ALKALINE PRETREATMENT AND AIR MIXING FOR IMPROVEMENT OF METHANE PRODUCTION FROM ANAEROBIC CO-DIGESTION OF POULTRY LITTER WITH WHEAT STRAW

Alkaline pretreatment(AL)and air mixing(air)both have the potential to improve anaerobic co-digestion(Co-AD)of poultry litter with wheat straw for methane production.In this study,the effects of the combination of AL(pH 12 for 12 h)and air mixing(12 mL·d^(−1))on the Co-AD process were investigated.The substrate hydrolysis was enhanced by AL,with soluble chemical oxygen demand increased by 4.59 times and volatile fatty acids increased by 5.04 times.The cumulative methane yield in the group of Co-AD by AL integrated with air(Co-(AL+air)),being 287 mL·(g VS_(added))^(−1),was improved by 46.7%compared to the control.The cone model was found the best in simulating the methane yield kinetics with R^(2)≥0.9979 and root mean square prediction error(rMSPE)≤3.50.Co-(AL+air)had a larger hydrolysis constant k(0.14 d^(−1))and a shorter lag phaseλ(0.99 d)than the control(k=0.12 d^(−1),λ=2.06 d).The digestate improved the removal of total solids and total volatile solids by 2.0 and 2.3 times,respectively.AL facilitated substrate degradation,while air can enrich the microbial activity,together enhancing the methane generation.The results show that AL+air can be applied as an effective method to improve methane production from the Co-AD process.

DEGRADATION OF ORGANIC POLLUTANTS IN FLOCCULATED LIQUID DIGESTATE USING PHOTOCATALYTIC TITANATE NANOFIBERS: MECHANISM AND RESPONSE SURFACE OPTIMIZATION

Titanate nanofibers(TNFs)were synthesized using a hydrothermal method and were employed for the first time in this study to photocatalytically degrade organic pollutants found in flocculated liquid digestate of poultry litter.The photocatalytic performance of TNFs,with a bandgap of 3.16 eV,was tested based on degradation of organic pollutants and removal of color.Five combinations of pollutant concentration and pH were examined(0.2 to 1.3 g·L^(−1) at pH 4 to 10).Central composite design(CCD)and response surface methodology(RSM)were applied in order to optimize the removal rates of volatile fatty acids(VFA)and chemical oxygen demand(COD),and the decolorization rate.There were no significant differences between the regression models generated by the CCD/RSM and the experimental data.It was found that the optimal values for pH,dosage,VFA removal rate,COD removal rate and decolorization rate were 6.752,0.767 g·L^(−1),72.9%,59.1%and 66.8%,respectively.These findings indicates that photocatalytic TNFs have potential for the posttreatment of anaerobic digestion effluent,as well as other types of wastewater.