Effect Of Thermal Hydrolysis Research Articles

Correlation between sewage sludge pore structure evolution and water filtration performance: Effect of thermal hydrolysis with or without carbonaceous skeleton-assisted

Municipal sewage sludge contains a high water content and strong hydrophilicity, making mechanical dewatering a critical step in sludge treatment and disposal. To clarify the collapse of filtration channels within the sludge cake under high pressure and to develop more precise targeted conditioning methods, this study focused on the direct correlation between pore structure evolution and sludge dewatering performance. A self-designed online system was used to compare the dewatering processes of raw sludge, thermal hydrolyzed (TH) sludge, and carbonaceous skeleton-assisted thermal hydrolyzed (CSkel-TH) sludge. In-depth analysis was conducted on the structure scanning data of the filter cake at different time intervals and the corresponding filtrate mass data. The results showed that during the press filtration process, the raw sludge gradually transformed into a filter cake, with larger pores trapping the water. In the upper and bottom layers, regions with a porosity higher than 10 % appeared, forming a “water-locking layer” even with continued pressure, it became impossible to remove additional water. After separate hydrolysis, the porosity and pore connectivity of the sludge decreased, and the thickness of the “water-locking layer” increased as press filtration progressed, inhibiting water discharge and making cake formation difficult. Following CSkel-TH treatment, the number of pores with diameters ranging from tens to over a hundred micrometers increased, and the connectivity between pores was enhanced. In this case, the channels formed by interconnected small pores continuously transported the water trapped in the large pores outward, facilitating water discharge. This work provided a basis for further targeted regulation of pore structures to enhance the effectiveness of high-pressure dewatering of sludge.

Effects of thermal hydrolysis on anaerobic digestion and abundance of antibiotic resistance genes during recuperative thickening digestate treatment of sewage sludge

The effects of recuperative thickening (RT) and thermal hydrolysis during anaerobic digestion (AD) on AD performance, microbial communities and reduction of antibiotic resistance genes (ARGs) were investigated. Compared to the results in conventional AD (Phase I), biogas production increased slightly (10%) through RT (Phase II) but increased (63%) via RT with a digestate treatment system (DTS, thermal hydrolysis of thickened digestate) during AD (Phase III). Meanwhile, the three different operating conditions further influenced microbial community structures as well as efficiencies in reducing ARGs: The abundance of hydrolytic bacteria in Phase II and the abundance of acidogenic bacteria in Phase III increased, and 64.3% and 47.4% of the total sum of the relative abundance of ARGs in the substrate were removed in Phases II and III, respectively. Thus, RT-AD with DTS could represent a promising process for improved AD performance, but requires additional refinements to further reduce concentrations of residual ARGs in digestate.

Acidogenic fermentation of food waste and sewage sludge mixture: Effect of operating parameters on process performance and safety aspects

The production of added-value bio-products and energy from waste streams while minimizing environmental impacts is a crucial aspect within the circular economy’s principles. The biorefinery can be an exit to the constant increasing of organic food waste and sewage sludge to solve the issues of waste disposal. This work deals with the production of volatile fatty acids (VFA) as added-value products from food waste and sewage sludge mixture in a pilot scale acidogenic fermentation process. Moreover, due to the lack of information about safety aspects in the literature, the explosive risk of the fermenter has been assessed by means of the quantification of lower flammability limit (LFL) of the generated flammable gases. Different temperature and feedstock’s composition were tested, as well as the effect of thermal hydrolysis. Mesophilic fermentation (37 °C) on thermally hydrolysed feedstock (48 h at 72 °C) ensured stability in terms of VFA production at high concentration (30 ± 2 gCODVFA/L) and CODVFA/CODSOL ratio (0.86 ± 0.09). Such condition also showed high LFL (28.9%), corresponding to a less hazardous condition compared to the other investigated, especially the thermophilic ones where LFL changed between 18% and 26%.

Enhancement of sludge dewaterability via the thermal hydrolysis anaerobic digestion mechanism based on moisture and organic matter interactions

It is known that sludge dewaterability improves during the thermal hydrolysis process (THP); however, the effect of thermal hydrolysis and anaerobic digestion (THP-AD) on sludge dewaterability is unclear. Further, the difference between thermal hydrolysis as pre-treatment for anaerobic digestion (pre-THP-AD) and as post-treatment (post-THP-AD) is also unclear. Based on the evolution of the interaction between organic matter and moisture, the mechanism of pre-THP-AD and post-THP-AD improving the sludge dewaterability was explored. The capillary suction time values of pre-THP-AD and post-THP-AD increased by 58% and 59%, respectively, and the proportion of free moisture increased by 10.44% and 10.59%, respectively, compared with the conventional anaerobic digestion (CAD) process. The cell structure was destroyed and most organic matter was converted into dissolved form through THP, organic matter degraded during AD, the interaction between moisture and organic matter declined, and the mechanically bound moisture transformed into free moisture. Additionally, the intensity of hydrophilic functional groups, such as amide I decreased and amide II disappeared after (pre- and post-) THP-AD. The surface hydrophobicity of sludge samples was enhanced and sludge dewaterability improved. The mechanism of pre-/post-THP-AD enhanced sludge dewaterability based on the interaction between moisture and organic matter; additionally, this will provide a reference for optimised moisture-sludge separation processes and guidance for the optimisation of engineering operation parameters.

Microwave support of the alcoholic fermentation process of cyanobacteria Arthrospira platensis

The search for a balance between the energy-related challenges of the future and providing nutritional security has resulted in the development of a market for biofuels of successive generations. The larger their portion in biofuel production, the less the prices of agricultural products will increase. The use of algae, cyanobacteria and aquatic plants in the production of liquid fuels is an alternative. The aim of this study was to determine the effect of thermal hydrolysis on degradation of polysaccharides contained in biomass of cyanobacteria Arthrospira platensis and to assess the effectiveness of ethanol production from preconditioned biomass. The study is aimed at the selection of the most advantageous parameters of thermochemical hydrolysis to reach the experiment variant with the best effects, degree of polysaccharide degradation and effectiveness of alcohol fermentation. The experiment was divided into two stages; in stage I, the possibility of obtaining fermentable sugars by hydrothermal and chemical treatment of the substrate was tested. Stage II involved an assessment of the effectiveness of the pretreatment methods to produce bioethanol in alcohol fermentation. Yeast used in industrial ethanol production—Saccharomyces cerevisiae As4—was used in the alcohol fermentation. The results have shown that the temperature of 150 °C was the most beneficial for the process of thermohydrolysis, and the mash in the microwave-heated sample contained the highest concentration of alcohol (0.97 g/l), which is 98% more than in the control mash and 37% more than in the conventionally heated sample.

Effect of Thermal Hydrolysis on Anaerobic Digester Performance

Anaerobic digestion (AD) has been recently introduced as a promising technology for producing bioenergy around the world. Due to its especial characteristics, solid waste could be considered as a proper feedstock in the digester. Retention time (RT) and rate of biogas production are two major parameters affecting the efficiency of the process. The AD procedure of biogas production consists of hydrolysis, acidogenesis, acetogenesis, and methanogenesis such that feeding materials would be processed inside the digester. The experiments have been carried out using two bioreactors with volume of 5 liters in mesopihilic contitions at 35 ± 1 ◦ C. The purpose of this study is to accelerate the hydrolysis step. Pretreatment of the waste is accomplished using thermal hydrolysis in conditions of 155 ◦ C and 5 atm.The resultsofthisresearchindicated33.33%decreaseinRTand154.87%increase in amount of biogas production using pretreatment process in comparison without considering it.

Effect of thermal hydrolysis and ultrasounds pretreatments on foaming in anaerobic digesters

Foam appears regularly in anaerobic digesters producing operational and safety problems. In this research, based on the operational observation at semi-industrial pilot scale where sludge pretreatment mitigated foaming in anaerobic digesters, this study aimed at evaluating any potential relationship between foaming tools applied to activated sludge at lab-scale (foam potential, foam stability and Microthrix parvicella abundance) and the experimental behavior observed in pilot scale and full-scale anaerobic digesters. The potential of thermal hydrolysis and ultrasounds for reducing foaming capacity was also evaluated. Filamentous bacteria abundance was directly linked to foaming capacity in anaerobic processes. A maximum reduction of M.parvicella abundance (from 5 to 2) was reached using thermal hydrolysis with steam explosion at 170°C and ultrasounds at 66.7kWh/m3, showing both good anti-foaming properties. On the other hand, foam potential and stability determinations showed a lack of consistency with the bacteria abundance results and experimental evidences.

Effect of Thermal Hydrolysis on Rheological Behavior of Municipal Sludge

Properly understanding of sludge rheological properties is important for designing of pumping and translating. Effect of thermal hydrolysis on rheological properties of municipal sludge was studied using a rheometer (DHR-2) with concentric cylinder geometry. Test results indicated both raw and thermal treated sludge displayed non-Newtonian rheological behavior with shear thinning, exhibiting thixotropic properties and viscoelasticity. The Herschel–Bulkley model could represent their flow behavior more accurately than other models. However, for the raw sludge, as solid content reached 120 g/L, fluidity disappeared, and all the rheological models could not describe it accurately. After thermal hydrolysis, the consistency index (k) decreased significantly, while the flow index (n) increased, suggesting that thermal treated sludge was much closer to the Newtonian fluid compared to the raw sludge. Both raw and treated sludge exhibited strong dependence on solid content and temperature. Correlations between sol...

Effects of thermal hydrolysis on activated sludge solubilization, surface properties and heavy metals biosorption

The effects of 170°C treatment of activated sludge on cadmium and copper uptake were investigated. Biosorption tests were carried out in order to obtain uptake isotherms. These isotherms were modelled and model parameters were linked to the modifications of floc surface properties and metal uptake mechanisms. Soluble fraction biochemical composition and floc size measurements evidenced floc destucturation and the release of both organic ligands and orthophosphate ions in solution: for instance, 46% of total COD was solubilized by the treatment. Characterization of sludge samples by potentiometric titrations and IR spectra showed the transfer of functional groups from particulate to soluble fraction: the number of proton binding sites in the soluble fractions was multiplied by 4.7. Copper uptake mechanisms at pH 7 were governed mainly by precipitation whereas cadmium uptake was more dependent of interactions at floc surface (ion exchange, etc.): ion exchange ratio indeed ranged from 0.22±0.04 to 0.28±0.04μeq/μeq for cadmium and was around 0.06±0.02μeq/μeq for copper. Therefore, the affinity of sludge particles towards Cd(II) ions increased after thermal treatment from 13.8 to 36.9L/g due to both the extended surface area offered by smaller particles and the decrease in TSS concentration. On the contrary, copper precipitation was limited by complexation with soluble organic ligands released during the treatment and corresponding isotherms were S shaped. The increase in DOC concentration (from 13.4 to 494mgC/L) as well as its affinity towards Cu(II) ion (K constant ranging from 0.29 to 0.78L/mg C) was well described by the model. These mechanisms should be taken into account in order to assess the environmental sustainability of sludge thermal hydrolysis.