Evaluation of Nitrogen Supplements for Bioconversion of Municipal Solid Waste to Lactic Acid

Abstract

Previous studies conducted by the authors showed that the ingredients of Elliker broth could be used as fermentation adjuncts for the bioconversion of municipal solid waste (MSW) acid hydrolysate to lactic acid. Five kinds of inexpensive organic nitrogen supplements were evaluated for their potential to replace more expensive nitrogen sources derived from tryptone and yeast extract, which are the nitrogenous components of Elliker broth. At a soluble nitrogen concentration of 0.28%, which is equivalent to that supplied by tryptone and yeast extract, soybean meal and cottonseed meal were the best alternative nitrogen sources and compared favorably to tryptone and yeast extract in terms of lactic acid production. Soybean meal nitrogen of 0.21% was the minimum nitrogen requirement for maximum production of lactic acid. When soybean meal was used as the nitrogen source, the addition of 1.91% phosphate as monobasic potassium phosphate significantly improved lactic acid production, but no improvement occurred below 1.91%. Ascorbic acid and sodium acetate are also components of Elliker broth, and the omission of these from the fermentation substrate did not affect lactic acid production. When 0.21% soluble soybean meal nitrogen and 0.4% sodium chloride were supplied to double-sugar MSW (DSMSW) hydrolysate, the amount of carbohydrate used, the percent of carbohydrate converted, the amount of lactic acid produced, and the percent yield after 3 d of fermentation were 78.3 mg/mL, 91%, 68.7 mg/mL, and 88%, respectively.