Technology For Sewage Sludge Treatment Research Articles

Enhancing hydrochar production and mitigating heavy metal risks in sewage sludge: The role of ultrasonic pretreatment in hydrothermal carbonization

Hydrothermal carbonization (HTC) is a potentially valuable technology for sewage sludge treatment and resource utilization. This study proposes a combined process of ultrasonic pretreatment and HTC to improve the yield and properties of hydrochar derived from sewage sludge (SS). SS was ultrasonically pretreated at different sound energy densities (0.6 – 1.4 W/mL) and pretreatment times (5 – 30 min), and then HTC conducted for 4 h in an autoclave. Ultrasonic pretreatment markedly enhanced the apparent structure and particle size of the feedstock, thereby improving the hydrothermal reactivity of SS. After ultrasonic pretreatment at 1.4 W/mL for 15 min, the yield of hydrochar derived from SS was 11.25% higher than that obtained after direct HTC. The hydrochar yield was also correlated with the ultrasonic pretreatment parameters. Ultrasonic pretreatment increased the specific surface area and number of oxygen-containing functional groups of the hydrochar and increased the energy density and energy yield by at most 7.63% and 9.56%, respectively. The impact of ultrasonic pretreatment on the heavy-metal pollution risk of hydrochar was evaluated in terms of the geological acumination index. Pretreatment with appropriate ultrasonic parameters decreased the pollution risks of Zn, Cu, Cr, and Pb. This study provides a valuable perspective on combined feedstock pretreatment and HTC, increasing the product value of HTC of sewage sludge.

Techno-Economic and Environmental Analysis of a Sewage Sludge Alternative Treatment Combining Chemical Looping Combustion and a Power-to-Methane System

An innovative process layout for sludge waste management based on chemical looping combustion and flue gas methanation is analyzed in this work. The technical performance of the system was assessed by considering that the flue gas is first purified and then mixed with a pure hydrogen stream sourced from an array of electrolysis cells to produce methane. The life cycle assessment (LCA) and life cycle cost (LCC) methodologies were applied to quantify the environmental and economic performances of the proposed process, and a hotspot analysis was carried out to recognize its most critical steps. The proposed system was then compared with a reference system that includes both the conventional waste management pathways for the Italian context and methane production. Finally, to account for the variability in the future economic climate, the effects of changes in landfill storage costs on sewage end-of-life costs for both the proposed and reference systems were evaluated. With respect to 1 kg/h of sewage sludge with 10%wt of humidity, the analysis shows that the proposed system (i) reduces landfill wastes by about 68%, (ii) has an end-of-life cost of 1.75 EUR × kg−1, and (iii) is environmentally preferable to conventional sewage sludge treatment technologies with respect to several impact categories.

An evidence theory-based large group FMEA framework incorporating bounded confidence and its application in supercritical water gasification system

Supercritical water gasification (SCWG) is an advanced technology for sewage sludge treatment, which can effectively remove hazardous substances in it and realize the resource utilization of sludge. Given the harsh operating environment and complex operating process, it is particularly critical for SCWG system to adopt failure mode and effects analysis (FMEA) to ensure its reliability and security. In particular, the risk management process of SCWG system needs to include two considerations: the evaluation process requires the participation of a large number of team members (TMs) with different professional knowledge and operational skills, and the cross-correspondence between the factors within the system cannot be ignored in the analysis process. Thus, an FMEA framework is established to meet practical needs, which can model TMs’ personality traits and reflect the interdependencies between factors. First, assessments in the form of probability linguistic term sets (PLTSs) are converted into mass functions due to the excellence of evidence theory in information aggregation. Second, a bounded confidence-based clustering method is developed to consider TMs’ willingness to interact during clustering. Additionally, evidence conflicts are managed using a new discounting method that captures TMs’ stubbornness. Besides, the cross-correspondence between factors is analyzed by an evidence theory-based DEMATEL method. Further considering TMs’ bounded rationality, regret theory (RT) is used to distinguish and prioritize failure modes (FMs). Finally, a case study of an SCWG system is successfully solved by applying the proposed framework. The effectiveness and superiority are subsequently demonstrated by a series of analyses and discussions.

Socio-Economic, Technical and Environmental Indicators for Sustainable Sewage Sludge Management and LEAP Analysis of Emissions Reduction

The waste management sector is transitioning from a dirty and undesirable industry towards a green and sustainable future where energy and materials are recycled. Recycling has potential in sewage sludge treatment, where energy and highly valuable nutrients can be recovered through innovative and sustainable sludge management. Although there are many technologies and techniques already used for sewage sludge, the indicators for their sustainability are not developed. In terms of sustainable and innovative sewage sludge treatment, usually, only techno-economic aspects of existing and current technologies are considered. We explore the existing indicators and propose new indicators for sustainable and innovative sewage sludge treatment technologies. The indicators are differentiated into four main categories: technical, social, environmental and economic, where specific indicators are explained, followed by a description of their impact on sustainability. We also consider a case study using the LEAP tool, which considered GHG emissions when utilizing sewage sludge as an energy feedstock to replace existing fossil fuels in the energy mix in several scenarios. The results showed a significant emissions reduction when sludge is used—37.6% and 90.9% in 2030 and 2050, respectively.

Removal of organic pollutants (pharmaceuticals and pesticides) from sewage sludge by hydrothermal carbonization using response surface methodology (RSM)

AbstractBACKGROUNDConventional wastewater treatment plants (WWTPs) cannot degrade completely emerging pollutants such as pharmaceuticals and pesticides. The release of such contaminants through WWTP effluents or sludge disposal is of high environmental concern. Hydrothermal treatment has been adopted as alternative treatment technology for sludge to recover energy and valuable products. This study demonstrates the removal of inherent concentration levels of organic pollutants from the previous classes under variable reaction conditions, i.e. temperature, reaction time and sludge‐to‐water (%wt) ratio.RESULTSResponse surface methodology (RSM) was applied to model removal efficiency for the sum of detected pharmaceutical compounds and to evaluate the significant operational parameters. The results showed that higher values of temperature and time enhanced the percent degradation efficiency while sludge‐to‐water (%wt) ratio was not a significant factor affecting the removal process. The maximum removal efficiency of pharmaceutical residues reached 89.8% under the following conditions: 220 °C, 360 min reaction time, 7.50%wt sludge‐to‐water ratio. Additionally, hydrothermal treatment removed completely trace levels of detected pesticides, regardless of the applied conditions. RSM was also applied separately to those pharmaceuticals (i.e., amisulpride and amitriptyline) detected most frequently and at higher concentrations in sludge samples. Both compounds have been degraded at >90% using reaction temperatures from 205 to 220 °C and reaction time between 297 and 360 min with 7.5% sludge/H2O ratio.CONCLUSIONHydrothermal treatment is a suitable and promising technology for sewage sludge treatment for the efficient destruction of organic pollutants and the production of renewable hydrochars. © 2022 Society of Chemical Industry (SCI).

Transformation and Mobility of Cu, Zn, and Cr in Sewage Sludge during Anaerobic Digestion with Pre- or Interstage Hydrothermal Treatment.

Anaerobic digestion (AD) combined with hydrothermal treatment (HT) is an attractive technology for sewage sludge treatment and resource recovery. The fate and distribution of heavy metals in the sludge during combined HT/AD significantly affect the sludge final disposal/utilization options, yet such information is still lacking. This study systematically characterizes the transformation of important heavy metals Cu, Zn, and Cr in sewage sludge during AD with pre- or interstage HT (i.e., HT-AD or AD-HT-AD, respectively). Complementary sequential chemical extraction and X-ray absorption spectroscopy were used to characterize the speciation and mobility of metals. For the HT-AD system, both Cu and Zn predominantly occur as sulfides in HT hydrochars. Subsequent AD favors the formation of Cu2S and partial transformation of nano-ZnS to adsorbed and organo-complexed Zn species. HT favors the formation of Cr-bearing silicates in hydrochars, whereas Fe(III)-Cr(III)-hydroxide and Cr(III)-humic complex are the predominant Cr species in AD solids. Similar reaction pathways occur in the AD-HT-AD system with some minor differences in metal species and contents, as the first-stage AD changed the sludge matrix. These findings have important implications for understanding the fate and mobility of heavy metals in sludge-derived hydrochars and AD solids.

Sewage Sludge Thermal Treatment Technology Selection by Utilizing the Analytical Hierarchy Process

Sewage sludge management has gained significance in the last several years, due to its nutrient and energy content. However, technology selection is one of the greater challenges because it is not possible to implement a technology that covers all the requirements of the considered environments. Consequently, this paper shows an example of the utilization of an analytical hierarchy process, as a decision-making tool in terms of technology selection, for sewage sludge management in Rijeka, Croatia. The criteria structuring and evaluation process with the description of several possible alternatives for thermal treatment technologies are defined within this research. For the case of Rijeka, the best and most suitable technology for sewage sludge treatment is gasification, which coincides with the results obtained from the analysis of the literature review. According to the results in this paper, the possibilities of the use of this scientific method on the national level for the selection of sewage sludge treatment technology should be considered, due to the simplicity of its use and capability of its adaptation to various situations and areas.

Environmental impact and economic benefit evaluation of sewage sludge treatment technologies

In order to evaluate the environmental and economic performance of continuous thermal hydrolysis (CTH) of sludge disposal, we compare the CTH with three traditional technologies including anaerobic digestion, aerobic composting and dry-incineration. This study uses life cycle assessment (LCA) to assess their environmental impact of the above technologies, and selects ten characteristic indicators from e-Balance analysis software for quantification. We also adopt the cost-benefit ratio (B/C) to evaluate the technologies’ economic performances, and come to conclusion that the larger the value is, the more economically feasible it will be. The results show that, as a new sludge disposal technology, CTH has the best performance in both environmental and economic aspects, while dry-incineration and anaerobic digestion have the worst results in environmental and economic aspect respectively. Although sludge compost has a moderating effect on global warming, it could also be potentially toxic. Nevertheless, the use of raw materials and energy contributes significantly to the environmental impact of each scheme.

Competition Between Chemolithotrophic Acetogenesis and Hydrogenotrophic Methanogenesis for Exogenous H2/CO2 in Anaerobically Digested Sludge: Impact of Temperature.

Anaerobic digestion is a widely applied technology for sewage sludge treatment. Hydrogen and CO2 are important degradation products, which serve as substrates for both hydrogenotrophic methanogenesis and chemolithotrophic acetogenesis. In order to understand the competition between these processes for H2/CO2, sludge samples were incubated under H2/CO2 headspace at different temperatures, and analyzed with respect to turnover of H2, CO2, CH4 and acetate including their δ13C values. At 15°C, 13C-depleted acetate (δ13C of −41 to −43‰) and transient acetate accumulation were observed under H2/CO2, and CH4 accumulated with δ13C values increasing from −53 to −33‰. The copy numbers of the fhs gene, which is characteristic for acetogenic bacteria, were at 15°C one order of magnitude higher in the H2/CO2 incubations than the N2 control. At 30°C, however, acetate did not accumulate in the H2/CO2 incubation and the δ13C of CH4 was very low (−100 to −77‰). At 50°C, isotopically enriched acetate was transiently formed and subsequently consumed followed by the production of 13C-depleted CH4. Collectively, the results indicate a high contribution of chemolithotrophic acetogenesis to H2/CO2 utilization at 15°C and 50°C, while H2/CO2 was mainly consumed by hydrogenotrophic methanogenesis at 30°C. Fermentative production and methanogenic consumption of acetate were active at 50°C.

Perlite as the partial substitute for organic bulking agent during sewage sludge composting.

Composting is an efficient and cost-effective technology for sewage sludge treatment, and bulking agents are essential in sewage sludge composting. In this study, perlite was chosen as inorganic bulking agent to partially substitute for the organic bulking agent. Variations in the temperature, bulk density, moisture content, pH, electrical conductivity, organic carbon, nitrogen, phosphorus and potassium were detected during sewage sludge composting. The treatment with a mass ratio of spent mushroom substrate to perlite at 3:1 exhibited the highest pile temperature and the best effect on reducing bulk density and moisture content. In addition, Fourier transform infrared spectra showed that perlite promotes the degradation of organic matter during the composting process, and the germination index showed that the compost from all treatments was safe for agricultural application. When the mass ratios of spent mushroom substrate and perlite at 3:1 and 2:2 were chosen as bulking agents, the sewage sludge compost product could be used to produce plant cultivation substrate, and economic benefits could be obtained from sewage sludge composting according to comprehensive cost analysis.

Screw pyrolysis technology for sewage sludge treatment

Sewage sludge quantities have grown continuously since the introduction of the European Directive (UWWTD 91/271/EEC) relating to the treatment of urban wastewater. In the present, most of the sewage sludge is combusted in single fuels incineration plants or is co-fired in waste incineration or coal power plants. The combustion of sewage sludge is a proven technology. Other treatments, such as fluidized bed gasification, were successfully adopted to produce suitable syngas for power production. Besides, the number of large wastewater treatment plants is relatively small compared to the local rural ones. Moreover, alternative technologies are arising with the main target of nutrients recovery, with a special focus on phosphorus. The aforementioned issues, i.e. the small scale (below 1MW) and the nutrients recovery, suggest that pyrolysis in screw reactors may become an attractive alternative technology for sewage sludge conversion, recovery and recycling. In this work, about 100kg of dried sewage sludge from a plant in Germany were processed at the newly developed STYX Reactor, at KIT. The reactor combines the advantages of screw reactors with the high temperature filtration, in order to produce particle and ash free vapors and condensates, respectively. Experiments were carried out at temperatures between 350°C and 500°C. The yield of the char decreased from 66.7wt.% to 53.0wt.%. The same trend was obtained for the energy yield, while the maximum pyrolysis oil yield of 13.4wt.% was obtained at 500°C. Besides mercury, the metals and the other minerals were completely retained in the char. Nitrogen and sulfur migrated from the solid to the condensate and to the gas, respectively. Based on the energy balance, a new concept for the decentral production of char as well as heat and power in an externally fired micro gas turbine showed a cogeneration efficiency up to about 40%.

Historical development of wastewater and sewage sludge treatment technologies in Japan – An analysis of patent data from the past 50 years

It is well known that Japan has successfully dealt with severe water pollution that was caused during its rapid economic growth. The lessons learned by Japan, the technological developments that emerged and the policy measures Japan devised to cope with its pollution are shared widely with Asian countries that now face severe water pollution associated with economic growth. However, this information has been basically qualitative in nature. In this paper we discuss the potential of using patent data and perform analyses to substantiate the insights such data can yield in order to provide more quantitative information on historical trends in the development of essential technologies in this field. Specifically, we demonstrate an approach using patent data to verify the historical development of wastewater and sewage sludge treatment technologies over the past 50 years in Japan. We examined relevant patent data from 1961 onward and addressed technological development trends in relation to societal changes and the implementation of governmental policies during that period. As an example of the substantiating analysis, we applied principal component analysis and text mining to review the trends in a systematic manner. We demonstrate that the emergence of such developments can be closely associated with societal background factors such as the adoption of relevant governmental policies. We argue that this kind of patent data analysis, coupled with other essential data, can yield clues to the evolution of relevant technologies in the past, leading to useful implications for environmental management of economically developing nations.

Synergistic effect of rice husk addition on hydrothermal treatment of sewage sludge: Fate and environmental risk of heavy metals

Hydrothermal treatment (HTT) at 200°C was applied to immobilize heavy metals (HMs) and the effect of rice husk (RH) addition was investigated based on total HMs concentration, fractionation and leaching tests. The results indicated that a synergistic effect of RH addition and HTT could be achieved on reducing the risk of HMs from medium and low risk to no risk. Metals were redistributed and transformed from weakly bounded state to stable state during the HTT process under RH addition. Notably at a RH/sludge ratio of 1/1.75 (d.w.), all the HMs showed no eco-toxicity and no leaching toxicity, with the concentrations of leachable Cr, Ni, Cu and Cd decreased by 17%, 89%, 95% and 93%, respectively. This synergistic effect of RH addition and HTT on the risk reduction of HMs implies that HTT process with RH addition could be a promising and safe disposal technology for sewage sludge treatment in practice.

Hybrid Life-Cycle Environmental and Cost Inventory of Sewage Sludge Treatment and End-Use Scenarios: A Case Study from China

Sewage sludge management poses environmental, economic, and political challenges for wastewater treatment plants and municipalities around the globe. To facilitate more informed and sustainable decision making, this study used life-cycle inventory (LCI) to expand upon previous process-based LCIs of sewage sludge treatmenttechnologies. Additionally, the study evaluated an array of productive end-use options for treated sewage sludge, such as fertilizer and as an input into construction materials, to determine how the sustainability of traditional manufacturing processes changes with sludge as a replacement for other raw inputs. The inclusion of the life-cycle of necessary inputs (such as lime) used in sludge treatment significantly impacts the sustainability profiles of different treatment and end-use schemes. Overall, anaerobic digestion is generally the optimal treatment technology whereas incineration, particularly if coal-fired, is the most environmentally and economically costly. With respect to sludge end use, offsets are greatest for the use of sludge as fertilizer, but all of the productive uses of sludge can improve the sustainability of conventional manufacturing practices. The results are intended to help inform and guide decisions about sludge handling for existing wastewater treatment plants and those that are still in the planning phase in cities around the world. Although additional factors must be considered when selecting a sludge treatment and end-use scheme, this study highlights how a systems approach to planning can contribute significantly to improving overall environmental sustainability.

Novel Strategies in Sewage Sludge Treatment

AbstractSewage sludge is not only the sink for nutrients removed from wastewater but also for hazardous substances. When sewage sludge is reused in agriculture these hazardous substances can be harmful to the environment depending on their concentration. Nevertheless, the mere disposal of sewage sludge cannot be purposeful as the contained nutrients and the organic material offer a biologically valuable fertilizer. Currently, agricultural reuse of sewage sludge is discussed controversially in Germany. Changes in legal requirements for sewage sludge application are planned that will set lower limit values for hazardous substances and higher quality requirements in general. With these new restrictions, sewage sludges may not be suitable for agricultural reuse any longer. The focus is on alternative sewage sludge treatment technologies that gain the most economic and ecological benefit from the sludge's valuables. Several technologies for nutrient recovery, especially phosphorus, have been developed to recycle finite natural resources. This article will provide an overview on novel strategies for sewage sludge treatment and management especially in regard to new legal requirements.

Attribution of sewage sludge and sludge-based char in a fluidized bed reactor

Fluidized bed pyrolysis has been recognized as an innovative technology for sewage sludge treatment. The physical and attrition properties of sewage sludge are changed through the fluidized bed pyrolysis. The minimum fluidization velocities and attribution rate constants for sewage sludge and sludge based-char were obtained from pressure drop and attribution tests. As a result, sewage sludge with 20% moisture content and char were classified as Geldart B solids and the superficial gas velocity for bubbling fluidization was 0.2142-0.8755 m/s. In addition, attribution of the sewage sludge and char was more affected by particle size than by material type. The equations for the overall attrition rate constants are Ka × 105 = 1.09U − 14.82 for sludge and ln ka = 0.1(U−Umf)− 13.63 for char, respectively.