Two-Stage Vs Single-Stage Anaerobic Digstion:Comparison Of Performance And Microbial Community

The two-stage process is distinguished from traditional one-stage anaerobic digestion (AD) process by splitting acidification stage and methanogenesis stage in two separated bioreactors in series. However, it remains unclear whether the splitting will optimize the performance of both stages or hinder the synergistic effect of them. Thus, the advantages of two stage anaerobic digestion technology are disputed. This work presents a comparison between two-stage (reactors Ra and Rm) and one-stage (reactor Rs) AD systems, focusing the attention on biogas production, energy output, system stability, and microbiological dynamics. The reactors were fed with three kinds of identical organic substrates including lignocellulosic material, easily degradable material and high sulfate wastewater. The results were summarized as follows:(1) For the lignocellulosic material, the specific methane production and energy output of two-stage AD system is7.2%-32%and7.25%-32%higher than that of single stage process, respectively. Ra enhanced the degradation of lignocellulose and stalized the production of hydrogen and VFA. The dominant community of Ra, Rm and Rs were Bacteroidetes, Firmicutes, Proteobacteria, etc. With Prevotellaceae played a major role in acidification, Ra has a lower microbial diversity than Rm and Rs. Rm has a higher microbial diversity than Rs and they were different in abundance of dominant communities. The total16s rRNA gene concentration of Methanogenic archaea in Rm is higher than that in Rs. The prevalent methanogenic archaea were MMB�'�MBT.(2) For the easily degradable material, at the HRT(30d), the specific methane production and energy output of Rs were respectively3.8%and3%higher than of Ra+Rm; while at the HRT of15d, the specific methane production and energy output of Ra+Rm were respectively8.6%and9.2%higher than those of Rs. Two-stage AD system showed higher stability and shorter fermentation period but it was accompanied with higher carbon loss. The dominant community of Ra, Rm and Rs included Bacteroidetes, Firmicutes, Proteobacteria, etc. Ra, in which Prevotella and Lactobacillus take the major function of fermentation and acidification, has a lower microbial diversity than Rm and Rs. Rm and Rs were similar in taxons but different in abundance, In Rm, Syntrophomonas、 Syntrophobacter、 Desulfovibrio are more abundant than in Rs. At HRT (30d), the16S rRNA gene concentration of Methanogenic archaea in Rs is higher than in Rm while at HRT(15d)+pH, the opposite is in the case In both Rs and Ra, MMB and MBT dominate in the microbial community while their gene concentrations are higher in Rm than in Rs.(3) For high sulfate wastewater, with COD/SO4-2ratio decreased from10to1.25, FABR prevailed in the methane-producing efficiency and removal efficiency of COD and SO-2.The splitting effect was pronounced in FABR. The first three compartments took the removal of COD and SO-2, and the last compartment took the methanogenesis. The FABR has higher microbial diversity than AF, with Proteobacteria、Bacteroidetes、Firmicutes as dominant taxons and Desulfovibrio and Desulforhabdus-Syntrophobacter as the main sulfate reducing bacteria in FABR and AF. The dominant Methanogenic archaea in both FABR and AF were MMB and Mst. The gene concentrations of Methanogenic archaea are higher in FABR than in AF.As a whole, two-stage and single-stage (AD) process showed significant difference under variable feedstock, HRT, OLR and pH. With lignocellulosic material as feedstock, two-stage AD system showed higher biogas production and energy output under any conditions in this study, as a result from the enhanced degradation of cellulose and hemicellulose in the acidification stage. When easily-degradable material feedstock, the single-stage AD process have advantage over two-stage process under long HRT; while under short HRT, it was opposite in the case. When treating sulfate FABR showed higher efficiency in biogas production and SO4-2removal wastewater than AF.