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Pulp and paper effluent organic constituents interactions with soil matrices

The land application of pulp and paper effluents has the potential to be a long-term sustainable solution for the requirements of industry and regulatory control of environmental impacts. A critical aspect of its success will be that the soil matrix onto which the effluents are applied is able to assimilate and remove effluent organic constituents of environmental concern. Two important processes are required for this. Firstly, the soils need to rapidly attenuate the movement of these materials through the soil column to ensure that groundwater and surface water contamination is minimised. Secondly, the accumulated constituents need to be mineralised/degraded to ensure the capacity of the soil is not exceeded with repeated effluent applications. This study aimed to use laboratory-scale systems to determine the contribution of these mechanisms to the fate and behaviour of environmentally-significant pulp and paper effluent constituents. Resin acids (major effluent toxicants, bioaccumulative and persistent) and phytosterols (potential endocrine disruptors) were the focus of this work. Three potential land application soil types, sand, Kawerau soil, and Whakarewarewa soil were considered. Thermomechanical pulping effluent was the principal waste source for the study since it is most suitable for land application. Given the potential for effluents from other pulp and paper processes to be land applied to some degree, two other wastestreams, chemi-thermomechanical and bleached kraft effluents, were considered in a more limited fashion. Resin acids were readily degradable in all the selected soils and with all effluent types. In most cases nearly 100% removal was obtained within 6 months incubation. The sand substrate was particularly effective in removing the compounds, possibly because of a lack of alternative carbon sources in the sand matrix. Effluent-derived acclimated microbiota may have been the principal degraders responsible for resin acid degradation. Resin acids were substantially degraded under both aerobic and anaerobic conditions. Thus, land application systems may be able to sustain resin acid removal performance even if anaerobic conditions are produced in the soils as a result of high rainfall/water table increases or over-irrigation. Resin acids were rapidly absorbed to the soil matrices. A significant proportion of the resin acids were irreversibly adsorbed to the organic soils. The capacity and intensity of adsorption was correlated with soil carbon content. Whakarewarewa soil had the greatest sorption capacity and sand was least attentuative. High concentrations of dissolved organic carbon were leached from the Kawerau and Whakarewarewa soils. This soluble material may influence the partitioning behaviour of lipophilic compounds, such as resin acids, and thus their mobility. Overall, this study has shown that resin acids can be very effectively removed from pulp and paper effluents when applied to a range of soils. Phytosterols were not attenuated as efficiently but are likely to be relatively immobile in the upper layers of the soil column. Other factors, such as salinity and nutrient loadings, are therefore likely to be more important limitations for the future utilisation of land application systems in the pulp and paper industry.
Type of thesis
The University of Waikato
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