Abstract
Food waste and municipal sludge were used as the substrates for the biosynthesis of lactic acid in a batch fermentor. The probiotic bacterial strainLactobacillus rhamnosusAW3 isolated from date processing waste was used to produce lactic acid in a batch fermentor. Co-fermentation enhanced the biosynthesis of lactic acid and decreased substrate inhibition more than mono-substrate fermentation. A maximum yield of 28.4 +/- 0.87 g/L of lactic acid was obtained through co-fermentation of food waste and municipal sludge at an optimized ratio of 2:0.5. Lactic acid production was improved by the supplementation of fructose, peptone, and sodium dihydrogen phosphate at pH 5.5 after 48 h fermentation. This production was approximately three-fold higher than that during mono-fermentation of food waste. The tested bacterial strains were obtained from the Microbial Type Culture Collection (MTCC). Lactic acid showed potent antimicrobial activity against pathogenic organisms, such asBacillus subtilisMTCC 5981 (14 mm),Staphylococcus aureusMTCC 737 (20 mm),Pseudomonas aeruginosaMTCC 424 (24 mm),Enterobacter aerogenesMTCC111 (19 mm),Escherichia coliMTCC 443 (18 mm),Penicillium chrysogenumMTCC 5108 (19 mm), andAspergillus nigerMTCC 282 (19 mm). The antimicrobial properties of lactic acid have significant potential to inhibit the growth of pathogenic bacteria and fungi and improve probiotic properties. The lactic acid extracted fromL. rhamnosusAW3 decreased the pH value of soil (p< 0.01) and increased the availability of soil phosphorus (p< 0.01). These findings demonstrate the bioconversion of food waste and municipal sludge into lactic acid, and the recycling of food wastes in urban areas to enhance soil nutrients.