Effects Of Orange Peel Biochar On Anaerobic Co-digestion Of Sewage Sludge And The Organic Fraction Of Municipal Solid Waste

Municipal sewage treatment plants produce large amount of sewage sludge(SS)and the proportion of stabilization treatment of SS is quite low.Reasonable disposal of sewage sludge has become a matter of great concern due to the rapid expansion of wastewater treatment capacities and the increasingly stringent disposal regulations in China.Anaerobic digestion,during which SS is stabilized,is a widespread and promising bioenergy recovery method and could alleviate environmental pollution and energy crisis.On the other hand,organic fraction of municipal solid waste(OFMSW)in China are featured with high content of organic matter and huge amount.Unfortunately,it has not been utilized as a resource.Anaerobic co-digestion(AcoD)of SS and OFMSW is considered to promote the efficiency and economy of digestion.However,OFMSW is highly variable in nature,and its ingredients might differ significantly in spatial and temporal scale,which can be an obstruction to determine its reasonable blending ratio and the stability of AcoD is difficult to guarantee.Biochar is an environmentally friendly,inexpensive and readily available material.Researchers have found that biochar can improve the efficiency of anaerobic digestion and stability.Chongqing is rich in citrus resources,a large number of citrus peel waste has not been a good use of resources.On the basis of the preliminary results,this study applys biochar made from orange peel(OPBC)to the AcoD of SS and garden waste or food waste for the first time in order to explore the impact of OPBC on the AcoD of SS and OFMSW as well as underlying mechanism.In this study,orange peel was used as raw material and it was pyrolyzed at 500?and maintained for 1 h in a tubular furnace with nitrogen as shielding gas.The obtained OPBC was mesoporous carbon and its specific surface area was 6.59 m~2/g.The dominant elements in OPBC were C,N,O and H and it contained calcite crystal and dolomite crystal.The ash content of OPBC was 15.34%and it was rich in alkali metals(Na,K),alkaline earth metals(Ca,Mg)and basic functional groups which made it basic in nature with a pH of 10.06.OPBC had a good buffering capacity against typical volatile fatty acids.OPBC had a negative effect on biogas and methane production in the AcoD of SS and garden waste with a ratio of 1:1 in VS.But it slightly increased the content of methane in biogas.In comparison with the methane production of A0,cumulative methane production in the experimental groups decreased by 31.3%,10.3%,15.6%and 3.4%while methane content increased by 2.8%,9.5%,10.5%and 6.9%,respectively.OPBC had no significant effect on the removal efficiency of organic matter in the digestive system,but OPBC could increase the alkalinity and dehydration performance.Meanwhile,the richness and diversity of microorganism also got promoted.Due to the alkalinity of biochar,the concentration of VFAs in the experimental group was lower than that in the A0 as a result of the addition of OPBC.OPBC had a positive effect on biogas and methane production as well as methane content in the AcoD of SS and food waste.In group A(SS/FW=1/1 in VS),methane production and methane content increased by up to 147.7%and 48.9%.In group B(SS/FW=1/2 in VS),methane production and methane content of B3 was 39.88 times and7.63 times that of B0 as a result of acidification.The addition of OPBC could alleviate acidification and shorten the lag phase.Moreover,the stability of the system and the ability of degrading organic matter were improved remarkably.Besides,OPBC could promote dehydration performance as well as the richness and diversity of microorganism.Meanwhile,OPBC could also improve the relative abundance of Methanosaeta and Geobacter,and it could establish DIET between syntrophic microorganisms.OPBC could alter the metabolic pathway of organic acids and lift the efficiency of anaerobic digestion.