| Waste activated sludge (WAS) as the by-product of wastewater treatment plant(WWTP), the corresponding production has been increased rapidly, and WAS treatment is the bottleneck link for zero-waste water technology of WWTP. The main component of WAS is the organic matter, if these organics can be recycled by power source, which will bring great economic and energy efficiency. Currently, the main factor limiting the resource efficiency of WAS is the pretreatment stage, aiming to improve hydrolysis rate of WAS. It is the entry point of this research to improve the WAS resource efficiency. After three kinds of WAS pretreatments, performances of anaerobic coupled microbial electrolysis cell(AD-MEC) for hydrogen production and anaerobic digestion (AD) for methane production had been studied, respectively. And finally, the results of this research can provide important theoretical and technology support for the energy application of WAS.Three typical WAS pretreatment methods had been used in this study to investigate pretreatment performances, namely thermal-alkaline, freeze-thaw, ultrasonic pretreatment,respectively. Results showed that, these three pretreatment methods were all effective and efficient to promote the rupture of the sludge floc and microbial cell, resulting in releasing the organic matter to the sludge supernatant, and greatly improving the content of soluble organics of sludge mixture supernatant. Ordering the SCOD concentrations by descending sequence was the followings: thermal-alkaline pretreatment > ultrasonic pretreatment >freeze-thaw pretreatment, the corresponding SCOD concentrations were more than blank 28.89, 15.74 and 9.13 times, respectively. And the corresponding WAS crack rates were 20.80%, 10.99% and 6.07%, respectively.Results of AD-MEC process for hydrogen production after different WAS pretreatments showed that, during the whole operating time, concentrations of SCOD and soluble carbohydrates decreased rapidly at earlier 6 h in the MEC system. And for soluble proteins,concentrations decreased rapidly at earlier 3 h except for thermal-alkaline experimental group at earlier 12 h. Meanwhile, it could be found that components of volatile fatty acids had different removal efficiencies in the MEC system. Ordering the removal efficiencies by descending sequence was the followings: acetic acid> propionic acid > n-butyric acid > n-valeric acid > iso-valeric acid > iso-butyric acid. The average energy recovery and hydrogen production efficiencies of thermal-alkaline test were all the highest, 160.16% and 1.12 m3 H2·(m3 reacto·d)-1, respectively. Ordering average energy recovery and hydrogen production efficiencies by descending sequence was the followings:thermal-alkaline test > ultrasonic test > freeze-thaw test > blank test. Therefore, the thermal-alkaline pretreatment coupled AD-MEC system for hydrogen production has better energy recovery efficiency from WAS than other tests in this study.Results of AD process for methane production after different WAS pretreatments showed that, during the whole experimental time, concentrations of SCOD and volatile fatty acids had the same change trends, first increased, then decreased, and finally became stable.The maximum SCOD concentrations of blank, thermal-alkaline, freeze-thaw and ultrasonic test were 684 mg/L, 5688 mg/L, 1675 mg/L and 2894 mg/L, respectively. Concentrations of soluble carbohydrates and proteins of all the tests decreased rapidly at earlier phase, then became stable. There were no significant difference between blank and freeze-thaw test for cumulative CH4 productions,were 22.71 and 26.01 mL,respectively. And cumulative CH4 productions of thermal-alkaline and ultrasonic test were almost the same, were 147.01 and 147.39 mL, respectively. Wherefore, both thermal-alkaline and ultrasonic pretreatment coupled AD process for methane production could reach better energy recovery efficiency from WAS than other tests in this study.Conclusions of this research have important reference on energy recovery from WAS. |
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