Mechanism Of Synergistic Bioevaporation Treatment Of Food Waste By Adding Biomass

In recent years,food waste(FW)with high moisture and organics content has increased dramatically and constituted the majority of municipal waste,which caused a critical global issue.If it was not handled properly,it is very easy to cause environmental pollution such as water and air,and cause the spread of diseases.Recent studies have successfully developed a novel process termed as bioevaporation,which aimed at treating highly concentrated organic wastewater including FW.During the process,biogenerated heat that is produced from the aerobic microbial degradation of organic substances and evaporates the water contained in FW itself,so that simultaneous removal of organic matter and water is achieved.During the bioevaporation process,biogenerated heat produced from organics degradation is crucial for driving water evaporation.And bulking agents and microbial carriers used in the process could not only adjust the moisture content and free air space but also provide carbon source and promote the degradation of organics and evaporation of water.Microorganisms attached on the carriers are the root cause that drives the degradation of organics and the generation of metabolic heat during the process.Thus,this study was carried out to investigate the degradation of biochemical fractions and their contribution to biogenerated heat during the FW bioevaporation process,combined the in-situ distribution of organics and cells,and the determination of their related enzymatic activities.Meanwhile,agricultural wastes(rice straw,wheat straw,sawdust,corncob,luffa cylindrica and palm)were used as additional biomass to synergistically enhance the bioevaporation process,and the corncob was chosen as a favorable bulking agent and microbial carrier.Then the mechanism of synergistic bioevaporation was explored through the variation of water form and the evolution of microbial viability,community and their associated function.Finally,degradation pattern and interaction of organic matter during the synergistic bioevaporation process under energy-saving intermittent ventilation strategy was investigated.The main results found in this study was shown as below:(1)During the food waste bioevaporation process by using biofilm-developed sponge as a bulking agent and microbial carrier,amylums were significantly decomposed in the whole process due to the high activity of amylase.The mass loss of amylums was the greatest and followed by lipids,which were degraded 118.3 g and 77.3 g respectively in the 2^nd cycle.Carbohydrates and lipids successively served as the main substrates for producing biogenerated heat and their total contribution was more than 88.0%.However,the content of protein was increased due to the proliferation of microorganisms and secretion of enzymes,and its contribution to the metabolic heat was relatively low during the bioevaporation process.(2)Through Illumina sequencing,it was found that thermophilic microorganisms were the dominant microorganisms during the synergistic bioevaporation process by using agricultural waste as bulking agents and microbial carriers.In the pile with corncob,they hold the most variety such as Bacillus,Oceanobacillus,Paenibacillus,Geobacillus,Virgibacillus,Brevibacillus,Streptomyces,Aspergillus,Mycothermus,and Thermomyces.Meanwhile,their abundance was the highest among all the piles(thermophilic bacteria was 22.3%–88.0%and thermophilic fungi was 82.0%–99.3%),as well as the removal of organic matter and water.Biogenerated heat contribution from organics degradation of corncob was the largest and reached70.4%due to its greatest content of easily biodegradable organics(55.2%)and lower content of lignin among all the agricultural wastes used in this research.However,sawdust and palm had no contribution to the process due to their great content of lignin.And the piles of rice straw and luffa cylindrica were easy to be collapsed.Thus corncob could be applied as a favorable bulking agent and microbial carrier for synergizing the bioevaporation process.(3)During the synergistic bioevaporation process with the corncob,the VS removal reached274.1%–171.1%and the MC removal reached 292.8%–198.8%due to the longer thermophilic phase.Results from the low-field NMR suggested that part of the bound water was transformed into adsorbed water and then transformed into free water.Finally,a large amount of free water was removed by ventilation and the removed mass of water was 3098.9 and 2103.8 g in the 1^stand 2^nd cycle,respectively.Fluorescent labeling combined with CLSM showed that the thickness of the biofilm attached to the corncob was near 350–450?m,which was mainly composed of live bacteria on the outer layer.And abundant organic matter and the mesophilic environment were beneficial for the development of the biofilm.The degradation of organic matter and the evaporation of water that drove by microorganisms significantly reduced the size of the corncob and even gradually destroyed its lignocellulosic structure.(4)Results from Metagenomics suggested that functional microorganisms were successfully domesticated in the 1^st cycle of the synergistic bioevaporation process.The total abundance of bacteria and fungi was above 98.0%during all temperature stages.At the genus level,Bacillus was the functional microorganisms in the peak-temperature stages(>50.4%),while Aspergillus,Burkholderia,Ktedonobacter,Streptomyces,Pseudoxanthomonas,Paenibacillus,Thermobacillus,Cohnella,and Myceliophthora were mainly active in the mesophilic phase to synergistically degrade easily biodegradable organics and lignocellulose and their abundance reached 67.3%and 58.2%,respectively in the final stages of the 1^st and 2^nd cycles.The pile temperature had a significant impact on the evolution of the microbial community,followed by organic matter.Microbes were rich in metabolic genes with an abundance of 29.3%–38.5%.And the abundance of carbohydrate transport and metabolism genes was the lowest in the peak-temperature stage,while lipids carbohydrate transport and metabolism genes were not greatly affected by pile temperature.(5)The energy consumption of the synergistic bioevaporation process under intermittent ventilation(IV)with 10 min on and 20 min off was nearly half of that under continuous ventilation(CV),and the generated metabolic heat was 3.6 times as much as that of the bioevaporation process using the biofilm-developed sponge as a bulking agent and microbial carrier.The removal ratio of water and VS reached 193.3%and 168.6%,realizing both energy-saving and efficiency.The microbial viability was high enough under both ventilations to degrade organic matter synergistically during the process.The degradation rate of organic matter was affected by its structure and content.The polysaccharides in corncob and FW are simple in structure and rich in content(>50%),while lignin has a complex structure and low content(<5%),which resulted in the degradation rate of polysaccharides was faster than that of lignin under both IV and CV ventilations.In CV,the distribution of live bacteria in the outer layer of corncob was similar to that of polysaccharides and lipids,which resulted in their preferential degradation,while the distribution of viable bacteria in the inner layer in IV was similar to that of lignocellulose,causing the degradation of polysaccharides and lipids to lag behind that of lignocellulose.The different degradation rates and patterns of organic matter under different ventilation resulted in a different degradation degree,which further affected metabolic heat generation.This study explored the degradation of organic matter and its contribution to biogenerated heat during the bioevaporation process.The corncob was optimized for synergistic bioevaporation of food waste and the mechanism of the process was explored.Meanwhile,the degradation pattern and interaction relationship of organic matter was clarified,results from this study could provide theoretical support for the application of energy-saving and efficient bioevaporation technology.