The Metabolic Regulation Of Mictomolecule Substrate The Anaerobic Digestion System

In consideration of the increasing depletion of the fossil energy, and theaccelerated energy consumption result from human activities, the energy crisisis gradually emerged. In this process, as a representative of green energy, theutilization of biomass energy arouse passions and concerns of the world.Among the biomass energy productive processes, anaerobic digestion can beapplied to a wide range of substrates, where obtained an effective treatmentability of organic waste. On the other side, as a big catering country, the foodwaste emission of China greatly increases the volume of municipal waste, andthe ensuing consequences could not be underestimated. The combine ofanaerobic digestion technology and food wastes disposal can solve theproblem efficiently. The present study investigated the phenomenon ofN-inhibition （nitrogen inhibition） during the anaerobic digestion processdeeply,especially the mechanism and the performance of the N-inhibition; andduring the study, the promotive ability of buffer system was discovered in thesemi-continuous anaerobic digestion operation. In order to maintained a stableand efficient condition of anaerobic digestion with a buffer supply-operation,the buffer function and characteric was comprehensively investigated also.The optimum buffer addition concentration, addition way, inoculumconcentration were investigated, and also the anaerobic fermentation floravariation during the buffer addition digestion process. At the end of theresearch, the food wastes were regarded as a substrate for the semi-continuousanaerobic digestion, the main results are as follow:1. In the AD system, different inorganic nitrogen ions caused a severe drop ofthe biogas productive capacity with the increasing concentration, and theNO₂^--N exhibited the most drastic inhibition. At the same time, the highNH₄⁺-N concentration improved the activity of the methanogenic, when the C/N=0.5, the group obtained a10%higher CH₄concentration than theblank. The lower NO₃^--N concentration improved the biogas production ofthe system also, but when the NO₂^--Nconcentration reached48.8ppm, theimprovement disappeared, and inhibited the AD at NO₂^--N concentrationof84.8ppm. Compared with C/N=1group of NH₄⁺-N batch, the C/N=28group of NO₃^--Nbatch exhibited a9.2%higher TOC utilization rate, whichmeans, lower NO₂^--N concentration group boosted the AD activity moreefficient than higher NH₄⁺-N concentration group. The main N-removalroute of anaerobic digestion was nitrificationâ†'denitrification, theactivity of other nitrogen metabolic pathway was lower, Compare withNH₄⁺-N, NO₃^--N and NO₂^--N maintained a higher N-removal efficiency inthe AD system. In addition, plenty of NO₂^--N was oxidated to NO₃^--N dueto the instability of NO₂^--N at the end of the digestion.2. The characteristics of the long term （90d） anaerobic semi-continuousdigestion of FW/AS wastewater with different C/N ratio were investigated.During the whole process, the system obtained a higher tolerance ofNH₄⁺-N accumulation. The lower C/N substrate provides promotiveconditions for microbial activity during the first two periods of digestion（0⁶0d）, increase the utilization of TOC, although the concentration ofNH₄⁺reached5.65g/L and the concentration of VAFs around12g/L. Andthe TOC utilization of C/N=6.5case was11.1%higher than C/N=26case,which means the long time AD result in the extra NH₄⁺and VFAs（by-products of TOC） form an active buffer system, thus increasing boththe CH₄production and TOC utilization; and also maintained ahigher tolerance to NH₄⁺and VAFs concentration, which defusing theimpact of NH₄⁺and VAFs to the substrate. In the the third period ofdigestion （61d⁹0d）, with the increasingly accumulated of NH₄⁺, thebuffer system was broken up, and then, caused N-inhibited. The resultsindicated that the management of C/N of the the semi-continuous digestionprocess boost the stability because of the formation of buffer system, andin a certain extent, promoting the CH₄production and TOC utilization.3. When the HRT=1d, the system exhibited a significant inhibition with thebuffer addition, which result form the simpler substrate and fastermetabolism velocity. When the ammonium acetate concentration were4g/L,2g/L and1g/L, the total biogas production decreased66.1%,31.2% and17.5%, respectively, compare with the blank. In addition, theexogenous buffer improved the CH₄concentration efficiently, the CH₄concentration of4g/L group reached73.66%, however, the the CH₄concentration of blank group was just42.72%at the same time. With theaddition of exogenous ammonium acetate buffer, the system obtained asignificantly safeguard of the pH value, which defused the impact of highNH₄⁺-N or VFAsconcentration, kept a constant pH in the digestor. On theother side, compared with the other aerogens, Methanogen need a longerrecovery period formed the N-inhibition for the biogas productive ability.During the semi-continuous anaerobic digestion, when the additioninterval was2ds, the1.5g/L of glucose and2g/L of ammonium acetatewas regard as exogenous buffer, which could promote the endogenousformation, and also improve the efficient of the digestion. The optimumTOC utilization was843.31mL CH₄/g TOC in the process. With theexogenous buffer, the dilution ratio of the seed sludge exhibited a negativeeffect to the biogas production, and a positive effect to the CH₄concentration. When the VS of sludge was3.5%, the biogas production ofthe system was just49.77%of the origin sludge （VS=17.0%）, however,the CH₄concentration was13%higher than the VS=17.0%group. TheVS=8.1%group obtained the similar condition but when the VS rose to10.2%, the biogas production was just3.2%lower than the origin sludgegroup. The result means that, the exogenous ammonium acetate buffercause the generation of the biomass, and improved the activity of theMethanogen.4. The AD system maintained the optimum condition with the HRT=2ds, and1d added length for the ammonium acetate buffer, the system obtained thebest TOC utilization rate:901.11mL CH₄/g TOC. When the HRT=2ds,and the added length was3ds, although the NH₄⁺-N and VFAsconcentration was3.27g/L and12.46g/L, respectively, the systemmaintained the TOC utilization of802.65mL CH₄/g TOC. The CH₄concentration was promoted result from the shorter added cycle, however,caused a lower biogas production becauese of the high bufferconcentration, even the inhibitory phenomenon. During the inhibitionperiod, the amount of bacteria PCR-DGGE bands obtained a significant downward tendency, even disappeared; on the contrary, the methanearchaea PCR-DGGE bands （Methanobacterium aarhusense strain H₂-LRmainly） weren`t significant effected result from the buffer addition, whichmeans, the methanogens exhibited a higher tolerance of exogenous buffer，and the characteric of buffer could improved the formation of endogenousbuffer in the system, without the significant inhibition of the Methanogen.5. The addition of exogenous buffer in the food waste AD system maintaineda stable fermentative condition, boost the biogas and CH4production ofthe system. With the same additive buffer concentration, HRT=3dsobtained the optimum average CH4concentration,5522%, which was28.0%higher than the blank group; when the HRT was1d, the systemexhibited the average CH4concentration of54.87%, and a inhibitionphenomenon emerged during the period; when HRT=5ds, the average CH4concentration was just52.61%. Compare with the simple substrate, thefood waste defused the impact of the buffer addition, and during the period,there was no significant accumulation of the NH4+-N. In the30ds foodwastes digest operation, the AD system obtained the optimum condition inHRT=3ds, and the additive cycle=1d.