Abstract

Abstract - Recovery of spores and crystals from the fermentation broth of Bacillus thuringiensis (Bt) was studied using the membrane separation technology. Four types of polymeric membranes, with different characteristics, in the range of microfiltration (MF) and ultrafiltration (UF) were used for evaluating their permeate flux and spore–crystal recovery capacity. Results indicated that both MF and UF membranes are effective for spore–crystal recovery. The hydrophobic MF membrane made of polyvinylidene fluoride (PVDF) achieved a better performance compared to the one made with hydrophilic cellulose acetate (CA). Both had a 0.22 µm pore size, under the condition of an upper range of feed pressure. Also, with the increase of the feed flow rate, a higher flux was achieved for the PVDF membrane. A UF membrane made of polyethersulfone (PES) polymer was also used effectively for spore/crystal recovery from the broth, but under a higher operating pressure. In the entire experiment, a 99.9% rejection factor was measured with the applied membranes for the spore/crystal in the fermentation broth.

Highlights

  • About three million tons of chemical pesticides worth 20 billion dollars are sold all over the world annually

  • Half a billion dollars worth of the pesticide trade is biopesticides, and more than 60% of this amount is related to the commercial products of Bacillus thuringiensis (Bt)

  • The membranes used for the experiments included two MF membranes made of cellulose acetate (CA) and polyvinylidene fluoride (PVDF), with the same pore size of 0.22 μm, supplied by MembraneSolutions and Sepro companies, and two UF membranes made of polyethersulfone (PES) with different molecular weight cut-offs (MWCO) of 6 kDa and 10 kDa, supplied by Membrane-Solutions Co

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Summary

INTRODUCTION

About three million tons of chemical pesticides worth 20 billion dollars are sold all over the world annually. During the downstream step of the Bt production process, the main broth components, that is, the spores and crystals, must be recovered effectively. Other methods of recovery currently employed, such as immobilization (Prabakaranand Hoti, 2012), take time and are laborious, with a complicated scale-up process. In this context, membranebased recovery processes, such as microfiltration (MF) and ultrafiltration (UF), have been considered to be effective techniques for various applications (Mirtalebi et al, 2014; Shirazi et al, 2013a and 2013b), for biological solution treatment (Kristic et al, 2001; de la Casa et al, 2007; Li et al, 2008; Tang et al, 2010). Cross-flow MF and UF processes were applied to observe the recovery of spores and crystals from the Bt fermentation broth. To the best of our knowledge, this is the first attempt to investigate the effect of membrane characteristics on the recovery performance of Bt fermentation broth

MATERIALS AND METHODS
Method Precipitation Evaporation
RESULTS AND DISCUSSION
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