Anaerobic digestion (AD) is one of the traditional technologies for treating organic solid wastes, but its
economic bene
fi
t is sometimes questioned. To increase the economic feasibility of the treatment process,
the aim of this study was to recover not only biogas from food waste but lactic acid (LA) as well. At
fi
rst,
LA fermentation of food waste (FW) was conducted using an indigenous mixed culture. During the
operation, temperature was gradually increased from 35
Cto55
C, with the highest performance
attained at 50
C. At 50
C and hydraulic retention time (HRT) of 1.0 d, LA concentration in the broth was
40 kg LA/m
3
, corresponding to a yield of 1.6 mol LA/mol hexose
added
. Pyrosequencing results showed that
Lactobacillus
(97.6% of the total number of sequences) was the predominant species performing LA
fermentation of FW. The fermented broth was then centrifuged and LA was extracted from the super-
natant by the combined process of nano
fi
ltration and water-splitting electrodialysis. The process could
recover highly puri
fi
ed LA by removing 85% of mineral ions such as Na
þ
,K
þ
,Mg
2
þ
, and Ca
2
þ
and 90% of
residual carbohydrates. Meanwhile, the solid residue remained after centrifugation was further fer-
mented to biogas by AD. At HRT 40 d (organic loading rate of 7 kg COD/m
3
/d), the highest volumetric
biogas production rate of 3.5 m
3
/m
3
/d was achieved with a CH
4
yield of 0.25 m
3
CH
4
/kg COD. The mass
fl
ow showed that 47 kg of LA and 54 m
3
of biogas could be recovered by the developed process from 1
ton of FW with COD removal ef
fi
ciency of 70%. These products have a higher economic value 60 USD/ton
FW compared to that of conventional AD (27 USD/ton FW).