Moisture Content Of Sewage Sludge Research Articles

Thermodynamic analysis of a supercritical water gasification – oxidation combined system for sewage sludge treatment with cool wall reactor

A novel supercritical water system was proposed to treat sewage sludge harmlessly in this work, with its core to produce syngas by supercritical water gasification (SCWG) of sewage sludge and dispose of the residual liquid organics by supercritical water oxidation (SCWO) for heat release and harmless disposal. Moreover, a cool wall reactor was employed to solve corrosion and salt deposition, while the reaction heat was recovered for power generation, and the heating exchange net was optimized. The effects of SCWG temperature (400–550 °C), moisture content of sewage sludge (87–95 wt%), pressure (23–29 MPa), and oxidation coefficient (0–0.5) on the characteristics of the SCWG-SCWO combined system, and the influence of heating method for supercritical water on the exergy destruction and system efficiency, were investigated and discussed. The results showed that an increase in SCWG temperature, the decrease in moisture content and oxidation coefficient, except for the effect of pressure, could significantly improve the net exergy efficiency of the system. Under the condition of SCWG temperature being 450 °C, moisture content of 87 wt%, 25 MPa and oxidation coefficient being 0, the electricity self-sufficient rate, cold gas efficiency, exergy efficiency and net exergy efficiency were 18.08%, 13.09%, 15.94%, 15.41% and 10.06%, respectively. Inputting external energy could tremendously impact the whole system. When the temperature of heat source for heating water was higher than the reaction temperature of SCWO, the net exergy efficiency of the system could reach 27.73%. The thermodynamic efficiency of the SCWG-SCWO combined system outperforms the single SCWO case. This study provided an industrial basis for the hierarchical treatment of sewage sludge, and offered a new direction for pollutant treatment by the combined supercritical water technologies.

하수슬러지 Bio-drying 시 발효조 온도와 수분 저감과의 관련성 연구

Since sewage sludge has a high moisture content even after dehydration, when used as energy such as fuel, the moisture content of sewage sludge must be reduced to 10% or less. In the case of using sewage sludge as fuel or reducing moisture, a fermentation and drying system by Bio-drying is introduced, and the Bio-drying system is generally dried by heat generated when aerobic microorganisms decompose organic matter in the sewage sludge, and the correlation between the temperature change and the water reduction of the fermentation tank is determined to be very important. The reduction of sewage sludge moisture by the bio-drying system was found to be most affected by the number of stirrings in the fermentation tank and the maintenance of high temperatures of 70oC or higher, and the reduction of temperature caused by excessive supply of air at 390 to 600mL/kg/min was found. In the case of experiments with one to five times more stirring times, the moisture reduction effect was 14.5% and 15.5%, which showed much greater reduction rate than the average reduction rate of 12.7%.

Supercritical water pyrolysis of sewage sludge

Municipal sewage sludge (SS) from wastewater treatment plant containing high water content (>85wt.%), lead to the difficulty of co-combustion with MSW or coal due to the high cost of drying. This study explores an alternative method by supercritical water (SCW) pyrolysis of sewage sludge (SS) in a high pressure reaction vessel. The effects of temperature and moisture content of SS on yield and composition of the products (bio-oil, bio char and non-condensable gas) were studied. A temperature of 385°C and moisture content of 85wt.% were found to be the optimum conditions for the maximum bio-oil production of 37.23wt.%, with a higher heating value of 31.08MJ/kg. In the optimum condition, the yields of aliphatic hydrocarbon and phenols were about 29.23wt.% and 12.51wt.%, respectively. The physical and chemical properties of bio-char were analyzed by using XRF and BET. Results of GC analyses of NCG showed that it has the maximum HHV of 13.39MJ/m3 at 445°C and moisture content of 85wt.%. The reaction path from SS to bio-oil through SCW pyrolysis was given. Moreover, carbon balance was calculated for the optimal condition, and finding out that 64.27wt.% of the carbon content was transferred from SS to bio-oil. Finally, this work demonstrates that the SCW pyrolysis is a promising disposal method for SS.

Effect of adding alum sludge from water treatment plant on sewage sludge dewatering

Alum sludge from water treatment plant contained residual polyaluminum chloride (PACl) and large amount inorganic matters. Alum sludge acted as chemical conditioner and physical conditioner improved the sewage sludge dewatering. It indicated that the addition of alum sludge reduced the dosage of polyacrylamide (PAM) and decreased the moisture content of sewage sludge. The moisture content was 64% when the blend ratio was 1kg/kg (dry alum sludge/dry sewage sludge) with plate-and-frame filter press. The 3D-excitation–emission matrix (3D-EEM) was used to analyze the sludge dewatering process. A mechanism hypothesis of adding alum sludge in sewage sludge for improving the sludge dewatering was proposed. Alum sludge implements the charge neutralization and adsorption bridging effect, provides friction and squeeze for crushing sludge particles even cell, and acts as skeleton builders in the sludge to improve the sludge dewatering.

ICOPE-15-C083 Study of Numerical Simulation and Field Test for Co-Combustion of Sewage Sludge on a 100 MW Coal Fired Boiler

A series of field test and numerical simulations was carried out to evaluate the characteristics of coal combustion and coal combined firing with sewage sludge in a 100 MW tangentially coal fired utility boiler. The simulation results was highly consistent with the experimental data when the moisture content of sewage sludge was 56% with mass blending ratio less than 10%: the flue gas temperature decreased, char burnout rate fell, unburned carbon in fly ash and NOx emissions, but the differences were small. Both the experimental and simulation results indicated that small mass ratio of sewage sludge co-combustion has little effect on the operation of boiler. Additionally, the influence of combustion characteristics and pollutant emissions when co-combustion high blending ratio of sewage sludge was further studied. Results showed that the decrease of sewage sludge moisture content was helpful in improvement of the boiler combustion characteristics, besides, the NOx emission also reduced. The NOx emission increases and the flue gas temperature and the burnout rate of char decreases when increasing the sewage sludge blending ratio up to 30%. And the changes become more and more significant. In addition, the NOx reduction strategy and the slagging tendency caused by the co-combustion of sewage sludge were also studied.

Sewage Sludge Torrefaction in an Auger Reactor

A lab-scale auger reactor was used for the study of dry sewage sludge torrefaction. The influence of the torrefaction temperature (between 250 and 300 °C) and the solid residence time (between 13 and 35 min) on the product distribution and properties was investigated. The results have shown that both parameters affect dry sewage sludge torrefaction products to a similar extent within the ranges of study. The yield of torrefied sewage sludge decreases when increasing the torrefaction temperature and the solid residence time, while the yields of liquid and noncondensable gases show the opposite trend. Carbon dioxide and hydrogen sulfide are the major noncondensable products. The yield of water is higher than the initial moisture content of sewage sludge. Organic compounds are also released during torrefaction, especially under severe conditions. Torrefaction liquid separates into an organic phase and an aqueous phase. The former is rich in oxygen-containing aliphatic compounds and steroids and their derivat...

Comparison of the Composting Performance of Four Different Sewage Sludge Amendments

ABSTRACT.High moisture content of sewage sludge is a major constraint in composting, and therefore sewage sludge needs to be mixed with bulking agents that have a high water absorption ratio and better structural stability. In this study, dewatered sludge has been mixed with four different bulking agents in terms of physicochemical properties, with a 1:1 (v/v) proportion of sawdust (SW), hazelnut husk (HH), corn straw (CS), or pine litter (PL), and the composting performances of bulking agents were investigated by considering temperature rise, CO2, H2S evolution, organic matter (OM) removal, C/N ratio, and dissolved organic carbon (DOC) removal. Three of the mixtures, namely, HH, PL, and SW, provided better initial composting conditions, ensuring an appropriate water–air balance within the compost matrix. CS was not able to supply sufficient porosity due to the smaller water absorption ratio and higher degradation rate, which induced anaerobic conditions. Among the mixtures, a higher and faster temperature rise (max 56.5°C) and CO2 release was provided by HH, while OM removal (53%) and DOC degradation were higher with the CS mixture, despite the low temperature rise and low peak value of CO2 release. Relatively low degradable carbonaceous contents of SW delayed all the composting indicators measured in the study. HH significantly enhanced bioreactions and accelerated the stability of sludge compost by providing both structural stability and a readily available carbon source, significantly shortening the composting time.

Investigation of the Effects of Hygienization and Moisture Content of Sewage Sludge on Pyrolysis Products

The effects of hygienization and moisture content on pyrolysis of sewage sludge obtained from wastewater treatment plants were examined in this study. The sewage sludge samples with CaO, without CaO, dry and wet (70 wt.% moisture) were used. The pyrolysis experiments were conducted in two reactor setups at 750 °C and 850 °C. The effect of pyrolysis temperature, heating rate on the gaseous pyrolysis products as well as thermal behavior of sewage sludge were investigated. The CaO addition increased the total yield of pyrolysis gaseous products, whereas moisture significantly increased CO2 production as well as CO and CH4.

Importance of Initial Moisture Content and Bulking Agent for Biodrying Sewage Sludge

For the final disposal and reutilization of organic wastes, reduction of moisture content (MC) is essential because water contained in the organic waste generates leachate, lowers energy content, and indirectly causes odor problems. MC also directly determines the drying cost. In this study, MC of sewage sludge was effectively decreased by applying a biodrying process in which the microbial metabolic heat evaporated the water. By controlling the initial MC through air drying and its subsequent biodrying, it was found that 50–70 wt% was the optimal initial MC range for the sludge biodrying process. In this range, 33.7–47.1% of the initial water was removed by consuming 12.3–21.2% of the volatile solids (VS) initially contained in the sludge during 10 days of biodrying. When treating the same amount of raw sludge, air-dried and biodried sludge showed better performance as bulking agents than rubber and sawdust. About 55.1% of the initial water was removed from the mixture with air-dried sludge by consuming 23.8% of the initial VS and 38.3% of the initial water was lost from the sludge mixture with biodried sludge by consuming 14.0% of the initial VS during 12.1 days of biodrying. When rubber and sawdust were used as the bulking agents, only 18.2 and 16.5% of the initial water was removed, respectively. It was thought that the easily biodegradable VS contained in the air-dried sludge produced more heat and consequently removed more water. Although air-dried sludge showed better performance than biodried sludge, the use of biodried sludge as a bulking agent was thought to be more practical than air-dried sludge because biodried sludge can be used as bulking agent for the next round of biodrying in a repeated operation of the biodrying reactor. After biodrying, the lower heating value of the biodried sludge (51.5 wt% of MC) was 14.644 MJ kg−1, which was much higher than that of the original wet sludge.

Experimental Studey on Fuel Production with the Use of Sewage Sludge

The present study is to produce the high calorific fuel using sewage sludge. Consideration is given to the effects of implication water rate of sewage sludge, temperature, and vacuum pressure on the optimum production condition and the high calorific fuel. In order to reduce the initial moisture content of sewage sludge, the vacuum drying method which is modified here is employed. It is found from the study that the lower implication water rate causes the higher caloric fuel and the maximum calorific value developed here is similar to that of woody pellet for reference. This application will accelerate the reuse and reduce of sewage sludge.

Effect of moisture content on the characterization of products from the pyrolysis of sewage sludge

Sewage sludge samples with moisture contents of 0%, 31%, 47% and 80% were pyrolyzed at 1000°C in a tubular furnace to evaluate the effect of moisture content on the pyrolysis process. The evaporation of water accelerated the evolution of porosity in the solid char and hence contributed to the devolatilization of sewage sludge, leading to an increase in the gas fraction and a decrease in the solid fraction. The steam-rich atmosphere generated by the high moisture content of sewage sludge favored the steam reforming reactions of volatile compounds and the steam gasification of solid char, enhancing the production of hydrogen rich fuel gas. A saturation value was also observed for the steam involved in the gasification and reforming reactions. GC–MS analysis showed that the increase of moisture content not only promoted the reduction of the species in the tar, but also improved the production of light aromatics, as a result, the toxic effect of tar decreased considerably. The decrease in the peak areas of organic functional groups of solid char demonstrated that the participation of steam promoted the ejection of volatile matters of sewage sludge during the pyrolysis process.

Hydrogen-Rich Gas Production from Microwave Pyrolysis of Sewage Sludge at High Temperature

Microwave pyrolysis of sewage sludge was conducted in a single-mode microwave oven. The influencing effects of experimental factors, including particle size and moisture content of sewage sludge, pyrolysis temperature, and shape of microwave adsorber, on concentration of pyrolysis gas products were studied. The results indicated that with the decrease of particle size, the H2 concentration increased from 31 vol.% to 34 vol.%, and CO concentration increased from 17 vol.% to 22 vol.%. When the moisture content of sewage sludge increased from 0 to 83 wt.%, the H2 concentration increased from 32 vol.% to 42 vol.%, and the CO concentration increased from 20 vol.% to 31 vol.%. Compared with microwave adsorber in powder phase, the microwave adsorber in fixed structure can transform more volatile compounds to uncondensable gas, and the concentrations of H2 and CO were also slightly increased.

Time domain reflectometry measured moisture content of sewage sludge compost across temperatures

Time domain reflectometry (TDR) is a prospective measurement technology for moisture content of sewage sludge composting material; however, a significant dependence upon temperature has been observed. The objective of this study was to assess the impacts of temperature upon moisture content measurement and determine if TDR could be used to monitor moisture content in sewage sludge compost across a range of temperatures. We also investigated the combined effects of temperature and conductivity on moisture content measurement. The results revealed that the moisture content of composting material could be determined by TDR using coated probes, even when the measured material had a moisture content of 0.581cm3cm−3, temperature of 70°C and conductivity of 4.32mScm−1. TDR probes were calibrated as a function of dielectric properties that included temperature effects. When the bulk temperature varied from 20°C to 70°C, composting material with 0.10–0.70cm3cm−3 moisture content could be measured by TDR using coated probes, and calibrations based on different temperatures minimized the errors.

A cost analysis of sewage sludge composting for small and mid-scale municipal wastewater treatment plants

Abstract The costs of building and operating windrow, aerated static pile (ASP), and horizontal agitated solids bed (HASB) sewage sludge composting facilities for small and mid-scale municipal wastewater treatment plants are analyzed. The capital costs and total annual costs of the composting facilities analyzed range from US$164 200 to US$349 000 and from US$100 000 to US$295 700, respectively. On a per-input-dry-Mg basis, composting costs range from US$55.31 to US$173.66/dry Mg handled depending on the type of system and the moisture content of sewage sludge. Moisture content of sewage sludge is the key factor of capital costs and operating costs for different composting facilities. The lower the moisture content of sewage sludge, the less the capital and operating costs for different composting facilities. A windrow composting facility is cheaper to build and operate than ASP and HASB composting facilities. The dominant components of capital costs for windrow are land acquisition and surfacing, and that for ASP and HASB is equipment. Bulking agents and labor are the key factors of operating costs for sludge composting facilities. The availability of land and the costs of bulking agent will significantly limit the spreading of windrow system in small and mid-scale municipal wastewater treatment plants; however, it is suitable for spreading ASP and HASB sewage sludge composting systems for small and mid-scale municipal wastewater treatment plants in China.