I-DEV0328: Calculation of the BOD5 for the dehydrated sludge disposed anaerobically

Deviation:
The anaerobic disposal of sludge is a contingency. This contingency started on the previous monitoring period (01 Jun 2006 – 31 Oct 2006) and was closed definitively on the present monitoring period.

According to the previous Request for Deviation presented and approved by the Board for the last monitoring period, the PP proposes to calculate the BOD5 of the sludge used to calculate the leakage from anaerobic disposal of sludge, instead of monitor this parameter as per AM0006.version 1. The proposed approach is to calculate the BOD5 of the sludge by means of a mass balance taking into account the monitored BOD5 of the manure flow or influent and the monitored BOD5 of the effluent of the treatment system. The following figure shows the inlet and outlet flows of the system:

The following equation represents the mass balance used to calculate the BOD5 of the sludge.

Influent flow, BOD5influent, BOD5effluent, and sludge flow are monitored. Effluent flow is considered to be influent flow minus sludge flow. Therefore, the BOD5 of the sludge can be calculated as follows:

NOTE:WHEN INSERTING THE INFORMATION FOR THIS DEVIATION WE ENCOUNTERED DIFFICULTIES WITH THE FORMATING OF THE ABOVE EQUATIONS. PLEASE REFER TO (REF-1) GRAPHICAL REPRESENTATION OF THE ABOVE INFORMATION IN .PDF FORMAT.

In order to calculate an average value of the BOD5 of the sludge in a monthly basis, as per the monitoring methodology AM0006 version 1 (page 20), it is required monthly registries of the monitored BOD5 of the influent, the monitored BOD5 of the effluent, the influent flow, and the sludge flow. The calculated monthly average value of the BOD5 of the sludge can be used on equation (4) from AM0006 version 1 to calculate the long term BOD to estimate methane leakage from sludge disposed anaerobically in a month basis using equation (14) from AM0006 version 1.

Reason for requesting a deviation:

During the monitoring period from 01 November 2006 to 31 December 2007 there was a contingency and the sludge from Pocillas was disposed anaerobically (from 01 November 2006 to 31 July 2007). This contingency started on the previous monitoring period. A Request for deviation was presented and approved by the board for this contingency, and this only the continuation of the same contingency on the current monitoring period.
This contingency was an isolated event, which the PP transparently disclosed with the DOE. Since July 2007 all the sludge is being managed aerobically. Agrosuper don’t expect to front contingencies regarding anaerobical management of the sludge in the near future.
The PP wants to emphasize that the anaerobic disposal of the sludge is a contingency that occurred after the registration of the project, so the original monitoring plan did not make any reference to the BOD5 of the sludge. Due to this contingency the leakages related to the anaerobic management of the sludge have to be accounted. Then, according to AM0006 version 1, a value of the BOD5 of the sludge is needed in order to estimate this leakage.


According to AM0006 version 1, “it is necessary to monitor the biochemical oxygen demand (BOD)” of the treated sludge (page 15). Nonetheless, in Chile there is not any standard and no laboratory has accreditation to measure the BOD5 of a dehydrated sludge. The Chilean norm for analytical methods of wastewaters “Norma Chilena Oficial NCh2313/5.Of96” and the accredited laboratories in Chile do not allow the measurement of BOD5 in a dehydrated sludge, because of the amount of dilutions that must be done to fulfil the conditions of the analytical method. This results in a high level of uncertainty. This is sustained by the fact that the international norms for BOD5 measurements:
(DIN-EN-1899-1: Water Quality -Determination of Biochemical Oxygen Demand After N Days (BODn) - Part 1: Dilution and Seeding Method with Allylthiourea Addition and DIN-EN-1899-2: Water Quality -Determination of Biochemical Oxygen Demand After N Days (BODn) - Part 2: Method for Undiluted Samples) do only include non-diluted water as applicability showing that a measurement of BOD5 in sludge (only possible through a dilution of the sample) is not regulated and therefore any measurement done is connected to a unknown uncertainty, which can not be acceptable for verification purposes.

Nonetheless, and against the laboratory will, a BOD5 analysis was performed on 29/08/2007 to a single sludge sample, in order to verify the calculated BOD5 using the proposed method for the present monitoring period. The laboratory stated that the analysis was only performed by Agrosuper request, but was not valid due to high error in the result. The result of the BOD5 laboratory tests in the sludge was of 20.100 mg/L. On the contrary, according to the proposed method, the monthly average BOD5 of the sludge calculated is between 58.863 and 87.018 mg/L for the period when the contingency occurred. Therefore, the proposed approach is more conservative as the suggested by the methodology.

It is important to remark that the Chilean standard “Norma Chilena Oficial NCh2313/5.Of96” re-quires the BOD5 analysis is performed 6 hours after the sample taking and never after 24 hours.
Agrosuper has monthly registries of the monitored BOD5 of the influent and the monitored BOD5 of the effluent and daily registries of the influent flow, and sludge flow for the monitoring period which was verified by the DOE. Then, considering these registries it is possible to estimate a monthly average value for the BOD5 of the sludge.

In order to get a reliable calculation of leakage of anaerobic sludge management, it is proposed to calculate the BOD5 by means of a mass balance. The PP and the DOE believe that this method of calculation is the most conservative and accurate approach to get the organic matter content in the dehydrated sludge, i.e., the BOD5, and not the way it is currently requested in the methodology.
For all these reasons, we would like to ask the Executive Board to consider this as satisfactory to comply with the monitoring procedure.

In order to be prepared for possible contingencies in the future, we are available for recommen-dations from the Executive Board regarding the implementation of international standard methods to measure de BOD5 of a dehydrated sludge. This procedure requires working with the Chilean Institute of Normalization (INN), which is part of the Chilean Quality System and represents the International Organization for Standardization (ISO). The implementation process may last several years.

The deviation does not require a revision of the monitoring plan because the sludge started to be composted.

The leakage for Pocillas in a theoretical scenario with measured BOD5 of the sludge (20.100 mg/L, single sample taken on 29/08/07, not certified laboratory analysis thus not reliable) is 921% lower than the leakage calculated using the proposed deviation:

Month/ Leakage - Non conservative[Ton CO2e]/Leakage - Conservative [Ton CO2e]
Nov 06/ 264/ 1,377
Dec 06/ 243/ 2,837
Jan 07/ 235/ 3,340
feb-07/ 192/ 2,191
mar-07/ 278/ 3,258
apr-07/ 346/ 6,063
may-07/ 500/ 6,189
jun-07/ 668/ 2,865
jul-07/ 479/ 4,619
TOTAL/ 3,205/ 32,739

The total emission reductions with and without the deviation are:

Site Total emission reductions without deviation
[Ton CO2e] Total emission reductions with deviation
[Ton CO2e]
Pocillas 219,145 189,611

NOTE: WHEN INSERTING THE INFORMATION FOR THIS DEVIATION WE ENCOUNTERED DIFFICULTIES WITH THE FORMATING OF THE ABOVE DATA SETS. PLEASE REFER TO (REF-1) TABULAR REPRESENTATION OF THE ABOVE INFORMATION IN .PDF FORMAT.

Therefore, the requested deviation is conservative against the methodology AM0006 version 1.