Temperature-phased Anaerobic Digestion Research Articles

A novel acetogenic bacteria isolated from waste activated sludge and its potential application for enhancing anaerobic digestion performance

The development of anaerobic digestion (AD) for volatile fatty acids (VFAs) production from waste activated sludge (WAS) is arrested due to low hydrolysis and acidification efficiency. This study proposed to enhance WAS reduction and VFAs accumulation during AD process via bioaugmentation of acetate-producing bacteria. Four acetogens were firstly isolated from a temperature-phased anaerobic digestion (TPAD) system. The acetate production efficiency of different isolates ranged from 15.8 to 73.7 mg acetate/g TOC, in which the bacterial strain NJUST19 was found to be the most effective strain. The results of morphological, biochemical characteristics as well as phylogenetic analysis showed that the isolate NJUST19 was Gram-positive and rod-shaped, catalase-negative, nitrate reduction-positive, methyl red-negative and capable of starch and gelatin hydrolysis, for which the name of Clostridium sp. NJUST19 was proposed. The optimal culture conditions (i.e. initial pH and temperature) were evaluated for their effects on microbe growth of selected NJUST19, and the maximum acetate production was observed at pH 9.0 and temperature of 40 °C. In the case of modified TPAD system inoculated with Clostridium sp. NJUST19, total suspended solids (TSS) removal rate and maximum VFAs accumulation increasing to 35.3% and 4200 mg/L, respectively, which was much higher than that of control (21.9% and 2894 mg/L). These results indicated that Clostridium sp. NJUST 19 is capable of enhancing digestion efficiency with a great benefit for VFAs production, offering potential prospects for bioaugmentation of WAS anaerobic digestion.

Strategy of adjusting recirculation ratio for biohythane production via recirculated temperature-phased anaerobic digestion of food waste

The stable H2 production is the important link in the anaerobic biohythane fermentation. In order to address the key parameters for the stable H2 production in the recirculated temperature-phased anaerobic digestion (R-TPAD) system, a critical strategy was proposed to adjust the recirculation ratio (R). The adjusting strategy was examined on a lab-scale R-TPAD system. The R-TPAD system was started up and operated with R = 1. Another system without recirculation (R = 0) was also operated as the control system. By narrowing the probable range from 0 < R < 1, the value of R = 0.4 was obtained for stable biohythane production from R-TPAD system. The harvested R-TPAD process achieved the volatile solids removal of 84.8% and the biohythane yield of 475 L/kg-VSfed with the H2 content of 10.5%, where the H2 yield efficiency was 248.0 mL-H2/CODremoved. The success of operating R-TPAD was attributed to the proposed strategy, which used the tendency of existing CH4 and the pH above 4.0 as the critical indicators for the stable H2 production.

Microbial population dynamics in temperature‐phased anaerobic digestion of municipal wastewater sludge

AbstractBACKGROUNDThe present study compared the performance and capability of thermophilic–mesophilic, temperature‐phased anaerobic digestion (TPAD) of wastewater sludge at 45 and 55 °C in terms of rate of hydrolysis and methanogenesis at two point interval times – December and January – with operational conditions kept constant (total solid content 6.5%, solids retention time 12.5 days).RESULTSThe reduction of volatile solids (VS) was 77% at 45 °C TPAD‐1 and 72% at 55 °C TPAD‐II. The accumulation of ammonia and volatile fatty acids (VFAs; propionic acid) were observed to be below the inhibitory range (&gt;3000 mg L−1), whereas the methane (CH4) production (45 °C, 3.55 ± 0.47 L CH4 L−1 day−1; 35 °C, 1.44 ± 0.12 L CH4 L−1 day−1) remained considerably higher in TPAD‐I than TPAD‐II. Furthermore, the TPAD‐II system suffered from certain degree of instability due to high level of total VFAs (6087 ± 1578 mg L−1), low buffering capacity, increased level of total NH3 (2982 ± 219 mg L−1) and free NH3 (246 ± 25 mg L−1), and relatively reduced CH4 production (1.69 ± 0.1 L L−1 day). The bacterial and archaeal population of the TPADs investigated by 454 pyrosequencing and Illumina sequencing showed, in both TPAD systems, a bacterial community dominated by Firmicutes, followed by Bacteriodetes, Proteobacteria, Synergistetes and Actiniobacteria. The archaeal community was dominated by Methanimicrobia (74–84% Methanosarcina) and Methanobacteria (15–27% Methanobacterium). A progression from genus Clostridium to Coprothermobacter and Tepidanaerobacter, and Methanocarcina to Methanothermobacter and Methanobacterium was observed in TPAD‐II.CONCLUSIONSThis study proved the processes driving the dynamics of key microbial population and its correlation with hydrolytic functionality of TPAD systems. © 2019 Society of Chemical Industry

Genomic dynamics of full-scale temperature-phased anaerobic digestion treating waste activated sludge: Focusing on temperature differentiation

A robust microbial community is essential for the overall stability and performance of the anaerobic digestion process. In this study, two digesters of a full-scale temperature-phased anaerobic digestion plant treating waste activated sludge were sampled for one year. The acidogenesis reactor (AR) was run at 45 ± 2 °C for six months in Period I and was run at 38 ± 2 °C for six months in Period II. While the methanogenesis reactor (MR) was run at 36 ± 3 °C throughout the year. 16S rRNA amplicon sequencing and GeoChip 5.0 results showed that samples were clearly differentiated by reactors and periods. The elevated temperature in AR during Period I improved the effects of phase separation between the AR and MR. In AR, Fervidobacterium, assigned to Class Thermotogae, had a higher relative abundance of 8.9% in Period I. The abundance of genes involved with carbon degradation was significantly higher in Period I than Period II. In MR, the relative abundance of Methanosarcina increased from 19.8% in Period I to 30.6% in Period II. In addition, the influent characteristics, reactor performance, and operating parameters were determined as the key variables shaping the microbial community, contributing to a total of 76.3% and 69.5% of the variance of the AR and MR, respectively. Combined, this study enriches our understanding of genomic dynamics in full scale temperature-phased anaerobic digestion process.

Biomethanation efficiency of para-grass in piggery wastewater in single stage and temperature phased anaerobic systems

Abstract Effects of para-grass (PG) addition to pig manure (PM) digester were evaluated at organic loadings 0.10–3.76 gVS/L.d by different PG mixing ratios 0–8% in mesophilic single-stage (MS) and temperature-phased anaerobic digestion (TPAD, comprising T1 and M2 reactors) systems. Results showed equivalent methane production between MS and TPAD until 4%PG mix. Highest biogas yields obtained were 271.7 and 264.0 m3/tondry for MS and TPAD, respectively. Even with intense VFAs accumulation, the acidification yield in T1 was less than M2 because of continuous conversion of VFAs to CH4. Only at higher loading (8%PG), reactor staging by temperature was justified for this co-digestion as TPAD exhibited a superior performance and lesser mass transfer impediment. Para-grass addition to PM digester shifted the domination of bacterial strains whereas achaea were steady. Higher microbial diversity and some evolving hydrolytic bacteria observed in T1 could contribute to greater system stability at high solid loading. An addition of small front-end thermophilic tank should be considered when expansion of the existing MS system is planned to process higher solid.

Novel Solutions in Modeling of Anaerobic Digestion Process - Two-Phase AD Models Development and Comparison

Abstract This work focuses on Two Phase Anaerobic Digestion – a novel approach to split reactions’ chain in two separated tanks, each with specialized microbe community to achieve the best possible efficiency for each part of conversion. More specifically, the article tackle the topic of evaluation the possibility to adapt a mathematical model, previously dedicated for Autogenerative High Pressure Digestion (AHPD), to make use of it in simulation of Temperature Phased Anaerobic Digestion (TPAD) process. A comprehensive study of available solutions for biogas production simulation in conventional and TPAD configuration is additionally performed. Basing on its results, a reference model from literature, for comparison purpose is selected. Revisions and modifications, necessary to adjust previously developed model, to TPAD process, are described. Also, additional improvements like redesigned pH calculating algorithm is presented. Finally, the comparison between model predictions, a reference model and pilot-scale data is carried out. The results show that our current model needs further optimization, however even at this stage it provides acceptable results in short-range simulations (not longer than 42 days). Further works should focus on process stability improvement, especially in the thermophilic stage of biogas production. There's an opportunity for innovation as the research shows that requirement of accurate, large-scale optimized TPAD process model, is still not fulfilled.

The hydrolytic stage in high solids temperature phased anaerobic digestion improves the downstream methane production rate

The role of the hydrolytic stage in high solids temperature phased anaerobic digestion was investigated with a mixture of cattle slurry and maize silage with variable ratios (100, 70 and 30% volatile solids coming from cattle slurry). It was incubated for 48 h at 37, 55, 65 and 72 °C. Soluble chemical oxygen demand and biochemical methane potential were measured at 0, 24 and 48 h. Higher temperatures improved the amount of solubilized COD, which confirmed previously reported results. Nevertheless, solubilization mostly took place during the first 24 h. The rate of methane production in post-hydrolysis BMPs increased after 48 h hydrolysis time, but not after 24 h. The first order kinetic constant rose by 40% on average. No correlation was observed between soluble COD and downstream methane production rate, indicating a possible modification of the physical structure of the particulate solids during the hydrolytic stage.

High solid temperature phased anaerobic digestion from agricultural wastes: Putting several reactors in sequence

High solid anaerobic digestion of agricultural wastes (manure and grass silage) was tested on temperature phased anaerobic digester (TPAD) at lab-scale. A 4days hyperthermophilic hydrolysis was followed by a 15days methanogenesis. The TPAD was divided into 4 or 5 tanks in series without recycling: 2 sectors for hydrolysis (2days HRT each) and 2 or 3 sectors for methanogenesis (5+10 or 3×5days HRT). Two different combinations of temperatures (65°C–37°C, 65°C–55°C) were investigated to assess the process efficiency.For all tested conditions, the TPAD operated steadily with a methane productivity of 235+/−3 mLCH4STPgVS−1. Using four or five reactors in series enabled to identify that during the two first days of hydrolysis, the hydrolysis yield and acidification yield were much higher (22% and 13%, respectively) than during the next two days (2% and 2% respectively). Moreover, concerning methanogenesis it appeared that the retention time may be shortened by 5days with little loss in methane production (11%). In the methanogenic sectors, the uptake of volatile fatty acids and the methane production were higher at 55°C than 37°C.The results suggest that the hydrolytic sector could be limited at 2days HRT, while the methanogenic sector would support a 10days HRT with the feedstocks used.

Temperature-phased anaerobic digestion of food waste: A comparison with single-stage digestions based on performance and energy balance

The temperature-phased anaerobic digestion (TPAD) of food waste was studied for the purpose of comparing with single-stage mesophilic and thermophilic anaerobic digestion. The biogas and methane yields in the TPAD during the steady period were 0.759 ± 0.115 L/g added VS and 0.454 ± 0.201 L/g added VS, which were lower than those in the two single-stage anaerobic digestion. The improper sludge retention time may be the reason for the lower biogas and methane production in TPAD. The removal of volatile solids in the TPAD was 78.55 ± 4.59% and the lowest among the three anaerobic digestion processes. The reaction ratios of the four anaerobic digestion steps in the TPAD were all lower than those in the two single-stage anaerobic digestion. The energy conversion efficiency of the degraded substrate in the TPAD was similar with those in single-stage mesophilic and thermophilic anaerobic digestion systems.

An Evaluation of the Efficiency of Different Hygienisation Methods

The aim of this study is to evaluate the efficiency of hygienisation by pasteurisation, temperature-phased anaerobic digestion and sludge liming. A summary of the legislation concerning sludge treatment, disposal and recycling is included. The hygienisation methods are compared not only in terms of hygienisation efficiency but a comparison of other criteria is also included.

Phase separation and microbial distribution in the hyperthermophilic-mesophilic-type temperature-phased anaerobic digestion (TPAD) of waste activated sludge (WAS)

In order to investigate the phase separation and microbial distribution in the TPAD, the conventional thermophilic-mesophilic type (TM-TPAD) and the hyperthermophilic-mesophilic type (HM-TPAD) were operated with a single-stage mesophilic anaerobic digestion (MAD) as control. HM-TPAD accomplished the volatile solids destruction 14.5% higher than MAD. Calculating conversion efficiencies distinguished the separation of acidogenic and methanogenic phases in HM-TPAD, which was not found in TM-TPAD. The differences on microbial distributions also reflected the phase separation in HM-TPAD. The protein degraders, Coprothermobacter had higher abundance in the first stage than the second stage of HM-TPAD but it had similar abundance between the two stages of TM-TPAD. Also, the archaeal communities from the two stages of HM-TPAD shared the least similarity but those from the two stages of TM-TPAD were closely similar.

Influences of low-energy input microwave and ultrasonic pretreatments on single-stage and temperature-phased anaerobic digestion (TPAD) of municipal wastewater sludge

The effect of low energy-input (2.5 kJ/g total solids) microwave (MW) irradiation and ultrasonication (US) on single-stage mesophilic anaerobic digestion (AD) and temperature-phased AD (TPAD) treating wastewater sludge was assessed. The goal was to achieve a higher net energy along with improved digestate for agricultural applications. At sludge retention times (SRT) of 20 and 14 days, TPAD achieved significantly (39–45%) higher methane production, pathogen destruction (4-log) and digester volume reductions compared to single-stage AD (controls). The higher methane yields resulted in higher net energies for TPAD (4.7–5.1 kJ/g volatile solids or VS) compared to controls (3.3–3.7 kJ/g VS). Although improvements in organic removals and methane yields were observed after MW and US, the energy input for pretreatments were not compensated by the increased methane production, and therefore were concluded to be infeasible for industrial applications for single-stage and TPAD. All TPADs provided the highest pathogenic removal, and met the Class A biosolids fecal coliform requirements, while MW pretreatment achieved the highest fecal coliform removal for single-stage AD with digestates classified as Class B. Digesters incorporating thermal pretreatment (MW and MW + TPAD) yielded the highest amount of extra heat (4.2–5.8 kJ/g VS) that could be utilized within/outside of the facility.

Temperature phased anaerobic digestion of municipal sewage sludge: a Bardenpho treatment plant study

The disposal of waste sludge generated from wastewater treatment plants (WWTPs) is a growing problem worldwide, and contributes to over 50% of the operating costs of current WWTPs. In this study, temperature-phased anaerobic digestion (TPAD) and conventional (single-stage) mesophilic anaerobic digestion were investigated in order to determine the most beneficial process for the intended digester facility to be constructed for the fermented primary and secondary sludge from a Bardenpho type biological nutrient removal plant. This was accomplished by considering several operational control parameters for three different sludge retention times. This study has shown that the TPAD system had significant improvement in biogas and methane production; solids and organic removal; pathogen reduction and dewaterability over the conventional digestion. In terms of overall volatile sulphur compounds formation normalized per volatile solids added, no significant effects were observed between TPAD and control digester.

Recovery of energy and nutrient resources from cattle paunch waste using temperature phased anaerobic digestion

Cattle paunch is comprised of partially digested cattle feed, containing mainly grass and grain and is a major waste produced at cattle slaughterhouses contributing 20–30% of organic matter and 40–50% of P waste produced on-site. In this work, Temperature Phased Anaerobic Digestion (TPAD) and struvite crystallization processes were developed at pilot-scale to recover methane energy and nutrients from paunch solid waste. The TPAD plant achieved a maximum sustainable organic loading rate of 1–1.5kgCODm−3day−1 using a feed solids concentration of approximately 3%; this loading rate was limited by plant engineering and not the biology of the process. Organic solids destruction (60%) and methane production (230LCH4kg−1 VSfed) achieved in the plant were similar to levels predicted from laboratory biochemical methane potential (BMP) testing. Model based analysis identified no significant difference in batch laboratory parameters vs pilot-scale continuous parameters, and no change in speed or extent of degradation. However the TPAD process did result in a degree of process intensification with a high level of solids destruction at an average treatment time of 21days. Results from the pilot plant show that an integrated process enabled resource recovery at 7.8GJ/dry tonne paunch, 1.8kgP/dry tonne paunch and 1.0kgN/dry tonne paunch.

Upgrading of mesophilic anaerobic digestion of waste activated sludge by thermophilic pre-fermentation and recycle: Process performance and microbial community analysis

In order to upgrade the conventional mesophilic anaerobic (MD) of waste activated sludge (WAS), a thermophilic pre-fermentation and a recycle system were introduced to form continuous thermophilic–mesophilic temperature-phased anaerobic digestion (TPAD) and TPAD with recycling capability (TPAD-R). The synchronous operation, with the MD as control, indicated significant improvements in reduction of solids and the ability to produce methane in the TPAD and TPAD-R, with a similar amount of improvement in both systems. VS reduction was improved from about 40% in the MD to 50%, and the methane recovery rates were improved from 0.53L/g VS destroyed in the MD to 0.63L/g VS destroyed accordingly. The thermophilic stage in the TPAD and TPAD-R made a large contribution to organic matter degradation and solubilization, and the specific hydrolysis rate in thermophilic stage attained 0.2gCOD/gVS/d. Furthermore, under experimental conditions, the thermophilic stage in the TPAD and TPAD-R also played an important role in acidogenesis and methanogenesis. The thermophilic pre-fermentation made Firmicutes and Methanosarcina become the main phylum and genus in the mesophilic stage, accounting for 44% and 54%, respectively. The recycle system improved the diversity of bacteria and archaea in the thermophilic stage of the TPAD-R. The TPAD and TPAD-R also achieved about twice the net energy of the MD.

Comparison of single-stage and temperature-phased two-stage anaerobic digestion of oily food waste

Anaerobic digestion is an effective technology to recover energy from oily food waste. A single-stage system and temperature-phased two-stage systems with and without recycle for anaerobic digestion of oily food waste were constructed to compare the operation performances. The synchronous operation indicated the similar ability to produce methane in the three systems, with a methane yield of 0.44L/g VSadded. The pH drop to less than 4.0 in the first stage of two-stage system without recycle resulted in poor hydrolysis, and methane or hydrogen was not produced in this stage. Alkalinity supplement from the second stage of two-stage system with recycle improved pH in the first stage to 5.4. Consequently, 35.3% of the particulate COD in the influent was reduced in the first stage of two-stage system with recycle according to a COD mass balance, and hydrogen was produced with a percentage of 31.7%, accordingly. Similar solids and organic matter were removed in the single-stage system and two-stage system without recycle. More lipid degradation and the conversion of long-chain fatty acids were achieved in the single-stage system. Recycling was proved to be effective in promoting the conversion of unsaturated long-chain fatty acids into saturated fatty acids in the two-stage system.

Semicontinuous Temperature-Phased Anaerobic Digestion (TPAD) of Organic Fraction of Municipal Solid Waste (OFMSW). Comparison with single-stage processes

The optimization of anaerobic digestion of organic wastes is a challenge to maximize energy production through biogas production process. In this study, semicontinuous TPAD (Temperature Phased Anaerobic Digestion) process has been used for the treatment of the Organic Fraction of Municipal Solid Waste (OFMSW) coming from a mechanical–biological-treatment (MBT) plant. TPAD combines the advantages of operating in different temperature ranges getting better efficiencies of organic matter removal and higher methane productivities than single-stage anaerobic digestion. In this study, the configuration used in the overall process was a thermophilic reactor (55–57°C) for the first phase followed by a mesophilic one (35–37°C) for the second phase. Two TPAD conditions have been tested in this paper: 4:10 and 3:6. The first digit means the SRT used in the first thermophilic phase while the second digit is related to the SRT used in the second mesophilic phase. Moreover, the performance of TPAD processes was compared with those from single-stage digesters operating at similar SRT (i.e., mesophilic and thermophilic reactors operating at 15days SRT and thermophilic reactor operating at 10days).The results showed that achievement reached in TPAD 4:10 was better than the corresponding one in TPAD 3:6, obtaining higher productivity of methane (35–45%) and removal of organic matter (6–19%).Moreover, the results indicate that TPAD processes reach higher efficiencies for organic matter removal (16%, 10% and 30% for DOC, CODsoluble and VS, respectively) and higher methane yields (26–60%) than single-stage systems operating at similar SRT.

Temperature-phased anaerobic digestion of the hydromechanically separated organic fraction of municipal solid waste with sewage sludge

This paper examines the temperature-phased anaerobic digestion (TPAD) process treating the mixture of municipal sewage sludge with the hydromechanically separated organic fraction of municipal solid waste (HS-OFMSW). The experiments showed that the performance of the TPAD process strongly depends on the conditions applied in the thermophilic stage. The TPAD system operated at a solids retention time (SRT) of 1 and 14 days in the first and second steps, respectively, achieved the overall methane yield of 333 l CH4 kgVS−1 and the volatile solids reduction of 52.1%, whereas the corresponding values reported for a control single-stage mesophilic process were 230 l CH4 kgVS−1 and 37.23%, respectively. However, when an SRT of the thermophilic reactor was extended to 2 days, the methane production in the subsequent mesophilic stage significantly decreased. It was therefore concluded that the prolonged exposure of feedstock to the thermophilic temperatures can lead to greater intensity of protein degradation. Consequently, higher amounts of ammonia are liberated to the liquid phase, which results in the inhibition of methanogenesis in the subsequent mesophilic step. Moreover, ammonia affects the release and distribution of volatile fatty acids, which also influences the performance of the whole TPAD system.

Quantification of viable but nonculturable Salmonella spp. and Shigella spp. during sludge anaerobic digestion and their reactivation during cake storage.

The presence of viable but nonculturable (VBNC) bacterial pathogens which often fail to be detected by cultivation and can regain the cultivability if the living conditions improve were reported. The objective of this study was to determine the occurrence of VBNC Salmonella spp. and Shigella spp. in the biosolids during anaerobic digestion and its reactivation during the cake storage. The occurrence of VBNC Salmonella spp. and Shigella spp. during mesophilic, temperature-phased, thermophilic anaerobic digestion of sewage sludge and the subsequent storage were studied by RT-qPCR and most probable number (MPN) method. The VBNC incidence of Salmonella spp. and Shigella spp. during thermophilic digestion was four orders of magnitude higher than those of mesophilic digestion. Accordingly, higher resuscitation ratio of VBNC pathogens was also achieved in thermophilic digested sludge. As a result, the culturable Salmonella typhimurium contents in thermophilic digested sludge after cake storage were two orders of magnitude higher than mesophilic digestion. Both quantitative PCR and reverse transcription quantitative PCR assay results showed the two bacterial counting numbers remained stable throughout the cake storage. The results indicate that the increase in the culturable Salmonella spp. and Shigella spp. after centrifugal dewatering was attributed to the resuscitation from the VBNC state to the culturable state. Thermophilic anaerobic digestion mainly induced Salmonella spp. and Shigella spp. into VBNC state rather than killed them, suggesting that the biological safety of sewage sludge by temperature-phased anaerobic digestion should be carefully assessed.

Volume ratios between the thermophilic and the mesophilic digesters of a temperature-phased anaerobic digestion system affect their performance and microbial communities

An experimental temperature-phased anaerobic digestion (TPAD) system, with the thermophilic digester operated at neutral pH and with a balanced acidogenesis and methanogenesis (referred to as NT-TPAD), was evaluated with respect to the microbial communities and population dynamics of methanogens when digesting dairy cattle manure at 15-day overall system hydraulic retention time (HRT). When fed a manure slurry of 10% total solid (TS), similar system performance, 36-38% volatile solid (VS) removal and 0.21-0.22 L methane g(-1) VS fed, was achieved between a 5-day and 7.5-day HRT for the thermophilic digester. However, the thermophilic digester achieved a greater volumetric biogas yield when operated at a 5-day RT than at a 7.5-day HRT (6.3 vs. 4.7 L/L/d), while the mesophilic digester had a stable volumetric biogas yield (about 1.0 L/L/d). Each of the digesters harbored distinct yet dynamic microbial populations, and some of the methanogens were significantly correlated with methane productions. Methanosarcina and Methanosaeta were the most important methanogenic genera in the thermophilic and the mesophilic digesters, respectively. The microbiological findings may help understand the metabolism that underpins the anaerobic processes within each of the two digesters of TPAD systems when fed dairy manure.