| With the aggravation of energy shortage and environmental pollution,many researchers focused on the energy recovery from municipal organic wastes,among which food waste(FW)and dewatered sludge(DS)were two typical streams.The high moisture content(MC)in these wastes restricted their energy recovery,and biodrying has been considered as a promising method to handle this issue.However,the environmental factors could easily affect the microbial activity,and led to unstable performance and low drying efficiency.In order to address these problems,FW and DS were treated as the co-substrates for biodrying.The results indicated that the co-substrates regulation enhanced the process stabilization.FW promoted water removal(84.28-92.71%),and DS improved the energy efficiency(62.96-68.13%).The co-biodrying presented high biodrying index(4.86 g H2O/g VS).During investigation of different variables,the bulking agent with a particle size<3 mm was found efficient for matrix heat preservation.The effect of microbial heat and air convection was enhanced at air-flow rate of 0.04 m3·h-1·kg-1,while initial MC of 60%was observed to improve the water removal(89.97%).At the optimized values of different variables,the co-biodrying of FW and DS synergistically enhanced the drying performance.Corresponding to physiochemical properties of bulking agents,the corncob matrix showed higher temperature and microbial activity,resulting in a higher biodrying index(5.97 g H20/g VS).Furthermore,corncob upgraded the amylase and lipase activities,and lipids were the important bio-heat sources(>40%).Compared with others,corncob showed less heat consumption for water evaporation(3.47 kJ/g H2O).In thermophilic and cooling phases,Bacillus(>50%)and Ochrobactrum(>40%)were the dominant genera with degradation capability of readily degradable organics and lignocelluloses,respectively.These results revealed the regulation mechanisms of bulking agents and provided some valuable information for engineering the co-biodrying process.In order to enhance the biodrying performance during cooling phase,the experiments on thermal assistance were conducted and revealed that the thermal assistance improved the matrix temperature.The microbial metabolism rate(0.0232-0.0292 vs.0.0151-0.0209 d-1)and water removal capacity(12.97-15.68 vs.5.05-8.23 kg·kPa)were enhanced.Meanwhile,thermal assistance stimulated enzymes activities and promoted biodegradation.With improved energy efficiency,thermal assistance reduced the external heat consumption(1.30-1.67 vs.2.38-2.56 kJ/g H2O)with less equipment investment and payback years.Compared with traditional drying methods,thermal assistance was proved to be energy efficient and more economical for biodrying enhancement in cooling phase.Based on the above results,thermally assisted biodrying was established.The results indicated that staged heating acclimation was efficient for thermophiles enrichment from DS with high bacteria and fungi abundance.By inoculation and thermal assistance(50?),the matrix increased to 58.1 0C in 8 h with high microbial activity[8.92-9.09 mg O2/(g TS·h)],which avoided the lag phenomenon with no volatile fatty acids accumulation.By air-flow regulation(0.8 L·min-1·kg-1),thermal assistance presented the synergetic enhancement with high bioheat proportion(86.63%)and energy efficiency.The MC of products reduced to below 30%with improved energy content(131.14%)in 4 days,which was close to the drying performance of conventional biodrying in 20 days.As for organics biodegradation,thermal assistance was proved to improve the activities of amylase,lipase and CMCase.Conversely,the protease activity was inhibited,which decreased the protein degradation.Though nitrification was also limited,thermal assistance reduced the NH3 emission(216.5 vs.280.8 mg).Among the microbes,Bacillus was dominant(>50%).In thermally assisted biodrying,instead of acid-resistant Weissella,Ureibacillus was enriched for organics degradation,and Pseudoxanthomonas and Saccharomonospora were associated with the lignocellulose degradation.According to network analysis,the bacterial genera with low proportions(such as Lactobacillus and Streptomyces)presented significant correlations with biodrying.For the same drying effect,the external heat consumptions for thermally assisted biodrying,conventional biodrying and thermal drying were 0.58,1.28 and 3.86 MJ/kg H2O,respectively.Thermal assistance was indicated to enhance the bioheat generation instead of excessive external heat consumption.In addition,the combustion characteristics of biodried products were investigated by thermogravimetric analysis.Based on Malek method and compensation effect,G(?)=-ln(1-?)was determined as the mechanism function.The results indicated that the bulking agents showed higher combustion indexes than organic wastes.Most of the biodried products(>50%)were decomposed in 500-600 K due to organics devolatilization and part of lignocelluloses degradation.The thermodynamic results indicated that biodegradation improved the stability of biodried product and the benefit for short-term storage.The biodried products exhibited high combustion indexes and energy content(11.97-12.66 MJ/kg),even higher than brown coal,and presented great potential for combustion utilization.In summary,the strategies of co-substrate regulation and thermal assistance were proved to be efficient to improve the stability of biodrying,upgrade the microbial metabolism and accelerate the water removal.This study provided an energy efficient and economical way for the management of high-MC organic wastes. |
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