The mechanism of supplementary cementitious materials enhancing the water resistance of magnesium oxychloride cement (MOC): A comparison between pulverized fuel ash and incinerated sewage sludge ash

Magnesium oxychloride cement (MOC) pastes incorporating supplementary cementitious materials (SCMs) including pulverized fuel ash (PFA) and incinerated sewage sludge ash (ISSA) were examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) with energy dispersive X-ray spectrometry (EDX). The result showed that the mechanism of PFA and ISSA in improving the water resistance of MOC paste is similar, even though the molar ratios of the hydration product in the ISSA-incorporated paste and the PFA-incorporated paste were different. The active phases in PFA or ISSA could react with MgO and produce an amorphous phase (amorphous magnesium aluminosilicate gel), which was interspersed with Phase 5 and changed the morphology of Phase 5 to fibroid or lath-like phases. These fibroid or lath-like phases interlocked with each other and also connected with the amorphous phase in the matrix to form a stable compact structure. Therefore, the water resistance of MOC was improved. The ISSA-blended MOC paste had higher water resistance compared to the PFA-blended MOC, which may be due to the different chemical composition of amorphous phase and the dissolved phosphorus from ISSA

Use of Mg/Ca modified biochars to take up phosphorus from acid-extract of incinerated sewage sludge ash (ISSA) for fertilizer application

Recovery of phosphorus (P) from incinerated sewage sludge ash (ISSA) by biochar is an attractive solution for mitigating the P scarcity and transferring waste to resources. This work used Mg/Ca-modified biochars to take up P from the acid-extract from ISSA at low pH (<2), which simplified the previous P recycling process. The hypothesis is to produce a P-enriched post-sorption biochar that can be directly applied as a P fertilizer. Wastes of peanut shell and sugarcane bagasse were used to synthesize Mg/Ca-modified biochars at pyrolysis temperatures of 450 °C, 700 °C and 850 °C. Preliminary results indicated Mg-modified sugarcane bagasse biochar pyrolysed at 700 °C produced optimal P-absorption. This biochar was positively charged and had a high specific surface area (1440 m2/g), consistent with a layered porous structure. The optimal biochar showed rapid adsorption of P which could be described by the pseudo-second-order model. Successful adsorption of P from the acid-extract by the optimal biochar was mainly due to chemical precipitation and its adsorption capacity is 129.79 mg P/g biochar

Sustainable management and recycling of food waste anaerobic digestate : a review

202203 bcfcNot applicableOthersHong Kong International Airport Environmental Fund (Phase 2); Hong Kong Environment and Conservation FundPublished24 month

Life-cycle assessment on food waste valorisation to value-added products

202308 bcchAccepted ManuscriptOthersHong Kong International Airport Environmental Fund; Environment and Conservation FundPublishe

Functionalized zeolite-solvent catalytic systems for microwave-assisted dehydration of fructose to 5-hydroxymethylfurfural

This study investigates the structure-performance relationships in different zeolite-solvent systems that are suitable for microwave-assisted dehydration of food waste-derived fructose to 5-hydroxymethylfurfural (HMF). Different types of zeolites (MFI, BEA, and Y) were examined as acid catalysts. Water was first tested as the greenest solvent (baseline), followed by dimethyl sulfoxide (DMSO), acetone, -valerolactone (GVL), and propylene carbonate (PC)/water (1:1 v/v) binary solvent systems. The results showed that the HMF yield was independent of particle size of MFI zeolite in water. The secondary porosities improved the HMF yield, while byproducts formation (via rehydration or polymerization) was also increased due to the enlarged channels in zeolites. All tested zeolites showed higher fructose conversion, HMF yield, and HMF selectivity in organic-water solvent systems than in water. The synergistic effects of the substrates, catalysts, and solvent-product interactions in the hydrophobic Y zeolite/DMSO system yielded the highest fructose conversion (72.4%) and HMF yield (49.2%). This study advances our understanding of green solvents and functionalized zeolites for microwave-assisted biomass conversion in sustainable biorefinery

Sustainable production of high-value gluconic acid and glucaric acid through oxidation of biomass-derived glucose : a critical review

202203 bcfcAccepted ManuscriptRGCOthersHong Kong International Airport Environmental Fund [Phase 2] Publishe

Recovery of phosphorus from incinerated sewage sludge ash by combined two-step extraction and selective precipitation

The recovery of phosphorus (P) from acid extracts of incinerated sewage sludge ash (ISSA) is invariably complicated by the co-dissolution of metal(loid)s. An extra purification treatment step is thus needed, which reduces the efficiency of P recovery. This study developed a two-step extraction method which can produce highly purified P-extract where ISSA is treated first with ethylenediaminetetraacetatic acid (EDTA) and then with sulphuric acid. The recovery conditions of this two-step extraction method were optimized (pre-extraction by 0.02 mol/L of EDTA at a liquid to solid ratio (L/kg) of 20:1 during 120 min, then extraction by 0.2 mol/L sulphuric and at a liquid to solid ratio of 20:1 during 120 min). Compared with direct extraction by sulphuric acid (namely, single-step leaching), the two-step extraction method dissolved 2.34 mmol/kg ISSA less of P, but with 5.16 mmol/kg ISSA less of metal(loid) contamination. Furthermore, the potential for co-precipitation of P and the metal(loid) contaminates in the extracts (both single-step extraction and the two-step extraction methods) was examined from pH 2 to 12 (adjusted by addition of NaOH and Ca(OH)2). By applying Ca(OH)2and at the optimal pH of 4, the two-step extraction method could significantly increase Ca-P in the precipitate and notably decreased the metal(loid) contaminants by 50% compared to the single-step method

Applications of Citric Acid Industrial Wastewater and Phosphonates for Soil Remediation: Effects on Temporal Change of Cadmium Distribution

Citric acid industrial wastewater (CAIW) and phosphonates are potentially useful for enhancing remediation of metal-contaminated soil. This study aimed to investigate the effects of these enhancement agents on temporal change of Cd distribution in a clayey soil, which probably correlates with the metal lability and bioavailability in the environment. Sequential extractions were performed on the soil samples from batch desorption experiments between 5 and 4320 min. The CAIW primarily enhanced Cd extraction from weakly bound fractions (i.e., exchangeable and carbonate fractions), which was relatively fast and took place in the first 60 min. On the other hand, (nitrilotrimethylene)-triphosphonic acid (NTMP) and ethylene diaminetetra-methylenephosphonic acid (EDTMP) provided a more significant Cd extraction from exchangeable, carbonate, and oxide fractions, with the change of Cd distribution occurring over the first 300 min. The differences in the extent and temporal change of metal extraction reflected the weaker complexation strength of CAIW compared to that of NTMP and EDTMP. Moreover, an increase of pH from 4 to 10 shifted the remaining Cd from exchangeable fraction to carbonate and oxide fractions. These distribution changes indicated that both CAIW and phosphonates were efficient at removing weakly bound Cd fractions in a short period of time, but alkaline conditions could hinder their effectiveness.Department of Civil and Environmental Engineerin

Valorization of humins from food waste biorefinery for synthesis of biochar-supported lewis acid catalysts

202303 bcfcAccepted ManuscriptRGCOthersHong Kong International Airport Environmental Fund (Phase 2); PolyU Project of Strategic ImportancePublishe