Jialin Liang,Siwei Zhang,Maoyou Ye,Jinjia Huang,Xian Yang,Shoupeng Li,Shaosong Huang,Shuiyu Sun
Zero-valent iron (ZVI) combined with oxidants is a promising conditioning strategy for improving sewage sludge dewaterability. However, challenges, such as a low dewatering rate and utilization efficiencies of ZVI, restrict further application of ZVI/oxidant treatments. This study employs, for the first time, rapid and cost-effective in-situ generation of Fe 2+ combined with common oxidants, namely H 2 O 2 , Na 2 S 2 O 8 , and KMnO 4 , to effectively improve sludge dewaterability. A comparative investigation of a standalone ZVI/oxidants treatment and when combined with a thermal and acid-wash (TA) pretreatment (TA/ZVI/oxidants) was systematically conducted to determine the sludge dewatering efficiency. Under the optimal operational conditions, the average water content of dewatered cake (Wc) was 18.47% less with the TA/ZVI/oxidants treatment when compared with the ZVI/oxidants treatment. The Wc values decreased to 54.81, 58.06, and 59.32 wt%, after the TA/ZVI/H 2 O 2 , TA/ZVI/Na 2 S 2 O 8 , and TA/ZVI/KMnO 4 treatments, respectively. The potential mechanism by which the TA/ZVI/oxidants treatment enhanced dewatering was investigated by determining the characteristics of both the sludge and the ZVI surface structure. Results indicate that the TA/ZVI/oxidants process caused more Fe 2+ dissolution, more strong oxidizing radicals and more strong flocculating Fe 3+ . The large amount of strong oxidizing radicals and strong flocculating Fe 3+ caused cell lysis and disrupted the protein-like and polysaccharide-like materials in the EPS, thereby decreasing the particle size, negative zeta potential, viscosity and colloidal forces, which then released the bound water trapped within the net-like floc and led to improved sludge dewaterability. In the ZVI reuse experiment, the TA/ZVI/oxidants treatment remained highly effective for sludge dewatering even after four cycles. Furthermore, economic analysis indicates that the TA/ZVI/H 2 O 2 treatment can save approximately 52.32% per year compared with using the traditional polyacrylamide (PAM) treatment.
In the realm of postcombustion carbon capture, diethylenetriamine (DETA), recognized for its substantial CO2 absorption capacity, presents a formidable challenge due to its corrosive impact on equipment. This study delves into the corrosion behavior of 20# carbon steel immersed in DETA solutions under varying conditions, employing weight loss and electrochemical methods. The investigation incorporates scanning electron microscopy/energy-dispersive spectroscopy and X-ray diffraction analyses for characterization. Corrosion experiments were also conducted in monoethanolamine (MEA) solutions for a comparative analysis. Results from the corrosion tests in DETA solutions mirror the temperature-dependent corrosion rate (CR) observed in MEA. However, a distinctive trend emerges as the CO2 loading of DETA increases from 0.2 mol CO2/mol amine to 1.2 mol CO2/mol amine, leading to a continuous decrease in the CR of carbon steel─contrary to MEA solutions. This anomaly is attributed to DETA’s robust complexing ability with metal ions and its elevated solubility of Fe2+ in solution. Additionally, an examination of the corrosion mechanism in the presence of oxygen was conducted through characterizing the specimen surface and solution precipitates postexperiment. The absence of a protective FeCO3 layer can be attributed to insufficient concentrations of free Fe2+ and CO32– in the solution, failing to achieve the minimum saturation required for protective film formation. The insights gained from studying the corrosion behavior of carbon steel in DETA solutions lay the groundwork for subsequent developments in corrosion inhibitors.
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