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Remediation of Pulp and Paper Mill Biosolids using Vermiculture

Historical wastewater treatment systems at a New Zealand pulp and paper mill, resulted in a biosolid mass in the K-basin at Kinleith mill. Products extracted during the pulping process include resin acids, which are further transformed in the K-basin by microbial activity into recalcitrant end products retene and fichtelite. These products are toxic to fish due to bioaccumulation and subsequent endocrine disruption. Traditional methods for diverting these toxins from waterways were deposition into landfills and incineration, neither of which are considered environmentally sound. The aim of this study was to investigate the viability of vermicomposting as a method for bioremediation of recalcitrant resin acid derivatives from biosolids. Vermicomposting is a cost-effective option for not only reducing toxicity but also reducing biomass. It was hypothesised that earthworms can degrade organic extractives, principally resin acids and derivatives, through microbial, enzymatic, and oxidative mechanisms. A series of vermicomposting experiments were set up, to test the ability of Eisenia fetida (the tiger worm) to reduce both the amount of resin acids and overall biomass in a range of substrates. These included the original biosolid collected from K-basin, a simulated biosolid containing potting mix with and without additional extractive resins, as well as sterilised and unsterilised controls. Five samples were taken from each experimental composter over 28 days and extracted into dichloromethane after removal of excess water followed by mechanical blending. Samples were concentrated and the amount of each extractive group was determined using gas chromatography mass spectroscopy. The overall biomass in each composter as well as the depurated earthworm mass was measured at the start and cessation of the experiment. A slight reduction in biomass was observed in two out of the three substrates. This reduction was slightly enhanced by the presence of earthworms in the composter, however, it was not significant. The use of methyl bromide to sterilise the substrate was also not a significant factor in biomass reduction. The overall weight of the earthworms decreased in all cases indicating the unsuitability of any of the substrates as a desirable food source. The addition of supplements such as yeast or manure to the biosolid composter may increase its appeal. There was a significant reduction in extractive content in all substrates over the 28 day period however no significant difference attributable to the presence or absence of worms was observed. It was hypothesised that the rigorous sampling process encouraged oxidative breakdown of the extractives due to increased exposure to both air and light. This was evident when the extractive content of K-basin measured in 1993 was compared to the samples used in this study collected in 2006. Whilst vermicomposting does not appear to be an effective treatment for removing resin acids from biosolid mass, the sampling processes used in this study highlighted the effect that rigorous stirring and increased exposure to air and light can have on the natural breakdown of these products. An effective treatment for the removal of resin acids from K-basin may be as simple as regular ploughing.
Type of thesis
Shannon, N. W. (2009). Remediation of Pulp and Paper Mill Biosolids using Vermiculture (Thesis, Master of Science (MSc)). The University of Waikato, Hamilton, New Zealand. Retrieved from https://hdl.handle.net/10289/4323
The University of Waikato
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