## 3 Results and Discussion
### Anaerobic Digestion (AD) of OFMSW and Bio-Delignificated GW  
In order to assess the effectiveness of bio-delignification in improving biodegradability and enhancing biogas generation, batch AD assays of untreated and bio-delignified GW co-digested with OFMSW were carried out. Figure 1 compares the cumulative biogas production as a function of time (30 days) that occurred during AD of OFMSW, untreated GW, OFMSW + untreated GW, and OFMSW + GW treated with BA. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Treatment** & **TS** **(\%)** & **VS*** **(\%)** \\ \hline BA * & 92.4 & 79.5 \\ Chlorine & 88.8 & 75.3 \\ Dil. sulfuric acid & 89.6 & 81.5 \\ Sodium hydroxide & 73.2 & 68.1 \\ \hline \hline \end{tabular}  
* BA = _Bjerhardera adusta,** TS = total solids; *** VS = volatile solids.  
\end{table} 
Table 3: Variation of the TS and VS content of GW with different delignification treatments. As seen, pretreatment of GW with BA was certainly advantageous in increasing biogas yield during co-digestion. After 30 days, the cumulative biogas production increased by more than 80% compared to the cumulative biogas production from the sole OFMSW, from 4720 to 8550 \(\mathrm{Nm^{3}}/\)ton SV, respective. This occurrence validates the fact that pretreatment with BA promotes lignin degradation and consequently promotes hydrolysis of the cellulose and hemicellulose present in GW and their biodgestibility to biogas. Compared with the co-digestion of OFMSW and untreated GW, it is evident how the presence of ligneous residues mixed with OFMSW has a slightly negative effect on the final cumulative yield, with a reduction of about 15% (4000 \(\mathrm{Nm^{3}}/\)ton FM), probably due to spatial interferences induced by untreated GW fragments that make it difficult for hydrolytic bacteria to reach the promptly fermentable sugars in OFMSW. Untreated GW alone obtained a cumulative production lower than 3000 \(\mathrm{Nm^{3}}/\)ton FM. These results suggest that bio-delignification is suitable as a pretreatments for AD, including accessibility of particles to microbial activity. As observed in Figure 2, about 90% of the overall biogas production from co-digestion of OFMSW and treated GW was obtained in the first 15 days, arriving at over 95% in 20 days. The two peaks, at days 5 and 12, were probably due to the different types of organic matters available for the hydrolytic microbial consortium. OFSMW shows a daily production, characterized by two peaks as well, the first due to promptly fermentable sugars in food waste and the second at days 7-20 by AD of slowly fermentable or complex organic matter. OFMSW + untreated GW had the same trend as the sole OFMSW, with smooth peaks of production. Figure 1: Cumulative biogas production during anaerobic co-digestion of OFMSW and GW, treated with BA and untreated, compared with AD of OFMSW and untreated GW. Control corresponds to the sole inoculum AD without the addition of biomass. Data are expressed as \(\mathrm{Nm^{3}}\) of biogas per ton of FM (OFMSW = organic fraction of municipal solid waste; GW = green waste; BA = _Bjerkandera adusta_; AD = anaerobic digestion; FM = fresh matter). Reduction in AD time along with an increased biogas production is another advantageous outcome of BA pretreatment of GW in co-digestion with OFMSW. A duration as short as possible is a pivotal parameter in the AD process setup, to increase plant productivity, use the smallest reactor volume, and reduce the cost of operation [74]. Moreover, the opportunity to increase substrate biodegradability also permits for the enhancement of the overall efficiency of the AD plant [75]. Table 4 shows the increase of productivity during co-digestion of OFMSW and treated GW based on 30 days of process compared with those of the other two cases. Moreover, considering the opportunity to reduce the hydraulic retention time to 20 days, productivity increased to 500 \(\text{Nm}^{3}/\text{ton FM}^{*}\)day. This could be of relevance in the case of application on a higher scale in terms of economic issues of the plant's management.