Sludge Organic Matter Research Articles

Combining chemical sequential extractions with 3D fluorescence spectroscopy to characterize sludge organic matter

The design and management of anaerobic digestion of sewage sludge (SS) require a relevant characterisation of the sludge organic matter (OM). Methods currently used are time-consuming and often insufficiently informative. A new method combining chemical sequential extractions (CSE) with 3D fluorescence spectroscopy was developed to provide a relevant SS characterisation to assess both OM bioaccessibility and complexity which govern SS biodegradability. CSE fractionates the sludge OM into 5 compartments of decreasing accessibility. First applied on three SS samples with different OM stability, fractionation profiles obtained were in accordance with the latter. 3D fluorescence spectroscopy revealed that the bioaccessible compartments were mainly constituted of simple and easily biodegradable OM while the unaccessible ones were largely made of complex and refractory OM. Then, primary, secondary and anaerobically digested sludge with different biodegradabilities were tested. Complexity revealed by 3D fluorescence spectroscopy was linked with biodegradability and chemical accessibility was correlated with sludge bioaccessibility.

Organic matter and pollutants monitoring in reed bed systems for sludge stabilization: a case study.

In this study, results about sludge stabilization and pollutant monitoring in a reed bed system (RBSs) situated in Central Italy (Colle di Compito, 4,000 p.e.) were presented. In order to evaluate the process of sludge stabilization, parameters that highlighted the biochemical, chemical and chemico-structural properties of organic sludge matter have been followed during the entire period of operation (7 years). Moreover, the trend of heavy metals (bioavailable fractions and total content) and toxic organic compounds (LAS, NPE and DEHP) was monitored during all the period. The trend of all parameters related clearly demonstrated that sludge stabilization successfully proceeded in RBS. Moreover, through statistical analysis modelling, it is possible to determine how the stabilization process proceeded in terms of organic matter mineralization and humification, and how these processes influenced the content of pollutant compounds present in the stabilized sludges.

Gas Extraction from Sludge as Acquired from Oxidation Ponds of Community Wastewater and Cassava-Factory Wastewater Treatment through Nature-by-Nature Processes

The study was aimed on determining the gas volume from sludge of oxidation ponds for community wastewater treatment and UASB tank of cassava factory for wastewater treatment in which the organic matters of both units were digested through the nature-by-nature process. The amounts of oven- dry weight sludge about 200 g were collected in the light brow glass bottle with 2.5-l capacity. The fermentation of organic matters in sludge is the process to produce gases and being transferred to store in chamber by fluid displacement. The gases from sludge of oxidation pond was occurred on the second day and the maximum on the sixth day with the rate of 70 ml/d and average of 36.02 ml/d (total 360.23 ml for 10 days) while cassava factory sludge found the maximum volume on the first day with the rate of 142.6 ml/d and average of 72.2 ml/d (total 649.97 ml for 9 days). In other words, the oxidation pond sludge can produce gas 1.8 ml/g (oven dry weight) while the cassava factory sludge found gas 3.25 ml/g (oven dry weight). Research results found gases of oxidation pond sludge on the range of methane concentration between 545,686 – 9,560,606 ppm, hydrogen sulfide 55.94 to 360.27 ppm, and ammonia ND to 36.22 ppm, while the cassava factory sludge found methane gas concentration between 729,404 to 9,900,837 ppm, hydrogen sulfide 5,894 to 68,050 ppm, and ammonia ND to 44.15 ppm.

Stabilisation and mineralisation of sludge in reed bed systems after 10–20 years of operation

Sludge stabilisation and mineralisation during periods of operation between 10 and 21 years were investigated in three different systems receiving sludge from urban wastewater treatment plants situated in Denmark. Samples were taken along the entire profiles, in order to compare the effectiveness of the sludge stabilisation process. Particular attention was given to the stabilisation process occurring within the reed beds; in fact, parameters correlated to biochemical properties of organic sludge matter were determined. Statistical procedures were used to evaluate how the biochemical processes influence the quality of sludge organic matter. The level of total organic carbon and total nitrogen had a similar trend along the profile: their concentration decreased with increasing depth, reaching very low levels at the deepest layers. The same trend was also observed for the water-soluble carbon, N-NH(3), β-glucosidase and urease activities, and hydrolytic enzymes linked to C and N cycles: their values decreased dramatically with increasing depth, meaning that the level of mineralisation of the organic matter was higher in the deepest layers. The determination of extracellular enzymes bound to humic substances and humic carbon permitted evaluation of the stabilisation of organic sludge matter, and also allowed individuation of the ways in which the sludge was stabilised, in terms of mineralisation and humification of the organic matter.

Organic matter stabilization in reed bed systems: Danish and Italian examples

In this study, results about sludge stabilization in reed bed systems (RBSs) after the entire period of operation in two different systems situated in Denmark (Helsinge 42,000 population equivalent (p.e.) - 10 years) and in Italy (La Fontina, 30,000 p.e. - 6 years) were presented. In order to evaluate the process of sludge stabilization, parameters that highlighted the biochemical and chemico-structural properties of organic sludge matter have been determined. The level of total and soluble nutrients, and enzyme activities, parameters related to overall microbial activity, showed that stabilization of the sludge similarly occurred in both RBSs, even though in different landscape ecosystems. The chemical-structural characterization of sludge organic matter highlighted how the processes of stabilization have occurred satisfactorily in both RBSs; in fact, significant levels of pyrolytic indices for mineralization and humification were reached. The successful stabilization of organic matter occurred in both RBSs and was confirmed by the absence of Escherichia coli, and also by the results of organic compounds (polycyclic aromatic hydrocarbons, linear alkyl benzene sulfonates, nonylphenol ethoxylates, di-2-ethylhexyl-phthalate) and heavy metals.

Review of Excess Sludge Disintegration Research

The resources of excess sludge exist in zoogloea and bacteria cells.Excess sludge disintegration technique enables the full release of the organic matter in sludge, so that nutrients, energy and other resources in sludge can be fully recycled, meanwhile, the reduction of sludge solids matter can be achieved.Excess sludge disintegration is necessary preprocessing to achieve the harmlessness, reduction and recycle goal of sludge disposal. This article describes the physical, mechanical, chemical, biological, and the combined sludge disintegration method, as well as the principle, characteristics, research progress, and the main research results of various sludge disintegration method.

Sewage Sludge Solar Drying: Experiences from the First Pilot-Scale Application in Greece

Increasingly strict regulations governing sludge management have raised interest in drying technologies. The feasibility of sewage sludge solar drying was experimentally evaluated in a 66-m2 pilot-scale greenhouse plant under typical weather conditions in Greece. The greenhouse was equipped with ventilation fans to maximize the drying process efficiency and a turning drum for efficient sludge mixing. The obtained results proved the applicability and the high performance of the solar drying technology. The time necessary to achieve a dry product with a dry solids content up to 95% ranged between 8 and 31 days, depending on the weather conditions. During drying, sludge organic matter was reduced by 5–21%, and total and fecal coliform content was also decreased up to three orders of magnitude. By taking into consideration the sludge content in heavy metals, the final product can partially or totally replace commercially available inorganic fertilizers in agricultural applications, in accordance with the restrictions imposed by national and European regulations. Based on a preliminary cost analysis concerning the construction of a solar drying facility covering a sum of 80,000 population equivalent (PE), a corresponding capital cost of 24 €/PE is anticipated.

The impact of intermediate thermal hydrolysis on the degradation kinetics of carbohydrates in sewage sludge

The purpose of this paper is to report the results, from laboratory-scale investigations, on the impact of intermediate thermal hydrolysis process (ITHP) on already digested sludge in general, and sludge carbohydrate content degradation process efficiency in particular. The ITHP performance data were compared with the performance of established conventional thermal hydrolysis process (THP). The degradation of sludge carbohydrates as a result of thermal pre-treatment and anaerobic digestion followed the first order kinetics. The overall sludge organic matter degradation kinetics rate constants indicated that the use of THP as an intermediate digestion step can enhance the already digested sludge organic matter degradation; further reducing the sludge mass and increasing its conversion to biogas.

Partial ozonation pre-treatment for sludge solubilization and simultaneous degradation of bisphenol A: quantification studies

Ozonation pre-treatment was investigated for the enhancement of sludge solids and organic matter solubilization and simultaneous degradation of bisphenol A (BPA), an endocrine disruptor compound from wastewater sludge (WWS). The ultrafast method (15 s per sample) used for the analysis of BPA in WWS is based on Laser Diode Thermal Desorption/Atmospheric Pressure Chemical Ionization coupled to tandem Mass Spectrometry. The statistical methods used for optimization studies comprised the response surface method with fractional factorial designs and central composite designs. The ozonation pre-treatment process was carried out with four independent variables, namely WWS solids concentration (15–35 g l −1), pH (5–7), ozone dose (5–25 mg g −1 SS) and ozonation time (10–30 min). It was observed that among all the variables studied, ozone dose had more significantly (probability (p)<0.001) affected the efficiency of the ozonation pre-treatment by increasing sludge solids (suspended solids (SS) and volatile solids) solubilization and organic matter (soluble chemical oxygen demand and soluble organic carbon) increment and BPA degradation from WWS. During the optimization process, it was found that higher BPA degradation (100%) could be obtained with 24 g l −1 SS, 6.23 pH with an ozone dose of 26.14 mg g −1 SS for 16.47 min ozonation time. The higher ozone dose used in this study was observed to be cost effective on the basis of solids and organic matter solubilization and degradation of BPA.

Alteration of sewage sludge biomass into oil-like products by hydrous pyrolysis methods

Various pyrolysis (also termed thermolysis) methods are common techniques that have been used to convert sewage sludge organic matter (OM) into useful fuels for energy. Reductive hydrous pyrolysis of OM increases the conversion yields of the sewage sludge. Our purpose is to study the effects of low temperature (<350°C) and experimental conditions in confined hydrous pyrolysis on the chemical compound compositions of the alteration products from municipal sewage sludge. These compositions have been determined by gas chromatography-mass spectrometry. Two sets of experiments were conducted at temperatures ranging from 200 to 350°C with contact periods of 48h. The reaction mixtures of the first set included only sewage sludge and water, whereas the second set also contained oxalic acid to provide excess hydrogen to enhance reduction of the organic matter of sewage sludge. The yields and the number of observed alteration products increased with higher temperature and presence of aqueous oxalic acid in the reaction mixtures. At lower temperatures n-alkanoic acids, n-alkanols and sterols were the major compounds. Hydrocarbon concentrations increased at higher temperatures in both experiment sets, except for UCM (unresolved complex mixture), which decreased >300°C. The n-alkanes increased dramatically with temperature increase both in the presence and absence of oxalic acid, where their yields were high in the former medium. Sterane concentrations also increased at elevated temperatures, being highest in the presence of oxalic acid. The products confirm that alteration of sewage sludge biomass in aqueous medium occurs rapidly and efficiently under reductive pyrolysis conditions, and in the temperature window of 250–350°C. These results show that the product yields are higher by a factor of 1.4 under reductive hydrous pyrolysis versus hydrous pyrolysis conditions.

Sludge Bio-drying Process at Low Ambient Temperature: Effect of Bulking Agent Particle Size and Controlled Temperature

Sludge bio-drying is an aeration process for the removal of water. The drying process utilizes the bio-heat generated from aerobic degradation of organic matter in sludge. In this study, four trials were run in the winter season at ambient temperatures of between 3°C and 9°C. The physical and chemical changes that occurred during the process were investigated and the impacts of the particle sizes of bulking agents and the controlled-matrix temperature were assessed. Results indicated that the process can start up in winter with a three-day lag, while the total duration was only seven days. The highest water removal rate (of 31.0%) with the least organic matter loss (of 12.2%) was obtained at a lower controlled matrix temperature (of 43°C) with a bulking agent of mixed particle size. As a common bulking agent, straw, which has a small particle size of 2–5 mm, was beneficial for organic matter degradation, while it had a negative effect on water removal. The use of different types of straw (with larger particle size of 20–30 mm) as the bulking agent gave poor performance, in which the organic matter degradation rate was 9.75% and the water removal rate was 25.9%. Higher controlled temperature (53°C) resulted in less aeration but degradation rates were enhanced to 16.8%. The using of lower temperatures (43°C) resulted in lower water removal rate (of 29.2%) and relatively lower biodegradation rate.

Anaerobic Removal of Trace Organic Contaminants in Sewage Sludge: 15 Years of Experience

Trace organic contaminants (TOCs) correspond to a broad range of molecules generated either directly or indirectly by human activity. Even though TOCs are found at low concentrations in the environment, they often accumulate by biomagnification and bioaccumulation into biological organisms and cause irreversible damages in biological systems through direct or indirect toxic effects such as endocrine disruption and tumour initiation. This manuscript presents the main findings of over fifteen years of research focusing on biological removal of various TOCs found in sewage sludge from urban treatment plants. A special focus of the research was made on microbial processes in complex anaerobic ecosystems. Four families of compounds mostly retrieved in urban plants were studied: the polycyclic aromatic hydrocarbons (PAHs), the polychlorobiphenyls (PCBs), the phthalic acid esters (PAEs), and the nonylphenol ethoxylates (NPEs). It was observed that the microbial capability for removing low amounts of TOCs required a long adaptation time and was often limited by the bioavailability of these compounds. In fact, the overall biodegradation resulted from the numerous interactions existing between the matrix (organic matter) and the microbial ecosystems according to the physico-chemical sorption properties of these compounds. Mechanistic aspects were also tackled in depth and specific models were developed for better understanding the network of interactions between TOCs, microorganisms, and organic matter. These findings could be extrapolated to other ecosystems such as soils and sediments. Finally, it was shown that microbial cometabolism was essential for TOC removal, and the concept of bioavailability was not only dependent on the nature, the level, and the sorption properties of TOCs but was also strongly dependent on the nature and the concentration of the sludge organic matter. Specific parameters were proposed for better evaluating the fate of TOCs in microbial anaerobic processes and technological solutions for efficient removal of these compounds were also proposed.

Pollutant monitoring in sludge treatment wetlands

Phragmites australis for sludge dewatering and stabilization processes have been widely proved. The presence of reeds, indeed, efficiently allows solids dewatering and organic matter stabilization in order to obtain a stabilised product that can be suitable for land application, even if its environmental impact has to be considered. The actual revision of the European Union's Working Document on Sludge (2000), in fact, seems to be addressed to detect two principal categories of pollutants in sludge for agricultural use: heavy metals and toxic organic compounds. In this study are presented results about sludge stabilization and monitoring of heavy metal fractionation and organic compounds in four urban wastewater treatment plants managed by Acque S.p.A., (Tuscany, Italy). To evaluate the process of sludge stabilization parameters were determined that highlight the biochemical and chemico-structural properties of sludge organic matter. The results showed that stabilization of the sludge over time occurred as shown by the low content of water soluble carbon and dehydrogenase activity, and by the re-synthesis of humic-like matter highlighted by the pyrolytic indices of mineralization and humification. Results about fractionation showed that heavy metals were retained in fractions related to the stabilized organic matter. Moreover, toxic organic compounds showed a drastic reduction at the end of the monitoring period.

Improved electricity production from sewage sludge under alkaline conditions in an insert‐type air‐cathode microbial fuel cell

AbstractBACKGROUND: Electricity can be generated directly from sewage sludge with a microbial fuel cell (MFC), combining degradation of organic matter. This study constructed a novel insert‐type air‐cathode microbial fuel cell (ITAC‐MFC) as an alternative to a sediment‐type MFC and a two‐chambered MFC for the generation of bioelectricity and the degradation of sewage sludge organic matter. Meanwhile, a pH adjustment was carried out to enhance substrate bioavailability of sludge and to suppress methane production in the MFC.RESULTS: A maximum power density of 73 ± 5 mW m−2 was obtained at sludge pH 10.0, much higher than those of 33 ± 3 and 4 ± 0.5 mW m−2 obtained at pH 8.0 and 6.0, respectively. It was observed that the soluble chemical oxygen demand (SCOD) of sewage sludge at pH 10.0 was almost three times greater than that at pH 6.0. At the same time, the total chemical oxygen demand (TCOD) removal and coulombic efficiency (CE) at pH 10.0 were also much higher than at the other two conditions.CONCLUSIONS: The results demonstrated that improved electricity production and organic degradation could be achieved by maintaining the sludge pH at 10.0 in an MFC. ITAC‐MFC offers an attractive alternative for the environmentally‐friendly removal of organic matter in sewage sludge. Copyright © 2011 Society of Chemical Industry

Efeito da digestão anaeróbia e da estabilizção com cal na mineralização do carbono e do azoto de lamas de ETAR

This work aims to evaluate the N and C mineralization in a Haplic Arenosol amended with 3 different sewage sludge: mixture of primary and secondary sewage sludge (MSS), anaerobically digested sewage sludge (DSS) and anaerobically digested sewage sludge treated with quicklime (LimeDSS). Two aerobic incubations, one to follow N mineralization and the other one to assess CO2 emissions, were performed during 140 days. MSS promoted soil N immobilization during the first days of incubation and higher CO2 emissions (46% of the applied C was lost), consequence of a high content of non-stabilized organic matter. In DSS there was nitrogen net mineralization but only 17% of the applied carbon was mineralized, showing that anaerobic digestion stabilized the sludge organic matter. Sewage sludge treatment with quicklime reduced its NH4+ content, but enhanced carbon (40%) and nitrogen (39.2%) mineralization after soil application. Anaerobic digested sewage sludge (DSS) seems to be the most interesting treatment, since it ensured a high level of available N to plants and a great contribution to C sequestration in soil.

Effects of thermally dried and composted sewage sludges on the fertility of residual soils from limestone quarries

Limestone quarrying reduces the land's capacity to support a complete functional ecosystem. Adding sewage sludge to mining residues facilitates the establishment of a vegetation cover and can stimulate C and N cycling. We aimed to evaluate the effects of three composted and three thermally dried sewage sludges, on some biological properties of two types of debris (extraction soil and trituration soil) from a limestone quarry. Lysimeters filled with debris-sludge mixtures and control soils were sampled immediately after preparation and after being left in the open for 13 months. Total carbohydrates (TCH), 0.5 M K 2SO 4 extractable (ECH) carbohydrates, 0.5 M K 2SO 4 extractable organic C (EOC), microbial biomass carbon (MBC), microbial respiration (MR), β-glucosidase activity and β-galactosidase activity were determined immediately after sampling. The treated soils were also analyzed for their more general physicochemical characteristics. Adding sewage sludge clearly improved the physicochemical and biological properties of the residual soil and the effect of the type of sludge was greater than that of the type of soil. The sludge effect was generally more durable over the trituration soil. The sludge effect decreased the most in MR and EOC followed by MBC and ECH. Total carbohydrates showed the least enhancement but the sludge effect on this endpoint had the smaller decrease with time. Root exudates and plant debris contributed to β-glucosidase and β-galactosidase activities in the treated soils. Activities present in mixtures partly corresponded to enzymes free in the soil aqueous face. β-Glucosidase was also partly associated with humified organic matter. Thirteen months after sludge addition a fraction of the organic matter present in soils was still moderately labile. Results observed in BMC and MR suggests the sludge did not cause major toxic effects on residual soils. The sludge effect differed with the pre and post treatments of the sludges; thermal drying made the sludge organic matter more easily decomposable.

Efficiency assessment of a reed bed pilot plant ( Phragmites australis) for sludge stabilisation in Tuscany (Italy)

‘Abstract The aim of this study is to investigate the efficiency of a reed bed pilot system planted with macrophytes ( Phragmites australis ) in the stabilisation and dewatering of sludge. The water content of sludge was positively correlated with the biochemical activity (i.e. dehydrogenase activity (DH-ase) and respiration rate) under a wide range of redox conditions (aerobic–anaerobic). Mineralization processes seemed to be uninfluenced by seasonal changing. The metabolic index given by the ratio DH-ase/WSC increased with time from 0.007 to 0.02, implying that sludge organic matter mineralization was approaching maximum efficiency. Aerobic mineralization processes were quickly activated, as shown by the production of ammonia at 3 days and nitrate at 15 days. Nitrates conditioned the redox potential of sludge to relatively high values: from +50 to +150 mV in summer and +10 to +100 mV in winter. The positive redox potentials supported the organic carbon respiration because nitrates function as electron acceptors in the absence or scarcity of free atmospheric oxygen in the deeper layers. All these factors allow the system to (i) operate longer, with high loads applications of sludge and in any climate conditions, thereby making feasible onsite sludge stabilisation and thickening, and (ii) avoid frequent sludge transportation outside the wastewater treatment plant.

Degradation and characteristic changes of organic matter in sewage sludge using microbial fuel cell with ultrasound pretreatment

Microbial fuel cell (MFC) could be an efficient sludge treatment unit in regard of rates and extents of total chemical oxygen demand (TCOD) removal, particularly when ultrasound was applied to pretreat the sludge. This study characterized the organic matter in sludge before and after MFC treatment, with or without ultrasound as a pretreatment stage. The 5-d MFC tests with electric load significantly enhanced TCOD removal rate from 11.3% to 19.2% for raw sludge and from 25% to 57% for sludge pretreated with >0.6 W ml(-1) ultrasound, using conventional anaerobic digestion test (without electric load) as control. The aromatic proteins, soluble microbial byproduct-like fluorescent compounds and carboxylic components, aliphatic components (C-H related), hydrocarbon and carbohydrate materials were identified to be principally released by ultrasound pretreatment and the fuels in the present MFC study.

Performances of soluble metallic salts in the catalytic wet air oxidation of sewage sludge

Various soluble transition metal salts were compared in the wet air oxidation of industrial and municipal sewage sludges (2.5–25 g L −1 total organic carbon) at 200–250 °C under 4–15 bar O 2 partial pressure. The evolution of the TOC content in both the liquid and solid phases, and the overall TOC conversion were monitored. While copper sulphate prevented the dissolution of the suspended organic matter due to strong bounding of copper to a fraction of the organic matter in sludge, and showed high activity in the mineralization of the solubilized organic compounds (liquid phase), the implementation of iron sulphate resulted in a higher transfer of the organic matter to the liquid phase but in a moderate activity in the oxidation of solubilized molecules. When used in combination, a synergetic effect between these two salts was evidenced.

Organic matter extracted from activated sludge with ammonium hydroxide and its characterization

In order to characterize the organic properties of waste activated sludge in a wastewater treatment plant, organic matter within sludge was extracted with NH 3·H 2O preferentially, and subsequently fractionated into five fractions using XAD-8/XAD-4 resins. Up to a 63.8%–71.1% of organic matter within the sludge could be efficiently extracted by NH 3·H 2O. Fractionation results showed that hydrophobic acid and hydrophilic fraction were two main components among the sludge organic matter (accounting for 32.2% and 48.0% of the bulk organic matter, respectively), whereas transphilic acid, hydrophobic neutral and transphilic neutral were quite low (accounting for 9.2%, 5.8% and 4.8%, respectively). Despite that the extractant of NH 3·H 2O showed a relatively higher extraction efficiency of the aromatic components, the relatively low aromaticity of the organic fractions implied that those non-aromatic components could also be effectively extracted, especially for neutral and hydrophilic fractions. In addition, acidic fractions contained more aromatic humic-like components, whereas the neutral fractions had a greater content of aromatic proteins and soluble microbial byproduct-like components. Extraction of sludge organics with NH 3·H 2O and subsequential fractionation using XAD resins could be a novel method for further characterization of sludge organics.