Anaerobic Digestion Of Municipal Sludge Research Articles

Comparative Study of High-Temperature Anaerobic Digestion of Municipal Sludge Under Acid/Alkali and Low-Temperature Hydrothermal Synergistic Pretreatment

Comparative Study of High-Temperature Anaerobic Digestion of Municipal Sludge Under Acid/Alkali and Low-Temperature Hydrothermal Synergistic Pretreatment

Advanced steam-explosion pretreatment mediated anaerobic digestion of municipal sludge: Effects on methane yield, emerging contaminants removal, and microbial community

Advanced steam explosion pretreatment, i.e., the Thermal hydrolysis process (THP) is applied mainly to improve the sludge solubilization and subsequent methane yield in the downstream anaerobic digestion (AD) process. However, the potential of THP in pretreating the high solids retention time (SRT) sludges, mitigating the risk of emerging organic micropollutants and effects on anaerobic microbiome in digester remains unclear. In this study, sludge from a sequencing batch reactor (SBR) system operating at a SRT of 40 days was subjected to THP using a 5 L pilot plant at the temperature ranges of 120–180 °C for 30–120 min. The effect of THP on organics solubilization, methane yield, organic micropollutant removal, and microbial community dynamics was studied. The highest methane yield of 507 mL CH4/g VSadded and volatile solids (VS) removal of 54% were observed at 160°C- 30min THP condition, i.e., 4.1 and 2.6 times higher than the control (123 mL CH4/gVSadded, 20.7%), respectively. The experimental values of hydrolysis coefficient and methane yield have been predicted using Modified Gompertz, First order, and Logistics models. The observed values fitted well with all three models showing an R2 value between 0.96 and 1.0. THP pretreated sludges showed >80% removal of Trimethoprim, Enrofloxacin, Ciprofloxacin, and Bezafibrate. However, Carbamazepine, 17α-ethinylestradiol, and Progesterone showed recalcitrant behavior, resulting in less than 50% removal. Microbial diversity analysis showed the dominance of Proteobacteria, Firmicutes, Chloroflexi, and Bacteroidetes, collectively accounting for >70–80% of bacterial reads. They are mainly responsible for the fermentation of complex biomolecules like polysaccharides, proteins, and lipids. The THP-mediated anaerobic digestion of sludge shows better performance than the control digestion, improved methane yield, higher VS and micropollutants removal, and a diverse microbiome in the digester.

Impact of Hydrothermal Pretreatment Parameters on Mesophilic and Thermophilic Fermentation and Anaerobic Digestion of Municipal Sludge

Four parameters affecting hydrothermal pretreatment (HTP) of municipal sludge prior to anaerobic digestion and fermentation were investigated. Partial factorial design including several key HTP parameters at two distinct levels, including temperature (170 and 190 °C), retention time (RT) (10 and 30 min), pH (4 and 10), and solid content (SC) (4% and 16%), were studied. Further, the impact of HTP parameters on mesophilic and thermophilic fermentation was explored and compared. Results revealed a significant effect of all HTP parameters on COD solubilization, VFA, and methane yield. There were correlations between HTP parameters and process responses such as VFA yield and methane yield. HTP was found to increase COD solubilization and VFA production between 15 and 20% during thermophilic fermentation in relation to mesophilic treatment. All parameters, including SC, temperature, pH, and RT, were important contributing factors affecting methane production during anaerobic digestion. The highest methane production yield of 269 mL CH4/g TCOD added was observed at the highest SC (16%) and pH (10) and at the lower temperature (170 °C) and RT (10). HTP is expected to be combined with other intensification routes to treat waste with high solid contents improving the fermentation and anaerobic digestion processes.

Insights into methanogenesis of mesophilic-psychrophilic varied anaerobic digestion of municipal sludge with antibiotic stress

Methane production through anaerobic digestion (AD) of municipal sludge is economic and eco-friendly, which is commonly affected by temperature and pollutants residues. However, little is known about methanogenesis in psychrophilic AD (PAD) with temperature variations that simulating seasonal variations and with antibiotic stress. Here, two groups of AD systems with oxytetracycline (OTC) were operated with temperature maintained at 35 °C and 15 °C or variation to explore the influence to methanogenesis. The acetic acid was noticeably accumulated in OTC groups initially (P < 0.001). Methane production was noticeably inhibited initially in PAD with OTC, but had been stimulated later at 35 °C. The dominant acetoclastic methanogens Methanosaeta gradually decreased to 15.48% and was replaced by methylotrophic Methanomethylovorans (73.43%) in PAD with OTC. Correspondingly, the abundances of functional genes related to methylotrophic methanogenesis were also higher in these groups. Besides, genes involving in methane oxidation had over 50 times higher abundances in PAD with OTC groups in the second phase. Further investigation is essential to understand the main dynamics of methanogenesis in PAD and to clear the related molecular mechanism for future methane production regulation in sludge systems.

Hydrothermal Pre- and Intertreatment for Anaerobic Digestion of Municipal Sludge

Hydrothermal Pre- and Intertreatment for Anaerobic Digestion of Municipal Sludge

Comprehensive Review of Hydrothermal Pretreatment Parameters Affecting Fermentation and Anaerobic Digestion of Municipal Sludge

Municipal solid waste treatment and disposal have become one of the major concerns in waste management due to the excessive production of waste and higher levels of pollution. To address these challenges and protect the environment in sustainable ways, the hydrothermal pretreatment (HTP) technique coupled with anaerobic digestion (AD) becomes a preferred alternative technology that can be used for municipal solid waste stabilization and the production of renewable energy. However, the impact of HTP parameters such as temperature, retention time, pH, and solid content on the fermentation of TWAS is yet to be well studied and analyzed. Hence this study was conducted to review the effect of hydrothermal pretreatment of thickened waste-activated sludge (TWAS) on fermentation and anaerobic digestion processes. Many studies reported that fermentation of TWAS at pretreatment temperature ranges from 160 °C to 180 °C resulted in a 50% increase in volatile fatty acid (VFA) yields compared to no pretreatment. However, for the AD process, HTP in the range of 175 °C to 200 °C with a 30–60 min retention time was considered the optimal condition for higher biogas production, with 30% increase in biodegradability and greater than 55% increase in biogas production. Even though there is a direct relationship between increased HTP temperature and the hydrolysis of TWAS, a pretreatment temperature range beyond 200 °C alters the biogas production. The solid content (SC) of sludge plays a crucial role in HTP, where in practice up to 16% SC has been utilized for HTP. Further, a combined alkaline-HTP enhances the process performance.

The responses of mesophilic and thermophilic anaerobic digestion of municipal sludge to periodic fluctuation disturbance of organic loading rate

Fluctuation disturbance of organic loading rate (OLR) is common in actual anaerobic digestion (AD), but its effects on AD of municipal sludge gets little attention. This study investigated the responses of reactor performance and active microbial community in mesophilic and thermophilic AD of municipal sludge before, during and after OLR periodic fluctuation disturbance. The performance of both reactors were similar before and after disturbance although some parameter values changed during the disturbance, which indicated their enough buffer capacity to OLR periodic fluctuation. Different microbial community at RNA level was observed in the two reactors. When the OLR disturbance commenced, the microbial community changed greatly in thermophilic AD. Error and attack tolerance of the microbial network was analyzed in order to learn the response mechanisms to OLR disturbance. The results assisted that the thermophilic microbial community was more vulnerable, but the reactor performance of which could be maintained using the functional redundancy strategy under OLR fluctuation disturbance.

Two-step activated carbon cloth enhances microbial interactions and methane production during anaerobic digestion of municipal sludge

This study investigated the effects of two-step activated carbon cloth (CC) on the syntrophic microbial associations during anaerobic digestion (AD) of municipal sludge. A simple two-step activation, acid pretreatment (H2SO4/HNO3) followed by air calcination (550 °C), was used to convert commercial untreated CC (U-CC) into high performance activated CC (A-CC). Biochemical methane potential (BMP) assays conducted at different CC dosages indicated that A-CC, at a dose of 0.80 g A-CC {1.48 g A-CC/g-VS (volatile solids)substrate}, enhanced methane yield from by 3.7× and reduced the lag phase up to 15.6-fold, compared to non-CC Control within 3 days. Characterization of CC surfaces and kinetic modeling indicated indicated that A-CC pore size area increased by 435× a (Barrett, Joyner, and Halenda, BJH) with the potential to promote electron transfer and accelerate kinetic rates of methane production. Consistent with these results, microbial community composition profiles of CC surfaces indicated rapid adherence of methanogenic archaea and bacterial syntrophs to A-CC within 3 days. Multi-variate statistical analyses indicated that these populations were highly enriched on 0.80 g A-CC dosage compared to U-CC and Controls. Based on these results it can be concluded that A-CC provides a robust selective environment for syntrophic energy metabolism driving enhanced methane production from municipal sludge.

Intermittent Microaeration Technology to Enhance the Carbon Source Release of Particulate Organic Matter in Domestic Sewage

Domestic sewage treatment plants often have insufficient carbon sources in the influent water. To solve this problem, the commonly used technical means include an additional carbon source, primary sludge fermentation, and excess sludge fermentation, but these methods are uneconomical, unsustainable, and not applicable to small-scale wastewater treatment plants. Intermittent microaeration technology has the advantages of low energy-consumption, ease of application, and low cost, and can effectively promote anaerobic digestion of municipal sludge; however little research has been reported on its use to enhance the carbon sources release of particulate organic matter (POM) from domestic wastewater. Therefore, the effect of intermittent microaeration on the carbon source release of POM was evaluated in this study, with POM as the control test. The results showed that the release concentration of soluble chemical oxygen demand (SCOD) was the highest on day 4 under microaerobic conditions, and the concentrations of SCOD, NH4+-N, and PO43−-P in the liquid phase were 1153, 137.1, and 13 mg/L, respectively. Compared with the control group, the SCOD concentration increased by 34.2%, and the NH4+-N and PO43−-P concentrations decreased by 18.65% and 17.09%, respectively. Intermittent microaeration can effectively promote the growth of Paludibacter, Actinomyces, and Trichococcus hydrolytic fermentation functional bacteria. Their relative abundances increased by 282.83%, 21.77%, and 23.47%, respectively, compared with the control group. It can simultaneously inhibit the growth of acetate-type methanogenic archaea, Methanosaeta and Methanosarcina, with a decrease in relative abundances of 16.81% and 6.63%, respectively. The aforementioned data show that intermittent microaeration can not only promote the hydrolysis of POM, but can also reduce the loss of acetic acid carbon source, which is a cost-effective technical way to enhance the release of a carbon source of particulate organic matter in domestic sewage.

Two-Step Activated Carbon Cloth Enhances Microbial Interactions and Methane Production During Anaerobic Digestion of Municipal Sludge

Two-Step Activated Carbon Cloth Enhances Microbial Interactions and Methane Production During Anaerobic Digestion of Municipal Sludge

Bioaugmentation with syntrophic volatile fatty acids-oxidizing consortia to alleviate the ammonia inhibition in continuously anaerobic digestion of municipal sludge

Ammonia inhibition easily affects the performance of anaerobic digestion (AD) for municipal sludge and the oxidization of volatile fatty acids (VFAs) is the rate-limiting step of this process. Bioaugmentation is considered to be an effective method to alleviate ammonia inhibition of AD, but most study used the hydrogenotrophic methanogens as the bioaugmentation culture. In this study, bioaugmentation of mesophilic AD (MAD) and thermophilic AD (TAD) under ammonia inhibition with syntrophic acetate and propionate oxidizing consortia was investigated. The results showed that the bioaugmented reactors recovered earlier than control reactors with 20 (MAD) and 8 (TAD) days, respectively. The high-throughput 16S rRNA gene sequencing indicated that the relative abundance of carbohydrates fermenter (Lentimicrobium), syntrophic VFAs-oxidizing bacteria (Rikenellaceae_DMER64, Smithella and Syntrophobacter) and acetoclastic and hydrogenotrophic methanogens (Methanosaeta, Methanolinea and Methanospirillum) increased in MAD after bioaugmentation. However, part of the bioaugmentation culture could not adapt to the high free ammonia (FAN) concentration in MAD and the effect was weakened. In TAD, proteolytic bacteria (Keratinibaculum and Tepidimicrobium), syntrophic VFAs-oxidizing bacteria (Syntrophomonas) and hydrogenotrophic methanogen (Methanosarcina) were strengthened. The effect of bioaugmentation in TAD was durable even at higher organic loading rate (OLR), due to its positive influence on microbial community. These results suggested that the different bioaugmentation mechanism occurred in MAD and TAD, which are derived from the synergetic effects of ammonia tolerance and microbial interactions. Our study revealed the VFAs-oxidizing consortia as bioaugmented culture could be the potential strategy to alleviate the ammonia stress of AD.

Fate of antibiotic resistance genes during temperature-changed psychrophilic anaerobic digestion of municipal sludge

The effects of anaerobic digestion (AD) on the abundance of antibiotic resistance genes (ARGs) are highly related to operational temperature. However, the removal performance of ARGs in psychrophilic AD and changed temperatures simulating variable seasonal temperatures is poorly understood. Herein, we investigated the fate of ARGs, correlated bacterial communities and physicochemical properties of AD operation at psychrophilic (15 ℃), mesophilic (35 ℃), and temperature changed conditions (15 to 35 ℃ and 35 to 15 ℃). The results indicated that ammonia release was positively correlated with temperature. The mesophilic AD facilitated phosphorous intake and ARGs proliferation and selection with oxytetracycline (OTC), while psychrophilic AD was conducive to the removal and control of ARGs if no OTC existed. The diversity and composition of AD bacterial communities were influenced more by temperature than OTC. The dominant genera like Candidatus_Microthrix and Acinetobacter had dramatical abundance discrepancies at different temperatures and were obviously positively correlated with ARGs (tet39, tetC and mexD), mobile genetic elements (MGEs) intI, insert sequences (IS) and plasmid. The physicochemical properties of AD influenced the bacterial richness, which in turn significantly correlated with the ARGs abundances. Therefore, ARGs removal could be potentially optimized by eliminating bacterial hosts with deteriorated living conditions and decreased nutrients. This study clarified the response of antibiotic resistome to different temperature variation and highlighted the potential strategies for improved ARGs removal in AD.

Aerobic post-treatment of anaerobic digested sludge with a focus on organic matter stability and the fate of antibiotic resistance genes

Abstract Digested residue remains after anaerobic digestion of municipal sludge (hereafter called anaerobic digested sludge, ADS) and needs further treatment to attain more sustainability. In this study, the compostability of ADS was assessed, focusing on the stability of organic matter and the fate of typical antibiotic resistance genes (ARGs). The results showed that ADS was not suitable as a fertilizer (reflected by a low germination index of 16.9%) due to very high concentrations of NH4+ and soluble total organic carbon. Composting post-treatment stabilized the ADS; the degradation efficiency of volatile total solids reached 18.5% within 37 d of composting. The physicochemical properties of the treated ADS indicated that a mature compost product was obtained. Real-time quantitative polymerase chain reaction analysis of typical ARGs revealed that ARG abundance was reduced four-fold during ADS composting due to a reduction in the typical ARGs and low horizontal gene transfer in host microbes. The analysis of bacterial communities revealed that members of the phyla Actinobacteria, Proteobacteria, Firmicutes, Bacteroidetes, and Chloroflexi are crucial for material transformation and ARG reduction during the ADS composting process. These results demonstrated that aerobic composting further stabilized the organic matter and reduced ARG abundance; therefore, it was found to be an effective method for ADS post-treatment.

Understanding the formation of recalcitrant dissolved organic nitrogen as a result of thermal hydrolysis and anaerobic digestion of municipal sludge

This study for the first time investigated the turnover of dissolved organic nitrogen in lab-scale thermal hydrolysis pretreatment at different temperatures with and without mesophilic anaerobic digestion at a solids retention time of 15 days.

Hydrothermal Pre- and Inter-Treatment for Anaerobic Digestion of Municipal Sludge

Hydrothermal Pre- and Inter-Treatment for Anaerobic Digestion of Municipal Sludge

Effect of SRT and digester staging on the anaerobic digestion of municipal sludge

The effect of solids retention time (SRT) on the mesophilic anaerobic digestion of a mixture of primary and waste activate sludge (WAS) was investigated. Twelve laboratory-scale (8 L) digesters were operated in triplicate at four different SRTs (5, 10, 20 and 40 days). The performance of the digesters was evaluated through measuring gas production and composition, total and volatile suspended solids (TSS & VSS) and other effluent quality parameters. VSS removal ranged between 37.6 and 53.6%. The rate of solids disintegration was modeled as a first-order decay reaction taking place in a plug-flow reactor with recycle. The calculated biodegradable fraction of the VSS and the first-order reaction rate constant were 55.3% and 0.38 d−1, respectively. During the second phase of the study, a comparison between multistage digesters in series versus a single-stage digester of equivalent total SRT was performed. Staging was found to always affect greater VSS destruction than single-stage operation. A mathematical model describing VSS destruction in a multistage reactor was developed.

Biochar as an Additive in Anaerobic Digestion of Municipal Sludge: Biochar Properties and Their Effects on the Digestion Performance

Fast pyrolysis of biomass pretreated with mineral acid produces high quality bio-oil, however, biochar produced from this process has not been characterized and its performance as an additive to an...

A comparative study of mesophilic and thermophilic anaerobic digestion of municipal sludge with high-solids content: Reactor performance and microbial community

This study involved a comparison between mesophilic (MAD) and thermophilic anaerobic digestion (TAD) of municipal sludge with high (10%) solids content; the reactor performance and the response of total and active microbial communities to changes in sludge properties were monitored. Both TAD and MAD were stably maintained. TAD performed better than MAD in biogas production and volatile total solids reduction upon feeding sludge 1. TAD was slightly inhibited by ammonia, whereas the performance of MAD was improved when sludge 2 was used as the feedstock. Alpha- and beta-diversity analyses revealed significant differences in the microbial community based on DNA and RNA datasets, indicating that not all microbes function in AD. The active microbial community diversity and composition in MAD and TAD were also driven by sludge properties. Moreover, MAD showed significantly higher richness and diversity of the active microbial community compared with TAD, regardless of changes in sludge properties.

Repurposing pre-pasteurization as an in situ thermal hydrolysis pretreatment process for enhancing anaerobic digestion of municipal sludge: a horizontal comparison between temperature-phased and standalone thermophilic or mesophilic anaerobic digestion

This study evaluated the effect of pre-pasteurization (70 °C for 45 min) on the performance of temperature-phased anaerobic digestion (TPAD) in horizontal comparison with standalone mesophilic and thermophilic anaerobic digestion (AD).

Aspects on Anaerobic Digestion of Municipal Sludge, Some Aspects on its Sustainability and Possible Enhancements

The anaerobic treatment of organic rich pollutants has a very long history within the water industry. Two major applications have been used: Treating sludge streams from midsized and large wastewater treatment plants and for industrial wastewater streams containing high concentrations of organic carbon. This paper presents the status of anaerobic digestion of sludge streams in municipal wastewater. The paper highlights both the potentials and limitations of the technology. Further the alternative or complementing HTC-technology is presented and analyzed. The constraints, limitations and options for the reuse of processed municipal sludge is accordingly pointed out. Our usage of water is found more and more complex, along with the addition of a number of synthetic agents, such as pharmaceuticals and other complex polluting agents we find that the traditionally acknowledged sludge treatment stabilization methods are not sufficient. The paper points out that the anaerobic digestion may be combined with for instance the HTC-process. In a longer perspective the HTC may even replace the current anaerobic digestion. However, the HTC-technology will raise further interesting questions: The important points that need further investigations are inter alia: 1) To further clarify the quality of reject water from the hydrochar, with respect to rest pollutants. 2) To evaluate to what extent the HTC process may become a feasible way to disintegrate pharmaceutical remains found in municipal sludge. 3) How to further enhance the ways to recover raw materials from the hydrochar, such as phosphorus and carbon. Nethertheless, the process may allow for some very promising pathways within the future municipal sludge management.