Sludge Stabilization Research Articles

Improving the quality of organic compost of sewage sludge using grass cultivation followed by composting

Composting is one of the main processes of stabilization of sewage sludge and its association with cultivation in this residue has a great potential to produce stabilized organic fertilizer and, or substrate for plant development. The aim of this work was to evaluate the physical, chemical, and microbial attributes of sewage sludge (SS) aerated and cultivated with Pennisetum purpureum or Urochloa brizantha and, later, composted. The study was installed in a 2x2+2 factorial scheme, with four replications. The factors consisted of cultivation of P. purpureum or U. brizantha in SS for 90 days, with or without intermittent aeration for 60 days. The control treatments were SS without cultivation, with the presence or absence of aeration. After 90 days of cultivation, the grass was cut, crushed, and incorporated into the SS for composting for 60 days. The composted sewage sludge showed an increase of 26, 24, 17, 123, 19, 32, and 7.7% in the levels of P, Ca, Cu, Fe, Mn, Zn, and Pb; and a reduction of 22, 5.2, 26, 30, 8.8, and 70% in the levels of C, N, K, Mg, Ni, and Na, respectively. The levels of Cu, Ni, Zn, and Pb remained below the maximum limit allowed by environmental resolution. The degradation of SS decreased the particle diameter, increasing the bulk density and total porosity, improving the physical properties of the compost. The SS cultivation and composting, regardless of the grass, led to a reduction in pH, basal and accumulated respiration, nitrification index, and C/N ratio and an increase in the CEC/C ratio, showing adequate maturation of the compost produced. Thus, the SS cultivation and composting with grasses were effective for producing matured and quality organic compost with low risk of environmental contamination.

Solar Drying as an Eco-Friendly Technology for Sewage Sludge Stabilization: Assessment of Micropollutant Behavior, Pathogen Removal, and Agronomic Value

Sewage sludge (SS) is a biosolid that includes nutrients, organic matter, and a mixture of micropollutants and pathogens. Regarding its final disposal, several criteria should be met to avoid the dissemination of the included micropollutants in the environment. Hence, an adequate treatment prior to SS disposal is highly required. Solar drying is being acknowledged as a sustainable process of SS treatment, yet it is still unclear to what extent this technique is efficient. This review aimed to assess the impact of solar drying on the composition of SS from environmental and agronomic standpoints. Herein, we present the state-of-the-art with regard to solar drying efficiency in terms of water content reduction, DM increase, agronomic parameters evolvement, and micropollutant stabilization including pathogens, heavy metals (HMs), and organic micropollutants. The reviewed literature is mostly focused on two drying cycles: summer and winter, thus addressing the extreme conditions met within a year with respect to temperature. Under different climatic conditions, more than 80% of dry matter is reached during summer. In winter, the efficiency decreases to an average of 50% of DM. Negatively correlated to DM content, pathogen concentration in SS significantly decreased, while DM increased. Thus, more efficiency in terms of pathogen abatement is reported in summer than in winter (e.g., 96% against 60% during summer and winter, respectively, under semi-arid climate). The high reliance of solar drying efficiency on weather has been deduced in terms of DM content increase and pathogen removal. Where climatic conditions are not favorable for solar drying, hybrid design and liming are the highly recommended methods to remove pathogens from SS. A few studies on the fate of HMs in SS during solar drying concluded that solar drying does not involve any removal mechanisms. Changes in HM speciation in solar-dried sludge were reported highlighting a decrease in their mobility. As for organic micropollutants (PAHs and antibiotics), only their occurrence in SS is reported in the literature, and their behavior during the solar drying process is still not addressed. This review allowed concluding the following: 1) solar drying is a sustainable, relevant process for SS handing in terms of volume reduction and pathogen removal, particularly in semi-arid regions; 2) solar drying does not lower the SS agronomic value and does not remove HMs, but under semi-arid climate, it changes HM speciation and reduces their mobility. The gap in research regarding organic micropollutant and heavy metal behavior during SS solar drying has been emphasized as a way forward for research within this topic. Hence, more research is required to help stakeholders decide on the feasibility of an agricultural disposal of solar-dried sludge.

Combining Shift to Biogas Production in a Large WWTP in China with Optimisation of Nitrogen Removal

Despite the huge current challenges in sewage sludge treatment and disposal in China, anaerobic sludge stabilisation (AnSS) is still not a state-of-the-art process in WWTP in the country. However, the potential benefits of anaerobic sludge stabilisation may outweigh the drawbacks. One of these drawbacks is the backload from the sludge liquor that increases the nutrient load in the biological treatment stage. This work shows via computer modelling that not only can the sludge production and disposal costs be significantly reduced, but also that, with sensible automation and operational strategies (e.g., bypass of primary clarifiers, use of a centrate dosing strategy, incorporation of ammonium nitrogen sensors, etc.), the effects of the backload can be counteracted for nitrogen removal, even considering that wastewater in China often has an unfavourable C/N ratio for nitrogen removal. The tested strategies would even improve the overall plant performance in terms of norm compliance, sludge production, energy use, and energy production

Polyaniline improves granulation and stability of aerobic granular sludge

Polyaniline improves granulation and stability of aerobic granular sludge

COD inhibition alleviation and anammox granular sludge stability improvement by biochar addition

High chemical oxygen demand (COD) in anaerobic ammonium oxidation (anammox) reactors may destroy the structure or inhibite the activity of anammox granular sludge (AnGS). Herein, the effects of adding different biochars on the alleviation of COD inhibition, performance of anammox reactors in phases I (fed with an initial COD = 100 mg L−1) and II (= 150 mg L−1), as well as their effect on the properties of AnGS granules were investigated. Results showed that nitrogen removal in biochar-added reactors was superior to that in reactors without biochar (the control). AnGS with biochar addition outperformed the control in terms of stability (EPS and particle size distribution) as the initial COD concentration increased. In the reactors amended with litchi biochar and chinar biochar, the respective average TN removal efficiencies were 86.49% and 85.70% in phase Ⅰ as well as 86.54% and 85.51% in phase Ⅱ; the proportion of AnGS particles with a diameter of 1–3 mm reached a respective maximum of 80.97% and 73.74% (much higher than 67.69% in the control); and the AnGS granules had better stability with a little change in the protein (PN) to polysaccharide (PS) (PN/PS) values, the PN/PS values were 4.18 and 4.77 in phase Ⅰ as well as 4.21 and 4.70 in phase Ⅱ. Even at increasing COD concentrations, no significant change in the relative abundance of Planctomycetes was observed in all the biochar-containing reactors (P value over 0.9), and the relative abundance of anammox-related functional genes (hzs, hdh) was higher than that in the control.

Effect of magnetic field intensity on aerobic granulation and partial nitrification-denitrification performance

Magnetic field, acknowledged as a sustainable approach, is a promising method to improve the formation, stability and treatment performance of aerobic granular sludge (AGS). In this study, partial nitrification-denitrification was achieved in three AGS sequencing batch reactors (SBRs), and the effect of magnetic field intensity on AGS formation and partial nitrification-denitrification performance were investigated. 50 mT magnetic field could accelerate complete granulation time from 45 d (0 mT) to 30 d (50 mT) by promoting the settling ability of AGS and stimulating the secretion of extracellular polymeric substances (EPS). With 50 mT magnetic field, partial nitrification-denitrification in AGS was enhanced, and the removal efficiency of chemical oxygen demand (COD), NH4+-N and TN increased by 7.6%, 26.2% and 41.5% comparing with the control (0 mT). Magnetic field balanced the dominant genera Thauera, Flavobacterium, Chryseobacterium and Meganema, which further enhanced the aerobic granulation and partial nitrification-denitrification in AGS. Thus, the application of magnetic field is reliable for accelerating aerobic granulation and enhancing partial nitrification-denitrification process.

Feasibility of vermicomposting combined with room drying for enhancing the stabilization efficiency of dewatered sludge

Vermicomposting is characterized by transforming organic waste into nutrient-rich organic fertilizer through the action of different earthworms and microorganisms. Although vermicomposting can recycle the excess sludge in an eco-friendly manner, the longer stabilization period has limited its industrial application. The present study sought to investigate a novel operation process of vermicomposting combined with room drying (VD) to improve the stabilization efficiency of dewatered sludge. Subsequently, the performance and efficiency of vermicomposting without room drying, room dry without vermicomposting, and VD for sludge stabilization were compared simultaneously. In the VD process, the sludge water content reduced from 60.8% to 1.64%, showing the highest electrical conductivity and lowest organic matter content, making the humus substances abundant in the final product. Moreover, the vermicomposting achieved the highest ammonia and nitrate content in final product. Additionally, the bacterial and eukaryotic abundances in the VD product were significantly higher (P < 0.01, i.e., 15.6% and 180.7%) than the vermicomposting product. The specific bacterial genus of Glutamicibacter, Chitinibacter, and Acidobacteria was dominated in the VD product. The Partial least squares-Path modeling (PLS-PM) results revealed that the maturity degree in the VD product was significantly associated with microbial component, and the organic form was strongly driven by the change in the physicochemical properties, which was contradictory to vermicomposting model. The study suggests that the VD process could shorten the vermicomposting period by rapidly accelerating the physical, chemical, and biological stabilization of sludge.

Reproducibility of Aerobic Granules in Treating Low-Strength and Low-C/N-Ratio Wastewater and Associated Microbial Community Structure

Long-term stability of the aerobic granular sludge system is essentially based on the microbial community structure of the biomass. In this study, the physicochemical and microbial characteristics of sludge and wastewater treatment performance were investigated regarding formation, maturation, and long-term maintenance of granules in two parallel sequencing batch reactors (SBR), R1 and R2, under identical conditions. The aim was to explore the linkage between microbial community structure of the aerobic granules, their long-term stability, as well as the reproducibility of granulation and long-term stability. The two reactors were operated with a COD concentration of 400 mg/L and a chemical oxygen demand to nitrogen (COD/N) ratio of 4:1 under anoxic–oxic conditions. It was found that although SVI30, sludge size, and distributions in R1 and R2 were different, aerobic granules were formed, and they maintained long-term stability in both reactors for 320 days, implying that a certain level of randomness of granulation does not affect the long-term stability and performance for COD and N removal. In addition, a significant reduction in the richness and diversity of microbial production was observed after the sludge was converted from inoculum or flocs to granules, but this did not negatively affect the performance of wastewater treatment. Among the predominant microbial species in aerobic granules, Zoogloea was identified as the most important bacteria present during the whole operation with the highest abundance, while Thauera was the important genus in the formation and maturation of the aerobic granules, but it cannot be maintained long-term due to the low food-to-microorganisms ratio (F/M) in the system. In addition, some species from Ohtaekwangia, Chryseobacterium, Taibaiella, and Tahibacter were found to proliferate strongly during long-term maintenance of aerobic granules. They may play an important role in the long-term stability of aerobic granules. These results demonstrate the reproducibility of granulation, the small influence of granulation on long-term stability, and the robustness of aerobic granulation for the removal of COD and N. Overall, our study contributes significantly to the understanding of microbial community structure for the long-term stability of aerobic granular sludge in the treatment of low-COD and low-COD/N-ratio wastewater in practice.

Stabilization of ferric arsenate sludge with ZVI intensive corrosion and enhancement of long-term arsenic immobilization via resin encapsulation

In this study, a novel stabilization/solidification (S/S) method, achieved by mechanochemically activated zero-valent iron (ZVI) intensive corrosion and resin encapsulation, was investigated for arsenic sludge disposal. The results showed that arsenic stabilization was enhanced by intensive corrosion process, with arsenic leaching concentration decreasing from 128.75 mg/L to 0.35 mg/L after stabilization treatment under optimized conditions. The residual state arsenic was increased from 96.32 wt% to 99.13 wt% after stabilization. The subsequent resin encapsulation solidification scheme has a significant effect on the low arsenic leachability of the stabilized sludge. The arsenic concentration of resin solidification matrix was 0.47 mg/L, which was significantly lower than that of cement solidification matrix (1.77 mg/L), as a control group. It also can be seen that resin curing showed much lower cumulative release rate (0.009 wt%) than cement curing (0.54 wt%) at the end of leaching test, under a 60-day long-term leaching test, indicating that resin curing has higher long-term arsenic stability. Resin curing can maintain the structure of the stabilized As-Fe phase by resin encapsulation, while the traditional cement curing would destroy the original stable As-Fe phase, and produce unstable As-Ca phase, resulting in the risk of arsenic pollution. Moreover, the matrix based on ZVI intensive corrosion and resin encapsulation scheme has great advantages in low compatibilization ratio and resistance to pH impact.

Optimising the Flux Enhancer Dosing Strategy in a Pilot-Scale Anaerobic Membrane Bioreactor by Mathematical Modelling.

Flux enhancers (FEs) have been successfully applied for fouling mitigation in membrane bioreactors. However, more research is needed to compare and optimise different dosing strategies to improve the filtration performance, while minimising the use of FEs and preventing overdosing. Therefore, the goal of this research is to develop an optimised control strategy for FE dosing into an AnMBR by developing a comprehensive integrated mathematical model. The integrated model includes filtration, flocculation, and biochemical processes to predict the effect of FE dosing on sludge filterability and membrane fouling rate in an AnMBR. The biochemical model was based on an ADM1, modified to include FEs and colloidal material. We developed an empirical model for the FE-induced flocculation of colloidal material. Various alternate filtration models from the literature and our own empirical models were implemented, calibrated, and validated; the best alternatives were selected based on model accuracy and capacity of the model to predict the effect of varying sludge characteristics on the corresponding output, that is fouling rate or sludge filterability. The results showed that fouling rate and sludge filterability were satisfactorily predicted by the selected filtration models. The best integrated model was successfully applied in the simulation environment to compare three feedback and two feedforward control tools to manipulate FE dosing to an AnMBR. The modelling results revealed that the most appropriate control tool was a feedback sludge filterability controller that dosed FEs continuously, referred to as _10. Compared to the other control tools, application of the _10 controller resulted in a more stable sludge filterability and steady fouling rate, when the AnMBR was subject to specific disturbances. The simulation environment developed in this research was shown to be a useful tool to test strategies for dosing flux enhancer into AnMBRs.

Uncover the secret of the stability and interfacial Gibbs free energy of aerobic granular sludge

Interfacial Gibbs free energy (IGFE) as a thermodynamic indicator characterize the stability of the natural system. For aerobic granular sludge (AGS), how IGFE determines the stability of sludge remains to be determined. The Gibbs free energy change at the AGS-water interface (ΔGswa) and AGS interfaces (ΔGsc) were selected as the main interfacial thermodynamic factors. Results indicated that the stable AGS was guaranteed with ΔGsc at the range of −31 to - 46 J m−2. Pearson correlation coefficients between ΔGswa/ ΔGsc and relative hydrophobicity, water content, SVI30, integrity coefficient were −0.9, 0.8, 0.85, and 0.84, which illustrated that the IGFE could be a more comprehensive thermodynamic indicator. Microbial community and EPS analysis verified the importance of denitrifiers, Amide III, protein-like substances for AGS stability. This work offers a new insight into the development of AGS stability based on IGFE.

Energy-Positive Disintegration of Waste Activated Sludge—Full Scale Study

This study aimed to evaluate the effects of mechanical disintegration of waste activated sludge (WAS) on full scale anaerobic digestion, considering the possibility of obtaining a positive energy balance. The results showed that an increase in energy density (εL) used in disintegration was accompanied by an increase in the release of organic compounds from sludge (SCOD increased from 211 ± 125 mg O2/L for εL = 0 kJ/L to 6292 ± 2860 mgO2/L for εL = 180 kJ/L). Some of them were volatile fatty acids. The percentage share of WAS subject to disintegration was also documented as a crucial parameter affecting the efficiency of biogas production. An increase in the value of this parameter from 25% to 100%, even at much lower εL used in disintegration (therefore with much smaller amounts of organic compounds released from sludge flocs) resulted in an increase in biogas production. Conducting disintegration of the entire stream of WAS directed to the fermentation tank at εL 30 kJ/L resulted in an increase in biogas production by 14.1%. Such a surplus would allow production of approximately 360 kWh/d net electricity. Mechanical disintegration of thickened WAS therefore may be an economically justifiable strategy for the intensification of anaerobic sludge stabilisation.

Electroosmotic Dewatering of Iron Ore Tailings: A Laboratory Study to Improve Geotechnical Properties

Minerals are subjected to ore processing to turn them into usable and saleable raw materials. First of all, the ore is reduced to the smallest size with the crushing‐grinding process, and after using water and chemical additives, according to the characteristics of the ore, useful minerals are taken, and unwanted minerals are stored in the tailings pools. Approximately, 26 million tons of mineral wastes were generated annually from ore processing facilities in Turkey. The construction of tailings pools, the stability of the tailing sludge, and the safety of dams are a burdensome issue faced by miners. In the ore plants, an average of 3 tons of water is used to enrich 1 ton of ore, and most of the wastewater cannot be removed by traditional methods, causing various economic, environmental, and stability problems. In this study, the dewatering of an iron ore tailing by applying different voltages by the electroosmosis method was investigated in the laboratory environment. By discharging the water of the iron ore tailings by the electroosmosis method, the solid content was increased from 43.01% to 87.63%. Thus, it has been observed that there will be a significant improvement in the geotechnical properties of the tailings’ material. It has been estimated that electroosmotic dewatering rises with increasing the voltage gradient and the energy consumption varies in the range of 0.588–30.645 kWh/dry ton. The void ratio decreased from 5.58% to 0.23%. In the dewatering experiments, different parameters such as the amount of water discharged, density, void ratio, water content, and power consumed were measured or calculated and the relationships between them were discussed with graphics. In electroosmosis experiments, it has been observed that besides the voltage applied in the discharge of water, the mineralogy of the tailings has a significant effect. Since there are serious abrasions on the electrodes used in the experiments, alternative electrodes should be tried.

Granular Stability, Nitrogen and Phosphorus Removal Pathways of Aerobic Granular Sludge Treating Real Municipal Wastewater at Different Temperatures

Granular Stability, Nitrogen and Phosphorus Removal Pathways of Aerobic Granular Sludge Treating Real Municipal Wastewater at Different Temperatures

Influence of Temperature on Aerobic Granular Sludge Formation and Stability Treating Municipal Wastewater with High Nitrogen Loadings

Influence of Temperature on Aerobic Granular Sludge Formation and Stability Treating Municipal Wastewater with High Nitrogen Loadings

Stability Analysis of Mechanical Sludge Dewatering Machine Frame Based on Numerical Simulation

Sludge is the inevitable product of sewage treatment plant and sewage treatment. Before sludge treatment, dewatering is generally required. Mechanical sludge dewatering machine is a common sludge dewatering equipment. Due to the complex operation conditions, the stability of sludge dewatering machine frame directly affects its reliability. In this paper, a mechanical sludge dewatering machine frame as the research object, based on ANSYS Workbench finite element analysis platform, static analysis and modal analysis. The analysis results show that: under normal working conditions, the maximum variable of the frame is 0.07mm, which can effectively ensure the normal operation of the sludge dewatering machine; the equivalent stress is 4.22Mpa, which is far less than the Xu Yong stress of the material; the vibration of the first two modes of the frame is relatively concentrated, and the corresponding motor speed under the interference frequency is 1241.4-1595.4r/min, which should be avoided in the use process.

Analysis of Toc Values of Mixed Sewage Sludge Following the Hydrodynamic Treatment, in Course of Pilot Experiment in the Framework of R&amp;D Ginop Ongoing Project

The primary and secondary stages in wastewater treatment generate a large amount of sewage sludge consisting of 90% water, mineral components, nutrients and also a variety of organic and inorganic contaminants. The contaminants do not degrade completely during these processes, thus an additional degradation is needed to stabilize the sewage sludge. The innovative technology is proposed consisting of hydrodynamic cavitation process along with the addition of Bakony brown coal as adsorbent. Hydrodynamic cavitation is known as an effective tool improving sewage sludge stabilization via aerobic degradation, while adsorbent, besides the adsorption ability, has microbial cells disintegration ability as well, further enhancing the biodegradation process. The changes in total organic carbon (TOC) values of sewage sludge after hydrodynamic treatment for various retention times (0, 5, 10, 15, and 25 minutes) was traced and interpreted.

Effects of Aerobic Granular Sludge Separator on the Stability of Aerobic Granular Sludge (AGS)

Effects of Aerobic Granular Sludge Separator on the Stability of Aerobic Granular Sludge (AGS)

Rapid granulation of aerobic granular sludge and maintaining its stability by combining the effects of multi-ionic matrix and bio-carrier in a continuous-flow membrane bioreactor

The present investigation aimed at providing a novel approach to promote the rapid granulation and stability of aerobic granular sludge (AGS) in a continuous-flow membrane bioreactor (MBR). By operating two identical MBRs with or with no bio-carrier for 125 days, it was found that the combination of multi-ionic matrix and bio-carrier could promote the rapid formation and maintain the long-term stability of AGS. The primary AGS was first observed inside the reactor on day 14, and the mature AGS appeared soon and kept stable for more than 4 months (its average size still was about 800 μm on day 125). Suitable filling ratio of bio-carrier was beneficial to form a stable and regular circulating water flow inside, and adding divalent metal ions quickly reduced the negative charges of tiny sludge particles, which were two essential factors leading to the rapid granulation of AGS and maintaining its stability. The multi-ionic matrix not only enhanced the biological aggregation process, but also facilitated the expansion of the cultivated AGS into a new multi-habitat system of Mn-AGS, in which, complex microbial communities with rich bio-diversity robustly promoted the efficient removal of organic pollutants and nutrients.

Strength of Chemically Stabilized Sewage Sludge—Some Inferences from Recent Studies

Although there has been a substantial body of research on the chemical stabilization of sewage sludge, most of these results are project-specific and relate mainly to the use of new binders and sewage sludge from specific sources. In this sense, much of the work to date is context-specific. At present, there is still no general framework for estimating the strength of the chemically treated sludge. This paper proposes one such general framework, based on data from some recent studies. An in-depth re-interpretation of the data is first conducted, leading to the observation that sludge, which has coarse, hard particulate inclusions, such as sand, premixed into it, gives significantly higher strength. This was attributed to the hard coarse particles that lower the void ratio of treated soil, are much less susceptible to volume collapse under pressure, and contribute to the strength through frictional contacts and interlocking. This motivates the postulation of a general framework, based on the premise that coarse, hard particulate inclusions in the sludge which do not react with the binders can nonetheless contribute to the strength of the treated soil. The overall void ratio, defined as the volume of voids in the cementitious matrix normalised by the overall volume, is proposed as a parameter for quantifying the combined effect of the coarse particulate inclusions and the cementitious matrix. The binder-sludge ratio is another parameter which quantifies the strength of the cementitious matrix, excluding the hard particulate inclusions. Back-analysis of the data suggests that the significance of the binder-sludge ratio may diminish as the content of hard particulate inclusions increases.