Dried Sewage Sludge Research Articles

Monitoring the Changes in the Microbial Dynamics of Calcareous Soil with the Amendment of Stabilized and Dried Sewage Sludge in Mediterranean Region of Turkey

Monitoring the Changes in the Microbial Dynamics of Calcareous Soil with the Amendment of Stabilized and Dried Sewage Sludge in Mediterranean Region of Turkey

Strength and durability of dry sewage sludge (DSS) as a replacement for fine aggregates

Sewage sludge disposal has become a challenging task in India. Central Pollution Control Board of India in 2011 stated that around 10.7 million tons of dry sewage sludge (DSS) is being disposed every year. Generally sewage sludge is disposed by means of incineration, buried in underground pits, disposed into water bodies and used in agricultural lands. These methods lead to air pollution, enhancing global warming through rising atmospheric temperature and affecting the environment's cleanliness. In this study, DSS is introduced in concrete as a replacement for fine aggregates (5, 10, 15 and 20%). All the concrete mixes were tested for its properties such as compressive strength, split tensile strength, flexural strength, abrasion resistance, impact resistance and durability properties in aggressive conditions like acid attack, and effect of sea water. Results reveal that up to 10% DSS incorporation has enhanced compressive strength by 9% and replacements till 15% enhanced flexural and split tensile strength up to 13%. In case of durability properties, incorporation of DSS up to 15% showed better results than control concrete in terms of acid attack, effect of sea water, abrasion resistance and impact resistance. Cost analysis indicated that DSS can reduce up to 2.5% of cost considering the efficacy of compressive strength.

Effect of sintering temperature and dwelling time on the characteristics of lightweight aggregate produced from sewage sludge and waste glass powder

Present study aims to explore the effect of sintering temperature and dwelling time on the characteristics and morphological structure of lightweight aggregates made from dry sewage sludge and waste glass powder. The mixtures were sintered at temperatures from 1100 °C to 1200 °C at a heating rate of 10 °C/min with a dwelling time of 10, 20, and 30 min to produce lightweight aggregate samples. The thermophysical behavior of the mixtures and the physic-mechanical properties (including water absorption, particle density, and compressive strength) of the obtained lightweight aggregates were studied. The microstructure of the lightweight aggregates was also analyzed using X-ray micro-computed tomography. Results indicate that increasing the sintering temperature or extending the dwelling time will reduce the particle density and compressive strength of lightweight aggregates. Moreover, the sintering temperature and dwelling time show a considerably influence on the pore structure of lightweight aggregates, which is strongly related to the physical characteristics of the lightweight aggregates. The lightweight aggregates obtained at optimized sintering temperature of 1180 °C with an optimal dwelling time of 10 min show water absorption of 1.01%, particle density of 0.78 g/cm3, and compressive strength of 7.10 MPa, thereby meeting the standard requirement of GB/T 17431.2–2010.

Bioremediation of potentially toxic elements of sewage sludge using sunflower (Heliantus annus L.) in greenhouse and field conditions.

The bioremediation of sewage sludge, containing potentially toxic elements (heavy metals), by the hyperaccumulator sunflower (Helianthus annus L.), was determined in greenhouse (G) and field (F) conditions in Isfahan, Iran. The soil pots, mixed with dried sewage sludge at 0, 15, 30, 45, and 60mg/kg, were planted with sunflower seedlings and kept in the greenhouse (G) and in the field (F). Different soil physicochemical and plant biochemical properties including heavy metal uptake of nickel (Ni), chromium (Cr), lead (Pb), and cadmium (Cd) were determined. In contrast with the soil pH, soil salinity, organic matter, nitrogen, and not soil CaCO3, were significantly enhanced by increasing sewage sludge. Sewage sludge was significant on plant uptake of Ni (2.27-4.25mg/kg), Cr (3.27-4.75mg/kg), Cd (13.85-15.27mg/kg), and total chlorophyll (1.69-1.99mg/g) in the greenhouse, and plant uptake of Ni (1.75-2.75mg/kg) and Cd (1.37-2.25mg/kg), and chlorophyll b (0.06-0.26mg/g), total chlorophyll (0.57-1.16mg/g), and carotenoids (1.10-1.61mg/g) in the field. Although Pb was not significantly affected by sewage sludge, it showed the highest bioaccumulation factor of 0.96 at 15mg/kg. Interestingly, the heavy metals were all positively and significantly correlated with each other and with plant carotenoids, similar to the positive and significant correlations between Pb with chlorophyll a and b. Accordingly, the increased levels of carotenoids, acting as antioxidant, may be an indicator of oxidative stress. Sunflower plants can be used as an efficient method for the bioremediation of the soils polluted with sewage sludge including Ni, Cr, and Cd.

Model-Based Evaluation of Hydrothermal Treatment for the Energy Efficient Dewatering and Drying of Sewage Sludge

This research paper evaluates hydrothermal carbonization (HTC) as a possible treatment for sewage sludge, including phosphorus recycling. German governmental requirements force a high number of wastewater treatment plants (WWTP) to recover phosphorus from sewage sludge above limits of 20 g kgTS−1 before further disposal (e.g., co-incineration). The results show that pH reduction has a positive effect on shifting phosphorus to the liquid phase during HTC. Although the experimental results of this research do not yet achieve the necessary phosphorus reduction, various calculations are made to achieve this goal in future experimental studies. In order to be able to assess the energy benefits of HTC, Aspen Plus modeling was used to show the positive impact of implementing this technology in a WWTP. It is shown that the mechanical dewaterability of sewage sludge (SS) increases after HTC enabling energy savings by means of subsequent thermal drying. A heat optimized HTC is able to cut energy expenses by half, further providing a phosphorus-depleted hydrochar for extensive energetic use.

TG pyrolysis of a mixture of dried sludge from urban wastewater and wood pellets and identification of the composition of the resulting gases by infrared spectroscopy

The recent tendency of sewage sludge disposal is targeted towards the gasification for heat generation in small towns far from waste incineration plants. The scope of this article is to present the investigation into the mixture of dried sewage sludge and wood pellets during pyrolysis by thermogravimetry (TG) with evolved gas analysis by TG-coupled Fourier transformation infrared spectroscopy (FTIR) method. The maximum intensity of mass loss of sewage sludge material occurs at 300–310°C temperature and it differs from wood cellulose case of 360°C. The 50:50% mixture of these materials was investigated in more details. Pyrolysis reaction kinetics is described by a variation of three constituent parts from TG data. Prefactor A and activation energy E of the Arrhenius law were found, and reaction order n was determined by the Ozawa method employing Avrami phase change. The maximum of gas evolution is always related to the most intense mass loss, and gas composition correlates with the initial material.

Enhancement of conductive drying of sewage sludge with mechanical compression: Drying kinetics, and interfacial heat transfer behavior

Improving sludge drying efficiency is of tremendous importance for public health, subsequent treatment, and comprehensive utilization. The interfacial thermal resistance between sludge and hot wall greatly limits the conductive drying performance. This study employed mechanical compression to decrease the interfacial thermal resistance. The drying kinetics and interfacial heat transfer behavior were investigated at mechanical loads of 25 to 200 kPa, temperatures of 120 to 210 °C, and sludge thicknesses of 1.0 to 3.0 mm, and were compared to those in the conventional drying process without mechanical load. The increase of temperature and mechanical load and the decrease of thickness improved drying rates. The drying experienced one warm-up period and two falling rate periods. The breakthrough of interfacial vapor film was responsible for the rapid rise in drying rates initially. At the thickness of 3.0 mm, 210 °C, and 100 kPa, the effective moisture diffusivity was increased by 2.5 times, and the apparent activation energy was reduced by 34% compared to the traditional process in the first falling rate period, implying that mechanical compression facilitated moisture migration and bound water desorption. The effective moisture diffusivity in the first falling rate period was increased by 35% compared to the diffusivity in the second falling rate period because of the pressure-driven flow. The decrease in drying rates was due to the transformation from the pressure-driven flow to vapor diffusion-limited flow in the first falling rate period. Additionally, this study provided essential information on developing a new sludge treatment method and establishing the drying model.

Analytical pyrolysis of poly(dimethylsiloxane) and poly(oxyethylene) siloxane copolymers. Application to the analysis of sewage sludges

Dimethicone (poly(dimethylsiloxane), PDMS) and its copolymers bearing a poly(ethylene glycol) (PEG) side chain (PEG-12 dimethicone and PEG-8 dimethicone) are utilised as ingredients in personal care products. These materials along with bis-PEG-18 methyl ether dimethyl silane were analysed by Py-GC–MS. The pyrolysates of dimethicone was dominated by cyclic dimethyl siloxanes from D3 to over D10. Besides Dn, the pyrolysates of PEG-dimethicone were featured by the presence of linear dimethyl siloxanes Ln. Hydroxylated siloxanes were also tentatively identified. Pyrograms were also characterised by PEG oligomers with different terminal groups (hydroxyl, ethyl, ethenyl). The molecular structure of pyrolysis products from the combined structural units of PDMS and PEG could not be assigned. Internal standard calibration protocols using pyrolysis products of PEG-12 dimethicone (L6, L8, L9, and triethyleneglycol monoethyl ether) exhibited satisfactory linearity (R2 > 0.992) in the 0.75−58 μg range and repeatability (RSD < 15 %). Three samples of dried sewage sludge from a municipal water treatment plant were extracted with tetrahydrofuran and the extracts analysed by Py-GC–MS. The pyrograms were characterised by intense signals due to the lipid matrix (hydrocarbons, fatty acids, steranes, sterenes, sterols). Dn and Ln were identified indicative for the presence of siloxanes at levels around 60−290 μg gdw−1, while pyrolytic markers of PEG were not revealed. The recovery of PEG-12 dimethicone (17 μg) in spiked sample was 76 %. Galaxolide, galaxolide lactone and triclosan were identified in the pyrograms. The results of this study evidenced the potential of Py-GC–MS as a screening tool for the determination of cosmetic ingredients in sewage sludge.

Analysis of Drying Performance and Cost of Large-Capacity Sewage Sludge Dryer

Analysis of Drying Performance and Cost of Large-Capacity Sewage Sludge Dryer

Dried sewage sludge as an efficient adsorbent for pollutants: cationic methylene blue removal case study

The research work was supported by Ministry of Energy, and Mines and the Environment within the Research Project with grant number 018-1212-00019.

Pyrolysis of Municipal Sewage Sludge to Investigate Char and Phosphorous Yield together with Heavy-Metal Removal—Experimental and by Thermodynamic Calculations

Sewage sludge is regarded as a potential source for soil fertilizer However, the direct utilization of sewage sludge in agricultural land is restricted since it also contains heavy metals, pathogens, and toxic compounds. Pyrolysis of the sewage sludge destroys the organic pollutants and partly volatilizes the heavy metals. In this study, pyrolysis of sewage sludge was carried out in order to determine the optimum residence time and temperature to recover the phosphorous and remove heavy metals from the resultant sewage sludge char (SSC). Pyrolysis was conducted on dried sewage sludge (DSS) by means of thermogravimetric analysis (TGA) and high-temperature oven with an N2-atmosphere. Microwave Plasma-Atomic Emission Spectroscopy (MP-AES) was used to determine the concentration of P and trace elements in the resulting solid char fraction. A combination of chemical fractionation (step-by-step leaching) of the DSS and thermodynamic equilibrium calculations were utilized to estimate the availability of phosphorous and removal of heavy metals in the SSC fraction at different temperatures. The results from the thermodynamics calculation were in line with the measured chemical composition of the SSC. Furthermore, the energy contents of the SSC obtained at different temperatures were measured. The pyrolysis evaluation results indicate that phosphorous was enriched in the char, while lead, zinc, and cadmium were significantly removed.

Microwave drying behavior, energy consumption, and mathematical modeling of sewage sludge in a novel pilot-scale microwave drying system.

Microwave drying is attracting increasing attention due to its energy efficiency. A self-developed pilot-scale microwave dryer was used in this study to dry two different common types of sewage sludge, namely mechanically dewatered sewage sludge and composting dewatered sewage sludge, by using two heating modes: constant temperature and constant power modes. The microwave drying behavior, specific energy consumption, average drying rate, energy efficiency, and drying effect were explored considering the influences of microwave output power, initial mass, and heating mode. Results showed that the output power had the largest influence on specific energy consumption, energy efficiency, and drying efficiency, followed by the constant temperature and initial mass. The specific energy consumption of mechanically dewatered sewage sludge decreased by roughly 14%. By contrast, the average drying rate increased by approximately 6%, and the energy efficiency increased by approximately 20% for each 1kW increase in output power. Meanwhile, composting dewatered sewage sludge displayed drying effects at an output power of 3kW, and the temperature exceeded 80°C. The comparison of the two modes suggested that the constant temperature mode was better than the constant power mode considering product quality and operational safety. Compared with six thin-layer drying mathematical models, the Midilli-Kucuk model could provide a good fit for the constant temperature mode. The proposed microwave drying process exhibited effective performance in drying rate. This process also demonstrated considerable application potential for sewage sludge drying.

Supercritical carbon dioxide drying of municipal sewage sludge – Novel waste-to-energy valorization pathway

Eighty percent of the world's wastewater is discharged back into nature without reuse and further treatment and solid byproduct of wastewater is either spread on land or landfilled. The valorization of municipal sewage sludge for energy use is a major opportunity for sustainable energy applications. This includes effective dewatering and drying of the sludge in addition to producing biogas during the anaerobic digestion. Supercritical CO 2 extraction process was investigated for the purpose of drying municipal sewage sludge. Remarkably our results showed that after sCO2 processing the higher heating value (HHV) of sludge at wet basis moisture content of 52% was 14 MJ/kg and thus higher than the HHV of brown coal with similar moisture level (12 MJ/kg). Our research also shows that under specific conditions sCO2 extraction reduces the moisture content of the municipal sludge from 89% to 53% in 15 min. Although, more research is needed this dewatering process could be considerably less energy intensive than conventional thermal and other drying processes. Another benefit is extraction of micro pollutants by sCO2 treatment and thus making the dried sludge more useable in energy applications as per regulations. Our results show an alternative and novel pathway for highly effective dewatering and drying of municipal and other types of sludge.

Extending disposal route of dewatered sewage sludge produced from the new wastewater treatment plant in Nicosia toward sustainable building materials

Due to urban development worldwide, disposing sewage sludge (SS) has become a major concern for many countries. SS produced from the New Waste Water Treatment Plant (NWWTP) in Nicosia has not been used for soil application as it was planned since late 2013 due to absence of legislations regarding this route. This issue has been and still a major concern for of Nicosia Turkish Municipality and its society for many years. This study investigates the potential use of SS as construction material by producing an artificial lightweight aggregate (ALWA) and cement replacement material. Fine dry sludge (FDS) and sewage sludge ash (SSA) were used as raw materials for ALWA production. FDS was incinerated at 850 °C for 1 and 2 h to produce SSA1 and SSA2, respectively. Both SSA1 and SSA2 were mixed separately with FDS in different proportions and incinerated at 1100 °C to produce lightweight aggregate AG1 and AG2, respectively. Potential use of SSA1 and SSA2 as cement replacement materials was assessed by measuring the Pozzolanic activity of both ashes throughout physical and chemical tests. It was found out that increasing amount of FDS reduced specific gravity of AG1 and AG2, while increasing amount SSA in the mix improved the surface texture and increased the specific gravity of both AG1 and AG2. Results also indicated that both SSA1 and SSA2 have Pozzolanic properties based in all tests performed. Therefore, using sewage sludge produced from the NWWTP in Nicosia as a sustainable construction material is potential and this could extend the disposal route of the sludge and resolve the accumulation problem in Nicosia.

Technical, Energetic and Economic Optimization Analysis of Selection of Heat Source for Municipal Sewage Sludge Dryer

The treatment of growing production of municipal sewage sludge has become a significant global problem. Drying of digested sewage sludge is a promising alternative to sludge disposal at dumping sites. The research objective of this study was to find the optimal heat source for a sludge drying plant in a large municipal sewage treatment plant (people equivalent: 250,000). Two boundary heat supply cases were analyzed in the paper: cogeneration of heat and power (CHP) units, internal combustion (IC) engines fired with natural gas, and plant supplied with a gas boiler. The aim of the research was to find the optimal size of the cogeneration unit cooperating with the gas boiler as heat sources for a given drying plant case with the maximum net present (NPV) value as the objective function. The results of the conducted optimization show higher profitability of cases with larger cogeneration unit. For the basic assumptions, the maximum NPV is obtained for the largest analyzed CHP unit: 1300 kW of thermal power output. Sensitivity analyses show that the varying gas and electricity prices can relocate the NPV maximum towards smaller CHP sizes. A supplementary energy analysis shows that implementing larger CHP units yields a higher energy efficiency of the system, up to 0.52.

Microplastic contamination in a conventional wastewater treatment plant in Thailand.

Plastic waste has become a global environmental concern. One type of plastic waste is microplastics (MPs), which can spread easily in the environment. Wastewater effluent is one of the land-based sources of MPs. This study investigates the amount of microplastic (MP) pollution in an urban wastewater treatment plant (WWTP) in Thailand. Water samples were collected and examined to find the types, morphology and sources of MPs. Wastewater was filtered through a set of sieves ranging from 5 mm to 0.05 mm. Sludge samples were also collected to find the potential risk from the application of dried sewage sludge. Fourier-transform infrared spectroscopy (FTIR) was used to confirm the types of MPs. The amount of MPs in the influent was 26.6 ± 11.8 MPs/L. More than one-third of MP particles were removed after a grit trap, followed by 14.24% removal in the secondary treatment. If the peak flow rate of the WWTP is reached, 2.32 × 109 MP particles can be released daily. The amount of MPs in a sludge sample was 8.12 ± 0.28 × 103 particles/kg dry weight. Dry sludge is one of the potential sources of MP contamination in agricultural soil. Most MPs in the liquid fraction and sludge sample were fibres. Results from FTIR analysis showed that the major types of MPs in the WWTP were polyester fibres, followed by polypropylene, polyethylene, silicone polymer and polystyrene. This finding indicates that a conventional WWTP may act as a path by which MPs enter the environment.

Two-Stage Gasification of Dried Sewage Sludge: Effects of Gasifying Agent, Bed Material, Gas Cleaning System, and Ni-Coated Distributor on Product Gas Quality

Two-Stage Gasification of Dried Sewage Sludge: Effects of Gasifying Agent, Bed Material, Gas Cleaning System, and Ni-Coated Distributor on Product Gas Quality

Study on Sewage Sludge Drying System With Built-in Solar Drying Bed

In this paper, the renewable energy solar energy is used as the heat source. The combination of solar drying bed and traditional hot air drying can effectively reduce energy consumption and operation cost. The drying chamber is divided into three layers. The top air supply outlet supplies hot air, the middle layer places wet sludge, and the bottom layer uses hot water coil to dry the sludge. The whole drying process is a heat and mass transfer process with convective heat transfer and radiation heat transfer. After analysis and comparison with traditional energy drying, it is found that drying 97.5kg of sewage sludge will save 79% energy, save 12.84 kg of standard coal, reduce 32 kg of carbon dioxide and 1.284 kg of sulphur dioxide.

Economic analysis on sewage sludge drying and its co-combustion in municipal solid waste power plant

Co-treatment in municipal solid waste power plant has been deemed to one of the most suitable ways to handle sewage sludge. Economy of the co-treatment process is very concerned in the waste incineration plant. Thermal calculation of sewage sludge co-combustion was done. Four common sludge drying schemes was compared: flue gas drying, steam drying, electric heating drying in the waste incineration plant and in situ electric heating drying in the sewage treatment plant. Sensitivity analysis was also performed. When the water content was 30–40% and the absolute-dry sludge ratio was 2–3%, the boiler efficiency was reduced by 0.56–1.12% compared with the case without mixing sludge, and the power generation decreased by 0.2568–0.3767 MW in steam drying scheme and by 0.0037–0.0094 MW in other schemes. Net present value (NPV) of flue gas drying was the highest among the four sludge drying schemes, which was more than 20 ¥ million, while the scheme of electric heating drying in the waste incineration plant had the lowest NPV, which can't recoup the initial investment. Sensitivity coefficient of flue gas drying was smallest among different schemes, showing that the risk of this program was the smallest. Absolute-dry sludge ratio and unit subsidy for sludge treatment were sensitive factors for NPV in flue gas scheme, which had a sensitivity coefficient of 1.123–1.171 and 1.232, respectively. Operating parameters optimization of co-combustion of sludge was done and ways to improve economic efficiency was discussed.

Determination Of Thermal Technical Characteristics Of Sewage Sludge

One of the largest environmental problems of the Russian Federation is the pollution of the territory waste. The focus is on waste generated during the treatment of urban wastewater - sewage sludge and sewage sludge (SS). The shortage of areas sharply raised the issue of eliminating these wastes. The main elimination method is high temperature combustion. The complex process of elimination requires preliminary heat engineering studies of sewage sludge. In the scientific work, gas-analytical studies of flue gases were carried out, the experimental process of preliminary drying of sewage sludge was reproduced, and calorimetric tests of specific samples of precipitation were calculated with recalculation to the lower calorific value.