Thermophilic Sludge Research Articles

In Situ Biogas Upgrading in a Randomly Packed Gas-Stirred Tank Reactor (GSTR)

This study evaluated different strategies to increase gas–liquid mass transfer in a randomly packed gas stirred tank reactor (GSTR) continuously fed with second cheese whey (SCW), at thermophilic condition (55 °C), for the purpose of carrying out in situ biogas upgrading. Two different H2 addition rates (1.18 and 1.47 LH2 LR−1 d−1) and three different biogas recirculation rates (118, 176 and 235 L LR−1 d−1) were applied. The higher recirculation rate showed the best upgrading performance; H2 utilization efficiency averaged 88%, and the CH4 concentration in biogas increased from 49.3% during conventional anaerobic digestion to 75%, with a methane evolution rate of 0.37 LCH4 LR−1 d−1. The microbial community samples were collected at the end of each experimental phase, as well as one of the thermophilic sludge used as inoculum; metanogenomic analysis was performed using Illumina-based 16S sequencing. The whole microbial community composition was kept quite stable throughout the conventional anaerobic digestion (AD) and during the H2 addition experimental phases (UP1, UP2, UP3, UP4). On the contrary, the methanogens community was deeply modified by the addition of H2 to the GSTR. Methanogens of the Methanoculleus genus progressively increased in UP1 (47%) and UP2 (51%) until they became dominant in UP3 (94%) and UP4 (77%). At the same time, members of Methanotermobacter genus decreased to 19%, 23%, 3% and 10% in UP1, UP2, UP3 and UP4, respectively. In addition, members of the Methanosarcina genus decreased during the hydrogen addition phases.

Oleate Impacts on Acetoclastic and Hydrogenotrophic Methanogenesis under Mesophilic and Thermophilic Conditions

This study investigated oleate inhibition concentration on mesophilic and thermophilic sludge by utilizing acetate and H2/CO2 (80:20, v/v) as substrate, respectively. In addition, another batch experiment was carried out to explore the influence of oleate loads (mM-oleate/g-VS) on methane production. Generally, the mesophilic anaerobic system was more stable than the thermophilic system, which embodied higher microbial abundance, higher methane yield, and higher oleate tolerance. Furthermore, this study provides a possible methanogenic pathway impacted by oleate under mesophilic and thermophilic conditions according to functional microbial composition. Lastly, this paper provides noticeable and avoidable oleate concentrations and loads under different experimental conditions as a guide for future anaerobic bioreactors of lipidic waste biodegradation.

Numerical Analysis of a Full-Scale Thermophilic Biological System and Investigation of Nitrate and Ammonia Fates

Thermophilic biological processes proved to be effective in aqueous waste (AW) and high-strength wastewater treatment. In this work, the monitoring of a full-scale aerobic thermophilic biological plant treating various high-strength AW in continuous mode is reported. This paper aims to: (i) provide models to help the AW utility manager in predicting the load of fed pollutants and performances, and (ii) fully investigate nitrogen transformations in biological reactor. Based on the results, the thermophilic sludge in the studied plant was able to degrade Chemical Oxygen Demand (COD) and remove nitrate nitrogen with very high efficiency (79.3% and 97.1, respectively). The monitoring was conducted following a statistical approach and searched for the possible correlations between the input parameters and the efficiency of removal of the plant. Moreover, a multivariate linear regression was carried out highlighting that the yield value of the removal of COD and nitrogen forms, apart from ammonia, was well explained (R2 = 0.9) by the linear regression against the other monitored parameters. As far as nitrification is concerned, there was, on the one hand, an increase in ammonium ions due to the hydrolysis of the organic substance that occurs in the reactor, and on the other hand, a stripping of the same ammoniacal nitrogen in the form of NH3. While nitrates were effectively removed, according to fluorescent in situ hybridization tests, sludge proved to be formed by minute flocs, where bacteria responsible for the oxidation of ammonium and nitrite seem to be unable to grow.

Thermophilic rather than mesophilic sludge anaerobic digesters possess lower antibiotic resistant genes abundance

For exploring the impact of temperature on antibiotic resistant genes (ARGs) during sludge anaerobic digestion (AD), the dynamic variations of sludge ARGs, plasmid ARGs, and cell-free ARGs in mesophilic (25 °C and 35 °C) and thermophilic (55 °C) digesters were investigated. The study revealed that the abundance of sludge ARGs and plasmid ARGs in thermophilic sludge AD was significantly lower than that in mesophilic digesters, while the cell-free ARGs abundance of the thermophilic digesters was similar to mesophilic digesters. Higher archaea abundance, lower bacteria abundance, and different microbial community were found in thermophilic digesters compared to that of mesophilic ones. Firmicutes might be a main group of potential hosts of ARGs in sludge AD. The distinct microbial community was the main contributor to the low ARGs abundance in thermophilic sludge AD. Thermophilic operation at 55 °C rather than mesophilic operation is more conducive to control ARGs in sludge anaerobic digestion.

Performance evaluation and microbial community analysis of mesophilic and thermophilic sludge fermentation processes coupled with thermal hydrolysis

This research aims to provide new insights into the performance and the microbial dynamics of the sludge fermentation process coupled with thermal hydrolysis. Two semi-continuous fermenters were operated under the mesophilic and thermophilic conditions at the retention time of three days. Thermal hydrolysis (TH) was applied either before (pre-hydrolysis) or after (post-hydrolysis) the fermentation process at a temperature, pressure, and stationary time of 170 °C, 115 psi, and 30 min, respectively. The process incorporating pre-hydrolysis achieved 10–16% higher solubilization and volatile fatty acids (VFAs) production than that of post-hydrolysis. Acetate and propionate prevailed in both process schemes. However, significantly higher iso-butyrate and lower butyrate were recovered through the fermentation of pre-hydrolyzed sludge. Pre-hydrolysis stimulated the growth of more kinetically efficient fermentative bacteria such as Bacteroidetes and Firmicutes due to the abundance of soluble organic matters; however, it reduced the overall microbial diversity. The findings of this research suggest that coupling TH and acidogenic fermentation can provide an opportunity to enhance the production of soluble organics (e.g., VFAs) from wastewater sludge, which can be utilized for various applications including as an external carbon source for the on-site biological nutrient removal.

Comparison between thermophilic and mesophilic anaerobic digestion of waste activated sludge by combined NaOH-microwave pretreatment

ABSTRACT The purpose of this study was to investigate the performance of the thermophilic and mesophilic anaerobic digestion process (TADP, MADP) fed with NaOH-microwave pretreated waste activated sludge. The experiment was conducted in anaerobic CSTR reactors. During this experiment, the reactors were stable in operation and were not inhibited by ammonia. The methane production and reduction of organic matters from MADP were less than those from TADP. The dewatering performance of mesophilic sludge was better than that of the thermophilic sludge. The experimental results showed that the continuous TADP and MADP were effective, when the reactors were fed with the waste activated sludge pretreated by NaOH-microwave. MADP was more suitable to combine the NaOH-MW pretreatment process than TADP.

Enhanced hydrogen production from sewage sludge by cofermentation with wine vinasse

The cofermentation of sewage sludge and wine vinasse at different mixing ratios to enhance hydrogen production was investigated. Batch experiments were carried out under thermophilic conditions with thermophilic sludge inoculum obtained from an acidogenic anaerobic reactor. The results showed that the addition of wine vinasse enhances the hydrogen production of sewage sludge fermentation. The highest hydrogen yields, 41.16 ± 3.57 and 43.25 ± 1.52 mL H2/g VSadded, were obtained at sludge:vinasse ratios of 50:50 and 25:75, respectively. These yields were 13 and 14 times higher than that obtained in the monofermentation of sludge (3.17 ± 1.28 mL H2/g VSadded). The highest VS removal (37%) was obtained at a mixing ratio of 25:75. Cofermentation had a synergistic effect the hydrogen yield obtained at a sludge:vinasse ratio of 50:50 was 40% higher, comparing to the sum of each waste. Furthermore, kinetic analysis showed that Cone and first-order kinetic models fitted hydrogen production better than the modified Gompertz model.

Microbial and Phenyl Acid Dynamics during the Start-up Phase of Anaerobic Straw Degradation in Meso- and Thermophilic Batch Reactors.

Aromatic compounds like phenyl acids derived from lignocellulose degradation have been suspected to negatively influence biogas production processes. However, results on this topic are still inconclusive. To study phenyl acid formation in batch reactors during the start-up phase of anaerobic degradation, different amounts of straw from grain were mixed with mesophilic and thermophilic sludge, respectively. Molecular biological parameters were assessed using next-generation sequencing and qPCR analyses. Metagenomic predictions were done via the program, piphillin. Methane production, concentrations of phenylacetate, phenylpropionate, phenylbutyrate, and volatile fatty acids were monitored chromatographically. Methanosarcina spp. was the dominant methanogen when high straw loads were effectively degraded, and thus confirmed its robustness towards overload conditions. Several microorganisms correlated negatively with phenyl acids; however, a negative effect, specifically on methanogens, could not be proven. A cascade-like increase/decrease from phenylacetate to phenylpropionate, and then to phenylbutyrate could be observed when methanogenesis was highly active. Due to these results, phenylacetate was shown to be an early sign for overload conditions, whereas an increase in phenylbutyrate possibly indicated a switch from degradation of easily available to more complex substrates. These dynamics during the start-up phase might be relevant for biogas plant operators using complex organic wastes for energy exploitation.

Evaluation of the methane production rate from an acidogenic effluent generated in a two-stage process treating winery wastewater

Three methodologies for the calculation of the methane production rate (MPR) were evaluated using an acidogenic effluent of a two-stage process for methane production. A simple method to evaluate the MPR was presented. The MPR was evaluated under different initial substrate concentrations (5, 10, and 15 g L−1), temperatures (35 and 55 °C), and adaptation periods of the thermophilic inoculum. Different patterns of methane were observed for the MPR. The mesophilic sludge degraded the substrate with high initial rates, whereas a thermophilic sludge, acclimated for 226 days, produced the maximal rate after 70 h. This behavior agrees with the different microbial communities observed for each inoculum. The proposed methodology, measuring the instantaneous rates from cumulative methane production, was accurate and straightforward to calculate the MPR independently of the different patterns generated due to the inocula tested.

Reduction of alkalinity supplementation for acid-based wastewater treatment using a thermophilic multi-feed upflow anaerobic sludge blanket reactor

ABSTRACT Generally, Shochu distillery wastewater treatment is required the addition of alkalinity agents for an increase of pH in the UASB reactor. However, to reduce the cost of alkalinity supplementation, cost-effective reactor operation method has been desired. This study aimed to reduce the alkalinity supplementation for a thermophilic (55°C) multi-feed up-flow anaerobic sludge blanket (MF UASB) reactor for the low-cost treatment of the wastewater from the production of the Japanese distilled alcohol called shochu. Shochu distillery wastewater contains high concentrations of organics (46,500–57,600 mgCOD L−1; COD: chemical oxygen demand) and volatile fatty acids (16,200–25,000 mgCOD L−1), and low pH (4.1–4.5). With alkalinity supplementation of 0.045 mgCaCO3 mgCOD−1 using 24% NaOH, the MF UASB reactor achieved an 87 ± 2% COD removal rate with an organic loading rate of 24 kgCOD m−3 day−1 for 554 days reactor operation (hydraulic retention time of 10 h and influent concentration of 10,000 mgCOD L−1). The organic removal rate decreased to 19 ± 3% in the MF UASB reactor when alkalinity supplementation was reduced to 0.015 mgCaCO3·mgCOD−1. In this study , the minimum alkalinity supplementation was 0.045 mgCaCO3 mgCOD−1 at an organic loading rate of 24 kgCOD m−3 day−1.

Short-chain fatty acid (SCFA) production maximization by modeling thermophilic sludge fermentation

Devising a model to optimize organic and microbial community inputs, temperature and solid retention time for production of more short-chain fatty acids.

Effect of Anaerobic Digestion Temperature on Sludge Quality

Sludge quality in terms of dewaterability, reject water characteristics as well as foaming phenomena is a concern either economically or environmentally. In this work the difference in sludge quality between mesophilic and thermophilic anaerobic digested waste activated sludge is compared using completely stirred tank reactors. For mesophilic sludge, the mean capillary suction time (CST) in seconds, extent of dewaterability (% water removed), ammonia nitrogen (Nammon in mg/l) and the soluble COD (CODsol in mg/l) are 852 ± 180, 62.9 ± 1.7, 1484 ± 153.5, and 2315.7 ± 407.6 respectively. Meanwhile the foaming potential (FP) and foam stability (IS) are 4.4 ± 1.7 and 0.7 ± 0.1. Whereas, the mean CST, extent of dewaterability, Nammon and CODsol are 1109 ± 211, 65 ± 1.8, 1581 ± 120.5, and 4740.6 ± 1122.8 for the thermophilic sludge respectively. With a maximum organic loading rate achieved at 2.82 g-VS/l/d, the CST, Nammon and CODsol concentration as well as the FP are significantly better as sludge quality for the mesophilic sludge.

Evaluation of process performance, energy consumption and microbiota characterization in a ceramic membrane bioreactor for ex-situ biomethanation of H2 and CO2

The performance of a pilot ceramic membrane bioreactor for the bioconversion of H2 and CO2 to bioCH4 was evaluated in thermophilic conditions. The loading rate was between 10 and 30 m3 H2/m3reactor d and the system transformed 95% of H2 fed. The highest methane yield found was 0.22 m3 CH4/m3 H2, close to the maximum stoichiometric value (0.25 m3 CH4/m3 H2) thus indicating that archaeas employed almost all H2 transferred to produce CH4. kLa value of 268 h−1 was reached at 30 m3 H2/m3reactor d. DGGE and FISH revealed a remarkable archaeas increase related to the selection-effect of H2 on community composition over time. Methanothermobacter thermautotrophicus was the archaea found with high level of similarity. This study verified the successful application of membrane technology to efficiently transfer H2 from gas to the liquid phase, the development of a hydrogenotrophic community from a conventional thermophilic sludge and the technical feasibility of the bioconversion.

Bioconversion of Sugarcane Bagasse into Value-Added Products by Bioaugmentation of Endogenous Cellulolytic and Fermentative Communities

The goals of this study were to describe a comprehensive taxonomic profile of bacterial communities endogenous from sugarcane bagasse (SCB) and from a thermophilic sludge formed mainly by Proteobacteria Actinobacteria and Firmicutes phylum and its potential as a bioaugmented inoculum for degradation of lignocellulosic biomass. Batch assays were performed using SCB as substrate at different condition: (RC) 2 g L−1 glucose, (R1i) 2 g L−1 unpretreated SCB, (R2i) 2 g L−1 hydrothermally pretreated SCB (at 210 °C for 15 min), (R3i) 2 g L−1 hydrothermally pretreated SCB (at 210 °C for 15 min) followed by alkaline delignification (NaOH—1 M), (R4i) 1 g L−1 unpretreated SCB plus 1 g L−1 hydrothermally pretreated SCB (at 210 °C for 15 min) followed by alkaline delignification. Hydrogen, methane and organic acids were the main metabolites produced during the fermentation. Maximum hydrogen (2.01 and 1.09 mol H2 mol−1 consumed soluble carbohydrates) were obtained in R1i and R2i, respectively. The highest organic acid (1051 mg L−1) and methane (0.92 mmo L−1) production were obtained in R4i.

Preservation of thermophilic mixed culture for anaerobic palm oil mill effluent treatment by convective drying methods

The generation of huge amount of liquid waste known as palm oil mill effluent is a major problem in oil palm industry. Meanwhile, anaerobic biodegradation of such organic effluent at thermophilic condition is a promising treatment technology due to its high efficiency. However, storage and transportation of thermophilic mixed culture sludge are challenging due to constant biogas generation and heating requirement. Hence, drying of thermophilic sludge was conducted to obtain dormant thermophiles and thus enables easier handling. In this study, thermophilic sludge was dried using heat pump at 22 and 32 °C as well as hot air oven at 40, 50, 60, and 70 °C. Subsequently, quality of dried sludge was examined based on most probable number enumeration, chemical oxygen demand, and methane yield. Average drying rate was found to increase from 3.21 to 17.84 g H2O/m2 min as drying temperatures increases while average moisture diffusivity values ranges from 5.07 × 10−9 to 4.34 × 10−8 m2/s. Oven drying of thermophilic mixed culture resulted in highest chemical oxygen demand removal and lowest log reduction of anaerobes at 53.41% and 2.16, respectively, while heat pump drying resulted in the highest methane yield and lowest log reduction of methanogens at 53.4 ml CH4/g COD and 2.09, respectively. To conclude, heat pump at 22 °C was most suitable drying technique for thermophilic mixed culture as the original methane-producing capability was largely retained after drying, at a slightly lower yet still comparable chemical oxygen demand removal when palm oil mill effluent was treated with the rehydrated culture.

Monitoring and Control Improvement of Single and Two Stage Thermophilic Sludge Digestion Through Multivariate Analysis

Stable operation of high-rate thermophilic sludge anaerobic reactors is sometime hard to achieve because of the nature of the anaerobic digestion (AD) process itself and the combination of biological and chemical reactions. An interesting and innovative way to handle AD data resides in multivariate statistical approaches since a more accurate analysis can be performed and fault or abnormal schemes detections can be enhanced. In this paper, principal component analysis (PCA) was the basic multivariate tool used to compare single and two stage AD process performances when treating waste activated sludge (WAS), in order to improve their monitoring and control. Two experiments were carried out to perform single and two-stage AD using WAS and fermented WAS as substrates, respectively. Findings from the PCA model agreed with results from the univariate data analysis but additionally showed a higher variability and changes on the stability trend in the AD of WAS. Besides, multivariate statistical process control using Hotelling T2 and Shewhart control charts combined with PCA displayed an out-of-control scheme revealing a transition period, in which the stability pattern of this experiment changed strongly, towards an accumulation of volatile fatty acids.

Thermophilic versus Mesophilic Anaerobic Digestion of Sewage Sludge: A Comparative Review.

During advanced biological wastewater treatment, a huge amount of sludge is produced as a by-product of the treatment process. Hence, reuse and recovery of resources and energy from the sludge is a big technological challenge. The processing of sludge produced by Wastewater Treatment Plants (WWTPs) is massive, which takes up a big part of the overall operational costs. In this regard, anaerobic digestion (AD) of sewage sludge continues to be an attractive option to produce biogas that could contribute to the wastewater management cost reduction and foster the sustainability of those WWTPs. At the same time, AD reduces sludge amounts and that again contributes to the reduction of the sludge disposal costs. However, sludge volume minimization remains, a challenge thus improvement of dewatering efficiency is an inevitable part of WWTP operation. As a result, AD parameters could have significant impact on sludge properties. One of the most important operational parameters influencing the AD process is temperature. Consequently, the thermophilic and the mesophilic modes of sludge AD are compared for their pros and cons by many researchers. However, most comparisons are more focused on biogas yield, process speed and stability. Regarding the biogas yield, thermophilic sludge AD is preferred over the mesophilic one because of its faster biochemical reaction rate. Equally important but not studied sufficiently until now was the influence of temperature on the digestate quality, which is expressed mainly by the sludge dewateringability, and the reject water quality (chemical oxygen demand, ammonia nitrogen, and pH). In the field of comparison of thermophilic and mesophilic digestion process, few and often inconclusive research, unfortunately, has been published so far. Hence, recommendations for optimized technologies have not yet been done. The review presented provides a comparison of existing sludge AD technologies and the gaps that need to be filled so as to optimize the connection between the two systems. In addition, many other relevant AD process parameters, including sludge rheology, which need to be addressed, are also reviewed and presented.

Relationship between microbial community dynamics and process performance during thermophilic sludge bioleaching.

Heavy metals can be removed from the sludge using bioleaching technologies at thermophilic condition, thereby providing an option for biotreatment of wasted sludge generated from wastewater treatment. The purposes of this study were to establish a molecular biology technique, real-time PCR, for the detection and enumeration of the sulfur-oxidizing bacteria during the thermophilic sludge bioleaching. The 16S rRNA gene for real-time PCR quantification targeted the bioleaching bacteria: Sulfobacillus thermosulfidooxidans, Sulfobacillus acidophilus, and Acidithiobacillus caldus. The specificity and stringency for thermophilic sulfur-oxidizing bacteria were tested before the experiments of monitoring the bacterial community, bacterial number during the thermophilic sludge bioleaching and the future application on testing various environmental samples. The results showed that S. acidophilus was identified as the dominant sulfur-oxidizing bacteria, while A. caldus and S. thermosulfidooxidans occurred in relatively low numbers. The total number of the sulfur-oxidizing bacteria increased during the thermophilic bioleaching process. Meanwhile, the decrease of pH, production of sulfate, degradation of SS/VSS, and solubilization of heavy metal were found to correlate well with the population of thermophilic sulfur-oxidizing bacteria during the bioleaching process. The real-time PCR used in this study is a suitable method to monitor numbers of thermophilic sulfur-oxidizing bacteria during the bioleaching process.

Changes of resistome, mobilome and potential hosts of antibiotic resistance genes during the transformation of anaerobic digestion from mesophilic to thermophilic

This study aimed to reveal how antibiotic resistance genes (ARGs) and their horizontal and vertical transfer-related items (mobilome and bacterial hosts) respond to the transformation of anaerobic digestion (AD) from mesophilic to thermophilic using one-step temperature increase. The resistomes and mobilomes of mesophilic and thermophilic sludge were investigated using metagenome sequencing, and the changes in 24 representative ARGs belonging to three categories, class 1 integron and bacterial genera during the transition period were further followed using quantitative PCR and 454-pyrosequencing. After the temperature increase, resistome abundance in the digested sludge decreased from 125.97 ppm (day 0, mesophilic) to 50.65 ppm (day 57, thermophilic) with the reduction of most ARG types except for the aminoglycoside resistance genes. Thermophilic sludge also had a smaller mobilome, including plasmids, insertion sequences and integrons, than that of mesophilic sludge, suggesting the lower horizontal transfer potential of ARGs under thermophilic conditions. On the other hand, the total abundance of 18 bacterial genera, which were suggested as the possible hosts for 13 ARGs through network analysis, decreased from 23.27% in mesophilic sludge to 11.92% in thermophilic sludge, indicating fewer hosts for the vertical expansion of ARGs after the increase in temperature. These results indicate that the better reduction of resistome abundance by thermophilic AD might be associated with the decrease of both the horizontal and vertical transferability of ARGs.

Mesophilic and thermophilic anaerobic co-digestion of winery wastewater sludge and wine lees: An integrated approach for sustainable wine production

In this work, winery wastes generated by a cellar producing approximately 300,000 hL of wine per year was monitored for a period of one year. On average, 196 L of wastewater, 0.1 kg of waste activated sludge (dry matter) and 1.6 kg of wine lees were produced per hectoliter of wine produced. Different winery wastes, deriving from different production steps, namely waste activated sludge from wastewater treatment and wine lees, were co-treated using an anaerobic digestion process. Testing was conducted on a pilot scale for both mesophilic and thermophilic conditions. The process was stable for a long period at 37 °C, with an average biogas production of 0.386 m3/kg CODfed. On the other hand, for thermophilic conditions, volatile fatty acids accumulated in the reactor and the process failed after one hydraulic retention time (23 days). In order to fix the biological process, trace elements (iron, cobalt and nickel) were added to the feed of the thermophilic reactor. Metals augmentation improved process stability and yields at 55 °C. The pH ranged between 7.8 and 8.0, and specific gas production was 0.450 m3/kg CODfed, which corresponded to dry matter and COD removals of 34% and 88%, respectively. Although the observed performances in terms of biogas production were good, the thermophilic process exhibited some limitations related to both the necessity of metals addition and the worse dewaterability properties. In fact, while the mesophilic digestates reached a good dewatering quality via the addition of 6.5 g of polymer per kg of dry matter, the required dosage for the thermophilic sludge was greater than 10 g/kg of dry matter.