Hydrothermal-enhanced pyrolysis for efficient NOX reduction and biochar valorization from food waste digestate.

Pyrolysis has emerged as a promising technology for valorizing digestate resulting from the anaerobic digestion of food waste. However, the high NOX emissions during pyrolysis limit its application. This study proposed a hydrothermal coupled pyrolysis process to control the element transfer in digestate during biochar production. The efficient reduction of NOX emissions and the improvement of biochar adsorbability were realized. The hydrothermal process reduced the nitrogen content in solid digestate by 49.10 %-81.79 %, thus reducing the NOX precursors in syngas and the N-containing substances in bio-oil. Additionally, the specific surface area and the total pore volume of biochar were enhanced from 25 m2/g to 60-73 m2/g and 0.06 cm3/g to 0.12-0.14 cm3/g, respectively. More defects, oxygen-containing functional groups, and doped Ca on the biochar resulted in a high phosphate removal efficiency of 94 %. The proposed technology provides an efficient and environmentally friendly way to utilize the digestate.

Ion-Imprinted Polymer-Based Sensor for the Detection of Mercury Ions.

In this work, the development of a novel method for the detection of mercury (II) ions in wastewater using a mercury ion-imprinted polymer (IIP) combined with a quartz crystal microbalance (QCM) is described. The IIP was successfully synthesized via the polymerization of a of a novel fluorescein- and 2-aminophenol-functionalized methacrylic acid monomer, which was noted to have high binding affinity to mercury (II) ions. This polymer was subsequently coated on a QCM chip to create an IIP-QCM sensor. This sensor was established to have high selectivity and good sensitivity to mercury (II) ions, and had a limit of detection (LOD) of 14.17 ppb, a limit of quantification (LOQ) of 42.94 ppb, a signal-to-noise ratio (S/N) of 4.29, good repeatability, and a working range of 42.94 ppb to 2 ppm. The sensor was also able to analyze tap water and wastewater samples. The IIP-QCM is, therefore, promising as a highly selective, cost-effective, and rapid mercury ion sensor for applications involving the detection of mercury in wastewater.

Impact of polysaccharide and protein interactions on membrane fouling: Particle deposition and layer formation.

Membrane fouling, which limits the application of membrane bioreactors, has received considerable research attention in recent years. In this work, filtration modeling was performed in combination with surface plasmon resonance (SPR) analysis to investigate the membrane fouling mechanism. Sodium alginate (SA) and bovine serum albumin (BSA) were used to perform dead-end filtration on hydrophilic and hydrophobic poly (vinylidene fluoride) (PVDF) membranes. The initial foulant deposition and layer formation on membranes as well as the interaction between the BSA and SA were comprehensively analyzed. Results indicated that during SA filtration, initial fouling on hydrophilic membranes were primarily attributed to the particle-membrane interactions, while the fouling on the hydrophobic membrane were dominantly caused by the interactions among SA particles. The interaction between BSA and SA led to more severe membrane fouling and hydrophobic membrane was more sensitive to it, especially in the initial filtration process. The SPR results helped clarify the in-situ deposition behavior of BSA and SA particles on the PVDF surface. Compared to SA, BSA adsorbed faster on the PVDF membrane, and specific interactions played an essential role in BSA adsorption, whereas the deposition of SA on PVDF could be easily removed by shear force. Interactions between BSA and SA could alleviate the bonding between BSA and the PVDF membrane.

Mechanism insights into hydrothermal dewatering of food waste digestate for products valorization.

Poor dewaterability is a bottleneck of the disposal of digestate from food waste (DFW). However, the dewatering mechanism remains unclear due to the complex composition of DFW. Understanding the dewatering mechanism, as well as the transformation of organic/inorganic matters is essential for the DFW management and valorization. In this study, the distribution, transformation, and complex interplay of organic and inorganic matters at different Hydrothermal treatment (HTT) temperatures were comprehensively analyzed to explore the hydrothermal dewatering mechanism of DFW. When HTT was conducted in the temperature range of 120-180 °C, the interstitial water was released as surface or free water because of membrane breaking and size reduction of the solid substrate. Releasing divalent cations increased the Zeta potential of the bulk solution. The weaker electrostatic repulsion between suspended particles made them easier to settle as the centrifugation cake. When the temperature of HTT was above 180 °C, polymerization and aromatization reactions took place gradually for organic matters, and the bound water was further removed. The generated humic substances were more hydrophobic than the raw material. In addition, the humic substance could combine with cationic metals, which decreased the zeta potential of the bulk solution but promoted the aggregation of nanoparticles and enhance the dewaterability of DFW.

Impact of bottom ash co-disposed with municipal solid waste on geotextile clogging in landfills.

Co-disposal of bottom ash (BA) with municipal solid waste (MSW) in landfills is commonly used for BA management. However, BA co-disposal may cause clogging of geotextiles in MSW landfills. This study investigated the effect of different BA co-disposal ratios on geotextile clogging, including MSW, low ash co-disposed (BA_L), high ash co-disposed (BA_H) landfills, and BA mono-fill. Results showed that the BA_L group increased the geotextile clogging by 0.1-0.6 times, compared to that in the MSW landfill. In contrast, the geotextile clogging of the BA_H and BA groups was reduced than that in the MSW landfill. The clogging was in a dynamic process during the experimental period in all the conditions, including chemical clogging and bio-clogging. Moreover, bio-clogging was the main contributor to the geotextile clogging, accounting for 64-83% of the total clogging mass. The BA co-disposal affected the leachate characteristics, such as pH, calcium concentration, and alkalinity, resulting in chemical clogging. When pH was above 7.0, calcium concentration and alkalinity were limiting factors for the calcium carbonate formation. In terms of the bio-clogging, the microbial analysis indicated that different BA co-disposal ratios influenced the diversity and structure of microbial community. These findings could help clarify the effect of BA co-disposal on geotextile clogging, thus useful to landfill operation in practice.

A label-free lead(II) ion sensor based on surface plasmon resonance and DNAzyme-gold nanoparticle conjugates.

Detection of lead(II) (Pb2+) ions in water is important for the protection of human health and environment. The growing demand for onsite detection still faces challenges for sensitive and easy-to-use methods. In this work, a novel surface plasmon resonance (SPR) biosensor based on GR-5 DNAzyme and gold nanoparticles (AuNPs) was developed. Thiolated DNAzyme was immobilized on the gold surface of the sensor chip followed by anchoring the substrate-functionalized AuNPs through the DNAzyme-substrate hybridization. The coupling between the localized surface plasmon (LSP) of AuNPs and the surface plasmon polaritons (SPP) on the gold sensor surface was used to improve the sensitivity. The substrate cleavage in the presence of Pb2+ ions was catalyzed by DNAzyme, leading to the removal of AuNPs and the diminished LSP-SPP coupling. The optimal detection limit was 80 pM for the sensor fabricated with 1 µM DNAzyme, corresponding to two or three orders of magnitude lower than the toxicity levels of Pb2+ in drinking water defined by WHO and USEPA. By tuning the surface coverage of DNAzyme, the sensitivity and dynamic range could be controlled. This sensor also featured high selectivity to Pb2+ ions and simple detection procedure. Successful detection of Pb2+ ions in groundwater indicates that this method has the prospect in the onsite detection of Pb2+ ions in water. Given the variety of AuNPs and metal-specific DNAzymes, this detection strategy would lead to the development of more sensitive and versatile heavy metal sensors. Graphical abstract.

Geotextile clogging at different stages of municipal solid waste landfills co-disposed with bottom ash.

Co-disposal of bottom ash (BA) with municipal solid waste (MSW) in landfills is a common way for BA management. However, BA co-disposal in MSW landfills may accelerate geotextile clogging and reduce the performance of leachate collection system. This study compared geotextile clogging in a simulated MSW landfill leachate (MSWL) and a BA co-disposed landfill leachate (BAL) at different landfill stages. Geotextile clogging test was conducted using the MSWL and BAL taken from the simulated landfills on the 10th, 80th, 140th and 200th day, respectively. The results demonstrated that geotextile clogging varied with landfill age, due to the change of leachate characteristics. The mass of clogging material in geotextiles with BAL increased from 0.45 g to 2.74 g, which was 43.87%-63.73% greater than those with MSWL. The formation of biofilm was the main contributor for the geotextile clogging. At the same stage, the amount of biofilm formed on geotextile in different leachate was comparable. However, the amounts of CaCO3 precipitation on geotextile in BAL were 3.85-10.44 times of those in MSW leachate. The pH of leachate played a critical role in CaCO3 precipitation. The microbial analysis revealed that the co-disposal of the BA greatly influenced the microbial community diversity and structure.

Enhancement of hydrogen production using untreated inoculum in two-stage food waste digestion.

This research investigated the possibility to enhance H2 production using untreated inoculum in a two-stage hydrogen-methane process from food waste. Batch experiments were conducted to evaluate the H2 production efficiency at different F/M ratios (ranging from 1:1 to 64:1). The results showed that when a proper F/M ratio was selected, significant H2 production was feasible to be achieved even inoculated with untreated anaerobic sludge. Among the F/M ratios studied, maximum H2 yield (217.98 mL H2 g VS-1 FW) was found in the digester at the F/M of 64:1, which was 93.75 times higher than that of the digester at the F/M of 1:1. Higher hydrogen yield was achieved at the greater F/M ratio, due to the enrichment of the H2 producing bacteria and the reduction of the antagonistic bacteria. The two-stage process allowed more stable methane production and higher overall energy yield compared to the single-stage process.

Characteristics of geotextile clogging in MSW landfills co-disposed with MSWI bottom ash.

As a main byproduct of municipal solid waste incineration (MSWI), bottom ash (BA) has become a big challenge in operating MSWI plants. The most common method for BA treatment is co-disposal with MSW in landfills, which may cause clogging in the leachate collection system (LCS). This research investigated the characteristics of geotextile clogging in landfills with BA co-disposal. The co-disposal of BA changed the characteristics of leachate, especially increasing the concentration of Ca2+. During the experiment, 0.14 g CaCO3 was precipitated in the MSW geotextile, while it increased to 0.52 g CaCO3 in the BA co-disposed geotextile. Based on mass balance of calcium and thermogravimetric (TG) analysis, the formation of biofilm was the main contributor to the mass increment, accounting for about 82% and 57% mass increment in the MSW and BA co-disposed geotextile, respectively. Moreover, CO2 in landfill gas played an important role in the clogging process, including CaCO3 precipitation and biofilm formation. The results suggested that the co-disposal of BA with MSW can increase the risk of geotextile clogging in landfills.

H2S adsorption by municipal solid waste incineration (MSWI) fly ash with heavy metals immobilization.

As a byproduct of municipal solid waste incineration (MSWI) plant, fly ash is becoming a challenge for waste management in recent years. In this study, MSWI fly ash (FA) was evaluated for the potential capacity of odorous gas H2S removal. Results showed that fly ash demonstrated longer breakthrough time and higher H2S capacities than coal fly ash and sandy soil, due to its high content of alkali oxides of metals including heavy metals. H2S adsorption capacities of FA1 and FA2 were 15.89 and 12.59 mg H2S/g, respectively for 750 ppm H2S. The adsorption of H2S on fly ash led to formation of elemental sulfur and metal sulfide. More importantly, the formation of metal sulfide significantly reduced the leachability of heavy metals, such as Cr, Cu, Cd and Pb as shown by TCLP tests. The adsorption isotherms fit well with Langmuir model with the correlation coefficient over 0.99. The adsorption of H2S on fly ash features simultaneous H2S removal and stabilization and heavy metals found in most MSWI fly ash, making fly ash the potential low cost recycled sorbent material.

Polyelectrolyte-single wall carbon nanotube composite as an effective cathode catalyst for air-cathode microbial fuel cells.

Polyelectrolyte-single wall carbon nanotube (SCNT) composites are prepared by a solution-based method and used as metal-free cathode catalysts for oxygen reduction reaction (ORR) in air-cathode microbial fuel cells (MFCs). In this study, two types of polyelectrolytes, polydiallyldimethylammonium chloride (PDDA) and poly[bis(2-chloroethyl)ether-alt-1,3-bis[3-(dimethylamino)propyl]urea] (PEPU) are applied to decorate the SCNTs and the resulting catalysts exhibit remarkable catalytic ability toward ORR in MFC applications. The enhanced catalytic ability could be attributed to the positively charged quaternary ammonium sites of polyelectrolytes, which increase the oxygen affinity of SCNTs and reduce activation energy in the oxygen reduction process. It is also found that PEPU-SCNT composite-based MFCs show efficient performance with maximum power density of 270.1 mW m(-2), comparable to MFCs with the benchmark Pt/C catalyst (375.3 mW m(-2)), while PDDA-SCNT composite-based MFCs produce 188.9 mW m(-2). These results indicate that PEPU-SCNT and PDDA-SCNT catalysts are promising candidates as metal-free cathode catalysts for ORR in MFCs and could facilitate MFC scaling up and commercialization.

Development of variable pathlength UV-vis spectroscopy combined with partial-least-squares regression for wastewater chemical oxygen demand (COD) monitoring.

To overcome the challenging task to select an appropriate pathlength for wastewater chemical oxygen demand (COD) monitoring with high accuracy by UV-vis spectroscopy in wastewater treatment process, a variable pathlength approach combined with partial-least squares regression (PLSR) was developed in this study. Two new strategies were proposed to extract relevant information of UV-vis spectral data from variable pathlength measurements. The first strategy was by data fusion with two data fusion levels: low-level data fusion (LLDF) and mid-level data fusion (MLDF). Predictive accuracy was found to improve, indicated by the lower root-mean-square errors of prediction (RMSEP) compared with those obtained for single pathlength measurements. Both fusion levels were found to deliver very robust PLSR models with residual predictive deviations (RPD) greater than 3 (i.e. 3.22 and 3.29, respectively). The second strategy involved calculating the slopes of absorbance against pathlength at each wavelength to generate slope-derived spectra. Without the requirement to select the optimal pathlength, the predictive accuracy (RMSEP) was improved by 20-43% as compared to single pathlength spectroscopy. Comparing to nine-factor models from fusion strategy, the PLSR model from slope-derived spectroscopy was found to be more parsimonious with only five factors and more robust with residual predictive deviation (RPD) of 3.72. It also offered excellent correlation of predicted and measured COD values with R(2) of 0.936. In sum, variable pathlength spectroscopy with the two proposed data analysis strategies proved to be successful in enhancing prediction performance of COD in wastewater and showed high potential to be applied in on-line water quality monitoring.

A combination of metabolomics and metallomics studies of urine and serum from hypercholesterolaemic rats after berberine injection.

Berberine, long used as a remedy in China and India for intestinal infections, has been discovered in recent years in western countries and is now being used to treat ailments ranging from urinary tract infections to diabetes and obesity. In order to study the effect of berberine more deeply, a combined metabolomic and metallomic approach was developed in this study using the hypercholesterolaemic rat model, which involved the use of proton nuclear magnetic resonance for the analysis of rat urine to achieve metabolic fingerprinting and inductively coupled plasma mass spectrometry for the analysis of rat blood serum to achieve metallomic fingerprinting. The results obtained indicated that major metabolic processes like Krebs cycle, cholesterol metabolism and osmoregulation in hypercholesterolaemic rats are perturbed upon berberine injection. In addition, the changes of some elements, such as V, Mn, Na and K, revealed in the metallomic study may contribute to the search of new biomarkers for hypercholesterolaemic disease. We concluded that both the metabolomic and metallomic profiles of berberine-treated hypercholesterolaemic rats were different from those of the control group and that the selected metabolites and elements could probably be applied as potential biomarkers for the understanding of the effect of berberine on biochemical process in the animal model. Such a multi-analytical approach will potentially provide an information-rich platform for the elucidation of effects of xenobiotics and drug efficacy studies.

Mechanism of mercury detection based on interaction of single-strand DNA and hybridized DNA with gold nanoparticles.

Mechanisms of interaction of single-strand DNA and hybridized DNA on gold nanoparticles in the presence of Hg(2+) was studied in this work. Recently the detection of Hg(2+) using unmodified gold nanoparticles (AuNPs) combined with DNA is becoming a promising technique with the advantages of simplicity, cost-effectiveness and high sensitivity. However, few studies focused on the interaction of ssDNA and hybridized DNA on AuNPs to date. In the present work, we compared the interactions of different DNA probes on AuNPs using both absorption and fluorescence detection. It was found that there were only small partial dsDNA dissociated from the surface of AuNPs after hybridization in the presence of Hg(2+). Moreover, we found that the aggregated AuNPs/DNA system tended to be dispersed again with increasing Hg(2+) concentration up to 250µM. Based on these results, the mechanisms of mercury detection based on interaction between DNA-conjugated gold nanoparticles were investigated. Positively charged dsDNA could bind to the surface of AuNPs and dominate the electrostatic interactions and consequently aggregation of the AuNPs/DNA system.