Sludge Piles Research Articles

Impact on the antioxidant system, histology, and cell death of zebrafish liver after exposure to industrial sludge leachate.

The improper disposal of sludge is a still-present phenomenon in China. The leachate formed at the bottom of the sludge pile would cause toxicological effects on aquatic organisms and affect the health of humans by entering the surrounding rivers and groundwater. In this study, the hepatotoxicity of zebrafish induced by sludge leachate was assessed by antioxidant enzyme activities, semi-quantitative histopathological assessment, and TUNEL apoptosis assay. The results indicated that the leachate would induce oxidative stress and eventually lead to an increase in lipid peroxide after a 7-day exposure. The histopathological indexes demonstrated that exposure to leachate would cause histological damage by circulatory disturbances, regressive changes, progressive changes, and inflammatory responses. According to the TUNEL results, it could be inferred that apoptotic hepatocytes increased after exposure for 7days due to oxidative stress and histological damage. Overall, this study provided a valuable approach to assessing the toxic effects of sludge leachate and described the underlying mechanism of leachate-induced hepatotoxicity in zebrafish. This work will generate new insights into the ecological toxicity of leachate and promote the development of sludge disposal in China.

Sludge Deposit Mapping for Steam Generators

During plant operation, corrosion products from feedwater, drain and condensate system accumulate on the secondary side of steam generator in form of scaled deposits around the tubes and sludge piles on top of the tubesheet. These deposits increase potential for corrosion, affect fluid flow and reduce heat transfer efficiency of the steam generator. Using data obtained during periodical eddy current examination of steam generator tubing, information on sludge deposit location and thickness is extracted from low frequency absolute channels. Sludge deposits can be detected over the whole length of the inspected tube. Using automatic analysis deposit results are provided within 36 hours after the inspection. Results are imported in Sludge Mapping software and presented in 3D visualization of steam generator. Both PWR and VVER steam generator visualization is supported. Sludge mapping software provides visual information on sludge deposit thickness using color code and by calculation position of sludge indication, software draws the indication on the location within the steam generator where indication was found. Sludge mapping software provides information on heavy sludge loading areas of steam generator and can help with tracking of sludge build-up over time that can be used for optimizing steam generator maintenance. This paper presents INETEC’s Sludge Mapping solution, its functionality and features for visualization of sludge deposit location and thickness within the steam generator.

Insights into the formation mechanism of hard sludge on the secondary side of PWR steam generators

• Mixtures of alumina, silica and magnetite have been aged in hydrothermal conditions. • Kaolinite has been identified as a cement binding the magnetite particles. • In presence of metallic iron, iron silicate precipitates. In the secondary circuit of nuclear Pressurized Water Reactors, corrosion products and impurities lead to the formation of undesirable hard deposits, called hard sludge, on the tube sheet of steam generators. Theses deposits are mainly composed of iron (magnetite), alumina and silica. The formation of hard sludge piles is investigated by reproducing the reaction of precursor oxides in the conditions of the steam generator (275 °C, 58 bar). Mixtures of magnetite, γ-alumina and amorphous silica in binary or ternary systems in an alkaline ethanolamine-ammonia solution at pH 25°C = 9.6 are studied. Carbon steel was tested as an alternative source of iron. The analysis of the evolution of the suspensions, completed by the industrial feedback, allows to explain the process of hard sludge formation in the steam generators. The following sequence is proposed: sedimentation of magnetite/confinement of the interstitial fluid/concentration of aqueous species such as aqueous silica and alumina/sorption of Al on magnetite and/or growth of boehmite/reaction with aqueous silica to form kaolinite as a resistant cement. Once formed, the kaolinite cement tends to densify over time while magnetite is passive. The absence of Fe-phyllosilicates predicted by thermodynamics is explained by the low solubility of magnetite making unfavorable the precipitation of Fe-silicate. By contrast, metallic iron is not stable at contact with water and the continual production of divalent iron, whose solubility is much higher than that of magnetite, allows to overpass a threshold concentration what makes possible the precipitation of a berthierine layer at the surface of corroded steel. This layer constitutes the nucleation site for the further precipitation of other aluminosilicates.

Open-air storage with and without composting as post-treatment methods to degrade pharmaceutical residues in anaerobically digested and dewatered sewage sludge

Over a period of 12 months, the fate of three hormones, 12 antibiotics and 30 pharmaceutically active substances (PhACs) was investigated during open-air storage without and with composting of anaerobically digested and dewatered sewage sludge. The effect of oxidation conditions during storage on degradation of hormones and PhACs in the sludge biomass was also examined. Under summer and winter conditions in Uppsala County, Sweden, two field-scale sludge windrows were constructed: open-air storage of sewage sludge windrow without composting (NO-COM)) and open-air storage windrow with composting (COM). NO-COM achieved effective removal of ∑Hormones (85%) and ∑Antibiotics (95%), but lower removal of ∑PhACs (34%), during the study year. The top layers of the sludge pile had significantly lower concentrations of ∑PhACs (3100–5100 ng/g ash) than deeper layers (8000–11,000 ng/g ash). After one year of composting, the degradation in the COM windrow resulted in concentrations of ∑Hormones (<LOD), ∑Antibiotics (<LOD), while the ∑PhCAs was 5% (730 ng/g ash) of initial (13,000 ng/g ash). The half-life of substances during composting in COM was within 7–100 days for all substances except ibuprofen (156 days). The first-order degradation constant (K) was the lowest for ibuprofen (0.0045 day−1) and the highest for oxazepam (0.0805 day−1). In conclusion, composting of sludge was effective in degrading the target hormones, antibiotics, and PhACs.

Stabilized sewage sludge: Sanitary aspects and potential for conversion to biosolids

The improvement of wastewater treatment techniques is of crucial importance for effluent quality, but it also results in an increased amount of waste sludge. Dehydrated sludge contains organic matter and nutrients, and therefore it can be used in agriculture and bioremediation, but it is considered a potential source of environmental pollution. As the sludge analyzed in the research does not contain impermissible levels of organic and inorganic pollutants, the aim of the research was to examine microbiological, particularly sanitary, aspects and potential for its further use. Microbial diversity was determined by the standard serial dilution technique and selective media, and sanitary quality indicators (total coliforms, fecal coliforms, Escherichia coli and Salmonella spp.) were determined by the MPN method. The abundance of fungi, actinomycetes, and bacteria (ammonifiers, spore-forming bacteria and Pseudomonas spp.) indicate possibilities for further use of the sludge. The chemical analysis included the following parameters: total nitrogen (N), phosphorus in the form of P2O5 (available P), organic carbon (C), C/N ratio, pH, and water content. The chemical composition indicates the potential of sewage sludge to be used as a soil fertilizer, but its C/N ratio is not adequate to enable successful conversion to biosolids by the composting process. The obtained results indicate a significant level of microbiological contamination, which was most pronounced in the centre of the stabilized sludge pile. The research showed the necessity to conduct further studies on the microbial diversity and sanitary aspects of sewage sludge for proper waste sludge management.

Evaluation of contaminants spreading from sludge piles, applying geochemical fractionation and attenuation of concentrations model in a tropical reservoir

Drinking water production may generate significant amounts of sludge, which may be contaminated with various metals. For the first time, the mobility/lability of contaminants from two water treatment sludge piles in the Juturnaíba Reservoir was evaluated by applying two geochemical approaches: sequential extractions and attenuation of concentrations model. Both procedures were applied to evaluate the mobility/lability of Al, Cr, Cu, Fe, Mn, and Zn on samples collected in the sludge piles and in the neighborhood of both water treatment plants. The results show that aluminum presents considerably higher concentrations in the sediments close to the sludge piles, with more labile phases; however, the attenuation of concentrations model indicates little spreading of this contaminant in the reservoir. Manganese was shown to be severely depleted in the sludge, indicating that it can be leached away, due to the reducing conditions of the pile. The other elements showed low concentrations and were shown not to affect the concentrations in the reservoir. While the geochemical fractionation indicates the possibility of dissolution to the water column, the attenuation of concentrations model gives information on the spatial dispersion of the contaminants, constituting interesting complementary approaches.

Biodegradation of triclosan and triclocarban in sewage sludge during composting under three ventilation strategies

Triclosan (TCS) and triclocarban (TCC) are widely used in home and personal care products as antimicrobial agents. After these products are used, TCS and TCC enter the terrestrial environment and pose a great risk to humans and animals. In this research, the biodegradation of TCS and TCC was investigated during sewage sludge composting with ventilation rates of 108, 92, and 79 m3/min. TCS and TCC were mainly biodegraded in the mesophilic and thermophilic phases, and the biodegradation rates improved with an increase in ventilation. After sewage sludge was composted for 16 days with forced ventilation (108 m3/min), the concentration of TCS decreased from 497.4 to 214.5 µg/kg, and the concentration of TCC decreased from 823.2 to 172.7 µg/kg. The biodegradation rates of TCS and TCC were 65.2% and 83.1%, respectively. However, after the sewage sludge was stacked for 16 days, the biodegradation rates of TCS and TCC were only 17.0% and 18.2%, respectively. The environmental risks of TCS and TCC in the sewage sludge piles significantly decreased after composting. In the sludge pile with a ventilation rate of 108 m3/min, the RQ values of TCS and TCC decreased from 8.29 and 20.58 to 3.58 and 4.32 after composting for 16 days, respectively. There is still a high risk if the sludge compost is directly used as a culture substrate. Nevertheless, the environmental risk could be decreased distinctly if a reasonable quantity of sludge compost is applied to land to ensure an RQ of < 1 for TCS and TCC.

Mercury contamination in the sludge of drinking water treatment plants dumping into a reservoir in Rio de Janeiro, Brazil.

Although sludge piles from drinking water treatment plants can contain harmful substances, in many countries, their disposal methods are still unregulated. Besides aluminum, which is a major constituent in these residues, many other contaminants-like trace metals-can be present and may result from the quality of the raw materials used for water treatment. The application of these chemicals for the treatment of drinking water can generate toxic sludge and contaminate the produced water. In the present work, mercury contamination in the sludge piles of two drinking water treatment plants located along the margins of the Juturnaíba Reservoir, Southeast Brazil, was evaluated to verify whether contaminants are incorporated during water treatment. In the summer 2012, five cores were collected from the piles, and were analyzed for Eh, granulometry, total carbon, total nitrogen, and total mercury. The results indicated an anoxic environment, reflecting composition of the suspended matter. Carbon and nitrogen presented elevated concentrations, but also seemed to reproduce the characteristics of the suspended matter in the raw water. The concentrations of mercury were extremely variable but presented unexpectedly high values in some of the layers, reaching 18,484 ng g-1. On the other hand, concentrations ten times lower than those observed in the natural system (8 ng g-1) could be observed. It was concluded that the only possible source for the contamination of the sludge was the chemicals used for water treatment.

Volumetric modeling of two sludge piles from water treatment plants in a Brazilian reservoir.

Water treatment plants are designed to continuously produce drinkable water, meeting defined criteria of potability. However, besides potable water, these plants produce sludges that are disposed of in the environment. The present work aimed to evaluate the sludges generated in two water treatment plants and disposed of in the margin of the Juturnaíba dam. Since alum has been used as a flocculating agent in these two plants, the concentrations of aluminum were measured in the sludges and in surface sediments. The generated piles are extremely soft to walk on and difficult to measure, so indirect modeling procedures had to be applied. The calculated mass of the sludge piles at each plant are similar and respectively 60,370 and 61,479 tons. The aluminum content of the residues, calculated according to its dosage, was 33.2 and 32.6 g kg-1 in the piles from the two plants. The amount of alum dosed to the water corresponds almost to the excess of aluminum in the sludge, compared to the sediments. It was concluded that regardless of the fact that residues are disposed of in very restricted areas, they are directly in contact with the water and may constitute a threat for the environment and humans' health.

Co-composting of organic solid waste and sewage sludge – a waste management option for University Campus

Co-composting organic solid waste with dewatered sewage sludge was carried out to determine its suitability for managing waste on a University campus. Windrow composting method was employed in which dewatered sewage sludge and organic solid waste were mixed at volume ratios: 1:1, 1:2, 1:3, 0:1 and 1:0 sludge/organic solid waste. Parameters such as pH, percentage N, C, P, K, Ca, Mg, organic matter, ash content and C/N ratio were determined weekly. Total and faecal coliform population were measured biweekly with Pb and Cd levels determined at the beginning and end of the composting. With the exception of ratio 1:0 sludge/organic solid waste, all other ratios attained a favourable Carbon to Nitrogen (C/N) ratio both at the start and end of the composting process. Levels of major nutrients measured were found to be favourable for use as organic fertilizer. There was a general decline in carbon and organic matter in all the compost piles except the sewage sludge pile (1:0). Apart from the compost ratio 1:0 sludge/organic solid waste, all other ratios attained a temperature of 55°C within 8 days of composting. Generally the compost ratios 1:2, 1:3 and 0:1 (sludge/organic solid waste) were found to be the most suitable for use as organic fertilizer. International Journal of Environment Vol. 5 (1) 2016, pp: 14-31

Impact of liming and drying municipal sewage sludge on the amount and availability of 14C-acetyl sulfamethoxazole and 14C-acetaminophen residues

Acetyl Sulfamethoxazole (AC-SMX) and acetaminophen (ACM) can be found in municipal sewage sludge, and their content and availability may be influenced by sludge treatments, such as drying and liming. A sludge similarly centrifuged with/without a flocculant was spiked with 14C-labelled AC-SMX or ACM. Then, it was either limed (20% CaO) or/and dried under different laboratory conditions (1 week at ambient temperature; and 48 h at 40 or 80 °C). The total amount and distribution of the 14C-compounds among several chemical fractions, based on the sludge floc definition, were assessed at the end of the treatments.All the 14C-activity brought initially was recovered in the limed and/or dried sludges for AC-SMX but only between 44.4 and 84.9% for ACM, with the highest rate obtained for the limed sludge. Drying at 80 °C or liming increased the percentage of the sludge total organic carbon recovered in the extracts containing soluble extracellular polymeric substances (S-EPS) and the percentage of the total 14C-activity extracted simultaneously. The non-extractable residues represented only 3.9–11.6% of the total 14C-activity measured in the treated sludges for AC-SMX and 16.9–21.8% for ACM.The presence of AC-SMX and ACM residues in the treated sludges, after liming and drying under different conditions, was shown using some 14C-labelled molecules. At this time scale and according to the extraction method selected, most of the 14C-residues remained soluble and easily extractable for both compounds. This result implies that certain precautions should be taken when storing sludges before being spread on the field. Sludge piles, particularly the limed sludge, should be protected from rain to limit the production of lixiviates, which may contain residues of AC-SMX and ACM.

Corrosion inhibition of steam generator tubesheet by Alloy 690 cladding in secondary side environments

Denting is a phenomenon that a steam generator tube is distorted by a volume expansion of corrosion products of the tube support and tubesheet materials adjacent to the tube. Although denting has been mitigated by a modification of the design and material of the tube support structures, it has been an inevitable concern in the crevice region of the top of tubesheet. This paper provides a new technology to prevent denting by cladding the secondary surface of the tubesheet with a corrosion resistant material. In this study, Alloy 690 material was cladded onto the surface of an SA508 tubesheet to a thickness of about 9mm. The corrosion rates of the original SA508 tubesheet and the Alloy 690 clad material were measured in acidic and alkaline simulated environments. Using Alloy 690 cladding, the corrosion rate of the tubesheet within a magnetite sludge pile decreased by a factor of 680 in 0.1M NiCl2 solution at 300°C, and by a factor of 58 in 2M NaOH solution at 315°C. This means that denting can drastically be prevented by cladding the secondary tubesheet surface with corrosion resistant materials.

SCC analysis of Alloy 600 tubes from a retired steam generator

Steam generators (SG) equipped with Alloy 600 tubes of a Korean nuclear power plants were replaced with a new one having Alloy 690 tubes in 1998 after 20 years of operation. To set up a guide line for an examination of the other SG tubes, a metallographic examination of the defected tubes was carried out. A destructive analysis on 71 tubes was addressed, and a relation among the stress corrosion crack (SCC) defect location, defect depth, and location of the sludge pile was obtained. Tubes extracted from the retired SG were transferred to a hot laboratory. Detailed nondestructive analysis examinations were taken again at the laboratory, and the tubes were then destructively examined. The types and sizes of the cracks were characterized. The location and depth of the SCC were evaluated in terms of the location and height of the sludge. Most axial cracks were in the sludge pile, whereas the circumferential ones were around the top of the tube sheet (TTS) or below the TTS. Average defect depth of the axial cracks was deeper than that of the circumferential ones. Axial cracks at tube support plate (TSP) seem to be related with corrosion/sludge in crevice like at the TTS region. Circumferential cracks at TSP seem to be caused by tube denting at the upper part of the TSP.

Experimental simulation of Na and Cl hideout in steam generator crevices

Some types of corrosion of steam generator tubes involve impurity concentration in a gap (“crevice”) between the tubes and supporting structures or sludge piles. The purpose of this work is to characterize the concentration of sodium and chlorine in the crevices using a crevice simulator in a model boiler. Magnetite-packed crevices with lower permeability and thermal conductivity are more appropriate for the simulation of actual SG crevices than diamond-packed crevices. A radial pH gradient was observed in the magnetite-packed crevice that was also reported by earlier work (Baum, 2002b). The crevice pH near the tube wall appears to be alkaline initially due to the volatility effect of Cl. As time progresses, the crevice pH becomes neutralized and even acidic because of delayed preferential Cl concentration. This is enabled by a reduced boiling rate near the tube wall due to the presence of a Na-rich liquid film. During one fuel cycle, the crevice chemistry would be in a transient condition rather than a steady state because of the low impurity exposure (∼10ppmh) unless some impurities remain after each fuel cycle.

Microbiological Evaluation of the Effectiveness of Sewage Sludge Sanitization with Solar Drying Technology

The aim of study was to estimate the sanitization effectiveness of the sludge solar drying process carried out on technical scale in Poland based on the inactivation of bacteria and parasite eggs. Sewage sludge samples inoculated withEscherichia coli,SalmonellaSenftenberg W775and enterococci and perlon bags containingAscaris suumeggs were placed inside the carriers fixed in the dried sludge pile and on the shovels and frame of the sludge turner. The number of reisolated microorganisms was determined with MPN method and the percentage of invasiveA. suumeggs—with the microscope counting. On the basis of regression equations, the theoretical survivability and elimination rate of bacteria and parasite eggs were calculated. Experiment showed low hygienization efficiency of solar drying method. The theoretical survival time was 46–104 days in summer and 90–98 days in winter forS.Senftenberg W775and, respectively 42–55 and 71–148 days forE. coli, depending on the carriers location. Enterococci were able to survive for 52–168 days in summer and in winter its number increased. The decrease in the percentage of invasiveA. suumeggs was almost not observed. Results indicated that solar drying is a technology, which does not guarantee biosafety of product.

Electrical conductivity measurements in sewage sludge pellets: Innovative techniques for environmental management

This paper presents research on the behaviour of electrical conductivity of sludge pellets resulting from the treatment of urban wastewater at the drying grounds of the El Trebal wastewater processing plant, located in the Mapocho river basin of the Metropolitana Region, Santiago, Chile. In the methodology used samples were taken that correspond to three horizons of the sewage sludge pile. The first horizon made up the upper portion of the pile (the surface), the second the central portion (mesophilous), and the third the lower one (thermophilous). Electrical conductivity measurements were taken in sewage sludge pellets under pressures on the order of 15–50 MPa with currents of 10 −15 A. Electrical conductivity measurements were also taken for different horizons, and innovative techniques and methodologies for sludge samples presented in the form of pellets are used for this purpose. Such pellets are easily reproduced with sufficient precision, and at the same time allow modifying other variables like mass, sample dimensions and compaction levels. The trends of the conductivity curves are similar for the sludge from the isolation surface horizon (H1) as well as for the mesophilous area horizon (H2). In the case of the thermophilous area horizon (H3), the electrical conductivity shows extremely high values when compared to horizons H1 and H2. This paper could be useful in establishing a general rule for taking electrical conductivity measurements in sewage sludge samples. Such a rule could bring accurate reproducible values, and be used for other types of dry wastes.

Root causes of intergranular attack in an operating nuclear steam generator tube

This paper reports the secondary side intergranular attack of an Alloy 600 tube, which was located within sludge piles in the hot-leg side of an operating nuclear steam generator. Carbide distribution along the grain boundaries and chromium depletion were analyzed using optical microscopy and transmission electron microscopy. Local crevice chemistry in contact with the defect was also assessed from the hideout return test data and oxide film analysis results using energy dispersive spectroscopy. The main causes of this defect are discussed based on the microstructure, local chemistry and operation temperature.

Distribution Characteristics of Stress Corrosion Cracks in a Retired Steam Generator

Steam generators(SG) of the Korean nuclear power plants were replaced with a new one after a 20 year operation. A metallographic examination of the defected tubes is needed for setting up a guide line for a safe operation of the other SG. A destructive analysis of 50 tubes was addressed, and a relationship between the SCC defect location and defect depth was obtained. Tubes extracted from the retired SG were transferred to a hot laboratory. Detailed nondestructive analysis examinations were taken, then the tubes were destructively examined. Types and sizes of the defects were characterized. A location and depth of the SCC were evaluated in terms of the location and height of the sludge. Most axial cracks were in the sludge pile, whereas the circumferential ones were around the top of the tube sheet(TTS) or below the TTS. Cracks were found with various lengths in a specific zone. Average defect depth of the axial cracks was deeper than that of the circumferential ones.

Composting anaerobic and aerobic sewage sludges using two proportions of sawdust

Sawdust has been proven to be a good bulking agent for sludge composting; however, studies on the most suitable ratio of sludge:sawdust for sludge composting and on the influence of the sludge nature (aerobic or anaerobic) on the composting reaction rate are scarce. In this study two different sewage sludges (aerobic, AS, and anaerobic, ANS) were composted with wood sawdust (WS) as bulking agent at two different ratios (1:1 and 1:3 sludge:sawdust, v:v). Aerobic sludge piles showed significantly higher microbial activity than those of anaerobic sludge, organic matter mineralization rates being higher in the AS mixtures. The lowest thermophilic temperatures during composting were registered when the anaerobic sludge was mixed with sawdust at 1:1 ratio, suggesting the presence of substances toxic to microorganisms. This mixture also showed the lowest decreases of ammonium during composting. All this matched with the inhibitory effect on the germination of Lepidium sativum seeds of this mixture at the first stages of composting, and with its low values of microbial basal respiration. However, the ANS + WS 1:3 compost developed in a suitable way; the higher proportion of bulking agent in this mixture appeared to have a diluting effect on these toxic compounds. Both the proportions assayed allowed composting to develop adequately in the case of the aerobic sludge mixture, yielding suitable composts for agricultural use. However, the ratio 1:1 seems more suitable because it is more economical than the 1:3 ratio and has a lower dilution effect on the nutritional components of the composts. In the case of the anaerobic sludge with its high electrical conductivity and ammonium content, and likely presence of other toxic and phytotoxic substances, the 1:3 ratio is to be recommended because of the dilution effect.

Mineralisation of hazardous organic compounds in a sludge reed bed and sludge storage

Linear alkylbenzene sulphonates (LAS) and nonylphenolethoxylates (NPE) may be detrimental to the environment if spread in inappropriately large concentrations. Mineralisation of LAS and NPE in mesophilic digested sludge was observed during a 9-month monitoring programme where three separate treatment methods were investigated. Sludge was treated in a sludge reed bed under aerobic conditions, by storage in a container under anaerobic conditions, and by storage in a sludge pile turned over mechanically at intervals to improve the oxygen influx. Treatment in a sludge reed bed was shown to be effective. Mineralisation of 98% of LAS and 93% of NPE was observed. Only limited mineralisation occurred on the surface of the sludge stored in a container. A reduction of LAS and NPE of 90% and 43%, respectively, was observed in the sludge which was stored in a pile and frequently turned.