Batch and fed-batch simultaneous saccharification and fermentation of primary sludge from pulp and paper mills

ABSTRACT

Primary sludge from a Portuguese pulp and paper mill, containing 60% of carbohydrates, and unbleached pulp (as reference material), with 93% of carbohydrates, were used to produce ethanol by simultaneous saccharification and fermentation (SSF). SSF was performed in batch or fed-batch conditions without the need of a pretreatment. Cellic^® CTec2 was the cellulolytic enzymatic complex used and Saccharomyces cerevisiae (baker's yeast or ATCC 26602 strain) or the thermotolerant yeast Kluyveromyces marxianus NCYC 1426 were employed. Primary sludge was successfully converted to ethanol and the best results in SSF efficiency were obtained with S. cerevisiae. An ethanol concentration of 22.7 g L⁻¹ was produced using a content of 50 g L⁻¹ of carbohydrates from primary sludge, in batch conditions, with a global conversion yield of 81% and a production rate of 0.94 g L⁻¹ h⁻¹. Fed-batch operation enabled higher solids content (total carbohydrate concentration of 200 g L⁻¹, equivalent to a consistency of 33%) and a reduction of three-quarters of cellulolytic enzyme load, leading to an ethanol concentration of 40.7 g L⁻¹, although with lower yield and productivity. Xylitol with a concentration up to 7 g L⁻¹ was also identified as by-product in the primary sludge bioconversion process.

KEYWORDS:

• Batch
• ethanol
• fed-batch
• primary sludge
• simultaneous saccharification fermentation

Acknowledgements

Cátia Mendes is grateful for the research grant provided – Project EMSURE (CENTRO-07–0224-FEDER-002004).

Disclosure statement

No potential conflict of interest was reported by the authors.

ORCiD

Cátia Vanessa Teixeira Mendes http://orcid.org/0000-0002-1301-5995

Jorge Manuel dos Santos Rocha http://orcid.org/0000-0003-3759-4730

Fabrícia Farias de Menezes http://orcid.org/0000-0002-9489-3502

Maria da Graça Videira Sousa Carvalho http://orcid.org/0000-0002-6636-3133

Additional information

Funding

This work has been framed under the Initiative Energy for Sustainability of the University of Coimbra and supported by the Project Energy and Mobility for Sustainable Regions - EMSURE (CENTRO-07-0224-FEDER-002004)