Effective Thermophilic Composting of Crop Residues for Inactivation of Tobacco Mosaic Virus

Abstract

An effective thermophilic composting bioreactor, in which a homogenous distribution of temperature was maintained at 63-65°C by the addition of a bioavailable carbon and low mixing, was developed. The bioreactor operated on a mixture of tomato plant residues-wood shavings-municipal solid waste compost infected with tobacco mosaic virus (TMV). The initial C: N ratio and moisture content of the compost mixture were adjusted to 30:1 and 60%, respectively. The composting process was successful in destroying the tobacco mosaic virus. The results showed that the ability of the untreated virus (inoculum) to infect tobacco plants (150 LL L^-1) was much higher than its ability to infect tomato plants (22 LL L^-1). The TMV completely lost its ability to infect the leaves of susceptible hosts (tobacco and tomato plants) after 96 hrs of controlled thermophilic (63-65 ºC) composting (or 126 h from the start of the composting process). Semilog plots of the ratio of the infection ability of the surviving virus to that of the initial inoculum (as measured by the number of local lesions) were developed. The decimal reduction time (the time necessary to reduce the infection ability of TMV by 1-log or 90%) was found to be 62.4 and 109.7 hrs for tobacco and tomato plants, respectively. The relatively short time required for complete inactivation of TMV in this study was achieved as a result of the extension of the thermophilic stage and maintaining a constant high temperature with a uniform temperature distribution by the continuous addition of the proper amount of bioavailable carbon (used cooking oil) and low mixing.