Wastewaters from the Sugar-Sweetened Beverage Industry: Advances on Simultaneous Biological Treatments and Valorization

Abstract

High-strength wastewaters from the non-alcoholicsugar-sweetened beverage industry comprise production streams discarded due todeficient bottling processes or those returned from the market due to qualityconstraints. The sugar content of these beverages (60−150 g/L) confers on theresulting effluents a high chemical oxygen demand (COD), which can reach levelsof up to 150000 mg of O2/L. Conventional treatments prior todischarging them into the environment involves anaerobic processes with highresidence times, high investment and operating costs. Thus, the efforts havebeen oriented on novel technologies. Alcoholic fermentation mediated by yeastof the Saccharomyces genus has beensuccessfully applied to treat these wastewaters. The process is based on thesame principle as biological treatment processes: the conversion of dissolvedorganic matter into compounds that can be easily removed. In conventionalprocesses, these compounds are gases, which separate spontaneously, andbiomass, which can be separated by decantation or filtration. In addition togases and biomass, the proposed process yields ethanol, that can be easilyseparated by distillation. Because bioethanol is currently one of the mostimportant worldwide renewable fuels and its production from biomass is apotential substitute for fossil fuels, the direct use of agro-industrial wastesas low-cost feedstock for second-generation ethanol production is an attractiveapproach. This chapter is focused on advances in the developmentof a robust process for alcoholic fermentation from sugar-sweetened beveragewastewaters. The impact of preservatives sodium benzoate and potassium sorbate,the initial sugar content and initial inoculum size on sugar consumption and ethanolyield were evaluated. The effect of the temperature, nutrients and carbonsource during yeast-proliferation stage was also considered. Fermentationassays were performed on different sugary drinks in batch mode under anaerobicconditions, and the concentrations of sugar, biomass and ethanol were monitoredover time. The process was optimized using surface-response methodology and it wasfound to allow 98% of the COD to be depleted. Complete sugars removal wasachieved in less than 14 h with ethanol yields of 0.44 gethanol/gsugarconsumed and ethanol specific production rate of 5.96 gethanol/(Lh). An industrial strategy based on simultaneous treatment and valorization ofwastewaters should be regarded as an environmental friendly tool and analternative and economically attractive bioprocess for production ofnon-lignocellulosic bioethanol.