Environmental Microbiology: Treatment of Water, Waste and Polluted Habitats

1. Environmental Microbiology:Treatment of Water, Waste and Polluted Habitats Chapter 31

2. Microbiology of Sewage Treatment • Wastewater or sewage composed of all materials of household plumbing system • Municipal wastewater includes industrial waste • Most obvious reason for sewage treatment • Eliminate potential pathogens in sewage • Less obvious problem • Impact of high nutrient content in sewage • Nutrients quickly utilized by aquatic organism • Effective treatment decreases level of organic compounds and eliminates pathogens and toxic materials

3. Microbiology of Sewage Treatment • Biochemical oxygen demand (BOD) is amount of oxygen required for microbial decomposition of organic matter in sample • BOD is roughly proportional to amount of degradable organic material • BOD of raw sewage is approximately 300 to 400 mg/liter of sewage

4. Microbiology of Sewage Treatment • Large scale wastewater treatment plants in U.S. use a two series process • Primary treatment • Secondary treatment • Once treated liquid portion termed effluent is discharged in body of water • Solid portion termed sludge is further treated in anaerobic digester

5. Microbiology of Sewage Treatment

6. Microbiology of Sewage Treatment • Primary treatment • Physical process designed to remove materials that settle out of liquid • Treatment removes nearly 50% of solids and 25% of BOD • Sewage passes through series of screens to remove large objects • Skimmers remove scum and floating debris • Sewage allowed to settle in sedimentation tank • Facilitates removal of solids • Sludge is removed after settling is complete • Primary sewage that remains is sent for secondary treatment

7. Microbiology of Sewage Treatment • Secondary treatment • Chiefly biological process • Designed to convert suspended solids to inorganic compounds and cell mass for removal • Eliminates nearly 95% of remaining BOD • Microbial growth encouraged during secondary treatment • Aerobic organisms degrade organic material to carbon dioxide and water

8. Microbiology of Sewage Treatment • Secondary treatment • Methods used in secondary treatment include • Activated sludge • Trickling filter • Lagoons • Artificial wetlands

9. Microbiology of Sewage Treatment • Activated sludge • System employs mixed aerobic microbes • Organisms grow in biofilms called flocs • Large number of organisms inoculated into sewage via addition of small amount of leftover sludge • Oxygen is supplied and organic matter converted to biomass or waste product • Sewage is sent to sedimentation • Flocs settle out and resulting sludge is removed • Portion of sludge is used for next “batch” • Complication of activated sludge is bulking • Interference of filamentous bacteria in sedimentation process

10. Microbiology of Sewage Treatment • Trickling filters • Frequently used in smaller treatment plants • Rotating arm sprays sewage over bed of course gravel and rocks • Rocks and gravel become coated with biofilms • Consists of heterogeneous mix of bacteria, fungi, algae, protozoa and nematodes • Organisms aerobically degrade organic material

11. Microbiology of Sewage Treatment • Lagoons • Sewage channeled into shallow ponds or lagoons • Remains there for period of time • Algae and cyanobacteria grow on surface to provide oxygen • Enable aerobic organisms to degrade sewage

12. Microbiology of Sewage Treatment • Artificial wetlands • Employ same principles as lagoons • More advanced design • Offers means to treat wastewater • Also provides habitat for birds and other wildlife

13. Microbiology of Sewage Treatment • Advanced treatment • Encompasses any purification process beyond secondary treatment • Includes tertiary treatment • May involve physical, chemical or biological processes • Tends to be expensive • Not common practice in the past • Designed to remove ammonia, nitrates and phosphates • Ammonia is removed through ammonia stripping • Liberates gaseous ammonia from water • Nitrates removed using denitrifying bacteria • Reduces nitrates to nitrogen gas • Phosphates removed through chemical precipitation

14. Microbiology of Sewage Treatment • Disinfection • Before discharge effluent is disinfected with one or a combination of the following • Chlorine • Ozone • Ultra violet light • These treatments decrease numbers of microorganisms and viruses

15. Microbiology of Sewage Treatment • Anaerobic digestion • Within anaerobic digester organisms act on solids removed through sedimentation • Varied populations act sequentially • Convert organism matter to methane • Organic matter  organic acids, CO2, H2 • organic acids  acetate, CO2, H2 • acetate, CO2, H2  methane • Many treatment plants use generated methane to power equipment • Remaining sludge dehydrated to form stabilized sludge • Nutrient rich product • Can be incinerated, placed in landfill or used to improve soil

16. Microbiology of Sewage Treatment • Individual wastewater treatment systems • Rural areas rely on septic tanks for sewage disposal • Wastewater collected in large tank • Solid material settles to bottom • Degraded by organisms • Fluid overflow has high BOD • Must be passed through drainage field • Field designed for oxidation of organic matter

17. Drinking Water Treatment and Testing • Large cities generally obtain drinking water from surface waters • Lakes or rivers • Surface waters may act as receiving waters for sewage effluent of cities upstream • Smaller communities often use groundwater as drinking water source • Occurs in aquifers contained in layers of rock, sand and gravel • Often protected from contamination due to depth

18. Drinking Water Treatment and Testing • Water treatment process • Treatment of metropolitan water supplies designed to provide safe water • Treatment process • Water flows into reservoir for period • Allows particulate to settle • Water transferred to tank and mixed with flocculent chemical • Causes suspended material to coagulate and sink • Water filtered to remove microorganisms • Organic chemicals can be removed by additional filtration • Through activated charcoal which absorbs dissolved chemicals • Water treated with chlorine or other disinfectant as final step

19. Water Treatment Process

20. Drinking Water Treatment and Testing • Water testing • Primary concern regarding safety of drinking water is possibility of gastrointestinal pathogens • Not feasible to test for all gastrointestinal pathogens • Test for indicator organisms • Routinely found in feces • Total coliforms most common group as indicator organism in U.S. • Fecal coliform is subset of total coliforms • More likely to be of intestinal origin • Most common fecal coliform is E. coli

21. Drinking Water Treatment and Testing • Water testing • ONPG/MUG • Water sample added to medium containing OPNG and MUG • Coliforms hydrolyze OPNG and turns media yellow • E. coli hydrolyzes MUG generating fluorescent compound

22. Drinking Water Treatment and Testing • Water testing • Presence/absence test • Water added to lactose medium with vial as gas trap • If gas produced sample is tested for presence of fecal coliforms • Most probable numbers method • Statistical assay • Employs successive dilution of water sample • Put in broth similar to presence/absence test • Positive MPN test tested to confirm coliforms

23. Drinking Water Treatment and Testing • Water testing • Sample is passed through membrane filter that retains bacteria • Concentrates bacteria in known volume of water • Bacteria then plated on lactose-containing media • Filter removed and placed on agar surface

24. Microbiology of Solid Waste Treatment • Sanitary landfills • Widely used to dispose of non-hazardous solid waste • Manner that minimizes damage to human health and environment • Must be located away from sensitive areas • Site is excavated, lined with plastic or membrane over clay • Minimize leaching • Waste is compacted and covered with layer of soil • This occurs daily • Landfills no longer in use covered with soil and plants • Can be used for recreation and construction • Methane and other gases are vented • Methane is burned or recovered for use

25. Microbiology of Solid Waste Treatment • Commercial and backyard composting • Alternative to landfills • Backyard composting involves mixing debris • Waste is reduced by 2/3 in matter of months • Black organic material can be used in garden beds • Compost pile usually starts with supply of organic material • Often some soil and water are added • Inside of pile heats to 55° to 60° C • Pathogens killed, thermophilic organisms unaffected • Aeration of pile via stirring when pile cools • Composting on large scale way to reduce garbage going to landfill • Special machinery used for large scale composting

26. Industrial and Backyard Composting

27. Microbiology of Bioremediation • Bioremediation is use of biological agents to degrade pollutants in given environment • Most organic compounds of natural origin can be degraded by one or more species of organism • Synthetic compounds are more likely to be degraded if they are similar to naturally occurring substances • Xenobiotics often persist for long periods of time

28. Microbiology of Bioremediation • Relatively slight change in chemical composition of pollutants markedly alter biodegradability • 2,4-D and 2,4,5-T • Only difference is additional chlorine atom on 2,4,5-T • 2,4-D disappears within weeks while 2,4,5-T present in environment more than a year • Most herbicides and insecticides are not only toxic but accumulate in wildlife • DDT in fatty tissues of birds as well as interfering with reproductive process • Fragile eggs

29. Microbiology of Bioremediation • Means of bioremediation • Many factors influence degradation rate of pollutants • Two general strategies • Biostimulation • Enhances growth of indigenous microbes in contaminated site by addition of nutrients • Fertilization of petroleum-degrading organisms • Bioaugmentation • Relies on activities of microorganisms added to contaminated materials • Complement resident flora

30. Microbiology of Bioremediation • Successful bioremediation may also involve controlling metabolic processes by manipulating availability of oxygen and growth substrates • Some pollutants only degraded when specific substrates are available • Called co-metabolism • Enzyme produced by organism for metabolism also degrades pollutant • Bioremediation may be done in place or off-site • In place generally relies on bioremediation • Off-site process may be performed in bioreactor designed to accelerate microbial process