2010-2 ppt-10 ? WastewaterDomestic sewage or liquid industrial wasteWastewater treatmentRelies on industrial-scale use of microbes for bioconversionFollowing treatment, the discharged treated wastewater (effluent water) is suitable forRelease into surface watersRelease to drinking water purification facilitiesWastewater treatment processesSimilar to self-purification processes observed in rivers and streams except are controlled and intensifiedWastewater and sewage treatmentWastewater treatment facilityIts goal is to reduce organic and inorganic materials in wastewater to a level that no longer supports microbial growth and to eliminate other potentially toxic materialsThe efficiency of treatment is expressed in terms of a reduction in the biochemical oxygen demand (= biological oxygen demand, BOD)The relative amount of dissolved oxygen consumed by microbes to completely oxidize all organic and inorganic matter in a water sample

Wastewater and sewage treatmentWastewater treatment is a multistep operation employing both physical and biological processesPrimary, secondary, and sometimes tertiary treatments are usedWastewater and sewage treatmentWastewater treatment processes

Primary treatment Uses physical separation methods to separate solid and particulate organic and inorganic materials from wastewater

Wastewater and sewage treatmentPrimary treatment of wastewater

Secondary Treatment Anoxic secondary treatment involves a series of digestive and fermentative reactions carried out by various microbes under anoxic conditionsThe process is carried out in large enclosed tanks (sludge digesters or bioreactors)

Wastewater and sewage treatmentSludge digester for anoxic secondary wastewater treatment

Secondary treatment (contd)Aerobic secondary treatment uses digestive reactions carried out by microbes under aerobic conditions to treat wastewater with low levels of organic materialsThe trickling filter ([]) and activated sludge ([ ]) are the most common decomposition processesWastewater and sewage treatmentAerobic secondary wastewater treatment processes

Trickling filter in a treatment facilityAerobic secondary wastewater treatment processes

Aeration tank of an activated sludge installation

Aerobic secondary wastewater treatment processesWastewater flow through an activated sludge installationIn the activated sludge process, wastewater is mixed and aerated in large tanks and slime-forming bacteria (e.g., Zoogloea ramigera) grow and form flocks

Most treatment plants chlorinate the effluent after secondary treatment to further reduce the possibility of biological contamination

Wastewater and sewage treatment

Tertiary TreatmentAny physiochemical or biological process employing precipitation, filtration, or chlorination procedures similar to those used for purification of drinking waterReduces the levels of inorganic nutrients (e.g., phosphate, nitrate, nitrite)Most complete method of treating sewage but it has not been widely adopted due to costs

Wastewater and sewage treatment

20modern conventional sewage treatment plantFrequently fail to work properly, contributing to groundwater contamination

Hone septic tank system21This system combines an anaerobic waste liquefaction unit (the septic tank) with an aerobic leach field. Biological oxidation of the liquefied waste takes place in the leach field, unless the soil becomes flooded. (bioremediation) * Mercury and heavy metal transformationsPetroleum biodegradation ()Biodegradation of xenobiotics * Xenobiotics: A completely synthetic chemical compound not naturally occurring on Earth

Microbial bioremediationMercury is of environmental importance because of its tendency to concentrate in living tissues and its high toxicityThe major form of mercury in the atmosphere is elemental mercury (Hgo) which is volatile and nontoxic and oxidized to mercuric ion (Hg2+) photochemicallyMost mercury enters aquatic environments as Hg2+ which is more toxic than Hgo

Microbial bioremediation: Mercury and heavy metal transformationsHg2+ readily absorbs to particulate matter where it can be metabolized by microbesSome microbes form methylmercury (CH3Hg+), an extremely soluble and toxic compound (100 times more toxic than Hg2+)Several bacteria can also transform toxic mercury to nontoxic forms - Transform CH3Hg+ to Hg2+ and Hg2+ to Hg0Microbial bioremediation: Mercury and heavy metal transformationsProkaryotes have been used in bioremediation of several major crude oil spills

Microbial bioremediation: Petroleum biodegradationEnvironmental consequences of large oil spills

Contaminated Beach in Alaska containing oil from the Exxon Valdez spill of 1989

Oil spilled into the Mediterranean Sea from a power plantEnvironmental consequences of large oil spills

Center rectangular plot (arrow) was treated with inorganic nutrients to stimulate bioremediationEnvironmental consequences of large oil spills

Taean oil spills

Taean oil spills

Taean oil spills

Taean oil spillsDiverse bacteria, fungi, and some cyanobacteria and green algae can oxidize petroleum products aerobicallyOil-oxidizing activity is best if temperature and inorganic nutrient concentrations are optimalHydrocarbon-degrading bacteria attach to oil droplets and decompose the oil and dispense the slick

Microbial bioremediation: Petroleum biodegradationHydrocarbon-oxidizing bacteria in association with oil

Gasoline and crude oil storage tanks are potential habitats for hydrocarbon-oxidizing microbes

- If sufficient sulfate is present, sulfate-reducing bacteria can grow and consume hydrocarbons

Microbial bioremediation: Petroleum biodegradationXenobiotic compoundSynthetic chemicals that are not naturally occurringe.g., pesticides, polychlorinated biphenyls, munitions, dyes, and chlorinated solventsMany degrade extremely slowly

Microbial bioremediation: Biodegradation of xenobioticsPesticidesCommon components of toxic wastesInclude herbicides, insecticides, and fungicidesRepresent a wide variety of chemistriesSome of which can be used as carbon sources and electron donors by microbesMicrobial bioremediation: Biodegradation of xenobioticsExamples of xenobiotic compounds

Persistence of herbicides and insecticides in soils

Persistence of herbicides and insecticides in soils

Plastics of various types are xenobiotics that are not readily degraded by microbes

Microbial bioremediation: Biodegradation of xenobioticsChemistry of synthetic polymers