Alkaline Additives Research Articles

Ocean alkalinity enhancement approaches and the predictability of runaway precipitation processes: results of an experimental study to determine critical alkalinity ranges for safe and sustainable application scenarios

Abstract. To ensure the safe and efficient application of ocean alkalinity enhancement (OAE), it is crucial to investigate its impacts on the carbonate system. While modeling studies reported a sequestration potential of 3–30 Gt carbon dioxide (CO2) per year (Oschlies et al., 2023), there has been a lack of empirical data to support the applicability of this technology in natural environments. Recent studies have described the effect of runaway carbonate precipitation in the context of OAE, showing that calcium carbonate (CaCO3) formation was triggered if certain Ωaragonite saturation thresholds were exceeded. This effect could potentially lead to a net loss of the initially added alkalinity, counteracting the whole concept of OAE. The related precipitation can adversely affect the carbon storage capacity and may in some cases result in CO2 emissions. Experiments at the Espeland marine biological station (Bergen, Norway) were conducted to systematically study the chemical consequences of OAE deployment. The experiments lasted for 20–25 d to monitor the temporal development of carbonate chemistry parameters after alkalinity addition and the subsequent triggered carbonate precipitation process. Identified uniform patterns before and during the triggered runaway process can be described by empirical functional relationships. For approaches equilibrated to the CO2 concentration of the atmosphere, total alkalinity (TA) levels of up to 6500 µmol kg−1 remained stable without loss of total alkalinity (TA) for up to 20 d. Higher implemented TA levels, up to 11 200 µmol kg−1, triggered runaway carbonate formation. Once triggered, the loss of alkalinity continued until the Ωaragonite values leveled out at 5.8–6.0, still resulting in a net gain of 3600–4850 µmol kg−1 in TA. The non-CO2-equilibrated approaches, however, only remained stable for TA additions of up to 1000 µmol kg−1. The systematic behavior of treatments exceeding this level allows us to predict the duration of transient stability and the quantity of TA loss after this period. Once triggered, the TA loss continued in the non-CO2-equilibrated approaches until Ωaragonite values of 2.5–5.0 were reached, in this case resulting in a net loss of TA. To prevent a net loss of TA, treated water must be diluted below the time-dependent critical levels of TA and Ωaragonite within the identified transient stability duration. Identified stability and loss patterns of added TA depend on local environmental conditions impacting the carbonate system, such as salinity, temperature, biological activity, and particle abundance. Incorporating such stability and loss patterns into ocean biogeochemical models, which are capable of resolving dilution processes of treated and untreated water parcels, would, from a geochemical perspective, facilitate the prediction of safe local application levels of OAE. This approach would also allow an accurate determination of the fate of added alkalinity and a more realistic carbon storage potential estimation compared to the assessments that neglect carbonate system responses to OAE.

Fixing collapsed dry anaerobic digestion system of kitchen waste caused by severe VFAs accumulation

Severe inhibition by volatile fatty acids (VFAs) frequently occurs during the dry anaerobic digestion of kitchen waste at high organic load rate (OLR), leading to decreased biogas production and even the collapse of the anaerobic digestion system. In this study, VFAs accumulation was significantly reduced by adding powder-activated carbon (PAC) or alkaline additives (AA), thus restoring the collapsed system to a stable operating state. With the addition of PAC or AA, the maximal OLR reached 11.14 g VS/(L·d), which was 30 % higher than observed without any additives (control group), while the VFAs concentration was maintained below 3000 mg/L. At this OLR, the volumetric biogas production rate stabilized at 5.1 L/(L·d) in the presence of PAC and AA, while that of the control group gradually decreased to zero. The VFAs concentration with PAC addition was 86 % lower than that of the control group, possibly because PAC might stimulate the formation of direct interspecies electron transfer between syntrophic bacteria and methanogens (Methanosarcina), thereby promoting VFAs degradation. The addition of AA, which resulted in a 95 % decrease in ammonia-nitrogen concentration, can provide a good growth environment for the microorganisms involved in acidogenesis and hydrogenotrophic methanogenesis.

Assimilatory sulphate reduction by acidogenesis: The key to prevent H2S formation during food and green waste composting for sustainable urbanization

Food and green waste composting is a nature-based process for sustainable management of municipal organic waste. Although widely used for these organic wastes, composting is hindered by rapid organic acidification and malodor emission, particularly hydrogen sulphide (H2S). Using genome-resolved metagenomics, this study aimed to decipher the underlying mechanisms of sulphate reduction to H2S by acidogenesis during food and green waste composting. Results showed that both volatile fatty acids (VFAs) and H2S were significantly produced within the first week of composting. Further analysis identified that bacteria (e.g. Lactobacillus) with acid-producing genes (ackA and LDH) were key accomplices to assimilatory sulphate reduction for producing H2S by providing VFAs, especially acetic and lactic acids, as a carbon source. Such sulphate reduction could be directly induced by bacteria (e.g. Bacillus, and Ureibacillus) with intact assimilatory sulphate-reducing genes (cysNC, cysH, and cysJ/I). Nevertheless, individual bacteria (e.g. Paenibacillus and Acetobacter) without any sulphate-reducing genes could collaborate with their partners carrying complemented genes to complete sulphate reduction toward H2S. Furthermore, VFAs production could acidify composting substrates to abiotically aggravate the conversion of sulphur ions (e.g. S2- and HS-) to H2S. Nevertheless, alkaline additives suppressed these mechanisms to prevent both acidogenesis and H2S production, thereby, reducing the global acidification and human toxicity potentials of food and green waste composting.

A self-isolated acid-tolerant Parachlorella kessleri with high efficiency in treating rare earth mining sewage

Rare earth mining sewage is a significant environmental concern due to its high acidity and ammonia nitrogen levels. Finding a sustainable and cost-effective treatment method is essential. Parachlorella kessleri FM2, a green algae strain isolated in-house, has demonstrated remarkable abilities to grow and remove ammonia nitrogen (NH4+-N) from highly acidic rare earth wastewater without the need for alkaline additives. After optimizing conditions, P. kessleri FM2 achieved an impressive NH4+-N removal rate of 7.94 mg/L/d and a removal efficiency of 98.71% in a 1.5-L photobioreactor. In semi-continuous culture, the average NH4+-N removal rate remained high at 6.67 mg/L/d. When scaled up to continuous culture in a 5-L photobioreactor, P. kessleri FM2 maintained stability with an NH4+-N removal rate of 6.79 mg/L/d. Additionally, we conducted a preliminary analysis of P. kessleri FM2's acid resistance mechanism, further highlighting its potential as a candidate for treating acidic wastewater.

Promoting enzymatic hydrolysis of corncob through alkaline hydrogen peroxide pretreatment and addition of additives

Promoting enzymatic hydrolysis of corncob through alkaline hydrogen peroxide pretreatment and addition of additives

Theoretical background and results of a study on changes in oil alkalinity of diesel engines

Abstract Alkalinity is a primary indicator for neutralizing insoluble impurities in oil. Alkaline additives decrease as oils interact with fuel combustion products containing significant amounts of sulfur and nitrogen. Literature data suggests that adding 2-3% of an effective ashless dispersant of a specified type can be equivalent to increasing the alkaline number of the oil by approximately 10 mg KOH/g through the addition of a metal-alkalinity additive to the oil. Based on operational study results, it can be concluded that after the first 100 hours of operation, the alkalinity value ranges from 6-4.3 mg KOH/g, and after 300 hours of operation, the alkalinity value reaches its maximum value of 2 mg KOH/g. Oils with an alkalinity of less than 2 mg KOH/g already indicate an unsatisfactory condition of the oil when lubricating the engine. To maintain the alkalinity value at a given level, it is recommended to continuously introduce tribomechanical stabilizers into the engine lubrication system.

On the emission-path dependency of the efficiency of ocean alkalinity enhancement

Ocean alkalinity enhancement (OAE) deliberately modifies the chemistry of the surface ocean to enhance the uptake of atmospheric CO2. The chemical efficiency of OAE (the amount of CO2 sequestered per unit of alkalinity added) depends, among other factors, on the background state of the surface ocean, which will significantly change until the end of this century and beyond. Here, we investigate the consequences of such changes for the long-term efficiency of OAE. We show, using idealized and scenario simulations with an Earth system model, that under doubling (quadrupling) of pre-industrial atmospheric CO2 concentrations, the simulated mean efficiency of OAE increases by about 18% (29%) from 0.76 to 0.90 (0.98). We find that only half of this effect can be explained by changes in the sensitivity of CO2 sequestration to alkalinity addition itself. The remainder is due to the larger portion of anthropogenic emissions taken up by a high-alkalinity ocean. Importantly, both effects are reversed if atmospheric CO2 concentrations were to decline due to large-scale deployment of land-based (or alternative ocean-based) carbon dioxide removal (CDR) methods. By considering an overshoot pathway that relies on large amounts of land-based CDR, we demonstrate that OAE efficiency indeed shows a strong decline after atmospheric CO2 concentrations have peaked. Our results suggest that the assumption of a constant, present-day chemical efficiency of OAE in integrated assessment modeling and carbon credit assignments could lead to economically inefficient OAE implementation pathways.

Ion Exchange Processes for CO2 Mineralization Using Industrial Waste Streams: Pilot Plant Demonstration and Life Cycle Assessment

AbstractAn attractive technique for removing CO2 from the environment is sequestration within stable carbonate solids (e. g., calcite). However, continuous addition of alkalinity is required to achieve favorable conditions for carbonate precipitation (pH>8) from aqueous streams containing dissolved CO2 (pH<4.5) and Ca2+ ions. In this study, a pH‐swing process using ion exchange was demonstrated to process 300 L of produced water brine per day for CO2 mineralization. Proton titration capacities were quantified for aqueous streams in equilibrium with gas streams at various concentrations of CO2 (pCO2=0.03–0.20 atm) and at various flow rates (0.5–2.0 L min−1). Energy intensities for the process were determined to be between 30 and 65 kWh per tonne of CO2 sequestered depending on the composition of the brine stream. A life cycle assessment was performed to analyze the net carbon emissions of the technology which indicated a net CO2 reduction for pCO2≥0.12 atm (−0.06–−0.39 kg CO2e per kg precipitated CaCO3) utilizing calcium‐rich brines. The results from this study indicate the ion exchange process can be used as a scalable method to provide alkalinity necessary for the capture and storage of CO2 in Ca‐rich waste streams.

Earth system responses to carbon dioxide removal as exemplified by ocean alkalinity enhancement: tradeoffs and lags

Carbon dioxide removal (CDR) is discussed for offsetting residual greenhouse gas emissions or even reversing climate change. All emissions scenarios of the Intergovernmental Panel on Climate Change that meet the ‘well below 2 °C’ warming target of the Paris Agreement include CDR. Ocean alkalinity enhancement (OAE) may be one possible CDR where the carbon uptake of the ocean is increased by artificial alkalinity addition. Here, we investigate the effect of OAE on modelled carbon reservoirs and fluxes in two observationally-constrained large perturbed parameter ensembles. OAE is assumed to be technically successful and deployed as an additional CDR in the SSP5-3.4 temperature overshoot scenario. Tradeoffs involving feedbacks with atmospheric CO2 result in a low efficiency of an alkalinity-driven atmospheric CO2 reduction of −0.35 [−0.37 to −0.33] mol C per mol alkalinity addition (skill-weighted mean and 68% c.i.). The realized atmospheric CO2 reduction, and correspondingly the efficiency, is more than two times smaller than the direct alkalinity-driven enhancement of ocean uptake. The alkalinity-driven ocean carbon uptake is partly offset by the release of carbon from the land biosphere and a reduced ocean carbon sink in response to lowered atmospheric CO2 under OAE. In a second step we use the Bern3D-LPX model in CO2 peak-decline simulations to address hysteresis and temporal lags of surface air temperature change (ΔSAT) in an idealized scenario where ΔSAT increases to ~2 °C and then declines to ~1.5 °C as result of CDR. ΔSAT lags the decline in CO2-forcing by 18 [14–22] years, depending close to linearly on the equilibrium climate sensitivity of the respective ensemble member. These tradeoffs and lags are an inherent feature of the Earth system response to changes in atmospheric CO2 and will therefore be equally important for other CDR methods.

Multiscale analysis of traditional and non-traditional additive amended expansive soil-A comparative evaluation

The expansive soils have always been complex and problematic for construction purposes and challenging for the geotechnical fraternity. However, structural alterations and chemical stabilization methods have been practiced successfully in many practical applications. These soils interact with the chemical additives based on the chemical composition, curing period and quantity. The stabilization methods have also focused on non-traditional, eco-friendly additives, which can be a suitable alternative to conventional alkaline additives. However, extensive experimentation is required at various testing levels to understand the stabilization mechanism and the longevity of the additives in the soil medium. The present study uses lime, a conventional additive and a non-traditional additive-lignosulphonate (LS), to stabilize the expansive soil. The interaction mechanism of soil and the additives is investigated at macroscale and microscale levels to understand the modifications rendered to the virgin soil. The effect of the additives in terms of quantity and curing period is studied with respect to plasticity characteristics, strength development and microstructural modifications. The interaction behaviour of soil and the additive is compared at each level, and a probable interaction mechanism is proposed for both additives from this study. The criticality of lime amendment depends on the curing effect and the quantity. A strength improvement factor of 9 and 2 is observed for lime and LS amendment. The compressive/tensile strength ratio is higher for lime amendment, indicating excessive brittleness compared to LS. The conventional additives contribute to higher strength and brittleness, as opposed to lower strength gain and less brittleness of non-conventional additives.

Highly efficient selective hydrogenation of isophthalonitrile to M-xylenedimethylamine over Co–CaO/g-C3N4 without alkaline additives

Highly efficient selective hydrogenation of isophthalonitrile to M-xylenedimethylamine over Co–CaO/g-C3N4 without alkaline additives

Short-chain carboxylate continuous production from food waste with in situ extraction: Novel design to reduce chemical input for pH control and alleviate membrane fouling

The production of short-chain carboxylates (SCCs) from readily degradable food waste exhibits superior product value compared to biogas production, but SCCs’ high solubility poses challenges in their production and recovery. In this study, we applied two novel modules to in-situ extract SCCs from the continuously produced fermentative broth, namely direct coupling of bipolar membrane electrodialysis (BPED) and the integration of upstream membrane permeation (MP) and BPED. The remarkable extraction efficiency of BPED effectively mitigated the inhibitory effects from the accumulation of SCCs products, yielding 475.2 mg gVS−1, which was 20.26% higher than the control phase. The OH− generated by the bipolar membrane was cycled back to regulate the pH of bioreactor, thereby completely eliminating the need for external alkaline additives. The upstream MP effectively prevented ion exchange membrane fouling, and the OH− generated by BPED achieved the in-situ regeneration of MP’s alkali extract, reducing the OH− demand by 40% in MP+BPED stage. It was also observed that BPED exhibited higher selectivity towards small-molecule acetic acid, while MP tended to recover larger-molecule caproic acid. Selective extraction of specific SCC drove the product spectrum of the bioreactor to produce more SCC that was selectively extracted.

Dechlorination of PVC at low temperature by solvothermal treatment with alkaline additives

In this research, a solvent thermal dechlorination method was adopted to remove chlorine from polyvinyl chloride (PVC) material, using ethylene glycol (EG) as solvent and adding alkaline additives, so as to improve the dechlorination efficiency and reduce the reaction temperature. KOH, NaOH and K2CO3 were selected as additives and their dechlorination activity was found to decrease in the following order: K2CO3 >KOH>NaOH. Afterward, the effect of K2CO3 concentration, reaction temperature and reaction time on the dechlorination of PVC was studied and a novel dechlorination mechanism was investigated. The results showed that solvothermal dechlorination may accomplish efficient dechlorination at low temperatures. The reaction temperature can be reduced to 180 ℃ in 0.5 M K2CO3/EG system with a solid-liquid ratio of 1:40(g:ml) and more than 97% dichlorination, which is 10 ℃ lower than the lowest temperature reported in published literature. Through the characterization and analysis of solid products, the dechlorination mechanism of PVC in K2CO3/EG system was proposed. Glycolate ion and OH- may be formed in the reaction and they both work to dechlorinate PVC by removing the Cl through two distinct substitution reactions.

Soil electrical conductivity as a proxy for enhanced weathering in soils

To effectively monitor and verify carbon dioxide removal through enhanced weathering (EW), this study investigates the use of soil electrical conductivity (EC) and volumetric water content (θ) as proxies for alkalinity and dissolved inorganic carbon (DIC) in soil water. EC-θ sensors offer a cost-effective and straightforward alternative to traditional soil and water sampling methods. In a lab experiment, three different substrates were treated with NaHCO3 solutions to increase the alkalinity of the soil water and analyze the response. The combination of EC and θ to track the increase in carbonate alkalinity due to EW, and therefore CO2 consumption, is applicable for low cation exchange capacity (CEC) soil-substrates like the used quartz sand. However, the presence of organic material and pH-dependent CEC complicates the detection of clear weathering signals in soils. In organic-rich and clay-rich soils, only a high alkalinity addition has created a clear EC signal that could be distinguished from a non-alkaline baseline with purified water. Cation exchange experiments revealed that the used soil buffered alkalinity input and thereby might consume freshly generated alkalinity, initially mitigating CO2 uptake effects from EW application. Effective CEC changes with pH and pH buffering capacity by other pathways need to be considered when quantifying the CO2 sequestration potential by EW in soils. This should be estimated before the application of EW and should be part of the monitoring reporting and verification (MRV) strategy. Once the soil-effective CEC is raised, the weathering process might work differently in the long term.

Alkaline humic acid fertilizer alters the distribution, availability, and translocation of cadmium and zinc in the acidic soil–Sauropus androgynus system

Humic acids (HA) are a popular soil additive to reduce metal availability, but they have the drawbacks of reduced effectiveness over time and a significant reduction in soil pH. An alkaline humic acid fertilizer (AHAF) combining alkaline additives with HA was developed to overcome such drawbacks. A field experiment was conducted to investigate the effects of different AHAF application rates on the physicochemical properties, bioavailability, accumulation, and translocation of Cd and Zn heavy metals in Sauropus androgynus grown in acidic soil. Based on our results, the 100AF (100% AHAF) treatment significantly increased soil pH, cation exchange capacity (CEC), and organic matter content (OM) after one year of application. Compared with the control treatment (CK), the application of different rates of AHAF resulted in a 37.1–40.3% decrease in soil exchangeable Cd fractions (Exc-Cd) and an increase in the humic acid-bound Cd fractions (HA-Cd) Fe- and Mn-oxide-bound Cd fractions (OX-Cd), and organic matter-bound Cd fractions (OM-Cd) by 9.5–64.6%, 24.8–45.1%, and 158.8–191.2%, respectively (P < 0.05). The different AHAF treatments decreased the Res-Zn, Exc-Zn, and OM-Zn fractions by 69.6–73.0%, 7.4–23.9%, and 18.1–23.2%, respectively (P < 0.05), and increased the HA-Zn fraction by 8.4–28.1%. In the control treatment, the bioconcentration factors (BCFs) for Cd and Zn in different S. androgynus plant organs were in the following order: (Cd) Leaves > Stems > Branches > Roots > Edible branches; (Zn) Roots > Stems > Leaves > Branches > Edible branches. The transfer factors (TFs) of Cd and Zn in S. androgynus were classified as follows: TF2 > TF1 > TF3 > TF4. Thus, S. androgynus stems, and roots had a strong ability to transport Cd and Zn to the leaves. Compared with CK, the 100AF treatment significantly increased the BCFs for Zn in all plant parts (except BCFedible branches). In contrast, it significantly decreased all BCFs and TFs for Cd and the TF4 for Zn, effectively reducing Cd and Zn accumulation in the edible branches of S. androgynus. Soil pH, CEC, OM, and HA-M fraction were highly and significantly negatively correlated with Cd and Zn content in edible branches (P < 0.001). Stepwise multiple linear regression analysis revealed that the soil HA-M fraction was the key contributing factor for Zn accumulation and translocation in S. androgynus. Moreover, based on our findings, the absorption, uptake, and translocation of Cd and Zn were mainly determined by metal speciation and the pH in the soil. Moreover, the competitive antagonistic mechanisms between Zn and Cd absorption also affected their accumulation in S. androgynus. Thus, AHAF can be used as a soil amendment to sustainably improve acidic soils and effectively reduce Cd and Zn accumulation in edible branches of S. androgynus.

Alkalinity biases in CMIP6 Earth system models and implications for simulated CO2 drawdown via artificial alkalinity enhancement

Abstract. The partitioning of CO2 between atmosphere and ocean depends to a large degree not only on the amount of dissolved inorganic carbon (DIC) but also on alkalinity in the surface ocean. That is also why ocean alkalinity enhancement (OAE) is discussed as one potential approach in the context of negative emission technologies. Although alkalinity is thus an important variable of the marine carbonate system, little knowledge exists on how its representation in models compares with measurements. We evaluated the large-scale alkalinity distribution in 14 CMIP6 Earth system models (ESMs) against the observational data set GLODAPv2 and show that most models, as well as the multi-model mean, underestimate alkalinity at the surface and in the upper ocean and overestimate it in the deeper ocean. The decomposition of the global mean alkalinity biases into contributions from (i) physical processes (preformed alkalinity), which include the physical redistribution of biased alkalinity originating from the soft tissue and carbonates pumps; (ii) remineralization; and (iii) carbonate formation and dissolution showed that the bias stemming from the physical redistribution of alkalinity is dominant. However, below the upper few hundred meters the bias from carbonate dissolution can gain similar importance to physical biases, while the contribution from remineralization processes is negligible. This highlights the critical need for better understanding and quantification of processes driving calcium carbonate dissolution in microenvironments above the saturation horizons and implementation of these processes into biogeochemical models. For the application of the models to assess the potential of OAE to increase ocean carbon uptake, a back-of-the-envelope calculation was conducted with each model's global mean surface alkalinity, DIC, and partial pressure of CO2 in seawater (pCO2) as input parameters. We evaluate the following two metrics: (1) the initial pCO2 reduction at the surface ocean after alkalinity addition and (2) the uptake efficiency (ηCO2) after air–sea equilibration is reached. The relative biases of alkalinity versus DIC at the surface affect the Revelle factor and therefore the initial pCO2 reduction after alkalinity addition. The global mean surface alkalinity bias relative to GLODAPv2 in the different models ranges from −85 mmol m−3 (−3.6 %) to +50 mmol m−3 (+2.1 %) (mean: −25 mmol m−3 or −1.1 %). For DIC the relative bias ranges from −55 mmol m−3 (−2.6 %) to 53 mmol m−3 (+2.5 %) (mean: −13 mmol m−3 or −0.6 %). All but two of the CMIP6 models evaluated here overestimate the Revelle factor at the surface by up to 3.4 % and thus overestimate the initial pCO2 reduction after alkalinity addition by up to 13 %. The uptake efficiency, ηCO2, then takes into account that a higher Revelle factor and a higher initial pCO2 reduction after alkalinity addition and equilibration mostly compensate for each other, meaning that resulting DIC differences in the models are small (−0.1 % to 1.1 %). The overestimation of the initial pCO2 reduction has to be taken into account when reporting on efficiencies of ocean alkalinity enhancement experiments using CMIP6 models, especially as long as the CO2 equilibrium is not reached.

Results of calculation of changing the pollution concentration and alkalinity of the gas engine oils

BACKGROUND: The issue of ensuring the reliability of internal combustion engines is a relevant composite task, solved in various directions. The important ones among them are the operation conditions, the type of fuel used, control of the motor oils condition, as well as justification of the service life of the latter. When ensuring the operational properties of engine oils of the dieselbased gas engines, the control of the main indicators of the operating oil is relevant.&#x0D; AIMS: Assessment of changes in the pollution load and alkalinity of the M10G2 oils of the dieselbased gas engines. Application of equations for the theoretical analysis of changes in the pollution concentration and decrease of alkalinity, as well as for building dependencies of oil indicators.&#x0D; METHODS: During the operation of internal combustion engines, thermochemical processes are actively developing in oils, leading to decrease in their quality due to the activation of additives and the accumulation of transformation products in oils. Mechanical impurities accumulate in the engine oil as a result of dust ingress with the sucked air or through leaks in the crankcase space, as well as due to the formation of insoluble oxidation products and wear of parts of the cylinder-piston group. The base number is a conditional measure of the oils ability to neutralize acids formed from the products of fuel combustion and oxidation of the oil base. The alkalinity specified by the presence of alkaline additives is consumed for the neutralization of acids at different rates.&#x0D; RESULTS: The process of oil aging in internal combustion engines and factors affecting the aging of engine oil are considered. Analytical equations are used to calculate changes in the pollution concentration and changes in the alkalinity of the diesel-based gas engine oil, graphical dependences of oil indicators on the service duration are given.&#x0D; CONCLUSIONS: The practical value of the study lies in the fact that, using the analytical equations, the value of changes in individual properties of diesel-based gas engine oils is analyzed. Operation of the engine with the oil which base number is below the limit leads to a decrease in engine reliability, accelerated wear of individual parts, lacquer formation and sludging on piston rings and cylinders. It is not allowed to use oils with the base number below 2 mg of KOH/g.

Enhanced treatment of sludge drying condensate by A/O-MBR process: Microbial activity and community structure

With the rapid increase of sludge production from sewage treatment plants, the treatment of sludge drying condensate rich in a large amount of pollutants urgently needs to be addressed. Due to the unique characteristics of sludge drying condensate (high ammonia nitrogen and COD concentration), there are almost no reports on biological treatment methods specifically targeting sludge drying condensate. In this study, A/O-MBR process was proposed for sludge drying condensate treatment and the effects of ammonia nitrogen loads, alkalinity and aeration intensity were explored. Experimental results show that under the ammonia nitrogen load of 0.35 kg NH4+-N/(m3·d) and the aeration intensity of 0.5 m3/(m2·min), the removal rate of COD and NH4+-N could reach 94% and 99.86% with the addition of alkalinity (m(NaHCO3): m(NH4+-N) = 7:1), respectively. The distribution of living and dead microbial cells in the activated sludge of three reactors also proved that the supplement of alkalinity in the influent can ensure the feasible living conditions for microorganisms. In addition to traditional nitrifying bacteria, through the supplementation of alkalinity and the reduction of aeration intensity, the system had also domesticated high abundance heterogeneous nitrification aerobic denitrification (HN-AD) and aerobic denitrification bacteria (both more than 10% of the total bacterial count). The denitrification process of sludge drying condensate was simplified and the denitrification efficiency was greatly improved. The findings of this study could provide important theoretical guidance for the biological treatment process of sludge drying condensate.

Effect of alkaline treatment time of fibers and microcrystalline cellulose addition on mechanical properties of unsaturated polyester composites reinforced by cantala fibers

Abstract The aim of this study is to investigate the effect of alkaline treatment and addition of microcrystalline cellulose (MCC) on the density, tensile strength, elastic modulus, impact strength, and Poisson’s ratio of unsaturated polyester resin composites reinforced by cantala fibers (UPR-CFs). The fibers were immersed in alkaline solution of 6% NaOH for 0, 3, 6, 9, and 12 h. The composite had cantala fibers (CFs) and MCC volume fraction (v f) of 30 and 5%, respectively. The results showed that the alkaline treatment for 6 h resulted in the highest density, tensile strength, and elastic modulus of the composites, while the highest Poisson’s ratio was achieved in UPR-untreated CF composites. The addition of MCC filler also increased the density, tensile strength, and elastic modulus of the composite significantly. Both alkaline treatment and MCC addition did not significantly affect the impact strength. With the increase in the strength and modulus of elasticity, composites can be applied more widely to structures that bear higher loads.

A Rhombus-Like Tetrameric Vanadoniobate Containing Pseudo-Sandwich-Type {Li ⊂ V2O8(Nb5O14)2} and Its Electrocatalytic Activity for the Selective Oxidation of Benzyl Alcohol.

Ongoing research on V-containing polyoxoniobates (PONbs) is driven by their diverse structures and potential applications. Although Lindqvist-type {Nb6O19} is a widely used building block in PONbs, vanadoniobates based on {Nb6O19} and/or its derivatives are still very limited. Herein, a discrete vanadoniobate, LiNa14K11[Li2 ⊂ VIV8Nb32O110]·45H2O (1), has been synthesized by a hydrothermal method, which shows a rhombus-like tetrameric structure composed of two {V2O6(Nb6O19)} and two {Li ⊂ V2O8(Nb5O14)2} subunits derived from {Nb6O19}. Notably, the {Li ⊂ V2O8(Nb5O14)2} subunit has an interesting pseudo-sandwich-type structure, where a {LiV2O8} belt is coordinated by two monolacunary {Nb5O14} molecules and the central site of the cluster is occupied by Li+. Considering that 1 has both basic hexaniobates and redox active V centers, 1 was used as a noble metal-free electrocatalyst for the selective oxidation of benzyl alcohol to benzaldehyde, achieving complete conversion of benzyl alcohol with 94% selectivity for benzaldehyde in 3 h under ambient conditions without using any alkaline additives. Moreover, the catalytic performance of 1 remained largely unchanged after four cycles.