Levels Of Sewage Sludge Research Articles

Industrial pilot scale slow pyrolysis reduces the content of organic contaminants in sewage sludge

Pyrolysis has been gaining global interest as a viable option for reducing organic contaminant levels in waste materials such as sewage sludge (SS) for their subsequent use as a soil amendment. However, publicly available knowledge on the capacity of pyrolysis to reduce the levels in SSs is mostly based on laboratory or bench scale studies. The aim of this study was to examine the effects of industrial pilot scale slow pyrolysis at two temperatures and retention times (450 °C, 1 h and 500 °C, 1.5 h) on a wide range of organic and inorganic contaminants in SSs. Pyrolysis at 500 °C decreased the concentrations of the detected per- and polyfluoroalkyl substances (PFASs, by 30–93 %), brominated diphenyl ethers (BDEs; by 97–98 %) and most endocrine disrupting compounds (EDCs, by 82–96 %) more efficiently than pyrolysis at 450 °C. Estrone and pharmaceuticals, with the exception of paracetamol, were removed to below quantification limits. Non-volatile inorganic contaminants concentrated to the chars (22–46 % increase). These results confirm that slow pyrolysis has the capacity to significantly reduce organic contaminant levels in SSs at an industrial scale, while content of inorganic contaminants depends mainly on the feedstock properties. Pyrolysis temperature of over 500 °C is advised to secure efficient removal of organic contaminants. However, it is anticipated that reactor design with good heat transfer and volatile removal could further improve the removal of organic contaminants from SSs. The results are especially valuable for sludge management operators planning to procure a pyrolysis plant.

Climate change impacts of conventional sewage sludge treatment and disposal

Sewage sludge (SS) management remains a challenge across the world. We quantified the potential climate change impacts of eight conventional technology configurations (TCs) for SS treatment and disposal by considering four different energy exchanges and using a life cycle assessment (LCA) model that employed uncertainty distributions for 104 model parameters. All TCs showed large climate change loads and savings (net values ranging from 123 to 1148 kg CO2-eq/t TS) when the energy exchange was with a fossil-based energy system, whereas loads and savings were approximately three times lower when the energy exchange was with a renewable energy system. Uncertainty associated with the climate change results was more than 100% with fossil-energy exchange and low TS content of SS but was lower for renewable energy. Landfilling had the greatest climate change impact, while thermal drying with incineration had the highest probability of providing better climate change performance than other TCs. The global sensitivity analysis identified nine critical technological parameters. Many of them can be easily measured for relevant SS and technology levels to improve specific estimates of climate change impact. When all scenarios were optimized to the 20% best cases, thermal drying with incineration outperformed the other TCs. This paper contributes to better quantifying the climate change impacts of different technologies used for sludge treatment given changing energy systems and identifies crucial parameters for further technological development.

Enhancing the sustainability of high strength concrete in terms of embodied energy and carbon emission by incorporating sewage sludge and fly ash

This paper discusses the properties of dried sewage sludge (SS) and its influence on the microstructure development of HVFA concrete when used as a partial replacement of binder material. A detailed characterization of dried sludge samples collected from a sewage treatment plant is carried out using XRF, XRD, TGA, and FTIR techniques. HVFA concrete mix is designed for 50 MPa with 50% fly ash of the total binder content. Sludge is ground to a particle size of 150 µ and 75 µ and replaced at levels of 5%, 10%, and 15% of the total binder content. The strength activity index of the dried sludge sample is acceptable as per standards. Taking concrete mixes with HVFA as a reference, the fresh properties of binder paste and concrete with sewage sludge have been studied. Mechanical properties that define the applicability to various infrastructure projects are reported for all the studied mixes. EI, CI, COST per unit compressive strength for all mixes are also determined to comment on the environmental impact of the use of SS in concrete. The compressive strength of concrete specimens decreases with the increase in replacement level of SS. However, in comparison with OPC concrete, 75 µm SS at 5% replacement level concrete mechanical strength is within the acceptable limit for M50 concrete mix. The addition of SS as a binder to the concrete has a lower environmental impact, embodied energy, CO2 emission, and cost per unit strength. But more than 10% replacement level resulted in reducing CS, FS, and STS by 11.17%, 6.23%, and 6.99%.Graphical abstract

Evaluation of municipal sewage sludge for Arbuscular mycorrhizal fungi inoculum production

This experiment was carried out to assess the effect of soil amendment with different concentrations of municipal sewage sludge (SS) as a substrate on inoculum production of two selected arbuscular mycorrhizal fungi (AMF) i.e., Glomus mosseae and Acaulospora laevis. The experiment was a 4 × 5 factorial design with four hosts including, maize (Zea mays L.), lemon grass (Cymbopogon nardus (L.) Rendle), palmarosa (Cymbopogon martini (Roxb.) Wats.) and Sesbania (Sesbania aculeata Poir.) and the following five SS concentrations 1) no substrate, 2) 25 g, 3) 50 g, 4) 75 g and 5) 200 g pot–1) with five replications. After 90 days, the host roots and its rhizosphere soil were examined for fungal mycorrhization in terms of percent of root colonization and AMF spore quantification. Furthermore, we calculated the response of each host in terms of increase in plant height (cm), root length (cm), root, fresh shoots, and dry weight (g). Mycorrhization pattern showed moderate to abundant intraradical mycelium, extraradical mycelium, vesicles, and arbuscules in all the host plants. This pattern varied with a change in the input level of SS. The 75 g treatment obtained the maximum mycorrhization of both the AMF, while the highest input level was detrimental to AMF and host plants' survival. Among the tested hosts, lemon grass and maize had a tremendous increment in G. mosseae and A. laevis inoculum respectively. Consequently, 75 g SS with lemon grass is the most compatible host–substrate combination capable of maximum G. mosseae and A. laevis spore production and root colonization and so far, highlights the significance of an alternative, cost–effective and affordable carrier medium that can be adopted by farmers as sustainable cultural practices for on farm AMF inoculum production.

Sewage sludge amendment affects spinach yield, heavy metal bioaccumulation, and soil pollution indexes

Use of sewage sludge (SS) in crop production is a feasible strategy for its disposal; however, its application may pose an adverse impact on soil and human health. Therefore, identification of the permissible level of SS is essential to prevent soil contamination. This research not only evaluated the impact of SS application on spinach (Spinacia oleracea L.) biomass yield but also tracked the accumulation of heavy metals in soil and plants. A pot experiment was conducted on Inceptisol with different levels of SS (0, 5, 10, 15, 20, 25, 30, 35, and 40 t ha−1) with recommended dose of fertilizers (RDF). The applications of SS at 20 t ha−1 resulted in the highest biomass yield; however, the concentration of zinc (Zn) and cadmium (Cd) has exceeded the safe limit in leaves. Heavy metal accumulation in the plant was the highest in SS at 40 t ha−1. Spinach grown at 20 t ha−1 and higher dose of SS exceeded the safe limit of Zn and Cd concentration in leaves, and the translocation factor (TF) of lead (Pb) and Cd was found to be > 1. The hazard quotient (HQ) of Pb > 1 at higher doses of SS indicates health hazard if spinach is used for consumption. Assessment of health risk showed that there was a possibility of Pb hazard at a high dose of SS (HI > 1). Evaluation of various soil pollution indexes revealed that the addition of SS enhanced the buildup of Cd and chromium (Cr) in soil. This study advocated the use of SS at 10 t ha−1 to sustain soil quality with no risk of food chain contamination.

Evaluation of newly reclaimed areas in Saudi Arabia for cultivation of the leguminous crop Phaseolus vulgaris under sewage sludge amendment

Herein, the cultivation of Phaseolus vulgaris was evaluated in newly reclaimed areas in Abha City, Saudi Arabia, following amendment with different rates of sewage sludge (SS) collected from a nearby municipal wastewater treatment plant. A pot experiment was designed to assess the soil heavy metal (HM) pools, growth, yield and HM uptake by P. vulgaris plants cultivated under different SS amendment rates (0, 10, 20, 30, 40 and 50 g kg−1). SS application was found to significantly change all of the chemical properties of the reclaimed soil (except Fe and Mn). The application of SS caused a gradual significant elevation in the soil organic matter content. The application of SS also led to a meaningful increase in the soil electrical conductivity and the Cd, Co, Cr, Cu, Mo, Ni, Pb and Zn contents. However, the soil pH decreased in reaction to the treatments. However, the measured HMs (except Fe) in the soil mixtures in all treatments after harvesting P. vulgaris plants were below the maximum permissible limits in agricultural soil. Generally, SS application up to 20 g kg−1 caused a significant increase in most of the morphological parameters and biomass of P. vulgaris compared to the plants grown in the control soil, followed by a decreasing trend at SS application rates of 30, 40 and 50 g kg−1. P. vulgaris flower production decreased with an increase in the SS application rate, and fruiting was only successful at rates of 10 and 20 g kg−1. All the HM contents in different tissues of P. vulgaris were meaningfully higher for plants treated with different SS levels matched to those grown in control soil. The highest contents of all of the HMs were documented at 50 g kg−1 SS in all P. vulgaris tissues. However, all HM contents (excluding Fe and Mn in the roots) were within safe limits, with most of the absorbed HMs persisting in roots. The regression analysis showed that P. vulgaris plants have an increasing ability to absorb more HMs with an increase in the SS amendment rate. Calculations of bioaccumulation factor (BAF) showed that the BAF for most investigated HM was < 1. This means that P. vulgaris is an excluder for these HMs. In addition, calculations of the translocation factor (TF) indicated that the capacity of P. vulgaris to translocate HMs from roots to shoots or pods is < 1 for most of the investigated HMs, indicating that the amounts of HMs that persisted in roots were always higher than those that travelled to the stems, leaves or pods. Taken together, our findings suggest that soil application of SS up to 20 g kg−1 can provide a sustainable safe practice for SS disposal and improve P. vulgaris growth and yield, while exerting no environmental threats provided there is no accumulation of HMs to toxic levels in shoots of the grown P. vulgaris plants or in the amended soils.

Kinetics of DTPA extraction of Zn, Pb, and Cd from contaminated calcareous soils amended with sewage sludge

The aim of this study was to determine the influence of sewage sludge (SLU) amendment on the desorption characteristics of zinc (Zn), lead (Pb), and cadmium (Cd) in contaminated calcareous soils. Three levels of SLU (0, 1, and 3% w/w) were added to the two calcareous contaminated soils. Samples were incubated for 30 days and equilibrated with 0.005 M DTPA for 0.25 to 240 h. The addition of SLU significantly increased the amount of DTPA-extractable Zn in soils. While the amounts of Cd, Pb, dissolved organic carbon (DOC), and pH showed a significant increase only in 3% w/w of SLU, with the exception of Cd desorption in 1% w/w of SLU, kinetics of Zn, Pb, and Cd extraction increased together with an increase in the level of applied SLU. The best models for describing desorption data were explicitly power function and Elovich. The rate constants of Zn and Pb had significant correlations with DTPA-extractable Zn and Pb, DOC and pH, which affect Zn and Pb desorption. Also, the rate constants of Cd had significant correlations with CEC that can be deemed as equivalent to the fact that Cd desorption is controlled by surface adsorption, particularly in the lower sludge application amount. These results can be used for management of sewage sludge application in contaminated calcareous soils.

Spatial and Temporal Variation of Mercury in Municipal Sewage Sludge in China

In order to determine the occurrence of mercury (Hg) in the dewatered sewage sludge (SS) from municipal wastewater treatment plants (MWTPs) in China, 315 SS samples were collected from 40 MWTPs. The total Hg (THg) contents of the sludge samples were analyzed using a DMA-80 Hg analyzer. It was found that THg in the samples ranged from 0.45-15.42 mg ·kg-1. The THg data followed a log-normal distribution with a geometric mean of (2.19±3.16) mg ·kg-1. THg contents in all the sludge samples meet the criteria set for disposal (by co-landfilling) of MWTPs sludge (GB/T 23485-2009). In terms of THg contents, 97.8% of the sludge was suitable for land application in neutral and alkaline soils, while 86.7% of the sludge was suitable for land application in acidic soil. THg in SS varied greatly, not only among cities (variation coefficient of 105%), but also in the same MWTP (variation coefficient of 0.6%-53.6% over seven days). Mercury contents in SS of China showed a descending trend of North > Northeast > Northwest > Southwest > East > Central > South China. Using the corresponding urban soil background values of THg as references, Hg pollution levels of SS were evaluated using the geological cumulative index method. It was found that SS from more than 60% of the cities sampled were heavily polluted by Hg. Mercury contents in the SS of China showed a temporal trend of increasing then decreasing, with 2000-2009 being the peak period. Results of the present study provide significant data support for the prevention and control of mercury pollution in sewage and SS in China.

Nutritional (Fe, Mn, Ni, and Cr) and growth responses of rice plant affected by perennial application of two bio-solids.

Trace toxic elements often restrict the land application of different bio-solids in agriculture. In order to evaluate the separate influence of the municipal solid waste compost (MSW), sewage sludge (SS) and combined application with inorganic fertilizers (chemical fertilizer (CF)) on nutritional (Fe, Mn, Ni, and Cr) and growth responses of rice plant, a research was conducted on paddy soil from 2013 to 2015. Obtained results showed that SS levels were superior to MSW in most studied traits. The maximum chlorophyll content (46.52), plant height (162.6cm), biomass (23.33tha-1), soil available Fe (206.26ppm), Ni concentration in the root (14.41ppm) and shoots (3.16ppm), Cr concentration in the root (12.43ppm) and grain (3.65ppm), and Mn concentration in grain (66.938ppm) belonged to SS levels, specially enriched 40tha-1, when it was added to the soil for three continuous years. The highest 1000-grain weight (29.89g), yield (6.86tha-1), harvest index (48.17%), and soil available Mn (712.7ppm), Fe, and Ni concentration in grain (107.92 and 8.79ppm, respectively) were recorded in 3years of applying the enriched 40tha-1 MSW. Accumulation of Ni in grain in critical levels and negative effects of CF treatments on toxic element entry to soil and plant were two important findings of this research that need management.

Temporal variation of total and DTPA-extractable heavy metal contents as influenced by sewage sludge and perlite in a calcareous soil

ABSTRACTContinuous application of sewage sludge (SS) as a source of organic matter, may increase available heavy metals (HMs) up to their critical levels. As a consequence their uptake by plants, risks of accumulation in food chain and groundwater pollution increases. To evaluate the effects of perlite and SS on total content and available fraction of iron (Fe), manganese (Mn), lead (Pb), copper (Cu), nickel (Ni), cadmium (Cd) and zinc (Zn) over 45 and 90 days a completely randomized pot experiment was conducted. Treatments consisted of SS (0, 2 and 4%) and combined SS and perlite levels (1:1, 1.5:0.5 and 0.5:1.5% SS:perlite). Mean available Fe, Ni, Cd, Mn and Zn fractions decreased over time by 7–27%, whereas, total contents did not change. Available HMs in SS-treated soils increased by 0.5–25%; whereas, only total Zn, Cu and Pb concentrations increased with SS application (although concentrations fall in the range of critical levels). The lowest (1.6 fold) and highest (22.1 fold) increases obtained for available Cu and Zn, respectively. Perlite could mitigate the adverse effect of high rate application of SS on amplification of HMs extractability. Therefore, their concomitant applications can be suggested considering the perlite durability and its positive effects on soil physical properties.

Effects of sewage sludge used as fertilizer on the yield and chemical contents of common vetch (Vicia sativaL.) and soil

This study was conducted to determine the effects of sewage sludge (SS) used as fertilizer at different concentrations [Control, 20 kg ha–1 nitrogen (N), 30 ton ha–1 SS (S1), 60 ton ha–1 SS (S2) and 90 ton ha–1 SS (S3), 20 kg ha–1 N + 30 ton ha1 SS (N + S1), 20 kg ha–1 N + 60 ton ha–1 SS (N + S2) and 20 kg ha–1 N + 90 ton ha–1 SS (N + S3)] on common vetch yields and chemical features. For this purpose, an increasing level of SS was applied to the soil samples. The residuals of some heavy metal (Hg, Cr, Fe, Ni, Zn, Mn, Cd, Pb, Cu, Co, and Se) and macro element (K, Ca, Na, Mg, C, and S) concentrations were measured in leafs, seeds and soils. According to the results of this study, SS, when applied to soil in increasing amounts, raised the mineral matter contents of the plants, which favorably affected plant growth. Accordingly, it affected the herbage yield, increasing the yield in parallel with the increasing SS concentrations. Applying N with the SS positively influenced the heavy metal contents on leafs and seeds of common vetch and residue in the soil. Besides, the heavy metal contents were found at below critical levels in the soil, leaf and seeds. Therefore, SS application as fertilizer used in appropriate concentrations did not pollute the soil very much, but did lead to an increase in plant products.

Effect of different levels of sewage sludge (citywaste) and inorganic fertilizers on the yield attribute and quality of mustard (Brassica juncea L.)

The influence of sewage-sludge and inorganic fertilizers (NPK) on growth, yield and quality of mustard was assessed from a field experiment on loamy soil in Rabi season of 2010-11. The levels of sewage sludge and inorganic fertilizers (NPK). The plant height (cm), seed yield (q ha-1) and content of oil and protein were significantly increased by the application of both sewage-sludge and inorganic fertilizer. The maximum growth and yield was obtained by the sewage-sludge application @12 t ha-1 and by the 75 per cent inorganic fertilizer. The interaction between sewage-sludge and inorganic fertilizer was found significant and the maximum increase in the growth, yield, oil (%) and protein (%) was obtained by applied sewage-sludge @ 12 t ha-1 and 75 per cent NPK. Four level of sewage-sludge (@ 0, 4, 8 and 12 t ha-1) through city waste and four level of inorganic fertilizers (@ 0, 50, 75 and 100 per cent of recommended dose were evaluated.

CO2, CH4 and N2O fluxes in an Ultisol treated with sewage sludge and cultivated with castor bean

Organic residue application into soil alter the emission of gases to atmosphere and CO2, CH4, N2O may contribute to increase the greenhouse effect. This experiment was carried out in a restoration area on a dystrophic Ultisol (PVAd) to quantify greenhouse gas (GHG) emissions from soil under castor bean cultivation, treated with sewage sludge (SS) or mineral fertilizer. The following treatments were tested: control without N; FertMin = mineral fertilizer; SS5 = 5 t ha-1 SS (37.5 kg ha-1 N); SS10 = 10 t ha-1 SS (75 kg ha-1 N); and SS20 = 20 t ha-1 SS (150 kg ha-1 N). The amount of sludge was based on the recommended rate of N for castor bean (75 kg ha-1), the N level of SS and the mineralization fraction of N from SS. Soil gas emission was measured for 21 days. Sewage sludge and mineral fertilizers altered the CO2, CH4 and N2O fluxes. Soil moisture had no effect on GHG emissions and the gas fluxes was statistically equivalent after the application of FertMin and of 5 t ha-1 SS. The application of the entire crop N requirement in the form of SS practically doubled the Global Warming Potential (GWP) and the C equivalent emissions in comparison with FertMin treatments.