Optimizing biohydrogen production from mushroom cultivation waste using anaerobic mixed cultures

The mushroom bag is a polypropylene bag stuffed with wood flour and bacterial nutrients. After being used for growing mushroom for one to two weeks this bag becomes mushroom cultivation waste (MCW). About 150 million bags (80,000 tons) of MCW are produced annually in Taiwan and are usually burned or discarded. The cellulosic materials and nutrients in MCW could be used as the feedstock and nutrients for anaerobic biohydrogen fermentation. This study aims to select the inoculum from various waste sludges (sewage sludge I, sewage sludge II, cow dung and pig slurry) with or without adding any extra nutrients. A batch test was operated at a MCW concentration of 20 g COD/L, temperature 55 °C and an initial cultivation pH of 8. The results show that extra nutrient addition inhibited hydrogen production rate (HPR) and hydrogen production yield (HY) when using cow dung and pig slurry seeds. However, nutrient addition enhanced the HPR and HY in case of using sewage sludge inoculum and without inoculum. This related to the inhibition caused by high nutrient concentration (such as nitrogen) in cow dung and pig slurry. Peak HY of 0.73 mmol H2/g TVS was obtained with no inoculum and nutrient addition. However, peak HPR and specific hydrogen production rate (SHPR) of 10.11 mmol H2/L/d and 2.02 mmol H2/g VSS/d, respectively, were obtained by using cow dung inoculum without any extra nutrient addition.

► Mushroom cultivation waste could be converted to produce H2 using waste sludges.
► Cow dung could directly degrade mushroom waste without any extra nutrients.
► The main soluble metabolic product during mushroom waste fermentation was acetate.