Effect Of Sludge Inoculum On The Acid Production Characteristics Of Natural Anaerobic Fermentation Of Different Wastes

At present,the increase of meat protein in the diet structure has led to a decrease in the carbon-nitrogen ratio（C/N）of food waste,while the upstream livestock industry,which provides meat protein,has been able to develop rapidly,generating a large amount of livestock manure.Anaerobic fermentation is a common technology for the treatment and disposal of organic waste.Volatile fatty acids（VFAs）are intermediate products of anaerobic fermentation and have high potential application value.Sludge contains a large number of microflora,which has an important influence on the fermentation results,and a suitable sludge inoculum can help to promote both substrate hydrolysis and VFAs production.Therefore,in this experiment,low-C/N food waste（C/N=9,C/N=16）,cow manure and sheep manure were selected as VFAs-producing fermentation substrates,and their hydrolysis effects and acid production characteristics of natural anaerobic fermentation under different sludge inoculum levels（0%,15%,25%,35%and 45%）were investigated,respectively,to screen the optimal sludge inoculum level and determine the optimal fermentation period.The main results of the study are as follows:（1）the effects of different sludge inoculation levels on the acid production characteristics of natural anaerobic fermentation of food waste were investigated.The test results showed that the dissolved chemical oxygen demand（SCOD）and VFAs production increased with the increase of sludge inoculation.The inoculation of sludge promoted the release of ammonia nitrogen（NH₄⁺-N）to maintain the p H in the range of 5.0～5.8.The maximum VFAs yield（12,489.75 mg/L）was obtained at 45%of sludge inoculation for food waste with a C/N of 9,which was about 1.14～6.54 times higher than the maximum of other treatment groups,and the maximum VFAs/SCOD was 75.31%.The maximum VFAs yield（7261.34 mg/L）was also obtained at 45%sludge inoculation for the food waste with C/N of 16,which was about1.23～7.72 times higher than the maximum value for the other treatment groups,and the maximum VFAs/SCOD obtained was 55.92%.In addition,the VFAs produced from food wastes with C/N of 9 and 16 were dominated by acetic acid,propionic acid and n-butyric acid at 45%sludge inoculum.The optimal fermentation acid production period for both types of food wastes was the same for the first 7 days.The yield of VFAs continued to increase after 7days,but the increase yields was smaller.（2）the acid production characteristics of natural anaerobic fermentation of cow manure under different sludge inoculation conditions were investigated.The results showed that sludge inoculation significantly increased the NH₄⁺-N concentration,and the NH₄⁺-N concentration in the inoculated sludge treatment group was 1.88～4.52 times higher than that in the uninoculated sludge treatment group,implying that sludge inoculation could improve the hydrolysis of organic nitrogen compounds.the best sludge inoculation level for VFAs production was 35%,and the VFAs production at this level reached the highest value was3006.47 mg/L at day 5,which was about 1.53 times higher than that of the uninoculated sludge treatment group,and the VFAs fraction was mainly acetic acid,propionic acid and isobutyric acid in the early stage,and changed to propionic acid in the later stage.（3）the acid production characteristics of natural anaerobic fermentation of sheep manure under different sludge inoculum conditions were investigated.The results showed that NH₄⁺-N concentration and p H in the fermentation broth increased with the increase of sludge inoculum.The best solubilization effect and the highest SCOD concentration were achieved when the sludge inoculum was 45%.15%sludge inoculum yielded the highest VFAs,up to4316.84 mg/L,which was 1.64 times higher than that of the control group in the same period,and the accumulation of VFAs in the system could be stabilized to more than 3500 mg/L within the second to tenth days of fermentation.In addition,the optimal fermentation time at this sludge inoculum can be selected according to the target products,and the highest yields of acetic acid and propionic acid occurred at d 4 and d 10,respectively.In summary,the inoculation of sludge into low-C/N food waste,cow manure and sheep manure anaerobic fermentation for VFAs production systems can all contribute to their degradation and VFAs production performance,but it is worth noting that the optimal sludge inoculation and the optimal VFAs production stage vary for different substrates and need to be determined depending on the substrate type.The results of this study provide basic information and scientific basis for promoting the future development of VFAs production from anaerobic fermentation of low-C/N food waste,cattle manure and sheep manure,especially for the high-quality resource utilization of cattle manure and sheep manure.