Wilson, Jonathan Alexander; (2003) Novel downstream processing for recovery of nematodes for biopesticides. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

The use of nematodes as a highly selective biopesticide is becoming established and the prospect of widespread horticultural use has now become a reality. To satisfy the requirements of a wider commercial market, a major increase in production scale is needed. This can only be achieved through technological advancement. The development of fermentation systems, for the production of nematodes has been rapid over the past couple of decades, however, downstream operations, particularly at a scale required to meet demand, have received less attention. Much development is still required if nematode-based biopesticides are to compete with much cheaper chemical agents and fulfil their potential. Large-scale liquid fermentation methods for the manufacture of nematodes as biopesticides produce the viable nematode life stage in a low concentration suspension containing large quantities of spent media and other waste material. The waste material includes non-viable nematode life stages, nematode debris and the nematodes' associated bacteria as well as the spent media. The presence of even small quantities of waste components has a detrimental impact on the quality and shelf life of the viable nematodes. Downstream operations for the recovery and concentration of viable nematodes and the consideration of flow phenomena form the foci of this Thesis. The physical characteristics of nematodes are very different from other more traditional biotech products, and material properties such as cuticle strength have been measured. Methods of recovery have been explored with particular emphasis on material properties, product specification and physical data. Two process options were considered; including a flow assisted wet sieving technique and a new vibrating filtration system. Batch and semi-batch experiments using conventional flow-assisted wet sieving and a novel cross-flow sieving technique were used to study the separation of juveniles from adult nematodes. The results were used to identify the sieve size and operating conditions for optimum juvenile recovery using an effectiveness factor. The use of a novel vibrating membrane filter for the combined recovery and concentration of nematodes from mature liquid cultures was also demonstrated. The results of the experiments, which showed the impact of operational and geometrical parameters on permeate flux, are used to demonstrate the potential of the vibrating membrane filtration as a flexible one-unit operation for the separation and concentration of viable nematodes from fermentation broth.

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