F Personal and Community health, population growth, natural resources, environmental quality, natural and human induced hazards, and science and technology in local, national and global challenges ; Teaching A Plan an inquiry-based science program for their students ; Teaching B Guide and facilitate learning ; Teaching D Design and manage learning environments that provide students with the time, space and resources need for learning science. ; Teaching E Develop communities of science learners that reflect the intellectual rigor of scientific inquiry and the attitudes and social values conducive to science learning.
1 The WaterCAMPWS Center for Advanced Materials for Purification of Water with Systems STEM Educational Curriculum Supplement
Materials required for this lesson are (for each group of students):
; 250 ml Erlenmeyer Flasks 1/group
; DO probe and associated equipment
; pH meter
; Teaspoon Sugar/group
; Boiled egg whites, chopped
Bioreactors result in the degradation of organic materials in an environmentally friendly way without the use of chemicals. Sludge or biomass is the microorganisms found in the bioreactors in wastewater treatment plants that degrade the waste. Microorganisms metabolize or “eat” the
biodegradable organics that flow into the bioreactor as their food, breaking down or rendering inert the harmful materials so that the final product can be safely re-entered into the environment. As the microorganisms “eat” the waste, oxygen will be consumed. Therefore the dissolved oxygen
(DO) will decrease with time in the bioreactor as the waste is degraded if additional oxygen is not added. The rate of degradation will vary according to the make up of the influent waste. For example, water entering a treatment plant may contain more organic material after heavy rains and less organic material during a time of drought. Sludge in water treatment plants are very diverse and consist of different kinds of microorganism that can degrade different types of wastes. Some microorganisms prefer “carbohydrate waste” and others prefer “protein waste”. For example, if the sludge came from a treatment plant that has sugary wastewater, the microorganisms in the sludge will be good at degrading carbohydrate waste, but they may not be good at degrading proteins. However, with time, it is possible for microorganisms in the sludge to grow and become acclimated to degrade proteins. The type of microorganisms will also affect the rate of DO consumption.
Aeration is needed to keep the microorganisms alive for proper degradation of the incoming organic material. Water treatment plants ensure the proper oxygen content of the sludge by aerating the tanks which contain the sludge/biomass and waste. Methods of aeration are:
; Diffused aeration - Air bubbles through water.
; Spray aeration - Water is sprayed through air.
; Multiple-tray aeration - Water flows through several trays to mix with air.
; Cascade aeration - Water flows downwards over many steps in the form of thin water falls.
; Air stripping - A combination of multiple tray and cascade technique plus random packed
blocks causing water to mix thoroughly with air.
The ratio of biodegradable organic materials to the number of microorganisms present influences the rate of degradation. The higher the number of microorganisms, the faster the degradation will be. More oxygen is needed for the degradation and keeping the microorganisms alive and supplying this oxygen will be costly. Higher oxygen levels results in more microorganism growth and thus more sludge needing disposal. However, if sufficient degradation is not achieved in the bioreactor, the effluent cannot be discharged into natural waters. Effluent is regulated in wastewater treatment plants through state and local agencies. Therefore, a good balance must be maintained to achieve both objectives.
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1. Have the students share their results for each of their tests.
Have the students clean up the lab. Collect the lab books at the end.
The lab book should provide an assessment tool for this lesson.
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A. Example of a Wastewater Treatment Plant – for more information go to this web site:
http://www.rdn.bc.ca/cms.asp?wpID=1164 All descriptions below are taken with permission from
the web site.
1. Preliminary treatment - The velocity of the wastewater from the sewer lines is reduced as it enters the treatment plant. This allows sand, gravel and other heavy materials to settle out into grit tanks. Mechanical cleaning bar screens then remove rags, sticks, plastic and other foreign objects from the wastewater; this part of the treatment plant is called the headworks. Bar screens may be used before or after the grit tanks. All removed material collected by grit tanks and bar screens is washed and then taken to a sanitary landfill for disposal.
2. Primary treatment - Primary treatment allows for the physical separation of solids and grease from the wastewater, and removes between 30-40 percent of Biological Oxygen Demand and 50 per cent of Total Suspended Solids.
The screened wastewater flows into a primary settling tank where it is held for several hours allowing solid particles to settle to the bottom of the tank. Fats, oil and grease (FOG) are skimmed from the tanks, dried and sent to the landfill. The settled particles are known as primary sludge, which is collected and pumped to large digestion or holding tanks for further treatment and solids processing.
3. Secondary treatment - Secondary treatment is a biological treatment process that removes up to 90 percent of BOD and TSS. Following primary treatment, effluent is pumped to the secondary treatment stage. It may take one of several forms; for example, either a trickling filter or sequencing batch reactor. The growth of microorganisms results from the consumption of organic matter in the wastewater as their food supply.
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The micro-organisms create a solid organic material (sludge), which just like the sludge from primary treatment. Secondary sludge is thickened and pumped to digesters for processing and solids processing.
4. Final treatment - The wastewater that remains can be disinfected to kill harmful micro-organisms before being released into receiving waters. Although there are many methods available to kill these micro-organisms, ultraviolet disinfection is the method used at Duke Point Pollution Control Centre. This is the only treatment plant in the RDN with this technology. At this stage, the treated wastewater, now called final effluent, is discharged into the marine environment. 5. Solids processing - Primary solids from the primary settling tank and secondary solids from the clarifier are sent to digesters for solids processing. During this process, micro-organisms use the organic material present in the solids as a food source and convert it to by-products such as methane gas and water. Digestion results in a 90% reduction of pathogens and the production of a wet soil-like material called "biosolids" that contain 95-97% water. In order to remove some of this water, mechanical equipment such as a belt filter press or centrifuge are used to squeeze water from the biosolids, reducing its volume prior to being used in soil amendment or composting. B. Aerobic metabolism of sugar:
CHO + 6O 6CO + 6HO + ~38 ATP 6126222
Anaerobic metabolism of sugar
CHO +2ATP 6CO+ 2CHCHOH + ~4 ATP 61262 32
C. Cost wise, anaerobic processes are better because they produce less sludge (i.e. growth rate of microorganisms are slower). This is validated by the 38 ATP in aerobic vs 2 ATP in anaerobic. High sludge production result in high sludge disposal costs. Aerobic is however much faster than anaerobic and since municipal wastewaters have low strength the overall sludge production will not be too high. If a high strength wastewater is treated, anaerobic has more advantages. D. Effluent is an outflowing of water from a natural body of water, or from a man-made structure. Effluent in the man-made sense is generally considered to be pollution, such as the outflow from a
Sewage treatment facility or the discharge from industrial works. An effluent sump pump, for
instance, pumps waste from toilets installed below a main sewage line.
E. In actual treatment plants, the DO level is measured in the liquid phase to ensure that there is sufficient DO for the organisms. For this experiment, since there is limited oxygen, the DO level in the liquid phase would be very low as it is being constantly taken up by the organisms. Measuring the DO level the air space make sense as it is this oxygen that the organisms consume at the end.
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