Wastewater Sewage Sludge Research Articles

Scaling up self-sustained smouldering of sewage sludge for waste-to-energy.

Self-sustained smouldering combustion presents strong potential as a green waste-to-energy technique for a range of wastes, especially those with high moisture content like wastewater sewage sludge. While well-demonstrated in laboratory experiments, there is little known about scaling up this process to larger, commercial reactors. This paper addresses this knowledge gap by systematically conducting and analyzing experiments in a variety of reactors extending beyond the laboratory scale. This work reveals a robust treatment regime; however, it also identifies potential complications associated with perimeter heat losses at scale. Two key impacts, on the smouldering reactions and the air flow patterns, are shown to potentially degrade treatment if not properly understood and managed. Altogether, this study provides novel insight and guidance for scaling up smouldering science into practical, waste-to-energy systems.

Mathematical modelling of water sorption isotherms and thermodynamic properties of wastewater sewage sludge

Abstract This study was aimed at determining wastewater sewage sludge moisture sorption characteristics using a static gravimetric method at 303 K, 313 K and 323 K. Eleven mathematical models were adopted to simulate the experimental data, and the optimal model was analysed. The indexes included the net isosteric heat of adsorption (qst), differential entropy (△S), spreading pressure (π), net integral enthalpy (qin) and net integral entropy (△Sin) to evaluate the thermodynamic properties of the sludge. The isotherm curves exhibited type II behaviour according to the Brunauer--Emmett--Teller classification. The sorption isotherm fitting showed that the Gugghenheim--Anderson--de Boer model was able to reproduce the equilibrium moisture content evolution with water activity for a moisture range varying from 6% to 89% (0.991 < R2 < 0.999). The net isosteric heat of sorption and differential entropy were evaluated through direct use of moisture isotherms via the Clausius–Clapeyron equation and used to investigate the enthalpy–entropy compensation theory. The net isosteric heat and differential entropy obviously decreased as the equilibrium moisture content increased, which satisfied the compensation theory. The spreading pressure of the sludge sorption process decreased as the temperature increased at a given water activity and increased as the water activity increased at a given temperature. When the spreading pressure was at a fixed level, the net integral enthalpy decreased as the equilibrium moisture content increased, whereas the net integral entropy decreased as the equilibrium moisture content increased to a minimum value of −93.17, −98.34 and −93.28 J/(mol.K) at 303 K, 313 K and 323 K, respectively, and then tended to increase.

Overview on Bioconversion of Domestic Wastewater Sewage Sludge into Green Energy: Biogas and Hydrogen

Municipal wastewater treatment plants generate large amounts of sludge after a set of unit processes. The sewage sludge is an important resource for energy production because of its high level of biodegradability. Sewage sludges are generally made of non-toxic and biodegradable organic compounds mixed with a small fraction of non-toxic and toxic inorganic compounds having a very low biodegradability. The large fraction of biodegradable matter constitutes a pool for green/clean energy to be used for industrial and domestic applications. The generated energy can also be used in the wastewater treatment plant. Currently, fossil fuels are leading the energy world, however, they are being depleted and are considered to be among the main causes contributing to climate change and global warming. Domestic sewage sludge can be converted sustainably into bio-hydrogen and bio- methane. This conversion is achievable through anaerobic digestion, combustion, pyrolysis and gasification. With regard to the last three conversion processes, the organic and inorganic toxic compounds are eliminated. Production of biogas from sewage sludge is being undertaken worldwide on small, medium, and large scales. However, hydrogen production from sludge is still developing. There is an existence of substantial knowledge in this field, the production of hydrogen and biogas from sewage sludge is gaining interest. This study analyses various possibilities of sewage sludge conversion into clean energy. The analysis focuses on the technology strengths, weaknesses and gaps to be improved in future studies.

Current status of biomethane production using aqueous liquid from pyrolysis and hydrothermal liquefaction of sewage sludge and similar biomass

Pyrolysis and hydrothermal liquefaction (HTL) are potential technologies for renewable energy production and waste valorization using municipal wastewater sewage sludge and other lignocellulosic biomass. However, the organic-rich aqueous pyrolysis liquid (APL) and HTL aqueous phase (HTL-AP) produced currently have no apparent use and are challenging to manage. Furthermore, the toxic organic compounds in them can be harmful to the environment. Anaerobic digestion (AD) may be a viable method to manage the liquids and recover energy in APL and HTL-AP in form of methane-rich biogas. Integrating thermochemical processes with AD could promote a circular economy by recovering resources and reducing environmental pollution. The challenge, however, is the presence of toxic compounds recalcitrant to anaerobic biodegradation such as phenols and nitrogen-containing organics that can inhibit methane-producing microbes. This review presents information on APL and HTL-AP characterization and biodegradability. Feedstock composition and process operational parameters are major factors affecting APL and HTL-AP composition, subsequent toxicity, and degradability. Feedstocks with high nitrogen content as well as increased thermochemical processing temperature and retention time result in a more toxic aqueous liquid and lower methane yield. Dilution and low AD organic loading are required to produce methane. More comprehensive APL and HTL-AP chemical characterization is needed to adopt suitable treatment strategies. Pretreatments such as overliming, air stripping, partial chemical oxidation, adsorption, and solvent extraction of toxic constituents as well as co-digestion and microbial acclimatization successfully reduce toxicity and increase methane yield.

Effect of Temperature on the Hydrotreatment of Sewage Sludge-Derived Pyrolysis Oil and Behavior of Ni-Based Catalyst

The high-energy potential of wastewater sewage sludge (SS) produced in large amounts around the world makes it an attractive feedstock for fuels and energy sectors. Thermochemical valorization relying on pyrolysis of SS followed by hydrotreatment of pyrolysis oil (Py-SS) might even allow the integration of SS into existing oil refineries. In the present study, catalytic hydrotreatment of Py-SS was performed over a NiCuMo-P-SiO2 catalyst in a batch reactor at temperatures in the range of 200–390 °C. Due to sulfur presence in the feed, the increasing reaction temperature induced in situ transformation of metallic Ni into Ni3S2 in the catalyst. In contrast, the Ni3P active phase possessed remarkable stability even at the harshest reaction conditions. The oxygen content in the reaction products was decreased by 59%, while up to 52% of N and 89% of S were removed at 390 °C. The content of free fatty acids was greatly reduced by their conversion to n-alkanes, while the larger amount of volatile aromatics was generated from high molecular mass compounds. The quality of oil-derived products greatly changed at elevated temperatures, providing strong evidence of effective upgrading via decarboxy(ny)lation, hydrogenation, and hydrocracking transformations.

Energy conversion from wastewater sewage sludge

AbstractNatural rubber‐based industries in Southern Thailand are generating concentrated latex sewage sludge (CLS), which is commonly managed by landfilling practice that is causing serious environmental hazards. The purpose of this study was to develop a method to produce pellets using CLS and para‐wood sawdust as a potential biomass source for energy generation. The process started with dewatering the CLS through a decanter centrifuge. Then a flat die pellet mill was applied for copelletization. Finally, the pellets were investigated to evaluate the higher heating value and toxic heavy metals (Cu, Zn, Cr, As, Cd, and Pb) using proximate ‐ ultimate analysis, fourier transform infrared analysis, scanning electron microscopy, calorific value, thermogravimetric analysis, atomic absorption spectrometer, and inductively coupled plasma optical emission spectroscopy. The results showed that the addition of the para‐wood sawdust resulted in higher heating value and lower ash content of 3,620 ± 12 kcal/kg and 4.93 ± 0.98%, respectively. Besides, it has increased the carbon content of the pellet from 28.23 to 46.26% highest among all the samples. Furthermore, the method developed in this study is not only environmentally friendly but also economically sound than the earlier management of CLS.

Aloe sp. leaf gel and water glass for municipal wastewater sludge treatment and odour removal.

Aloe gel (Alg), which is a natural extract from the Aloe sp. plant, was evaluated in this study for its potential use as a bioflocculant to treat urban wastewater sewage sludge. The gel was used alone and combined with water glass (WG) under controlled conditions in laboratory experiments. Alg was found effective to settle the flocculated sludge rapidly and remove distinctive unpleasant odours of the sludge as highlighted by gas chromatography-mass spectrometry (GC/MS) analysis. Furthermore, Alg was pH tolerant and had no effect in changing the pH of the wastewater. The optimum dose of Alg was 3% at which a sludge volume index (SVI) of 45.4 mL/g was obtained within 30 min settling time. To enhance the treatment performances of Alg, WG was also evaluated as an alkali agent to further reduce the chemical oxygen demand (COD) and ammonia (NH4-N) in the wastewater. At equal doses of 3% of WG and Alg each, the combined treatment outcomes showed high turbidity and NH4-N removals of 83 and 89%, respectively, but the overall COD removal was at best 25%. The settling rate of treated sludge with combined Alg/WG was very rapid giving an SVI of 25.4 mL/g within only 5 min.

Investigation of polycyclic aromatic hydrocarbons (PAHs) formed in three-phase products from the pyrolysis of various wastewater sewage sludge

This study investigated the presence and concentration of 16 U.S. EPA priority controlled PAHs in gas, bio-oil and residues from the pyrolysis of different sewage sludges. We studied the temperature as a key influential factor for the formation of 16 targets PAHs and the effect of sludge source on the distribution of different molecules’ PAHs were analyzed. Results showed that most of the 16 PAHs were formed during sludge pyrolysis and mainly ended up in bio-oil and gas. The distribution of PAHs in bio-oil was mostly dependent on pyrolysis temperature. With the increase of pyrolysis temperature from 450℃ to 850℃, it has been observed an increase of PAHs concentration in the bio-oils as follows: 16 % (ISS), 1.3 % (food manufacture wastewater sludge, FSS), 194 % (printing and dyeing wastewater sludge, PDSS), 334 % (DSS). 2, 3 and 4-ring PAHs dominate, and their total mass proportion is over 70 %. In gas, the types and concentrations of PAHs were less than in bio-oil. PAHs yield in solid was very low, and a trace content of PAHs of 0.0161 mg kg−1 was detected from the solid after the pyrolysis of DSS, while PAHs in solid for ISS and FSS are even non-existent and would cause fewer environmental problems.

Influence of drying methods on the thermodynamic parameters, effective moisture diffusion and drying rate of wastewater sewage sludge

In this study, thin layer drying experiments of direct and indirect natural convection solar drying of wastewater sewage sludge in Algeria were conducted. The purpose of these was to analyze the effect of two methods of drying on different parameters, namely: drying rate, efficient diffusion of moisture, and thermodynamic parameters. Three new universal drying kinetic models were proposed and compared with four other models existing in the literature to model the drying process. The effective diffusivity of moisture of sludge (Deff) changed from 1.91 10−8 to 9.12 10−8 m2 s−1. It was obtained by using Fick's second law, based on the resolution by Laplace's transformation method and the Fourier series. Thermodynamic parameters, to know, activation energy, free energy change, enthalpy and entropy change, were also determined using a new methodology build on the evolution of effective diffusion coefficient in terms of temperature by adopting the Eyring equation.

Biocarbon from Sewage Sludge As Anode Catalyst for the Production of Bioelectricity in an MFC

Over the last few years, the use of novel anode carbon catalysts from biomass as raw materials in Microbial Fuel Cells (MFC) has been increasingly investigated due to their catalytic properties and low cost compared to noble metals such as Pt. Nevertheless, it is acknowledged that the use of a catalyst in an MFC is not sufficient to generate bioenergy. A biofilm of electroactive bacteria must be grown on the catalyst surface, forming a bioanode. The combination of catalyst and biofilm oxidizes organic matter contained in substrate, promotes the electron transfer kinetics and thus enhances the generation of bioelectricity. In this work, a biosolid from waste water sewage sludge from the food industry has been pyrolyzed and activated with KOH in N2 atmosphere in order to obtain a biocarbon. The biocarbon has been further functionalized with methanol in different concentrations (0.15, 0.5 and 1.0 M) aiming to enhance its biocompatibility with electroactive Bacillus subtilis (B. subtilis), used as microorganism. With these components, bioanodes have been fabricated using gas diffusion carbon cloths on which a catalytic layer containing the biocarbon have been painted using the brush method, followed by the growth of a biofilm of B. subtilis for 6 days in broth media. The biocarbon was physicochemically characterized by XRD, SEM-EDS and FESEM. XRD patterns indicate that the material is amorphous in nature with a broad (002) peak attributed to graphitic structures. Some reflections attributed to crystalline phases are also observed. EDS analysis shows the presence of C, O, Na, Mg, Al, Si, P, S, Cl, K, Ca, Ti and Fe in the biocarbon. On this matter, the biosolid shows a composition of 72.0, 18.96, 2.96 and 0.22 (wt. %) of C, O, Si and K, respectively. The biocarbon has a reduction in C content (29.23 wt. %), with an increase in O (23.54 wt. %) and K (17.29 wt. %), attributed to the activation with KOH. Moreover, the biocarbon shows biocompatibility with B. subtilis as indicated by morphology analysis by FESEM. The biocarbon + B. subtilis bioanodes have been characterized in a half-cell with pharmaceutical waste water (PWW, pH= 6.1) as the electrolyte. The cyclic voltammograms (CVs) show their biocatalytic activity, generating a high current density from the PWW compared with the electrodes without biofilm. The results indicate that biocarbons from waste water sewage sludge are promising catalysts for MFC anode applications, due to their biocompatibility with bacteria and because their chemical composition may enhance the microbial metabolism mechanism, enhancing the performance of the bioelectrochemical device.

The Co-fermentation of Organic Substrates: A Review Performance of Biogas Production under Different Salt Content

Sustainable development is the projected demand of all nations at present. Only 20 percent of world’s primary energy requirement is met by renewable sources like solar and wind energy, hydropower, biomass, municipal and agri-wastes. Biomass, can be utilized to produce biogas due to its high biodegradability, calorific value and nutritive value to microbes, which will reduce our dependency on fossil fuels so that These organic wastes require being managed in a sustainable way to avoid depletion of natural resources, minimize risk to human health, reduce environmental burdens and maintain an overall balance in the ecosystem. The annal of the National Office of Statistics (NOS) indicated that municipal solid waste overtook more and more million tons in 2016, almost 3.5 times the 1992 rates. About 40–70% of civilian solid waste CSW is composed of civilian biomass waste (CBW), such as kitchen waste (KW), fruit/vegetable remains (FVR) and waste water sewage sludge (WWSS). There was a need to find several ways to deal with such wastes. One of these methods is the anaerobic digestion process, as a waste management system, has risen due to it has the usefulness of lowering volume and getting back energy. Several physical and chemical factors influence the creation of methane, and inhibition of bio-methane efficiency by certain materials (salts, oils, ammonia and toxic substrates ) may take place when inhibitors levels appear in high concentrations. In addition, high salt in the organic substrates can inhibit the activity of fermentation microbes by impacting the osmotic pressure of the cell wall of bacteria in the anaerobic system. The purpose of this study was to discuss the effect the types of substrates and salt content on biogas generation in anaerobic digestion.

Design and 3-D simulation of a mixed mode solar barn drier for drying wastewater sewage sludge

The paper presents a preliminarily study on an efficient, inexpensive and energy saving solar batch dryer for drying sludge. A concept of a mixed mode solar dryer was developed and designed. Air heated by the solar flat heater was forced through drying chamber by electric fans. A 3-D physical model was used to observe and predict the operation of the solar batch dryer at different time under designed conditions. The thermal performance and air movement of drying chamber in the designed dryer unit were evaluated through ANSYS-FLUENT software. By determining the external conditions, localization and the material properties, the model can predict temperature and humidity distributions in the designed drying chamber and sludge material layers, air-flow field according to the radiation and convection, as well as water quantity evaporated from the sludge. A special attention was paid to implementation of physical boundary conditions on the sludge surface, which is between air and dried sludge. The developed solar barn dryer can heat air at average temperature between 47?C and 57?C, which is optimum for dehydration of the sludge. The designed drying chamber can generate an adequate fow of hot air to increase the drying rate by above 30%.

An expeirmental investigation into mechanism of high temperature steam gasification of wastewater sewage sludge

High temperature steam gasification experiments were conducted to gasify sludge in an electrically heated tubular furnace at 650, 750, 850, 950, and 1050?C. The obtained results develop a mechanistic understanding on steam gasification of sludge from starting constituents to final products. The introduction of steam led to a steam reforming of the tar and CnHm compounds, and a partial gasification of the solid char and CH4, which contributed to the generation of rich H2 and CO. The steam gasification process can be divided into three significant stages. As temperature increased, a decreasing absorbance amount of C-Har and C-O and a large reduction of C = O were accompanied with an evident reduction of tar yield and an increasing gas yield, especially the increase of H2 and CO contents. The H2 and CO were the indicator for the occurrence of tar and CnHm steam reforming. In addition, more micro-pores generated in solid char and a sharp increase of Brunauer-Emmett-Teller (BET) surface from 24.2 m2g?1 to 75.4 m2g?1 showed the occurrence of char decomposition. An increasing content of polycyclic aromatic hydrocarbons (PAH) with 2 and 3 rings and a significant decrease of PAH with 4-6 rings in tar showed the tar cracking and reforming of non-condensable intermediates.

Enhanced sludge dewatering based on the application of high-power ultrasonic vibration

Interest in producing heat and power using municipal wastewater sewage sludge as a fuel is increasing worldwide. Since its water content is initially high, sludge must be dewatered and further dried if it is to serve as an effective fuel for combustion. However, to maximize net energy production, the drying processes must use as little energy as possible.The water content in sewage sludge comprises both unbound and bound water. Unbound water content is typically extracted using a number of mechanical dewatering techniques. In terms of total solids content (TS), dewatering processes can take sludge from an initial 3–5% to a more solid 25–45% TS with minimal energy expenditure. However, this level of dryness is not sufficient for effective combustion.To produce an effective fuel, TS levels must be increased. Achieving high level of dryness involves removing any remaining unbound water and substantial bound water content as well. Heat is normally applied to accomplish this by changing the phase of the water from liquid to vapor. Although dewatering is energy-efficient, thermal drying is not. The energy used to thermally dry sludge can be two orders of magnitude greater than the energy used for dewatering. Therefore, to expend as little energy as possible to achieve the needed dryness, conventional dewatering processes clearly must be improved.This paper describes work carried out to identify promising ways to efficiently enhance the dewatering and drying of sewage sludge. Available dewatering approaches were reviewed and experiments were carried out to examine the relative effects of temperature, atmospheric pressure, and high-power ultrasound. The high-power ultrasound approach seemed to be particularly effective. The mechanisms involved include atomization, microstructural effects, cavitation, and the sponge effect, which work to reduce both internal and external resistances. Applied in the right way, ultrasound could become a very effective way to enhance mechanical dewatering.

Simultaneous Determination of alfa-, beta- and gama-hexabromocyclododecane Diastereoisomers in Sewage Sludge using Liquid Chromatography Tandem Mass Spectrometry

Hexabromocyclododecane (HBCD) is a large-scale usage brominated flame retardant consisting of a mixture of diastereoisomers which has been reported as an ubiquitous environmental contaminant. HBCD has attracted much attention due to its toxicity and increasing levels in waste water sewage sludge. Since November 2014, HBCD was added to the Persistent Organic Pollutants list of the Stockholm Convention which generated a higher concern regarding its presence in the environment. A rapid (8 min) and accurate liquid chromatography electrospray ionization tandem mass spectrometry method (LC-ESI-MS/MS) was developed to separate and detect a-, b- and g-HBCD isomers from sewage sludge. Optimization of LC-MS parameters (column temperature, mobile phase composition and flow, collision energy, fragmentor voltage, capillary voltage and drying gas temperature) allowed complete separation of the three isomers and also very good detection sensitivity with instrumental quantitation limits (IQLs) between 0.3 and 0.6 ng/mL. The three isomers were separated on a C18 reversed-phase column, kept at 18�C, using a H2O/ACN/MeOH mobile phase mixture and detected by negative electrospray ionization using MRM mode with two transitions, one for quantitation and one for confirmation. MS detector response was linear in the range 1.0 � 100.0 ng/mL with correlation coefficients (R2) higher than 0.99 for all three isomers. A simple ultrasonic assisted liquid-solid extraction procedure using a solvent mixture was employed to extract HBCD isomers from WWTP sewage sludge. Overall method intra-day and inter-day precision (RSD%) were situated between 7.6 � 9.2% and 10.3 � 14.5%, respectively. LOQs for a-, b- and g-HBCD were 1.4, 0.7 and 1.0 ng/g, comparable and even lower to those reported by similar studies concerning HBCD presence in WWTP sewage sludge. HBCD presence was tested from several WWTP sludge samples. All three isomers were found with 100% detection frequency ranging from 3 to 76 ng/g.

Enhanced Biotransformation of Triclocarban by Ochrobactrum sp. TCC-1 Under Anoxic Nitrate Respiration Conditions.

Antimicrobial triclocarban (3,4,4'-trichlorocarbanilide, TCC) is frequently detected in soils and sediments for the widely reclaim of sewage sludge or biosolid in recent decades. This resulted from a weak removal of TCC during wastewater treatment, and most of it adsorbed onto sewage sludge. As the toxicity and persistence of TCC in the environment, the elimination of TCC from the source of output is of great importance, particularly in anoxic process. In this study, the biotransformation of TCC by a newly isolated TCC-degrading strain Ochrobactrum sp. TCC-1 under anoxic conditions was investigated. By testing different carbon nitrogen ratios (C/N), it showed that nitrate could support the growth of strain TCC-1 and enhance the hydrolysis of TCC to more biodegradable chloroanilines, especially with a higher C/N of 10 and under anaerobic conditions. In wastewater sewage sludge, strain TCC-1 colonized and maintained the TCC-hydrolyzing activity under the nitrate respiration mode. These results would lay a basic foundation for the potential bioremediation of TCC-contaminated anoxic sites with TCC-degrading strain.

Ex-situ catalytic pyrolysis of wastewater sewage sludge – A micro-pyrolysis study

Concerns over increasing amounts of sewage sludge and unsustainability of current disposal methods have led to development of alternative routes for sludge management. The large amount of organics in sewage sludge makes it potential feedstock for energy or fuel production via thermochemical pathways. In this study, ex-situ catalytic pyrolysis using HZSM-5 catalyst was explored for the production of olefinic and aromatic hydrocarbons and nutrient-rich char from sewage sludge. The optimal pyrolysis and catalysis temperatures were found to be 500°C and 600°C, respectively. Carbon yields of hydrocarbons from sewage sludge were higher than for lignocellulose; yield differences were attributed to the high extractives content in the sludge. Full recovery of most inorganic elements were found in the char, which suggests that catalyst deactivation maybe alleviated through ex-situ catalytic pyrolysis. Most of the nitrogen was retained in the char while 31.80% was released as ammonia, which suggests a potential for nitrogen recycling.

Distribution and Contamination Hazards of Heavy Metals in Solid Residues from the Pyrolysis and Gasification of Wastewater Sewage Sludge

Most of the targeted heavy metals (HMs) in sewage sludge ended up in solid residues after pyrolysis and gasification, such as Cu, Zn, Cr, Ni and Pb, which their residual rates were over 70%. The bioavailability of the HMs in residues decreased despite their concentrations being higher compared with in sludge. The potential eco-toxicity of each HM were ceased after pyrolysis and gasification of sludge. It was particularly noted that HMs in steam gasification residue exhibited the lowest contamination levels. In addition, the modification of pyrolysis temperature could pose a significant reduction on contamination level and environmental risk of HMs.

Influence of ionic conductivity in bioelectricity production from saline domestic sewage sludge in microbial fuel cells

This study aimed at manipulating ionic conductivity (EC) to harvest the maximum electrical energy from seawater-based domestic wastewater sewage sludge (SWS), unique to only a few cities, through microbial fuel cell (MFC). SWS has never been investigated as a MFC substrate before, and thus the influence of high in-situ EC on the energy recovery was unknown. In this study, the EC of the SWS was reduced through mixing it with fresh water-based domestic wastewater sewage sludge (FWS) or diluted 50% using deionized water while FWS and SWS were individually served as reference treatments. SWS:FWS mix (1:1) exhibited a maximum Coulombic efficiency of 28.6±0.5% at a COD removal of 59±3% while the peak power density was 20-fold higher than FWS. The improved performance was due to the lower ohmic internal resistance (36.8±4.2Ω) and optimal conductivity (12.8±0.2mScm−1). Therefore, dilution with FWS could enhance energy recovery from SWS.

Dynamics of brominated flame retardants removal in contaminated wastewater sewage sludge under anaerobic conditions

Disposal of solid waste to landfills from waste water sewage treatment plants (WWTPs) serves as a potential source of contamination by polybrominated diphenyl ethers (PBDEs) and hexabromocyclododecane (HBCD). Native microbial communities have been found to degrade a variety of xenobiotics, such as PBDEs and HBCDs. This study investigates the potential of autochthonous microflora to remove 11 PBDE congeners and HBCDs in waste water sludge under anaerobic conditions. Laboratory microcosms were constructed with sewage sludge from the WWTPs of Hradec Kralove and Brno. BDE 209 was detected as the prevailing congener in concentrations 685 and 1403ng/g dw and the total amounts of 10 lower PBDEs (BDE 28, 47, 49, 66, 85, 99, 100, 153, 154, 183) were 605 and 205ng/gdw in sludge from Hradec Kralove and Brno, respectively. The levels of HBCD were detected in both sludge lower than 24ng/gdw. The experiment was carried out for 15months. After three months of incubation, HBCD was completely degraded to below detection limits. In sewage from both WWTPs, the higher brominated DEs were removed faster than the lower brominated congeners. One exception was tri-BDE, which was degraded completely within 15months of cultivation. A significant increase in congener tetra-BDE 49 concentrations was observed over the course of the experiment in all tested sewage. The relative distribution of individual congeners among all PBDEs changed after 15months of the incubation in favour of lower brominated congeners. This indicates that debromination is the major mechanism of anaerobic biodegradation. Despite of the increase of BDE 49, the overall removal of all 11 PBDEs achieved the levels of 47.4 and 68.7% in samples from WWTPs Hradec Kralove and Brno, respectively.