Synergy between anaerobic digestion and a post-treatment based on Thermophilic Aerobic Membrane Reactor (TAMR)

This work concerns the treatment of the liquid fraction of digestate, derived from two-stage anaerobic digestion process that treats bovine manure and corn silage, with a thermophilic aerobic membrane bioreactor (called TAMR) at pilot scale. The pilot plant was daily monitored about for 4 months; the temperature was maintained equal to 50°C and the average Organic Loading Rate (OLR) is 5.3 kg COD m-3 d-1. Results highlight high removal efficiencies of COD (> 94%) and total phosphorous (> 87%). The liquid fraction of TAMR (permeate), in view of a treatment in a municipal wastewater treatment plant that works in mesophilic conditions, shows good biodegradability; moreover, high ammonia content could be recovered by stripping the permeate and submit the ammonia rich gas to acidic absorption to produce ammonia salt (a valuable fertilizer). The solid fraction of TAMR (concentrate) shows an important neutralization effect due to the presence of calcium carbonate that derives from the reaction between the lime added and the carbon dioxide produced from organic matter degradation. Moreover, good hydrolytic effect on protein/carbohydrate solid substrate and sulfate reduction suggest the use of TAMR concentrate as supplement in anaerobic digestion process.