CHEE 370Waste Treatment

Processes

Lecture #4

Wastewater Characterization Cont’d

Measurements of Gross Organic Content

Biochemical oxygen demand (BOD) Chemical oxygen demand (COD) Total organic carbon (TOC) Theoretical oxygen demand (ThOD)

Review from Last Class

Biochemical Oxygen Demand

“Carbonaceous” BOD

Measure of the amount of biodegradable organic matter in a WW sample

Oxygen consumed by bacteria as they use the organic matter in the WW as a food source to generate more bacteria

Organic Matter + O2 + bacteria CO2 + H2O + more bacteria

BODt=UBOD(1 - e-kt)

UBOD = measure of the initial amount of organic material in the WW minus the residual organic material

(recalcitrant organics) left after all the biomass decays

[BODt] = [UBOD] = mg/mL[k] = d-1

Typical k ~ 0.23 d-1 for municipal WWk is a function of temperature! (Recall CHEE 380)

BOD5 is the most common measure of organic pollution strength

Review from Last Class

Effect of Nitrification

Organic Matter + O2 + bacteria CO2 + H2O + more bacteria + NH3

NH3 + 3/2 O2 HNO2 + H20 (Nitrosomonas)

HNO2 + 1/2 O2 HNO3 (Nitrobacter)

When nitrification occurs:

BODmeasured = CBOD + NBOD

Overestimation of the organic content of the WW!

Chemical Oxygen Demand (COD)

Defined as the mass of oxygen theoretically required to completely oxidize an organic compound to carbon dioxide

Measured by mixing the WW with a very strong oxidant (i.e potassium dichromate)

Takes ~ 3 h (versus 5 days!)

BOD and COD

COD ≥ UBOD ≥ BOD5

If the organic content in the WW sample is completely biodegradable:

UBOD = COD

Total Organic Carbon (TOC)

Measure of WW pollutional characteristics Based on the chemical formula Test methods use heat and oxygen, UV

radiation, and/or chemical oxidants to convert organic carbon to carbon dioxide, which can then be measured

Can be assessed in 5 to 10 minutes Theoretical > Measured (but close!)

TOC Example

Glucose (C6H12O6)

Theoretical Oxygen Demand (ThOD)

WW generally contains a mixture of carbon, hydrogen, oxygen, and nitrogen

Calculated using stoichiometric equations

Considers both carbonaceous and nitrogenous oxygen demand

BOD, COD, and TOC

Typical range of BOD/COD for untreated municipal WW is 0.3 - 0.8

Typical range for BOD/TOC is 1.2 - 2.0

If BOD/COD > 0.5 WW is considered to be easily treatable by biological

means

If BOD/COD < 0.3 WW may have some toxic components and/or the addition

of acclimated micro-organisms may be required

Micro-organisms

Untreated wastewater includes a wide variety of pathogenic micro-organisms, such as:

Bacteria (i.e. E. coli, salmonella, vibrio cholerae) Protozoa (i.e. Balantidium coli, Entamoeba

histolytica) Helminths (i.e. pinworm, tapeworm) Viruses (i.e. Hepatitis, Norwalk agent, Parvovirus)

Refer to tables 2-23 and 2-24

Biological Characterization

Individual pathogenic micro-organisms are difficult to isolate and identify

Micro-organisms which are more numerous and more easily tested for can be used as indicators of biological contamination Indicator organism must be present when contamination is

present Indicator organism should have the same (or better) survival

characteristics as the pathogenic organism Procedure for identifying the indicator should be easier, faster,

and cheaper than looking directly for the pathogens NOTE: No “IDEAL” indicator has been found to date

Indicator Organisms

Every person discharges from 100 to 400 billion coliform bacteria every day

Coliform organisms are gram-negative, rod shaped bacteria whose normal habitat is the intestines of human and animals; some members are naturally found in the soil and vegetation Escherichia Enterobacter Klebsiella Citrobacter

Coliform Total Coliform

Species ferment lactose and produce CO2 gas when incubated at (35 ± 0.5) °C for (24 ± 2) h

Species produce a colony within (24 ± 2) h to (48 ± 3) h when incubated in a medium that facilitates growth Micro 221or 229- Agar Plates expts!

Fecal Coliform Species produce gas or colonies when incubated at the

higher temperature of (44.5 ± 0.2) °C for (24 ± 2) h

Total coliform is used as the indicator for drinking water and wastewater effluent

Bacterial Counts - Liquid Medium (Board EXAMPLE!)

Figure 3-23, Metcalf and Eddy

Bacterial Counts - Solid Medium

Figure 3-23, Metcalf and Eddy

Pass through 0.45 m

filter

Place filter on

agar dish

Reading: Textbook p. 118 - 130 on the experimental methods used for the characterization of bacteria and viruses in WW samples

Toxicity Testing (Overall Water Quality)

Performed on effluent before discharge

Measures the overall quality of the treated water and to establish acceptable discharge concentrations for conventional parameters (such as DO, pH, temperature, salinity, or turbidity)

Determines the efficacy of the waste treatment process

Determines compliance with federal regulations

Toxicity Testing - Bioassays Use “test”organisms (baby trout, minnows) sensitive to the

presence of contaminants in wastewater

Fish are placed in aquariums/vessels containing various dilutions of treated wastewater

Start test with about 10 fish/aquarium

Run the test for a fixed period of time (24, 48, 96 h) and count the number of dead fish

Plot results on semi-log paper

Toxicity Testing - Bioassays

LC50: Median lethal concentration for 50% of the organisms The diluted concentration of the wastewater that will kill

50% of the test population in a fixed time period

NOEC: No Observed Effect Concentration The highest concentration of diluted wastewater that has

no observable effect on the test organisms

What does a 96-h LC50 of 75% mean?

What is the 96-h LC50 measured?

Is the plant in compliance?

When the effluent is diluted to a concentration of 75% (v/v), 50% of the test organisms will die.

57%

No!

WW Flowrates

Rated capacity of a WW treatment plant is based on the average annual daily flowrate plus a factor of safety

Factors that can influence the plant design: WW characteristics Constituent concentrations Flowrates

Mass loading [kg/d] = (concentration [g/m3])*(flowrate [m3/d])(103 g/kg)

Design Flowrates and Mass Loadings

Process units and hydraulic conduits must be sized to accommodate the anticipated peak flowrates that will pass through the plant

Many WW treatment units are designed/sized based on the detention time or overflow rate (flowrate per unit surface area) required to achieve specific BOD and TSS levels in the effluent

Over-sizing the equipment can decrease the efficiency of the plant

Design Flowrates and Mass Loadings

A number of operating conditions must be considered in the design of a WW treatment facility: Peak hydraulic flowrate Minimum hydraulic flowrate Maximum mass loading Minimum mass loading Sustained mass loading

Refer to Table 3-20 in Metcalf and Eddy

Initial and future

Table 3-20, Metcalf and Eddy

Typical Municipal WW

TSS: 220 mg/L VSS: 165 mg/L BOD5: 220 mg/L COD: 500 mg/L TKN: 40 mg-N/L Ammonia: 25 mg-N/L TP: 8 mg-P/L Ortho-phosphate: 5 mg-P/L

Practice Problem

An industrial wastewater stream is known to contain only steric acid (C18H36O2), glycine (C2H5O2N), and glucose (C6H12O6). Laboratory analysis revealed the following: Organic N = 11 mg/L Organic C = 130 mg/L COD = 425 mg/L

What is the concentration of each of the constituents? SA ~ 45 mg/L

Gly ~ 59 mg/LGlu ~ 192 mg/L