Dry Sludge Research Articles

Determination of the Self-Ignition Behavior of the Accumulation of Sludge Dust and Sludge Pellets from the Sewage Sludge Thermal Drying Station

Sewage sludge may pose a fire risk. The safe storage of biomass waste is a challenge due to self-heating processes. This study aims to assess the propensity to spontaneously combust of sewage sludge in order to determine safe storage and transport conditions. The evaluation of spontaneous ignition hazard was assessed according to EN 15188, by the determination of the self-ignition temperature. Certain parameters assumed to affect the inclination of sewage sludge to self-ignite, including the moisture content, bulk density, elemental composition, and particle size, were discussed. The results showed the risk of self-ignition during the storage and transport of sludge dust and pellets. The usage of the smallest basket volume resulted in the highest self-ignition temperatures, which were 186 °C and 160 °C for sludge pellets and dust, respectively. The comparison of the two forms of thermally dry sludge showed, that despite sludge pellets being easier to store and handle issues, the more favorable conditions for the management in terms of fire risk is sludge dust. Its temperatures for safe storage are slightly higher. The results highlighted that future research should focus on the hazards of silo fires and explosions in terms of silo fire prevention and management.

The phosphorus harvest from low-temperature mainstream wastewater through iron phosphate crystallization in a pilot-scale partial nitritation/anammox reactor

The phosphorus harvest along nitrogen removal in the partial nitritation/anammox (PNA) reactor is promising for saving space and simplifying the management of mainstream wastewater treatment facilities. In this study, the phosphorus recovery from the low-temperature mainstream wastewater was explored through iron phosphate crystallization in a pilot-scale PNA reactor. With the COD-alleviated municipal wastewater as the influent, the ammonium concentration of about 50 mg/L and the phosphorus concentration ranged from 5.4 to 7.1 mg/L, under the temperature of 15 °C and the addition of external ferrous iron of 14 mg/L, the achieved nitrogen removal efficiency and the phosphorus removal efficiency were 37.6 % and 62.7 %, respectively. The good settleability of sludge indicated that the formed iron phosphate was well combined with the biomass. The quantitative analysis confirmed that the main iron phosphate in dry sludge was graftonite, and qualitative analysis confirmed that the equivalent of P2O5 content in the sludge was 5.8 %, which was suitable as fertilizer on agricultural land to realize the direct recycle of discharged phosphorus. In all, this study proposed a pioneering scheme to realize the nitrogen removal and phosphorus cycle in human society and given a meaningful reference for further research and application.

Suitability of treated FS using Jatropha curcas on unplanted sand drying beds for agricultural use in Dar es Salaam, Tanzania

Abstract The huge amount of water in faecal sludge (FS) has been presented as one of the major faecal sludge management (FSM) challenges and concerns. Jatropha curcas (JC) has been adopted as a dewatering and disinfection solution for FS treatment. However, very little is known about the agricultural suitability of their physical–chemical characteristics, nutrient and pathogen levels. The agricultural suitability of by-products from the unplanted sand drying beds was investigated by assessing the physical–chemical parametric indices, Wilcox diagram and pathogen removal rate. The qualitative method was adopted for both untreated and treated FS samples. A total of 60 samples for dry sludge and 70 samples for both leachates from control and JC chambers were analyzed for three months. Its agricultural suitability was judged by the level of salinity and sodium hazard in leachate and pathogen levels. The results showed that the salinity level of leachate from the JC chamber falls under medium- and low-risk levels. The removal efficiency of Escherichia coli by JC in leachate was from 7 ± 2 × 109 CFU/g to 6 ± 1 × 102 CFU/100 mL. Treating FS with JC is suitable for reducing salinity and sodium hazards in leachate hence favourable for irrigation. Further treatment of dry sludge is required before being used for agriculture.

Numerical Simulation of Heat and Mass Transfer in Sludge Low-Temperature Drying Process.

Based on the sludge mass transfer flux model, this paper conducts a simulation study on the drying characteristics of sludge under low-temperature environment and compares it with the previous experimental results. It is found that when the sludge moisture content is low, the change of its drying curve is basically consistent with the experimental results, but there is a large error when the sludge moisture content is 0.4-0.6. In order to better simulate sludge drying characteristics, a model of cracking and shrinkage coefficients based on sludge moisture content is proposed, and the effective diffusion coefficient and mass transfer coefficient are modified. The maximum error between simulation and experiment is reduced to 23.78%. Based on this model, the sludge drying mechanism was studied. It was found that heat transfer and diffusion played a major role in the initial stage of sludge drying, and diffusion played a major role in sludge drying 30 min later.

Production of biocoal from wastewater sludge and sugarcane bagasse using hydrothermal carbonization

AbstractThe growing demand for fuel in South Africa coupled with the depletion of fossil fuel reserves demonstrates the need for alternative energy sources. A renewable resource such as biomass can be optimized as an energy source. Wastewater sludge and bagasse have the energy potential to produce high calorific value biocoal; this will contribute to the supply of energy in South Africa. The synthesis of biocoal from wastewater sludge and bagasse through an artificial synthetic coal production process, i.e. hydrothermal carbonization, is preferred over other thermal conversion techniques as hydrothermal carbonization is capable of handling feed having a high (75–90%) moisture content. In this study, wastewater sludge and sugarcane bagasse were subjected to hydrothermal carbonization, and the effect of temperature was explored at 180, 210, 240 and 260°C. Variation of the ratio of dry sludge to bagasse of 100:0, 80:20, 60:40, 40:60, 20:80 and 0:100 and the composition of solid to liquid (solid loading wt%) of 1:10, 2:10, 3:10 and 4:10 (SB:H2O) corresponding to 9.09, 16.67, 23.08 and 28.57 wt% loading was investigated. The results obtained in this study reveal that solid loading, temperature, biomass type and ratio variation had a substantial impact on the yield and calorific value of the biocoal produced. The highest biocoal yield of 23.36 wt% was achieved at 210°C and derived from sludge/bagasse with a sludge content of 20%. Across all of the runs, the highest calorific value of 20.21 MJ kg−1 was achieved at 260°C when pure bagasse was employed (0% sludge content). © 2022 The Authors. Biofuels, Bioproducts and Biorefining published by Society of Industrial Chemistry and John Wiley & Sons Ltd.

Study of Solidifying Surplus Sludge as Building Material Using Ordinary Portland Cement

In an attempt to effectively utilize a multitude of surplus sludge from sewage treatment plants, ordinary Portland cement was used to solidify the dry surplus sludge as a building material. The dry surplus sludge and cement were mixed at different proportions with a certain dosage of water and then cured for 3–60 days at room temperature. The unconfined compression strength (RC) of solidified blocks was investigated with respect to the effects of the ratio of liquid to solid (Rl/S), surplus sludge dosage (DS), the dosage of sodium silicate (DNa2SiO3), and the proportion of fly ash (WF). The fabricated solidified blocks were characterized by scanning electron microscopy (SEM), Fourier transform-infrared spectroscopy (FT-IR), and X-ray Diffraction Analysis (XRD). The results demonstrated that RC at 60 days reduced obviously with the increase in Rl/s when Ds was given, whereas RC reduced with DS increased to 15.0 wt% from 5.0 wt% for solidified blocks. When DS was 5.0 wt%, RC of 28 days was reduced from 20.87 MPa to 14.50 MPa, with an increase in Rl/s from 0.35 to 0.55. For the given Rl/s, such as Rl/s = 0.35, RC at 60 days was 23.75 MPa, 2.80 MPa, and 2.50 MPa when DS were 5.0 wt%, 10.0 wt%, and 15.0 wt%, respectively, which were relatively lower in comparison to that of Portland cement solidified blocks without surplus sludge (51.40 MPa). In addition, the addition of Na2SiO3 and fly ash was favorable in terms of improving the RC for solidified blocks. RC of 60 days increased initially and then reduced with the increase in DNa2SiO3 from 0.0 wt% to 9.0 wt% at Rl/s = 0.45 and DS = 5.0 wt%. At DNa2SiO3 = 7.5 wt%, Rl/s = 0.45, and DS = 5.0 wt%, the highest RC value of 34.70 MPa was achieved after being cured for 60 days. Furthermore, RC of 60 days increased initially and then reduced with WF increasing from 0.0 wt% to 25.0 wt%, and the highest RC value of 34.35 MPa was achieved at WF = 10.0 wt%, Rl/s = 0.45, and DS = 5.0 wt%. At the ratio of DNa2SiO3 = 7.50 wt%, Rl/S = 0.35, WF = 20 wt%, DS = 15.0 wt% and M = 1.00, RC of 28 days reached 26.70 MPa. With these values, the utilization of sludge utilized (DS = 15.0 wt%) was increased by double compared with DS = 5.0 wt% (20.87 MPa). To investigate the effect of environmental temperature on the mechanical properties and mass of solidified blocks, the freeze-thaw cycling experiment was carried out. The RC of 28 days and the mass of the solidified block reduced with the number of freeze-thaw cycles, increasing for solidified blocks with DS of 5.0 wt%, 10.0 wt%, and 15.0 wt%, manifesting a decrease of 25.60%, 32.30%, and 40.60% for RC and 3.40%, 4.10%, and 4.90% for mass, respectively. This work provides sufficient evidence that surplus sludge has a huge potential application for building materials from the perspective of improving their mechanical properties. It provides an important theoretical basis for the disposal as well as efficient utilization of sludge.

Insight into the effect of calcium carbonate filler on the dewatering performance of simulated pulp & paper mill sludge

The dewatering of large amount of industry sludge is one of the significant environmental problems in the pulp and paper industry. Calcium carbonate fillers are an important component in primary sludge from paper mills. In this paper, the role of precipitated calcium carbonate (PCC) on the dewaterability of simulated mixed paper mill sludge (the mixture of PCC and secondary sludge) without and with FeCl3 conditioning was studied. The results showed that when the PCC content increased from 0 to 600 mg/g dry sludge (DS) without FeCl3 conditioning, the moisture content (MC) and the specific resistance to filtration (SRF) decreased from 89.4% and 3.1 × 1013 m/kg to 66.7% and 2.4 × 1012 m/kg, respectively. However, when the PCC content was high enough (> 444 mg/g DS), the effective moisture content (MC*) changed little and the net sludge solid yield (YN) decreased, indicating that the non-conditioning effect of PCC dominated at high PCC content. Furthermore, increasing PCC content reduced the compressibility coefficient, although the change was insignificant from 1.06 to 0.91. When FeCl3 was used as the chemical conditioner, FeCl3 and PCC had additive effects on improving the sludge dewaterability (such as MC, SRF and compressibility). The improving mechanism of PCC on the sludge dewaterability can be explained by the release of Ca2+ from PCC caused by lower pH, the bridging effect of multivalent cation and the formation of more rigid sludge flocs.

Characterization of microplastics in the septic tank via laser direct infrared spectroscopy

Microplastics (MPs) are emerging pollutants that have been widely detected in the atmosphere, hydrosphere, lithosphere, and biosphere. Such wide spread of MPs indicates that the effective control in different environmental sectors is in an urgent need, and the first step in meeting this need is to identify the occurrence of MPs in the relevant environment. However, research on MPs in septic tanks has not been reported so far. This study investigated the distribution characteristics of MPs in septic tanks with a size detection limit of as low as 20 μm detected by laser direct infrared spectroscopy. Results showed that the number of MPs in the septic tank was reached 2803 (1489–4816) particles/g dry sludge, and the amount detected in the sediments was one order of magnitude higher than that in the scums. A total of 36 types of MPs were found in the septic tank, and 26 types were found in both sediments and scums, but the type in the scums was 21% higher than that in the sediments. The size was mostly 20–100 μm, accounting for 86.3% and 91.2% in the sediments and scums, respectively. Four shapes of MPs were detected in the septic tank, namely, fiber, bead, granule, and fragment. Our study revealed that septic tanks are both sinks and sources of MPs, which are reflected in the fact that MPs are not only large in number but also abundant in types. Thus, significant attention should be paid to septic tank-based microplastic pollution, which may lead to environmental and health risks without proper control and management.

The effect of microwave hydrothermal treatment on the combustion behavior of sewage sludge

In this study, the thermal behavior of microwave hydrothermal char of sewage sludge (MTC) was compared with dried sludge (DS) and char produced by electric hydrothermal treatment (ETC). The retention ratio of volatile matter in MTC was raised by 51.2% compared with in HTS, while their dewaterability by centrifugation were very close. The kinetic parameters of thermal disposal process of the DS and hydrochars were determined from TG analysis. It was found that the activation energy of combustion was reduced from 44.20 kJ/mol of DS to 47.29 kJ/mol for ETC. For MTC, the activation energy was slightly decreased (43.22 kJ/mol). In addition, the highest weight loss rate (0.49%/min) in combustion was also found for MTC. The evolution of gaseous nitrogen compounds was obtained by FTIR analyzer combined with TG. The results indicated that in devolatilization process, the emission of NH3, the main precursor of NOx in combustion, was postulated to higher temperature for MTC. In conclusion, MTC has a better combustion performance and a close dewaterability compared with to ETC. This study provided a new choice for the pre-treatment method of sewage sludge before combustion.

Thermodynamic and economic analyses of sewage sludge resource utilization systems integrating Drying, Incineration, and power generation processes

In an effort to beneficially utilize sewage sludge as a resource, a process system integrating sewage sludge drying, incineration, and power generation are proposed and subjected to thermodynamic and economic analysis. The proposed system comprises wet sewage sludge drying using a low pressure steam, dry sewage sludge incineration in a boiler to raise steam for power generation in a steam turbine whose exhaust facilitates the drying of the wet sewage sludge. Three alternative schemes are considered. Scheme 1 features higher temperature and pressure of the turbine exhaust for drying without auxiliary fuel; Scheme 2 includes an external steam input while Scheme 3 incorporates firing of coal as auxiliary fuel. The results indicate that the energy efficiency of Schemes 2 and 3 can reach up to 49.93 % and 48.69 %, respectively. The economic analysis suggests that Scheme 2 outperform Schemes 1 and 3. The cost of electricity for Schemes 2 and 3 are as low as 0.037 and 0.039 USD/kWh, respectively, with corresponding dynamic payback period being 13.63 and 13.70 years. The net present value attains 48.67 million and 48.62 million USD, respectively. Therefore, the proposed schemes 2 and 3 are suitable and promising for sewage sludge resource utilization from the viewpoint of thermodynamics and economics. Moreover, a conceptual proposal for renewable energy dispatch is presented and analyzed, which would provide a reference for practical engineering application.

Sustainable usage and the positive environmental impact of wastewater dry sludge-based concrete

The paper examined the application of dry sludge in lightweight concrete and the associated environmental risk. Population growth has led to an increase in residential and commercial wastewater sludge production. The sludge is deposited to a designated landfill, rendering the area useless and posing a significant environmental concern. The need for lightweight materials in the construction sector has resulted in the replacement of dry sludge for the basic components of concrete. The dry sludge came from the WWTPs in Polokwane, Limpopo Province, was used as a partial replacement for sand (0, 2.5, 5, 7.5, 10, and 12.5%) in concrete. The samples prepared were cured in wastewater and potable water. The results showed that the partial substitution of sand with 7.5% dry sludge in the concrete mixture reached the desired strength of 25 MPa and can be employed in lightweight structural applications. Concrete cube unit weight reduced by 0.8, 2.3, 2.6, 3.9, and 4.6% compared to the control sample when 2.5, 5.0, 7.5, 10, and 12.5% of the sand was substituted with sludge. Concrete samples were submerged in iodine water for 28, 90, and 140 days to test the leaching of soluble metals. The levels of heavy metals in leachate were far lower than what the US Environmental Protection Agency (EPA) considers to be safe, under their Toxicity Characteristics Leaching Procedure (TCLP) standards. EDX examination of sludge-based concrete showed a considerable reduction in metal weight percentage, the concentration of calcium increased by 69% due to the cement content; and the blending aggregates lowered silicon, aluminium, iron, and potassium by 33.3, 66.9, 34.2, and 77.8%. Therefore, wastewater may be utilized as a concrete curing medium, and sludge-based concrete can be used for simple structural repairs at WWTPs.

Insights into the characteristics and mechanism of vacuum drying technology for municipal sludge processing

Vacuum drying is an effective approach for sludge treatment and valorization. However, the vacuum drying of sludge has not been industrialized at present. The objective of this study was to elucidate the vacuum drying characteristics of static sludge and crack initiation mechanism. Our results indicate that crusting on the sludge surface under a high vacuum inhibited drying by reducing major cracks at sludge thicknesses of 13.6 and 10.2 mm. The inhibition effect weakened with decreasing sludge thickness. At 6.8 mm, the mean drying rate (VM) was the lowest at 0.08 MPa, while VM decreased with increasing vacuum degree at thicknesses of 13.6 and 10.2 mm. The decrease in drying rate could be attributed to rapid evaporation on the sludge surface under a high vacuum, leading to crusting, which inhibited crack initiation. VM was raised by 67.9–162.2% from 10.2 to 6.8 mm because the suction force of vacuum on water was much higher than the resistance to water diffusion of small isolation piles at 6.8 mm. Additionally, this study provided essential information to improve existing sludge treatment methods.

A performance comparison of cyclopentyl methyl ether (CPME) and hexane solvents in oil extraction from sewage sludge for biodiesel production; RSM optimization

A comparative study of oil extraction from secondary dry sludge was performed via Reflux and Folch methods by cyclopentyl methyl ether (CPME) and hexane as green and organic solvents, respectively. Response surface methodology based on Box-Behnken design (RSM-BBD) was utilized to optimize and predict the impact of influential factors, including sludge amount (4–6 g), the volume of solvent (12–16 mL), and extraction time (2–6 h). The maximum oil extraction efficiency was 8.078 % and 4.076 % under the optimal conditions: 5.15 g, 16 mL, 2 h for CPME, and 4.22 g, 11 mL, 2 h for hexane. The raw sludge was characterized by FESEM and XRF analyses, while the extracted oil characteristics were determined by GC-Mass and FTIR methods. As a result, the Folch method by CPME solvent was a more efficient way to extract oil from sewage sludge. Finally, biodiesel was produced via the transesterification double-step process (TDSP) using NaOH/Clinoptilolite-Fe3O4 magnetic catalyst. The production efficiency of biodiesel from the oil extracted by CPME and hexane is 6.94 % and 4.1 %, respectively. The maximum yield of biodiesel production was6.94 % under the optimum reaction conditions: methanol to oil molar ratio of 10:1, catalyst weight of 0.45 wt%, and reaction time of 2.5 h with the help of the electrolysis method.

Plasma-Chemical Synthesis and Properties of Oxide Compounds of Cobalt

To date, the possibilities of using metal oxide particles in various fields have been developed [1]. At the same time, their characteristics largely depend on the method of preparation, which usually determines their structure, size, and physicochemical properties [2].Among the methods for obtaining nanosized particles, one can single out methods of green synthesis [3], electrochemical [4], electropulse [5], and plasmachemical [6] synthesis based on the reduction or oxidation of metal ions in solutions under favorable conditions, followed by aggregation of nanoparticles.The purpose of this work is to analyze the technology for the synthesis of cobalt oxide compounds using contact nonequilibrium low-temperature plasma and to determine the directions for its further improvement.The object of the study was the process of obtaining particles of cobalt oxide using contact non-equilibrium low-pressure plasma during the processing of a liquid medium.The study was carried out using laboratory equipment and software modules of the HSC Chemistry 5.11 package. To find the preliminary conditions for the formation of interphase boundaries, diagrams were used in the coordinates of the E-pH potential of the aquatic environment (Pourbaix diagrams). It has been established that, depending on the initial state of Co(OH)2 in solution, the mass fraction of oxygen in the precipitate can change. In this case, the addition of hydrogen peroxide leads to a decrease in the proportion of hydroxide compounds in sediments. X-ray phase analysis showed the presence of CoO, CoOOH, Co3O4, β-Co(OH)2, Co in dry sediments. It has been established that the particle sizes lie in the range of 10 – 110 nm. The micrographs confirm the agreement between the calculated values and the experimental data.The phase composition of the deposit is influenced by the following factors: current density and anion concentration, process temperature. Increasing the temperature increases the diffusion coefficient but requires a higher current density to produce a powder. It has been established that a decrease in the liquid layer contributes to an increase in the yield of oxide compounds. The results of the analysis allow us to conclude that when using the technologies of plasma-chemical processing of liquid media to obtain compounds of the ultra- and nanoscale range, it becomes necessary to choose the parameters that are optimal for this process. The results of the analysis allow us to conclude that this technology can be optimized by controlling the initial pH of the solution; use of the spent solution in a container with the initial solution for its acidification; refinement of the reactor block for treating the solution in a film mode or close to it; choice of rational parameters for sludge drying. Laurent S., Boutry S., Muller R. N. Metal oxide particles and their prospects for applications //Iron oxide nanoparticles for biomedical applications. – Elsevier, 2018. –P. 3-42.Wang L. et al. Rational design, synthesis, adsorption principles and applications of metal oxide adsorbents: a review //Nanoscale. – 2020. – Vol. 12. – №. 8. – P. 4790-4815.El Shafey A. M. Green synthesis of metal and metal oxide nanoparticles from plant leaf extracts and their applications: A review //Green Processing and Synthesis. – 2020. – Vol. 9. – №. 1. – P. 304-339.Lawrence M. J., Kolodziej A., Rodriguez P. Controllable synthesis of nanostructured metal oxide and oxyhydroxide materials via electrochemical methods //Current Opinion in Electrochemistry. – 2018. – Vol. 10. – P. 7-15.Gan Z. et al. A laser and electric pulse modulated nonvolatile photoelectric response in nanoscale copper dusted metal‐oxide‐semiconductor structures //Advanced Electronic Materials. – 2018. – Vol. 4. – №. 11. – P. 1800234.Shamanin I. et al. Plasmachemical synthesis and evaluation of the thermal conductivity of metal-oxide compounds for prospective nuclear fuel //Journal of Physics: Conference Series. – IOP Publishing, 2019. – Vol. 1145. – №. 1. – P. 012057.

Development of Inorganic Sludge Drying System Technology Applied with Ejector by Air Velocity

Development of Inorganic Sludge Drying System Technology Applied with Ejector by Air Velocity

Construction of iterative algorithm and economic optimization analysis of co-combustion of sewage sludge with coal

ABSTRACT To govern the sewage sludge, which restricts the development of urbanization, the co-combustion of sewage sludge in coal-fired power plants is considered one of the most appropriate methods. Two methods, flue gas dehydration and electric heating dehydration, are used to dry sewage sludge to the target moisture content. And the economic impact of the two methods was evaluated on coal-fired power plants. The boiler efficiency and fuel consumption are obtained by the thermal balance calculation. When the anhydrous sludge ratio was 2% and the water content was 30%, the fuel consumption was 81.11 kg/s and the boiler efficiency was 91.32%. As the water content and the anhydrous sludge ratio increase, the fuel consumption gradually increases, while the boiler efficiency gradually decreases. And the net present value is used to evaluate the economic impact of the co-combustion of sewage sludge in coal-fired power plants. Among them, the maximum NPV value of the flue gas dehydration scheme with a sludge mass ratio of 3% and a moisture content of 40% reached 1163.34 million. Furthermore, the sensitive factors that affect the net present value are obtained as the anhydrous sludge ratio and government subsidies through sensitivity analysis. Combined with the combustion characteristics in the boiler, the recommended range for the moisture content of the sludge is 30%~40%, and the recommended range of anhydrous sludge ratio is 3–5%.

Rapid enrichment of anammox bacteria and transformation to partial denitrification/anammox with nitrification/denitrification sludge

The stable nitrite (NO2−-N) generation and rapid startup of anammox-based process are the main bottlenecks hindering its application in mainstream municipal wastewater treatment. In this study, a Partial-Denitrification (PD) system reducing nitrate (NO3−-N) to NO2−-N was rapidly developed within 40 days, using the nitrification/denitrification sludge from wastewater treatment plant. The NO3−-N to NO2−-N transformation ratios achieved 80.6 %. Significantly, a fast self-enrichment of anammox bacteria in this system was subsequently obtained, resulting in the successful transformation to an efficient PD/Anammox (PD/A) process after 79-day operation. The total nitrogen removal efficiency increased from 12.4 % to 90.0 % with influent ammonia and nitrate of 45.9 mg N/L and 62.2 mg N/L, corresponding to the anammox activity significantly increasing to 6.0 mgNH4+-N/g VSS/h without seeding anammox sludge. Abundance of anammox increased from 6.7 × 108 to 2.0 × 1011 copies/g dry sludge. High-throughput sequencing results showed that Candidatus Brocadia was the only known anammox genus and accounted for 1.08 % during the PD/A stage. Functional bacteria for PD, assumed to be the Thauera, was enriched from 1.99 % to 60.06 % but decreased to 32.49 % during the improvement of anammox activity. It demonstrated that the PD system with stable NO2−-N accumulation enabled a rapid self-enrichment of anammox bacteria and sufficient nitrogen removal with ordinary nitrification/denitrification sludge. This provides new insights into the scaling application of anammox by integrating PD with shortened startup periods and improved TN removal efficiency.

Efficient Wastewater Treatment via Aeration Through a Novel Nanobubble System in Sequence Batch Reactors

The aerobic wastewater treatments depend on the aeration. Hence, the size of the bubbles used in the aeration system may play a crucial role in this regard. This study attempted to investigate the effects of aeration bubble size on wastewater treatment efficiency of a “sequence batch reactor” (SBR) system at a laboratory scale using a novel designed fine/nanobubble forming instrumentation system. Based on the presence of microorganisms in the stationary phase, chemical oxygen demand removal efficiency on the 15th day (80.0 and 95.0%) was majorly better than on the 10th and 15th days in fine and nanobubble aeration systems. Moreover, with increasing sludge age, the “sludge volumetric index” (SVI) increased up to 170.0 ml g−1 on the 15th day. In addition, sludge rate and F/M ratio were much higher and expressively less in the nanobubble system rather than in the fine-bubbles system in which sludge was majorly denser. Therefore, the sludge was more easily deposited and the percentage of dry sludge was higher compared with the fine-bubble system. Thus, oxygen and specific oxygen uptake rate consumption were significantly reduced. The efficiency of the phosphorus removal was estimated to be between 54.0–60.0% for nanobubble aeration, compared to the general systems such as the SBR (10–20%) under similar conditions. In addition, the efficiency of the nitrogen removal in the nanobubble aeration system with different densities of 40.0, 50.0, and 60.0 ml g−1 was found as 99.0%, relatively higher compared to fine bubble with 96.0% nitrogen efficiency. In conclusion, a nanobubble aeration system could give considerably promoted efficiencies in all terms of the tested treatment effective parameters.

Pyrolysis and Co-Combustion of Semi-Dry Sewage Sludge and Bituminous Coal: Kinetics and Combustion Characteristics

To reduce the energy consumption and cost of the drying of sewage sludge (SS) and to ensure stability during combustion, the pyrolysis and co-combustion characteristics of semi-dry SS after the dehydration of flocculant and bituminous coal (BC) were studied in this work. The results show that the decrease in moisture content accelerates the release of volatile substances, and the increase in heating rate can also enhance the release of water and volatile matters. Furthermore, in the co-combustion of semi-dry SS and BC, the increase in mixing ratio (from 0% to 60%) of semi-dry SS caused the ignition and burnout temperature to decrease from 481 °C to 214 °C and from 702 °C to 627 °C, respectively. During co-combustion, the infrared spectra showed that the temperature range of 300–700 °C was the main gas precipitation area, and the main gaseous products were CO2, NOx, SO2, and volatile organic pollutants (VOCs).

The physico-chemical properties of sewage sludge processed for agricultural use from the Nyeri-Kangemi wastewater treatment plant, Nyeri county, Kenya

This study was conducted to assess the physico-chemical properties and changes that occur in the composting process between raw sewage sludge inflow at the sludge tank and the composted end product in the dry beds used for agricultural application at the Nyeri-Kangemi wastewater treatment plant in Nyeri County, Kenya. Sludge samples were collected between June and October in different stages of the sludge treatment process; the sludge tank received from the primary and secondary wastewater treatment processes and the composted sludge from the dry beds. Results showed the final composted dry sludge had a pH ranging from 5.53 to 6.52. The mean values were; EC was 3.77 ± 0.05 mS/cm, TOC of 2.03 ± 0.05 per cent, ON of 0.19 ± 0.01 per cent, TOP 88 ± 1.6 mg/L, Temperature 21.03 ± 0.06 °C, particle density of 2.30 ± 0.02 g/cm3, Bulk density of 0.24 ± 0.02 g/cm3, 90.7 ± 0.01 per cent pore space, moisture content of 11.3 ± 0.70 per cent, TS of 53.40 ± 8.82 per cent and VS of 29.79 ± 9.94 per cent. The concentrations of Fe, Ca, Mg, Mn, K, Na, Zn and Cu were 1896.15 ± 106.2 mg/l, 266.42 ± 27.55 mg/l, 190.52 ± 4.82 mg/l, 139.3 ± 0.29 mg/l, 114.38 ± 4.81mg/l, 84.61 ± 0.71 mg/l, 39.18 ± 0.36 mg/l and 5.65 ± 0.12 mg/l respectively. This study recommends the need to do more research on how to improve and stabilise the physico-chemical parameters in the sludge treatment before agricultural use.