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Microbe Use for Wastewater Treatment

Info: 2286 words (9 pages) Essay
Published: 10th May 2021 in Environmental Sciences

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 Microbes contribute more to daily life than most people realize.  A peak interest of the writer is wastewater treatment with the use of microbes.  Most people do not stop to think about the methods in which wastewater is cleaned and returned to the environment.  The term wastewater treatment plant is most often associated with the knowledge of sewer plants.  However, there are a variety of factories that treat their own wastewater as well as agricultural applications. This paper will cover the treatment of wastewater to the point of environment return and the use of microbes along the way.  With 331,883,986 people living in the United States [5], it would be hard to have enough clean water to go around.  This paper should explain the importance of treated water in daily life.

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To begin, the reader might as, “What steps are needed to treat water?  How are the microbes maintained?  How does a person know if the microbes are working efficiently?”  It is actually rather simple when broken down.  According to information provided by South Gippsland Water,“Wastewater treatment generally involves 3 stages of treatment: primary, secondary and tertiary treatment.  Primary treatment consists of temporarily holding the sewage in a basin or clarifier where heavy solids can settle to the bottom while oil, grease and lighter solids float to the surface. The settled and floating materials are removed and the remaining liquid is transferred to the next stage of treatment.  Secondary treatment removes dissolved and suspended biological matter. Secondary treatment is typically performed by water-borne micro-organisms in a managed habitat. Secondary treatment may require a separation process to remove the micro-organisms from the treated water prior to discharge or tertiary treatment.  Tertiary treatment allows further disinfection either chemically or physically (for example, by lagoons and microfiltration) prior to discharge into a creek or river or it can be used for the irrigation of pastures or sporting fields.” [10]  See process flow diagram below for complete route of wastewater to clean effluent.

Researchgate.net [2]

  In the first stage, wastewater is collected into concrete pits called basins.  At this point the water will rest, or be undisturbed, and the heavy matter and larger particles, known as sediment, will begin to fall out, dropping to the bottom of the sediment tank/basin.  Some plants will implement a preliminary treatment stage where filtration of large objects, such as rock and sticks, will occur.  “During primary treatment, somewhere between twenty-five and fifty percent of biochemical oxygen demand is removed, along with fifty to seventy percent of solids, oils, and greases. Some organic nitrogen and phosphorus, as well as heavy metals associated with solids are also removed during primary sedimentation, but smaller and dissolved particulates are not. The effluent created in the primary stages is often referred to as primary effluent.” [1]  Once separation has occurred, the effluent will move into the secondary stage of treatment. 

“The secondary stage of treatment utilizes trickle filters and activated sludge processes.  These methods remove about eighty-five percent of the organic matter in sewage by making use of the bacteria in it.” [4]  Often so, this stage is found to be one of the most interesting as this is where the microbes are utilized and the process becomes more complex.  The terms activated sludge and aerobic/anaerobic digesters are used here.  Activated sludge is desirable because it is effective and economically favorable.    As aerobic bacteria are oxygen loving, “As aerobic bacteria move about the oxygen rich aeration tank, they quickly use all the organic matter contained inside the influent.  They bacteria prosper in the abundance of food and air, producing new cells at a rapid rate.  It rakes roughly four to eight hours for waste to gather at the bottom of the tank.  When this separation does occur, a clearer liquid becomes the supernatant which will move forward in the treatment processes.  The sludge left will be pumped back into the aeration tank and for recycle.  As sludge builds, it becomes waste that receives separate treatment.” [6]  The sludge is made up of protozoa, metazoan, bacteria (including filamentous), fungi, and algae cultures.  As long as the “bugs” are being cared for, they can be recycled back into the system for further water treatment.  It is important to check the health and morphology of the microbes, as well as viable cell count, via microscope, to understand the adjustments to be made for enhancement of “sludge bugs”.  Plant personnel will observe overgrowth of certain types of microbes and adjust the treatment system for balance the desired levels of microbes. While this is a lengthy excerpt from Water Tech, the information was too valuable to be cut. The following list describes the function of each microbe in the secondary stage of water treatment:  “Aerobic bacteria remove organic nutrients, Protozoa remove and digests dispersed bacteria and suspended particles, Metazoa dominate longer age systems including lagoons, filamentous bacteria cause a bulking of sludge (poor settling & turbid effluent), algae and fungi are present with pH changes and older sludge”  To further that information, “Bacteria are primarily responsible for removing organic nutrients from the wastewater while protozoa play a critical role in the treatment process by removing and digesting free swimming dispersed bacteria and other suspended particles. This improves the clarity of the wastewater effluent. Like bacteria, some protozoa need oxygen, some require very little oxygen, and a few can survive without oxygen. The types of protozoa present give us some indication of treatment system performance which are classified as follows: 1. Amoebae-Little effect on treatment & die off as amount of food decreases 2. Flagellates-Feed primarily on soluble organic nutrients 3. Ciliates-Clarify water by removing suspended bacteria 4. Ciliates; Free-swimming-Removes free-dispersed bacteria 5. Ciliates; Crawling (grazing)-Dominate activated sludge/good treatment 6. Ciliates; Stalked (sessile)-Dominates at process end Protozoa.  Metazoa are multi-cellular organisms which are larger than most protozoa and have very little to do with the removal of organic material from the wastewater. Although they do eat bacteria, they also feed on algae and protozoa. A dominance of metazoa is usually found in longer age systems; namely, lagoon treatment systems.  Although their contribution in the activated sludge treatment system is small, their presence does indicate treatment system conditions. Three most common metazoa found in the activated sludge treatment system. 1. Rotifers-Clarify effluent & are first affected by toxic loads 2. Nematodes-Feed on bacteria, fungi, small protozoa & other nematodes 3. Tardigrades (water bear)-Survive environmental extremes & toxic sensitivity Metazoa images are below: 4. Filamentous bacteria are present when operational conditions drastically change. These bacteria grow in long filaments begin to gain an advantage. Changes in temperature, pH, DO, sludge age, or even the amounts of available nutrients such as nitrogen, phosphorus, oils & grease can affect these bacteria. The dominance of filamentous bacteria in the activated sludge treatment system can cause problems with sludge settling. At times excessive numbers of filamentous microorganisms interfere with floc settling and the sludge becomes bulky. This bulking sludge settles poorly and leaves behind a turbid effluent. Some filamentous microorganisms may cause foaming in the aeration basin and clarifiers. Filamentous images are below: 5. Algae and fungi which are photosynthetic organisms and generally do not cause problems in activated sludge treatment systems, however their presence in the treatment system usually indicate problems associated pH changes and older sludge.” [9]  The easiest way to check the activity of the microbes in the plant is to samples various stages of the treatment process for BOD or Biological Oxygen Demand.  “Biochemical oxygen demand (BOD) represents the amount of oxygen consumed by bacteria and other microorganisms while they decompose organic matter under aerobic (oxygen is present) conditions at a specified temperature.” [3]

The tertiary stage is the final stage of water clean up before it is released back to the environment.  In this stage the effluent, or water going out, is clarified and purified to state regulations, meaning it is safe for any animals that should consume or inhabit the water.  “Any inorganic compounds such as nitrogen and phosphorus, or any other substances left in the effluent, are removed in this final purification stage.  Any pathogens that can be harmful to humans, such as parasites, viruses, and bacteria, are also removed at this time.  The water has to then flow through a series of sand filters to capture any flocculating matter created as a result of the addition of aluminum sulfate.  While the floc is caught in the sand filters, the clear water can move forward to chlorination vessels.  Chlorine is used to disinfect the water as it kills particularly harmful viruses and bacteria, such as Cryptosporidium, Giardia, and other microorganisms.  This can be a slow process, but once complete, the water lacks only one step to being released.  On the contrary, any remaining chlorine must be removed from the water as it can cause harm to aquatic life and water quality.  This is done so by adding sodium bisulphite.  [8]  Microbes have undoubtedly helped people manage to recycle the water in which all walks of life need for survival.  The water leaving the treatment facility may end up as drinking water or water being released back to a nearby river.  Farmers have also been able to take advantage of the water recycling programs to irrigate their cropland, as water must be clean enough to come into contact with food products.   With drinkable water sources scarce in so many countries, the ability to use naturally occurring microbiota is ideal, if funding for such facilities can become available. 

An additional question can be asked after understanding the wastewater treatment process, “What uses are there for the build up of sludge and organic particulate?”  Most of these biosolids can be moisture reduced to a wet cakey matter with the implementation of industrial centrifuges.    Farmers and landscapers alike can use the wet cake in land applications as it is high in nutrients and nitrogen for the soil.  For doubts about safety of land applying said biosolids, there are federal regulations that control the amount of biosolids that can be utilized.  These regulations are in place to limit introduction of pathogens, metals, and over exposure of nutrients such as nitrogen or phosphates.               

Overall, the benefits of being able to treat wastewater are abundant.   “It has been said to be of paramount importance to both environmental standpoints and public heath perspective, to have capability to effectively treat wastewater and return it as well as sewer sludge to the environment in a protected form.  In 1972, congress passed the Clean Water Act (CWA) in recognition of this ability.  The federal government also funded over sixty one billion dollars in grants plus another sixteen billion dollars of low interest loans for use by municipal and local governments.  Between 1972 and 1999, these loans were used to support the construction costs of necessary sewage-sludge and wastewater treatment facilities, as well as dispositon of biosolids”. [?]  It would seem impossible to live in sanitary conditions without the use of wastewater treatment.  It is important remember and recognize the contributions microbes can make on everyday life and to consider ways in which they can continue to improve the environment.


[1] 3. Wastewater Treatment, www.fao.org/3/t0551e/t0551e05.htm.

[2] Azadi, Ali. “Wastewater Diagram.” Flow Diagram-California Dairy, 2015, www.researchgate.net/figure/Flow-diagram-of-wastewater-treatment-plant-at-Sanandaj-dairy_fig1_287643591.

[3] Biological Oxygen Demand (BOD) and Water, www.usgs.gov/special-topic/water-science-school/science/biological-oxygen-demand-bod-and-water?qt-science_center_objects=0#qt-science_center_objects.

[4] EPA, EPA. “Wastewater Treatment: The Basics.” Wastewater Treatment: The Basics, 1998, www3.epa.gov/npdes/pubs/bastre.pdf.

[5] “U.S. and World Population Clock.” Population Clock, www.census.gov/popclock/.

[6] NSFC, NSFC. “Explaining the Activated Sludge Process.” Pipeline, 2003, www.nesc.wvu.edu/pdf/WW/publications/pipline/PL_SP03.pdf.

[7] “Read ‘Biosolids Applied to Land: Advancing Standards and Practices’ at NAP.edu.” National Academies Press: OpenBook, www.nap.edu/read/10426/chapter/4#32.

[8] Sydney Water Tour, www.sydneywater.com.au/Education/Tours/virtualtour/html/reuse-and-recycling.html.

[9] Theobald, Dan. “Microorganisms in Activated Sludge.” Water Tech Online, 20 Jan. 2017, www.watertechonline.com/wastewater/article/15545467/microorganisms-in-activated-sludge.

[10] “Wastewater Treatment.” Wastewater Treatment – South Gippsland Water, www.sgwater.com.au/services/wastewater/wastewater-treatment/.


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