Fraction Of Sewage Sludge Research Articles

Structural Analysis of Heat-Calcined Modified Sewage Sludge From WWTP in Gas Complex For Environmental Risk Assessment

Thermal processing of sewage sludge (SS) wastewater treatment plant WWTP has received increasing attention in recent years. Heat calcination valorise the carbon rich organic fraction of SS, while effectively reducing SS volume. The refractory metals (thermally stable, i.e. Zn, Cu and Cr) are less volatile at different temperatures at 200 and 400 °C of thermal processes and they are enriched in the residues. To gain insights into mineralogical analysis, physicochemical, microstructure properties and heavy metals ( HMs ) were characterized by proximate, ultimate field emission x-ray fluorescence ( XRF ), scanning electron microscopy ( SEM ), attenuated total reflectance-Fourier transform infrared ( ATR-FTIR ) spectroscopy, x-ray diffraction ( XRD ) and UV-vis spectrophotometer. Such analysis plays a crucial role in the effective management of WWTPs and in evaluating the environmental risks associated with the disposal of wastewater sludge’s. It aids in assessing the potential value of these sludge’s as fertilizer, considering factors such as the presence of potash and iron, for agricultural purposes, or as building materials, considering the presence of silica and calcium oxide. The assessment is carried out utilizing X-ray fluorescence (XRF) technology. Furthermore, a case study is included to illustrate typical situations in a WWTP, emphasizing the main challenges and limitations linked with ships, as well as wastewater management and disposal. Additionally, the specific scenario of gas complex GP1/Z is scrutinized to suggest a wastewater treatment solution, which involves evaluating potential locations for the treatment plant and determining the appropriate treatment methods to be implemented.

Long chain fatty acid (LCFA) occurrence in primary and secondary sewage sludge fractions

Sewage sludge produced in municipal wastewater treatment plants (WWTPs) is stabilized to produce methane/energy and a final stabilized biosolid suitable for land use using anaerobic digestion (AD) process. Fat, oil, and grease (FOG) matter present in the sewage sludge and their products, long chain fatty acids (LCFA), are not monitored qualitatively and quantitatively for their contribution or inhibition to methane production during the process. AD is designed and operated based on average volatile solid (VS) removal criteria. LCFA can be both present in the sewage sludge and produced as intermediate products during the hydrolysis of FOG. A 1.5-year monitoring of the primary sludge (PS) and secondary sludge (SS) fractions was conducted and evaluated in a timely base in a municipal WWTP. According to the results, the most common and highest presence belonged to palmitate (C16:0) and total LCFA occurred up to 11963 and 927 mg/L in PS and SS, respectively. Detected LCFA species were mostly saturated as laurate, myristate, palmitate, stearate, oleate and elaidate. The level in the mixed sludge feed complied with the inhibitory threshold values neglecting the accumulation in the anaerobic digesters.

Mixing effect on bio-methanation, settleability and dewaterability in the anaerobic digestion of sewage sludge fractions

Biomethanation and dewaterability characteristics of primary sludge (PS), secondary sludge (SS) and mixed sludge (MS) fractions were assessed after anaerobic stabilization under parallel batch and continuous mixing conditions at 35℃ in order to investigate the performance of the separate digestion system. Similar methane conversion/yield values were obtained in PS, SS and MS digestion with continuous mixing’s positive effect only in PS digestion. Continuous mixing resulted in 50% increase in the methane yield (600(+/-100) mL/g VSadd.d. SS digestion produced a comparable methane yield at 650(+/-100) mL/g VSadd.d showing no effect due to mixing pattern. Settling and dewaterability characteristics of the stabilized PS were superior to stabilized SS samples. A reverse relationship was obtained between settling and dewaterability characteristics where intermittent mixing enhanced settling ability while continuous mixing resulted in higher dewaterability of the stabilized sludges. Polyelectrolyte (PE) addition showed a negative effect on the settleability of the sludges. Low degree mixing resulted in 50% sludge volume reduction and an SVI of 64 mL/g VS compared to 25% volume reduction and 82 mL/g SVI in the continuous mixing mode for the stabilized PS. A similar trend for the stabilized SS but weaker values with 25% volume reduction and an SVI 182 mL/g in the intermittent mixing mode compared to 15% volume reduction and 200 mL/g VS SVI indicated a much lower settleability in the continuous mixing mode and compared to stabilized PS.

Anaerobic Co-digestion of sewage sludge and organic fraction of municipal solid waste: Focus on mix ratio optimization and synergistic effects

The utilization of municipal solid waste (MSW) and sewage sludge (SS) as a source of renewable energy is crucial in achieving sustainable and integrated MSW management. SS and organic fraction of municipal solid waste (OFMSW) can be anaerobically digested to produce methane for energy. However, anaerobic digestion of specific substrates is challenging with respect to substrate characteristics. The problem of mono-digestion can be mitigated by co-digestion of these two major organic wastes because of their complementary characteristics. Moreover, there is a lack of studies on optimization of different mix ratios of organic fraction of municipal solid waste (OFMSW) and sewage sludge (SS) based on total solids (TS). The study aims to optimize the mix ratio for anaerobic co-digestion of OFMSW and SS. The study further elucidates synergistic effects associated with the co-digestion process. Different mix ratios of SS and OFMSW (0:100, 20:80, 40:60, 60:40, 80:20, 100:0) at 5, 7.5 and 10% TS were assessed for biomethane potential assessment. The results showed that with an increase in SS in the mix ratio feed the methane yield increased by 91% and 50% as compared to mono digestion of sewage sludge and OFMSW respectively at TS 7.5%. Based on the kinetic analysis, it was observed that the lag phase reduced for 60:40 mix ratio leading to higher rate of biodegradation. Positive synergistic effects were observed for 40:60, 60:40 and 80:20 mix ratio of SS:OFMSW based on co-digestion impact factor value. Response surface modelling was used to get the optimized mix ratio and TS %. The optimum mix ratio with the highest methane yield (388 ml/gVS added) was 70:30 (SS: OFMSW) at TS 7.5% with a desirability value of 0.98. These findings demonstrate that co-digesting SS and OFMSW is a preferable alternative for harnessing renewable energy and managing organic waste in a sustainable manner.

Quantitative Distribution and Contamination Risk Assessment of Cu and Zn in Municipal Sewage Sludge

One of the methods of managing sewage sludge (SS) is its soil application. This possibility is promoted by the chemical composition rich in organic matter and nutrients. However, heavy metal contents in SS must meet respective permissible limits. Among the heavy metals in SS, Cu and Zn are found in the largest amount; thus, this study focuses on these elements. The main aim of the study is to investigate the quantitative distribution of metals in sequentially separated fractions of sewage sludge. Additionally, the potential risk of environmental contamination with heavy metals was assessed in the case of SS application for agricultural purposes. The relevant analyses were conducted on four different examples of municipal SS. Based on the total amounts as well as those determined in the SS fractions, the following indices were calculated: Igeo (geoaccumulation index), ICF, (individual contamination factor), and RAC (risk assessment code). The use of data from the sequential analysis as well as the calculated indices made it possible to assess the usefulness of SS in practice in terms of potential introduction of Cu and Zn into the environment with the sludge dose. It was found that total Cu (Cutot) and Zn (Zntot) did not exceed the permissible limits binding within respective Polish and international regulations. Regardless of the years of study and the analyzed SS, Cutot ranged from 260.9 to 393.5 mg·kg−1, and Zntot from 475.5 to 1153.1 mg·kg−1. The amounts of Cu and Zn were predominantly reducible (bound to iron and manganese hydroxides, Fr. II) and oxidizable complexes (bound to organic matter and sulfides, Fr. III). The average amounts of Cu in Fr. II ranged from 149.4 to 172.4 mg·kg−1, while those of Zn in Fr. II ranged from 370.9 to 754.6 mg·kg−1. Cu amounts in Fr. III were from 160.9 to 183 mg·kg−1 and Zn amounts in Fr. III were from 104.9 to 171.9 mg·kg−1. Total content of metals as well as TOC values strongly determined the quantitative level of both elements in the SS fractions. Generally, with the increase in the total amount of metals, their levels in the sludge fractions increased. In turn, the increase in TOC resulted in a decrease in the amounts of Cu and Zn in the sludge fractions. Calculated Igeo and ICF ratios showed high and very high SS contamination with Cu and Zn. Igeo values for Cu, regardless of the year of study and sludge sample, that ranged from 4.62 to 5.43 and for Zn from 3.41 to 4.86. At the same time, the ICF values for Cu ranged from 8.59–23.04, and for Zn 15.42–44.47. The RAC values indicated a low (Cu) and medium (Zn) risk of using SS in terms of the potential metal availability in the environment. The RAC values ranged from 1.46 to 4.40% for Cu and from 9.63 to 23.13% for Zn.

Boosting butyrate and hydrogen production in acidogenic fermentation of food waste and sewage sludge mixture: a pilot scale demonstration

Within the urban scenario, the application of a biorefinery technology value chain can foster the conversion of different organic substrates into marketable and added-value products. In this work, a pilot-scale dark fermentation (DF) process has been carried out as a key step for volatile fatty acids (VFA) and hydrogen production from the liquid fraction of sewage sludge and food waste mixture. Six operating conditions have been monitored in terms of yield and process stability, by changing the hydraulic retention time (HRT) from 4 to 6 days and applying a short-term hyper-thermophilic hydrolysis (70 °C, 8 h) on the same feedstock mixture. A tubular centrifugation was utilized to remove part of the biosolids (driven to biogas production) before the DF step, which was applied on the soluble and/or colloidal organic matter only. The hydrolysis step favored the following acidification process, in which a fermentation yield up to 0.42 g CODVFA/g VS0 was achieved at 5 days as HRT. Hydrogen production (up to 34.4% v/v and 0.046 m3 H2/kg VS0) was positively affected by the hydrolysis application and by the decrease of the HRT, highlighting the possibility to produce biohythane in the modeled two-phases anaerobic bioprocess. On the other hand, without the application of the hydrolysis, a selective production of butyric acid (up to 75% COD basin) was achieved, furnishing a different valorization route for the chosen urban organic feedstock. Changes in operating conditions and performances were also reflected by the adaptation of the microbial community, whose characterization highlighted the occurrence of several fermentative microorganisms (e.g., Clostridiaceae, Ruminococcaceae).

Key element course-tracked copyrolysis of sewage sludge and biomass for resource recovery and pollution control through kinetic and thermodynamic insights

Ameliorating sewage sludge (SS) pyrolysis process with biomass increasingly becomes an effective strategy to utilize SS-entraining resources and depress pollutant evolution, while real-time track of SS and biomass copyrolysis as well associating thermochemical reactions in aspects of kinetics and thermodynamics is yet to be unveiled. Here a combinative thermogravimetry combined with Fourier transform infrared spectroscopy and gas chromatography-mass spectrometry (TG-FTIR-GC/MS) pyrolysis system, lab-scale furnace and theoretical calculation were adopted to develop a key element course-tracked copyrolysis of SS and corn stalk (CS) for simultaneous accommodation of profitable products and derived pollutants. The formation of alkanes and alkene with small carbon number (below 4) was promoted during copyrolysis, while those with heavy carbons (over 5) were contributed by the inherent organic fraction of SS. The release of those nitrogen (N)-/sulfur-/chlorine-involving inorganic pollutants was depressed with the increase in the CS addition. The increased release of CO2 and H2O as well carboxylic volatiles with a high CS addition evidenced the promoted dehydroxylation and decarboxylation. Consequently, the speciation of N and phosphorus (P) and the bioavailability of toxic metals (TMs) were regulated with the increasing CS addition, that is, enhancements of proteins and protein-like N transformation to the other nitrogen species, P within orthophosphate diesters to orthophosphate monoesters, and TM reactivity-dependent bioavailability depression. A low addition (below 20 %) was prone to maintain a congruent mechanism, while the total Gibbs energy tended to decrease with an increasing addition and pyrolysis temperature, leading to a converged pressure-constant heat capacity (∼1430 J/K) at 700 °C. Those thermochemical reactions occurring over sewage sludge ash matrix were pivoted with biomass addition, which can be adopted as a useful strategy for an efficient, cleaner and sustainable mining of waste resources.

Enhanced sewage sludge treatment via parallel anaerobic digestion at the upper mesophilic level

Sewage mixed sludge (MS) digestion performance was ameliorated implementing the parallel digestion model for primary sludge (PS) and secondary sludge (SS) (waste activated sludge) as domestic sewage sludge fractions rich in oil and grease content at the upper mesophilic level (40 °C). Optimization of the organic loading rate (OLR) was conducted in parallel semi-continuous bench-scale digesters for PS, SS and MS. Comparatively evaluated performance and biosolid quality parameters were methane production rates, volatile solid (VS) reduction, oil and grease and nutrient content, dewaterability and electrical conductivity (EC). OLR optimization indicated different retention time needs for PS and SS stabilization and enabled 18% and 93% higher VS loading and reduction, respectively, compared to MS digestion. Inhibitory effect followed an ascending pattern as a result of OLR increase in each digestion line acting on the hydrolysis of proteinaceous matter and acetogenesis rather than methanogenesis. A high number of long chain fatty acids was detected in the raw sludges. The enhancing effect of the upper mesophilic temperature was significant in SS digestion with increased biodegradability, oil and grease removal and microbial growth compared to digestion at 35 °C. The parallel digestion system and upper mesophilic temperature proved a useful tool to enhance VS loading and reduction without worsening the stabilized biosolids’ dewaterability as a feasible model in the existing and prospective municipal wastewater treatment plants (WWTPs). The weakness of the MS digestion was diagnosed as the lower synthesis degree of biomass induced by the dilution of the substrate in PS by SS mixing which weakened the microbial tolerance to high OLR and inhibition. The output indicated the potential of parallel AD, importance of the optimization for OLR and temperature to advance the performance and flexibility of the sludge line practice in municipal WWTPs.

Distribution of Oxyphinic Elements in Sewage Sludge Fractions Based on Manganese and Nickel

Distribution of Oxyphinic Elements in Sewage Sludge Fractions Based on Manganese and Nickel

Combustion characteristics of co-combusted municipal solid wastes and sewage sludge

ABSTRACT Incineration is an effective way to manage and utilize sewage sludge (SS). In this study, thermogravimetric analysis and infrared spectroscopy were used to study the characteristics of co-combusted municipal solid wastes (MSW) and SS, as well as the pollutant emission characteristics. Positive interaction was found in the co-combustion. Combustion characteristic index increased from 1.71 × 10−6 min−2°C−3 to 1.73 × 10−6 min−2°C−3 when the mass fraction of SS increased from 0% to 10%. Activation energy decreased as the proportion of sludge increased. Activation energy of the main reaction stage of MSW and SS was 321.12 KJ/mol and 63.15 KJ/mol, respectively. The emission of HCl and NO decreased during co-combustion. Considering combustion intensity, activation energy, and pollutant emission, 10% SS was the optimal blend. CaCO3, CaO, Ca(OH)2, or natural limestone decreased the emission of HCl and NO, and decreased the activation energy in the first stage but increased it in the second stage.

Feasibility and potential of separate anaerobic digestion of municipal sewage sludge fractions

Feasibility of the separate anaerobic stabilization of primary (PS) and secondary (SS) sludge fractions produced in municipal wastewater treatment plants (WWTP) was studied at volatile loading rates (VLR) of 0.57–2.05 and 0.27–0.57 kg VS/(m3∙d) for PS and SS, respectively, corresponding to 16–30 and 14–28 d of hydraulic retention time (HRT). Laboratory-scale semi-continuous anaerobic reactors were operated at 35°C. The operational performance and quality of the final stabilized sludge were monitored. PS and SS showed opposite thickening abilities exhibiting a need for direct feeding of PS to the digesters. Biodegradability was obtained as 52(±1) and 40(±5)% volatile solid (VS) removal for PS and SS, respectively. Optimum VLR was determined according to the highest methane yield (specific methane production), VS reduction and dewaterability of the stabilised sludge. An inhibitory effect was observed at higher VLRs in PS digestion inducing a gradual reduction in the methane yield and daily production. High oil and grease content was subject to a substantial reduction in PS digestion showing a dependency on HRT. Conversely, a considerable degree of augmentation took place in the stabilised SS with no correlation to HRT at values lower than 30 d. Efficient reduction in the oil and grease content improved dewaterability in stabilised PS whereas high oil and grease content prevented an improvement for stabilised SS. Major benefits were obtained as lower HRT and high stability with higher methane production and fertilizing (N and P content) characteristics for digestion performance and stabilized SS, whereas direct feeding and higher HRT for PS digestion were determined as beneficial.

Feasibility and potential of separate anaerobic digestion of municipal sewage sludge fractions

Feasibility of the separate anaerobic stabilization of primary (PS) and secondary (SS) sludge fractions produced in municipal wastewater treatment plants (WWTP) was studied at volatile loading rates (VLR) of 0.57–2.05 and 0.27–0.57 kg VS/(m3∙d) for PS and SS, respectively, corresponding to 16–30 and 14–28 d of hydraulic retention time (HRT). Laboratory-scale semi-continuous anaerobic reactors were operated at 35°C. The operational performance and quality of the final stabilized sludge were monitored. PS and SS showed opposite thickening abilities exhibiting a need for direct feeding of PS to the digesters. Biodegradability was obtained as 52(±1) and 40(±5)% volatile solid (VS) removal for PS and SS, respectively. Optimum VLR was determined according to the highest methane yield (specific methane production), VS reduction and dewaterability of the stabilised sludge. An inhibitory effect was observed at higher VLRs in PS digestion inducing a gradual reduction in the methane yield and daily production. High oil and grease content was subject to a substantial reduction in PS digestion showing a dependency on HRT. Conversely, a considerable degree of augmentation took place in the stabilised SS with no correlation to HRT at values lower than 30 d. Efficient reduction in the oil and grease content improved dewaterability in stabilised PS whereas high oil and grease content prevented an improvement for stabilised SS. Major benefits were obtained as lower HRT and high stability with higher methane production and fertilizing (N and P content) characteristics for digestion performance and stabilized SS, whereas direct feeding and higher HRT for PS digestion were determined as beneficial.

The effect of mineral additives on the process of chlorine bonding during combustion and co-combustion of Solid Recovered Fuels

The use of solid recovered fuels (SRF) is often associated with an increased risk of chloride corrosion because these fuels can be high in chlorine and alkali. One way to reduce the risk of chloride corrosion is the co-combustion of fuel mixtures in the presence of a mineral additive containing chemical compounds that bind the emitted chlorides. This paper concerns the influence of mineral additives – constituting waste material, on the process of the binding of emitted chlorides. One of these waste materials could be a halloysite, not yet used in power industry. The research has shown its high chloride binding effectiveness, comparable to that of kaolin (known in literature as a mineral additive effectively binding chloride). Moreover, the studies have shown that SRF combustion in the presence of stabilized, dried and granulated sewage sludge, with a 25% mass fraction of sewage sludge, allows reducing chloride emissions. Studies are based on tests in a calorimetric bomb.

Direct Lewis-Brønsted acid ethanolysis of sewage sludge for production of liquid fuels

Ethanolysis carried out under Lewis-Brønsted acid catalysis was investigated as a possible process to valorize the organic fraction of urban sewage sludge, with the aim of selectively obtaining liquid biofuels. In a single reactive step, the conversion of lipids into fatty acid ethyl esters, of carbohydrates into ethyl levulinate, furanic compounds and ethyl glycosides and of proteins into ethyl ester of amino acids was achieved. The optimization of reactive conditions was conducted using pure chemicals as model compounds. The effect of the co-presence of water was also considered. Then, real samples of sewage sludge (as dried and wet centrifuged samples) were reacted in ethanol in the presence of the appropriate combination of homogeneous Lewis-Brønsted acid catalysts, namely 1 %wt aluminium chloride hexahydrate and sulfuric acid respect to ethanol. After 6 h at 453 K, 99% of lipids and almost 60% of initial complex sugars were effectively converted into the abovementioned target products. Conversions and yields were quite similar to those obtained by reacting pure compounds singularly, confirming the robustness of the process and its applicability to differently composed sludge. At the end of the reaction, products were easily recovered and purified from the alcoholic phase, whereas only a very limited amount of solids remain as inert materials. Final refined biofuels have high calorific values (37 and 40 MJ kg−1) and actually represent the 68.5 and 59.2% of the initial energy content of starting sludge, respectively. This strategy combines valorization of the starting organic fraction of sewage sludge and a considerable reduction of final solid waste (in a stabilised form) to be disposed of. Finally, through a preliminary feasibility study, this acid ethanolysis resulted in a competitive alternative to the anaerobic digestion of mixed sewage sludge to obtain biofuels.

Heavy metals volatilization characteristics and risk evaluation of co-combusted municipal solid wastes and sewage sludge without and with calcium-based sorbents

Heavy metals, especially gaseous heavy metals, have high toxicity and do harm to human. Heavy metal volatilization characteristics of co-combusted municipal solid wastes (MSW) and sewage sludge (SS) from different mass fraction of MSW and SS, different temperature and different O2 concentration atmosphere was investigated. Performance of calcium-based sorbents was also studied. Volatilization efficiency of As, Cr, Cu, Ni, Pb and Zn in MSW was 100%, 45.89%–66.58%, 75.62%–92.45%, 42.33%–65.70%, 39.25%–68.76% and 53.57%–84.62%, and that in SS was 28.37%–40.75%, 33.78%–43.42%, 46.08%–56.69%, 35.04%–51.52%, 18.54%–44.99% and 14.72%–48.88%. Volatilization efficiency of heavy metals increased as mass fraction of SS in a blend decreased and as temperature increased. Volatilization efficiency of all heavy metals examined decreased as O2 concentration increased at high temperature and that of Cu, Pb and Zn increased as O2 concentration increased at low temperature. CaO, Ca(OH)2 and CaCO3 declined the volatilization of As, Cr, Cu, Ni, and Zn, while enhanced that of Pb. With calcium-based sorbents, volatilization efficiency of As, Cr, Cu, Ni, and Zn decreased from 70.06%, 39.91%, 75.52%, 44.08% and 40.10% to 54.24%, 33.73%, 39.98%, 20.56% and 32.06%, while that of Pb increased from 47.23% to 100%. Fitting formula was set to predict the heavy metals volatilization, and risk evaluation of gaseous heavy metals was exhibited.

МАТЕМАТИЧЕСКОЕ МОДЕЛИРОВАНИЕ СОВМЕСТНОЙ КОНВЕРСИИ УГЛЯ И ШЛАМА СТОЧНЫХ ВОД В ОБРАЩЕННОМ СЛОЕВОМ ГАЗОГЕНЕРАТОРЕ

Актуальность исследования обусловлена необходимостью утилизации бытовых и промышленных отходов. Утилизация горючих отходов, таких как шламы сточных вод, может быть совмещена с производством энергии для небольших потребителей. Одним из способов такой утилизации может стать газификация, позволяющая получить горючий газ, пригодный для получения тепловой и электрической энергии. Цель: на основании результатов математического моделирования оценить эффективность совместной конверсии шлама с более качественным топливом (бурым углем) при разных условиях проведения процесса (коэффициент избытка окислителя, состав топливной смеси, начальная влажность шлама сточных вод); оценить допустимую долю шлама в смеси с углем. Объект: процесс обращенной слоевой газификации смесей бурого угля и шлама сточных вод. Метод: математическое моделирование процесса слоевой термохимической конверсии твердых топлив с помощью разработанной ранее автором стационарной одномерной модели. Результаты. Построены расчетные зависимости характеристик процесса газификации (химический КПД, состав и калорийность газа) от удельного расхода дутья, отношения уголь/шлам (0–100 %) и начальной влажности шлама (10–40 %). Определены максимальные значения доли шлама в смеси с углем при фиксированном на уровне 60–70 % химическом КПД и максимальные значения химического КПД при фиксированной на уровне 20–30 % доле шлама в смеси с углем (для того чтобы избежать спекания слоя). При влажности шлама 40 % его максимальная доля в смеси с углем может достигать 50 % (при исключении спекания). Влага, содержащаяся в шламе, испаряется и выступает в качестве дополнительного газифицирующего агента. При ограничении доли шлама в смеси с углем на уровне 20–30 % эффективность газификации падает незначительно по сравнению с углем без добавок шлама.

Effects of Medium-Term Amendment with Diversely Processed Sewage Sludge on Soil Humification-Mineralization Processes and on Cu, Pb, Ni, and Zn Bioavailability.

The organic fraction of sewage sludge administered to agricultural soil can contribute to slowing down the loss of soil’s organic carbon and, in some cases, can improve the physical and mechanical properties of the soil. One of the main constraints to the agricultural use of sewage sludge is its heavy metals content. In the long term, agricultural administration of sewage sludge to soil could enhance the concentration of soil heavy metals (as total and bioavailable fractions). The aim of this research was to evaluate the effects of medium-term fertilization with diversely processed sewage sludge on the soil’s organic carbon content and humification–mineralization processes, on the physical–mechanical properties of soil and their influence on the pool of potentially bioavailable heavy metals, in order to assess their effectiveness as soil organic amendments. After eight years of sludge administration; an increase in the concentrations of bioavailable form was evidenced in all the heavy metals analyzed; independently of the type of sludge administered. The form of sludge administration (liquid, dehydrated, composted) has differently influenced the soil humification–mineralization processes and the physical–mechanical properties of soil. The prolonged amendment with composted sewage sludge contributed to keeping the soil humification–mineralization process in equilibrium and to improving the physical and mechanical qualities of the treated soil.

Occurrence, distribution, and potential influencing factors of sewage sludge components derived from nine full-scale wastewater treatment plants of Beijing, China

Millions of tons of waste activated sludge (WAS) produced from biological wastewater treatment processes cause severe adverse environmental consequences. A better understanding of WAS composition is thus very critical for sustainable sludge management. In this work, the occurrence and distribution of several fundamental sludge constituents were explored in WAS samples from nine full-scale wastewater treatment plants (WWTPs) of Beijing, China. Among all the components investigated, active heterotrophic biomass was dominant in the samples (up to 9478mg/L), followed by endogenous residues (6736mg/L), extracellular polymeric substances (2088mg/L), and intracellular storage products (464mg/L) among others. Moreover, significant differences (p<0.05) were observed in composition profiles of sludge samples among the studied WWTPs. To identify the potential parameters affecting the variable fractions of sludge components, wastewater source as well as design and operational parameters of WWTPs were studied using statistical methods. The findings indicated that the component fraction of sewage sludge depends more on wastewater treatment alternatives than on wastewater characteristics among other parameters. A principal component analysis was conducted, which further indicated that there was a greater proportion of residual inert biomass in the sludge produced by the combined system of the conventional anaerobic/anoxic/oxic process and a membrane bioreactor. Additionally, a much longer solids retention time was also found to influence the sludge composition and induce an increase in both endogenous inert residues and extracellular polymeric substances in the sludge.

Composição química da matéria orgânica de lodos de esgoto

Sewage sludge can be recycled in agricultural soil as a source of plant nutrients and in order to increase the organic matter content. The objective of this study was to characterize the organic fraction of sewage sludge (contents of carbon, nitrogen and total organic and inorganic phosphorus; concentrations of protein, fat, fiber, phenol and tannin) in order to assist in planning their use in agriculture. Five types of sewage sludge with differences were used for the later stages of chemical conditioning and / or complementary treatment for dehydration, three from anaerobic process: lime and ferric chloride, mechanically dehydrated (LAC); synthetic polymer and dehydrated mechanically (LAP); synthetic polymer and thermally dehydrated (LAS), and two aerobic digestion process: etching synthetic polymers with drying beds (LLP); LLP after the composting process in aerated piles mixed with bagasse from sugar and urban pruning debris, sludge compost (CL). The conditioning polymer and heat drying the organic matter retained in the residue, which was evidenced by the presence of higher concentrations of readily degradable organic compounds and carbon (337.24 g kg-1), nitrogen (39.02 g kg-1) and phosphorus (2.93 g kg-1) in the organic compartment. In all sludge was significant participation of the protein content in organic matter, which was approximately 43, 42, 28 and 25% for sewage sludge LAC, LAP, LAS, LLP and CL, respectively.

Enhanced Control of Fine Particle Emissions from Waste Biomass Combustion Using a Hybrid Filter

This work demonstrates the feasibility of a robust and effective control of the emissions of particulate matter (PM) and heavy metals (HMs) from olive tree pruning combustion, as well as from its blends with two customary local components (a composted fraction of sewage sludge and a fraction of municipal solid waste with a high plastic content), in an approximated proportion of 50/50 (% w.t) to mimic the seasonal supply variability. The study was carried out during a 5 weeks experimental campaign in a 1MWth fluidized bed combustor. The combustor was equipped with a hybrid filtration system, consisting of an electrostatic precipitator and a bag filter module serially connected, for an enhanced control of the PM emissions when dealing with a realistic suite of fuel blends. Raw aerosol showed high concentrations in both PM and HMs, substantially dependent on the blend. However, the hybrid filter (HF) showed a good performance irrespective of these variable loads, leading to emission concentrations below 7 mg/Nm3 (max. 7% O2, total basis), ensuring compliance with the probable emission limit values. Both mass and number filtration efficiencies ranged within 95–99%. The fractional efficiency has been measured in quasi-real time, thus enabling an assessment of the suitable operating conditions, as well as an evaluation of the reliability of HF operation. Removal efficiency for HMs was obtained and discriminated by size; results show differences among the elements considered, reflecting the differences in the chemical distribution over the size of the raw aerosol.