| Waste activated sludge(WAS) contains large amounts of organic matter.Hydrolysis and acidification of the WAS can reduce the sludge concentration andproduce volatile fatty acids (VFAs), which can be used as carbon source forbiological nutrient removal process to promote the removal efficiency of nitrogenand phosphorus. However, the C/N ratio of WAS is not suitable for anaerobicfermentation. This study added corn straws into sludge as induce carbon sourceto promote C/N ratio and consequently to increase the production of VFAs.Firstly, sequencing batch experiment was conducted to examine the effect ofdifferent dose ratio of corn straws on the hydrolysis and acidification of WASpretreated by ultrasound. The result showed that the performance of the VFAsproduction can be promoted in the maximum extent when the mass ratio ofstraw/WAS was1:2gVSSstraw/gVSSsludge.Under that condition, the VFAsproduction increased20.2%, compared to the14.5%from the ratio of1:1, andnegligible promotion from the1:3and1:4groups. Besides, the contribution ofunit mass of corn straw to the promotion of VFAs production is biggest under theratio of1:2, so the optimal dose ratio was1:2.The result of the batch experiment also showed that the hydrolysis of WASwas promoted after adding corn straws, leading to the increase of substrateconcentration in the system, and consequently much more VFAs were found inco-fermentation reactors than those in the blank test reactors which onlycontained WAS. The percentage of acetic acid increased with the increasing ofcorn straws, while the valeric acid and butyric acid decreased.Semi-continuous-flow fermentation reactor was started and operated underdifferent SRT conditions with the optimal ratio of corn straw to examine thehydrolysis and acidification performance of WAS with corn straws as extracarbon source. The experimental result showed that the mean concentration ofVFAs during the stabilization period of each operation phase (SRT=10d,8d and5d) were9569.1，10015.7and11191.1mgCOD/L respectively and the productionratio of VFAs to unit biomass of WAS were0.45,0.47and0.53respectively. Thefermentation system crashed when SRT was shortened to3d.According to the current experimental result, the performance of thesemi-continuous fermentation reactor with the adjusted WAS by adding cornstraws was stable and impressive. With considerable production of VFAs andrelatively high bearing capacity for organic biomass load (the optimal SRT is5d),this method was predicted with a promising application prospect. The kinetic model of the fermentation process of WAS with corn straws ascarbon source in the semi-continuous flow reactor was established based onADM1model and some simplifications were made according to the specificexperimental conditions and substrate characteristics. The sensitive parameters,i.e., the key parameters were selected by sensitivity analysis and then estimatedby the experimental data of1:2group in the former batch test. After calibration,the model was verified by the measured data in the semi-continuous flowfermentation experiment, and the result indicated that the model was able toreflect the trends which were observed from the experimental data, with a relativeerror of about10%.By comparing the sensitive parameters estimated by experimental data of1:2group and blank group, conclusions can be made that adding corn straw cannot only provide more substrate for acidification bacteria but also hasten thehydrolysis process of WAS by increasing the hydrolysis rate and the activity ofrelevant enzymes of protein and carbohydrtate in the fermentation system.Methods to further promote the production performance of VFAs were predictedby analysis of simulation results under different conditions, including the use ofcontinous flow operation, fixed SRT operation (theoretical optimal SRT is3d)and improve the initial sludge concentration. |
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