Commercial enzyme is usually needed for the bioconversion of organic waste or biomass. The overall cost could be reduced very significantly if enzyme production could be integrated with its application, avoiding unnecessary steps in enzyme production (such as concentration, recovery and transportation). This investigation attempted to integrate crude glucoamylase production with lactic acid fermentation of food waste. A maximum glucoamylase activity of 1850 U g −1 was obtained with Aspergillus niger during solid-state fermentation (SSF) of food waste, 14.8 times more than that obtained during submerged fermentation (SmF). The optimum pH for producing glucoamylase was 4.6, and glucoamylase retained 83.5% of peak activity at pH 3.0. Without any recovery treatment, the glucoamylase produced by SSF could be used directly for lactic acid fermentation of food waste. Lactic acid concentration reached 45.5 g L −1 with the addition of the crude enzyme, 72% higher than the control. No side-effects were caused by the viable A. niger in the crude enzyme. This work successfully integrated glucoamylase production with lactic acid fermentation. The enzyme produced by SSF of food waste had sufficient activity to be used directly without any treatment. The integrated process proposed in this study was very economical and may be helpful to other bioconversions.

Kitchen waste from dining rooms accounts for a considerable proportion of municipal solid garbage, and economical recycle ways are needed to be developed. This study investigated glucoamylase production from kitchen waste and the feasibility of kitchen waste hydrolysis by the crude enzymes produced. The key problems of high water content and poor porosity in kitchen waste for glucoamylase production under solid-state fermentation could be solved readily by the addition of corn stover or paddy husk. As a support medium, corn stover was better than paddy husk. Smashed kitchen waste (sKW) mixed with corn stover in the ratio of 3.75 : 1 (dry basis) produced 1838 U g(-1) of glucoamylase by Aspergillus niger UV-60 within 96 h. The enzyme productivity from kitchen waste was over two-fold higher than that from wheat bran with additional nutrients. Without any recovery treatment, the produced glucoamylase could be used directly to hydrolyse sKW slurry. The optimum enzyme dose 8% (crude enzyme/kichen waste, w/w) was not too big, and was sufficient to hydrolyse 10% (dry basis) sKW slurry to produce a maximum amount of reducing sugar of 55.4 g L(-1).

The industry of biomass power in China has been growing tremendously in recent years, but it is faced with many challenges now. The low efficiency of straw combustion in the boiler results in that the carbon content in the fly ash could reach 15~30%. The ash is also rich in silica, potassium, calcium and has a lot of microelements. A kind of fly ash from a biomass power plant mainly uses corn straw as feedstock was studied. XRF analysis showed that the contents of K2O, CaO and MgO in the ash were 7.22%, 13.61% and 7.22%, respectively. Leaching experiments were conducted to evaluate the solubility of nutritive elements K, Ca and Mg in the ash. The results indicated that acid could enhance the solubility compared with pure water. Under the optimal conditions of filtrate final pH neutral, leaching time 20min, ratio of liquid to solid (L/S) 2, reaction temperature 40°C and stirring time 1min just for homogenization, 36.9% of K, 42.8% of Ca and 10.1% of Mg in the ash could be extracted. These dissolution rates were still very low, that means, the thorough extraction is not very easy and further research should be continued to make the straw power industry ecological and sustainable.

BACKGROUND The biomass‐fired power in China is mainly fueled by agro‐residue, and is suffering the bottlenecks of feedstock supply, super heater corrosion and nutrient cycle. How to recycle the ash nutrient to farmland is crucial for ecological sustainability. This work investigated potassium recovery from the fly ash of a grate boiler firing agro‐residue using leaching methods. RESULTS The studied ash contains a massive amount of fixed carbon (158.92 mg g−1) and little volatile matter (39.44 mg g−1). The unburnt carbon strongly decreases the concentration (CK) in the leachate and recovery percentage (RPK) of potassium nutrient by 17.6–24.1% and 9.0–18.8%, respectively. Calcination pretreatment in air at 500 °C for 30 min should be employed before leaching to remove the unburnt carbon. Mineralogy analysis shows that low‐temperature pre‐calcination (≤575 °C) does not affect potassium solubility. Under the optimal leaching of calcined ash in water with liquid‐to‐solid ratio 3 for 30 min at room temperature, CK in the leachate, dissolution percentage (DPK) and recovery percentage (RPK) of potassium element reached 17.21 g L−1, 82.0%, and 62.6%, respectively. CONCLUSIONS The fly ash from grate boilers firing agro‐residue is much better than other marginal potash sources. This work is helpful to improve the technology of agro‐residue fired power. © 2016 Society of Chemical Industry

BACKGROUND: Glucoamylase hydrolysis is a key step in the bioconversion of food waste with complicated composition. This work investigated the effect of lactate on glucoamylase from Aspergillus niger UV-60, and inhibition mechanisms of glucoamylase by lactate during food waste hydrolysis.