Effect of temperature and organic loading rate on siphon-driven self-agitated anaerobic digestion performance for food waste treatment

•Siphon-driven self-agitated anaerobic reactors was used for actual food waste treatment.•The effects of organic loading rate (OLR) and operating temperature were investigated.•Scum appeared in the mesophilic reactor at OLR of 7.3 kg-COD/m3/d.•Thermophilic reactor endured the increase in OLR up to 14.4 kg-COD/m3/d.•Sludge distribution and mixing frequency in the reactors were evaluated. The effects of organic loading rate (OLR) and operating temperature on the performance of siphon-driven self-agitated anaerobic reactor (SDSAR) in an on-site food waste (FW) treatment system were investigated. Two reactors were operated in parallel for comparison between mesophilic condition (35 ± 1 °C) and thermophilic condition (55 ± 1 °C). With HRT above 15 d and OLR below 4.8 kg-COD/m3/d, relatively high COD removal in the range of 84.5–92.3% was obtained in both reactors. The limits of the loading capacity of the mesophilic SDSAR were observed when OLR was further increased to 7.3 kg-COD/m3/d by shortening HRT. Blocking and gas production reduction occurred and COD removal decreased sharply to 75.9% in the mesophilic reactor. In contrast, the thermophilic reactor can be operated at this OLR with satisfactory COD removal and biogas production. Furthermore, at OLR of 14.4 kg-COD/m3/d, the COD removal was maintained as high as 87.5% in the thermophilic reactor. The conversion of influent COD to methane was maintained above 80% at all the OLR applied in both reactors. The results of this study indicated that thermophilic SDSAR is preferred for the on-site FW treatment.