A brackish water source containing high magnesium concentration (333 mg/L as CaCO₃) for reverse osmosis (RO) was studied for silica scaling. Threshold limit for RO recovery and required silica removal were firstly determined by a removal–saturation–recovery curve. Three different ratios of lime/soda ash combination were used to test the efficiency of silica removal as well as the impact of calcium and magnesium. Higher pH was more effective for silica removal due to electrostatic attraction since H₃SiO⁻₄ and H₂SiO⁻²₄ were dominant when pH >9.9. The precipitation of Mg(OH)₂(s) has assisted more for silica removal than that of CaCO₃(s) and the ratio of 0.044 mg SiO₂/mg Mg(OH)₂(s) and 0.027 mg SiO₂/mg CaCO₃(s) were statistically determined. Moreover, the presence of high magnesium causes Mg(OH)₂(s) to precipitate at lower pH (9.41) instead of formation of forsterite (Mg₂SiO₄(s)), which typically occurs at pH >12.3. Therefore, no forsterite was observed and was verified by X-ray diffraction (XRD) analysis. Consequently, adsorption is more dominant than chemical reaction in this study. Silica removal was also enhanced by coagulation. With the addition of coagulant (PACl), highest silica removal was achieved at pH of 10, but was decreased when the pH was over 10, due to the amphoteric properties of aluminum hydroxide to reduce the electrostatic attraction to silica at higher pH. Since both softening and coagulation were effective for silica removal, seven decision-making criteria were developed to compare the pros and cons of these two processes.

In 2019, Taiwan completed its first thorough heavy metal investigation of irrigation canal sediments by this study with the support of Taiwan Environmental Protection Administration. Box-and-whisker plots were used to analyze the sediment distribution and to define metal concentrations. Possible metal pollution sources, the polluted agricultural land, irrigation area, and water sources were also evaluated using spatial analysis to understand the possible causes of sediment pollution. Results showed that the main heavy metal in agricultural land was Cu, found in 77% of contaminated agricultural land sites. Most sites with Cu pollution in sediments were in Taoyuan City and Changhua County. The heavy metals present in the sediment pollution sites in Taoyuan were consistent with those of possible pollution sources upstream, namely, Cr, Cu, and Pb. The main heavy metals in sediment pollution sites in Changhua were Cr, Cu, Ni, Pb, and Zn, whereas those for the polluted agricultural land sites were Cr, Cu, Ni, and Zn, without Pb. The main irrigation water sources in Changhua include drainages and rivers, with some receiving most wastewater pollution mass of release of Changhua, and functions as an irrigation water source with a high release mass in Cr, Cu, Ni and Zn. These findings indicate that the sites of sediment pollution, sites of polluted agricultural land, and the sources of pollution share corresponding heavy metal characteristics. Therefore, in Changhua, the sediments were polluted mainly because (1) the irrigation canals received the highest masses of pollutant releases into drainage wastewater of the county; and (2) the return flow from irrigation and the illegal discharge of wastewater. The preliminary assessment results for sediment pollution in Taoyuan also suggest that the main causes may be irrigation by polluted rivers or drainages and return flows.

In this study, kaolinite, carbon black (CB), iron sulfide (FeS), hydroxyapatite (HAP), and oyster shell powder (OSP) were selected as potentially ideal amendments to immobilize metals in sediment, including Ni, Cr, Cu, Zn, and Hg. In aqueous batch experiments, the five adsorbents were tested for capturing the five potential toxic metals individually at various concentrations. HAP and OSP showed the largest removal efficiencies towards Ni (OSP: 76.47%), Cr (OSP: 100.00%), Cu (HAP: 98.39%), and Zn (HAP: 64.56%), with CB taking the third place. In contrast, FeS and CB played a more significant role in Hg removal (FeS: 100.00%; CB: 86.40%). In the modified six-column microcosm experiments, five mixing ratios based on various considerations using the five adsorbent materials were tested; the water samples were collected and analyzed every week for 135 days. Results showed that caps including CB could immobilize the release of Hg and methylmercury (MeHg) better than those with FeS. More economical caps, namely, with a higher portion of OSP in the mixed capping, could not reach comparable effects to those with more HAP for immobilizing Ni, but performed almost the same for the other four metals. All columns with active caps showed greater metal immobilization as compared to the controlled column without caps.

The Extended Producer Responsibility (EPR) concept involves having producers take environmental responsibility for post-consumer products. Based on this principle, the Waste Electrical and Electronic Equipment (WEEE) Directive of the European Union, enacted in 2006, is the most representative management program in the world and the most popular recycling policy many countries follow. Taiwan’s version of EPR for WEEE recycling, set up in 1998, had a focus on recycling fees determined by a recycling fee equation. Nowadays, the equation takes into account the consideration of the environment in the designs of products, in addition to the cost needed for recycling. The environmental performance upgrades in products, encouraged by the financial incentives from these considerations, is a side-benefit of this program. In this paper, the functions of the recycling fee equation that consider environmental costs are reviewed. It was found that in spite of the difficulty in determining the real environmental costs in practice, pricing is a mechanism which helps us to consider the cost of e-waste recycling, not only in terms of labor and administration, but also environmental quality.

This study assessed heavy metal contents and their mobility, bioaccessibility, environmental risk, and health effects in the farmland soils of Drinking Water Source Quality Protection (DWSQP) areas contaminated by livestock manure and a paddy field contaminated by co-use of irrigation and drainage canals in Taiwan. The risk assessment code (RAC) and synthesis toxicity index (STI) for the soils were obtained. The potential health effects caused from soil direct ingestion by hand-to-mouth activity and dermal contact frequently occurring to farmers were further evaluated. The Cu, Zn, and Cr levels in DWSQP areas and the Changhwa (CH) paddy field exceeded the standards promulgated by Taiwan Environmental Protection Administration (EPA). Nevertheless, RAC in DWSQP areas was in low risk levels. In contrast, RAC from Cu and Zn in CH paddy soils was in medium levels. Non-carcinogenic risks for farmers based on the total and bioaccessible metals in DWSQP areas and CH soils were all <1. However, carcinogenic risks based on bioaccessible Cr still exceeded 10⁻⁶ in several soils, indicating that the potential impacts on environmental and human health due to direct and indirect exposures to these contaminated soils should be concerned.