The RURAL (reciprocal upgrading for recycling of ash and lignocellulosics) process: a simple conversion of agricultural resources to strategic primary products for the rural bioeconomy.

Abstract Rice straw (RS), an agricultural resource for lignocellulosic biorefineries, can deteriorate when sun-drying is ineffective. Poultry litter ash (PLA) has been considered as a renewable phosphorus source for crops but is highly alkaline. Here, a simple process was developed for their reciprocal upgrading. RS, PLA, and water were mixed for wet storage and alkali pretreatment of the RS at 25 °C for 14 d, and solid–solid separation was performed to obtain PLA-treated RS (PT-RS) and RS-treated PLA (RT-PLA). PT-RS was susceptible to enzymatic saccharification, and 65.5-68.6% of total sugar residues in PT-RS was converted to lactic acid by its nonsterile application for simultaneous saccharification and fermentation using Bacillus coagulans. RT-PLA exhibited 1.8-points lower pH and a more sensitive response of phosphorus solubilization to acid than those of PLA. This process could thus provide a breakthrough for the rural bioeconomy by manufacturing two strategic primary products for various commercial bioproducts.