Seminar on

Biological Wastewater Treatment Processes

Past, Present and Future

Dr. Ajit P. AnnachhatreEnvironmental Engineering ProgramAsian Institute of Technology

Keywords Wastewater Biological Processes Treatment Processes Applications Ongoing Research Activities

Biological Wastewater Treatment

1.Wastewater Domestic Wastewater

Industrial Wastewater Present State of Wastewater

Domestic Wastewater over 80 % - untreated in Asian mega cities

major components- COD = 250-1000 mg/L Total N = 20-90 mg/L Total P = 4-15 mg/L effects of discharging into natural receiving bodies

oxygen demand by carbon and nitrogen

Industrial Wastewater...Eg: Starch industry wastewater major component-COD = 10,000-20,000 mg/L

effects of discharging into natural receiving bodies - 20 m3/ton of starch- high COD - high suspended solids- cyanide exposure

Industrial Wastewater...Starch industry wastewater factory with 300 T/d of starch

wastewater generation 6000m3/d

COD 14,000 mg/L

population equivalent 1000,000

Industrial Wastewater present treatment method: Anaerobic ponds

typical loading rates:800-1000kg COD /ha/d

area requirement: 100 ha

2.Biological Processes aim: any form of life- survive & multiply

need for energy & organic molecules as building blocks

made of C, H, O, N, S, P and trace elements

Biological Processes... cell: derives energy from oxidation of reduced food sources (carbohydrate, protein & fats)

MicroorganismsClassification: Heterotrophic- obtain energy from oxidation of organic matter (organic Carbon)

Autotrophic- obtain energy from oxidation of inorganic matter(CO2, NH4, H+ )

Phototrophic- obtain energy from sunlight

Biochemical Pathways oxidation of organic molecules inside the cell can occur aerobic or anaerobic manner

generalized pathways for aerobic & anaerobic fermentation

Biochemical Pathways Glucose

EPM Pathway

Pyruvic Acid ADP ATPEnergyLactic Acid TCA Cycle H+ Respiration H2O CO2 O2

aerobic pathways contains- EMP pathways, TCA cycle, respiration

anaerobic pathways contains- EMP pathways

released energy stored as ATP molecules

excess food is stored as Glycogen

C6H12O6 + 6O2 +38 ADP + 38 Pi 6 CO2 +38 ATP + 44 H2O Biochemical Pathways

Biological growth

- exponential growth (batch)

- Monod kinetics

- Haldane kinetics

under toxic conditions

exponential growth

Biological growth...

= (X

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Monod kineticsBiological growth...

( = (m

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Haldane kinetics (under toxic conditions)

Biological growth...

( = (m

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3.Applications1. Carbonaceous removal - aerobic- anaerobic

2. Nitrogen removal- nitrification- denitrification

3. Sulfide removal- anaerobic SO4 reduction- aerobic HS- oxidation

Biological Carbonaceous Removal aerobic- oxidation bacteria CHONS + O2 + Nutrients CO2 + NH3 + C5H7NO2 (organic matter) (new bacterial cells)+ other end products- endogenous respiration bacteriaC5H7NO2 + 5O2 5CO2 + 2H2O + NH3 + energy (cells)

Biological Carbonaceous Removal anaerobic

Schematic of the Anaerobic Process

Biological Nitrogen Removal nitrification-energyNitrosomonasNH4+ + 1.5 O2 NO2- + H2O + 2 H+ + (240-350 kJ) (1) NitrobacterNO2- + 0.5 O2 NO3- + (65-90 kJ)(2)

-assimilationNitrosomonas 15 CO2 + 13 NH4+ 10 NO2- + 3 C5H7NO2 + 23 H+ +4 H2O(3) Nitrobacter 5 CO2 + NH4+ +10 NO2- +2 H2O 10 NO3- + C5H7NO2 + H+(4)

- overall reaction

NH4+ +1.83 O2 + 1.98 H CO3- 0.021 C5H7NO2 + 0.98 NO3- + 1.04 1H2O + 1.88H2CO3

Biological Nitrogen Removal factors affecting nitrification

* temperature

* substrate concentration

* dissolved oxygen

* pH

* toxic and inhibitory substances

Biological Nitrogen Removal denitrification* assimilatory denitrification- reduction of nitrate to ammonium by microorganism for protein synthesis

* dissimilatory denitrification- reduction of nitrate to gaseous nitrogen by microorganism- nitrate is used instead of oxygen as terminal electron acceptor- considered an anoxic process occurring in the presence of nitrate and the absence of molecular oxygen- the process proceeds through a series of four steps

Biological Nitrogen Removal denitrification

* heterotrophic denitrification

- denitrifiers require reduced carbon source for energy and cell synthesis

- denitrifiers can use variety of organic carbon source - methanol, ethanol and acetic acid

Biological Nitrogen Removal factors affecting denitrification

* temperature

* dissolved oxygen

* pH

Biological Sulfate Removal * Sulfate removal cycle

anaerobicSO4 -- HS - S 0 (O2 deficient) (O2 excess)

4.Treatment Processes pond treatment

activated sludge process

biofilm process

- no biomass recirculation- high HRT- high land area- O2 transfer limitations- inadequate mixing- excess loading (anaerobic condition-H2S generation)Pond Treatment

Activated Sludge ProcessFE

Activated Sludge Process...- aerobic

- suspended-growth

- Design equations

Activated Sludge Process... typical values of cell residence time (c )

- c for C removal ~ 3-10 days - c for N removal ~ 5-30 days

- loading rates ~ 2-3 kg COD/m3/d

- drawbacks: O2 requirements, inlet conc.

Biofilm Processesadvantages of biofilm processes:

- higher process productivity (loading rates)- higher biomass holdup- higher mean cell residence time- no need for biomass recirculation- creates suitable environment for each type of bacteria- sustains toxic loads

Biofilm Processes... types of biofilms: aerobic, anaerobic, anoxic

process of biofilm formation

- formation of diffuse electrical double layer due to electrostatic forces and thermal motion

- transfer of microorganism to surface

- microbial adhesion

- biofilm formation

Biofilm Processes... biofilm operation

Biofilm Processes... biofilm operation

- diffusion resistance

- inadequate supply of nutrients to inner

portions of Biofilm

- limitations on product out diffusion

- attrition of reaction conditions

Biofilm Processes... biofilm operation as biofilm thickness increases effectiveness factor () decreases

average rate of substrate consumption

Effectiveness factor ( =----------------------------------------------

substrate consumption at biofilm surface

Anaerobic biofilm processes

Conversion of Ethanol to Methane

Conversion Reaction

(Go (kJ)

Ethanol

CH2CH2OH (aq) + H2O (l) = CH3COO- (aq) + H+ (aq) + 2H2 (g)

+09.65

Hydrogen

2H2 (g) + CO2 (g) = CH4 (g) + H2O (l)

- 65.37

Acetate

CH3COO- (aq) + H+ (aq) = CH4 (g) + CO2 (g)

- 35.83

Net

CH2CH2OH (aq) = 3/2 CH4 + CO2 (g)

- 91.55

Anaerobic biofilm processes... importance of H partial pressure

loading rates 10-15 kg COD/m3/d against 2-5 kg COD/m3/d in suspended growth processes

Ongoing Research ActivitiesBiological Processes

aerobic anoxic anaerobic

nitrificationdenitrification SO42-- reduction

HS- oxidation detoxification

Ongoing Research Activitiesaerobic

nitrification HS- oxidation

inhibition aniline modeling biofilm in ASP degradation processes in SBR ShabbirJega Sunil & Keshab Savapak Shabbir & Shabbir

Ongoing Research Activitiesanaerobic

SO42--reductiondetoxification& modeling& modeling

Savapak Amara

Ongoing Research Activitiesanoxic

denitrification

toxic chemicalsmembraneas C sourcebio reactor

Krongtong Tran

membrane processes Piyaputr

Study of nitrification process inside a spherical biofloc particle based on biofilm kinetics.

determination of effectiveness factor for substrate consumption and thus the substrate removal rates.

Mathematical model consists of a system of second order differential equations based on steady state material balance and appropriate boundary conditions.

Model is solved numerically using a computer program developed in Macsyma 2.3, which uses 4th order Runge-Kutta method for solving system of ODEs

Assumptions:Spherical bioflocDouble substrate limited kinetics based on Michaelis - Menten equationSteady State conditions.Constant Kinetic and Diffusional parameters, and biomass density inside the floc.Evaluation of concentration profile for the substrates inside a spherical biofloc

Substrate : Oxygen and Ammonia-nitrogen Material Balance Equation:Mass transfer limitations due to diffusional resistances and biochemical reactions taking place inside the biofloc are considered.

Boundary Conditions:Depend on, Degree of penetration Partial or Full Limiting Substrate Substrate-1 (Oxygen) Substrate-2 (Ammonia)Case : Full Penetrationat r = 1.00 ,s1 = 1.0, s2 = 1.0 at r = 0, s1 = s1,0, s2 = s2,0, ds1/dr = 0, ds2/dr = 0

Chart1

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0.1

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0.15

0.2

0.25

0.3

0.4

0.5

0.75

1

1.5

2

3

4

6

8

10

Biofloc diameter (mm)

Effectiveness factor (h)

Fig. Variation of effectiveness factor with the size of biofloc and bulk DO to bulk NH4+ conc. ratio for constant bulk DO conc = 4 mg/l

Sheet1

4

406080100150200300400

0.10.99130.97560.93590.85560.659080.52640.37190.2867

0.1250.99130.97560.93590.85560.659140.52640.37190.2867

0.150.99130.97560.93590.85570.659210.52650.3720.2868

0.20.99130.97560.93590.85580.659260.52650.3720.2868

0.250.99130.97560.9360.85580.659310.52660.37210.2868

0.30.99130.97560.9360.85590.659380.52670.37210.2869

0.40.99120.97560.9360.8560.65930.52680.37220.287

0.50.99120.97560.93610.85610.659430.52690.37230.287

0.750.99120.97550.9360.85630.659710.52710.37250.2872

10.99110.97530.93590.85640.659910.52730.37270.2873

1.50.99080.97470.93520.85610.660210.52750.37280.2875

20.99030.97360.93360.8550.659640.52710.37260.2874

30.9890.96990.92560.84540.651410.52010.36760.2834

40.9870.9630.89840.79940.601010.47560.33330.2561

60.98050.93070.81360.70310.513750.40190.27880.2132

80.970.87670.74140.63180.454820.35350.24390.186

100.95480.82450.68440.57830.412380.31920.21940.167

Sheet1

00000000000000000

00000000000000000

00000000000000000

00000000000000000

00000000000000000

00000000000000000

00000000000000000

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0.1

0.125

0.15

0.2

0.25

0.3

0.4

0.5

0.75

1

1.5

2

3

4

6

8

10

Biofloc diameter (mm)

Effectiveness factor (h)

Variation of effectiveness factor with the size of biofloc and bulk DO to bulk NH4+ conc. ratio for constant bulk DO conc = 4 mg/l

Sheet2

Sheet3

Ongoing Research Activities

Cyanide Degradation in Ananerobic Processes

_957784459.doc

Feeds Tank

Water

Seal

Biogas

10 cm dia.

300 cm tall

Acrylic tube

Sampling Port

Effluent Outlet

Gas Solid Liquid

(GSL) Separator

Sludge Blanket

Glass Beeds

Wash-out

Biomass

Settler

Effluent

Gas Measurement Unit

U

Feed Pump

(peristaltic)

Recirculation Pump

(peristaltic)

Ongoing Research ActivitiesFludized Bed for Sulfide Oxidation ProcessUASB for Sulfide Removal

Fluidized Bed For Sulfide Oxidation Process

Recycle

pH electrode

Aeration

Tank

Effluent

Air

Nutrients

Na2S/NaHCO3

Solution

HCl (NaOH)-pump

Sand

Ongoing Research Activities

Bio-Chitosan Membrane Reactor for Denitrification

Feed Side

NaNO3 Solution

C = 50 (mg NO3-- N/L)

V = 3.5 (L)

Weir

Denitrifying Bacteria

Sampling Point

Recycle Pipe

Feed Tank

NaNO3 Solution

C = 50 (mg NO3-- N/L)

V = 4.0 (L)

Influent

Permeate Side

V = 3.5 (L)

Sampling Point

Chitosan Membrane Stirrer

Magnetic Stirrer

Feed Pump

Ongoing Research Activities

EMBED Visio.Drawing.4

_957776719.vsd

THE END