uo Jiang

Volatile fatty acids production from food waste: effects of pH, temperature, and organic loading rate.

The effects of pH, temperature, and organic loading rate (OLR) on the acidogenesis of food waste have been determined. The present study investigated their effects on soluble chemical oxygen demand (SCOD), volatile fatty acids (VFAs), volatile solids (VS), and ammonia nitrogen (NH4(+)-N). Both the concentration and yield of VFAs were highest at pH 6.0, acetate and butyrate accounted for 77% of total VFAs. VFAs concentration and the VFA/SCOD ratio were highest, and VS levels were lowest, at 45 °C, but the differences compared to the values at 35 °C were slight. The concentrations of VFAs, SCOD, and NH4(+)-N increased as OLR increased, whereas the yield of VFAs decreased from 0.504 at 5 g/Ld to 0.306 at 16 g/Ld. Acetate and butyrate accounted for 60% of total VFAs. The percentage of acetate and valerate increased as OLR increased, whereas a high OLR produced a lower percentage of propionate and butyrate.

Polyethyleneimine–nano silica composites: a low-cost and promising adsorbent for CO2 capture

Adsorbents for CO2 captured with nano silica as support were synthesized by impregnating polyethyleneimine (PEI) into nano silica. For impregnation of PEI into nano silica, the 2–40 nm pore of silica support plays an important role in the synthesis process of adsorbents. The PEI loading content, adsorption temperature and CO2 partial pressure influenced CO2 adsorption capacity and PEI utilization efficiency. At 105 °C and under 1 atm CO2 partial pressure, the adsorbent with 60% PEI loading content obtained a CO2 adsorption capacity of 186 mg g−1 adsorbent and a PEI utilization efficiency of 304 mg g−1 PEI. The CO2 cycling adsorption–desorption was tested under the condition as follows: adsorption at 90 or 105 °C under pure CO2 and desorption at 120 °C under pure N2 showed relatively good adsorption–desorption stability, and no evident deactivation of amines was observed under this condition. However, for adsorption at 90 or 105 °C under pure CO2 and desorption at 135 or 150 °C under pure CO2, evident deactivation of amines occurred, and the formation of linear or cyclic urea is one reason which led to the decrease of CO2 adsorption capacity.

A novel calcium looping absorbent incorporated with polymorphic spacers for hydrogen production and CO2 capture

High temperature looping cycles can be used to produce hydrogen or capture CO2 from power stations, though sintering of absorbents is frequently a problem, reducing reactivity. In this work we develop materials, in which the crystal structure and volume of polymorphic materials change with temperature, as active spacers to reduce sintering.

Effects of ultrasound pre-treatment on the amount of dissolved organic matter extracted from food waste

This paper describes a series of studies on the effects of food waste disintegration using an ultrasonic generator and the production of volatile fatty acids (VFAs) by anaerobic hydrolysis. The results suggest that ultrasound treatment can significantly increase COD [chemical oxygen demand], proteins and reducing sugars, but decrease that of lipids in food waste supernatant. Ultrasound pre-treatment boosted the production of VFAs dramatically during the fermentation of food waste. At an ultrasonic energy density of 480W/L, we treated two kinds of food waste (total solids (TS): 40 and 100g/L, respectively) with ultrasound for 15min. The amount of COD dissolved from the waste increased by 1.6-1.7-fold, proteins increased by 3.8-4.3-fold, and reducing sugars increased by 4.4-3.6-fold, whereas the lipid content decreased from 2 to 0.1g/L. Additionally, a higher VFA yield was observed following ultrasonic pre-treatment.

A novel low temperature vapor phase hydrolysis method for the production of nano-structured silica materials using silicon tetrachloride

Here we report for the first time, a novel method of low temperature vapor phase hydrolysis for the production of nano-structured silica particles. Silica nanoparticles were obtained by the hydrolysis of silicon tetrachloride vapor with water vapor at a low temperature range (150–250 °C). The effects of reaction temperature and residence time on the specific surface area and size distribution were determined to obtain optimal synthesis conditions. Silica nanoparticles with a specific surface area of 418 m2 g−1 and an average size of 141.7 nm were obtained at a temperature of 150 °C and with a residence time of 5 s. The particle morphology, phase composition, chemical composition, thermal analysis, and chemical functional groups present were determined by TEM, XRD, XRF, TGA, and IR methods, respectively. Results indicated that silica synthesized by low temperature vapor phase hydrolysis method is an amorphous mesoporous material, with an approximately spherical shape, a mass friction demission of 2.29, and a high hydroxyl density of 13.03 nm−2. This method provides a simple and environmentally benign way for the mass production of silica nanoparticles, as well as a quick method for the preparation of functional silica materials.

Ultrasound coupled with Fenton oxidation pre-treatment of sludge to release organic carbon, nitrogen and phosphorus ☆

We focused on the effects of ultrasound and Fenton reagent in ultrasonic coupling Fenton oxidation (U + F) pre-treatment processes on the disintegration of wastewater treatment plant sludge. The results demonstrated that U + F treatment could significantly increase soluble COD, TOC, total N, proteins, total P and PO4(3-) concentrations in sludge supernatant. This method was more effective than ultrasonic (U) or Fenton oxidation (F) treatment alone. U + F treatment increased the soluble COD by 2.1- and 1.4-fold compared with U and F alone, respectively. U + F treatment increased the total N and P by 1.7- and 2.2-fold, respectively, compared with F alone. After U + F treatment, sludge showed a considerably finer particle size and looser microstructure based on scanning electron microscopy, and the highest OH signal intensity increased from 568.7 by F treatment to 1106.3 using electron spin resonance. This demonstrated that U+F treatment induces disintegration of sludge and release of organic carbon, nitrogen and phosphorus better.

Synthesis of Highly Efficient CaO-Based, Self-Stabilizing CO2 Sorbents via Structure-Reforming of Steel Slag

Capturing anthropogenic CO2 in a cost-effective and highly efficient manner is one of the most challenging issues faced by scientists today. Herein, we report a novel structure-reforming approach to convert steel slag, a cheap, abundant, and nontoxic calcium-rich industrial waste, as the only feedstock into superior CaO-based, self-stabilizing CO2 sorbents. The CO2 capture capacity of all the steel slag-derived sorbents was improved more than 10-fold compared to the raw slag, with the maximum uptake of CO2 achieving at 0.50 gCO2 gsorbent(-1). Additionally, the initial steel slag-derived sorbent could retain 0.25 gCO2 gsorbent(-1), that is, a decay rate of only 12% over 30 carbonation-calcination cycles, the excellent self-stabilizing property allowed it to significantly outperform conventional CaO, and match with most of the existing synthetic CaO-based sorbents. A synergistic effect that facilitated CO2 capture by CaO-based sorbents was clearly recognized when Mg and Al, the most common elements in steel slag, coexisted with CaO in the forms of MgO and Al2O3, respectively. During the calcium looping process, MgO served as a well spacer to increase the porosity of sorbents together with Al2O3 serving as a durable stabilizer to coresist the sintering of CaCO3 grains at high temperatures.

Pine cone shell-based activated carbon used for CO2 adsorption

In this study, pine cone shell-based activated carbons were used to adsorb CO2. After a carbonization process at 500 °C, the resulting preliminary activated carbons (Non-PAC) were activated under different conditions. The results indicated good CO2 adsorption performance of pine cone shell-based activated carbons. For example, after activation at 650 °C and with a KOH:Non-PAC ratio of 2, the activated carbon (named as PAC-650/2) achieved a high CO2 adsorption capacity of 7.63 mmol g−1 and 2.35 mmol g−1 at 0 °C under 1 and 0.15 bar pressure, respectively. To determine the potential correlation between the amount of CO2 adsorbed and micropore distribution, linear correlations between cumulative pore volume over different ranges and amount of CO2 adsorbed were analyzed. Results showed that pores <0.70 nm played an important role in the CO2 adsorption process at 0 °C and 0.1 bar, and in contrast to previous research, pore volumes <0.80 nm or 0.82 nm did not show good linear correlation with the amount of CO2 adsorbed at 0 °C and 1 bar, and we inferred that this was most likely due to the unique pore structure of pine cone shell-based activated carbons. The highest Brunauer–Emmett–Teller (BET) surface area of 3931 m2 g−1 was obtained after activation at 800 °C and with a KOH:Non-PAC ratio of 2, but the highest BET surface area did not result in the highest CO2 adsorption capacity. This is mainly due to the BET surface area having regions unavailable for CO2 adsorption. X-ray photoelectron spectroscopy (XPS) analysis results for all activated carbons indicated a higher stability of pyridonic-N than pyridinic-N. Furthermore, in order to better understand the interaction between CO2 and pine cone shell-based activated carbons, we analyzed the isosteric heat of adsorption (Qst). Qst was higher than 22 kJ mol−1 for all activated carbons, and the highest initial isosteric heat of adsorption of 32.9 kJ mol−1 was obtained for the carbon activated at 500 °C and a KOH:Non-PAC ratio of 1. The optimal Qst (Qst,opt) under the conditions of a vacuum swing adsorption (at 25 °C, adsorption under 1 bar and desorption under 0.1 bar) process was 30 kJ mol−1.

A green and scalable synthesis of highly stable Ca-based sorbents for CO2 capture

High-temperature sorption of CO2via calcium looping is a promising technology for the implementation of carbon capture and storage (CCS). However, the rapid deactivation of CaO sorbents due to sintering is currently the major drawback of this technology. We, for the first time, report an economical and environmentally benign strategy to reduce sintering by adding fly ash, a waste stream of coal-fired plants, into Ca-based sorbents through a simple dry process. The as-synthesized sorbents were tested using a TGA and showed an extremely high stability under the most severe multi-cycle conditions (calcined at 920 °C in pure CO2). Upon 100 cycles, its CO2 capture capacity was 0.20 g(CO2) g(sorbent)−1, and the average deactivation rate was only 0.18% per cycle. The most possible stabilization mechanism was discussed on the basis of a range of characterizations including N2 physisorption, SEM, TEM (coupled with EDX mapping) and XRD; it was concluded that stable and refractory gehlenite (Ca2Al2SiO7) particles were formed and evenly dispersed around CaO crystal grains during calcination at 950 °C, leading to sintering resistance. This strategy achieved superior enhancement in the cyclic stability of Ca-based sorbents as well as the reuse of industrial solid waste, and is thus a green technology for scaled-up CO2 capture.

Biological nitrate removal using a food waste-derived carbon source in synthetic wastewater and real sewage.

The production of volatile fatty acids (VFAs) from food waste to improve biological nutrient removal has drawn much attention. In this study, acidogenic liquid from food waste was used as an alternative carbon source for synthetic wastewater treatment. C/N ratios of 5 and 6 were suitable for denitrification, and the change in acidogenic liquid composition had no negative effect on denitrification. The denitrification rates using optimal carbon-to-nitrate ratios of acidogenic liquid were more than 25xa0mg NO3-N/(gVSS·h). At the same time, acidogenic liquid was used to improve nutrient removal from summer and winter sewage. C/N ratios of 5 and 6 were acceptable for summer sewage treatment. Total nitrogen in the final effluent was less than 7xa0mg/L. Two additional hours were required for winter sewage treatment, and the C/N ratio had to be >6.