40 CFR § 98.353 - Calculating GHG emissions.

(a) For each anaerobic reactor and anaerobic lagoon, estimate the annual mass of CH4 generated according to the applicable requirements in paragraphs (a)(1) through (a)(2) of this section.

(1) If you measure the concentration of organic material entering the anaerobic reactors or anaerobic lagoon using methods for the determination of chemical oxygen demand (COD), then estimate annual mass of CH4 generated using Equation II-1 of this section.

${CH}_4{G}_n=\sum _{w=1}^{52}\left[{\mathrm{Flow}}_w*{\mathrm{COD}}_w*B_o*\mathrm{MCF}*0.001\right]\text{(Eq. II-1)}$

Where:

CH4Gn = Annual mass CH4 generated from the nth anaerobic wastewater treatment process (metric tons).

n = Index for processes at the facility, used in Equation II-7.

w = Index for weekly measurement period.

Floww = Volume of wastewater sent to an anaerobic wastewater treatment process in week w (m 3/week), measured as specified in § 98.354(d).

CODw = Average weekly concentration of chemical oxygen demand of wastewater entering an anaerobic wastewater treatment process (for week w)(kg/m 3), measured as specified in § 98.354(b) and (c).

B0 = Maximum CH4 producing potential of wastewater (kg CH4/kg COD), use the value 0.25.

MCF = CH4 conversion factor, based on relevant values in Table II-1 of this subpart.

0.001 = Conversion factor from kg to metric tons.

(2) If you measure the concentration of organic material entering an anaerobic reactor or anaerobic lagoon using methods for the determination of 5-day biochemical oxygen demand (BOD5), then estimate annual mass of CH4 generated using Equation II-2 of this section.

${\mathrm{CH}}_4{G}_n=\sum _{w=1}^{52}\left[{\mathrm{Flow}}_w*{\mathrm{BOD}}_{5,w}*B_o*\mathrm{MCF}*0.001\right]\text{(Eq. II-2)}$

Where:

CH4Gn = Annual mass of CH4 generated from the anaerobic wastewater treatment process (metric tons).

n = Index for processes at the facility, used in Equation II-7.

w = Index for weekly measurement period.

Floww = Volume of wastewater sent to an anaerobic wastewater treatment process in week w(m 3/week), measured as specified in § 98.354(d).

BOD5,w = Average weekly concentration of 5-day biochemical oxygen demand of wastewater entering an anaerobic wastewater treatment process for week w(kg/m 3), measured as specified in § 98.354(b) and (c).

B0 = Maximum CH4 producing potential of wastewater (kg CH4/kg BOD5), use the value 0.6.

MCF = CH4 conversion factor, based on relevant values in Table II-1 to this subpart.

0.001 = Conversion factor from kg to metric tons.

(b) For each anaerobic reactor and anaerobic lagoon from which biogas is not recovered, estimate annual CH4 emissions using Equation II-3 of this section.

${\mathrm{CH}}_4{E}_n={\mathrm{CH}}_4{G}_n\text{(Eq. II-3)}$

Where:

CH4En = Annual mass of CH4 emissions from the wastewater treatment process n from which biogas is not recovered (metric tons).

CH4Gn = Annual mass of CH4 generated from the wastewater treatment process n, as calculated in Equation II-1 or II-2 of this section (metric tons).

(c) For each anaerobic sludge digester, anaerobic reactor, or anaerobic lagoon from which some biogas is recovered, estimate the annual mass of CH4 recovered according to the requirements in paragraphs (c)(1) and (c)(2) of this section. To estimate the annual mass of CH4 recovered, you must continuously monitor biogas flow rate and determine the volume of biogas each week and the cumulative volume of biogas each year that is collected and routed to a destruction device as specified in § 98.354(h). If the gas flow meter is not equipped with automatic correction for temperature, pressure, or, if necessary, moisture content, you must determine these parameters as specified in paragraph (c)(2)(ii) of this section.

(1) If you continuously monitor CH4 concentration (and if necessary, temperature, pressure, and moisture content required as specified in § 98.354(f)) of the biogas that is collected and routed to a destruction device using a monitoring meter specifically for CH4 gas, as specified in § 98.354(g), you must use this monitoring system and calculate the quantity of CH4 recovered for destruction using Equation II-4 of this section. A fully integrated system that directly reports CH4 quantity requires only the summing of results of all monitoring periods for a given year.

$R_n=\sum _{m=1}^M\left[{\left(V\right)}_m*{\left(K_{\mathrm{MC}}\right)}_m*\frac{{\left(C_{\mathrm{CH}4}\right)}_m}{100\%}*0.0423*\frac{520°R}{{\left(T\right)}_m}*\frac{{\left(P\right)}_m}{1\mathrm{atm}}*\frac{0.454}{\mathrm{1,000}}\right]\text{(Eq. II-4)}$

Where:

Rn = Annual quantity of CH4 recovered from the nth anaerobic reactor, sludge digester, or lagoon (metric tons CH4/yr)

n = Index for processes at the facility, used in Equation II-7.

M = Total number of measurement periods in a year. Use M = 365 (M = 366 for leap years) for daily averaging of continuous monitoring, as provided in paragraph (c)(1)of this section. Use M = 52 for weekly sampling, as provided in paragraph (c)(2)of this section.

m = Index for measurement period.

Vm = Cumulative volumetric flow for the measurement period in actual cubic feet (acf). If no biogas was recovered during a monitoring period, use zero.

(KMC)m = Moisture correction term for the measurement period, volumetric basis.

= 1 when (V)m and (CCH4)m are measured on a dry basis or if both are measured on a wet basis.

= 1−(fH2O)m when (V)m is measured on a wet basis and (CCH4)m is measured on a dry basis.

= 1/[1−(fH2O)m] when (V)m is measured on a dry basis and (CCH4)m is measured on a wet basis.

(fH2O)m = Average moisture content of biogas during the measurment period, volumetric basis, (cubic feet water per cubic feet biogas).

(CCH4)m = Average CH4 concentration of biogas during the measurement period, (volume %).

0.0423 = Density of CH4 lb/cf at 520 °R or 60 °F and 1 atm.

520 °R = 520 degrees Rankine.

Tm = Average temperature at which flow is measured for the measurement period (°R). If the flow rate meter automatically corrects for temperature to 520° R, replace “520° R/Tm” with “1”.

Pm = Average pressure at which flow is measured for the measurement period (atm). If the flow rate meter automatically corrects for pressure to 1 atm, replace “Pm/1” with “1”.

0.454/1,000 = Conversion factor (metric ton/lb).

(2) If you do not continuously monitor CH4 concentration according to paragraph (c)(1) of this section, you must determine the CH4 concentration, temperature, pressure, and, if necessary, moisture content of the biogas that is collected and routed to a destruction device according to the requirements in paragraphs (c)(2)(i) through (c)(2)(ii) of this section and calculate the quantity of CH4 recovered for destruction using Equation II-4 of this section.

(i) Determine the CH4 concentration in the biogas that is collected and routed to a destruction device in a location near or representative of the location of the gas flow meter at least once each calendar week; if only one measurement is made each calendar week, there must be least three days between measurements. For a given calendar week, you are not required to determine CH4 concentration if the cumulative volume of biogas for that calendar week, determined as specified in paragraph (c) of this section, is zero.

(ii) If the gas flow meter is not equipped with automatic correction for temperature, pressure, or, if necessary, moisture content:

(A) Determine the temperature and pressure in the biogas that is collected and routed to a destruction device in a location near or representative of the location of the gas flow meter at least once each calendar week; if only one measurement is made each calendar week, there must be at least three days between measurements.

(B) If the CH4 concentration is determined on a dry basis and biogas flow is determined on a wet basis, or CH4 concentration is determined on a wet basis and biogas flow is determined on a dry basis, and the flow meter does not automatically correct for moisture content, determine the moisture content in the biogas that is collected and routed to a destruction device in a location near or representative of the location of the gas flow meter at least once each calendar week that the cumulative biogas flow measured as specified in § 98.354(h) is greater than zero; if only one measurement is made each calendar week, there must be at least three days between measurements.

(d) For each anaerobic sludge digester, anaerobic reactor, or anaerobic lagoon from which some quantity of biogas is recovered, you must estimate both the annual mass of CH4 that is generated, but not recovered, according to paragraph (d)(1) of this section and the annual mass of CH4 emitted according to paragraph (d)(2) of this section.

(1) Estimate the annual mass of CH4 that is generated, but not recovered, using Equation II-5 of this section.

${CH}_4{L}_n=R_n*\left(\frac{1}{\mathrm{CE}}-1\right)\text{(Eq. II-5)}$

Where:

CH4Ln = Leakage at the anaerobic process n (metric tons CH4).

n = Index for processes at the facility, used in Equation II-7.

Rn = Annual quantity of CH4 recovered from the nth anaerobic reactor, anaerobic lagoon, or anaerobic sludge digester, as calculated in Equation II-4 of this section (metric tons CH4).

CE = CH4 collection efficiency of anaerobic process n, as specified in Table II-2 of this subpart (decimal).

(2) For each anaerobic sludge digester, anaerobic reactor, or anaerobic lagoon from which some quantity of biogas is recovered, estimate the annual mass of CH4 emitted using Equation II-6 of this section.

${\mathrm{CH}}_4{E}_n={\mathrm{CH}}_4{L}_n+R_n\left[1-[\left(D_{E1}\times f_{\mathrm{Dest}\_1}\right)*\left({\mathrm{DE}}_2\times f_{\mathrm{Dest}\_2}\right)]\right)\text{(Eq. II-6)}$

Where:

CH4En = Annual quantity of CH4 emitted from the process n from which biogas is recovered (metric tons).

n = Index for processes at the facility, used in Equation II-7.

CH4Ln = Leakage at the anaerobic process n, as calculated in Equation II-5 of this section (metric tons CH4).

Rn = Annual quantity of CH4 recovered from the nth anaerobic reactor or anaerobic sludge digester, as calculated in Equation II-4 of this section (metric tons CH4).

DE1 = Primary destruction device CH4 destruction efficiency (lesser of manufacturer's specified destruction efficiency and 0.99). If the biogas is transported off-site for destruction, use DE = 1.

fDest_1 = Fraction of hours the primary destruction device was operating calculated as the annual hours when the destruction device was operating divided by the annual operating hours of the biogas recovery system. If the biogas is transported off-site for destruction, use fDest = 1.

DE2 = Back-up destruction device CH4 destruction efficiency (lesser of manufacturer's specified destruction efficiency and 0.99).

fDest_2 = Fraction of hours the back-up destruction device was operating calculated as the annual hours when the destruction device was operating divided by the annual operating hours of the biogas recovery system.

(e) Estimate the total mass of CH4 emitted from all anaerobic processes from which biogas is not recovered (calculated in Eq. II-3) and all anaerobic processes from which some biogas is recovered (calculated in Equation II-6) using Equation II-7 of this section.

${CH}_4{E}_T=\sum _{n=1}^j{CH}_4{E}_n\text{(Eq. II-7)}$

Where:

CH4ET = Annual mass CH4 emitted from all anaerobic processes at the facility (metric tons).

n = Index for processes at the facility.

CH4En = Annual mass of CH4 emissions from process n (metric tons).

j = Total number of processes from which methane is emitted.

[75 FR 39767, July 12, 2010, as amended at 76 FR 73903, Nov. 29, 2011; 78 FR 71972, Nov. 29, 2013]