Predicting Biological Removal of Contaminants in Wastewater Treatment: QSBR Modeling

Abstract

Contaminant fate and transport models are a highly desirable alternative to direct measurement of environmental behavior for the very large number of so-called "emerging contaminants". In particular, it is desirable to estimate what fraction of emerging contaminant loading is removed by conventional wastewater treatment plant processes, so that the loading of organic wastewater contaminants (OWCs) into the environment can be assessed. In this thesis, we focused on prediction of biodegradation rate constants for removal of OWCs during activated sludge treatment. A Quantitative Structure-Biodegradability Relationship (QSBR) modeling approach was used to predict pseudo first-order biodegradation rate constants (k b ) based on molecular descriptors from commercially available computational chemistry software.A training dataset comprising 65 previously measured molecular structures was collected from nine different literature sources. This data was then used to create four QSBR models using

Transition-state rate theory sheds light on ‘black-box’ biodegradation algorithms

“…QSBRs may apply to specific media/inocula, 21 e.g. wastewater/ sludge, 22,23 sediment or surface water, 15 only. Low precisions [24][25][26] (e.g.…”

“…Indeed, limited information on the media and inocula may be available 3,21,35 which hampers model improvement. 3,22,[36][37][38] We can expect that after accounting for many such test-specific phenomena, the 'intrinsic biodegradability' of chemicals becomes apparent. 23,27,[39][40][41][42] Such an 'intrinsic biodegradation rate' might not entail information on microbial processes: adaptation, active transport, 43,44 the involvement of medium ( pH; organic carbon), nutrients, 45 and back-transformation 46 (i.e.…”

“…102) and V MAX ∝ K OW −0.35±0.09 (with V MAX in μmol min −1 mg PROTEIN −1 for aldehyde dehydrogenase activity), 80 depending on the limiting factor. 54 The influence of diffusion on biodegradation has previously been documented for specific chemical classes, shapes, and biotransformation pathways via surface area, 27,32 weight, 22 van der Waals radii, 103 or geometrical descriptors. 80 Taken together, electronic, steric, electrostatic, and/or hydrophobic factors determine k b values, thereby affecting the observed scaling factors with individual geometric descriptors.…”

“…On the basis of E HOMO , trifluoroacetate and oxalate are expected to have a low and high k b , respectively. In general, frontier orbital energies have been used widely to describe biodegradation, 22,32,112 as well as biotransformation. 80,84 The relation between k b and E HOMO characterizes a linear free-energy relationship (LFER) on the basis of ΔG r , 115,116 in which the thermodynamic driving force is oxidative.…”

Disentanglement of the chemical, physical, and biological processes aids the development of quantitative structure-biodegradation relationships for aerobic wastewater treatment

“…Thus, programs like STPWIN TM in EPI Suite emerged specifically for STPs but most predictions are semi-quantitative. In turn, Burgis (2012) sought to develop a quantitative model for biological removal in wastewater sludge, based on OECD tests and other laboratory assays. The authors found that test outcomes varied substantially between experiments, greatly hampering model development.…”