Batch Reactor Research Articles

Multi-stage anoxic/oxic sequencing batch reactor realizes shortcut nitrogen removal for anaerobically co-digested liquor of municipal sludge and urban organic wastes

Multi-stage anoxic/oxic sequencing batch reactor realizes shortcut nitrogen removal for anaerobically co-digested liquor of municipal sludge and urban organic wastes

Dark Fermentation of Fruit Juice Effluents: Effects of Substrate Concentration

This study explores the impact of initial substrate concentrations on biomass growth, hydrogen production, and acid generation during acidogenic fermentation of a synthetic fruit juice wastewater. Four substrate concentrations, within the range 0.30–2.12 C mol·L−1, were tested using a mixed acidogenic bacterial culture. Batch reactors were employed to conduct the study, and the results were analyzed to determine inhibition effects. The highest hydrogen production (6.1 L H2·substrate C mol−1) and hydrogen percentage in the gas phase (57%) were achieved at a substrate concentration of 0.30 C mol·L−1. Higher substrate concentrations reduced the hydrogen production due to substrate and product inhibition events. The maximum H2 potential production was 4.15 Nm3/m3 reactor at a substrate concentration of 0.91 C mol·L−1. Biomass growth and VFA production followed exponential trends at low substrate concentrations, 0.30 and 0.091 C mol·L−1, while high concentrations resulted in linear trends due to inhibition effects caused by the substrate. The main acids produced were lactic at low concentrations, and acetic when dealing with high concentrations. The highest final acid concentrations were obtained with the highest initial substrate concentration, but their yields were significantly lower due to the substrate and product inhibitions experienced by the biomass.

Entrapment of protease from Bacillus sp. in polyvinyl alcohol hydrogels

This study highlights the effective immobilization of protease from Bacillus sp. in polyvinyl alcohol hydrogels and its characterization. Both free and entrapped proteases exhibited optimal activity at pH 8.0 and 55°C, indicating that the immobilization did not significantly alter the enzyme's fundamental properties. The entrapment in polyvinyl alcohol hydrogels significantly enhanced thermal stability. After 24 hours at 55°C, the free protease retained only 19% of its initial activity, whereas the entrapped protease retained 72%. The entrapped protease showed a longer half-life of 53.3 hours compared to 10.6 hours for the free protease. The Km and Vmax values of free protease were determined to be 0.5 mg/mL and 23.3 U/mg protein, respectively, for casein. These values were found to be 0.2 mg/mL and 23.8 U/mg protein, respectively for the entrapped protease. The entrapped protease retained 58% of its initial activity after 5 reuses in a batch reactor. As a result, the entrapment of Bacillus sp. protease in polyvinyl alcohol is an effective immobilization method due to its simplicity, low cost, and ability to provide a 5-fold increase in thermal stability.

Native microorganisms for sustainable dye biodegradation in wastewaters from jeans finishing.

The textile mill is one of the most water-consuming industries. Wastewater production is very high, and among the main generated pollutants are dyes. In particular, jeans finishing, which is performed all over the world, generates wastewater with indigo dye that has to be eliminated before discharge. This work studies the biological treatment of this type of wastewater using native microorganisms, i.e., without the need for external seed sludge to start-up the process. Two strategies for starting up the biological treatment using laboratory sequencing batch reactors have been compared: the addition of seed sludge from a biological reactor of a wastewater treatment plant and the non-addition of seed sludge, which means that native microorganisms (those in wastewater coming from the industry facilities) are responsible for COD and color degradation. Special attention is paid to biomass shift in both reactors, analyzing both bacterial and fungal populations. Results yielded more than 90% of COD and color removal after 25days in both reactors. MLSS increased in both reactors during the operation, reaching very similar values (around 1840mg/L). Rozellomycota was the predominant phylum in the reactors. Concerning bacteria, Planctomycetota abundance increased considerably in both reactors, which shows the important role of these bacteria in the treatment. It can be concluded that the lower bacterial diversity in the native population in comparison with the seeded sludge was shifting to a higher microbial diversity during the process, achieving a similar microbial population in reactors. It implies that it is not necessary to either work with isolated cultures or seeded sludge, which leads to a simpler and more sustainable solution for textile wastewater treatment in areas all over the world.

Conversion of Penta‐Acetyl‐Xylitol to 3‐Acetoxymethylene‐Tetrahydrofuran by a Combined Hetero‐/Homogeneous Tandem Catalyst System

A tandem catalyst system comprised of trifluoromethanesulfonic (triflic acid, HOTf) or Hafnium tetratriflate (Hf(OTf)4) and Ru/C in glacial acetic acid (HOAc) as the solvent at 200 °C and ~ 7 MPa hydrogen pressure in a batch reactor converts penta‐acetyl‐xylitol ((2R,3R,4S)‐Pentane‐1,2,3,4,5‐penta‐acetoxy‐pentane) or unprotected xylitol to 3‐acetoxymethylene‐tetrahydrofuran (3‐AMT) in up to 15 % yield at full conversion. A comparative analysis by SEM‐EDS and XPS of the fresh commercial Ru/C catalyst vs catalyst reused and recovered after 5 cycles shows increasing aggregation of ruthenium to larger particles with a concomitant decrease in yield of 3‐AMT to 8‐9 % for cycles 4 and 5. 3‐AMT or its hydrolysis product 3‐hydroxymethyl‐tetrahydrofuran (3‐HMT) are valuable synthons for the preparation of agrochemicals, pharmaceuticals and specialty polyurethanes and polyesters.

Visible Light Excitation of Poly‐(para‐Phenylene Ethynylene) Enables Heterogeneous Photocatalytic Oxidations of Amines in Flow

AbstractHeterogeneous visible light photocatalysis is a compelling approach to address sustainability in synthetic photochemistry. However, the use of solid‐state photocatalysts remains very unpopular in organic synthesis because of their limited accessibility and the black‐box effect associated to the lack of rational between their molecular structure and their photochemical properties. Herein, we disclose the synthesis, characterization, photocatalytic properties and synthetic applications of a simple and readily available solid‐state conjugated organic polymer, poly‐(para‐phenylene ethynylene) 1, which exhibits a strong oxidative power upon irradiation with visible light (E(1*/1⋅−)=+1.67 V vs SCE). Comparisons with structural analogues highlighted the superior photocatalytic activity of this linear semiconductor, on account of its fully conjugated architecture. The associated excited‐state reactivity enabled the transformation of various amines into imines in batch and continuous flow reactors together with straightforward photocatalyst recycling. Mechanistic investigations revealed concomitant photoredox and energy transfer pathways, that led to the formation of the desired products. Ultimately, the inline generation of imines was exploited in telescoped three‐component Ugi reactions (3CR) in batch and flow toward biologically relevant α‐acylaminoamides.

Acclimatation of Microbial Biomass to Effluents From a Swine Slaughterhouse in Batch Reactors

Objective: To evaluate the acclimatization of microbial biomass in sequential reactors to optimize the treatment of wastewater from pig slaughterhouses. Theoretical framework: The meat industry generates highly contaminated wastewater. Biological treatments, such as aerobic and anaerobic systems, are more efficient and sustainable than physicochemical ones. Materials and methods: Industrial effluents were collected in a pig slaughterhouse and then characterized. The microbial biomass was collected from the same slaughterhouse and was subjected to an acclimatization process in a sequential batch reactor. Results and discussion: The results showed that the wastewater from the pig slaughterhouse had high levels of BOD, COD and suspended solids, exceeding the limits established by local regulations. During the acclimatization process, the microbial biomass demonstrated a gradual improvement in its COD removal capacity, reaching efficiencies greater than 70%. The positive correlation observed between volumetric organic load and organic matter removal efficiency indicates that acclimated biomass has a greater capacity to treat effluents with high levels of organic load. Research implications: Biomass acclimatization is essential to improve the efficiency of biological treatment in slaughterhouse effluents, reducing its environmental impact and the need for costly treatments. Value/originality: This study proposes a more sustainable and efficient solution for the treatment of slaughterhouse wastewater, highlighting the importance of biomass acclimatization.

Splitting tensile strength of shale cores: intact versus fractured and sealed with ureolysis-induced calcium carbonate precipitation (UICP)

AbstractUreolysis-induced calcium carbonate precipitation (UICP) is a biomineral solution where the urease enzyme converts urea and calcium into calcium carbonate. The resulting biomineral can bridge gaps in fractured shale, reduce undesired fluid flow, limit fracture propagation, better store carbon dioxide, and potentially enhance well efficiency. The mechanical properties of shale cores were investigated using a modified Brazilian indirect tensile strength test. An investigation of intact shale using Eagle Ford and Wolfcamp cores was conducted at varying temperatures. Results show no significant difference between shale types (average tensile strength = 6.19 MPa). Eagle Ford displayed higher strength at elevated temperature, but temperature did not influence Wolfcamp. Comparatively, cores with a single, lengthwise heterogeneous fracture were sealed with UICP and further tested for tensile strength. UICP was delivered via a flow-through method which injected 20–30 sequential patterns of ureolytic microorganisms and UICP-promoting fluids into the fracture until permeability reduced by three orders of magnitude or with an immersion method which placed cores treated with guar gum and UICP-promoting fluids into a batch reactor, demonstrating that guar gum is a suitable inclusion and may reduce the number of flow-through injections required. Tensile results for both delivery methods were variable (0.15–8 MPa), and in some cores the biomineralized fracture split apart, possibly due to insufficient sealing and/or heterogeneity in the composite UICP-shale cores. Notably in other cores the biomineralized fracture remained intact, demonstrating more cohesion than the surrounding shale, indicating that UICP may produce a strong seal for subsurface application.

CNN-LSTM-Based Nonlinear Model Predictive Controller for Temperature Trajectory Tracking in a Batch Reactor

CNN-LSTM-Based Nonlinear Model Predictive Controller for Temperature Trajectory Tracking in a Batch Reactor

Innovative Strategies for Tannery Wastewater Remediation with Sequential batch reactor and phycoremediation

<p style="line-height:150%;text-align:justify;"><span style="font-family:"Times New Roman",serif;font-size:12.0pt;" lang="EN-IN">This research assessed the performance of combining Sequential Batch Reactor (SBR) and phycoremediation method used for tanning effluent. The SBR system obtained high removal efficiencies with Chemical Oxygen Demand (COD)  is reduced by  85%, Biological Oxygen Demand (BOD) is reduced  by 80% as well as ammonia by more than 75%. Chromium and lead were dropped by 65% and 60% correspondingly after treatment. Following SBR process, inclusion of Chlorella vulgaris in the phycoremediation stage further improves the removal of pollutants achieving 95% COD and 92% BOD reductions. Heavy metal removal was enhanced with chromium and lead by reducing 85% each. Kinetic analysis indicated that ammonia and COD removal followed first-order kinetics with high model fit (R2=0.93 for COD; R2=0.91 for ammonia). Heavy metal removal using Chlorella vulgaris also conformed to first-order kinetics. A temporary increase in ammonia levels was observed due to nitrification inhibition during periods of high organic loads in the wastewater discharged from tanneries into rivers or lakes without treatment facilities such as oxidation ditches or stabilization ponds used in some cases. Finally, it can be concluded that an integrated SBR phycoremediation process shows very good potentialities with respect to good performances in treating wastewater efficiently.</span></p>

In‐Silico Optimization of a Bi‐Enzymatic Reactor for Mannitol Production Using Pareto‐Optimal Fronts

AbstractFor multi‐enzymatic cases, the determination of the batch reactor (BR) optimal operating policy often translates into a difficult multi‐objective problem. Exemplification is made here for the enzymatic reduction of D‐fructose to mannitol by using the mannitol dehydrogenase (MDH) enzyme and nicotinamide adenine dinucleotide (NADH) cofactor, with in situ regeneration of NADH at the expense of formate degradation by using the FDH enzyme. This paper presents an original rule to in silico generate the problem solution, by using the Pareto optimal‐front approach with accounting for pairs of competing economic goals and constraints. The optimal BR is then compared to an optimal fed‐BR (FBR), or a series of equal BRs (SeqBR). As proved, the Pareto‐optimal front alternative is an advantageous option, compared to the classical nonlinear programming technique, being simple to apply, by considering pairs of opposite objective functions. In the present case study, the Pareto‐optimal BR operating mode predicts an M‐productivity 1.5x better than those of an optimized FBR, with comparable enzymes consumption. The MDH consumption of this Pareto‐optimal BR is 10x smaller than an optimal SeqBR, and 130x smaller vs. heuristic (sub)optimal BR.

Fibrillated Films for Suspension Catalyst Immobilization—A Kinetic Study of the Nitrobenzene Hydrogenation

The immobilization of suspension catalysts in flexible, fibrillated films offers a promising solution to the mass transfer limitations often encountered in three-phase hydrogenation reactions. This study investigates the catalytic performance and mass transfer properties of fibrillated films in the hydrogenation of nitrobenzene to aniline, comparing them to free-flowing powdered catalysts. Fibrillated films were prepared from Pd/C catalysts with varying thicknesses (100–400 µm), and their performance was evaluated through kinetic studies in both batch reactors and microreactors. The specific activity of the films was significantly influenced by film thickness with thinner films demonstrating lower mass transfer limitations. However, mass transfer limitations were observed in thicker films, prompting the development of alternative film designs, including enhanced macro-porous films and sandwich structures. These modifications successfully minimized diffusion limitations, achieving similar specific activity to the powder catalysts while maintaining the mechanical stability of the films. This work demonstrates the feasibility of using fibrillated films for continuous catalytic processes and highlights their potential for efficient catalyst reuse, avoiding filtration steps and enhancing process sustainability. Furthermore, while PTFE remains indispensable for producing such films due to its mechanical and thermal stability, ongoing research focuses on identifying more environmentally friendly alternatives without compromising performance.

Impact of low temperature on bacterial community dynamics and process efficiency in anaerobic ammonia removal: A network analysis of metagenomic data

The implementation of anaerobic ammonia removal has potential for reducing the operating costs in wastewater treatment plants. However, the application of this process in mainstream treatment presents various challenges, particularly due to the sensitivity of anammox bacteria to low temperatures. To address these challenges, changes in the bacterial community were investigated under decreasing temperatures (from 30 to 12 °C) within a deammonification process conducted in a 10-L sequencing batch reactor (SBR) over a period of 114 days. The aim of the study was to determine which groups of microorganisms are most strongly linked by ecological relationships with anammox bacteria and how these relationships change in response to decreasing temperature. Community dynamics were analyzed by combining metagenomics, network analysis, and specific process rates. The nitrification process was most efficient at 25 °C, as indicated by high values of the ammonia and nitrite utilization rate, and nitrate production rate, all of which declined as the temperature decreased. In contrast, the activity and abundance of anammox bacteria remained stable throughout all phases of the experiment. The decreasing temperature negatively impacted Nitrospira bacteria, the main competitors of anammox in the deammonification system. Despite the reduced process efficiency, the SBR maintained stable functionality even at temperatures as low as 12 °C. Network analysis identified which bacterial groups most frequently co-occurred and interacted, as well as those most sensitive to temperature fluctuations. Among the bacterial nodes, Nitrospira, Phycisphaerae, and Prosthecobacter exhibited the highest degree of connectivity, suggesting that they participate in multiple interactions, such as metabolite exchange, cooperation, or competition. Nevertheless, the temperature node had a greater number of connections than any bacterial node, indicating that this environmental factor had a more important effect on microbial community formation than direct ecological relationships. These results contribute to a comprehensive understanding of the role of anammox bacteria in deammonification systems, their ecological interactions within microbial networks, and their activity under suboptimal temperature conditions, which is crucial for future practical applications.

Enhanced Production of Furfural via Methanolysis of Wood Biomass with HCl Gas.

This study explores the production of furfural, xylose and methylxylosides through the methanolysis of wood flour using anhydrous HCl gas. The process involves methanolysis of wood flour with HCl gas under pressure to generate methylxylosides, which are subsequently converted to xylose and furfural via autohydrolysis in a Parr batch reactor system. The methanolysis was conducted in temperature-controlled HCl gas reactor employing 24 h reaction time and 50 % methanol content in wood flour. During the methanolysis step with HCl gas, 65 % of the available xylan in wood flour was converted to water-soluble methylxylosides, xylose, xylooligosaccharides (XO) and water-soluble methyl xylooligosaccharides (MXO). Methanolysis filtrates were then autohydrolyzed with Parr 50 mL batch reactor system to xylose and furfural in two different pH values at 180 °C. The highest furfural yield of 91 % from methanolysis filtrate was achieved with pH 1.2 and 25 min reaction time.

Interval Analysis of Volatile Solid (VS) and Biochemical Oxygen Demand (BOD) in Batch Anaerobic Fermentation of Selected Agrowaste

This study investigated the degradation of volatile solids (VS) and biochemical oxygen demand (BOD) during the anaerobic digestion of selected agro-waste, specifically cassava peels, maize husks, pig slurry, and the composite. The objective was to evaluate the biodegradability of these feedstocks, in line with their potential for biogas production. The Research was conducted at the National Centre for Energy Research and Development (NCERD) laboratory, University of Nigeria Nsukka (UNN). Batch reactors were used to conduct experiments over a period of 45 days. The digesters were operated under controlled conditions, and samples were analyzed at three (3) different points: 24 hours, peak of gas production (day 30), and at the end of the digestion (day 45). The results demonstrated that all the substrates exhibited a reduction in VS and BOD in the course of digestion. However, the most significant reduction in VS and BOD occurred around the peak of gas production. This entails that this period is critical for microbial activity and biogas yield. Corn husks had high initial VS and BOD values of 4.73±0.22 % and 92.80±3.26 mg/L respectively. However, that did not translate to higher biogas production compared with the composite that had initial values of 4.34±0.19 % and 88.00±5.50 mg/L respectively. By the end of the digestion, an average VS reduction of 65% and a BOD reduction of 70% were observed across all substrates, indicating a substantial degradation of organic material. Biogas production was better in the composite (72.580±4.53 %), an indication that higher VS and BOD do not automatically translate to higher gas yield. Thus, factors like multiple substrate interaction affect gas yield and process efficiency.

Insights into the effect of various supports on hydrothermal liquefaction of food waste over iron-oxide nano-catalysts

This work investigates the effect of supported iron-oxide nano-catalysts for hydrothermal conversion of food waste. The studied supports were Vulcan carbon (VC), CeO2, ZSM-5 and amorphous SiO2-Al2O3. Catalytic hydrothermal liquefaction experiments were carried out in a batch reactor at 16 MPa and 300 °C maintained for 1 h. Different fractions of Fe(0), Fe2+ and Fe3+ alter its tendency toward deoxygenation, hydrogenations and condensation reactions, which influence the bio-crude yield, elemental compositions, and energy recoveries. The fresh and spent catalysts were characterized using X-ray photoelectron spectroscopy, physisorption analysis, thermogravimetric analysis, transmission and scanning electron microscopy. It was found that the change in catalyst support influences HTL pathways and product compositions. The results reveal that the inclusion of FeOx catalyst on Vulcan carbon, SiO2-Al2O3 and ZSM-5 supports can increase the bio-crude yield by ~7–9 wt% compared to their FeOx-free yields. The increase in bio-crude yield was associated with the decrease in the surface ratios of Fe3+/Fe2+ at the range of 0.8–1.6. In overall, catalysts that had higher tendencies in converting amines into oil-soluble compounds increased the bio-crude yield, while catalysts that promoted dehydration and decarboxylation route decreased the bio-crude yield. The maximum energy recovery in bio-crude was obtained using FeOx/SiO2-Al2O3 catalyst with values ~95 %. The deactivation of catalysts was associated with the increase in Ca and P poisonous elements on catalytic sites, which decreased the energy recovery of recycled FeOx/SiO2-Al2O3 to ~85 % after three cycles.

Olive pomace waste conversion to bio-fuel by application of integrated configuration of pyrolysis/hydrodeoxygenation process

Bio-oil obtained from non-catalytic pyrolysis of biomass, consists of a large number of oxygenated compounds. Hence, it is essential for the bio-oil to go through upgrading processes such as hydrodeoxygenation (HDO) to reform these compounds to aliphatic and aromatic hydrocarbons. This study works towards this purpose by initially deriving raw bio-oil from olive pomace waste biomass in a non-catalytic pyrolysis process at temperature of 400–700 ºC. Then for reducing the oxygen content of derived bio-oil, HDO of the raw bio-oil over NiMo/Al2O3 catalyst was performed in a batch reactor, in varying operational parameters: temperature of 200–250 °C, reaction time of 1–3 h, hydrogen pressure of 2–6 bar and catalyst: bio-oil ratio of 1:20, 1:10, 1:5. The results revealed that the catalytic HDO is an appropriate procedure, as fatty acids as the main oxygenated components in bio-oil were reduced from 81.8 % to 56.7 %, aldehydes and ketones were entirely removed, and there was a noticeable rise in aliphatic hydrocarbons from 2.8 % to 33.9 % at temperature of 250 ºC, hydrogen pressure of 6 bar and reaction duration of 3 h. In addition, by raising the catalyst to bio-oil ratio to 1:5, the content of fatty acids reached 47.6 %. Furthermore, a comparison was made between the O/C and H/C ratios of the obtained biofuels and the raw bio-oil, which results exhibited that this method worked successfully in substituting oxygen atoms of the raw bio-oil with hydrogen atoms.

Role of perovskite non-stoichiometry on catalytic oxygen dark activation for the removal of azo dyes from wastewater

Effluents of the dying and printing industries are a significant contributor to water pollution. Since synthetic dyes are primarily resistant to natural degradation, they remain in water bodies for an exceptionally long time if discharged untreated. Oxygen dark activation is a promising candidate for the degradation of azo dyes as it does not require the use of additional reagents or even the presence of light. It is an advanced catalytic oxidation process that converts oxygen dissolved in wastewater into reactive oxygen species, which subsequently break down dye molecules. The role of the catalyst is to accelerate the process by acting as a bridge for the electron transfer between the dye molecule and adsorbed oxygen. It has been reported that the textural and structural properties of the catalyst play a key role in generating reactive oxygen species. In this work, we synthesized, characterized, and evaluated a series of strontium-based perovskite oxides for the catalytic degradation of azo dyes under dark conditions. The degradation of different dyes was studied in a batch reactor under various conditions, and the reaction progress was monitored by UV-vis absorption spectroscopy. The results showed that the degradation of azo dye was faster when the azo bond was weakened by either electron-withdrawing groups or due to the formation of a stable hydrazone structure. To evaluate the effect of structural defects on the oxygen dark activation process, cation non-stoichiometry was separately introduced in the parent perovskite SrFeO3 at both A and B sites. Under identical reaction conditions, the degradation efficiency of A-site deficient perovskite Sr0.90FeO3 (94%) and B-site deficient SrFe0.80O3 (95%) was higher than the stoichiometric perovskite SrFeO3 (46%). These results demonstrate that cation deficiency in the SrFeO3 structure strongly favors the catalytic degradation of azo dyes via oxygen dark activation.

Kinetics of continuously catalyzed peroxymonosulfate in a fixed-bed reactor

Most studies have been conducted in batch reactors. Therefore, understanding the catalytic reaction kinetics and mass transfer in continuous catalytic reactors is essential for the design of heterogeneous catalysts and optimisation of catalytic degradation processes in heterogeneous systems. In this research, granular catalysts (Co-600/AlSi-0.25/AP) is used to investigate the kinetic constants and mass transfer resistance for the continuous catalytic decomposition of peroxymonosulfate (PMS) and degradation of p-nitrophenol (PNP) in a fixed bed reactor. The flow rate is 5 mL/min and reaction temperature is 30 °C, intrinsic kinetic constants of PMS decomposition and PNP degradation are 48 and 195 kg−1·min−1·L, respectively, which are 20–30 times of the apparent kinetic constants of PMS decomposition and PNP degradation in fixed bed reactors, respectively. The decomposition rates of PMS and PNP are controlled by mass transfer, and the reaction takes place in the diffusion-controlled regime. The mass transfer kinetic model based on the plug-flow model shows a good agreement between the calculated data and the experimental data. Which indicate that PMS decomposition and pollutant degradation in a fixed-bed reactor can be predicted by mass transfer kinetic modelling, guide the design of catalysts and the optimisation of heterogeneous catalytic reaction system in a fixed-bed reactor.

The effect of burning on the dissolution behaviour and silicon and oxygen isotope composition of phytolith silica

Theδ30Si andδ18O values of opal-A precipitated in plants (silica phytoliths) have been shown to be useful for paleoenvironmental reconstructions. Here, the effects of burning and partial dissolution of phytoliths on their isotopic compositions and dissolution behaviour were examined. Phytoliths were heated to 700 °C and then dissolution experiments were conducted in batch reactors under a range of pH (4–8) and temperature (4–19 °C) conditions. Heating caused a −2.6 ‰ shift in phytolithδ18O values. NMR results suggest that heating reduces the number of surface vicinal silanols, which likely results in the formation of strained SiOSi bonds which incorporate oxygen from18O-depleted hydroxyl groups. During dissolution, theδ18O of burned phytoliths increased by up to 3.5 ‰ (average 1.8 ‰) until 15–45 % saturation was reached, and then adsorption of silica on the surface of the solid began to reducethe δ18O value of solid silica despite a net dissolution. The maximum increase in δ18O during dissolution of burned phytoliths is 1.8 ‰ smaller than previously observed for unburned silica subjected to partial dissolution under the same conditions. Heating did not cause a significant change inδ30Si values, and partial dissolution of burned phytoliths caused a slight increase inδ30Si values that was smaller in magnitude than for unburned phytoliths. Dissolution of burned phytoliths progressed more slowly than dissolution of fresh phytoliths in low pH and temperature conditions, but was faster than the dissolution of fresh phytoliths when pH > 6 and temperature = 19 °C. We propose that because fewer hydrolysis sites exist on the surface of burned phytoliths that the isolated silanols that remain after heating are difficult to deprotonate at low pH resulting in slower dissolution. However, at higher pH the breakage of strained SiOSi bonds in burned phytoliths may explain their higher dissolution rate relative to fresh phytoliths. We recommend caution in using theδ18O values of soil phytoliths in paleoclimate reconstructions as they can be altered during both heating and partial dissolution. For phytolith assemblages collected from archaeological hearths or grasslands prone to wildfires, the shift towards lowerδ18O values caused by heating would result in overestimations of temperature using paleothermometer equations. Care must be taken to identify alteration by dissolution or burning, which may not always be visually evident.