NaOH Dosage Research Articles

Preparation of controlled low-strength materials from alkali-excited red mud-slag-iron tailings sand and a study of the reaction mechanism.

To address the low utilization of fines in iron tailings sand (IOTs), a controlled low-strength material (CLSM) was prepared from a combination of fine IOTs and red mud (RM) slag. The 7-day unconfined compressive strength (7-d UCS), slump and cost were used as evaluation indicators, and 16 sets of tests were designed with the Box-Behnken design (BBD) response surface method. X-ray diffraction (XRD), Fourier transform infrared (FTIR), and scanning electron microscopy (SEM)-energy dispersive spectroscopy (EDS) were used to study the microscopic morphology and reaction mechanism of the CLSM samples made with the optimal ratios. The results show that the best matching ratio for the alkali-activated RM-slag-IOTs CLSM was a sand ratio of 0.797, an NaOH dose of 3.667% and a mass concentration of 80.657%, and the 7d-UCS, slump and cost indicators verified the feasibility of applying the CLSM to the base course of pavement. Alkali activation of the CLSM also showed that the RM-slag cementation system produced new substances. Internal calcium-silicate-hydrogel (C-S-H) and calcium-aluminosilicate-hydrogel (C-A-S-H) agglomerates were the main sources of strength, and hydration products were interwoven to form a dense structure with crystals as the framework and gels as fillers.

Hydrothermal and thermal-alkali pretreatments of wheat straw: Co-digestion, substrate solubilization, biogas yield and kinetic study

Agro-waste having lignocellulosic biomass is considered most effective (heating value 16 MJ/kg) for energy production through anaerobic digestion (AD). However, recalcitrant lignocellulosic fraction in agro-waste obstructs its biotransformation and is a rate-limiting step of the process. This study investigated the effects of hydrothermal and thermal-alkaline pretreatment on anaerobic co-digestion of wheat straw (WS). The hydrothermal pretreatment of WS revealed that 60 min was the best pretreatment time to achieve the highest substrate solubilization. It was employed for thermal-alkali pretreatment at variable temperatures and NaOH doses. Thermal-alkali pretreatment at 125°C-7% NaOH shows the highest (34%) biogas yield of 662 mL/gVS, followed by 646 mL/gVS biogas yield at 150°C-1% NaOH assay (31% higher) over control. Although the 125°C-7% NaOH assay achieved the highest biogas yield, the 150°C-1% NaOH assay was found more feasible considering the cost of a 6% higher chemical used in the earlier assay. The thermal-alkali pretreatment was observed to reduce the formation of recalcitrant compounds (HMF, Furfural) and increase the buffering capacity of the slurry over hydrothermal pretreatment. Principal component analysis (PCA) of the various pretreatment and AD operational parameters was carried out to study their in-depth correlation. Moreover, a kinetic study of the experimental data was performed to observe the biodegradation trend and compare it with the Modified Gompertz (MG) and First Order (FO) models.

Enhanced Enzymatic Saccharification of Tomato Stalk by Combination Pretreatment with NaOH and ChCl:Urea-Thioure in One-Pot Manner

In this study, the mixture of NaOH and deep eutectic solvent (DES) ChCl:UA-TA was firstly used to pretreat waste tomato stalk (TS). The effects of pretreatment time, pretreatment temperature, NaOH dosage, and DES dose were investigated, and the synergistic effects of dilute NaOH and DES combination pretreatment were tested on the influence of enzymatic saccharification. It was found that the relationship between delignification and saccharification rate had a significant linear correction. When TS was pretreated with NaOH (7 wt%)–ChCl:UA-TA (8 wt%) in a solid-to-liquid ratio of 1:10 (wt:wt) at 75 °C for 60 min, the delignification reached 82.1%. The highest yield of reducing sugars from NaOH–ChCl:UA-TA-treated TS could reach 62.5% in an acetate buffer (50 mM, pH 4.8) system containing cellulase (10.0 FPU/g TS) and xylanase (30.0 CBU/g TS) at 50 °C. In summary, effective enzymatic saccharification of TS was developed by a combination pretreatment with dilute NaOH and ChCl:UA-TA, which has potential application in the future.

The effect of microwave pyrolysis on product characteristics and bromine migration for a non-metallic printed circuit board

At present, it is necessary to carry out environmentally friendly treatment of non-metallic fractions (NMFs) of waste printed circuit board (WPCB) to improve resource utilization. NMFs of WPCB are pyrolyzed by microwave heating to determine the effect of different operating conditions on the characteristics of pyrolysis products. The results show that yields for residue, oil and gas are 59.03–67.63, 7.10–28.46 and 4.86–33.88 wt%. A high temperature promotes a decrease in oil yield and an increase in non-condensable gas yield. An increase in the NaOH dose results in a more significant cracking of the oil to gas. Increasing the concentration of NaOH increases the mass fraction of the total Br in residues (from 23.62 to 86.94 %), so the addition of NaOH is beneficial to the fixation of Br. A kinetics study shows that there are two thermal decomposition regions (398–625 K and 675–925 K), and NaOH-catalyzed pyrolysis reduces the activation energy to 18.91 and 31.95 kJ mol−1, respectively. The formation of Br-containing substances in the pyrolysis oil and gas can be inhibited if the bromine fixation in pyrolysis residue increases. NaOH-catalyzed pyrolysis can reduce bromine and also reduce energy recovery efficiency. This pyrolysis process still requires further research to improve the recovery of energy and valuable materials.

Engineering properties and pore structure of lightweight aggregates produced from off-spec fly ash

• High- and low-calcium off-spec fly ash based lightweight aggregate (LWA) was produced. • Engineering properties and pore structure of LWA was characterized. • Small dose of NaOH as fluxing agent can result in off-spec fly ash based LWA with desired engineering properties. This study characterizes the engineering properties of lightweight aggregate (LWA) manufactured from low calcium (F-FA) and high calcium (C-FA) waste fly ash that were designed using a previously-developed thermodynamics-guided process. LWA properties that were characterized include specific gravity, vacuum water absorption, water absorption over time, water desorption, porosity, pore size distribution, and permeability. The LWA studied had a low oven dry specific gravity ranging from 1.22 to 1.45. The vacuum absorption and total open porosity of F-FA LWA decreased as the fluxing agent (NaOH) concentration increased while the values for C-FA LWA varied with increasing amounts of fluxing agent. All LWA passed the ASTM C1761 water absorption/desorption requirements for application to the internal curing of concrete. X-ray computed tomography (XCT) and dynamic vapor sorption analyzer (DVSA) techniques were used to characterize the LWA pore structure. It was found that for F-FA LWA the normalized porosity, counting only pores smaller than 50 nm (gelpores + mesopores), ranged from 4 % to 11.5 %, while for C-FA LWA, this same pore size range had porosity ranging from 1.7 % to 2.8 %. Pore size distribution measurements of F-FA LWA using XCT showed that the pores became larger and the predicted permeability coefficient increased as the fluxing agent concentration increased. For C-FA LWA, the predicted permeability increased with increasing NaOH concentration. Since the pore size distribution had greater variability and did not follow a specific increasing trend, the increase in C-FA permeability could only be due to an increase in pore connectivity.

Orthogonal Experiments and Neural Networks Analysis of Concrete Performance

In order to explore the possibility that adding an appropriate amount of alkaline activator into fly ash cement may improve the early activity of fly ash and ensure the strength performance of concrete, this study analyzed the influence of 0–30% fly ash substitute on the early and late (3–28 days) compressive strength of concrete by using three methods, namely, the concrete laboratory test, orthogonal test, and neural network, under the condition of 0.5 water binder. We obtained the following results: (1) The strength of the concrete mixed with fly ash at the same alkali and the same age decreases with the increase of fly ash content and decreases with the decrease of age; the strength is the highest when the alkali content is 6% or 5%. (2) The higher the content of fly ash, the lower the strength of the mixture, and the greater the decrease of the early strength of the mixture, while the optimum dosage of NaOH is the same. (3) Orthogonal experimental design can be effectively used to analyze the primary and secondary degree of each factor and the best combination of them (cement, fly ash, NaOH, standard, water, etc.). (4) High correlations between the compressive strength and the component composition of concrete can be obtained using the prediction abilities of the neural networks. The above test results show that on the basis of the concrete compressive strength test, the comprehensive application of the orthogonal test and the neural network method can be used to analyze the relationship between strength and the variables and to test the influence of the variables and their interaction on concrete strength, and the results are accurate and reliable.

Evaluation of parameters controlling calcium recovery and CO2 uptake from desalination reject brine: An optimization approach

A multistage process scheme for extracting valuable minerals from desalination reject brine while simultaneously sequestering CO2 has been proposed. As a part of the proposed scheme, simultaneous removal of calcium ions and CO2 uptake of a magnesium free reject brine was investigated in an inert particle spouted bed reactor (IPSBR) by reacting CO2 with reject brine in presence of NaOH. Response surface methodology was applied to optimize the effect of NaOH dosage, gas flowrate and salinity on the reaction with the target of maximizing calcium removal and CO2 uptake. A second order regression model was generated for both target responses. The predicted responses for both targets were in good agreement with the obtained experimental response. Based on a multivariate optimization, the optimum conditions for NaOH, flowrate and salinity for simultaneous calcium removal and CO2 uptake were found to be 5 g/L, 2 L/min and 75 g/L, respectively. Under these conditions, 100% removal of Ca2+ ions from the brine could be achieved with a CO2 uptake of 5.4 g/L. Moreover, the solid products obtained under the optimum conditions were characterized confirming the formation of high purity calcium carbonates. Based on optimized conditions, the proposed multistage process scheme promises to produce highly pure Mg(OH)2 and CaCO3, while sequestering 5400 tons of CO2 for every million tons of brine treated. The scheme can be further improved by incorporating an electrolysis unit to produce HCl along with NaOH that can be recirculated to eliminate the need for any external addition of NaOH, thus, creating a sustainable process for reject brine management and CO2 sequestration.

Influence of CO2 inleakage on the slight-alkalization of generator internal cooling water

The slight-alkalization of generator internal cooling water (GICW) is widely used to inhibit the corrosion of hollow copper conductor and thereby ensure the safe operation of the generator. CO2 inleakage is increasingly identified as a potential security risk for GICW system. In this paper, the influence of CO2 inleakage on the slight-alkalization of GICW was theoretically discussed. Based on the equilibriums of the CO2-NaOH-H2O system, CO2 inleakage saturation was derived to quantify the amount of the dissolved CO2 in GICW. This parameter can be directly calculated with the measured conductivity and the [Na+] of GICW. The influence of CO2 inleakage on the slight-alkalization conditioning of GICW and the measurement of its water quality parameters were then analyzed. The more severe the inleakage, the narrower the water quality operation ranges of GICW, resulting in the more difficult the slight-alkalization conditioning of GICW. The temperature calibrations of the conductivity and the pH value of GICW show non-linear correlations with the amount of CO2 inleakage and the NaOH dosage. This study provides insights into the influence of CO2 inleakage on the slight-alkalization of GICW, which can serve as the theoretical basis for the actual slight-alkalization when CO2 inleakage occurs.

Optimization technology and kinetic studies of Acer truncatum seed oil saponification and crystallization separation of nervonic acid.

Acer truncatum seed oil (ATSO) contains abundant unsaturated fatty acids, with significant quantities of nervonic acid (NA,>5%), which was authenticated as a new food resource in China. For the sake of minimizing animal consumption and the importance of NA for human health, extraction of NA from plants has become a research hotspot. In the present study, three extraction factors were determined to significantly influence the saponification reaction based on single-factor experiments: NaOH dosage, reaction time, and reaction temperature. These three factors were used to further optimize the saponification process through the response surface methodology, and the highest yield of mixed fatty acids was 83.12%. Moreover, the activation energy (40.8228kJ/mol), the pre-exponential factor [2.568 × 106 m3 /(kmol·min)], and the kinetic equation [rA =kcA cB =2.568 × 106 ·exp(- cA cB ] of the ATSO saponification reaction were determined by combining the chemical reaction rate equation of the elementary reaction, the Arrhenius equation, and the NaOH concentration in the substrate. Finally, the mixed fatty acids of ATSO were crystallized by triple-stage low-temperature crystallization, and we achieved 25.05% purity for NA. This study provides a technological basis and strategy for specific fatty acid production from ASTO, as well as other vegetable oils important in the field of food and health supplement products. PRACTICAL APPLICATION: Nervonic acid (NA) is an essential component of neural cells and neural tissue, and it is vital for maintaining the normal work of nerve tissues in organisms and promotes neurodevelopment. NA has traditionally been mainly obtained from shark hunting, which is now restricted due to an international ban on shark fishing. The alternative way to produce NA cheaply and in large quantities is from plant sources. The techniques utilized in this study provide an effective method of NA separation from Acer truncatum seed oil for industrial production.

Response surface methodology (RSM) and artificial neural network (ANN) approach to optimize the photocatalytic conversion of rice straw hydrolysis residue (RSHR) into vanillin and 4-hydroxybenzaldehyde

Abstract Effective use of waste lignin is always a challenging task, technologies have been applied in the past to get value-added compounds from waste lignin. However, the existing technologies are not economical and efficient to produce the value-added chemicals. Alkali soluble lignin from rice straw hydrolysis residue (RSHR) is subjected to photocatalytic conversion into value-added compounds. Photocatalysis is one of the multifarious advanced oxidation processes (AOPs), carried out with TiO2 nanoparticles under a 125 W UV bulb. Gas chromatography mass spectroscopy (GCMS) confirmed the formation of vanillin and 4-hydroxybenzaldehyde. RSM and ANN techniques are adopted to optimize the process conditions for the maximization of the products. The response one (Y 1) vanillin (24.61 mg) and second response (Y 2) 4-hydroxybenzaldehyde (19.51 mg) is obtained at the optimal conditions as 7.0 h irradiation time, 2.763 g/L catalyst dose, 15 g/L lignin concentration, and 14.26 g/L NaOH dose for alkali treatment, suggested by face-centered central composite design (CCD). RSM and ANN models are statistically analyzed in terms of RMSE, R 2 and AAD. For RSM the R 2 0.9864 and 0.9787 while for ANN 0.9875 and 0.9847, closer to one warrant the good fitting of the models. Therefore, in terms of higher precision and predictive ability of both models the ANN model showed excellence for both responses as compared to the RSM model.

Ultrafine Ru nanoparticles confined in graphene-doped porous g-C3N4 for effectively boosting ammonia borane hydrolysis

Ammonia borane (AB) hydrolysis is a promising strategy for the development of hydrogen energy, and ultrafine metal nanoparticles (NPs) are attractive catalysts owing to their abundant active sites. In this work, porous graphitic carbon nitride (CN) are doped with reduced graphene oxide (rGO) and used as supports to evenly confine ultrafine Ru NPs with an adsorption-chemical reduction method. The results show that the different assembly methods and compositions affect the geometric and electronic characteristics of the composites, thus affecting the catalytic behavior in AB hydrolysis. Also, the effects of different Ru loadings and NaOH dosages are researched to improve the hydrolysis efficiency. Specifically, the optimal Ru/CN-rGO catalysts display exciting catalytic performance due to the proper porous structure, N, O co-doping and highly dispersed ultrafine Ru NPs. The corresponding turnover frequency (887.2 min−1) in the presence of NaOH (1.00 mol L−1) and the apparent activation energy (21.7 kJ mol−1) are superior to many previous results. The facile fabrication strategy and robust performance attest to a promising potential for Ru/CN-rGO in the fields of hydrogen energy.

Optimization of NaOH–Na2CO3 brine purification method: From laboratory experiments to industrial application

The NaOH–Na2CO3 brine purification method is an efficient method to prevent the scaling caused by scale-forming ions (Ca2+, Mg2+, and CO32–) in evaporation systems. Because of high CO32− residual concentration and large reagent consumption during brine purification, the thermodynamics of the deposition reaction of Ca2+ and Mg2+ was calculated using thermodynamic calculation software. The results show that the removal efficiencies of Ca2+ and Mg2+ can be improved by increasing the pH value. The experimental results show that the brine pH increased from 10.6 to 11.6 when the alkali solution and raw brine were added simultaneously, increasing the removal efficiency of Ca2+ and Mg2+. The residual total concentration of Ca2+ and Mg2+, CO32– concentration at the optimal dosage of 1.30 g/L Na2CO3 and 0.25 g/L NaOH is 13.9 mg/L and 135.0 mg/L, respectively. The deposition reaction efficiency of Na2CO3 and Ca2+ is improved, and the Na2CO3 consumption is reduced by increasing the NaOH dosage. Moreover, the HCO3– in raw brine can be transformed into CO32–, increasing the CO32– production and rate of CaCO3 deposition reaction. In the industrial production, the average removal efficiency of Ca2+ and Mg2+ is 98.5% and 99.6%, respectively; the residual CO32– concentration is reduced from 231.2 mg/L to 117.3 mg/L. The experiments and economic feasibility analysis results show that the optimized NaOH–Na2CO3 brine purification method not only effectively controls the concentration of Ca2+ and Mg2+ in the refined brine, but also reduces the residual CO32– concentration and reagent consumption, thus effectively preventing the scaling of evaporation system.

Enhanced bio-methane and bio-hydrogen production using banana plant waste and sewage sludge through anaerobic co-digestion

The yield of bio-methane and bio-hydrogen was enhanced by co-digesting banana plant waste (BPW) and sewage sludge (SS). In stage 1, acclimatisation of the inoculum SS is performed in a continuous stirred tank reactor (CSTR), and its various parameters are analyzed daily. In stage 2, six different BPW to SS ratios is optimized and incubated in manual methane potential test setup (MMPTS) for 40 days. The highest bio-methane and bio-hydrogen yields were observed from R4 (60% BPW and 40% SS). In stage 3, the best-achieved ratio of BPW and SS are then treated with different doses of NaOH as an alkaline pre-treatment. The highest bio-methane was achieved from dose 2 (0.75 mol NaOH) as 620.8 NmL/day. The study shows that the co-digestion of the BWP with SS has promising potential for enhanced bio-methane and bio-hydrogen production.

Lignin-first biorefinery of corn stalk via zirconium(IV) chloride/sodium hydroxide-catalyzed aerobic oxidation to produce phenolic carbonyls

Lignin-first biorefinery of corn stalk via ZrCl4/NaOH-catalyzed aerobic oxidation for phenolic carbonyls production was reported. Under the co-catalysis of ZrCl4 and NaOH, lignin in corn stalk was oxidized into phenolic aldehydes (p-hydroxybenzaldehyde, vanillin, and syringaldehyde), ketones (p-hydroxyacetophenone, acetovanillone, and acetosyringone), acids (p-hydroxybenzoic acid and vanillic acid), and other derivatives. Reaction conditions, including time, temperature, ZrCl4 dosage, NaOH dosage, MeCN/H2O ratio, and initial O2 pressure were comprehensively screened, and the optimal lignin-derived monomer yields of 13.2 wt% was obtained. Among these aromatic compounds, phenolic aldehydes were the main products, and the overall selectivity of phenolic carbonyls was as high as 93%. Cellulose-rich residues after lignin-first oxidation were further characterized by thermogravimetry and analytical pyrolysis with corn stalk as the control, proving the good fragmentation and dissolution of lignin streams. In general, ZrCl4/NaOH-catalyzed lignin-first oxidation provided a novel approach for lignin valorization, and achieved the highest reported phenolic carbonyls selectivity.

New insights into thermal-chemical pretreatment of organic fraction of municipal solid waste: Solubilization effects, recalcitrant formation, biogas yield and energy efficiency

This study investigates the effects of thermal and thermal-chemical pretreatments on organics solubilization, biogas yield, recalcitrant formation, and energy efficiency at variable temperatures and alkali dosage. The organic fraction of municipal solid waste (OFMSW) was subjected to thermal pretreatment (100-200℃, 1.6–15.8 bar pressure, and 30–120 min reaction time) alone and in conjugation with alkali dosage (1–7 g/L NaOH). The thermal reaction time of 30 min and alkali dosage of 3 g/L NaOH were optimised for variable temperatures, based on solubilisation of chemical oxygen demand (COD). The highest biogas yield increment of 43% (474 mL/gVSadded) and 87% (618 mL/gVSadded) was observed at 125℃ and 125℃+3g/L NaOH dose, respectively, over control (331 mL/gVSadded). Above 150℃, a significant decrease of biogas yield was observed due to recalcitrant formation, i.e., 5-HydroxyMethyl furfurals (5-HMF) and furfurals. In terms of biogas yield, energy recovery was 44% higher in thermal-chemically pretreated substrate than in the thermally pretreated feedstock. The kinetic analysis of different experimental and operational parameters was carried out using principal component analysis (PCA). The experimental values of biogas yield and hydrolysis coefficient have been predicted by the First order model (FO). The FO model justified the biogas production with an R2 value of ≥ 0.91.

Recovery of NaCl and Na2SO4 from high salinity brine by purification and evaporation

High salinity brine is the main resource for NaCl and Na2SO4. An industrial production test and application for Na2CO3-NaOH brine purification methods were carried out and operated for different periods. The total concentration of Ca2+ and Mg2+ was reduced from 513.49 mg/L to 12.01 mg/L at the optimal doses of NaOH = 0.25 g/L and Na2CO3 = 1.3 g/L. This extended the production periods from 60 to 70 days to 90–100 days during the industrial application. In addition, the degree of CO32− accumulation in the circulating feed brine was decreased, and the deposition of CaCO3 was inhibited. Narrow NaCl and Na2SO4 crystals with good anti-caking properties were prepared from high salinity brine by regulating the evaporation temperature and pressure in a multi-effect evaporation system. Moreover, the crystal growth direction of NaCl and Na2SO4 was observed by optical microscopy at different supersaturation degrees. The long-term, low-energy operation of brine purification and evaporative crystallization industrial production were realized, which are of great significance to the treatment of salinity wastewater in the chemical industry and metallurgy fields.

Feasibility of substituting old corrugated carton pulp with thermal alkali and enzyme pretreated semichemical mechanical rice straw pulp

In this study, we separately used a laboratory Hollander beater, a pilot scale 12″ single-disc refiner and an expanded trial with a commercial paper mold mill to investigate the feasibility of using thermal-alkali/enzyme pretreated rice straw semi-chemical mechanical pulp to substitute portions of old corrugated carton board (OCC) pulp in the paper industry. In the laboratory plan, sequential treatments of NaOH at a 5–10% dosage and enzymes at a 0.2–4% dosage were applied to rice straw, followed by beating using a Hollander beater for 1–2 h to complete the rice straw semi-chemical mechanical pulping process. When the NaOH dosage, enzyme dosage and refining time were 10%, 0.2% and 1 h, the best quality rice straw pulp was obtained. Along with the increase in NaOH dosage, the pulp freeness decreased significantly, and the pulp accepted rate increased. Enzymatic treatment enhanced rice straw quality only after NaOH dosage treatment, which then reacted with rice straw to increase the quality of pulp. In the expanded trial, the rice straw semi-chemical mechanical pulp was blended with OCC pulp (0%, 25%, 50%, 75% and 100%) to form handsheets. Along with an increase in rice straw proportions, the tensile index, burst index, and ring-crush index increased by 109–200%, 13–196%, and 124–187%, respectively. In an online commercial paper mold mill trial, blending rice straw pulp with OCC could successfully make paper-mold egg cartons, with both mill operation and product smoothness appearance being highly acceptable.

Magnesium recovery from desalination reject brine as pretreatment for membraneless electrolysis

Alkali-earth metals pose a significant challenge to water treatment technologies and electrochemical processes due to their propensity to precipitate as metal hydroxides, which can deposit on membranes and/or electrodes and reduce their efficiencies. Membraneless electrolyzers can partially overcome this issue because they lack membranes or diaphragms, however their electrodes are still susceptible to fouling. To overcome this issue, electrolyzers can be incorporated into a recirculating electrolyte scheme where magnesium is removed in the form of Mg(OH)2 before reaching the electrolyzer. Motivated by this system, the first part of this study focuses on the optimization of magnesium recovery from desalination brine by adding NaOH using response surface methodology. Brine salinity, NaOH dose, and temperature were optimized with complete magnesium removal set as the target response using central composite design. Results showed that 98.8% of magnesium can be removed at brine salinity, NaOH dose, and temperature of 73.5 g/L, 8.22 g/L and 45.5 °C, respectively. The second part of this study investigated the influence of Mg2+ concentration on the performance of a cathode within a membraneless electrolyzer. Experimental demonstrations show that Mg2+ concentrations below 5 mM can be used as a feed stream without any noticeable build-up of Mg(OH)2 deposits on the cathode surface over 3 h during electrolysis at 50 mA/cm2. Finally, an analysis is presented to predict how long a cathode can operate in Mg2+-containing electrolyte as a function of current density and superficial velocity of brine solution before the electrode reached its maximum tolerance of Mg(OH)2 deposits.

Bio-Methane Potential (BMP) of Cassava Pulp Waste and Effect of Alkaline Pre-Treatment

Cassava starch processing industry produces cassava pulp as a by-product or waste. In the well-known Duong Lieu village, this waste is released in surrounding environment without treatment causing serious environmental problems. The study aimed to (1) determine the Biomethane Potential (BMP) of the waste and to (2) find out if alkaline pre-treatment would improve it. Different cassava pulp samples were going through BMP test: untreated sample; pre-treated samples at different NaOH doses of 2, 6, 8 wt.% (dry weight-based) and pre-treated samples at different NaHCO3 doses of 2, 4, 6, 8 wt.% (dry weight based). BMP assays were conducted in 590mL bottles at 37oC for 40 days. As the result, BMP of the untreated waste was 281 NmLCH4/gVS and alkaline pretreatment increased BMP of the waste up to 479 mLCH4/gVS by treatment with NaOH 6 wt.% and 450 mLCH4/gVS by treatment with NaHCO3 6 wt.%. In addition, there was a significant reduction of lignin content of the substrate after alkaline pre-treatment. The results show that cassava pulp waste has moderate potential for biogas recovery. In addition, alkaline pre-treatment by either NaOH or NaHCO3 would significantly improve its BMP, possibly thanks to the reduction of lignin content.

Novel Technology for Vanadium and Chromium Extraction with KMnO4 in an Alkaline Medium.

This paper focused on the oxidation–alkaline extraction process of vanadium–chromium–reducing residue. The affected parameters including reaction temperature, KMnO4 dosage, reaction time, NaOH dosage, and liquid-to-solid ratio on the extraction process were investigated. The E–pH diagram and the thermodynamic analysis indicated that KMnO4 was suitable for the oxidation of low-valence vanadium and chromium. Vanadium (97.24%) and chromium (56.20%) were extracted under the following optimal reaction conditions: reaction temperature of 90 °C, reaction time of 90 min, dosage of KMnO4 at m(KMnO4)/m(residue) = 0.40, dosage of NaOH at m(NaOH)/m(residue) = 0.30, and liquid-to-solid ratio at 5:1 mL/g. The extraction process of vanadium was controlled by the reactant through the solid product layer and the extraction kinetics behavior fitted well with the shrink core model with an Ea of 15.37 kJ/mol. At the same time, the surface chemical reaction was the controlling step for chromium extraction, which was difficult with an Ea of 39.78 kJ/mol.