Temperature-phased Anaerobic Digestion Process Research Articles

Temperature-phased anaerobic sludge digestion effectively removes antibiotic resistance genes in a full-scale wastewater treatment plant

Sludge is a major by-product and the final reservoir of antibiotic resistance genes (ARGs) in wastewater treatment plants (WWTPs). Temperature-phased anaerobic digestion (TPAD), consisting of thermophilic anaerobic digestion (AD) (55 °C) and mesophilic AD processes (37 °C), has been implemented in WWTPs for sludge reduction while improving the biomethane production. However, the impact of TPAD on the ARGs' fate is still undiscovered in lab-scale experiments and full-scale WWTPs. This study, for the first time, investigated the fate of ARGs during the TPAD process across three seasons in a full-size WWTP. Ten typical ARGs and one integrase gene of class 1 integron (intI1) involving ARGs horizontal gene transfer were examined in sludge before and after each step of the TPAD process. TPAD reduced aac(6′)-Ib-cr, blaTEM, drfA1, sul1, sul2, ermb, mefA, tetA, tetB and tetX by 87.3–100.0 %. TPAD reduced the overall average absolute abundance of targeted ARGs and intI1 by 92.39 % and 92.50 %, respectively. The abundance of targeted ARGs in sludge was higher in winter than in summer and autumn before and after TPAD. During the TPAD processes, thermophilic AD played a major role in the removal of ARGs, contributing to >60 % removal of ARGs, while the subsequent mesophilic AD contributed to a further 31 % removal of ARGs. The microbial community analysis revealed that thermophilic AD reduced the absolute abundance of ARGs hosts, antibiotic resistant bacteria. In addition, thermophilic AD reduced the abundance of the intI1, while the intI1 did not reproduce during the mesophilic AD, also contributing to a decline in the absolute abundance of ARGs in TPAD. This study demonstrates that TPAD can effectively reduce the abundance of ARGs in sludge, which will suppress the transmission of ARGs from sludge into the natural environment and deliver environmental and health benefits to our society.

Comparative analysis between a conventional and a temperature-phased anaerobic digestion system: Monitoring of the process, resources transformation and energy balance

This study was carried out with the principal aim of obtaining reliable outcomes for the future implementation of a temperature-phased anaerobic digestion (TPAD) process in a large (2 M population equivalent, p.e.) WWTP. With the aid of pilot-scale (10 L) reactors fed by pure primary sludge (PS), a TPAD process, where the first and the second reactor were operated at 50 °C and 38 °C, respectively, was compared with a conventional mesophilic (38 °C) anaerobic digestion (AD) process. The initial hydraulic retention time (HRT) of the first, acidogenic, reactor of the TPAD was reduced from 3 to 2 days in the second part of the test.The results demonstrated that the TPAD system had been stable for all the duration of the test (approx. 100 days), as testified by the steady values of pH and tVFAs/TA ratio, notwithstanding the decrease in the HRT. The TPAD proved to be more efficient in volatile solid (VS) reduction and methane generation, compared to the conventional mesophilic AD process. In fact, the VS reduction increased from 42% to approx. 55% and the specific methane potential (SMP) from 280 to 332 NL/kg VS added. An excellent phase separation was observed between the two acidogenic and methanogenic reactors, as demonstrated by the low SMP (only 3% of the overall production) recorded from the first reactor of the TPAD system.However, the energy analysis demonstrated that the higher SMP obtained in the TPAD was not sufficient to compensate the higher amounts of heat required for sludge heating and heat loss compensation. Only a process of heat recovery could make the TPAD system really profitable, thus increasing the aliquot of energy in the form of methane, available for users external to the WWTP, by 20%. This result represents a step in the evolution of traditional WWTPs towards more energy efficient and sustainable facilities.

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.

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.

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.

Temperature-phased anaerobic digestion of Industrial Organic Fraction of Municipal Solid Waste: A batch study

Anaerobic digestion of the Organic Fraction of Municipal Solid Wastes from non-selective collection systems is widely implemented at industrial scale. Classically, single-temperature anaerobic digestion systems (mesophilic or thermophilic) have been used although some limitations were found in the processes performance. However, the specific advantages of the two processes could be exploited by using a temperature-phased anaerobic digestion (TPAD). Thus, in this paper, the application of a TPAD process without microbiological separation (thermophilic 55°C–mesophilic 35°C) to the biomethanation of OFMSW has been studied.The TPAD assays were carried out in batch reactors. The processing times for the thermophilic (55°C) stage have been located in the range from 12 to 3days. After the first stage, the waste treatment was continued in a second mesophilic reactor (35°C) until completing the degradation process.The higher values for the organic matter removal (VS removal 82–85%) and the maximum specific growth rates of microorganisms (0.31–0.43days-1), were obtained for thermophilic phase operation at 5 and 4days, respectively. Lower operation times, namely 3-days, for thermophilic first-phase are viable and the methane productivity obtained was comparable with respect to that obtained in the above mentioned conditions (0.6L/gVSremoved). However, in this conditions, a decrease in the maximum specific growth rate of microorganisms (0.26days−1), a lower SV removal (75%), and a higher final amount of non-biodegradable substrate (1231mg/L) were obtained, working at 3days, despite of using higher operational times (29days). According to these results, it can be concluded than the optimum time for the thermophilic first-phase in TPAD would be between 5-days and 4-days.

Upgrading the temperature-phased anaerobic digestion of waste activated sludge by ultrasonic pretreatment

Abstract Biochemical methane potential assays were performed to assess the influence of ultrasonic pretreatment on the temperature-phased anaerobic digestion (TPAD) of waste-activated sludge (WAS). Ultrasound (specific energy = 3380 kJ kg−1 TS) was applied to the WAS before the thermophilic stage or to the effluent after the thermophilic stage. In addition, a control system without pretreatment was also carried out. No significant differences were found in the overall performance of the TPAD process, but different behaviours were observed between the thermophilic and mesophilic stages. Total methane production was enhanced by more than 50% and the volatile solid removal increased by 13% in comparison to the TPAD control process. Finally, a previously defined kinetic model was applied successfully to the experimental data and showed an excellent fit.

Variation of ADM1 by using temperature-phased anaerobic digestion (TPAD) operation

The objective of the study was to examine the application of the Anaerobic Digestion Model No. 1 (ADM1) developed by the IWA task group for mathematical modelling of anaerobic process. Lab-scale temperature-phased anaerobic digestion (TPAD) process were operated continuously, and were fed with co-substrate composed of dog food and flour. The model platform implemented in the simulation was a derivative of the ADM1. Sensitivity analysis showed that k m.process (maximum specific uptake rate) and K S.process (half saturation value) had high sensitivities to model components. Important parameters including maximum uptake rate for propionate utilisers ( k m.pro ) and half saturation constant for acetate utilisers ( K S.ac ) in the thermophilic digester and maximum uptake rate for acetate utilisers ( k m.ac ) in the mesophilic digester were estimated using iterative methods, which optimized the parameters with experimental results. Simulation with estimated parameters showed good agreement with experimental results in the case of methane production, uptake of acetate, soluble chemical oxygen demand (SCOD) and total chemical oxygen demand (TCOD). Under these conditions, the model predicted reasonably well the dynamic behavior of the TPAD process for verifying the model.

Anaerobic co-digestion of sewage sludge and food waste using temperature-phased anaerobic digestion process

This study was performed to overcome the low efficiency of anaerobic digestion of sewage sludge and food waste by combining temperature-phased digestion, sequencing batch operation, and co-digestion technology. It was demonstrated that the temperature-phased anaerobic sequencing batch reactor (TPASBR) system for the co-digestion of sewage sludge and food waste resulted in enhanced volatile solids (VS) reduction and methane production rate. At the organic loading rate (OLR) of 2.7 g VS/l/d, the TPASBR system showed the higher VS reduction (61.3%), CH4 yield (0.28 l/g VS(added)) and CH4 production rate (0.41 l CH4/l/d) than those (0.29 l CH4/l/d) of the mesophilic two-stage ASBR (MTSASBR). In the specific methanogenic activity (SMA) tests on thermophilic biomass of the TPASBR system, the average SMA of acetate (93 ml CH4/gVSS/d) was much higher than those of propionate (46 ml CH4/g VSS/d) and butyrate (76 ml CH4/g VSS/d). Also, higher specific hydrolytic activity (SHA, 217 mg COD/g VSS/d) of the biomass supported fast hydrolysis under thermophilic conditions. The track study revealed that the most active period of the 24 h cycle was between 6 and 12 h. The enhanced performance of the TPASBR system could be attributed to longer solids retention time, fast hydrolysis, higher CH4 conversion rate, and balanced nutrient condition of co-substrate. It was verified that this combination could be a promising and practical alternative for the simultaneous recycling of two types of organic fraction of municipal solid waste (OFMSW) with high stability.

Cattle waste treatment and Class A biosolid production using temperature-phased anaerobic digester

The performance of the temperature-phased anaerobic digestion (TPAD) process in the digestion of livestock wastes has never been evaluated, though the process has proven advantages over other high-rate anaerobic digestion processes in the treatment of municipal wastewater sludge. This study investigated the applicability of the TPAD process in the stabilization of dairy cattle manure. For the organic loadings investigated from 1.87 to 5.82 g VS/l/day, volatile solids (VS) reduction in the range 36–41% was achieved with biological conversion efficiency of 0.52–0.62 l methane/g of VS destroyed. Fecal Coliform and Salmonella counts in the residual solids were less than the limits specified by U.S.E.P.A. to meet Class A Standards. The high volatile fatty acid concentrations in the thermophilic effluent were reduced significantly by the mesophilic stage and ammonia nitrogen concentrations in the reactors were below inhibitory levels. The process was stable at all the organic loading rates studied.

Effect of varying solids concentration and organic loading on the performance of temperature phased anaerobic digestion process.

The effect of varying total solids (TS) and volatile solids (VS) concentrations and organic loading on the performance of a temperature phased anaerobic digestion (TPAD) system treating a mixture of primary and waste activated sludges was evaluated. An optimum volatile solids destruction of 61.5% occurred at a feed concentration of 4.9% (corresponding to 3.8% VS concentration) in the system operated at a total detention time of 20 days. At a total solids concentration of 7.9% (5.8% VS concentration), the volatile solids destruction efficiency dropped to 52.5%. At all conditions (4.4 to 7.9% TS) the TPAD system was able to meet the requirements for Class A biosolids, including those for fecal coliform and volatile solids destruction. The effluent fecal coliform concentration never exceeded 628 most probable number (MPN)/g TS. Thermophilic biomass activity tests were run on both the thermophilic (55 degrees C) and the mesophilic (35 degrees C) sludge. Biomass from the thermophilic reactor showed much greater activity at 55 degrees C than at 35 degrees C. However, significant activity was still present when the test was run at 35 degrees C. Activity tests completed on samples from the mesophilic reactor also had high activities at 55 degrees C, sometimes equal to the activity of the thermophilic biomass. These results suggest that the bacterial consortia in the TPAD system may be temperature-tolerant and not necessarily two distinct communities with two distinct temperature regimes as had been previously assumed.