Digestion Of Activated Sludge Research Articles

Deep insights into the roles and microbial ecological mechanisms behind waste activated sludge digestion triggered by persulfate oxidation activated through multiple modes

Persulfate oxidation (PS) is widely employed as a promising alternative for waste activated sludge pretreatment due to the capability of generating free radicals. The product differences and microbiological mechanisms by which PS activation triggers WAS digestion through multiple modes need to be further investigated. This study comprehensively investigated the effects of persulfate oxidation activated through multiple modes, i.e., ferrous, zero-valent iron (ZVI), ultraviolet (UV) and heat, on the performance of sludge digestion. Results showed that PS_ZVI significantly accelerated the methane production rate to 12.02 mL/g VSS. By contrast, PS_Heat promoted the sludge acidification and gained the maximum short-chain fatty acids (SCFAs) yield (277.11 ± 7.81 mg COD/g VSS), which was 3.41-fold compared to that in PS_ZVI. Moreover, ferrous and ZVI activated PS achieved the oriented conversion of acetate, the proportions of which took 73% and 78%, respectively. MiSeq sequencing results revealed that PS_Heat and PS_UV evidently enriched anaerobic fermentation bacteria (AFB) (i.e., Macellibacteroides and Clostridium XlVa). However, PS_Ferrous and PS_ZVI facilitated the enrichment of Woesearchaeota and methanogens. Furthermore, molecular ecological network and mantel test revealed the intrinsic interactions among the multiple functional microbes and environmental variables. The homo-acetogens and sulfate-reducing bacterial had potential cooperative and symbiotic relationships with AFB, while the nitrate-reducing bacteria displayed distinguishing ecological niches. Suitable activation modes for PS pretreatments resulted in an upregulation of genes expression responsible for digestion. This study established a scientific foundation for the application of sulfate radical-based oxidation on energy or high value-added chemicals recovery from waste residues.

Limitations of a biokinetic model to predict the seasonal variations of nitrous oxide emissions from a full-scale wastewater treatment plant

A biokinetic model based on BioWin's Activated Sludge Digestion Model (ASDM) coupled with a nitrous oxide (N2O) model was setup and calibrated for a full-scale wastewater treatment plant (WWTP) Amsterdam West, in the Netherlands. The model was calibrated using one year of continuous data to predict the seasonal variations of N2O emissions in the gaseous phase. This, according to our best knowledge, is the most complete full-scale data set used to date for this purpose. The results obtained suggest that the currently available biokinetic model predicted the winter, summer, and autumn N2O emissions well but failed to satisfactorily simulate the spring peak. During the calibration process, it was found that the nitrifier denitrification pathway could explain the observed emissions during all seasons while a combination of the nitrifier denitrification and incomplete heterotrophic denitrification pathways seemed to be dominant during the emissions peak observed during the spring season. Specifically, kinetic parameters related to free nitrous acid (FNA) displayed significant sensitivity leading to increased N2O production. The obtained values of two kinetic parameters, i.e., the FNA half-saturation during ammonia oxidising bacteria (AOB) denitrification and the FNA inhibition concentration related to heterotrophic denitrification, suggested a strong influence of the FNA bulk concentration on the N2O emissions and the observed seasonal variations. Based on the suboptimal performance and limitations of the biokinetic model, further research is needed to better understand the biochemical processes behind the seasonal peak and the influence of FNA.

Urine pretreatment significantly promotes methane production in anaerobic waste activated sludge digestion

Methane production of waste activated sludge (WAS) in anaerobic digestion is hindered due to the rate-limited hydrolysis process and the low methane potential of WAS. Pretreatment of WAS is a common and appealing strategy to improve methane production in anaerobic digestion. In this study, we proposed to use urine, an easily obtained human waste with high ammonium concentration and pH, as a novel pretreatment strategy for anaerobic WAS digestion. Urine pretreatment at levels of 5–30 % (Vurine/Vurine+WAS) could substantially enhance methane production by 5–35 % in biochemical methane potential (BMP) tests, with the highest methane production of 179.6 ± 3.3 mL/g volatile solids (VS) achieved under the highest level of urine (i.e. 30 % urine addition). Based on the model analysis, the biochemical methane potential (B0) and hydrolysis rate of WAS (k) rose from 131.9 mL/g VS and 0.19 d−1 in the control without pretreatment to 136.3–178.2 mL/g VS and 0.22–0.30 d−1, respectively, after the urine pretreatment (5–30 % addition). Urine pretreatment with 5–30 % addition also improved the degradation extent (Y) of WAS by 3–35 %. The promising results indicate that urine pretreatment in anaerobic digestion is a promising technology to improve the efficiency of anaerobic digestion with environmental and economic benefits.

Bacterial community dynamics in tropical soil after sewage sludge amendment.

Although the widespread use of sewage sludge in developing countries is common, little is known about how sludge disposal can affect the microbial composition and diversity of tropical soils. We evaluated the effects of the sewage sludges of two types of anaerobic digestors differing, by the biological treatment they have undergone (uplow anaerobic sludge blanket and activated sludge digester), and two different disposal methods (surface and incorporated) on tropical soils. Samples were taken from topsoil (0-10 cm) and analyzed by amplifying the 16S rRNA genes to study the microbial community, and physicochemical analysis was performed concomitantly. The results indicated that, in general, sewage sludge amendment (SSA) significantly changed the tropical soil bacterial community by the sludge type and by application method. Moreover, the redundancy analysis diagram indicates that changes in soil chemical parameters over time due to SSA resulted in changes in the bacterial community's composition, increasing the population responsible for recycling nutrients in the soil.

Effect of Adding Drinking Water Treatment Sludge on Excess Activated Sludge Digestion Process

Drinking water treatment sludge (DWTS) is a waste by-product from water treatment plants where aluminum and iron salts are the most commonly used coagulants. DWTS was reused to investigate the effects of DWTS on the digestion liquid quality and microorganism activity of excess activated sludge (EAS). DWTS with four suspended solid (SS) concentrations (0%, 2%, 5% and 10%) was added to EAS which was sampled during aerobic and anaerobic digestion processes, then batch tests were carried out which followed the coagulation-flocculation process. It was found that DWTS can improve total dissolved nitrogen (TDN) and dissolved phosphorus (DP) removal efficiencies for anaerobic EAS. The highest removal efficiency of TDN (29.97%) as well as DP (55.38%) was observed when DWTS dosage was SS = 10%. The release of dissolved organic matter (DOM) by DWTS could increase dissolved organic carbon (DOC) concentration and lead to the accumulation of non-biodegradable humic acid-like substance in aerobic and anaerobic digestion liquid. The dehydrogenase activity (DHA) values of anaerobic EAS were higher than aerobic EAS. DWTS could reduce DHA for both EAS. These results indicate that potential risk of release of DOM should be considered when reusing DWTS in future research.

An evaluation of lysozyme enzyme and thermal pretreatments on dairy sludge digestion and gas production.

Anaerobic digestion is one of the common methods of managing and stabilizing sludge. However, due to the limitations of the biological sludge hydrolysis stage, anaerobic decomposition is slow and requires a long time. This study evaluated the effects of thermal (80 °C) (TH-PRE) and a combination of thermal with the lysozyme enzyme (LTH-PRE) pretreatments on the enhancement of anaerobic activated sludge digestion. Response surface methodology was implemented to optimize enzyme pretreatment conditions (enzyme and mixed liquid suspended solids concentration). The results showed that both pretreatment methods increase soluble chemical oxygen demand (COD) and reduces total and volatile suspended solids (VSS), and phosphate concentration. The COD removal rate in LTH-PRE and TH-PRE was 95% and 81%, respectively. The value of VSS reduction in LTH-PRE and TH-PRE was 41% and 31%, more than the control operation, respectively. The biogas production in LTH-PRE and in TH-PRE also increased by 124% and 96%, respectively.

Effect of Ca:Mg ratio and high ammoniacal nitrogen on characteristics of struvite precipitated from waste activated sludge digester effluent

This study revealed the relationship between the presence of calcium impurities and ammoniacal nitrogen concentration upon crystallization of struvite. The research hypothesis was that the presence of both calcium and high concentrations of ammoniacal nitrogen (328–1000 mg/L) in waste activated sludge may influence the struvite quality and acid stability. Hence, we studied the impact of Ca:Mg ratio upon morphology, particle size, purity and dissolution of struvite, in the presence of varying levels of excess ammoniacal nitrogen. X-ray diffraction revealed that up to 31.4% amorphous material was made which was assigned to hydroxyapatite. Increasing the ammoniacal nitrogen concentration and elevation of the Mg:Ca ratio maximized the presence of struvite. Struvite particle size was also increased by ammoniacal nitrogen as was twinning of the crystals. Tests with dilute solutions of organic acid revealed the sensitivity of struvite dissolution to the physical characteristics of the struvite. Smaller particles (21.2 μm) dissolved at higher rates than larger particles (35.86 μm). However, struvite dissolved rapidly as the pH was further reduced irrespective of the physical characteristics. Therefore, addition of struvite to low pH soils was not viewed as beneficial in terms of controlled nutrient release. Overall, this study revealed that waste activated sludge effluent with high ammoniacal nitrogen was prospective for synthesis of high quality struvite material.

Microbial community response and SDS-PAGE reveal possible mechanism of waste activated sludge acidification enhanced by microaeration coupled thermophilic pretreatment

Aiming to strengthen the performance of waste activated sludge digestion, pretreatment is a prerequisite for keeping operations within an industrially acceptable time- frame. In this study, the performance of microaeration coupled with thermophilic (MT) pretreatment on waste activated sludge solubilization and acidification was investigated. The results showed that the maximum soluble organics concentrations, including soluble proteins and carbohydrates, reached 2290 mg COD/L in 24 h when the ventilation rate and temperature were 0.05 vvm and 70 °C. SDS-polyacrylamide gel electrophoresis (SDS-PAGE) test on pure-culture (E.coli) and scanning electron microscopy analysis indicated that MT pretreatment effectively destroyed microbial cell wall and resulted in an increase in soluble proteins. Polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) analysis revealed that MT pretreatment reduced the diversity of the bacterial community during pretreatment. Along with the dissolution of a large quantity of organic matter, microbial species such as Lactococcus and Methyloversatilis bloomed at the end of acidification period, which contributed to SCFAs production. This study revealed that MT pretreatment facilitated the WAS hydrolysis efficiency and enhanced SCFAs (3149 mg COD/L with fermentation for 96 h) production, especially for acetic acid (50%) accumulation, which provides a new perspective for the application and recovery of sludge resources.

Interactive effect of trivalent iron on activated sludge digestion and biofilm structure in attached growth reactor of waste tire rubber

ABSTRACTWaste tire rubber (WTR) has been introduced as an alternative, novel media for biofilm development in several experimental systems including attached growth bioreactors. In this context, four laboratory-scale static batch bioreactors containing WTR as a support material for biofilm development were run under anoxic condition for 90 days using waste activated sludge as an inoculum under the influence of different concentrations (2.5, 6.5, 8.5 mg/l) of trivalent ferric iron (Fe3+). The data revealed that activated sludge with a Fe3+ concentration of 8.5 mg/l supported the maximum bacterial biomass [4.73E + 10 CFU/ml cm2]; besides, it removed 38% more Chemical oxygen demand compared to Fe3+ free condition from the reactor. Biochemical testing and 16S rDNA phylogenetic analysis of WTR-derived biofilm communities further suggested the role of varying concentrations of Fe3+ on the density and diversity of members of Enterobacteria(ceae), ammonium (AOB) and nitrite oxidizing bacteria. Furthermore, Fluorescent in situ hybridization with phylogenetic oligonucleotide probes and confocal laser scanning microscopy of WTR biofilms indicated a significant increase in density of eubacteria (3.00E + 01 to.05E + 02 cells/cm2) and beta proteobacteria (8.10E + 01 to 1.42E + 02 cells/cm2), respectively, with an increase in Fe3+ concentration in the reactors, whereas, the cell density of gamma proteobacteria in biofilms decreased.

Process assessment associated to microbial community response provides insight on possible mechanism of waste activated sludge digestion under typical chemical pretreatments

Current studies have employed various chemicals for disintegrating and hydrolyzing microbial cells in waste activated sludge (WAS). However, a comprehensive process assessment over the whole anaerobic digestion process has seldom been proposed. Besides, the characterization of microbial community responses to these chemicals is not well understood. In this study, the effects of five typical chemicals: solubilizer (β-cyclodextrin, CD), alkaline (NaOH), peroxide (peracetic-acid, PA), biological (rhamnolipid, RL) and chemical (sodium dodecylsulphate, SDS) surfactants on WAS digestion were examined. Higher efficiencies of WAS solubilization, hydrolysis and acidification were achieved by CD treatment, followed by RL and SDS. Methanogenesis was also strongly chemicals-dependent. Shifts in microbial community structure were observed in all chemical-pretreated WAS. The community in RL, CD and PA was dominated by microorganisms that anaerobically hydrolyze organics to acids, while that in NaOH and SDS was mainly associated to biogas production. This study proved that the overall performance of WAS digestion was substantially depended on the initial chemical pretreatments, which in turn influenced and was related to the microbial community structures. Although the economic advantage might not be clear yet, the findings obtained in this work may provide a scientific basis for the potential implementation of chemicals for WAS treatment.

Electrochemical reduction of carbon dioxide to formate with Fe-C electrodes in anaerobic sludge digestion process

Electrochemical reduction of carbon dioxide (CO2) to useful chemicals is an attractive strategy to cut its emission in atmosphere. However, high overpotential and energy consumption required in the electrochemical reduction are the major barriers of this process. In this study, a new CO2 reduction technique for production of formic acid was proposed from waste activated sludge digestion in a microbial electrosynthesis system (MES) with iron plate and carbon pillar as the electrodes. Compared with other reactors, methane production of the Fe-C MES reactor was slightly lower and CO2 was undetectable. Instead, considerable formate (672.3 mg/L) and H2 (45.8 mL) were produced in this Fe-C MES reactor, but not found in the other reactors. It should be ascribed to the reduction of CO2 and H+ at cathode. The reduction of H+ resulted in a weak alkaline pH (9.3), which made the methanogenesis slightly lower in Fe-C MES.

Acid Mine Drainage (AMD) Treatment with Sludge from Wastewater Treatment Plant in a Two-Chamber Microbial Fuel Cell

There are almost 46,000 abandoned mines all over the United States. These mines produce heavy-metal-rich sulfuric acid solution called acid mine drainage (AMD), which has brought long-term water and soil pollution impact, according to the US department of the interior [1]. Different technologies have been used to remediate the surface water, groundwater and soil contaminated by the AMD. These methods include physical, biological, and chemical methods which are generally chemical intensive or the treatment period is relatively long. A better approach for AMD treatment is using microbial fuel cell (MFC), a type of bioelectrochemical systems (BES). MFC uses microorganisms to convert the chemical energy in the biodegradable materials to electricity and at the same time removes the heavy metals in AMD by precipitation and enhances the pH of the drainage. Dry sludge from wastewater treatment plant was used as electron donors for the first time for AMD remediation in the MFC. This treatment technology offers a cheap and environmentally benign approach for integrated waste utilization, energy production and wastewater treatment. Using BES with different mechanisms, different heavy metals have been removed, such as nickel, copper, lead, cadmium and zinc. [2&3&4]. In this study, AMD was treated in the cathode chamber of the MFC with continuous air injection into the chamber, and dry sludge was placed in the anode chamber of the MFC. AMD samples were taken from an abandoned coal-mine in Illinois Coal Basin around Carbondale IL, and the dry sludge was from Carbondale Southeast Wastewater Treatment Plant in Carbondale, IL. The plant used activated sludge tank as secondary treatment process. The dry sludge was formed after activated sludge digestion and drying. Anion exchange membrane (Membrane International Inc) was used to separate the two chambers. Carbon fiber brush was used as the anode electrode, and platinum coated carbon sheet was used as the cathode electrode. With catalyst used, the removal speed of heavy metals can be enhanced. The volume of each chamber was 150 mL. The dry sludge in the anode chamber of the MFC was saturated with D.I. water and a mixture of bacteria from different sources was inoculated into the chamber. No external nutrients were added into the chamber as the dry sludge contains reach nutrition, including organic compounds and different salts. Air was injected into the cathode chamber filled with the AMD. A multimeter was used to record the whole cell potential with an external resistor of 1 kΩ resistance, and the potential of each half cell was also recorded by a data logger (DataLoggerInc) with an Ag/AgCl reference electrode placed in the cathode chamber. The results showed that the closed circuit voltage of the whole cell was kept increasing during the 5 days of operation with the maximum reached voltage of 0.1 V. With the density peak method, the internal resistance of the MFC was measured to be 650 Ω. The pH and the ORP of the AMD changed from 2.57 and 619.9 mV to 4.49 and 263.2 mV respectively after 5 days. White-gray colored precipitation was observed to be formed on the bottom of the cathode chamber. The color of the AMD was changed from yellow-brown before the test to transparent after 5 days. Scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS) was used to test the composition of the precipitate and to observe its morphology. The EDS test showed the existence of Al, Cu, and Fe in the precipitation. Precipitates with different sizes were formed with the maximum less than 5 µm. The preliminary results from this study indicated the possible treatment pathway of AMD by MFC with electricity generation during the treatment process and by using dry sludge from the wastewater treatment plant; no additional chemicals are needed for the treatment process.

Enhanced waste activated sludge digestion using a submerged anaerobic dynamic membrane bioreactor: performance, sludge characteristics and microbial community.

Anaerobic digestion (AD) plays an important role in waste activated sludge (WAS) treatment; however, conventional AD (CAD) process needs substantial improvements, especially for the treatment of WAS with low solids content and poor anaerobic biodegradability. Herein, we propose a submerged anaerobic dynamic membrane bioreactor (AnDMBR) for simultaneous WAS thickening and digestion without any pretreatment. During the long-term operation, the AnDMBR exhibited an enhanced sludge reduction and improved methane production over CAD process. Moreover, the biogas generated in the AnDMBR contained higher methane content than CAD process. Stable carbon isotopic signatures elucidated the occurrence of combined methanogenic pathways in the AnDMBR process, in which hydrogenotrophic methanogenic pathway made a larger contribution to the total methane production. It was also found that organic matter degradation was enhanced in the AnDMBR, thus providing more favorable substrates for microorganisms. Pyrosequencing revealed that Proteobacteria and Bacteroidetes were abundant in bacterial communities and Methanosarcina and Methanosaeta in archaeal communities, which played an important role in the AnDMBR system. This study shed light on the enhanced digestion of WAS using AnDMBR technology.

Enhancing waste activated sludge digestion and power production using hypochlorite as catholyte in clayware microbial fuel cell

Waste activated sludge was digested in anodic compartment of dual chambered clayware microbial fuel cell (MFC). Performance of MFC was evaluated using oxygen (MFC-1) and hypochlorite (MFC-2) as cathodic electron acceptors. Power production of 8.7W/m3 was achieved using hypochlorite as catholyte, which was two times higher than using oxygen (4.2W/m3). Total chemical oxygen demand of sludge was reduced by 65.4% and 84.7% in MFC-1 and MFC-2, respectively. Total and volatile suspended solids reductions were higher in MFC-2 (75.8% and 80.2%, respectively) as compared to MFC-1 (66.7% and 76.4%, respectively). Use of hypochlorite demonstrated 3.8 times higher Coulombic efficiency (13.8%) than oxygen. Voltammetric and impedance analysis revealed increase in reduction peak (from 8 to 24mA) and decreased polarization resistance (from 42.6 to 26.5Ω). Hypochlorite proved to be better cathodic electron acceptor, supporting rapid sludge digestion within 8days of retention time and improved power production in MFC.

Enhancement of sludge decomposition and hydrogen production from waste activated sludge in a microbial electrolysis cell with cheap electrodes

Cheap Fe/graphite electrodes substantially enhanced hydrogen production from anaerobic waste activated sludge digestion in a microbial electrolysis cell.

Nitrogen in the Process of Waste Activated Sludge Anaerobic Digestion

Abstract Primary or secondary sewage sludge in medium and large WWTP are most often processed by anaerobic digestion, as a method of conditioning, sludge quantity minimization and biogas production. With the aim to achieve the best results of sludge processing several modifications of technologies were suggested, investigated and introduced in the full technical scale. Various sludge pretreatment technologies before anaerobic treatment have been widely investigated and partially introduced. Obviously, there are always some limitations and some negative side effects. Selected aspects have been presented and discussed. The problem of nitrogen has been highlighted on the basis of the carried out investigations. The single and two step - mesophilic and thermophilic - anaerobic waste activated sludge digestion processes, preceded by preliminary hydrolysis were investigated. The aim of lab-scale experiments was pre-treatment of the sludge by means of low intensive alkaline and hydrodynamic disintegration. Depending on the pretreatment technologies and the digestion temperature large ammonia concentrations, up to 1800 mg NH4/dm3 have been measured. Return of the sludge liquor to the main sewage treatment line means additional nitrogen removal costs. Possible solutions are discussed.

Start-Up of an Anaerobic Dynamic Membrane Digester for Waste Activated Sludge Digestion: Temporal Variations in Microbial Communities

An anaerobic dynamic membrane digester (ADMD) was developed to digest waste sludge, and pyrosequencing was used to analyze the variations of the bacterial and archaeal communities during the start-up. Results showed that bacterial community richness decreased and then increased over time, while bacterial diversity remained almost the same during the start-up. Proteobacteria and Bacteroidetes were the major phyla. At the class level, Betaproteobacteria was the most abundant at the end of start-up, followed by Sphingobacteria. In the archaeal community, richness and diversity peaked at the end of the start-up stage. Principle component and cluster analyses demonstrated that archaeal consortia experienced a distinct shift and became stable after day 38. Methanomicrobiales and Methanosarcinales were the two predominant orders. Further investigations indicated that Methanolinea and Methanosaeta were responsible for methane production in the ADMD system. Hydrogenotrophic pathways might prevail over acetoclastic means for methanogenesis during the start-up, supported by specific methanogenic activity tests.

Enhanced anaerobic digestion of waste activated sludge digestion by the addition of zero valent iron

Anaerobic digestion is promising technology to recover energy from waste activated sludge. However, the sludge digestion is limited by its low efficiency of hydrolysis–acidification. Zero valent iron (ZVI) as a reducing material is expected to enhance anaerobic process including the hydrolysis–acidification process. Considering that, ZVI was added into an anaerobic sludge digestion system to accelerate the sludge digestion in this study. The results indicated that ZVI effectively enhanced the decomposition of protein and cellulose, the two main components of the sludge. Compared to the control test without ZVI, the degradation of protein increased 21.9% and the volatile fatty acids production increased 37.3% with adding ZVI. More acetate and less propionate are found during the hydrolysis–acidification with ZVI. The activities of several key enzymes in the hydrolysis and acidification increased 0.6–1 time. ZVI made the methane production raise 43.5% and sludge reduction ratio increase 12.2 percent points. Fluorescence in situ hybridization analysis showed that the abundances of hydrogen-consuming microorganisms including homoacetogens and hydrogenotrophic methanogens with ZVI were higher than the control, which reduced the H2 accumulation to create a beneficial condition for the sludge digestion in thermodynamics.

Anaerobic membrane bio‐reactors for waste activated sludge digestion: Tubular versus hollow fiber membrane configurations

This article presents the results of pilot scale studies that examined the use of negative and neutral charged tubular and hollow fiber (HF) anaerobic membrane bio‐reactors (AnMBR) for anaerobic digestion of waste activated sludge. Both AnMBR configurations were operated at a hydraulic retention time of 15 days, a sludge retention time (SRT) of 30 days, and a total solids loading of 1.2–1.3 kg m−3 day−1. The results indicate that both membrane digesters showed comparable total chemical oxygen demand and volatile solids removals of 47.6 and 49.1% respectively while maintaining a throughput that was two times that of the completely stirred tank reactor (CSTR) type digesters. The performance of the AnMBRs was similar to that of CSTRs operating at 30 days SRT. The AnMBRs were operated for 160 days. During this period no significant fouling was observed and membrane cleaning was not required. The average fluxes for the neutral and negative tubular membranes were 32 and 39 LMH when operated at a trans‐membrane pressure TMP of 30 kPa. The HF membranes were operated at a constant flux of 11 LMH and the average TMP was less than 10 kPa. The critical flux measured for the tubular and HF membranes were near to 30 and 18 LMH mark respectively indicating a better performance by the former. However both AnMBR configurations generated comparable net energy. © 2012 American Institute of Chemical Engineers Environ Prog, 32: 598–604, 2013

Temperature phased anaerobic digestion increases apparent hydrolysis rate for waste activated sludge

It is well established that waste activated sludge with an extended sludge age is inherently slow to degrade with a low extent of degradation. Pre-treatment methods can be used prior to anaerobic digestion to improve the efficiency of activated sludge digestion. Among these pre-treatment methods, temperature phased anaerobic digestion (TPAD) is one promising method with a relatively low energy input and capital cost. In this study, an experimental thermophilic (50–70 °C)–mesophilic system was compared against a control mesophilic–mesophilic system. The thermophilic–mesophilic system achieved 41% and 48% volatile solids (VS) destruction during pre-treatment of 60 °C and 65 °C (or 70 °C) respectively, compared to 37% in the mesophilic–mesophilic TPAD system. Solubilisation in the first stage was enhanced during thermophilic pre-treatment (15% at 50 °C and 27% at 60 °C, 65 °C and 70 °C) over mesophilic pre-treatment (7%) according to a COD balance. This was supported by ammonia–nitrogen measurements. Model based analysis indicated that the mechanism for increased performance was due to an increase in hydrolysis coefficient under thermophilic pre-treatment of 60 °C (0.5 ± 0.1 d −1), 65 °C (0.7 ± 0.2 d −1) and 70 °C (0.8 ± 0.2 d −1) over mesophilic pre-treatment (0.2 ± 0.1 d −1), and thermophilic pre-treatment at 50 °C (0.12 ± 0.06 d −1).