Development of an innovative technology using side stream vacuum evaporation for anaerobic digestion intensification and ammonia recovery

This work evaluated the application of a novel ex-situ vacuum-enhanced anaerobic digestion technology, IntensiCarbTM (IC), which decouples hydraulic retention time (HRT) from solids retention time (SRT), and strips ammonia at neutral pH. Four bench-scale reactors were daily fed with a 50/50 (v/v) mix of primary sludge (PS) and thickened waste-activated sludge (TWAS). Three reactors were operated at SRT 20d and intensification factors (IF = SRT/HRT) of 1 (control), 2, and 3, while the fourth was operated at an IF4 at SRT 30d. The findings showed that at an OLR of 5.1 ± 0.79 kgCOD/m3/d, which was 3 times the control, the COD and volatile solids reduction were maintained at around 50 %. The methanogenic community, the most vulnerable ones to high ammonia toxicity, was dominated by Methanosarcinaceae in IC digesters versus Methanoseata in the control digester. Specific methanogenic activity (SMA) and biomethanation potential tests (BMP) on the digestates indicated 35 %-62 % higher activity, relative to the control. The enhanced performance of the IC was due to a combination of increased biomass concentration, mitigation of ammonia toxicity at high loadings, and a microbial shift. Reduced digester size and increased organic loading rates (OLR) are two main benefits of IC-AD technology. Recovery of 50 % of influent total nitrogen in clean water is another promising aspect of IC-AD technology which enables running at high OLR but comparable ammonia concentration. The water recovery and a reduced N loading in recycle streams, thus minimizing the need for side-stream treatment and mainstream nitrogen removal, are additional benefits.