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Quantifying Microorganisms and Their ActivityCE 421/521 Environmental BiotechnologyLecture for September 19, 2006Vaccari et al., Chapter 10
Two Events
• Microbial Growth (dX/dt)
• Substrate Disappearance (dS/dt)
• During balanced growth can use a surrogate measure of growth– Oxygen consumption– Carbon dioxide production– Methane production (anaerobic systems)
Growth vs Substrate Disappearance
0 0.1 0.2 0.3 0.4
T im e, h
0
0.4
0.8
1.2
1.6
2
Am
ou
nts
of S
ub
stra
te, B
iom
ass,
an
d O
xyg
en
, mg
CO
D L
-1
S ubstra te D isappearance
O xygen C onsum ed
B iom ass G enerated
Batch Growth Curve
Exponential Growth
• Doubling (generation) time
CSTR or Chemostat
V,X,S
Q, Xi, SiQ, Xe, Se
General mass balance;in – out – generation = accumulation
air
CSTR with settling
V,X,S
Q, Xi, SiQ+Qr, X, S
Q-Qw, Xe, S
Qr, Xr, S
Return activated sludge, RAS
http://www.water-technology.net/projects/chicago/images/Chicago01.jpg
Waste activated sludge, WAS
air
CSTR mass balance equations
Biogeochemcial Cycles (C, N, P, & S)
• composition of b_______ cell (molar formula: C5H7O2N with P 1/5 of the N requirement)
• limiting nutrients are _____ and _____
Nitrogen
• Atmosphere is _____% nitrogen, yet nitrogen is considered a l__________ n__________
• required in p____________
Organic nitrogen
N2NO3
- NH4+
NO2-
Nitrogen Cycle
Fixation
• 2x108 metric tons/y compared to 2.5x1010 metric tons C/y
• cyanobacteria & few others – non-symbiotic – Clostridia– symbiotic – Rhizobium
• .nitrogenase – requires Mg2+ & ATP (15 to 20 ATP/N2)
Assimilation• NH3 (NH4
+) preferred, will use NO3- but has to be
reduced to NH4+
• C/N ratio is approximately – 10:1 for aerobes– 150:1 for anaerobes– 50:1 for anaerobes in highly loaded (high rate)
system• cell composition is characterized by the empirical
formula: ______________with the P requirement as 1/5 the N requirement (alternatively C60H87O23N12P)
• in general cell composition is » 50% C» 20% O» 10-15% N» 8-10% H» 1-3% P» 0.5-1.5
Ammonification
• Breakdown of organic N to NH4+
• Examples:– Urea– proteins
Nitrification
• Two step process:
• requires 4.57 mg O2/mg NH4+- N
converted to NO3- – N
Nitrification Kinetics
m ax S
K S
S
K SNH
S NH
O
O O
4
4
2
2
where μmax = maximum specific growth rate, h-1KS = half saturation coefficient for ammonia, mg/L as NH4-NKO = half saturation coefficient, mg/L as O2Yield = mg biomass formed/mg ammonia utilized
Nitrosomonas Nitrobacter
parameter range typical (@20°C)
range typical (@20°C)
μmax
KS
KO
Yield
0.014 - 0.0920.06 - 5.60.3 - 1.30.04 - 0.13
0.0321.00.50.1
0.006 - 0.060.06 - 8.40.3 - 1.30.02 - 0.07
0.0341.30.680.05
Optimum pH for nitrifiers is around 8.0, range 7.5 - 8.5 (higher than for most other biologicalprocesses).
Nitrification Kinetics