Leachate biotic and abiotic effects on solid state anaerobic digestion

Batch mode solid state anaerobic digestion (SSAD), with leachate recirculation, is the most adapted technology to treat manure with high solid content. Leachates play an important role for this process. Then biotic and abiotic effects of leachates were studied with six small scale SSAD reactors (6 L). In the first experiment, reactors were fed with cow manure and 4 different leachates with different origins (anaerobic wastewater sludge, agricultural SSAD) or biologically inert (phosphate buffer, autoclaved). And in the second experiment microbial impact of leachate was revealed by following bacteria and archaea into the manure-leachate system. Results highlight the beneficial role of leachate for a quick start, mainly due to its buffer capacity also, the presence of an inoculated leachate is not necessary for the proper operation of SSAD process using manure. For the biotic point of view, observation suggests that the bacterial and archaeal communities’ structure observed during the second experiment gradually changed towards an “optimal”, more stable structure for manure and for leachates, communities were only slightly affected by the process.