Effects of co-substrates’ mixing ratios and loading rate variations on food and agricultural wastes’ anaerobic co-digestion performance

Abstract

Tunisia is one of the developing countries which faces crucial challenges, the most prominent of which are the production of organic waste, the need for an appropriate waste treatment, and the demand for water and energy conservation. To this end, the present research was designed to develop a technical concept on closed cycle “biowaste to bioenergy” treating food waste (FW) through combined biological processes. In this approach, semi-continuous anaerobic co-digestion (ACoD) of FW, wheat straw (WS), and cattle manure (CM) was tested to investigate the relationship between the effect of the feedstock mixtures and C:N ratio on biogas and digestate generation at different organic loading rates (OLRs) ranging from 2 to 3.6 kg VS/m3.d. Results showed that the mono-digested FW was optimal and reached 565.5 LN/kg VSin at an OLR of 2.4 kg VS/m3.d, and then a drop of biogas production was recorded. However, for co-digested substrates, the optimum mixture ratio was FW:CM 75:25, where 62%, 39.89%, 91.26%, 130.9%, and 119.97% of the biogas yield improved for OLRs ranging from 2 to 3.6 kg VS/m3.d, respectively. Admittedly, the target of this work was to enhance the ACoD process, but it also examined the exploitation of different AD effluents. Therefore, special attention was paid to the generated digestates to decide how it can be efficiently upcycled later. Thus, the closed cycle “biowaste to bioenergy” treatment met two of the major Tunisian concerns: efficient organic waste management and sustainable bioenergy production.

Impacts of Anaerobic Co-Digestion on Different Influencing Parameters: A Critical Review

“…The major drawback of food waste digestion is the fast hydrolysis rate and the resulting drop in pH (<5.5) because of the accumulation of volatile fatty acids [80]. Therefore, co-digestion of food waste with stubborn feedstocks can help to retard the hydrolysis rate and reduce the VFAs [81]. El et al [81] co-digested agricultural waste, such as wheat straw and cow manure, with food waste in semi-continuous mesophilic AD and considered the effect of mixing ratio, C/N ratio, and variation of organic loading rates from 2 to 3.6 kg VS/m 3 d on the digester performance.…”

“…Therefore, co-digestion of food waste with stubborn feedstocks can help to retard the hydrolysis rate and reduce the VFAs [81]. El et al [81] co-digested agricultural waste, such as wheat straw and cow manure, with food waste in semi-continuous mesophilic AD and considered the effect of mixing ratio, C/N ratio, and variation of organic loading rates from 2 to 3.6 kg VS/m 3 d on the digester performance. The result demonstrated that the highest biogas yield increased by 119.97% for the organic load of 3.6 kg VS/m 3 d fed with the optimum mixing ratio of FW:CM (75:25) and a C/N ratio of 20.03.…”

Digestate Post-treatment and Upcycling: Unconventional Moisturizing Agent for Food Waste In-Vessel Composting

“…In fact, the feasibility of anaerobic treatments depends significantly on the effectiveness of end-products uses. Therefore, to unlock the sustainability of anaerobic process, digestate-uses gain progressively attention [35]. To this end, the current research work investigated whether the generated AD-effluent met the required criteria to be efficiently exploited for agricultural purposes.…”