Key factors governing alkaline pretreatment of waste activated sludge

Alkaline pretreatment is an effective technology to disintegrate sewage sludge, where alkali dosage and sludge concentration are two important factors. p H value or alkali concentration is usually adjusted in order to determine a proper dosage of alkali. Our work has found that this is not a good strategy. A new parameter, the ratio of alkali to sludge(Ra/s), is more sensitive in controlling the alkali dosage. The sludge concentration Csand retention time t are two other important factors to consider. The validity of these arguments is confirmed with modeling and experiments. The individual effect of Ra/s, Csand t was studied separately. Then the combined effect of these three factors was evaluated. The sludge disintegration degree of 44.7% was achieved with the optimized factors. Furthermore, an alkaline-microwave combined pretreatment process was carried out under these optimized conditions. A high disintegration degree of 62.3% was achieved while the energy consumption of microwave was much lower than previously reported.

Enhanced anaerobic digestion and sludge dewaterability by alkaline pretreatment and its mechanism

To investigate the influences of alkaline pretreatment on anaerobic digestion （AD） and sludge dewaterability after AD, waste activated sludge was adjusted to different pH values （8, 9, 10, 1 1, 12） and placed at ambient temperature for 24 hr. The samples were then adjusted to the initial pH and subjected to 25 days of AD. The results showed that, when compared with the control （pH 6.8）, total suspended solids （TSS） and volatile suspended solids （VSS） reduction following pretreatment at pH 9-11 increased by 10.7%-13.1% and 6.5%- 12.8%, respectively, while biogas production improved by 7.2%-15.4%. Additionally, significant enhancement of sludge dewaterability after AD occurred when pretreatment at pH 8-9 was conducted. The proteins and carbohydrates transferred from the pellet and tightly bound extracellular polymeric substances （TB-EPS） fractions to the slime and loosely bound EPS （LB-EPS） fractions after pretreatment and during the AD process, and the concentrations of proteins and carbohydrates in the slime fraction had a good linear relationship with the normalized capillary suction time （CST）. During the AD process, the normalized CST was positively correlated with the organic materials in the loosely bound fraction of the sludge matrix （R2/〉 0.700, p 〈 0.01）, while it was negatively correlated with the organic materials in the tightly bound fraction （R2≥ 0.702, p 〈 0.01）. These results suggest that alkaline pretreatment could break the EPS matrix and release inner organic materials, thus influencing the efficiency of the AD process and dewaterability after AD.

Enhancement of thermophilic anaerobic digestion of thickened waste activated sludge by combined microwave and alkaline pretreatment

Pretreatment of thickened waste activated sludge （TWAS） by combined microwave and alkaline pretreatment （MAP） was studied to improve thermophilic anaerobic digestion efficiency. Uniform design was applied to determine the combination of target temperature （110-210°C）, microwave holding time （1-51 min）, and NaOH dose （0-2.5 g NaOH/g suspended solids （SS）） in terms of their effect on volatile suspended solids （VSS） solubilization. Maximum solubilization ratio （85.1%） of VSS was observed at 210°C with 0.2 g-NaOH/g-SS and 35 min holding time. The effects of 12 different pretreatment methods were investigated in 28 thermophilic batch reactors by monitoring cumulative methane production （CMP）. Improvements in methane production in the TWAS were directly related to the microwave and alkaline pretreatment of the sludge. The highest CMP was a 27% improvement over the control. In spite of the increase in soluble chemical oxygen demand concentration and the decrease in dewaterability of digested sludge, a semi-continuous thermophilic reactor fed with pretreated TWAS without neutralization （at 170~C with 1 min holding time and 0.05 g NaOH/g SS） was stable and functioned well, with volatile solid （VS） and total chemical oxygen demand （TCOD） reductions of 28% and 18%, respectively, which were higher than those of the control system. Additionally, methane yields （L@STP/g-CODaded, at standard temperature and pressure （STP） conditions of 0°C and 101.325 kPa） and （L@STP/g VSadad） increased by 17% and 13%, respectively, comoared to the control reactor.

Performance of alkaline pretreatment on pathogens inactivation and sludge solubilization

Inactivation of pathogen indicators(i.e.,faecal coliforms,Salmonella spp.,faecal streptococcus,and helminth eggs)were investigated during alkaline pretreatment(pH=10 and 12)in this study.The performance of alkaline pretreatment on the inactivation pathogens,kinetic of pathogens inactivation and sludge solubilization was evaluated.Results of alkaline pretreatment showed that the complete inactivation periods of pathogens time were 1.5 d,1.5 d,2 d,2.5 d,3 d,3 d and 3 d for faecal sludge total solids(TS)of 1%,2%,4%,6%,8%,10%and 12%,respectively.The kinetics of pathogen inactivation can be predicted better by Weibull than the first-order model.Meanwhile,the relationship between alkaline pretreatment time and the TS content of the sludge agrees with the exponential equation(y=1.3543e10.002x,1%≤x≤8%)and logarithmic equation(y=3,8%≤x≤12%).Furthermore,alkaline pretreatment can improve sludge solubilization and has a more significant effect on protein solubilization than on soluble chemical oxygen demand(SCOD).

Biotreatment of Wastewater from Soda-pretreatment Process of Corn Stover Using White-rot Fungus Z-6

Alkaline pretreatment of straw materials prior to enzyme hydrolysis is a key step for bioconversion of lignocellulose to bioethanol and chemicals.Wastewater from the alkaline pretreatment process must be treated before discharge to minimize its environmental impact.In this study,biotreatment of the wastewater from soda-pretreatment process of corn stover was investigated using fungus Z-6,and some indexes such as color,chemical oxygen demand(COD),and lignin content of wastewater before and after biotreatment were determined to assess the effect of the biotreatment.Results showed that fungus treatment could remove color up to approximately 72%after 2 d,and decrease COD and lignin content by about 63%and 60%,respectively after 3 d.The wastewater was fractionated using dynamic ultrafiltration method,and the changes in lignin contents of the effluent fractions with different molecular weights before and after biotreatment were analyzed.Some compounds produced by the fungus during treatment were identified using gas chromatography-mass(GC-MS)spectrometer,which revealed that depolymerization of lignin occurred during the biotreatment process.

Quantitative Extraction of p-Coumaric Acid and Ferulic Acid in Different Gramineous Materials and Structural Changes of Residual Alkali Lignin

Ferulic acid(FA)and p-coumaric acid(pCA)in bagasse,wheat straw,corn straw,and corncob were extracted by alkaline hydrolysis and characterized by gas chromatography(GC)and gas chromatography-mass spectrometry(GC-MS).It was found that the FA and most of the pCA in gramineous biomass could be dissociated and released after being treated with 1 M NaOH at 100℃for 4 h.The yields of pCA/FA in bagasse,wheat straw,corn straw,and corncob determined by GC-FID are 39.8/11.5,13.7/11.0,28.0/11.0,and 35.1/14.5 mg/g,respectively.The raw materials and the treated solid residues were characterized by gel-state 2D Heteronuclear Single Quantum Coherence Nuclear Magnetic Resonance(2D HSQC NMR).It was found that only a small amount of lignin was detected in the residue after alkali treatment,indicating that the alkali treatment conditions can effectively cleave the FA and pCA.Additionally,the lignin in the alkali solution was recovered and characterized by 2D HSQC NMR.The FA was not able to be detected by NMR,whereas a small amount of pCA remained in the alkali lignin.This study reveals the structural change of residual lignins during the quantitative isolation of FA and pCA,which is essential for the selective isolation of pCA/FA and valorization of residual alkali lignin.

Effect of various aromatic compounds with different functional groups on enzymatic hydrolysis of microcrystalline cellulose and alkaline pretreated wheat straw

Low molecular aromatic compounds are detrimental to the enzymatic hydrolysis of lignocellu-lose.However,the specific role of their functional groups remains unclear.Here,a series of nine aromatic compounds as additives were tested to understand their effect on the hydrolysis yield of microcrystalline cellulose(MCC)and alkaline pretreated wheat straw.Based on the results,the inhibition of aldehyde groups on MCC was greater than that of carboxyl groups,whereas for the alkaline pretreated wheat straw case,the inhibitory effect of aldehyde groups was lower than that of carboxyl groups.Increased methoxyl groups of aromatic compounds reduced the inhibitory ef-fect on enzymatic hydrolysis of both substrates.Stronger inhibition of aromatic compounds on MCC hydrolysis was detected in comparison with the alkaline pretreated wheat straw,indicating that the substrate lignin can offset the inhibition to a certain extent.Among all aromatic com-pounds,syringaldehyde with one aldehyde group and two methoxyl groups improved the glucan conversion of the alkaline pretreated wheat straw.

Characterization of Lignins Isolated from Alkali Treated Prehydrolysate of Corn Stover

Lignins were isolated and purified from alkali treated prehydrolysate of corn stover. The paper presents the structural features of lignins in a series purification processes. Fourier transform infrared spectroscopy, ultraviolet-vis spectroscopy and proton nuclear magnetic resonance spectroscopy were used to analyze the chemical structure. Thermogravimetric analysis was applied to follow the thermal degradation, and wet chemical method was used to determine the sugar content. The results showed that the crude lignin from the prehydrolysate of corn stover was a heterogeneous material of syringyl, guaiacyl and p-hydroxyphenyl units, containing associated polysaccharides, lipids, and melted salts. Some of the crude lignin was chemically linked to hemicelluloses （mainly xylan）. The lipids in crude lignin were probably composed of saturated and/or unsaturated long carbon chains, fatty acids, tdterpenols, waxes, and derivatives of aromatic. The sugar content of purified lignin was less than 2.11%, mainly composed of guaiacyl units. DTGmax of purified lignin was 359 ℃. The majority of the hydroxyl groups were phenolic hydroxyl groups. The main type of linkages in purified lignin was β-O-4. Other types of linkages included β-5, β-β and α-O-4.

Characterization of an iron oxy/hydroxide(gossan type) bearing refractory gold and silver ore by diagnostic leaching

A detailed characterization of an iron oxy/hydroxide(gossan type) bearing refractory gold/silver ore was performed with a new diagnostic approach for the development of a pretreatment process prior to cyanide leaching. Gold was observed to be present as native and electrum(6-24 μm in size) and associated with limonite, goethite and lepidocrocite within calcite and quartz matrix. Mineral liberation analysis(MLA) showed that electrum is found as free grains and in association with beudantite, limonite/goethite and quartz. Silver was mainly present as acanthite(Ag2S) and electrum and as inclusions within beudantite phase in the ore. The cyanide leaching tests showed that the extractions of gold and silver from the ore(d80: 50 μm) were limited to 76% and 23%, respectively, over a leaching period of 24 h. Diagnostic leaching tests coupled with the detailed mineralogical analysis of the ore suggest that the refractory gold and silver are mainly associated within iron oxide mineral phases such as limonite/goethite and jarosite-beudantite, which can be decomposed in alkaline solutions. Based on these characterizations, alkaline pretreatment of ore in potassium hydroxide solution was performed prior to cyanidation, which improved significantly the extraction of silver and gold up to 87% Ag and 90% Au. These findings suggest that alkaline leaching can be used as a new diagnostic approach to characterize the refractoriness of iron oxy/hydroxide bearing gold/silver ore and as a pretreatment method to overcome the refractoriness.

Producing durable pellets from barley straw subjected to radio frequency-alkaline and steam explosion pretreatments

Pelletization,a form of densification,increases bulk density and improves the convenience and accessibility of biomass feedstock due to the uniform shape and size.Pretreatment of biomass enhances the breakdown and accessibility of the cross-linking lignin,which acts as a binding agent.In this study,pelletization of radio frequency-alkaline and steam explosion pretreated barley straw was performed.Three levels of temperature(70oC,80oC,and 90oC),five levels of the mass ratio of biomass to NaOH solution(1:4,1:5,1:6,1:7,and 1:8),one hour equilibration time,biomass screen size of 1.6 mm,1%NaOH concentration,and 20 min residence time in the radio frequency chamber were used for the radio frequency-alkaline pretreatment.Three levels of steam temperature(140oC,160oC,and 180oC),three levels of moisture content of 8%,30%,and 50%(mass fraction of total mass),and 5 min and 10 min exposure to steam were tested for the steam explosion pretreatment.The effects of both pretreatment methods were evaluated by pelletizing the pretreated and non-pretreated barley straw samples in a single pelleting unit.The pellet density,tensile strength,durability,dimensional stability,and color of the pellets were determined.Radio frequency-alkaline pretreatment with the use of 1%NaOH solution and a ratio of biomass:NaOH solution of 1:8 has significant effect(P<0.05)on the breakdown of the lignified matrix,resulting in pellets with superior physical characteristics.The steam exploded samples pretreated at higher temperatures(180ºC)and retention time of 10 min resulted into pellets with good physical qualities.

A METHOD TO IMPROVE DIMENSIONAL STABILITY OF PF PARTICLEBOARD

A method of alkaline pretreatment of particles was designed to produce three types of chips. The pretreatmentet of particles in 1% water solution of NaOH for 30 minutes offered a possibility of producing PF bonded particleboards with minimal irrecoverable swell and a reduction in thickness swelling. The method used in this work could be used to produce more stable PF particeboard.

Saccharification of Sugarcane Bagasse Using an Enzymatic Extract Produced by Aspergillus fumigatus

This study investigates the efficiency of a crude enzymatic extract produced by Aspergillus fumigatus SCBM6 by solid state fermentation(SSF)in the hydrolysis of alkali pretreated sugarcane bagasse(PTB).After SSF using in natura sugarcane bagasse(SCB),the enzymatic extract presented 21.33 U.g^-1 of β-glucosidase and 544.46 U.g^-1 of xylanase.The alkaline pretreatment with sodium hydroxide 2%NaOH(w/v)removed 43% of the lignin from PTB and the cellulosic fraction increased to 75%.The hydrolysis was optimized as a function of time,temperature,and concentration of PTB.After hydrolysis,the maximum yield(30.05%)of total released reducing sugars(TRS)was obtained under the following conditions:24 h,55℃,2% of PTB and 3 U.g^-1 of β-glucosidase(CBU).Furthermore,an approximate TRS value(26.4%)was also obtained after saccharification carried out during 6 h,55℃,4% of PTB and 1 CBU.These results indicate that hydrolysis can be performed in a short incubation period and with low enzymatic load for reasonable TRS release.

A Comparative Study on the Utilization of Corn Pericarp and Peanut Hull in the Production of Ethanol and the Impact on Food Economics

Corn pericarp and peanut hull (lignocellulosic materials) which are food industry by-products were used as substrates in this study. Alkaline hydrogen peroxide (H2O2) pretreatments at 0%, 2.5% and 5% were used for the removal of lignin. Simultaneous Saccharification and Fermentation (SSF) and Separate Hydrolysis and Fermentation (SHF) were conducted using Aspergillus niger (strain 201201) and Saccharomyces cerevisiae (strain 26603). Aspergillus niger was added on day 1 to all samples with inoculation treatments of S. cerevisiae at one-day intervals (A = Day 1, B = Day 2, C = Day 3 and D = Day 4). Pretreatment with 2.5% H2O2 was more beneficial in the removal of lignin for both substrates. Corn pericarp yielded an ethanol concentration of 22.2 g/L in C and 21.78 g/L in D of 2.5% H2O2 pretreatment. Peanut hull with 2.5% H2O2 pretreatment in D yielded a higher concentration at 10.38 g/L compared to other inoculation treatments. The highest ethanol yielded on a percentage basis for corn pericarp was 45.04% in C of 2.5% H2O2 pretreatment and 24.6% in D of 2.5% H2O2 pretreatment for peanut hull.

Improving biomethane yield by strengthening acidification of maize stover in two-phase anaerobic digestion

In this study,the acidification and two-phase anaerobic digestion(AD)were conducted in batch and continuous stirred tank reactors,respectively,to determine the effect of acidification on methane production in AD.The results showed that two-phase AD achieved an observable enhancement in the methane production under optimal acidification conditions(organic loading rate of 60 g TS/L,the ratio of raw material to inoculum(based on dry weight)of 2:1,the temperature of 45℃,urea concentration of 4%,and time of 6 d).Under these conditions,the daily biogas and biomethane productions were 0.48 L/g TS and 0.30 L/g TS,respectively,which were 26.32%and 57.89%higher than those of the untreated group,respectively.The ammonia nitrogen(AN),alkalinity,and pH value of the methanogenic phase of C4 continued to increase up to 956 mg/L,5680 mg/L,and 7.41,respectively,after 60 d,which might have destroyed the stability of the system.Therefore,for the purpose of reusing the nitrogen source,reducing AN,and maintaining the stability of the reaction system,another set of acidification and two-phase AD with water pretreatment using the discharge of the methanogenic phase of C4 as the inoculum was subsequently conducted.The results showed that the daily biogas productions of single-phase and two-phase AD were 5.26%and 15.79%higher than that of the untreated group,respectively;similarly,their daily methane yields were 10.42%and 21.05%higher than that of the untreated group.

ZnCl2 Enhanced Acid Hydrolysis of Pretreated Corncob for Glucose Production:Kinetics,Thermodynamics and Optimization Analysis

The biomass of agricultural wastes as a source of fermentable sugars for biofuels production will address the food security and environmental preservation issues.These wastes are rich in lignocellulosic materials which can be hydrolyzed into fermentable sugars.However,low sugar yield and high energy consumption are some of the challenges faced in the process of hydrolization.This study investigated the low-cost corncob substrate for glucose production by dilute sulphuric acid hydrolysis in the presence of ZnCl_(2) at temperatures below 100℃after pretreatment with 10%NaOH.Time dependent hydrolysis data were analyzed by Saeman model,thermodynamic parameters were obtained using Erying and Arrhenius equations while Box-Behnken model(Design Expert 6.0 version)was used for experimental design.As the substrate concentration increased from 50 mg/L to 150 mg/L,glucose yield increased from 10.4 mg/g to 14.6 mg/g for pretreated corncob while an increase from 3.4 mg/g to 8.6 mg/g was noted for untreated corncob.The hydrolysis rate constant was two orders of magnitude higher than the degradation rate constant.Thermodynamic parameters revealed endothermic process with positive Gibb’s free energy of hydrolysis having average values of 84.76 kJ/mol and 79.87 kJ/mol for pretreated and untreated samples respectively.The optimum yield from the model was found to be 177.44 mg/g with 3.94%H_(2)SO_(4) and 0.43 mol/L ZnCl_(2) for 200 g/L compared with optimum yield of 46.37 mg/g obtainable without ZnCl_(2).The results of this study showed that the alkaline pretreatment of corncob increased the accessibility of cellulose from the solid fraction and increase glucose production.

Delignification of disposable wooden chopsticks waste for fermentative hydrogen production by an enriched culture from a hot spring

Hydrogen （H2） production from lignocellulosic materials may be enhanced by removing lignin and increasing the porosity of the material prior to enzymatic hydrolysis. Alkaline pretreatment conditions, used to delignify disposable wooden chopsticks （DWC） waste, were investigated. The effects of NaOH concentration, temperature and retention time were examined and it was found that retention time had no effect on lignin removal or carbohydrate released in enzymatic hydrolysate. The highest percentage of lignin removal （41%） was obtained with 2% NaOH at 100℃, correlated with the highest carbohydrate released （67 mg/gpretreated DWC） in the hydrolysate. An enriched culture from a hot spring was used as inoculum for fermentative H2 production, and its optimum initial pH and temperature were determined to be 7.0 and 50℃, respectively. Furthermore, enzymatic hydrolysate from pretreated DWC was successfully demonstrated as a substrate for fermentative H2 production by the enriched culture. The maximum H2 yield and production rate were achieved at 195 mL H2/g total sugarsconsumed and 1 16 mL Hz/（L.day）, respectively.