Composition Of Sewage Sludge Research Articles

Ultrasound-Assisted Community Bureau of Reference (BCR) Procedure for Heavy Metal Removal in Sewage Sludge

Sewage sludge (SS) resulting from wastewater treatment plants (WWTP) is commonly applied worldwide as a fertilizer in agriculture. This can be done following a rigorous analysis of the sewage sludge composition. Due to its toxic potential, heavy metal ion content is one of the key parameters to test when evaluating SS sample usage as fertilizer. The distribution of metals present in SS samples produced by five municipal WWTPs in Romania was studied. To obtain information regarding metal distribution in SS, a modified ultrasound-assisted extraction procedure of the Community Bureau of Reference (BCR) was employed for As, Cd, Cr, Cu, Mo, Ni, Pb, Zn, and Co quantitation. Concentrations of these metals were measured using ICP-EOS spectrometry. Method extraction accuracy was verified using CRM-483 certified reference material. Results show that extraction efficiency was lowest for the exchangeable fraction for all studied metals. The detected ion metals were found distributed in fractions (F) 2 and 3, which are unavailable for plants and groundwater under natural environmental conditions. One noteworthy finding was that using ultrapure water for the leachate test resulted in low metal solubility, indicating slight metal desorption in real environmental samples. Furthermore, maize stalk bio-adsorbent was used to minimize metal ion content in WWTP leachate samples produced by the storage of SS in terms of metal ion adsorption.

Primena vodenih eutektičkih rastvarača za hemijsku valorizaciju otpadnog mulja - određivanje mineralnog sadržaja

Sewage sludge is a by-product of municipal wastewater treatment processes with significant soil-forming and fertilizing characteristics. However, if sewage sludge contains heavy metals, it can negatively affect the soil environment. The accumulation of heavy elements in the soil can negatively affect the circulation of elements in the natural environment, regarding plants, animals, and humans. The primary sources of heavy metals in human and animal food are plants, which are also the primary consumers of mineral nutrients from soil and water. Even a very small amount of heavy metals in the body can create metabolic problems, reduced body functions, and compromised immune and enzymatic processes, all of which contribute to various diseases and may even cause death. The aim of this study was to find a suitable system for mineral extraction from the municipal sewage sludge after water purification, collected from the wastewater treatment plant in Vlasotince, so the real composition of sewage sludge could be obtained. For that purpose, different aqueous deep eutectic solvents were applied: choline chloride:lactic acid (ChCl:LA), choline chloride:urea (ChCl:U), choline chloride:glycerol (ChCl:G), choline chloride:propylene glycol (ChCl:PEG), choline chloride:citric acid (ChCl:CA), and choline chloride:ethylene glycol (ChCl:EG).The concentrations of minerals after wet digestion were determined by Inductively Coupled Plasma - Optical Emission Spectrometry (ICP-OES). The results showed that the highest amounts of minerals, especially Ca, P, and Fe, were extracted using aqueous acidic deep eutectic solvent systems (ChCl:LA and ChCl:CA). Also, the mineral composition of sewage sludge indicates the possibility of its use as a significant soil fertilizer supplement.

Seasonal Variations in the Composition of Sewage Sludge in the Observation of a Sewage Treatment Plant

AbstractDurch die Auswertung von Klärschlammanalysedaten einer großen deutschen Kläranlage (>1 Mio. Einwohnerwerte) konnten jahreszeitliche Schwankungen in der Zusammensetzung des Klärschlamms identifiziert werden. Diese Schwankungen beinhalten eine periodische Abnahme des Kohlenstoffgehaltes sowie eine Zunahme des Aschegehaltes in der Jahresmitte. Als Ursachen für diesen Trend konnten verschiedene Verfahren der Abwasser‐ und Schlammbehandlung sowie klimatische Einflüsse identifiziert werden. Die Untersuchung der Gehalte verschiedener Schwermetalle und Spurenelemente im Klärschlamm zeigte darüber hinaus ebenfalls zum Teil starke Schwankungen im Jahresverlauf, die Einfluss auf die Verwertungsmöglichkeiten des Klärschlamms haben können.

Opportunities for resource recovery from Latvian municipal sewage sludge

Sewage sludge is a type of waste that has high health and environmental risks associated with its reuse. Moreover, sludge has been neglected in global circular economy targets because it is generated in considerably lower quantities than municipal solid waste. At the same time, European Union's transition towards circular economy has set the need to reduce the amount of waste and to promote the production of secondary raw materials. Many countries have developed national strategies for sludge management to reach their sustainability goals. In Latvia, the current sludge management approaches include land application, composting and anaerobic digestion which all utilize sludge as an organic fertilizer. As an alternative to current management practices, resource recovery is put forward as a solution that is in agreement with EU policy. Carbohydrates (including cellulose), proteins and lipids were selected as candidates for energy and materials recovery from sludge. For the first time, this study demonstrates a comprehensive assessment of Latvian municipal sewage sludge composition and offers the theoretical yields of secondary resources on a yearly basis. Primary, secondary, and anaerobically digested sludge from 13 wastewater treatment plants (WWTPs) in Latvia was characterized in this study. The most abundant sludge type – secondary sludge – contained 18.5% proteins, 9.8% lipids and 2.6% cellulose per TS. On a yearly basis, secondary sludge from all Latvian WWTPs could provide 2530 t proteins, corresponding to 750 t protein-based fertilizer. Primary sludge contained 23.9% proteins, 9.1% lipids and 7.1% cellulose per TS. Primary sludge could provide 763 t/a carbohydrates, including 545 t/a cellulose. The currently available secondary and digested sludge would yield 727 t bioethanol, corresponding to 4.0% of the national biofuel consumption. This work applies the concept of resource recovery to the Latvian wastewater sector and shows the potential of simultaneously addressing waste and wastewater management issues.

Characteristics of sewage sludge composition for agricultural use

Characteristics of sewage sludge composition for agricultural use

Hydrothermal carbonization of sewage sludge coupled with Fenton oxidation pretreatment: Moderate oxidation to enhance hydrochar yield and properties

Hydrothermal carbonization (HTC) is a promising technology for sewage sludge (SSL) utilization. However, the yield and performance of hydrochar need to be further improved produced when SSL is used as a feedstock must be improved further. Herein, a process combining physicochemical pretreatment, namely, Fenton oxidation (FO) and HTC was developed for SSL utilization. Moderate oxidation was found to improve the yield and performance of the produced hydrochar. The product distribution, yield, and properties of the hydrochar produced using the proposed combined process were compared with those of the hydrochar produced via direct HTC treatment. The pretreatment affected the surface structure and organic composition of SSL and promoted the carbonization of the intermediate products. Thus, compared with the yield of hydrochar (50.7 %) obtained via the direct HTC treatment, the yield of the hydrochar obtained using the combined process increased to 55.0–65.2 % (depending on the pretreatment condition). Hydrochar properties were enhanced using the combined process, and the energy density of hydrochar slightly decreased after pretreatment (1.2–13.1 %); however, the energy yields increased by 0.6–30.1 % due to the enhanced hydrochar yield. The carbonization degree of hydrochar improved, the carbon in the feedstock distributed to the hydrochar increased from 33.40 % to 46.09 %. Moreover, the hydrochar showed more distinct pore channels, slightly improving its combustion activity. This study shows the efficacy of the combined pretreatment–HTC process and provides an experimental basis for the combined hydrothermal treatment of SSL.

Combined Use of Sewage Sludge Ash and Silica Fume in Concrete

The lack of adequate space for sewage sludge disposal has become a significant challenge in many countries. Landfilling and using sewage sludge as fertilizer in agricultural lands are the main methods for disposal. However, these methods can result in soil and groundwater contamination as well as heavy metal and microbial pollution in soil. An alternative disposal method is using sewage sludge ash (SSA) in concrete production. If the sludge ash is reactive, it can replace a portion of cement in concrete; otherwise, it can be used as a filler. In the present study, X-ray fluorescence (XRF) experiments were conducted to determine the elemental composition of sewage sludge. Then, the sewage sludge was incinerated, and XRF and X-ray diffraction (XRD) tests were performed on the resulting sewage sludge ash. The ash was utilized in different proportions in the mortar and concrete specimens, and compressive strength tests were conducted on the resulting specimens. The results indicate that using 20% SSA instead of cement resulted in a 25% reduction in compressive strength in concrete specimens. However, the combination of 10% silica fume and 10% SSA was the optimal combination to compensate for the reduction in compressive strength caused using SSA.

Production of bio-briquettes from pineapple peels and sewage sludge as an alternative renewable energy

The need to investigate an eco-friendly and renewable alternative energy source has been prompted by issues relating to the depletion of conventional fuel resources. One of the best green energy alternatives is bioenergy, which also encourages the sustainable use of agricultural waste. This study was carried out to investigate the utilization of pineapple peels for bio-briquette production. This study aimed to determine the characterization of bio-briquette by using different variations in the composition of sewage sludge, pineapple peels, and adhesive types, and to investigate the effect of different adhesive types on briquette characteristics. This research used rejected papaya, cow dung, and starch as the adhesive. The sludge, peels, and adhesives were blended in the ratios of (90:0:10); (70:20:10); (60:30:10); (30:60:10); (20:70:10); and (0:90:10). The result shows that the optimum briquettes were produced from (0:90:10) composition which was 0% sludge, 90% peel, and 10% starch. These briquettes with (0:90:10) composition had a water content of 5%, ash content of 11%, volatile matter of 13%, fixed carbon of 76%, and calorific value of 4,753.99 Cal/g. Calorific values increased as the composition of pineapple peels increased. Moreover, briquette with starch as the adhesive had better physical properties compared to adhesive from rejected papaya and cow dung.

Changes in Speciation and Bioavailability of Trace Elements in Sewage Sludge after the Ozonation Process

This work aimed to detect changes in trace element chemical speciation in sewage sludge (SS) after the ozonation process. The modified Community Bureau of Reference (BCR) sequential extraction procedure was performed to determine the chemical speciation of trace elements in SS after the ozonation process. To assess potential soil contamination with trace elements from sewage sludge after the ozonation process, the risk assessment code (RAC) coefficient was used. The bioaccumulation factor (BAF) and translocation factor (TF) values were also calculated to characterize the efficiency of trace element accumulation in the studied plant species from soil fertilized with sludges after the ozonation process. Generally, the mean concentration of total trace elements in the SS after the ozonation process was higher, but the differences were statistically significant only in the case of Mn, Cu, Pb, and Cd. The dominant fraction of Fe, Cr, Pb, and Cd was the residual fraction F4, while the extractable/exchangeable fraction F1 was present in the smallest amount. Therefore, in the case of Mn, Zn, and Ni, the ozonation process had a significant impact on the increase in the content of these elements in the F1 fraction. The application of the SS stabilized by ozonation process for maize and wheat fertilization did not significantly affect the bioaccumulation of most of the analyzed metals in aboveground biomass. Higher values of BAF coefficients after the application of ozonated SS were found only in the case of Cu and Ni. In turn, the determined TF coefficients were lower than 1 in most cases. The obtained results showed that the slight change in the concentration of Zn, Mn, and Ni in fraction F1 causes a specific risk of their mobility in the soil environment. It should be noted that due to the variable composition of sewage sludge, an analysis of the content of individual trace elements in chemical fractions should be carried out to assess its actual impact on the environment. This can help to indicate further actions that should be undertaken to limit their negative impact on the environment.

Prediction of char yield and nitrogen fixation rate from pyrolysis of sewage sludge based on machine learning

Based on sewage sludge composition and pyrolysis processing conditions, machine learning was employed as a tool to predict the nitrogen fixation rate and char yield of sewage sludge pyrolysis. Multiple linear regression, decision tree, support vector machine, random forest, and gradient boosting tree methods were used in the research to model the collected data, and the model results were further discussed. The required data set is sorted by the existing articles, and the missing values are filled by k-Nearest Neighbors method. Predicting the char yield and nitrogen fixation rate by considering the ultimate and proximate composition of the sewage sludge can give good results. The results showed the gradient boosting tree method is the most accurate in predicting nitrogen fixation rate and char yield, with the coefficient of determination for char yield and nitrogen fixation rate reaching 0.864 and 0.860, respectively. Fusion of existing models by voting or stacking methods revealed promising further improvement in prediction accuracy, but it was limited. In further analysis, using the mean decrease impurity and SHapely Additive exPlanations methods to more accurately evaluate the feature importance. For example, HTT was the most important feature affecting char yield and nitrogen fixation rate, especially when predicting the nitrogen fixation rate, with a feature importance of 0.625. This study also quantified the effects of different features on char yield and nitrogen fixation rate using partial dependence and individual condition expectation plots to provide a reference for the utilization and research of sewage sludge pyrolysis.

РОССИЙСКИЕ И ЗАРУБЕЖНЫЕ ПРАКТИКИ ОБРАЩЕНИЯ С ОСАДКОМ СТОЧНЫХ ВОД

Purpose: to analyze the best practices for sewage sludge management both in our country and abroad. Discussion. The qualitative composition of sewage sludge varies depending on the wastewater composition, the characteristics of treatment facilities and the treatment methods used. The choice of sludge disposal method depends primarily on environmental and social factors. The environmental factor is determined primarily by the presence of pathogenic microorganisms and helminths, heavy metals and biogenic substances. The problem with helminths and pathogenic microorganisms is solved by disinfection and stabilization of sewage sludge. The problem with heavy metals is solved by their immobilization. The biogenic composition of sewage sludge, and primarily the nitrogen and phosphorus content, predetermines its fertilizer value for crop production. The main negative component that determines the quality of sewage sludge is the presence of heavy metals in them. The statistical data on the content of heavy metals in sewage sludge from various countries are presented. The social aspect determines the availability of agricultural areas, appropriate technologies, demand for a certain type of resource, as well as economic indicators of the result obtained. Conclusions. Currently, in world practice there is no consensus on the permissible content of pollutants in sewage sludge when they are used as fertilizers. The Russian standards are no exception, which require scientifically based revision to improve the requirements for the sewage sludge quality for their further use in the country's agriculture.

МИРОВЫЕ ТЕНДЕНЦИИ В НОРМИРОВАНИИ ОСАДКОВ СТОЧНЫХ ВОД ПРИ ИСПОЛЬЗОВАНИИ ДЛЯ ПОВЫШЕНИЯ ПЛОДОРОДИЯ ПОЧВ

Purpose: to assess global trends in rationing the sewage sludge qualitative indicators when used in agriculture as ground and fertilizers. Discussion. Two components are requires for effective treatment of sewage sludge: a regulatory and legal framework in this area and economic interest, which implies the use of various incentives to achieve more favorable environmental performance, for example, state subsidy mechanisms, environmental payments for waste disposal, income from the sale of finished products from production waste, tax benefits on profits from the sale of a secondary resource, etc. In the developed standards and regulations regarding the use of sewage sludge in agriculture and as ground for biological reclamation, the environmental requirements are of particular importance. The paper reviews foreign and Russian documents and standards containing requirements for the sewage sludge composition used as ground and fertilizers. Differences in the approaches of national systems of standards are revealed. However, there are general requirements when using sewage sludge to improve soil properties. According to the Russian standards data, the requirements related to a single rationing object – sewage sludge, do not match in terms of the list of agricultural crops acceptable for growing, which causes some uncertainty when assessing their suitability indicators and decision making on its use for a specific crop cultivation. Conclusions. An analysis of a number of foreign and Russian standards has shown a particular interest in rationing, first of all, the content of pollutants in sewage sludge. However, at present there is no consensus in global practice on the permissible content of pollutants in them for agricultural use.

Impact of High-Intensity Static Magnetic Field on Chemical Properties and Anaerobic Digestion of Sewage Sludge

The increasing production of sewage sludge at global level has addressed the search for technical solutions to take advantage from it, reducing the environmental burden originating from its disposal. Anaerobic digestion is a suitable option to handle sewage sludge in accordance with circular economy principles, as it generates a methane-rich biogas and a digestate with potential fertilizing properties. Several techniques have been proposed to enhance anaerobic digestion performances and, among these, the application of static magnetic field (SMF) has recently gained attention. Nonetheless, the effects of high-intensity SMF on the sewage sludge destined to anaerobic digestion and its impact on the anaerobic digestion process have not been evaluated yet. This study aims to determine the effects of a 1.5 T SMF on the chemical composition of sewage sludge as well as on methane generation during anaerobic digestion. The main parameters influencing the SMF (i.e., flow rate, mixing ratio of magnetized to non-magnetized sludge, number of pumping cycles, and total solid content) were varied to evaluate the impact of different exposure conditions on the chemical characteristics and methane potential of sewage sludge. An extensive exposure to the high-intensity SMF applied resulted in a 24% decrease of methane production, reduced the concentration of the monitored ionic species (i.e., NH4+, NO3−, PO43−, SO42− and Mg2+) in the liquid phase of sewage sludge, and promoted the precipitation of compounds with valuable fertilizing properties, e.g., struvite. These outcomes suggest that high-intensity SMF, although negatively influencing methane generation, can promote the precipitation, and possibly the recovery/recycle of valuable compounds from sewage sludge, enhancing its proper management in a circular economy perspective.Graphical abstract

Quantifying the thermochemical pathways of soluble organics in sewage sludge flocs during pyrolysis for precursor optimization and by-product control

The composition of sewage sludge is complex, and understanding the product contribution and pyrolysis pathways of typical components in sludge are important for product quality improvement and contaminant volatiles control. Here, three major sludge organics, i.e., protein (PR), polysaccharide (PS), and humic acid (HA), were extracted and pyrolyzed individually to quantify the correlation between sludge components and products. The temperature-response and sludge inorganics-response of pyrolysis processes were elucidated simultaneously. The main contributor to the carbonaceous components in char shifted from PR (from 51% to 7%) to HA (from 27% to 78%) as temperature increased from 250℃ to 850℃. Over 95% tar and 70% gas were originated from PR and PS at temperature above 550℃. Regarding the effect of inorganic matters, Ca/Si/Al-containing inorganics were the major inducement for the formation of nitrogenous tars and NOx, whereas polyferric chloride retained sludge organics in the carbon matrix in the form of C–C/C = C and heterocyclic-N/S, thus reducing the generation of volatiles. Based on pyrolysis product evolution and elemental flow analysis, sludge rich in HA and low in Ca/Si/Al-containing inorganics was found to be a promising source for carbonization at 550-850℃, while PR/PS-rich sludge was more suitable for pyrolysis or liquefaction at below 550℃. These findings provided reliable strategies for pyrolysis precursor selection, gas emission control, and potential application of pyrolysis product.

Agronomic valorization of sewage sludge: The potential of thermal drying to achieve sanitation and biological stability

This work aims to contribute to the discussion of using a waste (sewage sludge) to obtain a valuable product (organic-rich fertilizer), based on a circular economy perspective. The composition of sewage sludge (SS) was considered, highlighting important characteristics as raw material for fertilizer production (e.g., macronutrients, microbiological contamination, phytotoxicity). Particularly, the biological stability of SS was evaluated measuring the oxygen uptake rate (OUR) using the Oxitop® method, and the phytotoxicity using germination tests. The potential of thermal drying to stabilize the SS was evaluated at two temperatures (100 and 130°C). The results showed that the organic matter (OM), N, and P levels are within the range of interest for agronomic valorization, while the content of some potentially toxic metals (e.g., Zn and Cu) may exceed the legal limits. The phytotoxicity assessment showed that raw SS samples negatively impacted the germination phase. Concerning the biological stability, results showed that raw anaerobic digested samples were characterized by OUR values above 50 mmol O2/kg OM.h (the limit for stable SS). Although thermal treatment of SS at 100 and 130°C eliminated pathogens and significantly stabilized SS to OUR values below 50 mmol O2/kg OM.h, it was not enough to reach the limit established for a stable fertilizer (25 mmol O2/kg OM.h). Globally, SS has potential for soil application, within the scope of circular economy, but it is essential to control its microbiological contamination and stability.

ИССЛЕДОВАНИЕ ВЛИЯНИЯ ОСАДКА СТОЧНЫХ ВОД И ЦЕОЛИТА, ПРЕДПОСЕВНОЙ ОБРАБОТКИ СЕМЯН ЯРОВОГО ЯЧМЕНЯ НА ЕГО УРОЖАЙНОСТЬ

Purpose: to study the chemical composition of sewage sludge and zeolite, the sludge structure and also to evaluate the spring barley yield against the background of the ameliorant application and pre-sowing seed treatment with bischofite. Materials and methods. The object of research is the sewage sludge from the treatment facilities of Volzhsky and natural limestone zeolite. The chemical composition of sewage sludge and zeolite was studied under laboratory conditions. The study of sewage sludge structure was carried out by scanning electron microscopy. The field experiment was set up in accordance with generally accepted methods. Results. The chemical composition of the sewage sludge and the quality indicators of zeolite were determined. During the study, the increased content of nitrogen (6.7 %), phosphorus (2.8 %), potassium (0.21 %) was found in the sediment, the organic matter content was 80.0 %. Zeolite analysis data showed that it is based on silica SiO₂ (60.49 %) and alumina Al₂O₃ (12.1 %). When studying the structure of sewage sludge, it was found that the sample has a porous structure, particles of various sizes are found in it, meso- and macropores are present. Data on spring barley yield indicate that when treated with worked out sewage sludge, it increases to 3.15 and 3.25 t/ha against the background of control without seed treatment and with seed treatment with bischofite, respectively. In the variant without pre-sowing seed treatment and with the ameliorant introduction (sewage sludge + zeolite), the yield was 3.88 t/ha, in the variant with seed treatment with bischofite – 4.05 t/ha. Conclusions. To increase the productivity and yield of spring barley in the arid zone of the Volgograd region, it is advisable to use non-traditional ameliorant fertilizers with an optimal chemical composition. Pre-sowing seed treatment with bischofite had a positive effect on field germination and spring barley yield, however, additional studies of its effectiveness in pre-sowing seed treatment are needed.

ПРАКТИЧЕСКОЕ ПРИМЕНЕНИЕ ОСАДКА СТОЧНЫХ БЫТОВЫХ ВОД НА ПРИМЕРЕ ВОЗДЕЛЫВАНИЯ САФЛОРА КРАСИЛЬНОГО

Purpose: to study the main indicators of sewage sludge in the town Volzhsky and the possibility of its practical application on farmlands. Materials and methods. The object of research is sewage sludge from waste treatment plants of the town Volzhsky, Volgograd region. The chemical composition of sewage sludge was studied under laboratory conditions. Field experiments were laid in accordance with generally accepted methods. Results and discussions. Experimental studies have determined that high concentration of nitrogen (3.3 %), phosphorus (4.27 %), potassium (0.31 %) was noted in the sewage sludge, the organic matter content was 32.0 %. The water extract analysis data indicate a high concentration of calcium cations (33.25 mmol/100 g of soil) and magnesium (14.25 mmol/100 g of soil), as well as sulfate anions (5.80 mmol/100 g of soil). Heavy metals are present in the sludge, but their amount is much lower than the maximum permissible concentration. When testing sewage sludge in the field, it was found that, a decrease in soil bulk density to 1.10 t/m cub. is achieved in combination with chisel tillage. (dose of sewage sludge is 5 t/ha) and up to 1.07 t/m cub. (dose of sewage sludge is 10 t/ha). The data analysis on the safflower yield shows that the processed sewage sludge application increases the yield of safflower seeds in all years of research. The variant of combined action of sludge at a dose of 10 t/ha and chisel tillage turned out to be preferable, which made it possible to increase the safflower yield to 1.51 t/ha on average over the years of research. Conclusions: under the arid conditions of Volgograd region, it is advisable to use deep chisel tillage in combination with sewage sludge at a dose of 10 t/ha in order to increase the productivity of safflower and reduce the bulk density.

Investigation of the possibilities of dewatering sewage sludge by the method of electroosmosis in order to prevent land littering

Wastewater sludge from industrial enterprises is disposed of at disposal sites. This leads to a negative impact on the soil cover. The well-known methods of dehydration of moisture-containing materials have been studied. The chemical composition of sewage sludge was investigated. A technical solution for reducing the volume of wastewater sludge formation is considered on the example of cardboard and paper production. An electroosmotic installation is proposed. To study the process of sludge dewatering, a series of experiments was carried out on the installation with variable parameters of the voltage between the electrodes. A model of the particle velocity in the medium under study was presented. It has been proven that with the help of an electroosmotic device, up to 70% of moisture is effectively removed from the volume of waste sludge waste. This makes it possible to significantly reduce their volumes, reduce areas for possible or temporary placement and reduce the environmental load on the environment.

A contemporary and historical analysis of the trace element composition of sewage sludge in the United Kingdom

AbstractSewage sludge is the essential by‐product of wastewater treatment and approaching 100% of the sludge generated in the United Kingdom is recycled to agricultural land. In collaboration with three major Water Utility companies in the United Kingdom, a critical statistical analysis of historical and contemporary sludge quality data was completed to demonstrate the long‐term patterns and improvements in the trace element (TE) content of sludge recycled to agriculture since 1989, and to indicate the current status of sludge quality in the United Kingdom. Comparisons with pollutant emission inventory data showed most of the TE concentrations in sludge were strongly linked to declining environmental emissions. A soil accumulation model showed that zinc and copper would be the first to approach their statutory soil limits in the long term and that nickel, cadmium, lead and mercury are no longer significant and, from a practical perspective, could be removed from the regulatory controls on agricultural use.

New insights into impact of thermal hydrolysis pretreatment temperature and time on sewage sludge: Structure and composition of sewage sludge from sewage treatment plant

This work investigated the effects of THP temperature (140–200 °C) and time (10–60 min) on the surface morphology, pyrolysis properties, and soluble compounds of dewatered sludge. Results indicate that higher temperature and longer pretreatment time considerably improve organics hydrolysis (the SCOD content increased 1.4–2.46 times, increasing 2.46 times at 200 °C). In addition, high temperature also improved the sludge pyrolysis efficiency (the highest at 200 °C), and reduced the harmful gas release, especially HCN. Moreover, the surface morphology of the sludge changed, the gap and floccules on the surface of the sludge increased. The carbohydrate content increased the highest; approximately 91.9% at 170 °C. THP promoted the decomposition of the nitrogen compounds in the sludge and facilitated their transition to a liquid phase. The total nitrogen and ammonia nitrogen content doubled, and the organic nitrogen content decreased by 50% with time increased from 10 to 60 min.