Abstract
Freeze-thaw (F/T) and electrochemistry both are environment-friendly and efficient sludge treatment technologies. In this study, the sludge samples were frozen at - 15°C, and 20% g/gTss activated carbon (AC) was added to the dissolved sludge. Finally, the uniformly mixed sludge was treated at a voltage of 15V for 25min. During the experiment, the effect of F/T on the floc structure was analyzed by a laser particle analyzer and scanning electron microscope. F/T treatment improved the dewatering performance of the sludge and promoted the aggregation of sludge flocs into larger particles either. At the same time, the median diameter (D50) increased from 45.27 to 128.94μm. AC was added to the thawed sludge solution before electrochemical treatment (EP). The conductivity of AC enhanced the effect of EP, thereby cracking the sludge flocs. Therefore, the three-dimensional excitation-emission matrix (3D-EEM) intensity of tightly bound extracellular polymeric substances (TB-EPS) decreased significantly. The protein in TB-EPS decreased from 54 to 33%, and the D50 was also reduced to 105.3μm. The final specific resistance of filtration and water content were reduced by 96.39% and 32.17%, respectively. The dehydrated cake elemental analysis showed that increased AC improved the sludge cake's combustion efficiency significantly. Moreover, the preliminary economic analysis indicated that the cost of this research was low, which implied the potential application value of combined treatment.
Highlights
In recent years, the treatment of sludge has gradually been paid more attention, and sludge dewatering has been proven to be an effective means to save the operating cost of water plants and reduce the risk of environmental pollution
The reduction rate of sludge specific resistance of filtration (SRF) is 96.39%, and the reduction rate of water content (Wc) is 32.17%, which is better than F/T and F/T + electrochemical pretreatment (EP) alone
The analysis of the sludge floc structure during the research shows that the dewatering performance of the sludge is not always positively or negatively correlated with the size of the sludge, but the sludge is released when EP and F/T change the sludge floc structure
Summary
The treatment of sludge has gradually been paid more attention, and sludge dewatering has been proven to be an effective means to save the operating cost of water plants and reduce the risk of environmental pollution. According to Diak et al (Diak and Örmeci 2018), in the study of ferrate pretreatment combined with F/T dehydration, ice crystals formed by freezing would puncture part of the microbial cells to reduce the microbial activity and the content of harmful cells in the sludge. F/T has many advantages in sludge treatment, the large particles of sludge formed by the extrusion of ice crystals during freezing will cause the material and water inside the floc to be more tightly combined (Sun et al 2018). If such substances are released, the sludge dewatering performance will be improved
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