Application of solar drying as a pre-treatment method for storing wet feedstocks prior to use in anaerobic digesters: Effect on methane production and digestate composition

[Display omitted] •Solar drying process had small effect on pH, TOC, TKN and vS of the initial materials.•The addition of solar dried feedstocks increased the biogas production by 1.7 times.•In all cases, the estimated biodegradability of mixtures was over 50%•vS removal was 23% for the maximum biogas production. The objective of this study was to examine for the first time, the effect of solar-dried food waste (FW) and a mixture of FW with olive mill wastewater (OMW) on the anaerobic digestion of liquid pig manure (LPM) and cow manure (CM). A series of laboratory experiments were conducted using continuously operating reactors at mesophilic conditions. Solar-dried feedstocks were added to increase the initial volatile solids (VS) content in the feedstock (LPM and CM) by 20 % in both cases. The hydraulic retention time (HRT) was set at 20 days. The results show that the addition of solar dried feedstocks increased biogas production by 1.7 times. The reactor treating LPM and CM produced 403 – 427 ml/l/d biogas. After the addition of solar dried feedstocks, the biogas production reached the value of 711 ml/l/d and 676 ml/l/d for FW and the mixture of FW with OMW, respectively. In all cases, the estimated biodegradability of mixtures was over 50 %, while the VS removal was 23 % for maximum biogas production.