SUPPLEMENTARY MATERIAL
Title: Factors controlling nitrous oxide emissions from a full-scale activated sludge system in the tropics
Authors: Ariane C. Brotto, Débora C. Kligerman*, Samara A. Andrade, Renato P. Ribeiro, Jaime L. M.
Oliveira, Kartik Chandran, William Z. de Mello
*Correspondent author: kliger@ensp.fiocruz.br
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Online Resource 1: Calculation of nitrogen mass balance of the system in study
With the data collected during the monitoring campaign it is possible to calculate the N removal during the biological treatment, and N
2
O emissions in the aeration tank. However, it was not given the data on the daily sludge production and the content of N in the sludge. Therefore, equation below was used to estimating the daily sludge production rate (Grady Jr. et al., 1999):
𝑊 = 𝐹
[(1 + 𝑓 𝑑 𝑏
𝐻 𝜃 𝑐
)𝑌
𝐻
(𝑆
𝑆
0
1 + 𝑏
𝐻 𝜃 𝑐
− 𝑆
𝑆
)]
𝑊 = 2.3 𝑥 10 9 𝑚𝑔 𝐶𝑂𝐷 𝑑𝑎𝑦 where 𝐹 is the influent flow rate, 1.46 x 10
-7
L day
-1
; 𝑓 𝑑
is the fraction active biomass contributing to debris, 0.2 mg debris COD/mg biomass COD (Grady Jr. et al. 1999); 𝑏
𝐻
is the decay for heterotrophs at
25 o
C; 0.22 day
-1
(USEPA, 2010), 𝜃 𝑐
is the sludge retention time, 3 days, 𝑌
𝐻
is the true growth yield for heterotroph at 25 o
C, 0.5 mg COD/mg COD substrate (USEPA, 2010); 𝑆
𝑆
0 is the Chemical oxygen demand
(COD) influent, 464 ± 117 mg COD/L; 𝑆
𝑆
is the COD effluent, 120 ± 78 mg COD/L.
In order to estimate the N content in the sludge and, therefore, the biomass assimilation of N, it is used the N:biomass COD ratio represented by the empirical formula C
5
H
7
O
2
N, which is 0.087 mg
N/mg COD (Grady Jr. et al. 1999): 𝑚𝑔 𝑁
0.087 𝑚𝑔 𝐶𝑂𝐷
𝑥 2.3 𝑥 10 9 𝑚𝑔 𝐶𝑂𝐷 𝑑𝑎𝑦
= 2.0 𝑥 10 5 𝑔
𝑁 𝑑𝑎𝑦
Figure 1 summarizes the N mass balance of the system in study.
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Figure S1 . Nitrogen mass balance of the system in study.
Reference
1S. Grady Jr. CPL, Daigger GT, Lim HC (1999) Biological wastewater treatment. Marcel Dekker, New
York.
2S. USEPA (2010) Nutrient Control Design Manual. EPA 600-R-1-100. Cincinnati, Ohio.
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Online Resource 2: Calculation of nitrogen requirement for nitrification
Calculation of the amount nitrogen required for assimilation per unit of substrate COD removed
(NR), determined directly from the stoichiometry of biomass growth:
𝑁𝑅 = 0.087 [
(1 + 𝑓
𝐷
. 𝑏
𝐻
1 + 𝑏
𝐻
. 𝜃
𝐶
. 𝜃
𝐶
) 𝑌
𝐻
] where, the amount of nitrogen required to form biomass that can be represented by the empirical formula
C
5
H
7
O
2
N is 0.087 mgN/mg biomass. If we assume that the nitrogen content of biomass debris is the same as that of active biomass, then the amount of nitrogen required per unit of substrate COD removed,
NR, is just 0.087 time the observed yield; f d
is the fraction of active mass contributing to biomass debris.
For the type of biomass normally found in biochemical operations for wastewater treatment it has a value of around 0.2 mg debris COD/mg biomass COD (Grady Jr. et al. 1999); b
H
is the decay coefficient for heterotrophs. For adjusted averaged temperature of 25 o C it is considered 0.22 day -1 (USEPA, 2010);
 c is the solids retention time of the bioreactor, which in this case is 3 days; Y
H
is the true growth yield for heterotrophs on COD/COD basis, assumed as 0.5 mg biomass COD/mg substrate COD (USEPA, 2010).
Table S1 . Nitrogen requirement for nitrification
Campaign COD removed
NR NR NH
4
+ removed a N avail b Nitrification
(month) (mg L -1 ) (mg N mg COD removed
-1 ) (mg N L -1 ) (mg N L -1 ) (mg N L -1 ) occurring?
April
May
June
459
228
375
0.031
0.031
0.031
July 306 0.031 a removed = influent - effluent b nitrogen available for nitrification
14.1
7.0
11.6
9.4
29.5
6.3
16.3
13.1
15.4
-0.7
4.7
3.7
Yes
Yes, low rate
Yes
Yes
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Reference
1S. Grady Jr. CPL, Daigger GT, Lim HC (1999) Biological wastewater treatment. Marcel Dekker, New
York.
2S. USEPA (2010) Nutrient Control Design Manual. EPA 600-R-1-100. Cincinnati, Ohio.
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