1. Fundamentals of Biological Treatment

2. 1. OVERVIEW OF BIOLOGICAL WASTEWATER TREATMENT
Objectives of Biological Treatment
transform(i.e., oxidize) dissolved and particulate biodegradable constituents into acceptable end products
(2) capture and incorporate suspended and nonsettleable colloidal solids
into a biological floc or bio-film
(3) transform or remove nutrients, such as nitrogen and phosphorus
(4) in some cases, remove specific trace organic constituents and compounds
Role of Microorganisms in Wastewater Treatment

3. Figure Typical(simplified) flow diagrams for biological processes used for wastewater treatment: (a) activated-sludge process, (b)aerated lagoons, (c) trickling filters, and (d) rotating biological contactors.

7. Types of Biological Processes for Wastewater Treatment
suspended growth and attached growth(or bio-film) processes

9. Suspended Growth Processes

10. Attached Growth Processes

11. 2. COMPOSITION AND CLASSIFICATION OF MICROORGANISMS
Cell components (2) cell composition
(3) environmental factors that affect microbial activity
(4) methods used to identify and classify microorganisms
Cell Components

14. Cell Composition
80% : water
20% : dry material
90% : organics
10% : inorganics

15. 3. INTRODUCTION TO MICROBIAL METABOLISM
Carbon and Energy Sources for Microbial Growth
Carbon and Energy Sources : substrates
Carbon Sources : heterotrops : organic carbon new biomass
autotrops : carbondioxide cell carbon
Energy Sources : phototrops : light energy source
chemotrops : carbondioxide cell carbon

16. Nutrient and Growth Factor Requirements
Principal inorganic nutrients : N, S, P, K, Mg, Ca, Fe, Na, and Cl
Minor nutrients : Zn, Mn, Mo, Se, Co, Cu, and Ni
Required organic nutrients, known as growth factors, are compounds needed by an organism as precursors or constituents of organic cell material, which cannot be synthesized from other carbon sources.
Although growth factor requirements differ from one organism to another, the major growth factors fall into the following three classes:(1) amino acids,(2) nitrogen bases (i.e., purines and pyrimidines),and (3) vitamins.

17. 4. BACTERIAL GROWTH AND ENERGETICS
bacterial reproduction
bacterial growth patterns in a batch reactor
(3) bacterial growth and biomass yield
(4) methods used to measure biomass growth
(5) estimating cell yield and oxygen requirements from stoichiometry
(6) estimating cell yield from bioenergetics
(7) observed versus synthesis yield O2
Orgainics
(BOD)
Bacteria
(C5H7O2N) O2 O2
End product
CO2, NH3 etc.

18. Bacterial Growth Patterns in a Batch Reactor
The lag phase
The exponential-growth phase
The stationary phase
The death phase

19. Bacterial Growth and Biomass Yield
The ratio of the amount of bio-mass produced to the amount of substrate consumed (g biomass/g substrate)
for nitrification the yield : g-biomass/g-NH4-N oxidized
for the anaerobic degradation of volatile fatty acids (VFAs)
to produce methane : g-biomass/g-VFA used
G-biomass/g-COD removed
or g-biomass/g-BOD removed
Measuring Biomass Growth
* volatile suspended solids (VSS) or particulate COD(total COD minus soluble COD)
* protein content, DNA, and ATP, a cellular compound involved in energy transfer

20. Estimating Biomass Yield and Oxygen Requirements from Stoichiometry
ThOD

21. The quantity of oxygen utilized
the oxygen used for substrate oxidation to CO2 and H2O
the COD of the biomass
the COD of any substrate not degraded
the oxygen consumed per unit of COD used

23. Estimating Biomass Yield from Bioenergetics

27. Stoichiometry of Biological Reactions

28. Biomass Synthesis Yields for Different Growth Conditions

29. 5. MICROBIAL GROWTH KINETICS
microbial growth kinetics terminology
Rate of utilization of soluble substrate
(3) other rate expressions for the utilization of soluble substrate
(4) rate of soluble substrate production from biodegradable particulate organic matter
(5) the rate of biomass growth with soluble substrates
(6) kinetic coefficients for substrate utilization and biomass growth
(7) the rate of oxygen uptake
(8) effects of temperature
(9) total volatile suspended solids and active biomass
(10) net biomass and observed yield.

30. Microbial Growth Kinetics Terminology

32. Other Rate Expressions for the Utilization of Soluble Substrate
Rate of Soluble Substrate Production from Biodegradable Particulate Organic Matter

33. Rate of Biomass Growth with Soluble Substrates

34. Kinetic Coefficients for Substrate Utilization and Biomass Growth

35. Determination of Kinetic coefficients
Laboratory reactor used for the conduct anaerobic treatment studies.
Bench-scale continuous flow stirred reactors
used for the determination of kinetic coefficients
(a) without recycle (b) with recycle

36. Intercept
Slope

37. Determination of kinetic coefficients

39. Y = 0.5
μmax = kY = × 0.5 = day-1

40. Rate of Oxygen Uptake
Effects of Temperature

41. Total Volatile Suspended Solids and Active Biomass

42. Net Biomass Yield and Observed Yield
(1) the net biomass yield
(2) the observed solids yield
Net Biomass Yield
Observed Yield

43. 6. MODELING SUSPENDED GROWTH TREATMENT PROCESSES
the development of biomass and substrate balances
the prediction of effluent biomass and soluble substrate concentrations
the prediction of the reactor biomass and MLSS/MLVSS concentrations and amount of waste sludge produced daily
(4) the prediction of the oxygen requirements
Description of Suspended Growth Treatment Processes
Figure 7-12 Schematic diagram of activated-sludge process with model nomenclature:
(a) with wasting from the sludge return line and (b)with wasting from the aeration tank.

45. specific substrate utilization rate
If it is assumed that the concentration of microorganisms in the influent can be
neglected and that steady-state conditions(dX/dt = 0),
average solids retention time (SRT)
specific substrate utilization rate

46. Substrate Mass Balance

47. Mixed Liquor Solids Concentration and Solids Production
the fraction of solids wasted per day and the mixed liquor can be assumed to be a homogeneous mixture of biomass and other solids
can be used to calculate the amount of solids wasted for any of the mixed liquor components.
For the amount of biomass wasted per day (Px ), the biomass concentration X can be used in place of XT in Eq.

48. Mixed Liquor Solids Concentration
materials balance on the inert material
Eq.

49. Solids Production
the amount of VSS produced and wasted daily is determined as follows

50. The total mass of dry solids wasted per day is based on the TSS, which includes the
VSS plus inorganic solids. Inorganic solids are in the influent wastewater (TSS - VSS)
and the biomass contains 10 to 15 percent inorganic solids by dry weight.
The influent inorganic solids are not soluble, and are assumed captured in the mixed liquor solids and removed in the wasted solids. Equation (7-52) is modified to calculate the solids production in terms of TSS by adding the influent inorganic solids and by calculating the biomass in terms of TSS by assuming a typical biomass VSS/TSS ratio of The ratio of VSS/TSS may vary from 0.80 to 0.90.

51. The Observed Yield S0>>S
For wastewaters with no nbVSS in the influent the solids production consists of only active biomass and cell debris, and the observed yield for VSS is as follows
For municipal wastewater X0,i/S0 values range from 0.10 to 0.30 g/g with primary treatment and 0.30 to 0.50 without primary treatment.
S0>>S

52. Oxygen Requirements

53. Design and Operating Parameters
Food to Microorganism (F/M) Ratio
Specific Substrate Utilization Rate
For systems designed for the treatment of municipal wastewater with activated-sludge
SRT values in the 20- to 30-d range, the F/M value may range from 0.10 to 0.05 g
BOD/g VSSd, respectively. At SRTs in the range of 5 to 7 d, the value may range from
0.3 to 0.5 g BOD/g VSSd, respectively.

54. Organic Volumetric Loading Rate

55. Process Performance and Stability
The critical SRT value(stabilization does not occur) is called the minimum solids retention residence time SRTmin . Physically, SRTmin is the residence time at which the cells are washed out or wasted from the system faster than they can reproduce.
The minimum SRT can be calculated using Eq , in which S = S0
When washout occurs, the influent concentration S0 is equal to the effluent waste concentration S.

56. In many situations encountered in waste treatment, S0 is much greater than KS so that
can be used to determine the SRT min
To ensure adequate waste treatment, biological treatment processes are usually designed and operated with a design SRT value from 2 to 20 times
SRTmin. In effect, the ratio of the design SRT (SRTdes) to SRTmin can be considered to be a process safety factor SF against system failure (Lawrence and McCarty,1970).

57. Modeling Plug-Flow Reactors

58. 7. SUBSTRATE REMOVAL IN ATTACHED GROWTH TREATMENT PROCESSES
Typical packing for trickling filters: (a) rock and (b) plastic.
diffusion limited
The bio-film thickness may range from 100 mm to 10 mm
Bio-film VSS concentrations may range from 40 to 100 g/L
Uniform growth across the support packing also does not occur, because of
periodic sloughing, as well as the hydrodynamics and media configuration

60. Substrate Flux in Bio-films
L = f(fluid properties, velocity)

61. Substrate Mass Balance for Bio-film
The substrate utilization rate within the bio-film at any point
Substrate Mass Balance for Bio-film
A substrate mass balance around a differential element (dx)
For steady-state

62. Need two boundary conditions
* first boundary condition is that the substrate flux at the bio-film surface equals
the substrate flux through the stagnant film
* second boundary condition is that there is no flux at the packing surface
Solutions vary, depending on
whether a deep bio-film exists such that the biofilm substrate concentration
approaches zero toward the support surface,
(2) whether a shallow film exists such that S is a finite value throughout the film,
(3) the relative concentration of S compared to K .

63. Substrate Flux Limitations

64. 8. AEROBIC BIOLOGICAL OXIDATION
(1) remove organic constituents and compounds to prevent excessive DO
depletion in receiving waters from municipal or industrial point discharges,
(2) Remove colloidal and suspended solids to avoid the accumulation of
solids and the creation of nuisance conditions in receiving waters,
(3) reduce the concentration of pathogenic organisms released to receiving
waters
Stoichiometry of Aerobic Biological Oxidation
Assuming ammonia will serve as the nitrogen source for cell tissue, oxygen is the electron acceptor, and fs for the reaction is 0.59

65. Growth Kinetics Typical k and Ks values at 20°C Environmental Factors
For carbonaceous removal, pH in the range of 6.0 to 9.0 is tolerable, while optimal performance occurs near a neutral pH. A reactor DO concentration of 2.0 mg/L is commonly used, and at concentrations above 0.50 mg/L there is little effect of the DO concentration on the degradation rate.

66. 9. BIOLOGICAL NITRIFICATION
Nitrification is the term used to describe the two-step biological process in which
Ammonia is oxidized to nitrite and nitrite is oxidized to nitrate
The need for nitrification
the effect of ammonia on receiving water with respect to DO concentrations
and fish toxicity,
(2) the need to provide nitrogen removal to control eutrophication,
(3) the need to provide nitrogen control for water-reuse applications including
groundwater recharge.
drinking water maximum contaminant level (MCL) for nitrate nitrogen is
45 mg/L as nitrate or 10 mg/L as nitrogen

67. Process Description

68. Stoichiometry of Biological Nitrification
Neglecting cell tissue, the amount of alkalinity required to carry out the reaction given in Eq. can be estimated by writing Eq. as follows:

69. The biomass synthesis reaction

70. Growth Kinetics
: g-VSS/g-VSS
Effect of DO

71. BIOLOGICAL DENITRIFICATION

72. Types of denitrification processes and the reactors used for their implementation
substrate driven (preanoxic denitrification) : Modified Ludzak-Ettinger (MLE) process
endogenous driven (postanoxic denitrification).

73. Stoichiometry of Biological Denitrification
In biological nitrogen removal processes, the electron donor is typically one of three
sources:
the bsCOD in the influent wastewater,
the bsCOD produced during endogenous decay,
an exogenous source such as methanol or acetate.
: often used to represent the biodegradable organic matter in wastewater