Pulp and paper mill solid wastes as substrates for single‐cell protein production

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Abstract
We have investigated the upgrading of some typical pulp and paper mill solid wastes into protein‐enriched animal feed using the cellulolytic fungus Chaetomium cellulolyticum. The waste residues used were six different primary clarifier sludges and a sample of tertiary centricleaner rejects. These were obtained from mills whose modes of operation spanned the range typically in present‐day usage: groundwood, sulfite, semichemical, Kraft, and thermomechanical pulping, with and without bleaching. Crude protein production from the solid waste residues is compared to that obtainable from fermentation of untreated or caustic‐pretreated sawdusts. Some of these waste residues, especially the Kraft pulp mill rejects, appear to be promising sources of substrate for single‐cell protein production. In these preliminary findings, up to 28% dry weight crude protein content of the product has been obtained at specific growth rates of up to 0.12hr−1 on direct utilization of the wastes.