Tufts Intro to Environmental Engineering
Terms
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- Watershed
- 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
- Alkalinity
- 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
- Compositing
- (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