One could use Douglas's Purity and Danger as an analytical tool in relation to Coetzee's Disgrace in that it helps to explain the role that the ritualized expelling of pollution plays in any given society.
The protagonist of Disgrace, David Lurie, has morally polluted the society in which he lives by engaging in all manner of sleazy, immoral behavior. Seeing himself as some kind of Byronic rebel against the restrictive norms of society, Lurie believes he can pretty much act how he pleases, irrespective of the emotional wreckage he leaves in his wake.
But as Mary Douglas shows us in Purity and Danger, each society has a mechanism in place for getting rid of dirt, which can broadly be defined as that which doesn't fit in, which doesn't belong. Lurie certainly doesn't belong in polite society, given his predilection for serial adultery. Nor, for that matter, does his daughter Lucy, who, as a lesbian, is one of society's outcasts.
Applying Douglas's concept of dirt and pollution to Disgrace, it becomes possible to see how even modern-day societies, those far removed from the primitive societies of old, still need to have certain values in place that remove from their midst what is generally regarded as unclean.