Effect of the hydrothermal pretreatment for the reduction of NO emission from sewage sludge combustion

Jin

Water Environment Research

et al. 2019

Sludge disintegration is an effective pretreatment to enhance the biodegradability of sludge. At present, the thermal-alkaline is one of the most commonly used methods, but it has a massive consumption of energy and chemical reagents. EDTA-enhanced thermal-alkaline treatment was used to strengthen the dewatered sludge disintegration at mid-low temperature in this study. Results showed that the dissolving-out quantity of soluble chemical oxygen demand and the volatile solid (VS) in residual sludge in the EDTA-added group were 14.7% higher and 7% lower than those in control system without EDTA, respectively, indicating that EDTA addition improved the performance of sludge disintegration. The addition of EDTA loosened the floc structure and enhanced the hydrolyzability of dissolved organic matters (DOM) with a narrower distribution of the relative molecular weight. The membrane damage of microbial cells in EDTA-added group reached 73.3% after 120 min, which was much higher than that in the control group (31.9%). EDTA contains a large number of hydrogen bond acceptors and could form hydrogen bonds with alcohols and phenols in solubilization products and DOM. It was speculated that the mechanism of EDTA-enhanced sludge disintegration was related to the formation of hydrogen bonds between EDTA and organic matter inside and outside the cell. © 2019 Water Environment Federation • Practitioner points• The addition of EDTA facilitated the thermal-alkali cracking of dewatered sludge. • EDTA increased the particle size of sludge and enhanced the hydrolysis of DOM. • The strengthening effect mainly occurred at the beginning of TB-EPS dissolving slowly. • Hydrogen bond played important roles in the enhanced disintegration of sludge by EDTA.

Section: Resultsmentioning

confidence: 93%

Effect on sludge disintegration by EDTA‐enhanced thermal‐alkaline treatment

Jin

Water Environment Research

et al. 2019

“…Moreover, the cleavage of weak bonds and covalent bonds is intensified, and the hydro‐char structure is clearly improved at the second (220–260 °C) and third stages (>260 °C) . For the HT of sludge, the main reaction mechanism is as follows: (1) direct solid–solid conversion to form hydro‐char. At solid–solid reaction stage, hydro‐char is made by the condensation, chemical dehydration, and decarboxylation reaction of long‐chain organic compounds, and this is the main reaction path.…”

Section: Resultsmentioning

confidence: 99%

“…It is probably related to the dehydration in the HT process. This result also indicated that the hydroxyl and carboxyl in the hydro‐char were reduced and converted into the H 2 O and CO 2 . The spectrum bands at 2800–2975 and 1375–1450 cm −1 zone, related to the aliphatic carbon –CHx and –C(CH 3 ) 2 deformation vibration, increased significantly for the HT‐SS solid product.…”

Section: Resultsmentioning

confidence: 99%

“…By using HT, SS with high moisture can be converted into high‐quality solid fuel but does not need to be dehydrated and dried . Moreover, many organic and inorganic pollutants are decomposed and removed, and heavy metals are stabilized in the HT solid product . However, the dry basis average calorific value of SS in China is only 11 000 kJ kg −1 , and moisture content is still up to 30 wt% after the HT process and pressure filtration, which cannot meet the requirement of reasonable net energy output in the next thermal conversion technologies.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Effect of the Amount of Sludge on Physicochemical Properties and Chemical Structure of Low‐rank Coal under Hydrothermal Conditions

Asia-Pacific J Chem Eng

Cardoso

Zhao

et al. 2017

Sewage sludge mixed with Yunnan low-rank coal was treated by hydrothermal treatment (HT) at mild temperature and high-pressure conditions. The fuel characteristics and chemical structure of HT solid products were investigated to explore the synergistic effects between low-rank coal and sludge. The results indicated that the fuel properties of HT solid products were negatively influenced as the amount of sludge increased, but there were synergistic positive effects on the content of volatile matter, fixed carbon, oxygen, and calorific value when the amount of sludge was more than 30 wt% in the HT at 300°C. More hydrogen groups in sludge were involved in the hydrogen transfer reactions between the low-rank coal and sludge, which promoted the occurrence of synergistic effects during the HT process. CO 2 and H 2 were the main gas products, but the yield of both gases produced by the HT of sewage sludge was significantly higher than that of low-rank coal. The aromaticity of HT solid products reduced from 60.65% to 51.83%, and the aliphaticity increased from 39.35% to 48.17% when the amount of sludge increased from 10 to 70 wt%.

Green Chemistry and Sustainable Technology

“…Tokyo Institute of Technology has been investigating sewage sludge hydrothermal treatment system, resulted in improved natural drying performance and reduced odor [22][23][24], and recent research confirmed that NO reduction occurred on the hydrothermally treated sludge compared to untreated sludge [25]. The proposed refuse-derived fuel (RDF) production system is shown in Fig.…”

Section: Hydrothermal Treatment Of Sludgementioning

confidence: 95%

Sewage Sludge Treatment by Hydrothermal Process for Producing Solid Fuel

Yoshikawa

Prawisudha

2014

Self Cite

Sludge treatment and disposal is one of the focus points in the waste treatment technology research due to the fact that sewage sludge is a form of pollution. One of the promising methods of sewage sludge treatment, considering its maximum sludge reduction and short processing time, is incineration. However, the usage of sewage sludge as fuel in incinerator is hindered by its high water content and high nitrogen content. A hydrothermal process for producing solid fuel from sewage sludge is developed by using saturated steam at 160-200°C and about 60 min holding time. It was shown that the product has improved dehydrability, but at the same time exhibiting higher solubility in the water, resulting in slightly lower calorific value due to the loss of dissolved solids, which have significant calorific value; therefore, an optimum operating condition is required to improve the dehydrability of sludge without reducing its solid content and calorific value. In the term of sewage odor, it was shown that after the hydrothermal treatment the sulfur-containing compound concentration was decreased, the same with the total odor intensity in the solid product. On the other hand, the odor intensity in the liquid and gaseous products were increased, suggesting the transfer of these compounds to the liquid and gaseous parts. During the combustion experiment, it was shown that the hydrothermally treated sludge emits lower NO emission compared to the raw sludge, promoting its possibility to be used in incinerator as direct or co-fuel without resulting in secondary pollution.