Abstract
The paper investigates mixed-culture lactate (LA) fermentation of cheese whey (CW) in order to verify the possibility of using waste materials as feedstock to produce a product with high economic potential. The fermentation performance of two reactors operating in repeated-batch mode under uncontrolled pH conditions and various hydraulic retention time and feeding conditions was evaluated in terms of LA production. Five experimental phases were conducted. The hydraulic retention time (HRT) was varied from 1 to 4 days to verify its effect on the process performance. The best results, corresponding to the maximum LA concentration (20.1 g LA/L) and the maximum LA yield (0.37 g chemical oxygen demand (COD)(LA)/g COD(CW)), were reached by feeding the reactors with cheese whey alone and setting the HRT to 2 days. The maximum productivity of lactic acid (10.6 g LA/L/day) was observed when the HRT was decreased to 1 day.
Highlights
Waste biomass from food processing industries can be seen as an abundant source for biorefineries that aim at the industrial production of biofuels and value-added chemicals [1]
The aim of this paper is to assess dark fermentative lactic acid production using cheese whey (CW) mediated by mixed cultures
The high organic carbon content and the prevalent rapidly biodegradable chemical oxygen demand (COD) fraction of CW allow for a promising conversion of this liquid effluent in dark fermentative bioreactors [27,28,29,30]
Summary
Waste biomass from food processing industries can be seen as an abundant source for biorefineries that aim at the industrial production of biofuels and value-added chemicals [1]. The generation of a liquid effluent, i.e., cheese whey (CW), is estimated at 0.8–0.9 L per litre of treated milk, or 9 kg per kg of produced cheese [2,4,5]. The total amount of produced CW worldwide is estimated to be around 180–190 million tons per year, and only half of this by-product is subsequently used for food or feed production [4]. Around 100 million tons per year are typically discarded as a waste by-product in the environment, representing a significant issue for traditional wastewater treatment plants. Other typical characteristics are: pH in the range 3.3–9.0, a phosphorus content of 0.006–0.5 g/L, a total Kjeldahl nitrogen (TKN) of 0.01–1.7 g/L, chemical oxygen demand (COD) values in the interval 0.8–102 g/L and biological oxygen demand (BOD) values in the range 0.6–60 g/L [2,3]. While CW processing in conventional wastewater treatment plants can be quite challenging, this waste biomass could be conveniently used as valuable feedstocks for the production of biofuels and biochemicals
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