Adsorption and desorption characteristics of heavy metals onto conventional and biodegradable plastics.

Biodegradable plastics have been widely used to replace conventional plastics to minimize environmental impacts of plastic packaging. However, before biodegradable plastics decompose in the environment, they could pose a threat to terrestrial and aquatic creatures by acting as vectors of contaminants in the food chain. In this study, conventional plastic bags (CPBs) made of polyethylene and biodegradable plastic bags (BPBs) made of polylactic acid were examined for their heavy metal adsorption. Effects of solution pHs and temperatures on adsorption reactions were investigated. Because of a larger BET surface area, presence of oxygen-containing function groups, and smaller crystallinity, the heavy metal adsorption capacities of BPBs are significantly larger than those of CPBs. Among Cu (up to 791.48 mg⋅kg-1), Ni (up to 60.88 mg⋅kg-1), Pb (up to 1414.58 mg⋅kg-1), and Zn (up to 295.17 mg⋅kg-1), Pb and Ni show the largest and the lowest extents of adsorption onto the plastic bags, respectively. In the different waterbodies in nature, Pb adsorption on the CPBs and the BPBs were 318.09-379.91 and 528.41-764.22 mg⋅kg-1, respectively. Consequently, Pb was selected as the target contaminant in the desorption experiments. After Pb was adsorbed onto the CPBs and the BPBs, Pb could be completely desorbed and released into simulated digestive systems in 10 h. In conclusion, BPBs could be potential vectors of heavy metals, and their suitability as a substitute for CPBs must be thoroughly investigated and confirmed.

Cytosolic condensates rich in polyserine define subcellular sites of tau aggregation.

Tau aggregates are a hallmark of multiple neurodegenerative diseases and can contain RNAs and RNA-binding proteins, including serine/arginine repetitive matrix protein 2 (SRRM2) and pinin (PNN). However, how these nuclear proteins mislocalize and their influence on the prion-like propagation of tau aggregates is unknown. We demonstrate that polyserine repeats in SRRM2 and PNN are necessary and sufficient for recruitment to tau aggregates. Moreover, we show tau aggregates preferentially grow in association with endogenous cytoplasmic assemblies-mitotic interchromatin granules and cytoplasmic speckles (CSs)-which contain SRRM2 and PNN. Polyserine overexpression in cells nucleates assemblies that are sites of tau aggregate growth. Further, modulating the levels of polyserine-containing proteins results in a corresponding change in tau aggregation. These findings define a specific protein motif, and cellular condensates, that promote tau aggregate propagation. As CSs form in induced pluripotent stem cell (iPSC) derived neurons under inflammatory or hyperosmolar stress, they may affect tau aggregate propagation in neurodegenerative disease.

Effect of light irradiation on heavy metal adsorption onto microplastics.

Microplastics are frequently found in many environmental media. Polypropylene (PP) is one of the plastics commonly used, resulting in more and more PP fragments in natural waters. Contaminants, such as lead (Pb), could get adsorbed onto microplastics after the exposure to sunlight, and pose a larger threat to aquatic species. In this study, the oxidative indices of PP pellets after different exposure times to a Xenon lamp were evaluated by Fourier transform infrared (FTIR) and energy-dispersive X-ray spectrometry. The results show that the percentage of oxygen content increased from 2.80 to 20.95 wt% and changes of characteristic peaks of the FTIR pattern, implying that the exposure to the Xenon lamp could initiate oxidation. Due to the changes of functional groups after the exposure to the Xenon lamp for 28 days, the adsorption capacities of the PP pellets were up to 274.4 mg⋅kg-1, 1.7 to 2.5 times higher than that of the raw PP pellets depending on the solution pHs. The adsorption behavior can be described by a pseudo-second-order model with rate constants of adsorption of 0.00212-0.01404 kg⋅mg-1⋅h-1. The increase of adsorption capacity due to changes of the PP pellets after the Xenon lamp exposure increased the potential risk to the aquatic species.

Efficient decomposition of perfluorooctanic acid by persulfate with iron-modified activated carbon.

Using persulfate (PS) oxidation to remove the persistent perfluorooctanoic acid (PFOA) in water typically requires an elevated temperature or an extended reaction time. Under relatively ambient temperatures (15-45 °C), feasibility of employing PS with iron-modified activated carbon (AC) for PFOA oxidation was evaluated. With presence of Fe/AC in PS oxidation, 61.7% of PFOA was decomposed to fluoride ions and intermediates of short-chain perfluorinated carboxylic acids (PFCAs) with a 41.9% defluorination efficiency at 25 °C after 10 h. Adsorption of PFOA onto Fe/AC can be regarded as a pre-concentration step prior to subsequent oxidation of PFOA. Fe/AC not only removes PFOA through adsorption, but also activates PS to form sulfate radicals that accelerate the decomposition and mineralization of PFOA. With Fe/AC in the PS system, activation energies (Ea) of PFOA removal and defluorination were significantly reduced from 66.8 to 13.2 and 97.3 to 14.5 kJ/mol, respectively. It implies that PFOA degradation and defluorination could proceed at a lower reaction temperature within a shorter reaction time. Besides, the surface characteristics of AC and Fe/AC before and after PS oxidation were evaluated by XPS and SEM. A quenching test used MeOH as an inhibitor and EPR spectra of free radicals were conducted to develop the proposed reaction mechanisms for PFOA oxidation.

Disinfection Processes.

A review of the literature published in 2017 on topics relating to disinfection processes is presented. This review is divided into the following sections: disinfection methods, disinfection byproducts (DBPs), microbiology and microbial communities, and distribution network and biofilm.

Disinfection Processes.

A review of the literature published in 2016 on topics relating to disinfection processes is presented. This review is divided into the following sections: disinfection methods, disinfection byproducts (DBPs), and microbiology and microbial communities.

Reductive defluorination of perfluorooctanoic acid by titanium(III) citrate with vitamin B12 and copper nanoparticles.

Perfluorooctanoic acid (PFOA) is widespread in the environment, which causes serious health and safety concerns. A mechanistic study on reductive defluorination of PFOA by titanium(III) citrate in the presence of catalysts was conducted. Vitamin B12 was used to catalyze reduction reactions by shuttling electrons from a reducing agent (electron donor) to PFOA to produce a Co-carbon bond intermediates. In the presence of copper nanoparticles, a precursor complex, B12-C7F14COOH, adsorbed on the metal surface, followed by a hydrogenolytic reaction to form less-fluorinated products. The synergistic effect between vitamin B12 and copper nanoparticles enhances the reductive activities by electron-transfer reactions and hydrogenolysis. The efficient reduction of PFOA to less-noxious compounds was demonstrated with a copper dose of 2gL-1, titanium(III) citrate (45mM), and vitamin B12 (0.2mM) with an initial pH of 9.0 and 70°C. In this anoxic aqueous solution, the biomimetic reductive system effectively removed 65% of PFOA. The mass balance on fluoride matched the observed degradation of PFOA, while no short-chain intermediates were detected.

Biogas production from anaerobic digestion of food waste and relevant air quality implications.

Biopower can diversify energy supply and improve energy resiliency. Increases in biopower production from sustainable biomass can provide many economic and environmental benefits. For example, increasing biogas production through anaerobic digestion of food waste would increase the use of renewable fuels throughout California and add to its renewables portfolio. Although a biopower project will produce renewable energy, the process of producing bioenergy should harmonize with the goal of protecting public health. Meeting air emission requirements is paramount to the successful implementation of any biopower project. A case study was conducted by collecting field data from a wastewater treatment plant that employs anaerobic codigestion of fats, oils, and grease (FOG), food waste, and wastewater sludge, and also uses an internal combustion (IC) engine to generate biopower using the biogas. This research project generated scientific information on (a) quality and quantity of biogas from anaerobic codigestion of food waste and municipal wastewater sludge, (b) levels of contaminants in raw biogas that may affect beneficial uses of the biogas, (c) removal of the contaminants by the biogas conditioning systems, (d) emissions of NOx, SO2, CO, CO2, and methane, and (e) types and levels of air toxics present in the exhausts of the IC engine fueled by the biogas. The information is valuable to those who consider similar operations (i.e., co-digestion of food waste with municipal wastewater sludge and power generation using the produced biogas) and to support rulemaking decisions with regards to air quality issues for such applications. IMPLICATIONS: Full-scale operation of anaerobic codigestion of food waste with municipal sludge is viable, but it is still new. There is a lack of readily available scientific information on the quality of raw biogas, as well as on potential emissions from power generation using this biogas. This research developed scientific information with regard to quality and quantity of biogas from anaerobic co-digestion of food waste and municipal wastewater sludge, as well as impacts on air quality from biopower generation using this biogas. The need and performance of conditioning/pretreatment systems for biopower generation were also assessed.

Disinfection Processes.

A review of the literature published in 2015 on topics relating to disinfection processes is presented. This review is divided into the following sections: disinfection methods, disinfection byproducts, and microbiology and microbial communities.

Efficient sonochemical degradation of perfluorooctanoic acid using periodate.

A rapid and efficient treatment method, using periodate (PI) for sonochemical oxidation of persistent and bioaccumulative perfluorooctanoic acid (PFOA) was developed. With an addition of 45 mM PI, 96.5% of PFOA was decomposed with a defluorination efficiency of 95.7% after 120 min of ultrasound (US). The removals of PFOA were augmented with an increase in PI doses. In all the PI+US experimental runs, decomposition efficiencies were essentially similar to those of defluorination, indicating that PFOA was decomposed and mineralized into fluoride ions. Lower solution pHs resulted in an increase in decomposition and defluorination efficiencies of PFOA due to acid-catalyzation. Dissolved oxygen increased the amount of IO4 radicals produced, which consumed the more effective IO3 radicals. Consequently, presence of oxygen inhibited the destruction of PFOA. The PFOA degradation rates with different gases sparging are in the following order: nitrogen>air>oxygen. Effects of anions follow the Hofmeister effects on PFOA degradation (i.e., Br(-)>none ⩾ Cl(-)>SO4(2)(-)). Br(-) could react with OH to yield radical anion Br2(-) that enhances the PFOA degradation. A reaction pathway was also proposed to describe the PI oxidation of PFOA under US irradiation.

Decomposition of perfluorooctanoic acid by ultraviolet light irradiation with Pb-modified titanium dioxide.

Perfluorooctanoic acid (PFOA, C7H15COOH) is widely used in industrial and commercial applications. It has become a global concern due to its widespread occurrence in water bodies and adverse environmental impact. PFOA could not be effectively removed by the conventional UV/TiO2 system. This study synthesized Pb-modified TiO2 catalyst and used it as a catalyst with light irradiation for PFOA decomposition. It was found that the Pb-TiO2 catalyst could produce traps to capture photo-induced electrons or holes that lead to better photocatalytic efficiencies. Rate constant values for PFOA decomposition by the UV/TiO2 and UV/Pb-TiO2 systems were determined to be 0.0158 and 0.5136 h(-1), respectively. The PFOA decomposition in the UV/Pb-TiO2 system is 32.5 times faster than that in the UV/TiO2 system. The UV/Pb-TiO2 system yielded a better performance than those of the UV/Fe-TiO2 and UV/Cu-TiO2 systems. During the reaction, PFOA decomposed stepwisely into shorter-chain perfluorocarboxylic acids and F(-).

Disinfection Processes.

A review of the literature published in 2014 on topics relating to disinfection processes is presented. This review is divided into the following sections: disinfection methods, disinfection byproducts, and microbiology and microbial communities.

Estimation of methane emission from California natural gas industry.

UNLABELLED: Energy generation and consumption are the main contributors to greenhouse gases emissions in California. Natural gas is one of the primary sources of energy in California. A study was recently conducted to develop current, reliable, and California-specific source emission factors (EFs) that could be used to establish a more accurate methane emission inventory for the California natural gas industry. Twenty-five natural gas facilities were surveyed; the surveyed equipment included wellheads (172), separators (131), dehydrators (17), piping segments (145), compressors (66), pneumatic devices (374), metering and regulating (M&R) stations (19), hatches (34), pumps (2), and customer meters (12). In total, 92,157 components were screened, including flanges (10,101), manual valves (10,765), open-ended lines (384), pressure relief valves (358), regulators (930), seals (146), threaded connections (57,061), and welded connections (12,274). Screening values (SVs) were measured using portable monitoring instruments, and Hi-Flow samplers were then used to quantify fugitive emission rates. For a given SV range, the measured leak rates might span several orders of magnitude. The correlation equations between the leak rates and SVs were derived. All the component leakage rate histograms appeared to have the same trend, with the majority of leakage rates<0.02 cubic feet per minute (cfm). Using the cumulative distribution function, the geometric mean was found to be a better indicator than the arithmetic mean, as the mean for each group of leakage rates found. For most component types, the pegged EFs for SVs of ≥10,000 ppmV and of ≥50,000 ppmV are relatively similar. The component-level average EFs derived in this study are often smaller than the corresponding ones in the 1996 U.S. Environmental Protection Agency/Gas Research Institute (EPA/GRI) study. IMPLICATIONS: Twenty-five natural gas facilities in California were surveyed to develop current, reliable, and California-specific source emission factors (EFs) for the natural gas industry. Screening values were measured by using portable monitoring instruments, and Hi-Flow samplers were then used to quantify fugitive emission rates. The component-level average EFs derived in this study are often smaller than the corresponding ones in the 1996 EPA/GRI study. The smaller EF values from this study might be partially attributable to the employment of the leak detection and repair program by most, if not all, of the facilities surveyed.

Enhanced sonochemical degradation of perfluorooctanoic acid by sulfate ions.

This study investigated the effects of sulfate ions on the decomposition of perfluorooctanoic acid (PFOA) by ultrasonic (US) irradiation at various pHs, sulfate doses, powers and temperatures. The removal of PFOA was augmented with an increased sulfate ion concentration, with PFOA being almost completely decomposed in 90min at 25°C with a sulfate dose of 117mM. The two major mechanisms in the sulfate-assisted sonochemical system are the direct destruction of PFOA by cavitation and the indirect destruction of PFOA by sulfate free radicals. The decomposition of PFOA followed pseudo-first-order kinetics and was not influenced by pH. The reaction rate constants decreased with increases in temperature due to decreases in the surface tension of the solution.

Microwave-enhanced persulfate oxidation to treat mature landfill leachate.

Microwave oxidation process (MOP) was evaluated for treatment of landfill leachate. Kinetics of persulfate oxidation in MOP, effects of pH and persulfate doses on fates of derivative organic acids, and the energy cost of MOP were evaluated. The results showed that total organic carbon (TOC) removal of 79.4%, color removal of 88.4%, and UV254 removal of 77.1% were reached at MOP 550 W/85 °C within 30 min. The kinetics of oxidation by MOP followed the first-order reaction. For a given persulfate dose, the reaction rate increased with the microwave power setting (775 W>550 W>325 W>128 W) with reaction rate constants ranging from 10(-5) to 10(-2) min(-1). The adverse effects on reaction rates under higher microwave power settings and high persulfate doses are plausibly caused by excessive persulfate oxidation and self-scavenging termination of free radicals. During the MOP treatment, TOC/COD ratio dropped with time and an 86.7% reduction in TOC/COD ratio after 120 min at pH 7. Oxalic acid was the major derivative and its concentrations were higher under acidic conditions. Malic, lactic, and acetic acids were formed and soon degraded, and the solution pH has an insignificant effect on their fates. The energy cost of MOP (USD$6.03/m(3)) is essentially similar to that of conventional heating oxidation (CHO) (USD$6.10/m(3)).

Promoted degradation of perfluorooctanic acid by persulfate when adding activated carbon.

Treatment of persistent perfluorooctanoic acid (PFOA) in water using persulfate (PS) oxidation typically requires an elevated temperature or UV irradiation, which is energy-consuming. Under relatively low temperatures of 25-45°C, activated carbon (AC) activated PS oxidation of PFOA was evaluated for its potential of practical applications. With presence of AC in PS oxidation, PFOA removal efficiency at 25°C reached 682% with a high defluorination efficiency of 549% after 12h and few intermediates of short-chain perfluorinated carboxylic acids (PFCAs) were found. The removal and defluorination rates with the combined AC/PS system were approximately 12 and 19 times higher than those of the PS-only system, respectively. Activated carbon not only removes PFOA through adsorption, but also activates PS to form sulfate radicals that accelerate the decomposition and mineralization of PFOA. The activation energy for PS oxidation of PFOA was reduced from 668 to 261kJ/mol by the catalytic effect of AC, which implies a lower reaction temperature and a shorter reaction time would suffice. A 2-cycle schematic reaction mechanism was used to describe PS oxidation of PFOA with the generation of various intermediates and end-products.

Derivative mechanisms of organic acids in microwave oxidation of landfill leachate.

This study compared formation and degradation behaviors of organic acids in landfill leachate under microwave oxidation process (MOP) and under conventional heating oxidation (CHO) and explored derivative mechanisms of organic acids in MOP. The results showed that formation and degradation behaviors of oxalic acid were very similar under CHO and MOP, in which its concentrations decreased in the temperature-raising period, then increased due to decomposition of TOC from 10 to 70 min, decreased due to persulfate oxidation from 70 to 130 min, and stayed the same afterwards. The pH values of the leachate solution dropped 0.51 and 0.65 pH units after MOP and CHO treatment, respectively. Oxalic acid was the dominant organic acid formed in MOP. The derivative mechanisms of organic acids were developed using the experimental results. Lactic acid was generated from decomposition of malic acid, and oxalic acid was formed from oxidation of its precursors. Acetic acid was formed and soon decomposed. Lactic acid had its maximum concentration with a persulfate dose of 0.5M, while lower or higher persulfate doses yielded few or no lactic acid in MOP.

A study on microwave oxidation of landfill leachate--contributions of microwave-specific effects.

Microwave oxidation process (MOP) was evaluated for treatment of landfill leachate. The experimental parameters include pH, temperature, oxidant doses, microwave power setting, and irradiation time. The study explored the microwave-specific effects of the MOP. The contributions of pure thermal, persulfate oxidation and microwave irradiation on TOC removal were quantified. It was then found the combinations of them were usually synergistic in MOP except two of them were antagonistic (128 W/85°C/1M Na(2)S(2)O(8) and 128 W/85°C/2M Na(2)S(2)O(8)). At the highest temperature tested (85°C) in this study, microwave irradiation may cause generation and termination of oxidizing radicals at adverse rates. The study also found that persulfate decayed rapidly in either MOP or conventional heating oxidation (CHO) treatment of landfill leachate.

Using pretreated waste oyster and clam shells and microwave hydrothermal treatment to recover boron from concentrated wastewater.

Boron is an essential nutrient for animals and plants, but it can be harmful in excessive levels. In this study, three types of crushed shells (oyster, hard clam and freshwater clam) were pretreated and then reused as mineralizers to remove and recover the boron from concentrated wastewater by using the microwave hydrothermal method. Chemical and physical properties of raw and pretreated crushed shells were determined and compared using SEM, XRD, BET and WD-XRF. Effects of pretreatment method (heated or pyrolysis), particle sizes, initial boron concentrations, reaction times and shells dosages on boron recovery were investigated. The oyster shells pretreated by heat performed better than heated hard clam and freshwater clam shells, and the boron recovery efficiency reached around 95% within 10 min of reaction time. The experimental results indicate that the pretreated oyster shell is an effective mineralizer for removal and recovery of boron from concentrated wastewater.