Understanding Biological Oxygen Demand and Chemical Oxygen Demand in Environmental Engineering

Jae K. (Jim) Park Department of Civil and Environmental Engineering University of Wisconsin-Madison 1

Energy Solar radiation: Photo-synthetic autotrophs, e.g., algae Organics: Heterotrophs, e.g., activated sludge biomass, denitrifiers, etc. Inorganics: Chemoautotrophs, e.g., nitrifiers Oxygen use Obligate (strict): use only one condition for growth Facultative: use either dissolved oxygen or chemically derived oxygen (from nitrate, sulfate or carbonate) for respiration and use organic materials for energy and growth Temperature Psychrophiles: < 20 C., opt. 13 C Mesophiles: 20~45 C, opt. 35 C Thermophiles: 45~60 C, opt. 55 C 2

Carbonaceous Energy: Carbon as energy source Heterotrophs Nitrogenous Energy: Nitrogen as energy source Chemoautotrophs 3

Theoretical Oxygen Demand (ThOD) Chemical Oxygen Demand (COD) Biochemical (Biological) Oxygen Demand (BOD) Carbonaceous BOD (C) Nitrogenous BOD (N) Total Organic Carbon (TOC) 4

Theoretical Oxygen Demand (ThOD) 1. Carbonaceous demand: C CO2; N NH3 2. Nitrogenous demand: NH3 HNO2; HNO2 HNO3 3. ThOD = O2 req. in steps 1& 2 Ex. Glycine (10 mg/L) [CH2(NH2)COOH] (MW = 75 g/mol) 1. Carbonaceous demand CH2(NH2)COOH + 1.5O2 2CO2 + H2O + NH3 2. Nitrogenous demand NH3 + 1.5O2 HNO2 + H2O; HNO2 + 0.5O2 HNO3 3. ThOD = [1.5 + (1.5+0.5)] mol O2/mol glycine = 3.5 32 g O2/mol = 112 g O2/mol = 112 75 g/mol = 1.49 g O2/g glycine Thus, ThOD = 1.49 x 10 mg/L = 14.9 mg/L Cannot be used if chemical composition is not known. 5

Chemical Oxygen Demand (COD) O2 req. for oxidation of organics Oxidize carbonaceous matter with a strong oxidant (e.g., hot dichromate sol. with sulfuric acid) + a 8c Heat + + + + + + 2 7 3 C H O cCr Dichromate O 8cH Catalyst silver sulfate nCO H O 2cCr n a b 2 2 2 2 H2SO4 2n a b = + c 3 6 3 Reduction of O2 4e- + 4H+ + O2 2H2O 1 mole of O2 (32 g) 4e- equivalents 1 g COD 1 g O2 1/8 electron equiv. NH3 not oxidized (carbonaceous energy only) Aromatic hydrocarbons (benzene and toluene) and pyridines are not oxidized 6

Domestic Wastewater COD Fractionation Influent COD (Sti) 100% Unbiodegradable COD (Sui) Biodegradable COD (Sbi) ~80% ~20% Particulate unbiodeg. COD (Supi) ~13% Soluble unbiodeg. COD (Susii) ~7% Partic. slowly biodegradable COD (Sbpi) ~60% Sol. readily biodegradable COD (Sbsi) ~20% 7

Biochemical (Biological) Oxygen Demand (BOD) O2 required for microbial decomposition Oxygen consumption by microorganisms BODu DO consumed, mg/L Nitrogenous energy BOD5 Inadequate to assess the electron donor capacity; after 5 days, still some biodegradable matters exist. Carbonaceous energy ~30 5 Time, days 8

Energy Measurement (5) Biochemical (Biological) Oxygen Demand (BOD) Carbonaceous BOD: aerobic heterotrophs Decompose organic molecules to minerals (CO2) and residues Obtain their cell carbon from the organic material Nitrogenous BOD: obligate aerobic chemoautotrophs Characteristics of nitrifiers (chemoautotrophs) DO < 2 mg/L action slow DO < 0.5 mg/L action ceases Optimum pH: 8.0; pH < 7.2: slows down More sensitive than heterotrophs to toxins Slow growers (longer sludge age required) 9

Measured with COD Not biodegraded, thus not measured with BOD5 Polymerized waste product Inert material from lysed cells Refractory organics: humic acid (M.W. 5,000~100,000); fulvic acid (2,000~10,000) Certain high M.W. carbohydrates alone or in combination with humic material are resistant to microbial attack. High M.W. carbohydrates are excreted at the end of the logarithmic growth phase and help forming flocs by bridging of bacterial cells. 10

Selection of populations by controlling environmental factors to encourage only the desired species. An increase in the biodegradation rate of a chemical after exposure of the microbial community to the chemical for some period of time. 11

Lag phase Acclimation Result of acclimation 25 Chemical concentration 20 CO 2 production, vol. Biomass conc., mg/L Concentration, mg/L 15 10 CO2 production 5 Microbial biomass 0 0 5 10 15 20 25 30 35 40 Days 12

Hazardous Industrial Wastewater NBW NBW NBW NBW RBW Feed ratio RBW RBW RBW Biological Treatment Day 1 Day 2 Day 3 Day 5 Day 4 RBW: Readily biodegradable wastewater, e.g., glucose, methanol, domestic wastewater, etc. NBW: Not readily biodegradable wastewater, e.g., industrial wastewater, hazardous wastewater, polychlorinated biphenyls (PCBs), pentachlorophenol, etc. 13

BOD5 equivalents Total COD BOD5 COD, mg/L Not readily Biodegradable COD Non-biodegradable COD Treated with unacclimated biomass Treated with acclimated biomass Untreated Raw BOD: Not affected by acclimation COD: Significantly affected by acclimation 14

Organic matter Unbiodegradable Biodegradable TOC CODCr Cl-, H2S CODMn Cl-, H2S BOD5 Nitrification 15

Energy Measurement (6) Total Organic Carbon (TOC) Oxidize in a combustion chamber with O2 Easy to measure O2 + 4H+ + 4 e- = 2 H2O TOC values are very similar for both glucose and glycerol; however, COD values are quite different. Thus, waste specific; cannot apply the result to other WWTPs. Good as an operational tool with previous historical data. Glucose, C6H12O6 (M.W. = 180) C6H12O6 + 6 O2 6 CO2 + 6 H2O 6 moles O2 6 4 = 24 e- 24/6 = 4 e- available per unit organic C Ex. 100 mg/L of glucose: TOC and COD = ? TOC: (6 12)/180 100 = 40 mg/L C COD: (6 32)/180 100 = 107 mg/L O Glycerol, C3H8O3 (M.W. = 92) C3H8O3 + 7/2 O2 3 CO2 + 4 H2O 7/2 moles O2 7/2 4 = 14 e- 14/3 = 4.67 e- available per unit organic C Ex. 100 mg/L of glycerol: TOC and COD = ? TOC: (3 12)/92 100 = 39 mg/L C COD: (3.5 32)/92 100 = 122 mg/L O Similar Different 16

BOD5/COD ratio: a good indicator for biodegradability of a specific wastewater Domestic wastewater BOD5/COD 0.4 ~ 0.8 BOD5/TOC 1.0 ~ 1.6 BOD5/COD 0.6: can be decomposed completely, biological treatment feasible BOD5/COD 0.2: cannot be decomposed easily, chemical or physical treatment desired BOD5/COD 0: has toxic materials 17

Measure the amount of total organic carbon present in a liquid sample; Convert inorganic carbon in the sample to CO2 after adding acid and strip CO2 by a sparge carrier gas; Oxidize organic carbon by either combustion, UV persulfate oxidation, ozone promoted, or UV fluorescence; and Measure CO2 stripped using the conductivity or non-dispersive infrared (NDIR) detection system. On-Line TOC Analyzer: a reagentless analyzer designed for continuous monitoring of organics. 18

BOD5 Good for regulating organic loading to a receiving water body for DO depletion by heterotrophs Not good for design since some organics biodegrade slowly or after acclimation COD Not good for regulation since it does not reflect true organic loading impact to aqua systems Good for design if the input and output within a biological system is monitored; true energy count for carbonaceous energy only TOC Good for operating a wastewater treatment plant due to real time monitoring capability Values cannot be transferred to other wastewater due to specificity of carbon in the wastewater in terms of electro donor capability 19

Priority Pollutants Designated by EPA in 1979 A list of 126 specific pollutants that includes 14 heavy metals and 112 specific organic chemicals Heavy Metals (Total and Dissolved): heavy, dense, metallic elements that occur only at trace levels in water, but are very toxic and tend to accumulate Pesticides: DDT, Aldrin, Chlordane, Endosulfan, Endrin, Heptachlor, and Diazinon Polycyclic Aromatic Hydrocarbons (PAHs): naphthalene, anthracene, pyrene, and benzo(a)pyrene Polychlorinated biphenyls (PCBs): organic chemicals that formerly had widespread use in electrical transformers and hydraulic equipment 20

Sewage backups and overflows can lead to costly clean ups and repairs, as well as public health concerns. Many utilities acknowledge fat, oil, and grease (FOG) as the main cause of sewer clogging. EPA estimated that utilities spend on average $33,000 per mile of sewer per year on capital project and $8,000 per mile for O&M (2004). The capital investment in wastewater infrastructure is over $13 billion annually (EPA, 2002). Local government and utilities pay up to 90% of capital expenditures on wastewater infrastructure (AMSA and WEF, 1999). 21

Line breaks (10%) Misc. (5%) Blockages (48%) Mechanical or power failures (11%) Wet weather I/I (26%) EPA, 2004 22

Roots and FOG (4%) FOG (47%) Roots (22%) Grit, rock, and other debris (27%) EPA, 2004 23

FOG Wastewater 24

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Crown corrosion of concrete pipes H2S + 2O2 H2SO4 Bacteria 26

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Created in an industrial process that adds hydrogen to liquid vegetable oils to make them more solid Easy to use, inexpensive to produce, and last a long time Give foods a desirable taste and texture Use trans fats to deep-fry foods because oils with trans fats can be used many times in commercial fryers Raise bad LDL (low density lipoproteins ) cholesterol levels and lower your good HDL (high density lipoproteins) cholesterol levels 28

Inefficient removal in conventional grease removal systems Potential foaming in wastewater treatment plant aeration basins No knowledge on the fate of zero trans fatty acids in sewers and wastewater treatment plants 29

Grease trap or interceptors, exhaust hood filters, and floor mats Proprietary grease removal devices Click here for information on Dormon WD Series Grease Interceptors 30

Chemicals and additives (emulsifiers, detergents or caustic substances) that claim to dissolve grease Prohibited for use as an additive because these substances reduce the efficiency of the interceptor or trap Best Management Practices (BMP) during daily operations to keep FOG out of drains leading to the sewer Enzymes Prohibited as additives due to the same effect as emulsifiers Microorganisms Not prohibited as an additive Education 31

Main species Organic nitrogen NH4+: Ionized ammonia, nutrient to algae NH3: Free (unionized) ammonia, toxic to fish NO2-: Intermediate byproduct of nitirification, < 1 mg/L, causes the hemoglobin in the blood to change to methemoglobin, cause methemoglobinemia ( blue baby syndrome) NO3-: Final product of nitrification, undeveloped digestive tracts of an infant possess bacteria that convert nitrate into nitrite, < 10 mg/L 32

Organic nitrogen (proteins, urea, etc.) Bacterial decomposition and hydrolysis Assimilation Ammonia nitrogen (NH3-N) Organic nitrogen (bacterial cells) Organic nitrogen (net growth) Lysis and autooxidation O2 Nitrite (NO2-) O2 Denitrification Nitrate (NO3-) Nitrogen gas (N2) Organic carbon (substrate) 33

Subdivision of Total Influent TKN Influent TKN (Nti) 100% Organically bound N (Nti - Nai) ~25% -(Nai) NH3&NH4 ~75% Biodegrad. N (Nai) ~12% Unbiodegrad. soluble N (Nui) ~3% Unbiodegrad. Particulate N (Npi) ~10% Total Kjeldahl Nitrogen (TKN): sum of organic nitrogen, ammonia (NH3), and ammonium (NH4+) in biological wastewater treatment 34

More toxic to fish More toxic to fish Temperature effect Ammonia not regulated in winter 35

Nitrification: Conversion from ammonia to NO2- / NO3- Nitrosomonas NH4+ + 1.5O2 NO2- + H2O + 2H+ + New biomass Nitrobactor NO2- + 0.5O2 NO3- + New biomass Oxygen demand Conversion + - 2 Conversion of NO to NO of NH to NO 3 4 2 g g 1.5 mol 16 O 2 0.5 mol 16 O 2 O g O g mol mol = = 3.43 1.14 g g N g N g mol 1 14 N mol 1 14 N mol mol Total oxygen demand for nitrification: 4.57 g O/g N 36

CO2 (carbonate): carbon source Ammonia: energy transfer source in a non- assimilative way so only a small amount of biomass (sludge) is produced Nitrosomonas NH4+ + 1.5O2 NO2- + H2O + 2H+ + New biomass H+ +CO32- HCO3-; H+ +HCO3- H2CO3 Alkalinity 2H+ 1 mol alkalinity [CaCO3 (40+12+16 3=100 g/mol)] 100 g Alk/14 g N = 7.14 g Alk consumed/g N nitrified 37

Example Influent TKN = 42 mg N/L; Effluent TKN 2 mg/L Alkalinity = 200 mg/L as CaCO3 Oxygen demand? 4.57 g O/g N (42 2) mg N/L = 182.8 mg O/L Alkalinity after nitrification? 7.14 g Alk/g N (42 2) mg N/L = 285.6 mg/L as CaCO3 Unless additional alkalinity (CaO, Na2CO3, NaOH, etc.) is added, nitrification will stop (see the next slide). Since the influent is 200 mg/L, 85.6 mg/L + 10~15 mg/L (residual) = 95.6~100.6 mg/L as CaCO3 required 38

Operational range Nitrifiers: very sensitive to pH Thus, buffer capacity (alkalinity) of wastewater important 39

2NO3-+ 10e-+ 12H+ N2 + 6H2O N g 14 mol 2 mol = 2.8 g N/e O g 10 e 8 O g O2+ 4e-+ 4H+ 2H2O mol e = 2.86 N g N g O g 2.8 2 mol 1 16 e = g 8 O/e e 4 O g 2.86 (denitrifi cation) N g = 100 saved O 63% O g 4.57 (nitrifica tion) N g 40

~1 mol of H+ is recovered from denitrification Thus, Alk of 3.57 g/g N recovered For low alkalinity water, denitrification is recommended. Denitrification conditions No O2 Readily biodegradable soluble substrate (COD) For complete removal of nitrogen species from wastewater: nitrification followed by denitrification 41

0.67 0.33 CODutilized = CODbiomass + O2 utilized = fcv X + O2 utilized = YCOD CODutilized + O2 utilized fcv = COD/VSS = CODbiomass/ X (mg COD/mg VSS) YCOD = CODbiomass/ CODutilized (mg COD/mg COD) O2 utilized = (1 - YCOD) CODutilized YCOD = fcv Yh (mg VSS/mg COD) C5H7O2N + 5O2 5CO2 + 2H2O + NH3 (5 16 2 g) (1 113 g) = 1.42 mg COD/mg VSS COD/VSS = 1.42 mg COD/mg VSS O2 = (1 - fcvYh) CODutilized Nitrate consumption per mg COD utilized 2.86 mg O2/mg NO3- N (1 - 1.42 0.47) mg O2/mg COD = 8.6 mg COD req./mg NO3--N denitrified Biomass empirical formula 0.67 42

Example CODinf = 400 mg/L, CODeff = 50 mg/L, TKNinf = 55 mg N/L, TKNeff = 5 mg N/L, Q = 10 MGD COD (methanol) required for denitrification? Solution (55-5) mg N/L 8.6 mg COD/mg N = 430 mg COD/L req. [430-(400-50)] mg/L = 80 mg COD/L req. Methanol (CH3OH) (MW = 32 g/mol) CH3OH + 1.5O2 CO2 + 2H2O 80 mg COD/L 10 MGD 1.5 16 2 g COD/32 g MeOH = 202 kg/day = 445 lb of MeOH/day 43

Phosphorus Source: human body waste, food waste, various household detergents Subdivision of Total Influent P Influent TP (Pti) 100% Organically bound P (Pti - Pbi) 10 ~ 30% Sol. PO4- (Psi) 70 ~ 90% 10 ~ 20% in the activated sludge process 44

mg/L Old Now Forms 5 4 Orthophosphate 3 0 Tripolyphosphate (detergents) 1 0 Pyrophosphate (breakdown of tri-P) 1 1 Organic phosphates 0 ? Hexametaphosphate (corrosion inhibitor) 10 5 Total Why? Ban of phosphate-based detergents 45

Addition to water Corrosion (and scale) control in drinking water Industrial water softening Boiler waters Cleaning compounds Sewage 1.2 lb/capita/yr from human and food waste 46

Mechanisms of Polyphosphate- Accumulating Organisms (PAOs) Short chain fatty acids (SCFAs) (Acetate) New Cell Organic substrate NADH, ATP PHA Glycogen ATP Glycogen ATP PHA Facultative microbes Poly-P Poly-P PAOs PO4 3- PAOs PO4 3- Anaerobic condition Aerobic condition PHA: Polyhydroxyalkanoates 47

Observations in Biological Phosphorus Removal (BPR) Systems AN O Ortho-P Bulk Liquid Acetate PHA Glycogen Biomass Poly-P Reaction Time PHA: Polyhydroxyalkanoates 48

Aerobic Anaerobic Ortho-P mg/L Acetate Time Biomass Biomass Poly- - hydroxybutyrate (PHB) (Storage) PHB Poly-P Poly-P 49

Anaerobic/Oxic Process Readily biodegradable soluble COD Vital for P Uptake Excess sludge Better SRT control SRT: Solid retention time, sludge age, or mean cell residence time (MCRT); total biomass in the system/biomass wasted/loss 50