Abstract
Abstract
Effects of two fungal additives used for improving settling of paper mill residue (sludge), was investigated. The laboratory-scale pilot reactor, equipped with two tanks—an anoxic and an aerobic—was fed by wastewater from an industrial paper mill and inoculated with industrial sludge. It was operated over 3 weeks with either additive containing three or four identified fungi species: Geotrichum sp., Trichoderma sp., Mucor sp., and Aspergillus sp. Several parameters were followed: settled sludge volume (SSV); sludge volume index; size of flocs; chemical oxygen demand (COD) removal; evolution of fungal cells; and bound and soluble extracellular polymeric substances (EPS). The COD removal was 86–95% throughout the pilot experiments. Both fungal additives showed a significant improvement of the SSV from ∼800–1000 mL/L to ∼200 mL/L after 20 days and an increase in the median floc sizes of >50%. The first improvement of settling observed after 5 days of fungal inoculation can be attributed to the filamentous nature of fungi immobilizing/entrapping the floc components; the second, after 20 days, can be attributed to enhanced production by sludge of bound EPS involved in cohesion of aggregates. However, fungal population decreased after 20 days of inoculation, likely due to unfavorable pH 7.7 in aerated tanks.
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