‘Hot topic’ – combined energy and process modeling in thermal hydrolysis systems

Sludge-to-energy approaches based on pathways that couple pyrolysis with anaerobic digestion (thermal hydrolysis pre/post-treatment): Energy efficiency assessment and pyrolysis kinetics analysis

Low-temperature thermal hydrolysis for anaerobic digestion facility in wastewater treatment plant with primary sludge fermentation

Thermal hydrolysis process (THP), as an emerging pretreatment step for anaerobic digestion process (ADP), improves sludge biodegradability and thus solids volume reduction and energy recovery. However, a lack of integrated data on the changes in sludge properties across the entire treatment train hinders the design of key energy-efficient units. To address this data gap, this study reports the physical and chemical properties of sludge sampled over 12 months at five crucial locations within a sludge treatment train. Along with measurements at 20°C, dynamic viscosity and thermal conductivity were measured based on actual temperature range up to 100°C. Detailed rheological modeling was also conducted using the Herschel-Bulkley equation to assess yield stress and flow index across the THP, cooling heat exchangers (CHEs), and ADP. Results showed that THP reduces yield stress from 34.3 to 8.0 Pa through CHEs and ADP and increases thermal conductivity by disrupting flocs and releasing bound water. ADP further lowered viscosity, shaping sludge into a more fluid state. Notably, a critical divergence was observed at operational temperature (70°C) while dynamic viscosity decreased remarkably (20%-50%), and thermal conductivity remained stable. Overall, it was proven that property changes are governed not only by total solids content but also by the fundamental restructuring of the physical and chemical composition (suspended vs. dissolved solids, organic vs. inorganic fractions), which are the primary drivers altering the thermal and rheological properties of sludge, deviating significantly from water in a predictable and quantifiable manner. This study provides the first stage-resolved analysis linking the changes in the physicochemical properties to real operational temperature regimes across a full-scale sludge treatment train. The knowledge provides valuable insights for design and operation of sludge treatment systems to reduce energy demand and improve sustainability.

Advanced steam explosion of mixed organic fraction of municipal solid waste and sewage sludge to determine biomethane potentials

Prospects and challenges of thermal hydrolysis pretreatment of microalgae for enhancing bioenergy and resource recovery in anaerobic bioprocesses.

Evaluation of thermal hydrolysis efficiency of mechanically dewatered sewage sludge via rheological measurement

In order to improve the energy footprint of Psyttalia wastewater treatment plant (WWTP) in Athens, the application of a thermal hydrolysis process (THP) was preferred to the option of constructing additional digesters. Since August 2015, approximately half of the generated waste activated sludge (WAS) has been treated by a Cambi B6-4 system, while the thickened primary sludge (PS) is by-passing the THP and is mixed with the hydrolysed WAS before entering the 4 digesters. The 4 other conventional digesters have treated the remaining sludge. The dewaterability of the mixed digested sludge has significantly been improved from 22% dry solids (DS) before THP installation, up to 31% DS after THP installation. This is providing substantial reduction of energy use and cost savings at the sludge drying plant of Psyttalia. In addition, biogas generation and digester efficiency (VSR) have been increased.

The aim of this work was to study in depth the behavior and optimization of a novel process, called advanced thermal hydrolysis (ATH), to determine its utility as a pretreatment (sludge solubilization) or postreatment (organic matter removal) for anaerobic digestion (AD) in the sludge line of wastewater treatment plants (WWTPs). ATH is based on a thermal hydrolysis (TH) process plus hydrogen peroxide (H(2)O(2)) addition and takes advantage of a peroxidation/direct steam injection synergistic effect. On the basis of the response surface methodology (RSM) and a modified Doehlert design, an empirical second-order polynomial model was developed for the total yield of: (a) disintegration degree [DD (%)] (solubilization), (b) filtration constant [F(c) (cm(2)/min)] (dewaterability), and (c) organic matter removal (%). The variables considered were operation time (t), temperature reached after initial heating (T), and oxidant coefficient (n = oxygen(supplied)/oxygen(stoichiometric)). As the model predicts, in the case of the ATH process with high levels of oxidant, it is possible to achieve an organic matter removal of up to 92%, but the conditions required are prohibitive on an industrial scale. ATH operated at optimal conditions (oxygen amount 30% of stoichiometric, 115 °C and 24 min) gave promising results as a pretreatment, with similar solubilization and markedly better dewaterability levels in comparison to those obtained with TH at 170 °C. The empirical validation of the model was satisfactory.

Challenges and opportunities of lignocellulosic biomass for anaerobic digestion

Effect of sludge retention time on microbial succession and assembly in thermal hydrolysis pretreated sludge digesters: Deterministic versus stochastic processes

This study investigated the integration of the thermal hydrolysis process (THP) as a pretreatment with thermophilic anaerobic digestion (TAD) at a pilot scale using sludge from a full-scale wastewater treatment plant.

To determine whether wastewater treatment plants (WWTPs) should use the thermal hydrolysis process (THP) or the thermal alkaline process (TAP) as sludge pretreatment or posttreatment methods, this study was conducted on five WWTPs implementing THP/TAP under seven different scenarios. The evaluation focused on impacts on energy, economic, and CO2eq. balances compared to conventional anaerobic sludge digestion. In this study, THP/TAP as a posttreatment method yielded better results in energy, economic, and CO2eq. balances than pretreatment. TAP of digested sludge (DS) at pH 9 achieved the highest net electricity generation of 344.7-472.3kWh/t total solids (TS). An economic profit of 29.9-171-3US$/tTS can be obtained from digesting the liquid fraction of THP-treated DS, and in this scenario, CO2eq. emissions can be further reduced by 149.8±42kg/tTS. However, additional space is required for the construction of a digester or an upflow anaerobic sludge blanket in the DS posttreatment.

Effects of oxytetracycline on mesophilic and thermophilic anaerobic digestion for biogas production from swine manure

Using IT development efforts for achieving new business goals is a challenging task. Optimally, IT projects and solutions should be aligned to answer the real requirements of actual business development targets. Process modeling has been widely applied as a tool for business process and IT development. The goal of this study is to investigate how to combine process modeling and requirements engineering (RE) in software development projects. We studied the use of process modeling focused Business-driven development (BDD) method and other modeling techniques to support complex large projects in the outsourced environment. The results presented here are based on 17 interviews, a study of 4 projects implemented with the BDD method and the experiences gathered from 11 other large projects at the case study organization. This report outlines the results of combining process modeling to use case, business rule and other requirements and architecture modeling. To a large extent, the results were positive and indicate the benefits for using business process modeling as a visual tool for combining business and IT development, and as a part of the requirements. However, the perspective and abstraction level for process modeling should be carefully selected. Our study concludes also that requirements modeling should cover different aspects from both project and enterprise context in a comprehensive manner.

A comparative study was performed to estimate biogas production from sludge produced by organic and inorganic chemically enhanced primary treatments (CEPTs). To this end, the effects of two coagulants, polyaluminum chloride (PACl) and Moringa oleifera (MO), on CEPT and biogas production in anaerobic digestion were surveyed within an incubation period of 24 days. The optimal dosage and pH of PACl and MO were optimized in terms of sCOD, TSS and VS parameters in the CEPT process. Next, the digestion performance of anaerobic digestion reactors fed with sludge obtained from PACl and MO coagulants at a batch mesophilic reactor (37 ± 1 °C) was surveyed from the biogas production, volatile solid reduction (VSR) and Gompertz model. At the optimal conditions (pH = 7 and dosage = 5 mg L-1), the removal efficiency of COD, TSS and VS in CEPT assisted with PACL was 63, 81 and 56%, respectively. Moreover, CEPT assisted with MO led to the removal efficiency of COD, TSS and VS until 55, 68 and 25%, respectively. The highest methane yield (0.598 L gVS removed-1) was obtained in an anaerobic digestion reactor with sludge from the MO coagulant. The anaerobic digestion of CEPT sludge instead of primary sludge resulted in higher sCOD removal efficiency, and 43-50% of sCOD was observed compared with the removal of 32% for the primary sludge. Furthermore, the high coefficient of determination (R2) demonstrated the trustworthy predictive precision of the modified Gompertz model with actual data. The combination of CEPT and anaerobic digestion, especially using natural coagulants, provides a cost-effective and practical way to increase BMP from primary sludge.