Bioremediation of a bleach plant effluent from the pulp and paper industry

[摘要] English: Bleach plant effluent was characterised by physico-chemical methods. The chemistry ofthe bleach plant effluent was examined to devise effective treatment methods. Effluentcontained trace amounts of nitrogen as well as carbohydrates and no ortho phosphatecould be detected in the wastewater.The best decolourisation activities were obtained using adsorption as treatment method,with activated carbon removing > 99% colour from effluent. Chitosan (81%) and chitin(77%) could remove appreciable levels of colour from bleach plant effluent, followed bybiomass from Rhizomucor pusillus, a mucoraelean fungus (71%). Chitosan and chitinfrom the cell wall of R. pusillus might be involved in the fungus decolourisation ability.Effluent pH was inversely related to effluent decolourisation when R. pusillus, chitosanor chitin was used as adsorbents. This might in part be due to acid catalysis duringnucleophilic addition reactions, where amino groups of chitin/chitosan react withcarbonyl groups in Eo-effluent. Also, chitin and chitosan amino groups can be protonatedunder acidic conditions and acquire positive charges that can interact with thechromophores found in Eo-effluent. However, pH exerted no significant effect ondecolourisation when activated carbon was employed as adsorbent of effluent colour.Decolourisation employing commercial adsorbents seemed to be mainly due tochemisorption. Adsorption experiments conducted at various ionic strengths indicatedthat coulombic interactions are responsible for a fraction of the decolourisation activity ofchitosan and chitin. Nevertheless, decolourisation obtained with RM7 and activatedcarbon was unaffected by the ionic strength. Flocculation of coloured compounds fromEo-effluent by chitosan containing solutions resulted in a maximum decolourisation of 75%. Anion-exchange treatment removed 96% colour from Eo-effluent. Ultravioletirradiation could decolourise the Eo-effluent by about 42 to 43%. Decolourisation usingorganic solvent extraction proved ineffective with a highest colour removal efficiency ofonly 21% being achieved.Biological methods used for effluent remediation were: 1) Trickling filters, 2) Activatedsludge reactors and 3) Rotating biological contactor reactors (RBC). Treatment using onebiological system was followed by treatment in another systemWith trickling filters containing immobilised white-rot fungi, the highest decolourisation(61%) was obtained with Coriolus versicolor. This fungus required a co-substrate toefficiently decolourise the effluent.Effluent treatment in an activated sludge reactor reduced toxicity, COD and chlorophenollevels. However, colour and high molecular mass compounds were not affected significantlyby this method of treatment.Decolourisation was studied in a RBC using immobilised C. versicolor and R. pusillus,respectively. The decolourisation rate by both fungi was proportional to initial colourintensities. Decolourisation was not adversely affected by colour intensity, except at thelowest level tested. Decolourisation of 53 to 74% could be attained using a hydraulicretention time of 23 h. Rhizomucor pusillus, removed 55% of AOX compared to a 40%AOX reduction by C. versicolor. Treatment employing R. pusillus and C. versicolor,respectively, rendered the effluent essentially non-toxic. Addition of nutrients to thedecolourisation media stimulated colour removal by C. versicolor, but not significantly inthe case of R. pusillus. Ligninolytic enzymes (manganese peroxidase and laccase) wereonly detected in effluent treated by C. versicolor. Decolourisation mechanisms wereinvestigated using gel permeation chromatography. Rhizomucor pusillus decolourised theeffluent by adsorption and C. versicolor removed effluent colour by adsorption as well asby biodegradation. Coriolus versicolor could decolourise the effluent for a period of 34 dwhereas R. pusillus decolourised the effluent up to 54 d. Further improvements in effluent quality could be attained when treatment using one system was followed by treatment inanother system, possibly because of toxicity reduction in the pre-treatment steps.

[发布机构] University of the Free State