Development of a Novel Helical-Ribbon Mixer Dryer for Conversion of Rural Slaughterhouse Wastes to an Organic Fertilizer and Implications in the Rural Circular Economy

Abstract

Organic wastes of rural slaughterhouses in developing countries comprise of blood and undigested rumen contents harboring infectious microbial pathogens and having impermissible BOD5 and COD values. Previously we demonstrated valorization of blood and rumen contents through drying and conversion to an efficacious organic fertilizer which was free from infectious pathogens and heavy metals. Here we describe fabrication of a novel helical-ribbon mixer dryer for transition from the current small-scale household cooking to equipment-driven sustainable production. Blood and rumen digesta mixed in a 3:1 ratio, having initial moisture of 85%, were dried at 90–110 °C for 3–4 h to attain 15.6% final moisture-containing organic fertilizer. Energy consumption and moisture extraction rate were 49.4 MJ per batch and 18.9 kg h−1 respectively. Using this method, small abattoir owners could emerge as multi-product producers to enhance earnings while farmers could source the fertilizer locally for organic farming. The two activities can be complementary to each other and become a sustainable circular economy model. We applied a spreadsheet-based model for calculation of cash flow, breakeven point and conducted financial cost–benefit analysis on the projected operation of the dryer. Fertilizer production parallel with the meat trade should be profitable for slaughterhouse owners and farmers apart from generating local employment opportunities.