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Biological treatment of highly polluted industrial effluent: With application to the wool scouring industry

Poole, Andrew James (1999) Biological treatment of highly polluted industrial effluent: With application to the wool scouring industry. PhD thesis, Murdoch University.

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Abstract

The effluent from the scouring of raw wool is the most polluted in the textile processing industry. It consists of a stable emulsion of wool wax in an aqueous medium containing dissolved organic and inorganic pollutants. The typical concentration of solvent extractable material is 9000 mg/L with a chemical oxygen demand (COD) of 30000 mg/L. The effective treatment of this effluent is necessary to ensure the future environmental and economic sustainability of the wool industry, however the effluent has so far eluded any universally acceptable means of treatment.

This study investigates two new biological approaches to treating wool scouring effluent. In accord with the contemporary trend toward treatment processes consisting of several unit processes, the biological systems studied were designed to form part of an overall combined technologies treatment package.

The first process biologically destabilises the wax emulsion, which allows the solvent extractable material to be recovered by centrifugation, whilst simultaneously degrading the biodegradable soluble pollutants. Aerobic continuous culture treatments achieved a 90% decrease in COD with over 99% removal of solvent extractable material. Retention times of less than 40 h were used with both laboratory scale (1.4 L) and pilot scale (100 L) reactors which operated without sludge recycle. A spadable sludge was produced which was approximately 22% by volume of the effluent. The removal of COD occurred non-stoichiometrically, requiring only one third of the amount of oxygen which would have been required by a conventional aerobic biological system. Emulsion destabilisation occurred partly due to degradation of the detergent used to stabilise the emulsion. However about 40% of destabilisation occurred before substantial degradation was shown in an initial destabilisation phase which corresponded to cleavage of the wool wax esters.

The second process complements a chemical flocculation procedure known as Sirolan CF. The Sirolan CF process removes virtually all of the wool wax and other insoluble material from the aqueous effluent to form a sparable sludge. However the soluble organic compounds are not removed and so the aqueous effluent retains 25% of the original COD and requires further treatment.

In this study, a survey to characterize the Sirolan CF effluent was conducted over a six month period and found the effluent had a high organic load with a COD of 5750 mg/L and a low biochemical oxygen demand (BOD5)/COD ratio of 0.29. Aerobic biological treatment was found to remove up to 65% of the COD and essentially all BOD5, detergent activity, and solvent extractable material. The corresponding growth yield coefficient was 0.5 to 0.75 mg biomass produced per mg of COD degraded. The treated effluent retained a COD of 2000 mg/L and an ammonia concentration 147 mg/L, which has a theoretical oxygen demand of 553 mg/L and necessitates discharge of the treated effluent to sewer. Continuous culture treatments used laboratory scale (3 L) and pilot scale (100 L and 3000 L) reactors without sludge recycle. It was found that retention times of about two days would be required for a full scale system due to the high oxygen demand of the effluent. The Sirolan CF process coupled with biological treatment gave a theoretical total COD removal of over 90% with essentially complete removal of solvent extractable material from the aqueous effluent.

The successful operation of both the microbial destabilisation and Sirolan CF effluent treatment processes at pilot scale indicated that they could be successfully developed into full scale processes and used industrially. Both processes offer a high degree of treatment, and are suitable to be integrated into combined technology treatment processes for the treatment of this highly polluted wastewater.

Item Type: Thesis (PhD)
Murdoch Affiliation: School of Biological and Environmental Sciences
Notes: Note to the author: If you would like to make your thesis openly available on Murdoch University Library's Research Repository, please contact: repository@murdoch.edu.au. Thank you.
Supervisor(s): Cord-Ruwisch, Ralf and Jones, B.
URI: http://researchrepository.murdoch.edu.au/id/eprint/52751
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