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Tufts Intro to Environmental Engineering


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Continuous land area defined by topography - all precip in area has a common exit point for surface runoff
Water balance
Change in storage = input - output
Runoff coefficient
k = Streamflow / Precipitation = Q/P
ABC Model
Rainfall-runoff model based on non-seasonal, lumped watershed, where Precip, Infil, EvapoTrans, and Groundwater storage contribute to runoff
ABC Model - parameters
a is fraction of rainfall that enters groundwater via infiltration; b is fraction that returns to atmosphere by EvapoTranspiration; c is fraction that flows into stream channel - 1/c can be viewed as G residence time
ABC Model - Solving
Data for groundwater unavailable, use solver to best fit a,b,c. Z = (Qmeas - Qcalc)^2...find a,b,c for min Z
Sum of all titratable bases in solution to the CO2 endpoint (pH approx 4.5)
Biochemical Oxygen Demand
Amount of oxygen consumed by microorganisms in process of utilizing organic material (carbon) for metabolism and growth
Processes affected DO in rivers
Oxygen demand from carbon and nitrogen, oxygen exchange with atmosphere (reaeration)
Streeter Phelps DO Sag Model
Describes DO changes resulting from processes of reaeration and CBOD - express CBOD and reaeration in terms of DO deficit
Wastewater Treatment Objective
Remove contaminants having an adverse human health or ecological impact when discharged into environment
Wastewater consituents - physical
Temperature, suspended and dissolved solids, volatile SS
Wastewater consituents - aesthetic
Color, turbidity, oil, odor, grease, surfactants (foam)
Wastewater consituents - chemical
Carbon, nutrients - nitrogen, phosphorous
Wastewater consituents - oxygen demand
Biochemical, Chemical Oxygen Demand (COD)
Municipal versus industrial wastewater quality
Municipal - heterogeneous; industrial - homogeneous
Wastewater treatment process - liquid line
Remove large and coarse solids, then remove settleable solids, remove dissolved and colloidal carbon, disinfection
Wastewater treatment process - solid line
Thicken by gravity, anaerobic digestion (stabilize organic mass), improve dewatering characteristics, dewater (filtration, centrifugation), dispose
Wastewater flow balances
Caution! Flow and concentration vary diurnally so conventional methods cannot be used. Mass flow computed by multiplying average diurnal flow times mass average concentration
(a) averaging as in a mass average concentration (b) mixing, as in composite sample
Composite Sample
Small samples taken at regular time intervals are mixed together in volumes proportional to flow rate at time of sampling
Preliminary treatment - objectives
Remove coarse solids, protect down stream equipment from abrasion
Biological treatment
Microorganism dissolve organic material (bacteria, algae), suspended growth: activated sludge, trickling filters

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