| Anaerobic digestion(AD)is the most sustainable and cost-effective technology for waste treatment and energy recovery.It generates bio-energy while reducing waste,and has been widely used in the reduction,stabilization and resource utilization of sludge.However,most of the anaerobic digestion facilities built in China currently use mesophilic anaerobic digestion with low solid content.So the digestion equipment is bulky and the investment is relatively high.In recent years,themophilic anaerobic digestion(TAD)technology has attracted more and more attention due to its higher processing efficiency and gas production rate in unit volume,but its disadvantages are the high energy consumption and instability of the system.In order to solve the above problems,this article first uses the calamus harvested in actual constructed wetlands as raw materials to produce biochar,and then uses the calamus biochar and iron powder as accelerators,respectively,to explore the effects of the conductivity accelerators on the themophilic anaerobic digestion of long-sludge sludge.Based on the effect of digestion,one of the accelerators was finally selected to carry out a continuous TAD test of long-SRT sludge.The main results obtained are as follows:(1)The addition of iron powder reduces the ORP value in the system,provides a better anaerobic environment for the methane production process,promotes the TAD process of long-SRT sludge and significantly increases the methane content in the biogas.In the batch test,the dosage of 10 g/L can increase the cumulative gas production by 8.38%,increase the methane content in the biogas from 68% to 74%,and reduce the phosphate concentration of the mixed liquor.(2)As a conductive material,calamus biochar is an efficient AD accelerator,which improves the conductivity of the AD system mixture and the efficiency of TAD of longSRT sludge.It indirectly proves that biochar can promote direct interspecific electron transfer(DIET)to improve the efficiency of TAD.Compared with the control group,when the dosage was 15 g/L,the maximum methane production potential(BMP)was increased by 36.8%,while the lag period was shortened by 0.6 d and the effective gas production time(Tef)was shortened by 3.2 d.(3)In the continuous test,the calamus biochar can increase the methane productionand gas production of sludge TAD during the entire operation period.When the load is increased from 1.79 g VS/L/d to 2.87 g VS/L/d,the daily output of methane increased significantly and the test group with calamus biochar added more stable gas production than the control group,but the influence of calamus biochar on the methane content in the biogas was not obvious.(4)Acorus calamus biochar and reduced iron powder can alleviate the acid accumulation of TAD to a certain extent,which can avoid the acid inhibition of the system and is conducive to the stability of the system.Thus,the calamus biochar has a more significant effect on reducing the accumulation of VFAs.(5)Due to the high nitrogen content of long-SRT sludge and the obvious alkaline characteristics of calamus biochar,the higher free ammonia(FAN)concentration of the long-SRT sludge TAD system after adding calamus biochar may inhibit methanogenesis.Similarly,excessive iron powder also produces negative effects.Therefore,the choice of the dosage of the accelerator is very important when the accelerator is introduced into the TAD system. |
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