Research On Enhanced Performance Of Anaerobic Biological Treatment Process With Biochar Addition Under High Organic Loading

Anaerobic biological treatment is a suitable technology for efficient treatment of industrial wastewater and recovery of resources and energy synchronously.It has been widely used for the treatment of high organic wastewater or toxic industrial wastewater.However,it still has several disadvantages,such as long start-up period and easily influenced by influent loading.In this thesis,the enhanced UASB reactors were built based on promoting interspecies electron transfer with addition of biochar.The enhancement of UASB system performance,influence of instantaneous organic shock loading,and possible mechanism of enhanced process were investigated with techniques of scanning electron microscopy(SEM),confocal laser scanning microscopy(CLSM),gold electrode conductivity measurement,high-throughput sequencing technology.The major results were as follows:1.The influence of different organic loading and hydraulic retention time on the pollutants removal,sludge granulation,gas production and its composition in UASB with addition of biochar(R1)and in normal UASB(R2)were studied.The results showed that the COD removal efficiency in R1 was 98.23±1.20%,improved obviously with addition of biochar.However,the COD removel efficiency in R2 was influenced by the change of the organic loading rate(OLR)and reached at 89.59±1.62%eventually.The average mixed liquor volatile suspended solids(MLVSS)of R1 increased from 9.12 g/L to 43.31g/L,higher than 35.10 g/L in R2.After operating for 70 days,the sludge was granulatee in R1 firstly,and the integrity coefficient and hydrophobicity of granular sludge reached 93.11%and 0.16 in the stable stage respectively.Analysis of volatile fatty acids(VFAs)and methane production indicated that the oxidation-reduction potential(ORP)and effluent VFAs of R1 were maintained at a low level favoring the stable operation performance and methane production capacity,and the methane production accounted for 59.78±2.19%.2.The influence of instantaneous organic shock loading on the pH,COD removal and methanogenic capacity in UASBs were studied.After operated at the organic loading rate of 20 kg COD/m3/d stably,two kinds of shocks were conducted with the organic loading rate of 80 kg COD/m3/d for 12 h and 24 h,respectively.After organic shock loading,R2 reactor acidified obviously and occurred irreversible collapse.Meanwhile,the capacity of methane production was inhibited and the sludge was washed out seriously.However,the MLSS and pH in R1 were still maintained at 6.5?7.5 and 45.96 g/L,respectively.The COD removal efficiency reached at 97.25%and the production of methane was stable.Further analysis of extracellular polymeric substances(EPS)content and structure indicated that after organic shock loading,the polysaccharide in R2 was accumulated and the sludge started viscosity bulking obviously.But the EPS of R1 reactor remained at the original level,the protein and a-polysaccharide were gathered inside the granules and ?-polysaccharide was wrapped up on the outside,favoring the stable performance of UASB under high organic shock loads.3.The conductivity of sludge in R1 reactor increased to 23.29±0.99 p.S/cm,which was higher than R1 reactor(11.62±1.30 ?S/cm).Results showed that addition of biochar enhanced the conductivity of sludge significantly,which was benefit for the electron transfer in the anaerobic methane production process.At the same time,the result of SEM showed that most of microorganisms were aggregated on the biochar's surface.Further analysis of microbial community in UASB indicated that the microbial diversity of granular sludge was increased with the addition of biochar.The microbes which can participate in direct interspecies electron transfer such as Geobacter spp.,Methanothrix spp.,Methanosarcia spp.were 5.42%,77.18%,11.65%in R1,higher than 1.46%,62.42%,5.33%in R2.In summary,the addition of biochar enhanced the pollutants removal and sludge granulation by adsorption and nucleation.Meanwhile,the microbial community of granular sludge was optimized by biochar,and then the DIET functional microbes were enriched and the conductivity of anaerobic sludge was increased for the improvement of the UASB process performance.