I happened to stumble along youre dialouge here while searching out industiral gas production rates as a fubnction of volatile solids destruction.
After reading your post's it seems to me that you need to broaden your scope in terms of obtaining a comprehensive understanding of Anaerobic digestion.
I currently operate two such bio-reactors in New Jersey and have operate dozens of others over the last thirty or so years.
I would suggest that you spend some time researching at the water Environment Fedration website and on their chat logs. http://www.wef.org/Home
By the way no reactor symply "dies" unless it has undergone some form of toxic shock most reactors will have tell-tale signs of loss of efficiency such as large swings in VA/ALK ratios or increased Co2 - Ch 4 ratios.
I fyoud like to talk about his further please email me at EXDIR@SMRSA.org and I will gladly arrange a telphone interview to get you started on the right foot.
I also have a ton of realtime data thatg may be of interest to you