Bioconversion of concentrated yeast wastewater and rice husks into bio-organic fertilizer via a one-time inoculation and composting

Yeast fermentation generates a large volume of wastewaters containing high levels of organic materials, so nanofiltration and distillation have been effectively used for the treatment of the effluent and the recycle of separated and cleaned water in industry. To further manage and utilize the remanent concentrate of yeast wastewater, a thermophilic bacterium simultaneously with the functions of cellulose degradation, nitrogen fixation and phosphorus and potassium solubilization was screened out and inoculated into the compost of concentrated yeast wastewater and rice husks. According to various parameter measurements, the inoculation promoted the temperature rise (> 60 °C), the composting maturity (C/N ratio < 15, E₄/E₆ value < 4 and seed germination index > 80% within 35 days) and the nutrient status (the increased contents of humus, total nitrogen, available phosphorus and available potassium all > 20% compared with uninoculated composting piles). Microbial community analyses showed that Bacillaceae, Fodinicurvataceae, Trueperaceae and Flavobacteriaceae had replaced indigenous enteric bacteria and composed the new dominant families. Meanwhile, the inoculation endowed composting products with enough viable microbial counts (> 5.0 × 10⁸ cfu/g) and profitably biochemical properties. These findings provided a strategy for using refractory organic wastes to produce bio-organic fertilizer via a one-time inoculation and composting.