Enhancing membrane separation performance in the conditions of different water electrical conductivity and fouling types via surface grafting modification of a nanofiltration membrane, NF90

A commercialized and widely applied nanofiltration membrane, NF90, was in-situ modified through a surface grafting modification method by using 3-sulfopropyl methacrylate potassium salt and initiators. The effects of water electrical conductivity (EC) and fouling types on membrane separation efficiency were examined before and after membrane modification. Results reveal that both the pristine membrane (PTM) and surface grafting modification membrane (SGMM) had a declining permeate flux and salt (NaCl) removal efficiency but an increasing trend of pharmaceuticals and personal care products (PPCPs) removal with increasing water EC from 250 to 10,000 μs cm-1. However, SGMM exhibited a slightly declining permeate flux but 13%-17% and 1%-42% higher rejection of salt and PPCPs, respectively, compared with PTM, due to electrostatic repulsion and size exclusion provided by the grafted polymer. After sodium alginate (SA) and humic acid (HA) fouling, SGMM had 17%-26% and 16%-32% higher salt rejection and 1%-12% and 1%-51% greater PPCP removal, respectively, compared with PTM due to the additional steric barrier layer contributed by the foulants. The successful grafting and increasing hydrophilicity of the SGMM were confirmed by contact angle analysis, which was beneficial for mitigating membrane fouling. Overall, the proposed in-situ surface grafting modification of NF90 can considerably mitigate organic and biological fouling while raising the rejection of salt and PPCPs at different background water EC, which is beneficial for practical applications in producing clean and high quality water for consumers.

Study on clogging mechanisms of constructed wetlands from the perspective of wastewater electrical conductivity change under different substrate conditions

Constructed wetland (CW) has obvious advantages in wastewater treatment of medium and small towns. However, there is a lack of health monitoring research on CW system clogging. The electrical conductivity (EC) of wastewater purified by CW is related to the concentration of pollutants, which can reflect the CW clogging. The objectives of this study are to reveal the mechanisms of CWs substrate clogging from the perspective of wastewater EC changes, and provide an important reference for the health evaluation of CWs. The EC changes of nine CWs substrates (quartz sand, zeolite, gravel, coarse sand, straw biochar, sludge biochar, clay ceramsite, fly ash ceramsite and shale ceramsite) under different conditions (purified water, wastewater and wastewater + NaCl) were tested, and comparative analysis was used to reveal the influence of different substrate materials on the change of wastewater EC. The results show that the adsorption ability of substrate material isn't the main factor affecting the EC of wastewater, and the soluble component in the material is the important factor to cause the difference of EC increment. Under the condition of 0.4-1.0 g L^-1 NaCl concentration, the adsorption of substrate materials had little effect on the EC of wastewater, and the effect of NaCl used in CW tracer experiment was good. Quartz sand, coarse sand, gravel and sludge biochar have little influence on the change of wastewater EC. Other materials that have great influence on the change of wastewater EC can be treated by modifying or controlling the mixing ratio. The results are of great significance to reveal the clogging state of CW system and to carry out health assessment research.

Nutrient solutions for Arabidopsis thaliana: a study on nutrient solution composition in hydroponics systems

BACKGROUND

There is little information on the effect of nutrient solutions composition on Arabidopsis growth. Therefore, we compared growth performance of Arabidopsis thaliana (Col-0) grown on the most commonly used nutrient solutions in deep water culture: Hoagland and Arnon, Murashige and Skoog, Tocquin, Hermans, and Conn. In addition to these nutrient solution composition experiments, we established Arabidopsis growth response curves for nutrient solution concentration and salt stress (NaCl).

RESULTS

Arabidopsis rosette fresh and dry weight showed an approximate linear decline with NaCl dose in deep water culture, i.e. 9% reduction relative to control per unit of electrical conductivity (EC in dS m-1, for scale comprehension 1 dS m-1 equals ~ 10 mM NaCl). The Tocquin, ½Hoagland and Conn nutrient solutions had equal and optimal growth performance. Optimal nutrient solution concentration for Tocquin and Hoagland was 0.8 to 0.9 dS m-1. Close to the EC of ½Hoagland (1.1 dS m-1), which is frequently used in Arabidopsis research. Conn solution showed optimal growth at much higher EC (2 dS m-1) indicating that it is a balanced nutrient solution that matches the needs of Arabidopsis. Full Murashige and Skoog solution (5.9 dS m-1) was lethal and diluted solutions (EC of 1.6 and 1.1 dS m-1) caused stress symptoms and severe growth retardation at later developmental stages.

CONCLUSIONS

Arabidopsis thaliana (Col-0) plants grown in deep water culture showed a sixfold growth difference when commonly used nutrient solutions were compared. Murashige and Skoog solution should not be used as nutrient solution in deep water culture. Conn, Tocquin and ½Hoagland are balanced nutrient solutions which result in optimal Arabidopsis growth in hydroponic systems.

Developing an empirical model from Landsat data series for monitoring water salinity in coastal Bangladesh

This study aims to develop an empirical model from Landsat data series to monitor the water salinity of coastal Bangladesh efficiently. Such a model can substitute expensive conventional techniques for assessing remote water quality. A set of equations connecting sensors 5 TM and 8 OLI were generated using multiple regression analysis. Radiometric and atmospheric corrections were carried out to enhance the quality of satellite images. Total 13 compositions of different bands including blue, green and red were considered to find the Coefficient of Determination (r²) with the field level EC (electrical conductivity) values collected from 74 sampling locations. Salinity data mainly EC values of coastal water were collected from primary and secondary sources. Considering the r² values, significant band compositions were identified and then employed to generate linear equations. Such equation for Landsat 5 TM could detect water salinity (i.e. EC) accurately of around 82%. Similarly, the r² value for Landsat 8 OLI was found as 0.76 that can confirm the applicability of Landsat data series to detect the change of salinity level of coastal water for a long period. The availability of coastal water was delineated by NDWI whereas salinity level was assessed using the developed equations for the year 2001 and 2019. Interestingly, it was observed that coastal areas having lower level of EC almost vanished whereas those of having higher level of EC were increased significantly between 2001 and 2019. Such increase in coastal water salinity is the result of combined effects of climatic and anthropogenic factors, which can pose a considerable risk to the coastal inhabitants including freshwater scarcity, food insecurity, and health hazard.