Optimization of solid state anaerobic digestion of the OFMSW by digestate recirculation: A new approach

•Solid State Anaerobic Digestion (SSAD) of OFMSW can be optimized by irrigation with digestate.•Digestate spreading allows keeping optimal process parameters and high hydrolysis rate.•The 18.4% of CH4 was produced in the reactor, leaving the 49.7% in the percolate.•Successive CSTR feed with percolate shows a biogas enriched in methane (more than 80%).•The proposed process allow producing the 68% of OFMSW potential CH4, getting high quality organic amendment.

Dry anaerobic digestion (AD) of OFMSW was optimized in order to produce biogas avoiding the use of solid inoculum. Doing so the dry AD was performed irrigating the solid waste with liquid digestate (flow rate of 1:1.18-1:0.9 w/w waste/digestate; 21 d of hydraulic retention time - HRT) in order to remove fermentation products inhibiting AD process.Results indicated that a high hydrolysis rate of organic matter (OM) and partial biogas production were obtained directly during the dry AD. Hydrolysate OM was removed from digester by the percolate flow and it was subsequently used to feed a liquid anaerobic digester. During dry AD a total loss of 36.9% of total solids was recorded. Methane balance indicated that 18.4% of potential methane can be produced during dry AD and 49.7% by the percolate. Nevertheless results obtained for liquid AD digestion indicated that only 20.4% and 25.7% of potential producible methane was generated by adopting 15 and 20 days of HRT, probably due to the AD inhibition due to high presence of toxic ammonia forms in the liquid medium.