Odour is a tricky business. There is possibly nothing more subjective than odour, or more subject to variability between subjects, and there is no getting around the fact that sewage is smelly, even when fresh. There are also psychological effects which can make even very low level of odour seem intolerable. Robust sampling and measurement of odorous air is expensive and time consuming. What constitutes a nuisance is therefore hard to pin down.
I tend not to bother too much with the psychology. As an engineer, I am interested in whether there are any problems with the specification, design, installation, operation or maintenance of the plant which would be expected to produce abnormal types or levels of odour.
I have also been designing and pricing debottlenecking modifications to a commercial effluent treatment plant this week, and bidding for a couple of interesting overseas contracts.
My plant layout book is now available in the UK at least via Amazon and Elsevier sites.