Water pollution prevention and state of the art treatment technologies.

This special issue (SI) of Environmental Science and Pollution Research (ESPR) includes a collection of 18 peer-reviewed articles relating to water quality and toxicity risk assessments, ecosystem protection, groundwater contamination assessment, soil and sediment remediation technologies, water treatment technologies, climate change adaptation and mitigation strategies, and control of carbon intensity that were formally presented at the 4th International Conference on Water Resources and Environment (WRE 2018), the 5th International Conference on Water Resources and Environment (WRE 2019), and the 1st International Conference on Advances in Civil and Ecological Engineering Research (ACEER 2019). WRE 2018 was held in I-Shou University, Kaohsiung, Taiwan, from July 17th to 21st, 2018. WRE 2019 was held in Macau University of Science and Technology, Macao, China, from June 16th to 19th, 2019. WRE conference started in 2015, when the first WRE was held in Beijing. As an annually held conference, the upcoming 6th WRE conference is prescheduled held in Tokyo, from 23rd to 26th, 2020; however, due to the outbreak of COVID-19 and for the safety of participants, WRE2020 will be held online via virtual presentation (http://www.wreconf.org/index.html). The WRE conference highlighted the needs to maintain the sustainability of indispensable water resources under increasing uncertainty and to protect the fragile water environments under the growing concern of intensive use of water we are facing today. While Civil Engineering provides us a better living environment, there is a need not only to protect our fragile environment but also to ensure it is sustainable for future generations. Thus, the initiation of ACEER 2019 is to emphasize links between civil engineering research and knowledge of ecological/environmental issues. The 2nd ACEER will be held on October 20th–23rd, 2020, in Beijing, China (http://www.aceerconf.org/index.html). The present SI of ESPR was guest-edited by Professor Chih-Huang Weng (I-Shou University, Kaohsiung, Taiwan). The papers selected in this SI were based on the ones originally presented at the conference; however, having gone through the regular peer-review process of ESPR, the contents of those papers have been changed. A brief highlight of the papers included in this SI is as follows:

Constantly consumption of caffeine around the world has led to increase in caffeine concentration in water bodies and agricultural soil, and thus the impact of caffeine on the environment should not be ignored. Korekar et al. (2019) review the caffeine occurrence, its persistence and remediation.

Cui et al. (2019) compared the acute toxicity of five oil spill dispersants to three organisms at different trophic levels. They found dispersants with Fuken-2 and HLD-501 exhibiting no acute toxicity to all tested organisms.

Miao et al. (2019) applied the remote sensing technique to develop models of Canadian Water Quality Index (CWQI) scores from satellite data to assess the water quality for two major urban rivers within the Linyi development area. Such advanced assessment approach is effectiveness and robustness and can indicate actual water quality patterns.

Yeh et al. (2020) demonstrate that the synergistic heavy metal contamination degree of an industrially affected river and its adverse biological effects can be assessed by employing the heavy metal pollution index, the degree of contamination index, the contamination factor, the index of geo-accumulation, and hazard quotients. This assessment practice can be quite useful to provide a reference for establishing river pollution control and management strategies.

With the help of ionic tracers and employing the spiraling curve characterization approach and the Michaelis–Menten equation, Song and Song (2019) revealed that the dynamic absorption characteristics of NO3–N in a rural–urban ecotone channel is slightly influenced by the hydrological factors, but significantly influenced by the geomorphic features of the channel.

On the basis of a 23-year dataset of eleven cities in the Songhua River Basin, Wanhong et al. (2019) ultimately developed two econometric models to quantify the industrial wastewater discharge allowance and ecocompensation of the investigated cities, respectively. They suggested that the ecosystem can be protected via an emissions trading program, which permits the wastewater discharge allowance to trading market.

Sekine et al. (2020) proposed a user-friendly procedure for estimating the performance of river fish habitat evaluation based on the comparison of width-to-depth ratio and ecoenvironmental diversity. This procedure is of particular applicability to small river construction works.

Gao et al. (2019) highlights the anomalous As and F− concentration in the phreatic and confined groundwater of Xi’an city, China, was not only attributed to the upward flow of geothermal water through faults and ground fissures but also related to the anthropogenic activities.

Zhou et al. (2019) present a case study of using aquatic chemistry and isotopic composition of groundwater to trace groundwater circulation in the Xinchang preselected site (China) that has encountered geological disposal of high-level radioactive waste.

Technologies of treating gray water (GW) as reclaimed water is now available. Based on a 1-year laboratory-scale experiment, Ren et al. (2019) claimed that GW treated by both membrane bioreactor (MBR) and biological aerated filter (BAF) all meet the criteria of water reuse for toilet flushing, but using GW purified by MBR is more viable for toilet flushing.

Li et al. (2019) adopted a sequencing biofilm batch reactor (SBBR) to perform comparative study of four different carriers on ammonia and COD removal from the effluent of zero-discharge marine recirculating aquaculture system (MRAS). They concluded that the ceramsite-packed SBBR is feasible for MRAS wastewater treatment.

Pang et al. (2019) synthesized a novel composite, titanium dioxide/activated carbon (TiO2/AC), where AC derived from oil palm empty fruit bunch, that could achieve a significantly degradation efficiency of organic dye under ultrasonic irradiation. The TiO2/AC composite remained effective in dye degradation even after second catalytic cycle, showing the possible future applicability to textile industry.

The production of nanoparticles can be more environmental-friendly without the use of chemical compounds. Chan et al. (2019) present a green synthesizing route using Clitoria ternatea Linn aqueous extract as reducing and stabilizing agents for synthesizing the silver-doped zinc oxide (Ag-doped ZnO) nanoparticles. The biosynthesized Ag-doped ZnO nanoparticles could significantly enhance its sonocatalytic activity over ZnO nanoparticles based on the test results of Congo red degradation efficiency.

Le et al. (2019) revealed that progressive freezing is a cost-effective technology for draw solute recovery in forward osmosis process. They also provided mass transfer coefficients depended on the ice front speed and the stirring rates for the needs of future scaling up experiments.

Using magnetite-carbon black composites as a persulfate activator, Dong et al. (2019) revealed that such PS oxidation processes could effectively degrade polycyclic aromatic hydrocarbons (PAHs) in sediment at circumneutral pH. They suggest that the cytotoxicity of the PAH degradation products assessed by the zebrafish (Danio rerio) embryonic cell line is more sensitive than human hepatoma carcinoma cell line.

Peng et al. (2019) found that poly-γ-glutamic acid (γ-PGA), an environmentally friendly washing reagent, is effective in removing heavy metals (Cu, Zn, Ni, and Cr) from metal-contaminated farmland soil. The efficacy of metal removal in the field pilot-scale tests is mainly governed by the order of γ-PGA concentration, washing time, liquid/soil ratio, and rotational speed.

Lee and Lin (2019) provide relationships between integrated vulnerability (biophysical and social) and personal ecological footprint of Taipei (urban) and Yunlin county (rural), Taiwan, for governments and communities to establish implementation strategies in risk areas to adapt and mitigate to climate change.

The carbon intensity of a country is closely related to its economic system. Based on a selection of 24 countries and application of endogenous growth model, Wang et al. (2020) revealed that countries with high or medium high income show convergence of carbon intensity; however, countries with medium or low income exhibit insignificant convergence tendency in carbon intensity.