The studies on waste biodegradation by <i>Tenebrio molitor</i>

Abstract

As cities are growing in size with a rise in the population, the amount of plastic waste generated is increasing and becoming unmanageable. The treatment and disposal of plastic waste is an urgent need of our present and future. It has been proved recently that mealworms, the larvae of Tenebrio molitor Linnaeus, are able eat styrofoam, a common polystyrene product. Polystyrene is one of the most widely used plastics, the scale of its production being several million tons per year. Tenebrio molitor is one of the largest pests found in stored-grain products. The insect is indigenous to Europe, but is currently cosmopolitan in distribution. The styrofoam is efficiently degraded in the larval gut by microorganisms. We have used the larvae of T. molitor to biodegrade three types of food packaging plastics: polystyrene (PS), polyvinyl chloride (PVC) and polylactide (PLA). PVC is a thermoplastic made of 57% chlorine (derived from industrial grade salt) and 43% carbon (derived predominantly from oil /gas via ethylene). It is the world's third-most widely produced synthetic plastic polymer, which is not biodegradable easily. On the other hand, PLA is an easily biodegradable and bioactive thermoplastic aliphatic polyester derived from corn and tapioca starch or sugarcane. Three groups of larvae were fed selected types of polymers as an only food, while a control population was fed on oatmeal. The mass loss, dry matter content and biochemical composition of mealworms were assessed in the performed laboratory experiments. The protein concentration in homogenates of the larvae was determined by the Bradford method. To determine the level of hydrolized carbohydrates we used anthrone method. The classical sulfo-phospho-vanillin assay (SPVA) was used to quantitate total lipids in mealworms. The results allowed to compare the decomposition efficiency of selected polymer materials by mealworms and to recognize the mechanism of decomposition contributing to the future use of these animals for the treatment and disposal of plastic waste.