The feasibility and applicability of sequential extraction of high value-added biogenic materials from sewage sludge.

The sequential extraction routes of biogenic materials from sewage sludge (SS) were investigated. Physical methods (ultrasound, heating) and chemical methods (sodium hydroxide, sodium carbonate) were used to extract extracellular polymeric substances (EPS) and alginate-like extracellular polymers (ALEs) from SS. The residues after extraction were further subjected to physical methods (heating) and chemical methods (sulfuric acid, sodium hydroxide) for protein extraction. A comparison was made between sequential extraction routes and direct extraction of biomaterials from sludge in terms of extraction quantity, material properties, and applicability. The results showed that sequential extraction of biomaterials is feasible. The highest extraction quantities were obtained when using sodium carbonate for EPS and ALE extraction and sodium hydroxide for protein, reaching 449.80 mg/gVSS, 109.78 mg/gVSS, and 5447.08 mg/L, respectively. Sequential extraction procedures facilitate the extraction of biomaterials. Finally, suitable extraction methods for different application scenarios were analyzed.

A bibliometric perspective on the occurrence and migration of microplastics in soils amended with sewage sludge.

The land application of sewage sludge from wastewater treatment plants has been recognized as a major source of microplastic contamination in soil. Nevertheless, the fate and behavior of microplastics in soil remain uncertain, particularly their distribution and transport, which are poorly understood. This study does a bibliometric analysis and visualization of relevant research publications using the CiteSpace software. It explores the limited research available on the topic, highlighting the potential for it to emerge as a research hotspot in the future. Chinese researchers and institutions are paying great attention to this field and are promoting close academic cooperation among international organizations. Current research hot topics mainly involve microplastic pollution caused by the land application of sewage sludge, as well as the detection, environmental fate, and removal of microplastics in soil. The presence of microplastics in sludge, typically ranging from tens of thousands to hundreds of thousands of particles (p)/kg, inevitably leads to their introduction into soil upon land application. In China, the estimated annual accumulation of microplastics in the soil due to sludge use is approximately 1.7 × 1013 p. In European countries, the accumulation ranges from 8.6 to 71 × 1013 p. Sludge application has significantly elevated soil microplastic concentrations, with higher application rates and frequencies resulting in up to several-fold increases. The primary forms of microplastics found in soils treated with sludge are fragments and fibers, primarily in white color. These microplastics consist primarily of components such as polyamide, polyethylene, and polypropylene. The vertical transport behavior of microplastics is influenced by factors such as tillage, wind, rainfall, bioturbation, microplastic characteristics (e.g., fraction, particle size, and shape), and soil physicochemical properties (e.g., organic matter, porosity, electrical conductivity, and pH). Research indicates that microplastics can penetrate up to 90 cm into the soil profile and persist for decades. Microplastics in sewage sludge-amended soils pose potential long-term threats to soil ecosystems and even human health. Future research should focus on expanding the theoretical understanding of microplastic behavior in these soils, enabling the development of comprehensive risk assessments and informed decision-making for sludge management practices. PRACTITIONER POINTS: Microplastics in sewage sludge range from tens to hundreds of thousands per kilogram. Sludge land application contributes significantly to soil microplastic pollution. The main forms of microplastics in sludge-amended soils are fragments and fibers. Microplastics are mainly composed of polyamide, polyethylene, and polypropylene. Microplastics can penetrate up to 90 cm into the soil profile and persist for decades.

Effect of separation pretreatment on environmental and economic performance of sludge resource utilization.

As a new technology for accurate utilization of sludge resources, sludge inorganic-organic matter separation (IOMS) has attracted wide attention. This study examined the impact of this pretreatment on environmental and economic performance of sludge composting and incineration using life cycle assessment (LCA) and whole life costing (WLC). LCA results indicated that IOMS pretreatment reduced the energy conservation and emission reduction (ECER) values of composting and incineration by 56 % and 76 %, respectively. Meanwhile, WLC exhibited that IOMS pretreatment could cut the break-even year of incineration from 11 years to 4 years. The combination of organic sludge incineration/composting with inorganic sludge sintering ceramsite reveals excellent environmental and economic performance. The application optimization hypothesis analysis of these two routes in various provinces of China indicates that Jiangsu has the greatest development potential and should become a major promotion region.

Enhanced medium-chain fatty acid production from sewage sludge by combined electro-fermentation and anaerobic fermentation.

Electro-fermentation (EF) was combined with anaerobic fermentation (AF) to promote medium-chain fatty acid (MCFA) from sewage sludge. Results showed that EF at acidification process significantly increased short-chain fatty acid (SCFA) production of by 0.5 times (82.4 mmol C/L). AF facilitated the chain elongation (CE) process by enhancing the SCFA conversion. Combined EF at acidification and AF at CE (EF-AF) achieved the highest MCFA production of 27.9 mmol C/L, which was 20 %-866 % higher than the other groups. Electrochemical analyses showed that enhanced SCFA and MCFA production was accompanied with good electrochemical performance at acidification and CE. Microbial analyses showed that EF-AF promoted MCFA production by enriching electrochemically active bacteria (EAB, Bacillus sp.). Enzyme analyses indicated that EF-AF promoted MCFA production by enriching the functional enzymes involved in Acetyl-CoA formation and the fatty acid biosynthesis (FAB) pathway. This study provided new insights into the production of MCFA from enhanced sewage sludge.

Study on the performance of biochar prepared from walnut shell and traditional graphene electrode plate in the treatment of domestic sewage in microbial fuel cells.

As a new pollutant treatment technology, microbial fuel cell (MFC) has a broad prospect. In this article, the devices assembled using walnut shells are named biochar-microbial fuel cell (B-MFC), and the devices assembled using graphene are named graphene-microbial fuel cell (G-MFC). Under the condition of an external resistance of 1,000 Ω, the B-MFC with biochar as the electrode plate can generate a voltage of up to 75.26 mV. The maximum power density is 76.61 mW/m2, and the total internal resistance is 3,117.09 Ω. The removal efficiency of B-MFC for ammonia nitrogen (NH3-N), chemical oxygen demand (COD), total nitrogen (TN), and total phosphorus (TP) was higher than that of G-MFC. The results of microbial analysis showed that there was more operational taxonomic unit (OTU) on the walnut shell biochar electrode plate. The final analysis of the two electrode materials using BET specific surface area testing method (BET) and scanning electron microscope (SEM) showed that the pore size of walnut shell biochar was smaller, the specific surface area was larger, and the pore distribution was smoother. The results show that using walnut shells to make electrode plates is an optional waste recycling method and an electrode plate with excellent development prospects.

Assessing infectivity of emerging enveloped viruses in wastewater and sewage sludge: Relevance and procedures.

The emergence of SARS-CoV-2 has heightened the need to evaluate the detection of enveloped viruses in the environment, particularly in wastewater, within the context of wastewater-based epidemiology. The studies published over the past 80 years focused primarily on non-enveloped viruses due to their ability to survive longer in environmental matrices such as wastewater or sludge compared to enveloped viruses. However, different enveloped viruses survive in the environment for different lengths of time. Therefore, it is crucial to be prepared to assess the potential infectious risk that may arise from future emerging enveloped viruses. This will require appropriate tools, notably suitable viral concentration methods that do not compromise virus infectivity. This review has a dual purpose: first, to gather all the available literature on the survival of infectious enveloped viruses, specifically at different pH and temperature conditions, and in contact with detergents; second, to select suitable concentration methods for evaluating the infectivity of these viruses in wastewater and sludge. The methodology used in this data collection review followed the systematic approach outlined in the PRISMA (Preferred Reporting Items for Systematic Review and Meta-Analysis) guidelines. Concentration methods cited in the data gathered are more tailored towards detecting the enveloped viruses' genome. There is a lack of suitable methods for detecting infectious enveloped viruses in wastewater and sludge. Ultrafiltration, ultracentrifugation, and polyethylene glycol precipitation methods, under specific/defined conditions, appear to be relevant approaches. Further studies are necessary to validate reliable concentration methods for detecting infectious enveloped viruses. The choice of culture system is also crucial for detection sensitivity. The data also show that the survival of infectious enveloped viruses, though lower than that of non-enveloped ones, may enable environmental transmission. Experimental data on a wide range of enveloped viruses is required due to the variability in virus persistence in the environment.

Global performance and trends of research on emerging contaminants in sewage sludge: A Bibliometric Analysis from 1990 to 2023.

The pervasive occurrence of emerging contaminants (ECs) in sewage sludge (SWS) poses significant safety challenges concerning the processing, disposal, and secure application, ultimately jeopardizing both human health and the ecological environment. To comprehensively comprehend the evolutionary trajectories, present state, and research advancements in the field of ECs in SWS, a systematic was conducted, scrutinizing the annual publication quantity, disciplinary distribution, core authors, involved nations/regions, pertinent keywords, and citation status of 2082 research publications related to ECs in SWS from 1990 to 2023. The results indicate a substantial upward trajectory in the research literature pertaining to ECs in SWS. The study of ECs in SWS encompasses 78 disciplines, including Environmental Sciences, Environmental Engineering, and Water Resources. China, Spain, and the USA ranked among the top three countries in terms of both total publications and citation frequency. The majority of publications were published in reputable high-impact journals such as Science of the Total Environment, Chemosphere, and Bioresource Technology. Based on high-frequency keywords, co-occurrence networks of keywords, and keywords burst analysis, it is found that the occurrence and environment behavior of ECs in SWS (ARGs, microplastics, PPCPs, and POPs), the detection and analytical methods, the impact on SWS treatment and disposal processes, and the accumulation and ecological risks in plants and soil during SWS land utilization, are the main research directions and hot topics in this field. In the future, the study of the impact of SWS treatment technologies on ECs removal is expected to receive increased research attention.

Subsurface wastewater infiltration systems for nitrogen pollution control.

Subsurface wastewater infiltration systems (SWISs) are suggested to be a cost-effective and environmentally friendly method for sewage treatment. However, a comprehensive summary of the relevant mechanisms and optimization methods for nitrogen (N) removal in SWIS is currently lacking. In this review, we first summarize the N transformation mechanisms in SWIS. The impact of operational parameters on the N removal efficiency is then delineated. To enhance pollutant removal and minimize resource wastage, it is advisable to maintain a wet-dry ratio of 1:1 and a hydraulic loading rate of 8-10 cm/day. The organic load should be determined based on influent characteristics to optimize the balance between sewage treatment and nitrous oxide (N2O) emission. Finally, various strategies and modifications have been suggested to enhance pollutant removal efficiency and reduce N2O emissions in SWIS, such as artificial aeration, supply electron donors, and well-designed structures. Overall, greater emphasis should be placed on the design and management of SWIS to optimize their co-benefits while effectively controlling N pollution. PRACTITIONER POINTS: SWISs are often considered black boxes with their efficiency depending on hydraulic characteristics, biological characteristics, and substrate properties. Biological nitrification coupled with denitrification is considered to be the major N removal process. Increasing the reduction of N2O to the inert N2 form is a potential mechanism to mitigate global warming. Strategies such as artificial aeration, supply electron donors, and well-designed structures are suggested to improve N removal performance.

Physico-chemical characterization and possible uses of sludge processed from an urban sewage treatment plant.

Nowadays, the challenge is to transform dehydrated sewage sludge resulting from wastewater treatment plants from waste into resource. Following this objective, the sludge was further dried and submitted to X-ray diffraction (XRD) and FTIR analysis. The sludge was first dried in ventilated and unventilated spaces at 50 ∘C and 100 ∘C, for 60 and 100 minutes (min) in each case. The final mass and evaporation degree of the sludge depends on the initial mass, ventilation type, drying time, and temperature. The ventilated drying space is preferred for temperature control, homogeneity, and higher evaporation degree. The influence of the drying process on the structure and behavior of the sewage sludge was emphasized through X-ray diffraction (XRD) and FTIR analysis. The XRD shows good structural properties of the sludge samples given by the reduction of the particle size through evaporation. According to FTIR, evaporation influences the depolymerization of the silicate network. The hydroxyl units and metallic ion modifiers can improve the sludge structure, but its intensity decreases through evaporation. With high content of solid substance, and good relation between the composition of the sludge and its structure and behavior, the dried sewage sludge can be used in: (i) agriculture, (ii) construction, (iii) the energy sector.

Detection and modeling of Staphylococcus aureus and fecal bacteria in Hawaiian coastal waters and sands.

Microbial pollution of recreational waters leads to millions of skin, respiratory, and gastrointestinal illnesses globally. Fecal indicator bacteria (FIB) are monitored to assess recreational waters but may not reflect the presence of Staphylococcus aureus, a global leader in bacterial fatalities. Since many community-acquired S. aureus skin infections are associated with high recreational water usage, this study measured and modeled S. aureus, methicillin-resistant S. aureus (MRSA), and FIB (Enterococcus spp., Clostridium perfringens) concentrations in seawater and sand at six beaches in Hilo, Hawai'i, USA, over 37 sample dates from July 2016 to February 2019 using culturing techniques. Generalized linear models predicted bacterial concentrations with physicochemical and environmental data. Beach visitors were also surveyed on their preferred activities. S. aureus and FIB concentrations were roughly 6-78 times higher at beaches with freshwater discharge than at those without. Seawater concentrations of Enterococcus spp. were positively associated with MRSA but not S. aureus. Elevated S. aureus was associated with lower tidal heights, higher freshwater discharge, onsite sewage disposal system density, and turbidity. Regular monitoring of beaches with freshwater input, utilizing real-time water quality measurements with robust modeling techniques, and raising awareness among recreational water users may mitigate exposure to S. aureus, MRSA, and FIB. PRACTITIONER POINTS: Staphylococcus aureus and fecal bacteria concentrations were higher in seawater and sand at beaches with freshwater discharge. In seawater, Enterococcus spp. positively correlated with MRSA, but not S. aureus. Freshwater discharge, OSDS density, water turbidity, and tides significantly predicted bacterial concentrations in seawater and sand. Predictive bacterial models based upon physicochemical and environmental data developed in this study are readily available for user-friendly application.

Application of Magnetic Materials Combined with Echo® Mass Spectrometry System in Analysis of Illegal Drugs in Sewage.

The aim of this study is to solve the problems of the complicated pretreatment and high analytical cost in the detection technology of trace drugs and their metabolites in municipal wastewater. A high-performance magnetic sorbent was fsynthesized for the enrichment of trace drugs and their metabolites in wastewater to develop a magnetic solid-phase extraction pretreatment combined with the acoustic ejection mass spectrometry (AEMS) analytical method. The magnetic nanospheres were successfully prepared by magnetic nanoparticles modified with divinylbenzene and vinylpyrrolidone. The results showed that the linear dynamic range of 17 drugs was 1-500 ng/mL, the recovery was 44-100%, the matrix effect was more than 51%, the quantification limit was 1-2 ng/mL, and the MS measurement was fast. It can be seen that the developed magnetic solid-phase extraction (MSPE) method is a good solution to the problems of the complicated pretreatment and analytical cost in the analysis of drugs in wastewater. The developed magnetic material and acoustic excitation pretreatment coupled with mass spectrometry analysis method can realize the low-cost, efficient enrichment, and fast analysis of different kinds of drug molecules in urban sewage.

Co-hydrothermal carbonization of municipal sludge and agricultural waste to reduce plant growth inhibition by aqueous phase products: Molecular level analysis of organic matter.

The organic matter molecular mechanism by which combined hydrothermal carbonization (co-HTC) of municipal sludge (MS) and agricultural wastes (rice husk, spent mushroom substrate, and wheat straw) reduces the inhibitory effects of aqueous phase (AP) products on pak choi (Brassica campestris L.) growth compared to HTC of MS alone is not clear. Fourier-transform ion cyclotron resonance mass spectrometry was used to characterize the differences in organic matter at the molecular level between AP from MS HTC alone (AP-MS) and AP from co-HTC of MS and agricultural waste (co-Aps). The results showed that N-bearing molecules of AP-MS and co-Aps account for 70.6 % and 54.2 %-64.1 % of all molecules, respectively. Lignins were present in the highest proportion (56.3 %-78.5 %) in all APs, followed by proteins and lipids. The dry weight of co-APs hydroponically grown pak choi was 31.6 %-47.6 % higher than that of the AP-MS. Molecules that were poorly saturated and with low aromaticity were preferentially consumed during hydroponic treatment. Molecules present before and after hydroponics were defined as resistant molecules; molecules present before hydroponics but absent after hydroponics were defined as removed molecules; and molecules absent before hydroponics but present after hydroponics were defined as produced molecules. Large lignin molecules were broken down into more unsaturated molecules, but lignins were the most commonly resistant, removed, and produced molecules. Correlation analysis revealed that N- or S-bearing molecules were phytotoxic in the AP. Tannins positively influenced the growth of pak choi. These results provide new insights into potential implementation strategies for liquid fertilizers produced from AP arising from HTC of MS and agricultural wastes.

Insights into effects of thermotolerant nitrifying and sulfur-oxidizing inoculants on nitrogen-sulfur co-metabolism in sewage sludge composting.

In this study, high temperature thermotolerant nitrifying bacteria (TNB) and high temperature thermotolerant sulfide oxidizing bacteria (TSOB) were obtained from compost samples and inoculated into sewage sludge (SS) compost. The effects of inoculation on physical and chemical parameters, ammonia and hydrogen sulfide release, nitrogen form and sulfur compound content change and physical-chemical properties during nitrogen and sulfur conversion were studied. The results showed that inoculation of TNB and TSOB increased the temperature, pH, OM degradation, C/N ratio and germination index (GI) of compost. Compared with the control treatment (CK), the addition of inoculants reduced the release of NH3 and H2S, and transformed them into nitrogen and sulfur compounds, the hydrolysis of polymeric ferrous sulfate was promoted, resulting in relatively high content of sulfite and sulfate. At the same time, the physical and chemical properties of SS have a strong correlation with nitrogen and sulfur compounds.

Gasification chars and activated carbon: Systematic physico-chemical characterization and effect on biogas production.

Gasification residues/chars (GR) and activated carbon (AC) are added to wastewater treatment processes mainly as a fourth purification stage, e.g., to adsorb heavy metals or pharmaceutical residues. However, the effects of GR or AC, which are transferred to the anaerobic digestion (AD) via the sludge, are not yet fully understood. Although, the positive effect of char addition on AD has been demonstrated in several investigations, systematic studies with chemically well described chars are still missing. Therefore, in this study, different chars were characterized in detail, subjected to AD in different concentrations, and their effect on methane production investigated. GR of a gasification plant with a floating fixed bed technology, carbon made by chemical impregnation with ZnCl2 from waste-wood, carbon produced by thermochemical activation with CO2 from GR and commercial powdered AC were used for the experiments. Among others, thermogravimetric analysis, physisorption, pH, and conductivity analysis were used to characterize the chars. Mesophilic AD batch tests with different concentrations (0.025, 0.05, 0.5, 1.0, 7.0, 14.0 gL-1) of all chars (GR and ACs, respectively) were performed with digester sludge from a wastewater treatment plant for a period of 47 d. Volatile fatty acids (VFA) as well as biogas production and CH4 concentrations were monitored. It could be shown, that concentrations below 1.0 g char L-1 did not result in significant effects on CH4 and/or VFA production, whereas high concentrations of GR and AC influenced both, the CH4 yield and kinetics. Depending on the production process and the characteristics of the chars, the effect on AD varied, whereby both, positive and negative effects on biogas yield and methane production were observed. This study provides the first systematic evaluation of char application to AD processes, and therefore allows for better predictions of char applicability and effect.

The complete genome sequence of Sedimentibacter sp. strain MB35-C1, isolated from the sewage sludge.

Here, we report the complete genome sequence of Sedimentibacter sp. strain MB35-C1, which was isolated from sewage sludge at the Wastewater Treatment Plant of Sanming Steel Co. Ltd. in Fujian, China. The resulting genome of strain MB35-C1 is a single contig of 3,621,605 bp.

Molecular surveillance of Helicobacter species with high prevalence from two streams with various wastewater pollution in Taiwan.

Helicobacter species are potential zoonotic pathogens classified as either enterohepatic or gastric. Helicobacter infection can be transmitted through wastewater from households and livestock and through water from irrigation and streams. In this study, the distribution and source of Helicobacter species in the Donggang and Yenshui rivers, two natural water bodies with different characteristics, were analyzed. A total of 44 water samples were collected over the four seasons. The samples were subjected to Helicobacter 16 s rRNA gene PCR, followed by sequencing and comparison for identification and analysis. The detection rate of Helicobacter species in both rivers was 79.55%, with H. kayseriensis (10/35, 28.57%) being the most common species. Analysis of the environment around the sampling sites showed a high detection rate in the livestock-rich area, and the results of BLAST for species identification and comparison indicated feces as the contamination source. The area around the Donggang River was developed for animal husbandry, led to a high detection rate of Helicobacter species. Many Helicobacter species were identified to have a risk of zoonotic transmission, especially if the stream is used as a source of drinking, agricultural, or even aquacultural water. The high presence of Helicobacter species in natural water bodies suggests that wastewater treatment is an effective strategy to control pathogen spread. Therefore, investigation and monitoring of pathogens in wastewater are highly important. However, methods for the isolation and culture of Helicobacter species in natural waters have yet to be developed. Hence, future research should focus on developing such methods.

Water quality assessment of Bheemasandra Lake, South India: A blend of water quality indices, multivariate data mining techniques, and GIS.

An integrated approach combining water quality indices (WQIs), multivariate data mining, and geographic information system (GIS) was employed to examine the water quality of Bheemasandra Lake, located adjacent to a sewage treatment plant (STP) in Tumakuru city, India. The analysis of 22 lake water samples, examined before and after the monsoons, revealed that the physicochemical parameters namely - electrical conductivity, biochemical oxygen demand, turbidity, total dissolved solids, ammoniacal nitrogen, nitrates, phosphates, magnesium, total hardness, total alkalinity, and calcium - exceeded the acceptable limits stipulated by national and international standards. The Canadian Council of Ministers of the Environment WQI (pre-monsoon: 25.3; post-monsoon: 33.9) and weighted arithmetic WQI (pre-monsoon: 3398; post-monsoon: 2093) designated the water as unsafe for drinking. Irrigation WQIs (sodium adsorption ratio, sodium percentage, residual sodium carbonate, magnesium hazard, permeability index, and potential salinity) implied water's suitability for irrigation. However, electrical conductivity indicated otherwise. Industrial WQIs (Larson-Skold Index, Langelier Index, Aggressive Index, and Puckorius Scaling Index) illustrated scaling propensity and the chloride sulfate mass ratio alluded galvanic corrosion potential. Hierarchical cluster analysis gathered 22 sampling points into two clusters (cluster 1: relatively lower polluted regions; cluster 2: highly polluted regions) for each season based on similarities in water features. Principal component analysis extracted four (79.07% cumulative variance) and six (87.14% cumulative variance) principal components before and after the monsoons, respectively. These components identified the primary pollution sources as urban sewage and natural lithological processes. WQI maps, created using the inverse distance weighted interpolation technique, enhanced the visualization of spatial-temporal variations. This study highlights the dire consequences of urbanization, STP pollution, and sewage management failures, necessitating that concerned authorities should implement policies and measures to curb the negative impacts on the environment and public health.

Phosphorus speciation in sewage sludge and their ashes after incineration as a function of treatment processes.

Phosphorus (P) is a key component in agricultural fertilizers, but it is also a scarce resource, why its recycling has been thoroughly investigated and one promising resources is sewage sludge. Because of stricter regulations in terms of sludge disposal, thermal treatment (e.g. incineration) has become an attractive option. The incineration process alters the chemical speciation of P in favour to calcium-associated (apatite, apatite phosphorus (AP)) species, which is preferred for P recovery. In order to achieve qualitatively transformation, it is important to identify limiting or promoting factors. This study reports on the impact of iron, aluminium and calcium on the transformation of iron- and aluminium-phosphate (NAIP) to AP species, assessed by studying sludge and ash from 10 municipal wastewater treatment plants in Sweden. The effect of iron and aluminium added in the treatment processes was also evaluated. The obtained results show that high calcium concentration favours formation of AP species in both sludge and ashes, whereas high concentration of iron and aluminium favours formation of NAIP species in the sludge. The transformation from NAIP to AP species is hampered by aluminium, irrespectively of its origin, whereas no such correlations could be seen for iron. Therefore, in order to enable efficient P recovery from sewage sludge ash, the amount of aluminium added in the treatment process, as well as its concentration in influent streams to the treatment plants, must be limited.

Life cycle assessment of sewage sludge treatment and disposal technologies based on carbon emissions and environmental impacts.

This study aimed to create a comprehensive evaluation method for sewage sludge (SS) treatment and disposal technologies, considering carbon emission and environmental impacts. Life cycle assessment (LCA) were conducted on six SS treatment and disposal technologies in China. The assessments used the IPCC emission factor approach to calculate carbon emissions and the CML2001 method to determine environmental impact factors. Additionally, a colour-coded method was implemented to quantify the evaluation results. The study found that S1 (anaerobic digestion + land application) had the lowest carbon emissions and environmental impact, making it the optimal technology. The S1 scenario had carbon emissions of 669 kg CO2(t DS)-1 and environmental impacts of 5.20E-10. A sensitivity analysis was conducted to show the impacts of each unit in the six technologies on total carbon emissions and environmental impacts. The results showed that landfilling has a high sensitivity to carbon emissions and environmental impacts. Therefore, controlling greenhouse gases and toxic substances in sludge landfills is crucial for reducing carbon emissions and environmental pollution.

Pre-drying limitedly affected the yield, fuel properties, pyrolysis and combusion behavior of sewage sludge hydrochar.

While pre-drying of sewage sludge prior to hydrothermal carbonization is rarely practiced, various pre-drying methods have been performed in literature at lab-scale for convenient solid-to-liquid ratio adjustment. This has created a barrier for comparing hydrochar quality between different studies. Given pre-drying can destroy the floc structure of sewage sludge, we hypothesize that pre-drying may promote the hydrolysis step during hydrothermal carbonization process, resulting in improved hydrochar quality with low nitrogen content. In the current study, the influence of different pre-drying methods (freeze-dry, air-dry and vacuum-dry at 70 °C and 105 °C) on the subsequent hydrothermal carbonization of sewage sludge at 220 °C was assessed in terms of sewage sludge and hydrochar's chemical composition, fuel properties, pyrolysis and combustion behavior, as well as the characterization of the liquid phase. The results indicate that although pre-drying impacts sewage sludge's chemical composition, pyrolysis and combustion behavior, no significant differences exist in the yield, chemical composition, fuel properties, and pyrolysis and combustion behavior of the hydrochar. Therefore, the use of pre-drying would not affect the hydrothermal carbonization process of sewage sludge, and a comparison can be made on hydrochar quality between different studies with or without pre-drying.