Wastewater Characteristics CE - 370

Importance of Characteristics The degree of treatment depends on: The degree of treatment depends on: Influent characteristics Influent characteristics Effluent characteristics Effluent characteristics Impurities come from: Impurities come from: Domestic activities Domestic activities Industrial activities Industrial activities Commercial activities Commercial activities Typical characteristics are shown in the following Table Typical characteristics are shown in the following Table

ConcentrationConstituents WeakMediumStrong Total Solids TDS Fixed TDS Volatile TDS TSS Fixed SS Volatile SS 357Settleable Solids (ml/l) BOD TOC COD Total Nitrogen 82040Organic Nitrogen 82035Free Ammonia 000Nitrite 000Nitrate 4815Total Phosphorous 135Organic Phosphorous 3510Inorganic Phosphorous Chlorides Alkalinity (CaCO 3 ) 52040Grease

Characteristics Physical Physical Chemical Chemical Biological Biological

Physical Characteristics Turbidity Turbidity Caused by the presence of organic suspended solids Caused by the presence of organic suspended solids Color Color Is light tan if fresh (2 to 6 hours old) Is light tan if fresh (2 to 6 hours old) Is grey if older than 6 hours due to biochemical oxidation in collection system Is grey if older than 6 hours due to biochemical oxidation in collection system Is dark grey or black if undergone extreme biochemical oxidation under anaerobic conditions (production of sulfides, particularly ferrous sulfide) Is dark grey or black if undergone extreme biochemical oxidation under anaerobic conditions (production of sulfides, particularly ferrous sulfide) Hydrogen sulfide is produced under anaerobic condition, which reacts with ferrous ions and produce ferrous sulfide Hydrogen sulfide is produced under anaerobic condition, which reacts with ferrous ions and produce ferrous sulfide

Physical Characteristics Odor Odor Soapy or oily odor if fresh (not offensive) Soapy or oily odor if fresh (not offensive) Stale, very offensive, if undergone extreme anaerobic biochemical oxidation, due to production of compounds such as hydrogen sulfide Stale, very offensive, if undergone extreme anaerobic biochemical oxidation, due to production of compounds such as hydrogen sulfide Total solids Total solids Suspended Suspended dissolved dissolved Volatile (evaporate at 550  C) Volatile (evaporate at 550  C) Fixed (remain after ignition) Fixed (remain after ignition) settleable settleable

Physical Characteristics Temperature is higher than that of water supply Temperature is higher than that of water supply Important parameter, particularly for biological processes Important parameter, particularly for biological processes Physical characteristics of industrial wastewater vary depending on the source of the wastewater Physical characteristics of industrial wastewater vary depending on the source of the wastewater

Chemical Characteristics Chemical Oxygen Demand (COD) Chemical Oxygen Demand (COD) Is a measure of organic materials (is based on measurement of the amount of oxidizing agent required to oxidize the organic materials) Is a measure of organic materials (is based on measurement of the amount of oxidizing agent required to oxidize the organic materials) Total Organic Carbon (TOC) Total Organic Carbon (TOC) Is a measure of organic materials (based on measurement of carbon in the organic materials by combustion and measurement of CO 2 evolves) Is a measure of organic materials (based on measurement of carbon in the organic materials by combustion and measurement of CO 2 evolves)

Chemical Characteristics Organic Nitrogen (amount of nitrogen in organic compounds such as protein and urea) Organic Nitrogen (amount of nitrogen in organic compounds such as protein and urea) Ammonia nitrogen (NH 3 ) Ammonia nitrogen (NH 3 ) Nitrite nitrogen (NO 2 - ) Nitrite nitrogen (NO 2 - ) Nitrate nitrogen (NO 3 - ) Nitrate nitrogen (NO 3 - ) Organic Phosphorous (in protein) Organic Phosphorous (in protein) Inorganic phosphorous (phosphates, PO 4 - ) Inorganic phosphorous (phosphates, PO 4 - ) Chlorides (Cl - ) Chlorides (Cl - ) Sulfates (SO 4 -2 ) Sulfates (SO 4 -2 ) pH pH Alkalinity Alkalinity

Chemical Characteristics Grease (interferes with oxygen transfer in activated sludge processes) Grease (interferes with oxygen transfer in activated sludge processes) Heavy metals such as Heavy metals such as Mercury (Hg) Mercury (Hg) Arsenic (As) Arsenic (As) Lead (Pb) Lead (Pb) Zinc (Zn) Zinc (Zn) Cadmium (Cd) Cadmium (Cd) Copper (Cu) Copper (Cu) Nickel (Ni) Nickel (Ni) Chromium (Cr) Chromium (Cr) Silver (Ag) Silver (Ag)

Chemical Characteristics Priority Pollutants (organic and inorganic) are: Priority Pollutants (organic and inorganic) are: Carcinogenic Carcinogenic Mutagenic Mutagenic Teratogenic Teratogenic High acute toxic High acute toxic

Biological Characteristics Biochemical Oxygen Demand (BOD 5 ) Biochemical Oxygen Demand (BOD 5 ) The amount of oxygen needed to stabilize organic matter by micro-organisms The amount of oxygen needed to stabilize organic matter by micro-organisms Time (5 days) Time (5 days) Temperature (20  C) Temperature (20  C) Nitrogenous Oxygen Demand Nitrogenous Oxygen Demand The amount of oxygen needed to convert organic and ammonia nitrogen to nitrates by nitrifying bacteria The amount of oxygen needed to convert organic and ammonia nitrogen to nitrates by nitrifying bacteria

Wastewater Microbial Life Wastewater contains Wastewater contains Bacteria Bacteria Protozoa Protozoa Fungi Fungi Viruses Viruses Algae Algae Rotifers Rotifers nematodes nematodes Sources Sources Soil (through infiltration) Soil (through infiltration) Human intestines (Escherichia coli and Aerobacter aerogenes) Human intestines (Escherichia coli and Aerobacter aerogenes)

Biochemical Oxygen Demand Organisms Organisms use organic matter, in wastewater, as a substrate use organic matter, in wastewater, as a substrate Need oxygen for respiration Need oxygen for respiration Produce end-products such as CO 2 and H 2 O Produce end-products such as CO 2 and H 2 O BOD is conducted under aerobic conditions BOD is conducted under aerobic conditions Up to 10 to 12 days, O 2 demand will be for oxidation of carbonaceous materials Up to 10 to 12 days, O 2 demand will be for oxidation of carbonaceous materials

Biochemical Oxygen Demand After 10 to 12 days, the NH 3 will be oxidized to nitrite and then nitrate After 10 to 12 days, the NH 3 will be oxidized to nitrite and then nitrate The next two Figures show: The next two Figures show: the BOD curve for both stages the BOD curve for both stages Carbonaceous stage Carbonaceous stage

Carbonaceous Stage Removal of organic matter is a pseudo-first-order reaction Removal of organic matter is a pseudo-first-order reaction dC/dt = rate of removal of organic matter dC/dt = rate of removal of organic matter k = rate constant to the base e k = rate constant to the base e C = concentration of organic matter remaining at time (t) C = concentration of organic matter remaining at time (t)

Carbonaceous Stage Rearrange and integrate the equation Rearrange and integrate the equation C 0 = concentration of organic matter initially C 0 = concentration of organic matter initially C = oxidizable organic matter remaining at time (t) C = oxidizable organic matter remaining at time (t) t = test duration t = test duration

Carbonaceous Stage Since the amount of organic matter oxidized is proportional to the amount of oxygen required, then: Since the amount of organic matter oxidized is proportional to the amount of oxygen required, then: C  L (where L is the BOD remaining at time t) C  L (where L is the BOD remaining at time t) Similarly Similarly C 0  L 0 C 0  L 0 Then, Then, L = BOD remaining at time t L = BOD remaining at time t L 0 = ultimate first-stage or carbonaceous BOD L 0 = ultimate first-stage or carbonaceous BOD k 1 = rate constant to the base e k 1 = rate constant to the base e t = test duration t = test duration K 1 = rate constant to the base 10 K 1 = rate constant to the base 10

Carbonaceous Stage Thus: Thus: So, BOD exerted (y) up to time (t) is: So, BOD exerted (y) up to time (t) is:

Example Example A wastewater has a BOD 5 of 200 mg/l, and the k 1 value is 0.34 day -1. Determine the ultimate first-state BOD, L 0. Solution y = L 0 (1 - e -k1t ) 200 = L 0 [1 - e -(0.34)(5) ] Thus, L 0 = 245 mg/l