MMG301 Dr. Frank Dazzo Aquatic & Wastewater MicrobiologyThe amount of biologically usable organic carbon in water is indirectly measured by its Biochemical Oxygen Demand (BOD).It represents the portion of total carbon that can be oxidized by microorganisms in a 5-day period under standard conditions.It equals the amount of dissolved O2 needed for microbial oxidation of biodegradable organic matter in a water sample.The effect of a point source discharge of an organic pollutant (e.g., untreated sewage) into a clean flowing river system is profound:Role of microorganisms in secondary treatment of domestic sewage:MMG301 Dr. Frank Dazzo Aquatic & Wastewater Microbiology• Natural aquatic habitats for microorganisms include lakes, ponds,rivers, springs, oceans estuaries, marshes.• The concentration, mixing and movement of nutrients, O2, andwaste products are the dominant factors controlling the abundance,distribution, and diversity of aquatic microbial communitiesTrophic levels and the microbial loop in aquatic ecosystems:In contrast to soil, phytoplankton (algae and cyanobacteria) are thepredominant photosynthetic organisms in aquatic habitats• Much of the organicmatter synthesized byphytoplankton duringphotosynthesis isreleased as dissolvedorganic matter (DOM).• This DOM isconsumed bybacterioplanktonwhich become part ofthe suspendedparticulate organicmatter (POM) pool.• A portion of thesebacteria are thenconsumed as food byprotozoa predators.• Some of the nutrients immobilized in bacteria and protozoa aremineralized and then assimilated directly by phytoplankton withouttransfer to higher trophic levels (e.g. fish) in the aquaticecosystem. This is called the "microbial loop" (arrows in red).O2 plays a key role in microbial activity in aquatic habitats:Photic zone, oxic zone, anoxic zone in lakes:O2 and organic nutrients are inversely interrelated in aquatichabitats. Nutrient-poor (oligotrophic, A) lakes recyclenutrients only within the water whereas nutrient-rich(eutrophic, B) lakes have major nutrient inputs from outside.Oligotrophic lakes are typically O2-saturated and have lowmicrobial populations. Eutrophic lakes develop highmicrobial populations that deplete the dissolved O2 byaerobic respiration during decomposition of abundantorganic matter, producing deep anoxic zones.Oligotrophic lakeEutrophic lakeTemperature also impacts on the status of O2 and nutrients intemperate lakes.• Anoxic conditions develop in the depths of the lake as a result ofthermal stratification.• The cool bottom waters (hypolimnion) are more dense and containH2S from anaerobic bacterial sulfate reduction.• The depth zone of rapid temperature change is the “thermocline.”• Typically as lake surface waters (epilimnion) cool in the fall andearly winter, they reach the temperature and density of thehypolimnionic waters and then they sink, displacing bottom watersand the sediments, affecting “lake turnover” and the redistributionof nutrients for the aquatic microorganisms.Marine microorganisms (eubacteria, archaea, and eukaryotes)• True marine microorganisms are moderate osmiophiles, requiringthe salinity and ions (esp. Na+) of seawater for cultivation• Most are psychrophiles (5°°°°C for most of ocean volume)• Barophiles in deep sea (hydrostatic pressures ≤≤≤≤ 1,100 atmospheres)• Most are oligocarbophiles adapted to the extremely lowconcentration of organic C in ocean seawater (∼∼∼∼ 1-2 mg C / liter)• Recent exciting find of endosymbiotic bacteria inside Riftia tubeworms that develop on sides of black smoker vents at deep seaocean floor →→→→ life sustained by geothermal energy rather than sun.Concept of Biochemical Oxygen Demand:• The amount of biologically usable organic carbon in water isindirectly measured by its Biochemical Oxygen Demand (BOD).• It represents the portion of total carbon that can be oxidized bymicroorganisms in a 5-day period under standard conditions.• It equals the amount of dissolved O2 needed for microbialoxidation of biodegradable organic matter in a water sample.The effect of a point source discharge of an organic pollutant (e.g.,untreated sewage) into a clean flowing river system is profound:• Heterotrophic bacteria, organic carbon, and BOD immediatelyincrease at the pollutant input, and correspondingly, dissolved O2levels decline due to the burst in microbial respiration. Kills allaquatic life (fish, etc) dependent on dissolved O2.• Microbes mineralize and oxidize the organic N and P into inorganicnutrients (NO3-, NH4+, and PO4-3), resulting in eutrophication, withdevelopment of noxious algal / cyanobacterial blooms.• Further downstream, self-purification processes result in a declineof BOD, the oligotrophic conditions and phototrophic microbialcommunities regain dominance, and dissolved O2 levels replenish.Microbiology of Domestic Sewage Wastewater Treatment• The treatment of human fecal wastes (→→→→ organic matter plus manybacterial, protozoan & viral pathogens) is one of the mostimportant factors in maintaining an advanced healthy society.• Effects of discharging organic wastes into aquatic ecosystemscan be drastic as described earlier• Fecal pathogens are shed from patients with disease and fromcarriers (maintain infection without expression of symptoms).• Conventional sewage treatment is a controlled intensification ofnatural self-purification processes involving 1°°°°, 2°°°°, and 3°°°° treatment.Primary treatment: removal ofinsoluble particulate materialsfrom raw sewage by screening gravitational settling in tanks.The resultant solid material iscalled sludge.Secondary treatment:microbial conversion oforganic matter into microbialbiomass and finaldecomposition products (90-95% reduction in BOD), plusremoval of many bacterialpathogens.Tertiary treatment: biologicaland chemical removal of inor-ganic nutrients (e.g., N and P)to reduce eutrophication ofreceiving ecosystem, virusremoval or inactivation, tracechemical removal.Role of microorganisms in secondary treatment of domestic sewage:Activated sludge process:Microbes (e.g., Zooglea ramigera)in a forced aeration tank formzooglea of activated sludge (activebiomass of suspended flocs) thataerobically decomposes organicmatter. A portion of the activatedsludge is recycled as inoculum tomaintain the process.Trickling filter system: arotating arm of an aerationbasin trickles wastewaterover a bed of rocks.
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