Anaerobic Sewage Sludge Research Articles

Energetic Potential for Biological Methanation in Anaerobic Sewage Sludge Digesters in Austria

Biological methanation as a method of sector coupling between electric and gas grids is expected to be an integral part of the green energy change. Wastewater treatment plants (WWTPs) involving anaerobic digestion (AD) allow existing infrastructure to operate as energy conversion plants, to close carbon cycles and to generate long-term storable energy in the form of biomethane. Therefore, municipal raw sludge and additional organic residuals (co-substrates) are converted into biogas. Hydrogen is added to convert the carbon dioxide in the biogas into methane via biological methanation (BM). In this study, the energy amount that is convertible via BM in municipal digesters in Austria was calculated. The amount of energy, which can be transformed from electric surplus energy into biomethane, was assessed. Operational data from lab-scale digesters were combined with data from 28 Austrian full-scale wastewater treatment plants with AD. They represent 9.2 Mio population equivalents (PE), or 68% of Austria’s municipal AD capacity for WWTPs > 50,000 PE (in sum, 13.6 Mio PE). Energy flows for BM including water electrolysis and anaerobic digestion were created on a countrywide basis. It was found that 2.9–4.4% (220–327 GWh·y−1) of Austria’s yearly renewable electricity production (7470 GWh·y−1) can be transformed into biomethane via BM in municipal digesters.

Agronomic performance and optimal ranges of attributes of substrates with biochar from anaerobic sewage sludge for black wattle (Acacia mearnsii) seedlings

Purpose The objective was to evaluate the agronomic performance of black wattle seedlings (Acacia mearnsii) grown on substrates with increasing proportions of biochar based on anaerobic sewage sludge (ASS-biochar). In addition, the present study proposed appropriate ranges for the main physical-hydraulic and chemical attributes of these substrates. Method The evaluated substrates included ten substrates with increasing proportions of ASS-biochar, combined with a “standard” mixture (organic compost, carbonized rice husk and vermiculite), in addition to three commercial substrates (references). The experimental design was randomized blocks, with four replications and eight plants per repetition. The physical-hydraulic and chemical attributes evaluated in all substrate formulations were: wet and dry density, total porosity, aeration space, easily available water, buffering water, available water, remaining water, pH and electrical conductivity (EC). The agronomic performance of the black wattle seedlings was evaluated through plant height, length of the root system, neck diameter, dry mass of aerial parts, dry mass of roots and Dickson's quality index. Results Biochar from anaerobic sewage sludge increased the chemical and physical-hydraulic quality of the substrates, particularly within the proportion of 45-50% of the substrate formulations, and thus positively affected the growth parameters of the black wattle plants. Conclusion The biochar produced from anaerobic sewage sludge is an efficient raw material to compose substrates for the production of seedlings. Transformation of anaerobic sewage sludge into biochar and its combination with other locally available raw materials can be considered a safe way of reusing this residue in agriculture.

Sodium nitrate as a methanogenesis suppressor in earthen separator microbial fuel cell treating rice mill wastewater.

The microbial fuel cell (MFC) is one of the sustainable technologies, which alongside treating wastewater, can generate electricity. However, its performance is limited by factors like methanogenesis where methanogens compete with the anode respiring bacteria for substrate, reducing the power output. Thus, sodium nitrate, which has been previously reported to target the hydrogenotrophic methanogens, was used as a methanogenic suppressor in this study. The performance of MFC with and without sodium nitrate was studied during the treatment of rice mill wastewater. A significantly higher power density and coulombic efficiency (CE) were noted in the MFC with sodium nitrate (MFCT) (271.26 mW/m3) as compared to the control MFC (MFCC) (107.95 mW/m3). Polarization studies showed lower internal resistance for the MFCT (330 Ω) as compared to MFCC (390 Ω). Linear sweep voltammetry and cyclic voltammetry indicated a higher electron discharge on the anode surface due to enhancement of electrogenic activity. Considerable reduction (76.8%) in specific methanogenic activity was also observed in anaerobic sewage sludge mixed with sodium nitrate compared to the activity of anaerobic sewage sludge without any treatment. Due to the inhibition of methanogens, a lower chemical oxygen demand (COD) and phenol removal efficiency were observed in MFCT as compared to MFCC. The COD balance study showed an increase in substrate conversion to electricity despite the increase in nitrate concentration. Therefore, selective inhibition of methanogenesis had been achieved with the addition of sodium nitrate, thus enhancing the power generation by MFCs.

Kinetic models describing the hydrolytic stage of the anaerobic co-digestion of solid vegetable waste and anaerobic sewage sludge

The hydrolysis of carbonaceous and nitrogenous materials in the anaerobic co-digestion process of solid vegetable waste and anaerobic sewage sludge (ASS) was studied from the perspective of zero-, first-, and second-order pseudo-kinetic models. It was found that the digestion of the chemical demand for particulate oxygen (CODP) and subsequent conversion to the filtered form (CODF) occurs in two stages of digestion, with significant differences between the kinetic constants of hydrolysis (kh) and half-life (t1/2). A simplified kinetic model based on the first-order differential equation was proposed to model the conversion rate between CODP and CODF, resulting in excellent calibration parameters (R-sqr> 0.99, Fcalc >> Ftable) and validation parameters (R-sqr = 0.99, intercept 0.001, and bisector 0.98). It was also observed that the formation of volatile fatty acids (VFA) and organic nitrogen ( N.org ) occurs in two kinetic stages, one rapid and the other slow, which coincide with those described for CODF. However, the decay of total nitrogen levels (TKN) occurs in a single step. Despite the mathematical simplicity, the kinetic models addressed in this study presented validation parameters suitable in statistical terms, both in the modeling tests and in the prediction tests, opening new possibilities in the environment of biodigestion process modeling.

Magnetic sludge byproducts for adsorptive phosphorus removal: Resource recovery from iron-based anaerobic sewage sludge

This study evaluated feasibility of resource recovery from iron-based sewage sludge from a novel Fe(III)-dosed anaerobic bioreactor used for wastewater treatment. Sludge samples were calcined at five different temperatures (300, 350, 400, 450, and 500 °C) to investigate the transformation of the sludge into different magnetic phases of iron oxide particles. The material phase analysis revealed the presence of 14 to 39 wt% magnetite and 8 to 19 wt% maghemite for different temperature treatments, which indicate the successful conversion of sludge materials into magnetic particles. This magnetic conversion was further confirmed by magnetization measurements of the sludge byproducts that found a 6.3 to 10.9 emu/g saturation magnetization and a 0.7 to 2.0 emu/g remanent magnetization. Due to surface effects phenomenon of nanocrystals, the magnetization values were observed to increase with calcination temperature along with the crystallinity and crystallite size of the thermally-treated sludge materials. This indicates the crystallinity of the samples played a significant role in determining the magnetization properties of the sludge byproducts. Phosphate adsorption capacity and kinetics of the sludge byproducts were evaluated for the samples calcined at 350 and 500 °C. Both samples showed a high phosphate adsorption capacity, but the sample treated at 350 °C showed relatively higher capacity presumably due to smaller crystallite size and reduced crystallinity of the particles in the sample. This study demonstrated that a simple thermal treatment of the sludge can render dual benefits of recovering magnetic particles and further utilizing them for beneficial applications.

Microbial Communities and Sulfate-Reducing Microorganisms Abundance and Diversity in Municipal Anaerobic Sewage Sludge Digesters from a Wastewater Treatment Plant (Marrakech, Morocco)

Both molecular analyses and culture-dependent isolation were combined to investigate the diversity of sulfate-reducing prokaryotes and explore their role in sulfides production in full-scale anaerobic digesters (Marrakech, Morocco). At global scale, using 16S rRNA gene sequencing, Proteobacteria, Bacteroidetes, Firmicutes, Actinobacteria, Synergistetes, and Euryarchaeota were the most dominant phyla. The abundance of Archaea (3.1–5.7%) was linked with temperature. The mcrA gene ranged from 2.18 × 105 to 1.47 × 107 gene copies.g−1 of sludge. The sulfate-reducing prokaryotes, representing 5% of total sequences, involved in sulfides production were Peptococcaceae, Syntrophaceae, Desulfobulbaceae, Desulfovibrionaceae, Syntrophobacteraceae, Desulfurellaceae, and Desulfobacteraceae. Furthermore, dsrB gene ranged from 2.18 × 105 to 1.92 × 107 gene copies.g−1 of sludge. The results revealed that exploration of diversity and function of sulfate-reducing bacteria may play a key role in decreasing sulfide production, an undesirable by-product, during anaerobic digestion.

Assessing the bioenergy potential of high-ash anaerobic sewage sludge using pyrolysis kinetics and thermodynamics to design a sustainable integrated biorefinery

A new opportunity for producing valuable biorefinery products can be found by integrating biochemical and thermochemical processing with municipal wastewater treatment. This study is the first to evaluate the kinetic triplet and thermodynamic parameters from the pyrolysis of typical Brazilian anaerobic sewage sludge performed in the framework of a multi-step solid-state process. The physicochemical characteristics of the anaerobic sewage sludge are comparable to those obtained from low-rank coals. The pyrolysis characteristics were analyzed by non-isothermal thermogravimetry under different heating rates (10, 25, 50, and 90 K min−1) in an inert atmosphere. Two devolatilization stages were distinguished from the active pyrolysis zone, with an average mass loss of 47.56 wt% (sum) in the range of 398–953 K. For each devolatilization stage, three isoconversional methods (Flynn–Wall–Ozawa, Kissinger–Akahira–Sunose, and Starink) were utilized to calculate the activation energy, and then the compensation effect method was applied to find the pre-exponential factor. The average activation energies calculated ranged from 113.7 to 117.3 kJ mol−1 for the first stage and from 115.7 to 121.9 kJ mol−1 for the second stage, with respective pre-exponential factors of 7.39 × 109 min−1 and 8.80 × 107 min−1. According to the master-plots method, it was found that the first stage followed the fourth-order (F4) model, while the second stage was described by the second-order (F2) model. Based on the statistical evaluation, the devolatilization behaviors reconstructed from overall kinetic expression agree reasonably well with the experimental data, proving its practical importance for designing a pyrolytic processing system using anaerobic sewage sludge as raw material. This study contributes by providing useful insights that can be applied to a large-scale biorefinery as a critical step towards producing biofuels coupled to municipal wastewater treatment in an environmentally sustainable manner.

Biogas potential and methanogenic community shift in in-situ anaerobic sewage sludge digestion with food waste leachate additions

The objective of this study was to determine methane yields (MY) of organic wastes in biogasification facilities according to the mixing ratio of food waste/food waste leachate and sewage sludge. One biogasification facility that treated sewage sludge only was compared with three biogasification facilities treating sewage sludge and food waste. The theoretical MY was derived based on analyses of carbohydrate, fat, and protein to examine the efficiency of the biogasification facility. The average actual MY was 0.424 Sm3CH4/kg volatile solids, which corresponded to 83.7% of theoretical MY. In the case of combined anaerobic digestion (CD) mixing with food waste/food waste leachate, inhibitory factors (volatile fatty acids [VFAs], total nitrogen [TN], and organic matter contents) showed the tendency to have relatively higher values in CD facilities than in the biogasification facility treating sewage sludge only. Mean concentrations of VFAs and TN in the anaerobic digester effluent, and the organic loading rate were 406 mg/L, 3,721 mg/L, and 1.62 kg volatile solids/m3 day, respectively. The influence of anaerobic digester effluent was in charge of 10% within the influent environmental loading rate from the sewage treatment plants associated with the biogasification facilities. Analyses of the microbial community showed that a remarkable change in the structure of methanogens was directly related to different MY in each plant. In particular, Methanoculleus and Methanosaeta increased with an increasing ratio of food waste/food waste leachate to sludge, while Methanococcus and Methanosarcina decreased. In conclusion, CD showed steady operational conditions and high efficiency of MY by injecting food waste/food waste leachate into the anaerobic digester. It met the current criteria for integrated treatment of organic waste in biogasification facilities in South Korea.

Agricultural use and pH correction of anaerobic sewage sludge with acid pH

Agricultural use is the main way of recycling sewage sludge. Besides providing nutrients and organic matter to crops and soils, it is an important alternative for recycling this residue. However, problems during the sewage treatment process may generate sludge batches with an acidic pH. Thus, it is essential to understand the consequences of using such sludge on soils and plants, and to explore ways to overcome this limitation. The objective of this study was to evaluate addition rates of anaerobic sewage sludge (ASS) with acidic compositions on the soil fertility and performance of lettuce plants. Additionally, a methodology for pH correction of ASS with acidic pH is proposed. An agronomic experiment was conducted in a greenhouse using seven addition rates of ASS (0.0, 0.25, 0.5, 1, 2, 4 and 8 g kg−1 in dry basis), treated with an additional step of disinfection (solarization), and applied in an Albaqualf soil cultivated with lettuce (Lactuca sativa). Soil and leaf chemical composition, as well as chlorophyll index and the dry matter of lettuce leaves were evaluated. Failures during the acidogenesis phase of the anaerobic digestion process were probably the cause of ASS acidification. Although this ASS increased soil fertility indicators and plant dry matter, it significantly reduced soil pH, thereby requiring a complementary assay to correct its pH up to 6.0, which was achieved through liming. Anaerobic sewage sludges with an acidic pH can be effectively used in agriculture after being dried and disinfected through solarization, followed by pH correction, avoiding negative impacts on soil chemical attributes and plant response.

Recovery of humic acids from anaerobic sewage sludge: Extraction, characterization and encapsulation in alginate beads

Wastewater production is rising all over the world and one of the most difficult problems is the disposal of sewage sludge (SS). It is known that SS contains certain quantities of added-value compounds, such as humic acids (HA) which in turn have beneficial effects on soil quality and plant growth. On the other hand, SS can retain many pollutants, such as heavy metals. The present work aimed to implement an HA alkaline extraction protocol from anaerobic sewage sludge (ASS). Subsequently, the HA were quantified in ASS, in HA extract and in commercial HA, used as a benchmark, which gave results of 12.53%, 26.87% and 77.87% (on dry matter basis), respectively. FESEM and EDX analyses on lyophilized HA extract confirmed that no heavy metals had passed into the extract. Afterwards, in order to allow controlled release of the HA in soils, alginate beads containing the HA extract were created. Finally, a pot experiment in a greenhouse was performed using Chilean lettuce plants (Lactuca sativa L.) treated with alginate-HA extract beads. At the end of the greenhouse experiments, the hypogean dry biomass of the treated plants was significantly higher than for non-treated plants. The relevance of this study relies not only on the exploitation of green chemistry principles, by converting a waste stream into a high-value product, but also on the application of an approach following a circular economy model.

Methanogens Diversity during Anaerobic Sewage Sludge Stabilization and the Effect of Temperature

Anaerobic sludge stabilization is a commonly used technology. Most fermenters are operated at a mesophilic temperature regime. Modern trends in waste management aim to minimize waste generation. One of the strategies can be achieved by anaerobically stabilizing the sludge by raising the temperature. Higher temperatures will allow faster decomposition of organic matter, shortening the retention time, and increasing biogas production. This work is focused on the description of changes in the community of methanogenic microorganisms at different temperatures during the sludge stabilization. At higher temperatures, biogas contained a higher percentage of methane, however, there was an undesirable accumulation of ammonia in the fermenter. Representatives of the hydrogenotrophic genus Methanoliea were described at all temperatures tested. At temperatures up to 50 °C, a significant proportion of methanogens were also formed by acetoclastic representatives of Methanosaeta sp. and acetoclastic representatives of the order Methanosarcinales. The composition of methanogens in the fermenter significantly changed at 60 °C when typically thermophilic species, like Methanothermobacter marburgensis, appeared. A decrease in the diversity of methanogens was observed, and typical hydrogenotrophic methanogenic archaea isolated from fermenters of biogas plants and anaerobic wastewater treatment plants represented by genus Methanoculleus were no longer present.

Anaerobic co-digestion of industrial landfill leachate and glycerin: methanogenic potential, organic matter removal and process optimization

ABSTRACT The objective of this study was to evaluate the performance of the anaerobic co-digestion of different concentrations of industrial landfill leachate associated with crude residual glycerin, in relation to the methanogenic potential, COD removal, accumulated methane production, the effects of the factors (food/microorganism ratio and percentage of glycerin added to the leachate) and their interactions on kinetic parameters of methane production (CH4) using the modified Gompertz model. Co-digestion tests were carried out in bench scale (400 mL of useful volume) under batch mode at 30 ± 1°C during 30-day incubation of anaerobic sewage sludge as inoculum. The parameters glycerin addition to the leachate (v/v) (0%, 1.5%, 5%, 8.5% and 10%) and F/M ratio (0.3, 0.5, 1, 1.5 and 1.7) were investigated using Central Composite Rotational Design method (CCRD). The results indicated significant effect to the response variables: methanogenic potential, COD removal, accumulated production of CH4 and maximum estimated production of CH4, considering a confidence interval of 95% (p < .05). The ideal mixture of 95.13% of leachate with 4.87% of raw glycerin was obtained by desirability test to F/M of 1.61 gCOD of substrate per gVSS (volatile suspended solids) of sludge. Methanogenic potential was 0.19 LNCH4 gTVSrem −1, and the average removal of COD was 92%, resulting in accumulated production and maximum estimated production of CH4 of 74 and 80 mL, respectively. It was noted that the process of co-digestion of the industrial landfill leachate with the crude residual glycerin is promising, due to is potential of complementing and balancing organic materials, nutrients and other components that influence the biological process. Abbreviations: AN: ammoniacal nitrogen; BMP: biochemical methane potential; CCRD: central composite rotational design; COD: chemical oxygen demand; F/M ratio: food/microorganism ratio; FSS: fixed suspended solids; NTP: normal temperature and pressure; TSS: total suspended solids; TA: total alkalinity; TFS: total fixed solids; TKN: total Kjeldahl nitrogen; TP: total phosphorus; TS: total solids; TVA: total volatile acids; TVS: total volatile solids; VSS: volatile suspended solids; WWTP: wastewater treatment plant

Anaerobic Degradation of the Plant Sugar Sulfoquinovose Concomitant With H2S Production: Escherichia coli K-12 and Desulfovibrio sp. Strain DF1 as Co-culture Model.

Sulfoquinovose (SQ, 6-deoxy-6-sulfoglucose) is produced by plants and other phototrophs and its biodegradation is a relevant component of the biogeochemical carbon and sulfur cycles. SQ is known to be degraded by aerobic bacterial consortia in two tiers via C3-organosulfonates as transient intermediates to CO2, water and sulfate. In this study, we present a first laboratory model for anaerobic degradation of SQ by bacterial consortia in two tiers to acetate and hydrogen sulfide (H2S). For the first tier, SQ-degrading Escherichia coli K-12 was used. It catalyzes the fermentation of SQ to 2,3-dihydroxypropane-1-sulfonate (DHPS), succinate, acetate and formate, thus, a novel type of mixed-acid fermentation. It employs the characterized SQ Embden-Meyerhof-Parnas pathway, as confirmed by mutational and proteomic analyses. For the second tier, a DHPS-degrading Desulfovibrio sp. isolate from anaerobic sewage sludge was used, strain DF1. It catalyzes another novel fermentation, of the DHPS to acetate and H2S. Its DHPS desulfonation pathway was identified by differential proteomics and demonstrated by heterologously produced enzymes: DHPS is oxidized via 3-sulfolactaldehyde to 3-sulfolactate (SL) by two NAD+-dependent dehydrogenases (DhpA, SlaB); the SL is cleaved by an SL sulfite-lyase known from aerobic bacteria (SuyAB) to pyruvate and sulfite. The pyruvate is oxidized to acetate, while the sulfite is used as electron acceptor in respiration and reduced to H2S. In conclusion, anaerobic sulfidogenic SQ degradation was demonstrated as a novel link in the biogeochemical sulfur cycle. SQ is also a constituent of the green-vegetable diet of herbivores and omnivores and H2S production in the intestinal microbiome has many recognized and potential contributions to human health and disease. Hence, it is important to examine bacterial SQ degradation also in the human intestinal microbiome, in relation to H2S production, dietary conditions and human health.

Characterization of biosurfactant from yeast using residual soybean oil under acidic conditions and their use in metal removal processes.

This study aimed at the production of biosurfactants from yeasts under acidic conditions using residual soybean oil as a carbon source, as well as the biosurfactant produced in the solubilization of metals in sewage sludge. The yeast Meyerozyma guilliermondii was considered the best producer in both pH 4.0 and 2.0; therefore, the product obtained by this yeast was characterized by Fourier transform infrared (FT-IR) and 1H nuclear magnetic resonance (NMR) spectroscopy. Moreover, it was applied in metal removal assays in anaerobic sewage sludge. The spectra obtained in FT-IR suggested that M. guilliermondii's biosurfactant had a similar structure to glycolipids from the sophorolipid class, and it was confirmed by 1H NMR spectroscopy. In the bioleaching assays, the application of biosurfactant (2%) produced by M. guilliermondii with pH adjusted to 2.0 was able to solubilize 15.9% of cadmium from the sewage sludge.

Primary and Activated Sludge Biogas Production: Effect of Temperature

Sewage sludge management is a problem of growing importance. Anaerobic sewage sludge stabilization is commonly used technology, where organic matter contained in primary and activated sewage sludge is converted into biogas, so both, pollution control and energy recovery can be achieved. The paper deals with the effect of process temperature (36 °C, 42 °C and 50 °C) on biogas production and quality during anaerobic stabilization of primary and activated sewage sludge generated during purifying process in low‑loaded activated sludge process. Primary and activated sewage sludge samples were taken at the wastewater treatment plant Brno, Czech Republic. The characteristics of sludges (dry matter and organic dry matter content, pH, conductivity, redox potential) were dermined. Biogas production and quality was measured using 3 anaerobic systems, each of 8 batch anaerobic fermenters, at the 3 different temperature conditions 36 °C, 42 °C and 50 °C. Hydraulic retention time was 20 days. Hypothesis, which predicts that the fermentation of primary and activated sludge provides dissimilar methane quantity and quality under different temperature conditions (36 °C, 42 °C and 50 °C), was partially confirmed. Temperature 42 °C significantly increased biogas production from primary sewage sludge (by 60 % in comparison with production at 36 °C). For activated sewage sludge samples no significant influence of temperature on the biogas production was observed.

Co-composting of anaerobic sewage sludge and biomass amended with biopreparations

Co-composting of anaerobic sewage sludge and biomass amended with biopreparations

Screening anodic inoculums for microbial fuel cells by quantifying bioelectrogenic activity using tungsten trioxide quantum rods

The aim of this research was to develop a procedure for rapid detection of electrogenic activity of the inoculums using electrochromic tungsten trioxide (WO3) quantum rods, which display blue colouration under an electric field. Optimum dosage of WO3 and sludge concentration to be used for absorbance measurement were determined to estimate electrogenic activity based on blue colouration. Performance of seven MFCs was evaluated using different volumetric ratios of mixed anaerobic sewage sludge and Shewanella putrefaciens as inoculums. Absorbance of inoculums used in MFCs was measured after addition of optimum dosage of WO3 and a correlation is established between this absorbance and respective current densities/CE, obtained in MFCs during steady state operation. This correlation of current densities/CE with absorbance of inoculum can be used to select proper inoculum having highest electrogenic activity, and to predict possible current generation of MFCs, even before start-up, based on the electrogenic activity of inoculum used.

Illumina sequencing-based analysis of a microbial community enriched under anaerobic methane oxidation condition coupled to denitrification revealed coexistence of aerobic and anaerobic methanotrophs.

Methane is produced in anaerobic environments, such as reactors used to treat wastewaters, and can be consumed by methanotrophs. The composition and structure of a microbial community enriched from anaerobic sewage sludge under methane-oxidation condition coupled to denitrification were investigated. Denaturing gradient gel electrophoresis (DGGE) analysis retrieved sequences of Methylocaldum and Chloroflexi. Deep sequencing analysis revealed a complex community that changed over time and was affected by methane concentration. Methylocaldum (8.2%), Methylosinus (2.3%), Methylomonas (0.02%), Methylacidiphilales (0.45%), Nitrospirales (0.18%), and Methanosarcinales (0.3%) were detected. Despite denitrifying conditions provided, Nitrospirales and Methanosarcinales, known to perform anaerobic methane oxidation coupled to denitrification (DAMO) process, were in very low abundance. Results demonstrated that aerobic and anaerobic methanotrophs coexisted in the reactor together with heterotrophic microorganisms, suggesting that a diverse microbial community was important to sustain methanotrophic activity. The methanogenic sludge was a good inoculum to enrich methanotrophs, and cultivation conditions play a selective role in determining community composition.

Biodegradation of tetrabromobisphenol A in the sewage sludge process

Anaerobic sewage sludge capable of rapidly degrading tetrabromobisphenol A (TBBPA) was successfully acclimated in an anaerobic reactor over 280days. During the period from 0 to 280days, the TBBPA degradation rate (DR), utilization of glucose, and VSS were monitored continuously. After 280days of acclimation, the TBBPA DR of active sludge reached 96.0% after 20days of treatment in batch experiments. Based on scanning electron microscopy (SEM) observations and denaturing gradient gel electrophoresis (DGGE) determinations, the diversity of the microorganisms after 0 and 280days in the acclimated anaerobic sewage sludge was compared. Furthermore, eleven metabolites, including 2-bromophenol, 3-bromophenol, 2,4-dibromophenol, 2,6-dibromophenol, tribromophenol and bisphenol A, were identified by gas chromatography–mass spectrometry (GC–MS). Moreover, the six primary intermediary metabolites were also well-degraded by the acclimated anaerobic sewage sludge to varying degrees. Among the six target metabolites, tribromophenol was the most preferred substrate for biodegradation via debromination. These metabolites degraded more rapidly than monobromide and bisphenol A. The biodegradation data of the intermediary metabolites exhibited a good fit to a pseudo-first-order model. Finally, based on the metabolites, metabolic pathways were proposed. In conclusion, the acclimated microbial consortia degraded TBBPA and its metabolites well under anaerobic conditions.

Evaluation of different types of anaerobic seed sludge for the high rate anaerobic digestion of pig slurry in UASB reactors

Three different types of anaerobic sludge (granular, thickened digestate and anaerobic sewage) were evaluated as seed inoculum sources for the high rate anaerobic digestion of pig slurry in UASB reactors. Granular sludge performance was optimal, allowing a high efficiency process yielding a volumetric methane production rate of 4.1LCH4L−1d−1 at 1.5days HRT (0.248LCH4g−1COD) at an organic loading rate of 16.4gCODL−1d−1. The thickened digestate sludge experimented flotation problems, thus resulting inappropriate for the UASB process. The anaerobic sewage sludge reactor experimented biomass wash-out, but allowed high process efficiency operation at 3days HRT, yielding a volumetric methane production rate of 1.7LCH4L−1d−1 (0.236LCH4g−1COD) at an organic loading rate of 7.2gCODL−1d−1. To guarantee the success of the UASB process, the settleable solids of the slurry must be previously removed.