Biodegradation in TMVOC
Quick question regarding how to incorporate the biodegradation into a TMVOC model. I would like to see what would be the significance of a biodegradation in a overall fate and transport of a contaminant. So, I added a number to the decay constant in CHEMP.9 tab (i.e. ALAM). However, when I look at the results I do not see any outputs pertaining to the biodegradation in the output file. The thing is for instance, if I activate the sorption onto the solid, there will be a column added in the output file under material balance section indicating how much of a particular chemical has been absorbed onto the grains. However, with the biodegradation regardless of the value (i.e. 0 or > 0) assigned to the “ALAM”, there is no additional information pertaining to biodegradation. How can I extract the biodegradation effect? Could anyone please advise on this?
An answer to an old post...
TMVOC (Pruess and Battistelli, 2002) implements a very simple VOC biodegradation capability based on a standard exponential decay law. It is the same approach previously used by T2VOC (Falta et al., 1995). The option works, but no specific printout for the degraded mass of VOCs was foreseen at the time.
Looking at the VOC mass inventory over time does not help much, as VOC mass can change because of degradation and inflows/outflows in/from the modeled domain.
From subroutine MULTI of TMVOC, below is reproduced the code fragment which is evaluating the VOC mass change due to decay (probably on a mole basis).
For debugging purposes, the possibility to printout the mass(mole) change for each element (for each component, at each iteration but only for the non incremented primary variables) due to biodegradation was included.
if(eosn(1).eq.'TMVOC1 '.and.nk.gt.2) then
200 FORMAT(' AT ELEMENT *',A5,'* ',8(1X,E12.6))
In principle the mass change due to biodegradation can be printed in the output file, but the printout will be hard to read and manipulate unless for quite simple grids. It could be feasible to ask for the printout just for a specific time, may be to be invoked using a restart.
Otherwise, the TMVOC code should be modified. D(K,1) values should be saved in a common for all elements and made available within sub OUT for a specific printout. Something similar could be done in sub BALLA too, for the cumulative degraded mass over time.
A more rigorous approach for the modeling of biodgradation reactions was implemented in TMVOCBio (Battistelli, 2004, Modeling Biodegradation of Organic Contaminants under Multiphase Conditions with TMVOCBio, VZJ Vol.3 No.3, p.875-883). TMVOCBio has been coupled to iTOUGH2 (Jung and Battistelli, 2016, User’s Guide for Biodegradation Reactions in TMVOCBio, LBNL-1005179).