Mixture Of Sewage Sludge Research Articles

Influence of soil structure of newly formed agricultural landscape of recultivated landfill of municipal solid waste on its humidity

The objective of the study is to justify the influence of different proportions of sewage sludge introduction into the soil of a newly formed agricultural landscape on a recultivated landfill site taken out of operation. To achieve this goal it is necessary to monitor the dynamics of humidity in the recultivated areas during the growing season of 2020 under actual weather conditions. The areas were recultivated applying various technologies and the irrigation mode was introduced on the Area No. 2. This area is characterized by three types of soil: test - ordinary chernozem; a mixture of chernozem and sewage sludge; pure sewage sludge. Area No. 1 is pure wastewater sludge. The studies on humidity dynamics show that the humidity is changeable in different periods of the growing season, but in the areas with wastewater sediments, the field humidity is higher than in the test area. Thus, it can be concluded that the introduction of sewage sludge influences the structure of the resulting soil, which favorably impacts its water-retaining capacity.

Pyrolysis of Solid Digestate from Sewage Sludge and Lignocellulosic Biomass: Kinetic and Thermodynamic Analysis, Characterization of Biochar

This study investigates the pyrolysis behavior and reaction kinetics of two different types of solid digestates from: (i) sewage sludge and (ii) a mixture of sewage sludge and lignocellulosic biomass—Typha latifolia plant. Thermogravimetric data in the temperature range 25–800 °C were analyzed using Flynn–Wall–Ozawa and Kissinger–Akahira–Sunose kinetic methods, and the thermodynamic parameters (ΔH, ΔG, and ΔS) were also determined. Biochars were characterized using different chemical methods (FTIR, SEM–EDS, XRD, heavy metal, and nutrient analysis) and tested as soil enhancers using a germination test. Finally, their potential for biosorption of NH4+, PO43−, Cu2+, and Cd2+ ions was studied. Kinetic and thermodynamic parameters revealed a complex degradation mechanism of digestates, as they showed higher activation energies than undigested materials. Values for sewage sludge digestate were between 57 and 351 kJ/mol, and for digestate composed of sewage sludge and T. latifolia between 62 and 401 kJ/mol. Characterizations of biochars revealed high nutrient content and promising potential for further use. The advantage of biochar obtained from a digestate mixture of sewage sludge and lignocellulosic biomass is the lower content of heavy metals. Biosorption tests showed low biosorption capacity of digestate-derived biochars and their modifications for NH4+ and PO43− ions, but high biosorption capacity for Cu2+ and Cd2+ ions. Modification with KOH was more efficient than modification with HCl. The digestate-derived biochars exhibited excellent performance in germination tests, especially at concentrations between 6 and 10 wt.%.

Strengthen “the sustainable farm” concept via efficacious conversion of farm wastes into methane

With escalating global demand for renewable energy, exploitation of farm wastes (i.e., agriculture straw wastes (ASWs), livestock wastewater (LW) and sewage sludge (SS)) has been considered to attain maximum methane yield (MY) via anaerobic digestion (AD). Results pointed that mixture of SS and LW as anaerobes’ source with 20 g of ASWs/300 mL of working volume achieved maximum MY and volatile solid (VS) removal efficiency of 0.44 (±0.05) L/gVS and 51.4 (±4.1)%, respectively. This was mainly because of emerging heavy duty bacterial species (i.e., Syntrophorhabdaceae and Synergistaceae) and archaeal community (i.e, Methanosarcina and Methanoculleus) after 70 days of anaerobic incubation. This was acquired along with boosting enzymatic activity, especially xylanase, cellulase and protease up to 71.5(±7.9), 179.3(±14.3) and 207.2(±16.2) U/100 mL, respectively. Furthermore, the digestate contained high concentrations of NH4+ (960.1±(76.8) mg/L), phosphorus (126.3±(10.1) mg/L) and trace metals, making it a good candidate as organic fertilizer.

Influence of Valorization of Sewage Sludge on Energy Consumption in the Drying Process

Valorization of digested sewage sludge generated in a medium-sized sewage treatment plant and the effect of valorization on energy consumption during sludge drying used for energy recovery are presented. Anaerobic digestion of sewage sludge reduces dry matter content compared to raw sludge. This lowers its calorific value leading to the lower interest of consumers in using it as fuel. The aim of the study was to valorize digested sewage sludge prior to drying with high-energy waste with low moisture content. The procedure led to the reduction in moisture content by about 50% in the substrate supplied for solidification and drying. The calorific value of digested sewage sludge increased by 50–80%, and the energy consumption of the drying process decreased by about 50%. Physical and chemical properties of sewage sludge and moisture content of substrates and mixtures after valorization were determined. The heat of combustion of valorized sewage sludge mixtures, their elemental composition, and ash content is investigated. Their calorific value in the analytical and working states of 10% H2O was calculated. The highest calorific value was obtained for the mixture of sewage sludge valorized with waste plastics or combined with wood dust, averaging 23 MJ/kg. A mathematical approximation of sewage sludge valorization is presented.

Acidogenic Fermentation of Urban Organic Waste: Effect of Operating Parameters on Process Performance and Safety

Biorefinery represents an innovative approach for waste management, where products at the end of their service life are seen as valuable resources for the production of high added value bio-products or bio-fuels. In this context, acidogenic fermentation is gaining scientific and commercial interest, since it allows to improve waste/wastewater treatability as well as additional recovery of volatile fatty acids (VFA), the building blocks for the chemical industry or precursors of reduced chemicals in conventional organic chemistry. This work illustrates the results of a study aimed at highlighting the effects of different inputs (feedstock composition and pre-treatment; temperature) on process performance and safety. The fermentation process was applied on a mixture of food waste and sewage sludge (FWs-SS) within the contest of Treviso municipality (northeast Italy). The VFA production and relative ratio respect to soluble chemical oxygen demand (CODSOL) were evaluated, as well as the variation of lower flammability limit (LFL) of flammable gaseous mixture, produced during the acidogenic fermentation. Thermal pre-treatment (72°C, 48 h) enhanced the solubilization of the organic matter, which was converted into VFA in batch mode under mesophilic conditions (37°C). The VFA level increased up to 30 ± 3 g COD/L, with high CODVFA/CODSOL ratio (0.86 ± 0.05). This condition was also characterized by the lowest level in volumetric percentage of flammable gases such as H2, CH4 and H2S. Variation of LFL of gaseous mixture as function of fermenter operating parameters has been investigated by Le Chatelier’s Law. The high concentration of CO2 (greater than 80% v/v) increased the LFL and therefore the flammable mixture was considered poorly hazardous. In practice, the variation of fermenter operating parameters to the final optimized protocol caused a continuous LFL growth, up to 29.3%, corresponding to a safer operation of fermentation reactor.

Single Pellet Combustion of Sewage Sludge and Agricultural Residues with a Focus on Phosphorus

Recycling of phosphorus in combination with increased utilization of bioenergy can mitigate material and global warming challenges. In addition, co-combustion of different fuels can alleviate ash-related problems in thermal conversion of biomass. The aim of this study is to investigate the ash transformation reactions of mainly P in co-combustion of P-rich sewage sludge (SS) with K-rich sunflower husks (SH) and K- and Si-rich wheat straw (WS). Single pellets of 4 mixtures (10 and 30 wt % SS in WS and 15 and 40 wt % SS in SH) and pure SS were combusted in an electrically heated furnace at process temperatures relevant for fluidized bed combustion (800 and 950 °C). Collected ash fractions were analyzed by inductively coupled plasma techniques, ion chromatography, scanning electron microscopy–energy-dispersive X-ray spectroscopy, and X-ray diffraction. Thermodynamic equilibrium calculations were performed to interpret the results. Over 90% of K and P was found to be captured within the residual ash with 30–70% P in crystalline K-bearing phosphates for mixtures with low amounts of SS (WSS10 and SHS15). The significant share of K and P in the amorphous material could be important for P recovery. For the lower percentage mixtures of SS (WSS10 and SHS15), P in crystalline phases was mainly found in K-whitlockite and CaKPO4. For the higher percentage SS mixtures, most of P was found in whitlockites associated with Fe and Mg, and no crystalline phosphates containing K were detected. For P recovery, co-combustion of the lower SS mixtures is favorable, and they are suggested to be further studied concerning the suitability for plant growth.

Co-pelletization of sewage sludge, furfural residue and corn stalk: Characteristics and quality analysis of pellets

In this study, pelletization of sewage sludge (SS), furfural residue (FR) and corn stalk (CS) and mixture of SS with FR and CS was performed, and various quality parameters and their dependency on process variables were investigated. Addition of SS in ratios of 20–40% to FR had not enhanced the pellet densities (e.g. particle and relaxed) of furfural residue sludge mixed pellets (FRSPs). However, mixing SS with CS in ratio of 20–80% had resulted in higher density, strength and hardness of corn stalk sludge mixed pellets (CSSPs). Addition of sludge to 20% with FR had resulted in higher strength and hardness (i.e. 7 ± 0.22 MPa and 508 ± 28.1 N/mm2) of pellets. While the highest strength and hardness i.e. 13.4 ± 0.12 MPa and 392 ± 5.96 N/mm2 were found for CSSPs-40 and CSSPs-80. Pelletization at 200 °C was found to be beneficial as it improved the mechanical characteristics of FRSPs and CSSPs and reduced the energy consumption. Energy consumption of pellets was decreased markedly with increasing sludge ratio and the lowest was found at SS proportion of 80%. Heating values of sludge mixed pellets were found higher than sewage sludge pellets. Compression models had well evaluated the compaction behavior of FR, SS, CS and their corresponding mixture with R2 ≥ 0.9. Using SS in lower proportion (e.g. 20%) could reduce the odor during pelletization or even in the pellets. The results showed that co-pelletization of SS with FR and CS could be feasible approach to enhance the characteristics of pellets and reduced the energy consumption.

Anaerobic co-digestion of sewage sludge and food waste: Effect of pre-fermentation of food waste in bench- and pilot-scale digesters

The effect of pre-fermentation of food waste (FW) for 48 h at 24 °C in anaerobic co-digestion with sewage sludge (SS) was studied in bench and pilot digesters (30 °C, HRT 30 d). The digesters fed with a mixture of SS and fresh or pre-fermented food waste (FW) (80:20% v/v) presented better performance (53% VSS reduction and 186–223 NmL biogas/g VSSadd) than the digester fed with only sludge (35% VSS reduction and 41 NmL biogas/g VSSadd). In both digesters, the pH quickly dropped in the first weeks of operation. However, the digester fed with SS and pre-fermented FW achieved 1.5 times faster pH recovery and relatively stable biogas production throughout the operation (186 ± 23 NmL biogas/g VSSadd). The pilot-scale results confirmed those obtained in bench-scale. Therefore, the pre-fermentation of FW did not affect long-term co-digestion but contributed to a better performance in the starting phase of the digesters.

Effect of compaction on physical properties of a sewage sludge and red gypsum mixture as intermediate landfill cover

This paper investigates the response of sewage sludge and red gypsum mixture under different compaction degree conditions in terms of hydraulic conductivity and unconfined compressive strength (UCS). The UCS and hydraulic conductivity assessments were undertaken using UCS machine and column test using the constant head method, respectively. Five samples were compacted to various degree of compaction (60, 70, 75, 80 and 85%) and percolated with distilled water for six months. The leachate samples from the column test were collected and analyzed at pre-determined days of 1, 3, 7, 14, 28, 42, 56, 75, 90, 120, 150 and 180. The UCS of samples increased with increasing degree of compaction, attributed to the increased number of contact and interparticle interaction between the particles. The degree of compaction appears to affect the initial hydraulic conductivity for the first three days of the experiment, however, gradually stabilize at 10-6 cm/s after 75 days for all samples. The concentration of leached metals and chemical oxygen demand (COD) is below the regulated limit that could affect the environment. The recommended degree of compaction is beyond 80% to achieve the required compressive strength of 345 kPa.

Evaluation of a mixture of sewage sludge and mine waste in reclamation of degraded areas

ABSTRACT The aim of this work was to evaluate the possibility of reclamation and management of mine dump material in degraded and devastated areas containing hazardous substances. In this study, we focused on the determination of changes in electrical conductivity (EC) coefficients and physicochemical parameters of mine soils for biological reclamation needs. The waste substrate material studied here showed significantly lower EC over time in tests, with a value of 6.54 dS m−1 decreased to 0.54 dS m−1. Increasing mine soil quality index corresponded with an increased concentration of exchangeable calcium ions. The cation ratio of soil structural stability indicator was positively correlated with increasing EC. Estimating the changes in physicochemical parameters of deposited reclamation material and its gradual transformation provides new knowledge that can be used for the management of mine waste for ecological purposes. In this investigation, we showed that technical activities connected with the management of opencast mining, which may involve removal of contamination from exploited areas, purification of exploited ground or pedogenesis process on waste dump, may be evaluated using the above indicators, artificial neural networks and principal component analysis.

Effect of sewage sludge and sugarcane bagasse biochar on soil properties and sugar beet production

Recently, biochar has shown to be an alternative to waste disposal and a source of nutrients, acting as a soil amendment. The effects of two types of biochar on soil properties and sugar beet production as well as potential for carbon (C) sequestration were evaluated: biochar produced from sewage sludge (SB) and biochar produced from a 1:1 mixture of sewage sludge and sugarcane bagasse (MB). A greenhouse pot experiment was conducted using a sandy loam soil from the Brazilian savanna under treatments of MB applications at 2.5%, 5.0%, 7.5%, and 10.0%, SB application at 5.0%, and a conventional fertilization (CF) using lime and mineral fertilizers, with no fertilization as a control. After incubation for 45 d, seedlings were transplanted into each pot and cultivated for 55 d. Biochar characterization showed that pyrolysis reduced the biomass volume drastically, but concentrated the trace elements per unit of biochar weight. The MB treatments increased soil total C (by 27.8%) and pH (by 0.6), reduced the concentrations of nutrients, except for potassium (K), and chromium (Cr), and did not significantly alter lead (Pb) and cadmium (Cd) concentrations. Results of stable isotopes showed that all biochar treatments increased the total soil C stock and stability, suggesting a potential for application in C sequestration, and improved overall soil fertility. However, the biochar treatments also increased the concentrations of trace elements in the soil and plants. The sugar beet yields at 10.0% MB and 5.0% SB corresponded to 55% and 29% of the yield obtained in the CF treatment, respectively. These results may be due to biochar nutrients not being bioavailable when required by plants or to biochar nutrient adsorption.

A comparative study on biogas production, energy balance, and nutrients conversion with inter-stage hydrothermal treatment of sewage sludge

As an alternative to pre-stage hydrothermal treatment (HT) before anaerobic digestion (AD), inter-stage HT (i.e., AD-HT-AD) has been proposed to increase biogas production and to further reduce the residual organic matter. The goal of this study was to evaluate the effect of inter-stage HT at 155 °C on the ultimate biodegradability and AD extent of sewage sludge mixture (i.e., primary and waste activated sludge). The sludge ultimate biodegradability was evaluated through biochemical methane potential tests. AD-AD and AD-HT-AD configurations were investigated in semi-continuously fed bench-scale digesters in terms of methane production, solids reduction, nutrients transformation, and energy balance. Results were compared with those of AD and HT-AD configurations from our previous study. Inter-stage HT increased the ultimate biodegradability of the sludge mixture; however, pre- and inter-stage HT resulted in comparable overall specific methane production. Compared to AD and HT-AD, AD-AD and AD-HT-AD had comparable methane production, higher VS destruction (by 3.4–9.3%), but lower overall crude protein removal (by 4.0–7.5%) and soluble orthophosphate concentration decrease (by 32.5–60.8%). There was minimal difference in net energy production by AD and AD-AD (single digester vs. two digesters; 1.4 GJ/d), as well as by HT-AD and AD-HT-AD (pre-HT vs. inter-HT; 0.4 GJ/d). High HT heat recovery is needed for HT-AD and AD-HT-AD to obtain energy balance comparable to AD and AD-AD. Compared to single-step AD, the two-step AD process is more complex and thus less attractive for the digestion of sewage sludge with a relatively high ultimate biodegradability as was the case in this study. However, AD-HT-AD may be more beneficial considering post-AD sludge handling processes.

Combined Pretreatment by Ultrasound and Struvite Precipitation of Raw Substrates: A Strategy to Overcome C/N Ratio Unbalance in Nitrogen-Rich Anaerobic Co-Digestion Systems

The present study aimed to optimize the struvite chemical precipitation process in nitrogen-rich anaerobic co-digestion systems. Struvite precipitation experiments were carried out using a mixture of cattle slurry liquid fraction and sewage sludge, with and without ultrasound pretreatment. Marine salt or MgCl2 were used as magnesium source in NH4+:Mg2+ stoichiometric proportions of 1:1.5 and 1:3. Under the tested conditions, ammonium nitrogen and orthophosphate were removed from the mixed liquor with a maximum observed efficiency of 43% and 92%, respectively, when the ultrasound treatment was applied prior to struvite precipitation, using MgCl2 as source of magnesium (NH4+:Mg2+ of 1:3). The operating time was 40 min. Different pretreatments were tested prior to the biomethanization experiments, struvite precipitation, ultrasound and a combination of both pretreatments. The application of ultrasound (with an energy input of 218 kJ L−1) and struvite precipitation (NH4+:Mg2+ of 1:3) increased the methane content in the biogas by 82% and reduced hydraulic retention time by 28%, when compared to the anaerobic co-digestion assays without pretreatment. The hydrolytic pretreatment increased the bioavailability of nitrogen by 5%, thus enhancing the removal efficiency of ammonium nitrogen by 20%. Consequently, an increase in the carbon to nitrogen ratio was observed, favoring the methanogenesis process.

Earthworm community development in soils of a reclaimed steelworks

Long-term studies are essential to learn earthworm community development and soil formation post reclamation. Investigations were undertaken at a former steelworks site at Hallside, near Glasgow, UK, reclaimed in the 1990s using a mixture of colliery spoil and sewage sludge. The site was largely planted for production of short rotation coppice willow (Salix spp.). Earthworm inoculation formed a part of the restoration process. Minimal monitoring occurred in the interim, but some records of earthworm sampling existed in 2000 and 2005. This study focused on monitoring earthworms and soil properties across the site, drawing comparisons with adjacent unspoiled soil. Results showed that after 22 years, a species-rich community of earthworms (n = 16) colonized the site, with endogeic Aporrectodea caliginosa being dominant by number and anecic A. longa by mass. Across the site, earthworm community density and biomass were 208 individuals m-2 and 71 g m-2, respectively. The Shannon diversity index for earthworms was 1.89, with an evenness of 0.68. The sewage sludge increased the soil organic matter, but the stone content of the colliery spoil prevented digging in some locations. Soil chemistry had no negative effect on earthworms, but the compacted substrate did hinder water infiltration. Earthworms colonized the reclaimed site from adjacent areas, and community structure and density below well-drained, scrub-free willow, birch, and grassland were not significantly different (P > 0.05) from those of the adjacent unspoiled areas. The results show that the historical earthworm inoculation was unnecessary and badly timed. Future reclamations of similar sites can learn from this investigation.

A Study on Optimal Conditions for Bio-drying with a Mixture of Sewage Sludge and Food Waste Compost

A Study on Optimal Conditions for Bio-drying with a Mixture of Sewage Sludge and Food Waste Compost

An eco-friendly way to valorize winery wastewater and sewage sludge: Anaerobic co-digestion

Anaerobic digestion (AD) of sewage sludge (SS) and anaerobic co-digestion (AcoD) of SS and wine distillery wastewater (WDW) was investigated at different hydraulic retention times (HRTs), ranging from 20 to 8 d. The mixture of SS and WDW resulted in a highly improved quality of feedstock: soluble organic matter and organic matter easily accessible for acidification increased substantially (>60%), while non-solubilized organic matter decreased (>160%). AcoD of SS:WDW consequently yields higher values of average organic matter removals (48–66%) compared to AD of SS alone (42–58%), in keeping with the increase in specific methane productivity (SMP) (around 45%). Increasing the organic loading rate (OLR) or decreasing the HRT resulted in an increase in methane production (MP) and a decrease in SMP. Maximum values of MP in AD and AcoD were respectively 0.9 ± 0.2 L CH4 d−1 at an OLR of 8.2 and 5.4 kg TCOD m−3 d, corresponding to an HRT of 8 d. SMP values in AD and AcoD fell within the 200–300 L CH4 kg VS−1 and 300–400 L CH4 kg VS−1 range, respectively. This paper presents a low-cost strategy for wine producing countries to increase energy generation at wastewater treatment plants, as well as providing them with an interesting source of income.

Increased power generation from a new sandwich-type microbial fuel cell (ST-MFC) with a membrane-aerated cathode

In this study, a new aeration approach was used for cathode by offering an efficient and cost-effective alternative for practical applications of microbial fuel cells. Therefore, a new sandwich type microbial fuel cell was constructed having three chambers (two anodes and one cathode) was constructed. This sandwich type microbial fuel cell was fed with a mixture of sewage sludge and algae biomass (at the ratio of 1:1). The pure oxygen gas was delivered to the cathode by using hydrophobic hollow fiber gas transfer membranes at different gas pressures (2, 4, 6, 8 and 10 psi). The results revealed that this new sandwich type microbial fuel cell achieved a good performance, and the max power density increased from 1448 mW m−2 to 26680 mW m−2 with an increase in oxygen pressure from 2 psi to 10 psi. The presence of electrochemically active bacteria-colonization on the anode's surfaces was revealed by microscopic observations and molecular analysis. This study demonstrated the feasibility of using a hollow fiber gas transfer membrane and a mixture of sewage sludge and algae biomass to enhance power production by sandwich type microbial fuel cell.

Thermodynamics, kinetics, gas emissions and artificial neural network modeling of co-pyrolysis of sewage sludge and peanut shell

The co-pyrolysis characteristics of sewage sludge (SS) and peanut shell (PS) under nitrogen atmosphere were studied by thermogravimetric – Fourier transform infrared spectrometry (TG-FTIR) and artificial neural network (ANN). The proportion of PS in the experimental samples is 0, 10, 20, 30, 40, 50, 60, 70, 80, 90 and 100%. The experiments were performed at three heating rates of 5 °C/min, 7 °C/min and 10 °C/min. The variation of sample mass with temperature and gas emission were detected in this paper. SS and PS in the co-pyrolysis experiment have a synergistic effect in terms of mass loss at 335 °C ∼ 500 °C. Gases generated by pyrolysis of the mixture of SS and PS include H2O, CH4, CO2, CO, phenol and NH3. The functional groups detected in the experiment include CO and C O. Apparent activation energy E was obtained by two non-isothermal kinetic analysis methods (Flynn–Wall–Ozawa and Kissinger–Akahira–Sunose). The artificial neural network method was used to predict the relationship between the mass loss of pyrolysis experiments and the change of temperature. The best ANN model (ANN21) for predicting SS and PS pyrolysis was identified.

BIODEGRADABLE CHELANTS FOR HEAVY METAL REMOVAL FROM SLUDGE AND SOIL-SLUDGE MIXTURES

Heavy metal extraction study was performed using five chelating agents with different biodegradability: EDTA, EDDS, MGDA, SCLC and citric acid. Aminopolycarboxylic acids EDDS and MGDA showed high heavy metal extraction capability from sewage sludge and sludge-soil mixtures. According to heavy metal removal efficiency investigated chelants can be ranked in the following order: EDTA≈ EDDS≈ MGDA> CA> SCLC. Extraction efficiency from sludge mixtures with clay soil was markedly lower than from the mixtures with sandy soil. Biodegradability of EDTA, MGDA, EDDS and CA was evaluated measuring BOD in water environment over 28 day period. According to the results of biodegradability test after 28 days the ranking order of the chelants was following: EDDS (99%)> CA (32.4%)> MGDA (29.2%)> EDTA (14.9%). Results showed that significantly easier than EDTA biodegradable chelating agents, such as EDDS and MGDA, can be successfully used for heavy metal removal from sewage sludge as well as metal-contaminated soil. &nbsp

Thermochemical equilibrium study of ash transformation during combustion and gasification of sewage sludge mixtures with agricultural residues with focus on the phosphorus speciation

The necessity of recycling anthropogenically used phosphorus to prevent aquatic eutrophication and decrease the economic dependency on mined phosphate ores encouraged recent research to identify potential alternative resource pools. One of these resource pools is the ash derived from the thermochemical conversion of sewage sludge. This ash is rich in phosphorus, although most of it is chemically associated in a way where it is not plant available. The aim of this work was to identify the P recovery potential of ashes from sewage sludge co-conversion processes with two types of agricultural residues, namely wheat straw (rich in K and Si) and sunflower husks (rich in K), employing thermodynamic equilibrium calculations. The results indicate that both the melting behavior and the formation of plant available phosphates can be enhanced by using these fuel blends in comparison with pure sewage sludge. This enhanced bioavailability of phosphates was mostly due to the predicted formation of K-bearing phosphates in the mixtures instead of Ca/Fe/Al phosphates in the pure sewage sludge ash. According to the calculations, gasification conditions could increase the degree of slag formation and enhance the volatilization of K in comparison with combustion conditions. Furthermore, the possibility of precipitating phosphates from ash melts could be shown. It is emphasized that the results of this theoretical study represent an idealized system since in practice, non-equilibrium influences such as kinetic limitations and formation of amorphous structures may be significant. However, applicability of thermodynamic calculations in the prediction of molten and solid phases may still guide experimental research to investigate the actual phosphate formation in the future.