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Increasing ozone concentration is one of the oxidative stresses that affects rice yield loss in many countries. Catechin and salicylic acid were proposed as tools for alleviating oxidative stress in plants, but their roles in protecting rice productivity under ozone stress still remained unknown. We investigated the mechanism of catechin and salicylic acid on rice under ozone stress at the vegetative stage and at the reproductive stage. Rice was sprayed with catechin and salicylic acid before exposure to ozone in the range of 100–150 ppb (8 h day −1 ). Ozone and salicylic acid led to a decrease in chlorophyll contents, magnesium contents, and stomatal conductance. This evidence led to a decrease in rice productivity and quality. In contrast, under rice + catechin, both ambient air and elevated ozone conditions had to higher rice productivity and quality than under rice alone and rice + salicylic acid conditions. Catechin could mitigate ozone stress in rice plants through maintaining chlorophyll contents, magnesium contents, and stomatal conductance. Moreover, catechin could induce an unregulation of ascorbate peroxidase, and catalase genes led to increasing their antioxidant enzyme activity. Increasing of antioxidant enzyme activity under rice + ozone + catechin conditions attributed to lower lipid peroxidation than under rice + ozone especially at vegetative stage. This study confirmed that catechin, which is naturally found in tea leaves, could be used as an ozone protectant. The protective role of catechin on chlorophyll contents and antioxidant systems at the vegetative stage attributed to maintaining rice yield under ozone stress. Graphical abstract

Cadmium (Cd) contaminated in rice grains is a serious problem because most Asians consume rice on a daily basis. Rice grown in Cd-contaminated soil normally did not have high concentration of Cd. However, soil samples used in this study had high concentrations of Cd. The purpose of this study was to clearly see the effects of biochar and microorganism addition in rice growing in Cd-contaminated soil. The initial Cd concentration in Cd-contaminated soil used in this study was about 650 mg kg −1 . Cadmium concentration in rice plants grown in Cd-contaminated soil with the addition of 1 % ( w / w ) different biochars such as sawdust fly ash (SDFA), bagasse fly ash (BGFA), and rice husk ash (RHA) was investigated. The results showed that SDFA was the best biochar in terms of reducing cadmium accumulation in rice grains when compared to BGFA and RHA under the same conditions. In addition, rice plants grown in Cd-contaminated soil with the addition of various nonpathogenic microorganisms, such as Pseudomonas aeruginosa, Bacillus subtilis , and Beauveria bassiana were also studied. The results showed that the addition of 2 % ( v / v ) microorganisms can reduce Cd accumulation in grains. It was found that grains obtained from Cd-contaminated soil with the addition of P. aeruginosa had the lowest cadmium concentration compared to the ones from soil amended with other strains. This was due to the fact that P. aeruginosa adsorbed more Cd itself into its cells than other strains. The rice plants grown in Cd-contaminated soil with the addition of biochars and microorganisms were also compared. The results showed that adding 2 % ( v / v ) microorganisms seemed to reduce Cd accumulation in rice grains better than adding 1 % ( w / w ) biochars. In addition, the amounts of calcium and magnesium in rice grains and the dry weight of plant in Cd-contaminated soil amended with P. aeruginosa were the highest in comparison to other microorganisms, biochars, and the soil without any amendments (Cd-soil control). It might be possible that microorganisms can cause leaching of Ca, Mg, etc. from contaminated soil and compete with Cd to be uptaken by plants. This would cause the increase in plant dry weight and higher mineral nutrients accumulation in grains. Both biochars and microorganisms are suitable for reducing the amount of Cd in rice grains. The application should depend on farmers, biochars available in nearby areas, etc. Therefore, microorganisms and biochars can be used to solve the problem of cadmium contamination in rice grains.

Phosphate (PO43−) and nitrate (NO3−) contamination causes the threatening issue of eutrophication. A major waste from seafood industries of various seashells including Anadara inaequivalvis, Saccostrea commercialis, Perna viridis, Tegillarca granosa, Filopaludina martensi, Babylonai areolate and Meretrix lusoria was thermally modified and investigated for PO43− and NO3− removal from synthetic and domestic wastewater. It was found that some raw seashells could remove ≥85% of PO43−, whereas their NO3− removal efficiency was poor. However, after calcination, among others, only M. lusoria pyrolysed at 800 °C (M. lusoria F800) was found as a novel adsorbent for both PO43− and NO3− removal. An increase in temperature and increased Ca(OH)2 content enhance the removal of PO43− and NO3− by precipitating with calcium ions (Ca2+). M. lusoria F800 was the best for PO43− and NO3− removal compared with commercial lime and other calcined seashells. The maximum adsorption capacity (Qmax) of M. lusoria F800 for PO43− and NO3− was 700 mg/g and 170 mg/g, respectively, which was higher than the Qmax of PO43− and NO3− by commercial lime Ca(OH)2 which was about 465 mg/g and 18 mg/g, respectively. The crystals of calcium phosphate-hydroxide and calcium nitrate-hydroxide complexes were mainly found in M. lusoria F800 that adsorbed PO43− and NO3, respectively, as confirmed by X-ray diffractometer (XRD). Also, M. lusoria F800 could completely remove PO43− and NO3− from domestic wastewater. Hence, easily handled and cost-effective M. lusoria F800 would increase the value of this waste material, increase water quality and mitigate eutrophication.

Botanical biofilters have been proposed as an effective technology for indoor air remediation. Plants, including Sansevieria trifasciata and Chlorophytum comosum, which remove VOCs effectively, can also reduce CO2 emission since S. trifasciata and C. comosum are CAM and C3 plant species, respectively. Therefore, a botanical biofilter using these plants together shows potential for use in contaminated sites. Herein, the potential of this mixed plant botanical biofilter was evaluated as a method of phytoremediation for multi-pollutants from cigarette smoke. The results showed that the combination of S. trifasciata and C. comosum in a botanical biofilter was highly effective in removing VOCs and PM2.5. In addition, this botanical biofilter can also successfully remove formaldehyde, acetone, benzene, and xylene, with low CO2 emission under indoor conditions of moderate light intensity (50 μmole PAR m−2 s−1). The system was also installed in a large volume room (24 m3) to test phytoremediation of multi-pollutants from cigarette smoke. The results showed that this mixed plant botanical biofilter can remediate indoor air pollution effectively under both light and dark conditions continuously for three cycles. The mixed plant botanical biofilter developed showed potential for use in real contamination sites.

Novel sources for a renewable energy supply have become a global challenge. Wetland-microbial fuel cells (WL-MFCs) are being considered as a high potential technology to combat this issue. The use of the plant-microbial interaction between Echinodorus cordifolius and Bacillus thuringiensis can promote long-term WL-MFC system operation. This study aims to present a suitable design for the application of an E. cordifolius -MFC inoculated with B. thuringiensis . The results show that the serial connection of two small WL-MFCs can increase the electrical density compared with a single WL-MFC system. Interestingly, the two connected small WL-MFCs can also produce better electrical density than a large WL-MFC cell. For low electric production in the large WL-MFC cell, the result can be explained by the high oxygen concentration in the anode part of the system, which is associated with a low oxygen concentration (anaerobic conditions). These two connected small WL-MFCs can generate an electrical supply of ~ 50–60 mW/m 2 for longer than 160 days. Although during the first 100–120 days of operation, the WL-MFC containing soil and B. thuringiensis can generate higher electric support than the WL-MFC containing soil, E. cordifolius and B. thuringiensis , with the plant, the WL-MFC can be operated for longer than WL-MFC without the plant. These results suggest that the application of WL-MFCs in a suitable design and operation can be good potential sources for a renewable energy supply. Graphic Abstract

The aim of this study is to compare amino acids and organic acids in the extraction of gold from silicate ore. Amino acids were found to have higher efficiency of gold extraction than organic acids at the same acid concentration, which is likely due to amino acids having both carboxylic and amine groups in their structure, while organic acids only have carboxylic groups. Five amino acids (glycine, aspartic acid, glutamic acid, lysine and tryptophan) and seven organic acids (citric, malic, tataric, fumaric, oxalic, succinic and ascorbic acids) were selected to investigate gold extraction efficiency. Aspartic acid was found to have greater capacity to extract gold than succinic acid. The optimal gold to aspartic acid molar ratio was 1:6, and low concentrations of aspartic acid extracted 35 to 42 percent of gold from silicate ore within 15 days. Further studies are needed to increase gold leaching and reduce incubation time. The results imply that aspartic acid can be used as an alternative reagent to traditional methods for extracting gold from ore. This method is nontoxic to humans, is environmentally friendly and can have real applications.

The air pollutant ozone (O3) is a phytotoxic oxidative stressor, leading to visible foliar injury and plant growth decline. Plant growth-promoting bacteria (PGPB) are emerging as an eco-friendly tool for improving plant growth under stress. In order to test PGPB as a tool for alleviating O3 stress in plants, an O3 sensitive genotype (Phaseolus vulgaris L. cv S156) was inoculated with native (rhizobacterial; B1 and B2) and non-native PGPB (Bacillus megaterium and B. amylolequefaciens) and exposed to realistic O3 exposure (ambient, AA with AOT40 = 0.53 ppm per hour, and twice ambient ozone concentration, 2XAA, AOT40 = 1.84 ppm per hour). The promoting effect was assessed by quantifying visible foliar O3 injury (PII), chlorophyll a fluorescence (Fv/Fm), contents of hydrogen peroxide (H2O2), malondialdehyde (MDA) and nitric oxide (NO), ethylene emission, 1-aminocyclo-propane-1-carboxylate (ACC) deaminase enzyme activity, above- and below-ground biomass. BM, BA and B1 showed higher ACC deaminase enzyme activity and Fv/Fm, while ethylene emission, PII, H2O2, MDA and NO contents were lower in the BM, BA and B1 plants than in the B2 and non-inoculated plants under 2XAA. Only BA increased above- and below-ground biomass under AA and 2XAA. We conclude that PGPB are able to ameliorate O3 stress through induction of systemic resistance; the level of bacterial ACC deaminase is one of the good markers for identifying effective strains and may be tested as an agricultural practice for improving crop yield under O3 pollution.

Indoor air pollutants comprise both polar and non-polar volatile organic compounds (VOCs). Indoor potted plants are well known for their innate ability to improve indoor air quality (IAQ) by detoxification of indoor air pollutants. In this study, a combination of two different plant species comprising a C3 plant ( Zamioculcas zamiifolia ) and a crassulacean acid metabolism (CAM) plant ( Sansevieria trifasciata ) was used to remove polar and non-polar VOCs and minimize CO 2 emission from the chamber. Z. zamiifolia and S. trifasciata , when combined, were able to remove more than 95% of pollutants within 48 h and could do so for six consecutive pollutant’s exposure cycles. The CO 2 concentration was reduced from 410 down to 160 ppm inside the chamber. Our results showed that using plant growth medium rather than soil had a positive effect on decreasing CO 2 . We also re-affirmed the role of formaldehyde dehydrogenase in the detoxification and metabolism of formaldehyde and that exposure of plants to pollutants enhances the activity of this enzyme in the shoots of both Z. zamiifolia and S. trifasciata . Overall, a mixed plant of Z. zamiifolia and S. trifasciata was more efficient at removing mixed pollutants and reducing CO 2 than individual plants.

Indoor air pollution is of increasing concern for human health. Amongst the volatile organic compounds (VOCs) found indoors, formaldehyde and toluene are two toxic compounds. Indoor plants have an innate capability to remediate indoor airborne pollutants. Zamioculcas zamiifolia is an ornamental plant local to Thailand reported to be very efficient for VOC removal. Indole acetic acid (IAA) was applied to shoots and roots of Z. zamiifolia to enhance the capability for removing a toluene and formaldehyde mixture. We found that 5 μM of exogenous IAA can enhance Z. zamiifolia efficiency about 20% and 40% for toluene and formaldehyde, respectively, after plant was exposed to initial toluene-formaldehyde mixture concentration 20 ppm (1:1) for 3 cycles (156 h). We found that 5 μM of exogenous IAA had a positive effect on the stomatal aperture opening and stomatal conductance. However, 10 μM of exogenous IAA had a negative effect on the opening of stomatal aperture, and thus initially decreased that remediating ability of Z. zamiifolia for formaldehyde and toluene. We investigated the formaldehyde dehydrogenase activity in shoots of Z. zamiifolia and found significantly enhanced FDH activity in plants supplied with exogenous IAA. We concluded that exogenous IAA in optimum amounts could enhance the mitigating ability of indoor plants for airborne air pollutants. However, our research indicated that the application of IAA to roots could have a negative effect on the remediating ability of Z. zamiifolia.

Bamboo chars and bamboo activated carbons prepared by steam activation were applied for ink wastewater treatment. Bamboo char at 800 °C was the best for the removal of color and chemical oxygen demand (COD) from ink wastewater compared to bamboo chars at 300 to 700 °C due to higher surface area and mesopore volume. Bamboo activated carbon at 600 °C (S600) was the best compared to bamboo activated carbon at 800 °C (S800), although S800 had larger surface area (1108 m²/g) than S600 (734 m²/g). S600 had higher mesopore volume (0.20 cm³/g) than S800 (0.16 cm³/g) and therefore achieved higher color and COD removal. All bamboo activated carbons showed higher color and COD removal efficiency than commercial activated carbon. In addition, S600 had the superior adsorption capacity for methylene blue (0.89 mmol/g). Therefore, bamboo is a suitable material to prepare adsorbents for removal of organic pollutants.