In this study, a comprehensive investigation was conducted to use municipal sewage sludge (MSS) as a promising feedstock for bioenergy production via pyrolysis process. Using thermogravimetric ...analysis (TGA), MSS was subjected to thermal decomposition experiments at four different heating rates of 5, 10, 30 and 50 °C/min. TGA curves were divided into three distinctive stages, namely drying zone (T ≤ 200 °C), active pyrolysis zone (200 < T < 600 °C), and char decomposition zone (T ≥ 600 °C). Moreover, the data were used to analyze thermo-kinetic parameters through Flynn-Wall-Ozawa (FWO), Kissenger-Akahira-Sunose (KAS), and Starink methods, where the average values of Ea (126.62–136.92 kJ/mol), Gibbs free energy (159.19–159.61 kJ/mol), and calculated high heating value (HHV, 16.47 ± 0.03 MJ/kg) showed the considerable bioenergy potential of the low-cost biomass. The low difference between Ea and ΔH (~ 5 kJ/mol) showed that product formation was favorable during pyrolysis. In addition, for the first time, the comparative study of the results predicted from support vector regression (SVR) model and the experimental data, showed a satisfactory agreement (R2 > 0.9999) and accurate results regarding different train-test data categories. Further employed was Pyrolysis–Gas Chromatography/Mass Spectroscopy (Py-GC/MS) at 700 °C to characterize the potential chemical products, which indicated the presence of a range of aromatic and aliphatic hydrocarbons, nitrogen-containing compounds, alcohol, furans and sulfur compounds. Finally, three alternative scenarios associated with the planned project were presented and techno-socio-economic assessment (TSEA) of the alternative scenarios were evaluated, for the first time, by means of economic indexes and considering social aspects. Net present value (NPV) of all alternative scenarios of the pyrolysis plant over the 20-year plant lifetime was positive compared to the base case, indicating that the project was feasible. Sensitivity analysis of the optimistic scenario showed that the profitability of pyrolysis plant was highly dependent on bio-oil selling price and total production cost.
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•Thermo-kinetics parameters of MSS pyrolysis were deciphered.•SVR model indicated good applicability to predict remaining mass.•Py-GC/MS analysis was conducted to characterize the potential chemical products.•Three alternative scenarios were designed for techno-socio-economic assessment.•Economic sensitivity analysis was carried out to identify most important variables.
The application of anaerobic membrane bioreactors (AnMBR) for mainstream municipal sewage treatment is almost ready for full-scale implementation. However, some challenges still need to be addressed ...to make AnMBR technically and economically feasible. This article presents an updated review of five challenges that currently hinder the implementation of AnMBR technology for mainstream sewage treatment: (i) membrane fouling, (ii) process configuration, (iii) process temperature, (iv) sewage sulphate concentration, and (v) sewage low organics concentration. The gel layer appears to be the main responsible for membrane fouling and flux decline being molecules size and morphology critical properties for its formation. The review also discusses the advantages and disadvantages of five novel AnMBR configurations aiming to optimise fouling control. These include the integration of membrane technology with CSTR or upflow digesters, and the utilisation of scouring particles. Psychrophilic temperatures and high sulphate concentrations are two other limiting factors due to their impact on methane yields and membrane performance. Besides the methane dissolved in the effluent and the competition for organic matter between sulphate reducing bacteria and methanogens, the review examines the impact of temperature on microbial kinetics and community, and their combined effect on AnMBR performance. Finally, the review evaluates the possibility to pre-concentrate municipal sewage by forward osmosis. Sewage pre-concentration is an opportunity to reduce the volumetric flow rate and the dissolved methane losses. Overall, the resolution of these challenges requires a compromise solution considering membrane filtration, anaerobic digestion performance and economic feasibility.
•Five main challenges were identified for mainstream AnMBR implementation.•Membrane fouling appears influenced by molecules size and morphology.•New AnMBR configurations are gaining attention to improve fouling control.•Psychrophilic temperatures and influent sulphate are limiting factors for AnMBRs.•Sewage pre-concentration could improve the applicability of AnMBR technology.
•An evaluation model of sustainable sludge management was established.•Model comprehensively considered the environmental, economic and social impacts.•Land application performed best in terms of ...environmental and economic impact.•Land application displayed the best performance in more than 80% weights.•A standard system for sludge land application should be established in China.
With rapid economic development and urbanization, there has been an increased generation and discharge of municipal sewage in China, ultimately increasing the amount of sewage sludge entering the treatment facilities. Given this rising problem, finding environmentally friendly, cost-effective, and socially acceptable disposal options for the municipal sewage sludge is crucial for sustainable development. This study evaluated various sludge disposal and treatment technologies for their environmental, economic, and social sustainability and developed an assessment model using multi-criteria decision-making methods. A combined Analytic Hierarchy Process and Vlsekriterijumska Optimizacija I Kompromisno Resenje approach was used for sequencing of the alternatives and evaluation of the most sustainable disposal system based on a set of sustainability indicators. The model results were validated using the Technique for Order Performance by Similarity to Ideal Solution method. Six typical municipal sewage sludge disposal technologies in China were selected for evaluation. The results showed that municipal sewage sludge disposal through land application revealed the best performance (Q = 0.000), and proved to be the ideal choice for sustainable sludge treatment. This was followed by building materials application (Q = 0.207) and disposal through pyrolysis (Q = 0.362), while landfill showed the highest environmental impact and least overall benefit (Q = 1.000). Then, a sensitivity analysis showed that the results obtained are robust and effective, and weight changes of more than 80% indicated land application to have the best performance. Finally, the predicaments and suggestions of municipal sewage sludge land application was analyzed in China from the aspects of standard and sludge quality.
Currently, it is a major challenge for waste water treatment plants (WWTPs) to achieve enhanced nitrogen removal economically and effectively from carbon-limited sewage to meet gradually stringent ...discharge quality standards. Enhanced nitrogen removal can be achieved by endogenous denitrification (ED) treatment of low C/N municipal sewage, but its application is limited by the slow reaction rate. In this study, a novel process of Sludge Double Recirculation-Anaerobic/Aerobic/Anoxic (SDR-AOA) was developed to improve nitrogen removal efficiency via ED. ED was successfully enhanced by an extra sludge recirculation to post-anoxic zone and the denitrification rate increased from 0.1 to 0.17 kgN/(m3·d). Moreover, the pre-anaerobic zone enhanced the intracellular carbon storage, which might also favor the ED process. Overall, under an influent C/N of 2.67, nitrogen removal efficiency of 97.7% was achieved with effluent total inorganic nitrogen (TIN) of 1.56 ± 1.77 mg/L and nitrogen removal rate (NRR) of 0.14 kgN/(m3·d). Therefore, this study provides a convenient approach to improve the nitrogen removal efficiency of municipal sewage with low C/N.
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•Enhance nitrogen removal treating municipal sewage via SDR-AOA process.•Average total inorganic nitrogen in effluent was 1.56 mg/L at C/N ratio of 2.67.•The second sludge recirculation was a key factor for high efficiency denitrification.•Endogenous denitrification enhanced by high MLSS and high CODintra.•Nitrogen removal rate was improved by partial nitrification.
•A novel sludge double recirculation AOA process was developed for the first time.•Stable NAR reached 91.4% in the continuous flow reactor treating low-strength sewage.•TN removal efficiency was ...95.6% in treating low C/N (3.19) sewage.
To achieve advanced nitrogen removal from municipal sewage with a low carbon/nitrogen (C/N) ratio, a novel Sludge Double Recirculation- Anaerobic/Aerobic/Anoxic process (SDR-AOA) was developed in a continuous-flow reactor. Low C/N (3.19 in average) sewage with the chemical oxygen demand (COD) concentration of 180.14 mg/L and the total nitrogen (TN) concentration of 56.19 mg/L was applied for long-term treatment in the SDR-AOA process. Results showed that, the average nitrite concentration in the effluent of the aerobic zone was increased from 0.15 mg/L (phase 1) to 16.46 mg/L (phase 3), and the nitrite accumulation ratio (NAR) remained between 85.87% and 94.85% in phase 3, for which the TN removal efficiency was increased from 91.40% (C/N: 5.14) to 95.60% (C/N: 3.19), and the low effluent TN concentrations was as low as 2.47 mg/L. The inhibitory effect of anoxic disturbance on nitrite oxidizing bacteria (NOB) might contribute to the effectiveness of partial nitrification, with the percentage of NOB accounting for total bacteria being declined from 4.66% (day 79) to 1.51% (day 135) on the genus level. Nitrogen mass balance analysis demonstrated that 27.77% of TN was removed through simultaneous nitrification and denitrification in the aerobic zone, while the remaining TN (62.25%) was removed through endogenous denitrification in the post-anoxic zone. Further Illumina MiSeq sequencing analysis demonstrated that the predominant bacteria were Rhodocyclaceae, Saprospiraceae and Comamonadaceae on the family level, and they were the key to nitrogen removal processes. In the end, the advanced nitrogen removal was realized in the SDR-AOA process for treating low C/N municipal sewage through the successful achievement of partial nitrification and endogenous denitrification.
As a low consumption and high efficiency process, Partial Nitrification-Anammox/denitratation (PNAD) was applied to co-treat mature landfill leachate with municipal sewage for 300 days. Specifically, ...ammonia (670.2 ± 63.7 mg N/L) contained in mature landfill leachate was firstly oxidized to nitrite (611.5 ± 28.1 mg N/L) in sequence batch reactor (SBRPN); meanwhile, organic matter in municipal sewage was partially removed in another reactor (SBROMR); finally, nitrite produced (611.5 ± 28.1 mg N/L) in SBRPN and ammonia (53.1 ± 6.4 mg N/L) residing in pretreated municipal sewage were simultaneously degraded through combined Anammox-denitratation process in an up-flow anaerobic sludge bed (UASBAD). A satisfactory effluent quality of 10.3 mg/L TN was obtained after long-term operation, with Anammox and denitrification contributing to 86.2% and 5.8% nitrogen removal efficiency, respectively. Mass balance confirmed 67.2% nitrate generated from Anammox could be reduced to nitrite and in-situ reused. Anammox bacteria genes and nitrate reductase/nitrite reductase ratio were highly detected, accelerating combined Anammox-denitratation. Further, Ca. Brocadia triumph among various Anammox bacteria groups, increasing from 1.2% (day 120) to 3.6% (day 280).
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•PNAD process was proposed to cotreat mature landfill leachate and municipal sewage.•Anammox and denitrification contributed to 86.2% and 5.8% nitrogen removal efficiency.•Candidatus. Brocadia was dominant genus (1.2-3.6%) among various Anammox bacteria groups.•PNAD process saved 25% aeration energy consumption and 100% carbon source demanding than traditional bioprocess.
•The co-combustion characteristics of sewage sludge (SS) and coal slime (CS) were investigated by thermogravimetric analyzer.•The interaction between SS and CS improved the ignition performance and ...burnout performance of the blends.•A synergy index was proposed to quantify the degree of synergy.•The reaction rate equations of SS-CS were obtain based on FWO and KAS methods combined with the master curve method.
Based on the physical and chemical properties of municipal sewage sludge (SS) and coal slime (CS), the combustion behaviors of SS, CS and their blends were investigated by the thermogravimetric analyzer. The interaction between SS and CS was evaluated, and the combustion reaction rate equations were obtained. The results suggest that during the co-combustion, SS could improve the ignition performance, while CS could enhance the activity in the high temperature zone and improve the slagging characteristics. There was the most significant interaction in 550–600℃, which had a positive effect on the entire combustion process, and the synergy reached its peak when the CS ratio was 40% with synergy index SI=1.53. The combustion of the blend was a multi-step process, which conformed to the nth-order model, and the addition of CS could reduce the apparent activation energy of SS during the entire combustion process.
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Co-pyrolysis of municipal sewage sludge (MSS) and microalgae Chlorella Vulgaris (MCV) was carried out in a fixed-bed reactor to investigate the effect of feedstocks interaction on pyrolysis products ...and synergistic effects. Based on previous authors' research, the optimum values of reaction parameters were T = 520 °C, mixing ratio (MCV/MSS) = 0.82, and an inert gas flow rate of 0.55 L/min. For the investigation of synergetic effects at optimum point, theoretical values anticipated from each characteristic were computed as an arithmetic sum of the single pyrolysis values obtained. For the first time, by using GC analysis, changes in gas components (H2, CO, CO2, CH4) at different temperatures (220–520 °C) and reaction times (0–30 min) have been investigated. Referring to GC-MS results the percentages of oxygen-containing species, alkanes, alkenes, aliphatic, aromatic, and total hydrocarbons were changed from the theoretical value of (41.719%), (6.004%), (11.215%), (17.219%), (4.317%), and (21.536%) to experimental value (39.292%), (3.693%), (12.103%), (15.796%), (0%), and (15.796%) respectively. Fatty acids and N&O-containing compounds (amides) were increased from (12.297%) to (26.009%) and (6.989%) to (16.217%), respectively. Co-pyrolysis bio-oil was rich in fatty acids and amides compounds. So, co-pyrolysis of sewage sludge and Chlorella Vulgaris provides a new orientation for high value-added utilization of biomass. It was observed that the nitrogen and oxygen content of biochar was reduced (0.29% and 1.01% respectively) compared to the theoretical condition. In the end, a comprehensive mechanism, synergistic, and reaction pathways of co-pyrolysis of MCV and MSS were presented.
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•Co-pyrolysis favored gaseous production and the inhibition of other products.•Prolonged reaction time favorable for non-condensable gaseous products.•Nitrogenous chemicals in bio-oil mainly were fatty amides.•The possible mechanism and reaction pathways were given.
Owing to the growing volumes of ash and sewage sludge waste, there is a requirement for theoretical and practical research into the use of these wastes as a source of nutrients. However, there are ...relatively few studies on the transfer of macronutrients in soil-plant systems amended with ash-sewage sludge mixtures under field conditions. The aim of the study was to determine the effect of bituminous coal ash (AC), biomass ash (AB), and municipal sewage sludge (MSS) on the quantity and quality of a grass-legume mixture. During a 6 year field experiment on a sandy loam soil treated with the wastes, applied as mixtures or separately, the plant yield; N, P, K, Na, Mg, and Ca uptake by plants; macronutrient content and ratios in the plant biomass; and the recovery rate of macronutrients by plants were evaluated. The AB-MSS treatment increased the yield in comparison to that where the wastes were applied separately. The N, P, and Ca contents in the plant biomass and N and P uptake under ash-sludge treatments were in the range observed for the ash and sewage sludge. The AB-MSS co-application resulted in the highest K uptake. The AC-MSS treatment increased K and Mg uptake in relation to AC treatment. When AC or AB was added to the MSS, the Ca uptake increased relative to the MSS treatment. The plant biomass under the AB treatment was optimal for biofuel purposes in terms of the chemical composition. The co-application of AC or AB with MSS resulted in the optimum Ca:Mg ratio for fodder purposes. The recovery rate of the macroelements decreased in the following order: K, N, P, Mg, Na, and Ca. The results support the co-application of solid wastes such as ash and municipal sewage sludge to improve productivity, support the recycling of macronutrients, improve sustainability through the reduction of ash and sewage sludge disposal, and reduce reliance on mineral fertilizer.
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•We examined ash and sewage sludge as a source of macronutrients.•Macronutrient cycling was assessed during a 6 year field experiment.•We evaluated plant yield, macronutrient content and ratios in plant biomass.•Uptake and recovery rate of macronutrients by plants were also examined.•Results can promote co-application of ash and municipal sewage sludge.
•Municipal sewage sludge and shale were used to prepared the fired bricks.•Amorphous phase and porosity were the crucial factors affecting the brick performance.•The appearance and phase gradient ...outside in were determined quantitatively.•Rising the temperature too quickly tended to form a heterogeneous structure.•The fitting analysis explored the optimization mechanism of calcination procedure.
The disposal of municipal sewage sludge (MSS) has long been a huge burden for metropolis. It has been proved that the MSS can be recycled in fired brick manufacture, but the influence mechanism of calcination procedure is still worth to be investigated deeply. And the shift from natural clay resources to rich shale and sludge resources is urgently needed in brick industry. In this study, 15% of MSS was used as pore-forming agent and mixed with 85% of shale for preparing the green body. The influence of calcination procedure (firing temperature and heating rate) on the overall performance, involving the volume stability, compressive strength and durability, was analyzed systematically. Results showed that 900 °C was the optimal firing temperature at which the compressive strength of bricks reached up to 34.4 MPa, the thermal conductivity was lower than 0.50 W/(m·K), and the water absorption and strength loss after freezing-thawing attack were both below 20%. Rising the temperature too quickly tended to form a highly heterogeneous structure characterized by the appearance and phase gradient distribution outside in. The quantitative microstructure determination and mechanism analysis further confirmed that amorphous phase content and porosity were the crucial factors affecting the brick performance. The leaching analysis confirmed that incorporating MSS in brick preparation achieved a safe disposal of heavy metals. The fundamental study would lay a solid foundation for the firing optimization and recycling sludge more efficient, and provide date support for complete usage of shale and MSS in fire brick manufacture.
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