Impact of C/N ratios and organic loading rates of paper, cardboard and tissue wastes in batch and CSTR anaerobic digestion with food waste on their biogas production and digester stability

The C/N ratio and organic loading rates (OLRs) are the main constraint factors of anaerobic digestion (AD) which symbols in digestion mortifications due to the rapid accumulation of volatile fatty acids (VFAs) and total ammonia nitrogen (TAN). In this study, the addition of high C-content wastes; paper waste (PW), cardboard waste (CW), and tissue waste (TW) into food waste (FW) feedstock is individually taken into consideration. At first, batch anaerobic digestion is conducted at a balanced C/N ratio of waste materials and then CSTR anaerobic digestion is carried out at different OLRs to investigate the potential of biogas production and process stability, under mesophilic conditions. In batch anaerobic digestion, co-substrate (PW + FW) feedstock is outperformed the other co-substrate feedstocks in terms of biogas production and process stability due to slow formation of VFAs and stable microbial conversion of VFAs into biogas fuel. The highest specific biogas yield (SBY) of 651 mL/gVS and specific methane yield (SMY) of 350 mL/gVS with a 57% rate of biodegradability are obtained from (PW + FW) feedstock at OLR of 15 gVS/L d. Furthermore, (PW + FW) feedstock with superb performance is then subjected to investigate the optimum OLR in CSTR digester for 30 days. The SBY of 22 L/gVS and SMY of 13 L/gVS is obtained with the utmost rate of VS reduction of 96%. The pH, alkalinity, COD, TS reduction, VS reduction, VFAs, and TAN concentration are all in the optimal range at the C/N ratio of 25 and OLR of 2 gVS/L d. This study provides new information regarding the C/N ratio and OLR for AD own great potential in improving the methane yield and productivity of PW and FW.