|dc.description.abstract||Woolscouring in New Zealand produces a highly concentrated wastewater stream "flowdown" and a lightly contaminated stream of rinse water. Flowdown contains wool grease which has nearly four times the COD loading of suint, the other major contaminant, but its presence as a stable colloidal dispersion makes it difficult to remove. Because of the large volume of flowdown produced, a high rate treatment system is required.
Anaerobic treatment is a potentially suitable economic treatment method, but its application to flowdown has not previously been successful. A suitable reactor configuration needs to be established which can then be used to determine the potential for removal of colloidal woolgrease under high rate anaerobic conditions, and to identify the mechanisms involved. An understanding of the mechanisms involved and the factors which affect them will enable the high rate anaerobic treatment process to be operated to maximise woolgrease removal.
A suitable reactor configuration was established. It was based on the anaerobic contact reactor configuration, except that mixing only occurred during a single daily feeding period. Solids from the reactor were separated, by flocculant addition and centrifuging at low speed, and recycled to the reactor. By varying the amount of solids recycled, the hydraulic and volatile solids retention times (HRT and VRT) were altered. The effect of the physical state of wool grease on its removal was determined by conducting experiments at two temperatures: 37°C, below the melting point of wool grease and 47°C, above the melting point of wool grease.
Partitioning and degradation of wool grease were determined at different HRT, VRT and temperatures. Two-way analysis of variants with different HRT and VRT was conducted to identify their effect on woolgrease removal from the system. VRT was shown to have a significant effect, but not HRT. The effect of temperature was determined using two one-way analysis of variance. Operation at 47°C did not give a significant improvement in woolgrease removal. Mass balances of COD and volatile solids, gas production and composition were used to confirm whether degradation or biotransformation of woolgrease was occurring. Extraction of wool grease with a solvents of different polarity confirmed that biotransformation was significant. Woolgrease degradation was low compared with other studies on high rate anaerobic treatment of wool scour wastewater and degradation of lipids.
The advantages of anaerobic treatment over direct flocculation of flowdown, on partitioning of woolgrease and separation of the solid and clarified phases, was carried out by centrifuging, dissolved air flotation, and gravity setting. Anaerobic treatment increased the partitioning of woolgrease with gravity settling and centrifuging, but DAF was ineffective. Experiments were conducted above and below the melting point of woolgrease to identify thermal effects, especially the effect of the physical state of woolgrease on partitioning. Gravity settling was significantly affected by temperature.
The effects of changing flowdown, as would occur under commercial conditions, was systematically assessed using six flowdown types with different characteristics. Partitioning of wool grease was assessed after slug doses of the various flowdown types to the reactors. Statistical analyses (General Linear Model) were used to identify the response and recovery from the slug doses. Anaerobic treatment of lowdown from crossbred wool scoured with an alcohol ethoxylate detergent showed the greatest removal of wool grease from the clarified. The effect of potentially inhibitory chemicals in flowdown, determined by monitoring the volume and composition of gas and concentration of volatile fatty acids showed that slipe and dag wool adversely affected gas production.
The roles of bioflocculation and adsorption on partitioning were investigated. Adsorption appeared to have a limited role, as shown by providing additional adsorption sites and attempting to saturate adsorption sites by increasing the concentration of wool grease in flowdown. The biological influence was shown to be important by comparing the effect of anaerobic sludge and flowdown sludge on woolgrease partitioning. Bioflocculation, with and without chemical flocculation, over different periods of incubation had the greatest effect when no chemical flocculant was added.
Radiolabelled model woolgrease substrates, cholesteryl stearate, cholesterol, and stearic acid were used to focus on the major steps of woolgrease degradation - ester hydrolysis, long chain fatty acid (LCFA) and cholesterol fermentation. LCFA was observed when used directly as a substrate, but degradation to of ester to LCFA when was very limited, although ester hydrolysis did occur. Sludge age had an effect, as more ester hydrolysis occurred at VRT 30 days compared to 10 days VRT. TLC confirmed changes in woolgrease composition was also greatest at 30 days VRT.
In this work the major mechanisms of wool grease removal are identified and their role discussed. Implications for operating a pilot plant anaerobic reactor are outlined and areas for further work to improve woolgrease removal are recommended.||en