Dissolved oxygen ä History ä When did dissolved oxygen levels in streams become an issue? ä What developments led to the problem? ä Dissolved oxygen models ä model components ä different models ä History ä When did dissolved oxygen levels in streams become an issue? ä What developments led to the problem? ä Dissolved oxygen models ä model components ä different models 

Excreta Disposal: Land Application ä When population densities were low excreta disposal was an individual problem. ä As cities grew it was no longer possible for individuals to practice “direct land application.” ä Before 1800 city residents placed “night soil” in buckets along streets and workers emptied the waste into “honeywagon” tanks. ä The waste was transported to rural areas for disposal on farm land. The honeywagon system preserved the essential feature of land application of the waste. ä When population densities were low excreta disposal was an individual problem. ä As cities grew it was no longer possible for individuals to practice “direct land application.” ä Before 1800 city residents placed “night soil” in buckets along streets and workers emptied the waste into “honeywagon” tanks. ä The waste was transported to rural areas for disposal on farm land. The honeywagon system preserved the essential feature of land application of the waste.

Toilets ä Until about 1850 even the members of Congress were required to go outside and walk down Capitol Hill to privy facilities. ä : The flush toilet came into general use in the U.S. during the last half of the nineteenth century. ä Introduction of the toilet coincided with ______ _____. ä Until about 1850 even the members of Congress were required to go outside and walk down Capitol Hill to privy facilities. ä : The flush toilet came into general use in the U.S. during the last half of the nineteenth century. ä Introduction of the toilet coincided with ______ _____. central heat

Night Soil vs. Sewers ä Dutch engineer Charles Liernur advocated dry disposal. He claimed underground sewers would be the source of ________ _____ giving rise to sickness and death. ä English engineer Baldwin Latham supported water carriage of excreta. Latham proceeded with the installation of a water carriage system for Croydon, where he was engineer of public works. ä The water carriage system led to an immediate decrease in the death rate in the cities that installed it. ä Dutch engineer Charles Liernur advocated dry disposal. He claimed underground sewers would be the source of ________ _____ giving rise to sickness and death. ä English engineer Baldwin Latham supported water carriage of excreta. Latham proceeded with the installation of a water carriage system for Croydon, where he was engineer of public works. ä The water carriage system led to an immediate decrease in the death rate in the cities that installed it. noxious gases But what about the cities downstream?

Storm Sewers ä Sewers similar to the Roman drains were used in medieval Europe ä Cities forbade the discharge of ______ to these conduits. ä London, Paris, and Boston excluded waste from their sewers until after the 1800’s. ä Toilets eventually were connected to storm sewers. ä Sewers similar to the Roman drains were used in medieval Europe ä Cities forbade the discharge of ______ to these conduits. ä London, Paris, and Boston excluded waste from their sewers until after the 1800’s. ä Toilets eventually were connected to storm sewers. excreta

Conversion of Storm Sewers to Wastewater Conveyance ä The storm drain systems naturally ended at watercourses ä Waterborne wastes were discharged directly to streams, lakes, and estuaries without treatment. ä Treatment of wastewater only became an issue after the self-purification capacity of the receiving waters was exceeded and ________ __________ became intolerable. ä The storm drain systems naturally ended at watercourses ä Waterborne wastes were discharged directly to streams, lakes, and estuaries without treatment. ä Treatment of wastewater only became an issue after the self-purification capacity of the receiving waters was exceeded and ________ __________ became intolerable. nuisance conditions

Wastewater into Streams: Enter Environmental Engineering! ä Drinking water treatment began to receive attention in the 1800s. ä London, and cities on the Great Lakes found themselves draining their raw sewage into the same body of water from which they took their drinking water. ä Chicago solved this problem by reversing the flow of the Chicago river and sending its waste through a canal to the Illinois River to the Mississippi. ä English engineers tackled the problem by developing treatment techniques for both wastewater and drinking water. ä Drinking water treatment began to receive attention in the 1800s. ä London, and cities on the Great Lakes found themselves draining their raw sewage into the same body of water from which they took their drinking water. ä Chicago solved this problem by reversing the flow of the Chicago river and sending its waste through a canal to the Illinois River to the Mississippi. ä English engineers tackled the problem by developing treatment techniques for both wastewater and drinking water.

ä Too expensive to remove all contaminants from the wastewater ä Continual effort to improve treatment processes ä Dilution... ä The critical stream flows are the ________ flows ä Q 7,10 7 day low flow with a ________________ ________________ ä Too expensive to remove all contaminants from the wastewater ä Continual effort to improve treatment processes ä Dilution... ä The critical stream flows are the ________ flows ä Q 7,10 7 day low flow with a ________________ ________________ 10% chance of annual exceedance drought Why not just stop dumping waste into the rivers?

What does a Dissolved Oxygen Sag Curve Look Like? C* C C x x C* = equilibrium concentration of DO

No Reaeration C* C C x x BOD = 5 mg/L BOD = 20 mg/L BOD = 5 mg/L BOD = 20 mg/L

Reaeration: Initial Oxygen Deficit, No BOD C* C C x x D o = 5 mg/L 5 mg/L

ä ___________________________ Bacteria concentration Substrate concentration Maximum utilization rate What Controls Oxygen Utilization? Bacteria Kinetics Half velocity constant

What Controls Reaeration? ä _____________________ Deficit Reaeration coefficient Turbulence Wind speed Waterfalls!! overall volumetric oxygen transfer coefficient

Reaeration Rate >> Microbial Oxygen Utilization Rate C* C C x x white water

Lots of Bacteria, No Reaeration? C* C C t t Endogenous respiration

Model Components ä Reaeration ä Endogenous decay ä Oxidation of BOD ä Reaeration ä Endogenous decay ä Oxidation of BOD

First Order ä Substrate concentration small relative to half velocity concentration ä Bacteria concentration constant ä Substrate concentration small relative to half velocity concentration ä Bacteria concentration constant

Zero Order ä substrate concentration large relative to half velocity concentration ä bacteria concentration constant ä substrate concentration large relative to half velocity concentration ä bacteria concentration constant

Laboratory Experiment: Scaling ä Real world sag curves have: ä Time scale of several days to several weeks ä Length scale of many kilometers ä Convert river into batch reactor (t = x/u) ä How can we speed the process up? ä _______________________________ ä Real world sag curves have: ä Time scale of several days to several weeks ä Length scale of many kilometers ä Convert river into batch reactor (t = x/u) ä How can we speed the process up? ä _______________________________ Concentrated bacteria suspension Easily biodegraded substrate Aeration

Comparison of Models