

	In/in the/at Midwest/np ,/, oxidation/nn ponds/nns are/ber used/vbn extensively/rb for/in the/at treatment/nn of/in domestic/jj sewage/nn from/in suburban/jj areas/nns ./.
The/at high/jj cost/nn of/in land/nn and/cc a/at few/ap operational/jj problems/nns resulting/vbg from/in excessive/jj loadings/nns have/hv created/vbn the/at need/nn for/in a/at wastewater/nn treatment/nn system/nn with/in the/at operational/jj characteristics/nns of/in the/at oxidation/nn pond/nn but/cc with/in the/at ability/nn to/to treat/vb more/ap organic/jj matter/nn per/in unit/nn volume/nn ./.


	Research/nn at/in Fayette/np ,/, Missouri/np on/in oxidation/nn ponds/nns has/hvz shown/vbn that/cs the/at BOD/nn in/in the/at treated/vbn effluent/nn varied/vbd from/in 30/cd to/in 53/cd mg/l/nn with/in loadings/nns from/in 8/cd to/in 120/cd lb/nn ./.
Since/cs experience/nn indicates/vbz that/cs effluents/nns from/in oxidation/nn ponds/nns do/do not/* create/vb major/jj problems/nns at/in these/dts BOD/nn concentrations/nns ,/, the/at goal/nn for/in the/at effluent/nn quality/nn of/in the/at accelerated/vbn treatment/nn system/nn was/bedz the/at same/ap as/cs from/in conventional/jj oxidation/nn ponds/nns ./.
Recent/jj studies/nns by/in Weston/np and/cc Stack/np had/hvd indicated/vbn that/cs a/at turbine/nn aerator/nn could/md be/be added/vbn to/in an/at oxidation/nn pond/nn to/to increase/vb the/at rate/nn of/in oxygen/nn transfer/nn ./.
Their/pp$ study/nn showed/vbd that/cs it/pps was/bedz possible/jj to/to transfer/vb 3/cd to/in 4/cd lb/nn of/in oxygen/nn //in hr./nn //in hp./nn 

	./.
O'Connor/np and/cc Eckenfelder/np discussed/vbd the/at use/nn of/in aerated/vbn lagoons/nns for/in treating/vbg organic/jj wastes/nns ./.
They/ppss indicated/vbd that/cs a/at 4-day/jj retention/nn ,/, aerated/vbn lagoon/nn would/md give/vb 60/cd to/in 76/cd per/in cent/nn BOD/nn reduction/nn ./.
Later/rbr ,/, Eckenfelder/np increased/vbd the/at efficiency/nn of/in treatment/nn to/in between/in 75/cd and/cc 85/cd per/in cent/nn in/in the/at summer/nn months/nns ./.
It/pps appeared/vbd from/in the/at limited/vbn information/nn available/jj that/cs the/at aerated/vbn lagoon/nn might/md offer/vb a/at satisfactory/jj means/nn of/in increasing/vbg the/at capacity/nn of/in existing/vbg oxidation/nn ponds/nns as/ql well/rb as/cs providing/vbg the/at same/ap degree/nn of/in treatment/nn in/in a/at smaller/jjr volume/nn ./.



Red/jj-tl-hl Bridge/nn-tl-hl Subdivision/nn-tl-hl 
With/in the/at development/nn of/in the/at Red/jj-tl Bridge/nn-tl Subdivision/nn-tl south/nr of/in Kansas/np-tl City/nn-tl ,/, Missouri/np ,/, the/at developer/nn was/bedz faced/vbn with/in the/at problem/nn of/in providing/vbg adequate/jj sewage/nn disposal/nn ./.
The/at sewage/nn system/nn from/in Kansas/np-tl City/nn-tl was/bedz not/* expected/vbn to/to serve/vb the/at Red/jj-tl Bridge/nn-tl area/nn for/in several/ap years/nns ./.
This/dt necessitated/vbd the/at construction/nn of/in temporary/jj sewage/nn treatment/nn facilities/nns with/in an/at expected/vbn life/nn from/in 5/cd to/in 15/cd Aj/nn ./.
For/in the/at initial/jj development/nn an/at oxidation/nn pond/nn was/bedz constructed/vbn as/cs shown/vbn in/in Figure/nn-tl 1/cd-tl ./.
The/at oxidation/nn pond/nn has/hvz a/at surface/nn area/nn of/in 4.77/cd acres/nns and/cc a/at depth/nn of/in 4/cd Aj/nn ./.
The/at pond/nn is/bez currently/rb serving/vbg 1,230/cd persons/nns or/cc 260/cd persons/nns per/in acre/nn ./.
In/in the/at summer/nn of/in 1960/cd the/at oxidation/nn pond/nn became/vbd completely/rb septic/jj and/cc emitted/vbd obnoxious/jj odors/nns ./.
It/pps was/bedz possible/jj to/to maintain/vb aerobic/jj conditions/nns in/in the/at pond/nn by/in regular/jj additions/nns of/in sodium/nn nitrate/nn until/cs the/at temperature/nn decreased/vbd and/cc the/at algae/nns population/nn changed/vbd from/in blue-green/jj to/in green/jj algae/nns ./.


	The/at anaerobic/jj conditions/nns in/in the/at existing/vbg oxidation/nn pond/nn necessitated/vbd examination/nn of/in other/ap methods/nns for/in supplying/vbg additional/jj oxygen/nn than/cs by/in sodium/nn nitrate/nn ./.
At/in the/at same/ap time/nn further/jjr expansion/nn in/in the/at Red/jj-tl Bridge/nn-tl Subdivision/nn-tl required/vbd the/at construction/nn of/in additional/jj sewage/nn treatment/nn facilities/nns ./.
The/at large/jj land/nn areas/nns required/vbn for/in oxidation/nn ponds/nns made/vbd this/dt type/nn of/in treatment/nn financially/rb unattractive/jj to/in the/at developer/nn ./.
It/pps was/bedz proposed/vbn that/cs aerated/vbn lagoons/nns be/be used/vbn to/to eliminate/vb the/at problem/nn at/in the/at existing/vbg oxidation/nn ponds/nns and/cc to/to provide/vb the/at necessary/jj treatment/nn for/in the/at additional/jj development/nn ./.



Pilot/nn-hl lagoon/nn-hl 
The/at lack/nn of/in adequate/jj data/nn on/in the/at aerated/vbn lagoon/nn system/nn prompted/vbd the/at developer/nn to/to construct/vb an/at aerated/vbn lagoon/nn pilot/nn plant/nn to/to determine/vb its/pp$ feasibility/nn for/in treating/vbg domestic/jj sewage/nn ./.
The/at pilot/nn plant/nn was/bedz a/at circular/jj lagoon/nn 81/cd ft/nn in/in diam/nn at/in the/at surface/nn and/cc 65/cd ft/nn in/in diam/nn at/in the/at bottom/nn ,/, 4/cd ft/nn below/in the/at surface/nn ,/, with/in a/at volume/nn of/in 121,000/cd Aj/nn ./.
The/at side/nn slopes/nns were/bed coated/vbn with/in fiberglas/nn matting/nn coated/vbn with/in asphalt/nn to/to prevent/vb erosion/nn ./.
The/at pilot/nn lagoon/nn was/bedz located/vbn as/cs shown/vbn in/in Figure/nn-tl 1/cd-tl to/to serve/vb the/at area/nn just/rb south/nr of/in the/at existing/vbg housing/nn area/nn ./.
The/at major/jj contributor/nn was/bedz a/at shopping/vbg center/nn with/in houses/nns being/beg added/vbn to/in the/at system/nn as/cs the/at subdivision/nn developed/vbd ./.
The/at pilot/nn lagoon/nn was/bedz designed/vbn to/to handle/vb the/at wastes/nns from/in 314/cd persons/nns with/in a/at 4-day/jj aeration/nn period/nn ./.
Initially/rb ,/, the/at wastewater/nn would/md be/be entirely/rb from/in the/at shopping/vbg center/nn with/in the/at domestic/jj sewage/nn from/in the/at houses/nns increasing/vbg over/in an/at 18-month/jj period/nn ./.
This/dt operation/nn would/md permit/vb evaluation/nn of/in the/at pilot/nn plant/nn ,/, with/in a/at slowly/rb increasing/vbg load/nn ,/, over/in a/at reasonable/jj period/nn of/in time/nn ./.


	The/at pilot/nn plant/nn was/bedz equipped/vbn with/in a/at 3-hp./jj turbine/nn aerator/nn (/( Figure/nn-tl 2/cd-tl )/) ./.
The/at aerator/nn had/hvd a/at variable-speed/nn drive/nn to/to permit/vb operation/nn through/in a/at range/nn of/in speeds/nns ./.
The/at sewage/nn flow/nn into/in the/at treatment/nn plant/nn was/bedz metered/vbn and/cc continuously/rb recorded/vbn on/in 24-hr./jj charts/nns ./.
The/at raw/jj sewage/nn was/bedz introduced/vbn directly/rb under/in the/at turbine/nn aerator/nn to/to insure/vb maximum/jj mixing/nn of/in the/at raw/jj sewage/nn with/in the/at aeration/nn tank/nn contents/nns ./.
The/at effluent/nn was/bedz collected/vbn through/in two/cd pipes/nns and/cc discharged/vbn to/in the/at Blue/jj-tl River/nn-tl through/in a/at surface/nn drainage/nn ditch/nn ./.



Analyses/nns-hl 
Composite/jj samples/nns were/bed collected/vbn at/in weekly/jj intervals/nns ./.
The/at long/jj retention/nn period/nn and/cc the/at complete/jj mixing/vbg concept/nn prevented/vbd rapid/jj changes/nns in/in either/cc the/at mixed/vbn liquor/nn or/cc in/in the/at effluent/nn ./.
Weekly/jj samples/nns would/md make/vb any/dti changes/nns more/ql readily/rb discernible/jj than/cs daily/jj samples/nns ./.
The/at composite/jj samples/nns were/bed normally/rb collected/vbn over/in a/at 6-hr./jj period/nn ,/, but/cc an/at occasional/jj 24-hr./jj composite/nn was/bedz made/vbn ./.
Examination/nn of/in the/at operations/nns of/in the/at shopping/vbg center/nn permitted/vbd correlation/nn of/in the/at 6-hr./jj composite/jj samples/nns with/in 24-hr./jj operations/nns ./.
The/at data/nn indicated/vbd that/cs the/at organic/jj load/nn during/in the/at 6-hr./jj composites/nns was/bedz essentially/rb 50/cd per/in cent/nn of/in the/at 24-hr./jj organic/jj load/nn ./.


	Grab/nn samples/nns were/bed collected/vbn from/in the/at existing/vbg oxidation/nn pond/nn to/to determine/vb its/pp$ operating/vbg conditions/nns ./.
Efforts/nns were/bed made/vbn to/to take/vb the/at grab/nn samples/nns at/in random/jj periods/nns so/cs that/cs the/at mass/nn of/in data/nn could/md be/be treated/vbn as/cs a/at 6-hr./jj composite/jj sample/nn ./.
A/at single/ap 24-hr./jj composite/jj sample/nn indicated/vbd that/cs the/at sewage/nn flow/nn pattern/nn and/cc characteristics/nns were/bed typical/jj ./.



Pilot/nn-hl plant/nn-hl operations/nns-hl 
The/at BOD/nn of/in the/at influent/nn to/in the/at pilot/nn plant/nn varied/vbd between/in 110/cd and/cc 710/cd mg/l/nn with/in an/at average/nn of/in 350/cd Aj/nn ./.
This/dt was/bedz equivalent/jj to/in 240/cd mg/lBOD/nn on/in a/at 24-hr./jj basis/nn ./.
The/at BOD/nn of/in the/at raw/jj sewage/nn was/bedz typical/jj of/in domestic/jj sewage/nn from/in a/at subdivision/nn ./.
The/at BOD/nn in/in the/at effluent/nn averaged/vbd 58/cd mg/l/nn ,/, a/at 76-per-cent/nn reduction/nn over/in the/at 24-hr./jj period/nn ./.
Examination/nn of/in the/at data/nn in/in Table/nn-tl 1/cd-tl ,/, shows/vbz that/cs a/at few/ap samples/nns contributed/vbd to/in raising/vbg the/at effluent/nn Aj/nn ./.
The/at periods/nns of/in high/jj effluent/nn BOD/nn occurred/vbd during/in cold/jj periods/nns when/wrb operational/jj problems/nns with/in the/at aerator/nn resulted/vbd ./.
Ice/nn caused/vbd the/at aerator/nn to/to overload/vb ,/, straining/vbg the/at drive/nn belts/nns ./.
The/at slippage/nn of/in the/at drive/nn belts/nns caused/vbd the/at aerator/nn to/to slow/vb down/rp and/cc reduce/vb oxygen/nn transfer/nn as/ql well/rb as/cs the/at mixing/nn of/in the/at raw/jj sewage/nn ./.


	The/at organic/jj loading/nn on/in the/at unit/nn averaged/vbd 32/cd lb/nn of/in BOD/day/nn or/cc about/rb 2/cd lb/nn BOD/day/1,000/nn cu/nn ft/nn aeration/nn capacity/nn ./.
Needless/jj to/to say/vb ,/, the/at organic/jj load/nn was/bedz very/ql low/jj on/in a/at volumetric/jj basis/nn ,/, but/cc was/bedz 270/cd lb/nn BOD/day/acre/nn on/in a/at surface/nn loading/vbg basis/nn ./.
It/pps seems/vbz that/cs the/at aerated/vbn lagoon/nn was/bedz a/at very/ql heavily/rb loaded/vbn oxidation/nn pond/nn or/cc a/at lightly/rb loaded/vbn activated/vbn sludge/nn system/nn ./.


	The/at flow/nn rate/nn remained/vbd relatively/ql constant/jj during/in the/at winter/nn months/nns as/cs shown/vbn in/in Table/nn-tl 1/cd-tl ./.
With/in the/at spring/nn rains/nns the/at flow/nn rose/vbd rapidly/rb due/rb to/in infiltration/nn in/in open/jj sewers/nns ./.
As/cs construction/nn progresses/vbz ,/, the/at volume/nn of/in storm/nn drainage/nn will/md be/be sharply/rb reduced/vbn ./.
The/at retention/nn period/nn in/in the/at aerated/vbn lagoon/nn ranged/vbd from/in 9.8/cd to/in 2.6/cd days/nns ,/, averaging/vbg 6.4/cd days/nns ./.


	The/at large/jj amount/nn of/in vegetable/nn grindings/nns from/in the/at grocery/nn store/nn in/in the/at shopping/vbg center/nn created/vbd a/at suspended/vbn solids/nns problem/nn ./.
The/at vegetables/nns were/bed not/* readily/rb metabolized/vbn by/in the/at bacteria/nns in/in the/at aeration/nn unit/nn and/cc tended/vbd to/to float/vb on/in the/at surface/nn ./.
A/at skimming/vbg device/nn at/in the/at effluent/nn weir/nn prevented/vbd loss/nn of/in most/ap of/in these/dts light/jj solids/nns ./.
The/at average/jj volatile/jj suspended/vbn solids/nns in/in the/at effluent/nn was/bedz 75/cd mg/l/nn while/cs MLSS/nn averaged/vbd 170/cd mg/l/nn volatile/jj suspended/vbn solids/nns ./.
The/at average/jj sludge/nn age/nn based/vbn on/in displacement/nn of/in solids/nns was/bedz calculated/vbn to/to be/be 14.5/cd days/nns ./.
The/at oxygen/nn uptake/nn rate/nn in/in the/at mixed/vbn liquor/nn averaged/vbd 0.8/cd mg/l/hr/nn during/in the/at first/od four/cd months/nns of/in this/dt study/nn ./.
Variations/nns in/in aerator/nn speeds/nns during/in the/at latter/ap two/cd months/nns of/in this/dt study/nn caused/vbd increased/vbn mixing/vbg and/cc increased/vbn oxygen/nn demand/nn ./.
The/at increase/nn in/in oxygen/nn uptake/nn rates/nns from/in 1.2/cd to/in 2.6/cd mg/l/hr/nn which/wdt followed/vbd an/at increase/nn in/in rotor/nn speed/nn was/bedz believed/vbn to/to be/be related/vbn to/in resuspension/nn of/in solids/nns which/wdt had/hvd settled/vbn at/in the/at lower/jjr rotor/nn speeds/nns ./.
It/pps appeared/vbd that/cs most/ap of/in the/at mixed/vbn liquor/nn suspended/vbn solids/nns were/bed active/jj microbial/jj solids/nns with/in the/at heavier/jjr ,/, less/ql active/jj solids/nns settling/vbg out/rp ./.


	The/at suspended/vbn solids/nns discharged/vbn in/in the/at effluent/nn were/bed found/vbn to/to be/be the/at major/jj source/nn of/in the/at Aj/nn ./.
Removal/nn of/in the/at suspended/vbn solids/nns by/in a/at membrane/nn filter/nn yielded/vbd an/at average/jj effluent/nn containing/vbg only/rb 20/cd mg/l/nn Aj/nn ./.
The/at BOD/nn in/in the/at drainage/nn ditch/nn receiving/vbg the/at pilot/nn plant/nn effluent/nn averaged/vbd 12/cd Aj/nn ./.
This/dt low/nn BOD/nn was/bedz due/jj to/in removal/nn of/in the/at excess/jj suspended/vbn solids/nns by/in sedimentation/nn since/cs the/at only/ap dilution/nn was/bedz surface/nn runoff/nn which/wdt was/bedz very/ql low/jj during/in this/dt study/nn ./.



Microscopic/jj-hl examination/nn-hl 
Routine/jj microscopic/jj examinations/nns were/bed made/vbn of/in the/at mixed/vbn liquor/nn as/cs indicated/vbn by/in McKinney/np and/cc Gram/np for/in the/at various/ap types/nns of/in protozoa/nns ./.
It/pps was/bedz found/vbn that/cs the/at aerated/vbn lagoon/nn was/bedz an/at activated/vbn sludge/nn system/nn rather/rb than/cs an/at oxidation/nn pond/nn ./.
At/in no/at time/nn were/bed algae/nns found/vbn in/in the/at mixed/vbn liquor/nn ./.
The/at bacteria/nns formed/vbd typical/jj activated/vbn sludge/nn floc/nn ./.
The/at floc/nn particles/nns were/bed all/abn small/jj as/cs the/at heavier/jjr floc/nn settled/vbd out/rp ./.


	Initially/rb ,/, the/at flagellated/vbn protozoa/nns predominated/vbd ,/, but/cc they/ppss soon/rb gave/vbd way/nn to/in the/at free/rb swimming/vbg ciliated/jj protozoa/nns ./.
As/cs the/at temperature/nn decreased/vbd ,/, the/at number/nn of/in free/rb swimming/vbg ciliated/jj protozoa/nns decreased/vbd ./.
Very/ql little/ap protozoa/nns activity/nn existed/vbd below/in 40-degrees-F/nns ./.
When/wrb the/at temperature/nn reached/vbd 32-degrees-F/nns all/abn protozoan/jj activity/nn ceased/vbd ;/. ;/.
but/cc as/cs the/at temperature/nn rose/vbd ,/, the/at numbers/nns of/in protozoa/nns increased/vbd rapidly/rb ./.
Only/rb once/rb were/bed stalked/vbn ciliates/nns found/vbn in/in the/at mixed/vbn liquor/nn ./.
The/at predomination/nn of/in free/rb swimming/vbg ciliated/jj protozoa/nns is/bez indicative/jj of/in a/at high/jj bacterial/jj population/nn ./.



Oxygen/nn-hl transfer/nn-hl 
One/cd of/in the/at important/jj aspects/nns of/in this/dt study/nn was/bedz to/to determine/vb the/at oxygen/nn transfer/nn relationships/nns of/in the/at mechanical/jj aerator/nn ./.
Routine/jj determinations/nns were/bed made/vbn for/in dissolved/vbn oxygen/nn in/in the/at mixed/vbn liquor/nn and/cc for/in oxygen/nn uptake/nn rates/nns ./.
The/at data/nns given/vbn in/in Table/nn-tl 2/cd-tl ,/, show/vb the/at routine/jj operation/nn of/in the/at aerator/nn ./.
The/at dissolved/vbn oxygen/nn in/in the/at aeration/nn unit/nn was/bedz consistently/rb high/jj until/in January/np 29/cd ,/, 1961/cd ./.
An/at extended/vbn cold/jj spell/nn caused/vbd ice/nn to/to build/vb up/rp on/in the/at aerator/nn which/wdt was/bedz mounted/vbn on/in a/at floating/vbg platform/nn and/cc caused/vbd the/at entire/jj platform/nn to/to sink/vb lower/rbr in/in the/at water/nn ./.
The/at added/vbn resistance/nn to/in the/at rotor/nn damaged/vbd the/at drive/nn belts/nns and/cc reduced/vbd the/at oxygen/nn transfer/nn capacity/nn ./.
It/pps was/bedz approximately/rb one/cd month/nn before/cs the/at belt/nn problem/nn was/bedz noticed/vbn and/cc corrected/vbn ,/, but/cc at/in no/at time/nn was/bedz there/ex a/at deficiency/nn of/in dissolved/vbn oxygen/nn ./.


	A/at series/nns of/in eight/cd special/jj tests/nns were/bed conducted/vbn at/in different/jj rotor/nn speeds/nns to/to determine/vb the/at oxygen/nn transfer/nn rate/nn ./.
Five/cd of/in the/at tests/nns were/bed conducted/vbn with/in a/at polyethylene/nn cover/nn to/to simulate/vb an/at ice/nn cover/nn ./.
The/at rate/nn of/in oxygen/nn transfer/nn at/in 1.0-mg./nn //in l./nn dissolved/vbn oxygen/nn concentration/nn and/cc 10-degrees-C/nns for/in various/ap rotor/nn speeds/nns is/bez given/vbn in/in Table/nn-tl 3/cd-tl ./.
The/at maximum/jj rate/nn of/in oxygen/nn transfer/nn at/in 1.0/cd mg/l/nn dissolved/vbn oxygen/nn was/bedz calculated/vbn as/cs 220/cd lb/day/nn at/in a/at maximum/jj rate/nn of/in 9.3/cd Aj/nn ./.
The/at actual/jj power/nn requirements/nns indicated/vbd 2/cd lb./nn oxygen/nn transfer/nn //in hr./nn //in hp./nn ./.
The/at polyethylene/nn cover/nn reduced/vbd the/at oxygen/nn transfer/nn rate/nn by/in 10/cd per/in cent/nn ,/, indicating/vbg that/cs the/at maximum/jj oxygen/nn transfer/nn is/bez at/in the/at rotor/nn rather/rb than/cs through/in the/at surface/nn ./.



Oxidation/nn-hl pond/nn-hl 
During/in this/dt study/nn septic/jj conditions/nns developed/vbd in/in the/at oxidation/nn pond/nn in/in the/at spring/nn when/wrb the/at ice/nn melted/vbd ./.
Shortly/rb after/cs this/dt study/nn ended/vbd septic/jj conditions/nns resulted/vbd which/wdt required/vbd the/at addition/nn of/in sodium/nn nitrate/nn ./.
The/at location/nn of/in the/at oxidation/nn pond/nn in/in a/at high-value/nn residential/jj area/nn makes/vbz odor/nn nuisances/nns a/at sensitive/jj problem/nn for/in the/at developer/nn ./.
The/at organic/jj concentration/nn in/in the/at influent/jj raw/jj sewage/nn ranged/vbd from/in 160/cd to/in 270/cd mg/l/nn of/in BOD/nn with/in an/at average/nn of/in 230/cd Aj/nn ./.
The/at BOD/nn data/nns are/ber given/vbn in/in Table/nn-tl 4/cd-tl ./.
A/at single/ap 24-hr./jj composite/jj sample/nn had/hvd a/at BOD/nn of/in 260/cd mg/l/nn ,/, indicating/vbg a/at typical/jj domestic/jj sewage/nn ./.
The/at daily/jj sewage/nn volume/nn to/in the/at oxidation/nn pond/nn averaged/vbd 147,000/cd gpd/nn ,/, giving/vbg a/at retention/nn period/nn of/in 42/cd days/nns ./.
The/at organic/jj loading/nn on/in the/at pond/nn was/bedz slightly/rb under/in 60/cd lb./nn BOD/np //in day/nn //in acre/nn ./.


	The/at effluent/nn BOD/nn averaged/vbd 34/cd mg/l/nn ,/, a/at little/ql lower/jjr than/cs that/dt of/in the/at study/nn at/in Fayette/np indicated/vbd for/in a/at loading/nn of/in 60/cd lb./nn Aj/nn ./.
The/at BOD/nn of/in the/at effluent/nn ranged/vbd from/in a/at minimum/nn of/in 13/cd to/in a/at maximum/jj of/in 47/cd mg./nn //in l./nn ./.
Microscopic/jj examination/nn of/in the/at effluent/nn showed/vbd that/cs minimum/jj BOD/nn occurred/vbd when/wrb the/at algae/nns began/vbd to/to decrease/vb with/in cold/jj weather/nn ./.
When/wrb the/at algae/nns began/vbd to/to build/vb up/rp again/rb ,/, the/at effluent/nn BOD/nn rose/vbd ./.
During/in the/at two/cd weeks/nns when/wrb the/at algae/nns disappeared/vbd from/in the/at effluent/nn BOD's/nn in/in the/at effluent/nn were/bed 18/cd and/cc 16/cd Aj/nn ./.

