Sludge Flow Research Articles

High-Temperature Ash Melting and Fluidity Behavior upon the Cocombustion of Sewage Sludge and Coal.

Wastewater treatment produces a large amount of sludge, where the minimizing of the disposed sludge is essential for environmental protection. The co-combustion of sludge with coal is a preferable method for sewage sludge disposal from the economic and environmental perspective. The co-combustion of sludge has been widely used in the industry with the advantages of large processing capacity. The melting characteristics of ash are an important criterion for the selection of the co-combustion methods and furnace types. In this study, two types of sludge and four types of coal with different ash melting points were selected, where the ash melting behavior upon co-combustion is investigated by experimental and thermodynamical approaches. Especially, the slag fluidity upon co-combustion is explored via a modified inclined plane method. It has been found that the presence of SiO2 and CaO in sludge substantially enhances its fusion temperature owing to the high content of CaO, while SiO2 acts as a solvent, facilitating the co-melting of other oxides and raising the sludge fusion temperature. Fe2O3 exhibits a specific mass fraction within the range of 10-20%. Furthermore, the presence of CaO and SiO2 prohibits the flow ability of the slag at high temperatures, and Fe2O3 promotes the flow ability for sludge at high temperatures. With increasing base/acid ratio, the sludge flow velocity increases remarkably and peaks at 1.6. The interaction between Fe-Ca and Si-AI significantly affects the fluidity significantly. The findings are expected to optimize the condition of co-combustion and desirable furnace design for the incineration of sludge.

P-recovery versus current sewage sludge treatment policy in the Czech Republic and Japan

Phosphorus is an important element for agriculture and industry, but its deposits are not uniformly distributed. Countries that do not have primary sources are dependent on imports or regeneration from secondary materials. A widely available secondary source is sewage sludge. Used environmental standards govern sludge treatment, but its inclusion in the raw material policy is often missing. We focus on the Czech Republic (a European Union member) and Japan, countries without phosphorus deposits. Based on our analysis of sewage sludge flows, legislation, and technologies used, we aimed to evaluate approaches towards sustainable phosphorus policy. We figured out that in the Czech Republic, sludge application to soil continues due to legislation deregulation and thus, various pollutants enter the soil along with the sludge. In Japan, thermal treatment predominates, but ash is not processed, and phosphorus is irreversibly lost in landfills or construction. By not implementing a functional P-recovery policy, both countries lose more than 13 % replacement of phosphorus fertilisers from their sources.Graphical

Enhancing Textile Wastewater Treatment Performance: Optimization and Troubleshooting (Decision Support) via GPS-X Model

Textile factory water consumption could be optimized to minimize the generation of wastewater, reduce treatment costs, and promote resource recovery. However, downstream plant operation and management is a prime concern in the textile industry, particularly bringing treated wastewater effluent to an acceptable discharge limit. The aim of the study was to optimize key process control parameters to the observed operational challenges of existing processes and suggest an operational guide to the operators and decision makers to enhance the treatment performance in GPS-X. The formulated troubleshooting and decision support strategy, and the optimization results of waste-activated sludge in the primary and secondary clarifiers, was within the range of 15 ± 5 m3/d and 83 ± 7 m3/d, respectively, with a recycle-activated sludge flow of 150 ± 10 m3/d. The sludge retention time was 5 ± 1 d and 6.7 ± 0.5 d in the secondary and primary clarifiers, respectively. The addition of a carbon source in the form of molasses had a flow of 0.5 ± 0.05 m3/d, and the variation in the influent due to wastewater characteristics and rainfall was optimized to 600 ± 50 m3/d. The optimum air flow into the aeration tank was 550 ± 5 m3/hr and saved 91.5% of energy in the optimized process. Thus, the study is indispensable for the effective and efficient operation of the plant and serves as a good guide to the plant operators and decision makers for the best course of action.

Slug flow in tubular membrane in which air and activated sludge flow: A CFD study

Air bubbles have been widely applied to alleviate membrane fouling of tubular membranes in membrane bioreactors. However, the impact of the air bubbles on the flow at the membrane surface as well as the removal of membrane foulant are not well understood. Therefore, a theoretical computational fluid dynamics model was established to address this. In the model, air and activated sludge flowed at the superficial velocities of 0.7 m/s and 0.3 m/s, respectively. Furthermore, sludge concentrations were 5 g/L and 10 g/L, respectively. The model showed that the activated sludge did not flow downwards in the film zone and eddies were not observed in the zone below the tail of a bubble. The viscosity of sludge varied significantly in the film zone. Mass transfer capacities at membrane surface gradually decreased from the nose to the end of a bubble. Moreover, a lower sludge concentration resulted in a higher mass transfer capacity. The highest shear stress at membrane surface was 14 and 11 Pa, which were significantly higher than the shear stress achieved in submerged membranes being aerated. Microparticles (3–10 µm) at membrane surface could be shifted towards the filtrated bulk solution and sucked at the membrane surface alternatively when a gas slug flowed nearby. Furthermore, the bubbles are not effective in shifting microparticles (<3 µm) toward a bulk solution.

Performance evaluation of an oily industrial wastewater treatment system using the application of activated sludge model No. 3

AbstractThe purpose of the present study was to adapt the activated sludge model No. 3 (ASM3) to the characteristics of oily industrial wastewater, determining the utmost significant and appropriate kinetic as well as stoichiometric parameters. An oily industrial wastewater treatment system was simulated to assess ASM3 validation and perform sensitivity analysis using the STOAT program. The obtained results revealed that the ASM3 model, which was calibrated after adding the Arrhenius equation into consideration, provided strong correlations with the analytical results of chemical oxygen demand (COD), total suspended solids (TSS), mixed liquor volatile suspended solids (MLVSS) and total suspended solids in the return activated sludge flow (TSS in RAS) concentrations. The values of modelled effluent COD and TSS are very close to those corresponding real values of the treated wastewater by a difference of between 0.5% and 1.5%. Thus, this model becomes successful in representing oily industrial wastewater treatment as a new trend added to the traditional modelling of sewage treatment.

Developing a practical model for the optimal operation of wastewater treatment plant considering influent characteristics.

Wastewater treatment plants (WWTPs) play an important role in protecting the quality of water sources. The optimum operation of WWTPs in response to continuous changes in the characteristics of the influent of the WWTP is very important, and it can improve the quality of the effluent of the WWTP. In this study, an approach for optimal operation of the WWTP has been presented considering the quantitative and qualitative variables of influent. In the proposed method, first, the simulation model of WWTP is developed and calibrated using the recorded data of its influent and effluent characteristics as well as operation conditions. Then, the influent is classified into clusters quantitatively and qualitatively k-means clustering method. In the final step, after determining the effective operation parameters, the AMOEA-MAP optimization algorithm is used to determine the optimal values of operation parameters for each cluster of influents based on its quantitative and qualitative characteristics including flow rate, COD, ammonium, and temperature. The proposed approach was implemented on a WWTP in the South of Tehran, the capital of Iran. Dissolved oxygen (DO) in the aeration tank, waste-activated sludge flow rate (QWAS) and the ratio of the supernatant flow rate of the sludge dewatering unit to the effluent flow rate (Qd/Qe) were considered as operation parameters affecting the performance of the system in removing pollutants and their optimal values were obtained as DO, 0.25-1.7mg/l, QWAS, 875-2000 m3/day, and Qd/Qe, 10-14%. Using this method, i.e., changing system operation conditions based on influent characteristics, has improved the performance of a system in reducing COD, ammonium, and nitrate in the effluent by 11-41, 17-20 and 15-34, respectively.

Mechanism insights into the nitrogen removal of bio-augmented AAO: Specifically focusing on the nitrogen metabolic pathways and microbial taxa-functional genes associations

Rapid loss of inoculant microorganisms and the slow-growth of autotrophic bacteria pose significant challenges to bio-augmentation technology. Given the low-cost of coal ash and its greater compatibility with nitrifiers, it was utilized as a carrier to maintain bio-augmentation performance and enhance the AAO's nitrogen removal. Results showed the bio-augmented system operated stably, and immobilized coal ash improved the efficiencies of NH4+-N from 67.6 ± 10.8 % to 94.3 ± 3.0 % and TIN from 63.2 ± 9.2 % to 84.3 ± 4.3 %. An in-depth analysis indicated bio-augmentation altered the microbial community structures and increased the relative abundance of bacterial associated with nitrogen removal, significantly increasing the abundance of Nitrosomonas and Nirospira. In addition, bio-augmentation enhanced the activity of nitrogen removal enzymes, especially amoABC, hao, narGH, nirK, and nosZ transporter genes, according to predicted function profiles. Network analysis between microorganisms and N-metabolic functional genes revealed bio-augmentation improved the complexity of network-structure and the sources of N-metabolic functional genes, thereby enhancing functional stability. Return sludge flow was the most significant factor in regulating the microbial community composition associated with N removal in the bio-augmented AAO system, followed by DO and internal recycle ratio. The aforementioned results obtained from the present study will enable the application of immobilized coal ash in wastewater treatment plants to improve N removal efficiency.

The Activated Sludge Flow Characteristics Required for The Design Of Pressure Pipeline

In This research studied the effect of the sludge characteristics such as settling propertiese and concentration of solids in the sludge on the flow propertiese of heterogeneous sewage sludges. The non-Newtonian (pseudoplastic ) and time-dependent (thixotropic) influence on the rheological characteristics of sewage sludge was calculated experimentally. Depending on these characteristics and during several experiments an empirical method has been developed to calculate the head losses in pressure pipes which convey these sludges under laminar flow conditions. The results showed that the torque (T) and shear stress (τ) decrease with time at constant rotational speed,and the time-independent behaviour was approached after 900sec.,where no further decrease in shear stress was observed after 900s. A relations has been plotted between the flow rate (Q) and maximum,minimum head losses by means of a design example , in addition to the head loss gradient decay along a pipeline and between Euler and Reynolds numbers .

Plant-wide modeling of a metropolitan wastewater treatment plant to reduce energy consumption and carbon footprint.

A real metropolitan wastewater treatment plant (RWWTP) serving a population equivalent of 1.55 million was modeled to reduce energy consumption and carbon footprint (CFP). An approach was proposed to handle the dilution factor and partial aeration due to discontinuous air diffuser locations in the Bardenpho-5 configuration. Various operational, structural, and configurational modifications were evaluated. Results indicated that management scenarios might provide conflicting outcomes for different targets. Reduced energy consumption may not result in lower CFP at the same time. Moreover, operational changes that would impact total nitrogen (TN) concentrations and N2O release may significantly impact CFP. A policy of using a modified Bardenpho-5 process with reduced internal recycle (IR) ratio, waste activated sludge (WAS), and return activated sludge (RAS) flow rates provided the lowest CPF. Modified Bardenpho-5 process and replacing belt thickeners with gravity thickeners supplied the highest savings in energy consumption. Overall, up to 14% and 20% reductions were possible in the energy consumption and CFP of the plant, respectively. The RWWTP may save up to 10% in energy expenses annually by operational modifications.

Revealing the microbial mechanism of Fe0 and MnO2 mediated microbial fuel cell-anaerobic digestion coupling system and its energy flow distribution

Microbial fuel cell-anaerobic digestion (MFC-AD) is a new sludge treatment technology with multi-path energy recovery. In this study, Fe0 and MnO2 with gradient concentration were added to investigate its effects on the sludge reduction, electrochemical performance, extracellular polymeric substances (EPS) of sludge, microbial community, electron distribution and energy flow of the MFC-AD system. Results showed that the highest sludge reduction 59% (49%), was obtained at 10 g/L Fe0 (5 g/L MnO2) adding and its total energy recovery efficiency increased by 100% (71%) compare to the control. Different Fe0 and MnO2 concentrations lead to different microbial mechanisms: at 10 g/L Fe0 or 5 g/L MnO2, it prefers to promote extracellular electrons transfer, favoring the Geobacter, Shewanella and Acinetobacter enrichment, while at 5 g/L Fe0 or 0.5 g/L MnO2 it plays a more important role in substrate metabolism of anaerobic digestion, with Clostridium, Roseomonas lacus, and Methylocystis enriched. Correspondingly, the electron quantity distribution from biomass to recovered energy ends (Current, CH4 and VFAs), was influenced by Fe0 and MnO2 concentration, indicating the controllability of the energy flow.

Improving wastewater treatment plant performance based on effluent quality, operational costs, and reliability using control strategies for water and sludge lines

As a result of urbanization and population growth, wastewater treatment plants (WWTPs) are experiencing increased influent flow rates, pollutant loads, and stricter standards for effluent quality. Therefore, implementing a control strategy is critical for improving the performance of WWTPs in response to highly variable effluent quality. In this study, different strategies for both water and sludge lines are deployed in WWTP model to control dissolved oxygen and biomass concentration in activated sludge system by manipulating aeration intensity and sludge flow rates. The efficiency of suggested control strategies is evaluated using different performance criteria, including effluent quality indicators, operational costs, and system reliability. The proposed method is applied in a real WWTP located in south of Tehran, the capital of Iran. According to the findings, controlling aeration system and sludge flow rate improve effluent quality and system reliability despite increasing operational costs. In the case of simultaneous control of water and sludge lines, the effluent quality index has improved by 9.3%, while the operational costs have increased by 1%. Moreover, the system reliability based on effluent ammonia, TSS, and COD concentration have increased by 33.4%, 9%, and 12.2%, respectively.

Biological treatment of slaughterhouse wastewater using Up Flow Anaerobic Sludge Blanket (UASB) - anoxic-aerobic system

Slaughterhouse wastewater (SWW) is heavily polluted wastewater. It contains high concentration of organic matters, suspended solids, nitrogen, phosphorus, oil and grease. Discharging of SWW without a proper treatment may cause many problems for the sewage network and municipal treatment plants. Thus, this study aims to investigate the treatability of SWW using a new treatment method consists of: Up-flow anaerobic sludge blanket (UASB) reactor, Anaerobic Anoxic and Oxic (A2/O), and Virginia Initiative Plant Method (VIP). The integrated process consists of UASB reactor, anoxic tank, aeration tank (UASBAA), and final settling tank, respectively.The value of the mixed liquor suspended solids (MLSS),and return activated sludge (RAS) flows from the final settling tank to the anoxic tank were 300% and 100% of the SWW inflow respectively. During the research the influence of HRT values in UASB, anoxic tank, and the aeration tank has been investigated on the efficiencies of pollutants removal that exist in SWW. The experiments proved that the suggested method achieved high removal efficiency of COD, BOD5, TS, TDS, TSS, NH4+, PO43−, and NO3−, respectively: 97.31%, 96.91%, 57.61%, 47.91%, 96.3%, 73.11%, 83.61%, 93.01%, at HRTs value of 24 h for UASB reactor; 12 h for anoxic tank: 24 h for aeration tank, and 3 h for final settling tank. The treated wastewater could be reused it in washing processes in the slaughterhouse or for the irrigation of industrial crops.

Design of Heat Exchanger for Solar Energy Application in Biogas Plant

Abstract: The main aim of this report is to reduce the retention period by adding microbes, pretreatment processes that is by Physical, Chemical and Biological like using the solar air heater with heat exchanger and this process ruptures the cell wall of sludge flow structure and facilitates release of intracellular matter into aqueous phase, improving biodegradability with lower retention time and higher biogas yield. Further, the residue of the Biogas plant can be treated as a manure to fertilise the Soil. After heating water up to 100oC in the solar water heater, maintaining the temperature of slurry taking heat capacity of both the fluids same. Gas yield of around 0.2-0.33 m3 /m3 will be obtained compared to conventional biogas plant i.e., 0.05m3 /m3 . Keywords: Cow dung; slurry; Solar water heater; Heat exchanger; biogas; water

Applying novel methods in conventional activated sludge plants to treat low-strength wastewater

Conventional activated sludge system is confidently widely used for biological treatment plants of municipal wastewater but suffering from operation problems that affect their efficiencies and effluent qualities, especially when treating low-strength wastewater with increasing incoming flow. The objective of this study is to evaluate and compare the novel methods used in upgrading conventional activated sludge treatment systems receiving low-strength wastewater to generate good effluent quality. GPS-X Simulator V 8.0 was used for model calibration and plant performance prediction. The calibrated GPS-X model proved that eliminating primary settling from the treatment process does not affect BOD5 and COD removal, while TSS removal is decreased, and NH4-N removal is increased. Increasing the return activated sludge flow from 50 to 150% of influent flow does not affect conventional activated sludge process, while the change of waste activated flow had a vital effect on process performance. The presence of an anoxic zone in conventional activated sludge processes treating low-strength wastewater has no significant impact on plant performance. Also, the model outputs proved that adding filling media to the aeration tank was able to handle an increase of influent flow and a stable performance of BOD5, and NH4-N removal was observed.

Mitigation of salinity buildup in hybrid flow-electrode capacitive deionization-osmotic membrane bioreactor for sludge anaerobic digestion

Osmotic membrane bioreactors (OMBRs) for anaerobic digestion of waste sludge have many advantages, but salt accumulation in the feed solution is a major problem. In this study, the feasibility of using flow-electrode capacitive deionization (FCDI) to mitigate salinity buildup was investigated. Three types of carbon materials, i.e., activated carbon (AC), carbon black (CB), and carbon nanotubes (CNTs), were tested as flow-electrode materials in desalination via FCDI. The results showed that, the salt removal efficiency (SRE) of CNTs was 110% higher than that of AC. Addition of CB and CNTs to 5.0 wt% AC as conductive additives at concentrations of 0.5 or 1.0 wt% synergistically enhanced the FCDI desalination performance. Cyclic voltammetry, galvanostatic charge–discharge, and electrical impendence spectroscopy showed that use of a combination of 5.0 wt% AC and 1.0 wt% CNTs gave an excellent capacitive performance, and the highest SRE, fastest average salt adsorption rate (0.84 μg cm−2 s−1), and the highest charge efficiency (85.0%) were achieved. The optimal voltage and sludge flow rate for FCDI of real OMBR sludge were 1.5 V and 80 mL min−1, respectively. In comparison with a control OMBR, a hybrid FCDI-OMBR system showed many advantages such as slower salinity buildup, alleviation of inhibition by ammonia, lower production of soluble microbial products, greater volumetric methane production, and higher net energy gains. The proposed hybrid FCDI-OMBR system provides a novel and cost-effective approach to recovering resources and energy from waste sludge or other types of biomass.

Centrifuge experimental study of behaviour of basal-reinforced rubble mound over soft soil

Large settlement and lateral deformation during construction of a rubble mound, such as a breakwater, over a soft clayey foundation are a challenge. Different mechanisms contribute to excessive settlement of marine clay, including consolidation, the size of the rubble particles, the penetration of individual rock particles and the flow of sludge through the rock pores. Placing a geotextile layer or sand mattress can restrict the amount of material loss caused by these mechanisms. To accurately assess the performance of a geotextile under a rubble mound, eight geotechnical centrifuge tests were conducted. The shear strength of the foundation and the type of the separator layer were the variables considered. The results indicate that the use of a geotextile as basal reinforcement reduced settlement at the breakwater crest and increased stability. In addition, the horizontal displacement of the rubble mound and the clayey foundation decreased remarkably.

Study on flow and heat performance of thermal-hydrolyzed sludge in a double-pipe heat exchanger with a series of inner corrugated tubes

In this paper, a double-pipe heat exchanger with a series of corrugated tubes as inner tubes is studied for the adequate cooling of thermal-hydrolyzed sludge. A numerical model, built on the Spalart-Allmaras model, is validated to have the ability for characterizing the flow and heat transfer performance of sludge. The influencing factors, including the flow parameters of the sludge and cooling water, and the geometric configurations of the corrugated tube are parametrically investigated. The ratio of Nusselt number (Nu/Nu0), the coefficient of flow resistance (f/f0) of the sludge, the synthesis factor of performance (η) and the ratio of the heat transfer increase over the pump power increase (ζ) are used as the performance assessment indexes. The results show that increasing Resludge can negatively affect η and η tends to be stable when Rewater is higher than 1.2 × 104. Decreasing S/D and increasing H/D result in a higher ratio of flow resistance f/f0 and a higher ratio of Nu/Nu0. The corrugation height (H) shows a larger effect than the corrugation length (S). In practical applications, the optimal flow rates of the sludge for the studied corrugated tubes are recommended to be within the range of 1.2–1.5 m/s.

Quantifying material flow of oily sludge in China and its implications

Oily sludge is classified as hazardous waste. If not treated properly, it can cause negative impacts on human health and the ecological environment. However, the current lack of macro and micro scientific understanding of the treatment of oily sludge hinders its sound management. In this study, at the microlevel, we selected two of the most common treatment processes of oily sludge and establish a database through data collection and estimation. Material flow analysis was adopted to reveal the generation, pretreatment, recycling, and disposal processes of mechanical separation and incineration. At the macrolevel, this article predicted the material flow of China's whole process management of oily sludge and analyzed the typical flow characteristics of valuable resources in the whole process to guide the formulation of relevant policies in the future. The annual generation of oily sludge in China was between 4.45 and 6.22 Tg, and the average comprehensive utilization rate was approximately 36%. We are still far away from a sound management system despite new legislative revisions. Close supervision and technical processes should be further enhanced shortly.

Two dimensional modeling of sewage sludge flow in a double-axis continuous paddle dryer

A two-dimensional model based on the theory of Markov chain has been developed to determine the Residence Time Distribution (RTD) of municipal sewage sludge in a double-axis continuous paddle dryer. Based on the experiments, the paper proposes further corrections to simulate the transition. To characterize the sludge transition in the dryer, the parameter of internal recirculation based on one dimensional model is further developed. In addition, two parameters, the internal forward coefficient between two axes and the internal forward coefficient in one axis are introduced to characterize the new model. In absence of available correlation, solid hold-up of each cell in dryer and both the recirculation parameters are identified by fitting the model to experiments. Through analysis, the model demonstrates its ability to describe the sludge flow in a double-axis continuous paddle dryer by the experimental and simulation RTD curve. Finally, an analysis of influence factors highlights that recirculation coefficients are critical for the model while solid hold-up Hu of each cell controls the mean residence time and the final moisture content. In addition, the geometric residence time of sludge flow has a negligible effect on sludge flow for it has no effect on dimensionless variance. Moreover, compared with the recirculation coefficient between different axes R, the recirculation coefficient in one axis r has a negligible effect. In addition, recirculation parameters have no effect on mean residence time of sludge flow.

Mechanistic insights into the effects of biopolymer conversion on macroscopic physical properties of waste activated sludge during hydrothermal treatment: Importance of the Maillard reaction

In this study, the molecular transformation of sludge biopolymers during hydrothermal treatment with the temperature ranging from 25 °C to 200 °C was examined and was seen to significantly affect the macrophysical properties (dewaterability and rheological property) of sludge. The results showed that the sludge dewaterability and flow ability under high shear stress deteriorated by a hydrothermal process at 25 °C to 120 °C, but the deterioration alleviated above the temperature threshold of 120 °C. The consistence of changes in sludge dewaterability and rheological property in HT process was mainly attributed to the variation in gel properties of soluble biopolymer. Two-stage changes in biopolymer transformation were identified, beginning with a solubilization stage from 25 °C to 120 °C in which a biopolymer with a gel-like network structure was released into liquid phase, creating flow resistance under high shear stress such that sludge dewaterability deteriorated. The second stage was identified as a conversion stage (120 °C–200 °C) in which proteins and polysaccharides hydrolyzed and experienced a Maillard reaction, leading to the degradation of the biopolymer network structure. The newly formed recalcitrant Maillard products showed weak flow response to high shear stress, allowing for an improvement in sludge dewaterability. The pathways of a Maillard reaction were identified via gas chromatography−mass spectrometer (GC–MS), 1H nuclear magnetic resonance spectroscopy (1H NMR) and two-dimensional correlation spectral analysis (2D-COS) of Fourier-transform infrared spectrometer (FTIR), etc. Three-dimensional excitation-emission matrix (3D-EEM) proved to be an applicable method for tracking Maillard reaction in sludge hydrothermal process due to the distinctive fluorescence characteristics of Maillard products. This study further clarifies the obscure process of sludge hydrothermal treatment and will help improve the accuracy of subsequent research.