ESM 214

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ESM 214

• Lecture 3 Wastewater Flows and Constituents
• W05
• T. Holden

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Wastewater

• Defined water supply of a community or industry
  after it has been used (Fig. 1.1 ME)
• Treatment onsite or offsite (centralized)
• Offsite treatment requires a collection and
  conveyance system

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What are the wastewater flows?

• Domestic (sanitary)
• Industrial
• Infiltration/inflow
• Stormwater

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Wastewater flow rates

• Rule of thumb
• US domestic is ca. 100 gpd/capita (ref. Tbl. 3-1
  ME)
• Developing countries 5 to 50 gpd/capita ( Tbl.
  3-9 ME)
• Other depends on facility (industry, commercial,
  etc.)
• I/I can be significant (Fig. 3.2 ME)
• Units
• 3.7854 liters per gallon
• In U.S., gallons most frequent unit of volume
• MGD million gallons per day
• Concentration mg/L or lbs/MG

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Wastewater flows why do we care?

• Collection and conveyance system design
• Treatment system design (ME Tbl. 3-20)
• Hydraulic criteria must be able to pass peak
  flows
• Treatment criteria meeting treatment standards
  depends often on hydraulic residence time
• Volume / flow rate (l3 / l3/time)
• e.g. MG / MGD days residence time
• Growth projections (population, development)

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Factors affecting flow rates

• Geographical location socioeconomic conditions
• Type of development
• Season
• Time of Day
• Climate (rain or dry)

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Diurnal variations in domestic wastewater flows
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Wastewater flows

• Flows are either normally distributed or
  log-normal (log of flows are normally
  distributed)
• Statistical procedures based on flow history used
  to determine average (dry weather, wet weather,
  annual daily), peak (instantaneous, hour),
  maximum (day, month), minimum (hour, day, month)
  (Table 3-11 ME)

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Wastewater loads

• Treatment is to decrease chemical constituents,
  but quantity to be treated depends on
• Concentration (typ. mg/L)
• Flow rate (typ. gpd or MGD)
• Mass loading
• Concentration x Flow mass /time

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Wastewater loading (example)

• If total suspended solids (TSS) in a wastewater
  sample at the treatment plant influent 100
  mg/L, and the flow rate of the wastewater is 100
  MGD, the mass flow rate (load to the treatment
  plant)
• (100 mg/L) x (100 MGD) x (8.34 lbs-L/MG-mg)
• 83,400 lbs / day influent TSS

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Wastewater constituents

• Refer to ME Tables 2-1, 2-2
• Major classes
• Suspended solids (TSS, VSS, etc.)
• Biodegradable organics (BOD, COD
• Pathogens (bacteria, viruses, protozoa, etc.)
• Nutrients (N, P, etc.)
• Priority pollutants (EPA designated toxics)
• Organics that dont biodegrade (refractory)
• Heavy metals (Cd, Zn, Pb, Hg, Cu)
• Ions (pH contribute to TDS e.g. Ca2, Na,
  SO4-2)
• Temperature
• toxicity

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Wastewater characterization

• In U.S., according to Standard Methods for the
  Examination of Water and Wastewater (a.k.a.
  Standard Methods)
• Performed routinely to characterize
• Influent for designing and protecting treatment
  works
• Effluent for permit compliance

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Solids

• rags (really 2x4s) to colloids (sizes Fig. 2-7
  ME)
• Defined by residue remaining following test
• TS whats left after evaporating at 103 C
• TVS the TS that combust at 500 C
• TFS residue of TS that remains after combustion
• TSS dry (103 C) solids retained on filter (2
  mm)
• VSS combustible TSS
• FSS noncombustible TSS
• TDS dry solids that pass through filter
• VDS and FDS (as above)
• Settleable solids what settles out over a set
  time period

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Suspended Solids
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Imhoff cone for settleable solids
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Solids who cares?

• Biological treatment demand
• Lots of organics associated with solids
• Has to be accounted for in design
• Physical demand
• Solids take up space in tanks
• Settleable solids dictate initial treatment steps
• Sand and grit wears pumps and pipes
• Attenuate UV light during disinfection
• Quantity of ultimate residue (sludge or
  biosolids) affected by influent solids

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Biochemical Oxygen Demand (BOD)

• Establishes biological strength based on oxygen
  uptake by microbes during aerobic metabolism of
  organics in waste
• 5-day (BOD5) and 20-day (BOD20)
• Carbonaceous (CBOD)
• Nitrogenous (NBOD)
• Ultimate (UBOD)

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BOD

• Standardized
• Need
• Incubator
• Bottles
• DO meter
• Dilution water
• Seed (opt.)
• Expressed in mg/L

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BOD Calculation
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Carbonaceous Nitrogenous BOD
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Influent Effluent BOD TSS

• Influent (ME Tbl. 3-13)
• TSS 100 to 300 mg/L
• BOD5 100 to 300 mg/L

• Effluent minimum 2 standards (avg 30-d)
• TSS 30 mg/L
• BOD5 30 mg/L

NOTE BOD is always less (ca. 0.5) than COD
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Nitrogen Phosphorus

• Nitrogen
• Urea mineralizes rapidly to NH4
• NH4 oxidizes to NO3 - (NBOD)
• Nitrifying bacteria use CO2-C (alkalinity)
• Influent N ranges (mg/L as N)
• Total 20 70
• Organic 8 25
• Ammonia 12 45
• No nitrate or nitrite typically

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Nitrogen Phosphorus

• Phosphorus
• Raw wastewater contains 4 16 mg/L as P
• Effluent may restrict to less than 1 mg/L as P
• Forms are
• Orthophosphate PO43-, HPO42-, H2PO4-, H3PO4
• Polyphosphate (polymerized important in
  biological phosphorous removal)
• Organic phosphorous (low in raw wastewater)

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Biological Constituents

• Many are human pathogens
• Most occupy a role in the treatment process
• They are
• Bacteria
• Archaea
• Fungi/yeast
• Protozoa
• Rotifers
• Algae
• viruses

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Indicator Organisms

• Indicators of fecal contamination
• Used to characterize wastewater in/out of
  treatment process, and to monitor water safety
• Total coliform, fecal coliform, entercocci

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Bacteriologic Indicators
Total Coliform
Fecal Streptococcus
Fecal Coliform
Escherichia
Enterococcus
E. Coli
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Indicator organisms the chain of inference
Indicator Organisms Waste Pathogens Disease
Epidemiology
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Indicator Organisms

• Raw Wastewater
• 106 - 1010 MPN TC
• 103 - 108 MPN FC

• AB411 (Beach stnd)
• 1000 MPN TC
• 400 MPN FC
• 104 MPN enterococcus

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Effect of input of sewage or other organic-rich
waste-waters into aquatic systems. (a) In a
river, an increase in heterotrophic bacterial
numbers and a decrease in O2 levels occur
immediately upon a spike of organic matter. If
ammonium is present in the input, for example,
from sewage, it is oxidized to by nitrifying
bacteria (Sections 12.3, 17.12, and 19.12).
Note how the rise in NH4 is followed shortly by
the rise in NO3-, as the two-stage process of
nitrification proceeds. The rise in numbers of
algae and cyanobacteria is primarily a response
to inorganic nutrients, especially PO43- Oxygen
levels return to their pre-input levels once most
of the oxidizable organic and inorganic
compounds are depleted.