Spatial and seasonal distribution of microplastic in surface water of Bueng Boraphet Wetland-a Ramsar wetland in Thailand.

This study sought to assess microplastic contamination in the surface water of the inland freshwater wetland, Bueng Boraphet Wetland, Thailand, which is a lentic system with various land-use patterns, including community areas, agricultural areas, and natural resource conservation areas. In 2019, water samples were collected during the wet and dry periods from the three land-use zones at depths of 0-30 cm using a plankton net with 333 µm in mesh size. The water samples were digested via a wet peroxide oxidation process prior to the identification of microplastic morphology using a stereomicroscope. The polymer types of microplastic were analyzed using Fourier transform infrared spectrophotometry. Microplastic was found to range from 0.00 to 4.61 particles/m2 (0.34 ± 0.81 particles/m2) or 0.0 to 19.57 particles/m3 (1.44 ± 3.4 particles/m3). Furthermore, significantly high amounts of microplastics were found in samples from the community area. No microplastic was detected in the sample from the natural resource conservation area. The quantity of microplastic did not significantly differ between the sampling periods. Polymer types, including polyester, polypropylene, and polyethylene terephthalate, were identified in this study. The microplastics were predominantly small and were colored black or red. Microplastic with a fiber shape (93.8%) was observed. Besides the specific gravity of the microplastic and hydrological characteristics, the high concentration of microplastics found in samples from the community area (0.62 ± 0.79 particles/m2 or 2.63 ± 3.36 particles/m3) is likely related to the high human pressure. As microplastic contamination can impact aquatic animals and wetland ecosystems, appropriate control measures for human activities and plastic waste management are required.

Emerging contaminants in aquatic environments and coastal waters affected by urban wastewater discharge in Thailand: An ecological risk perspective.

Emerging contaminants such as synthetic musks and UV-filters as ingredients personal care products were widely used in human daily life in Thailand. The occurrence and fate of four synthetic musks and nine UV-filters were investigated in eight full-scale sewage treatment plants (STPs) and their receiving aquatic environments in Bangkok and Pattaya, Thailand. All target compounds were detected in every single sample from STPs and surface water with magnitude from ng/L to µg/L. HHCB-lactone and HMS were found as the predominant musk and UV filter in influent and effluent of STPs, respectively. HHCB-lactone was also found with the highest concentration up to 79501 ng/g (dw) in the sludge. Low removal efficiency range from -37% (HHCB-lactone) to 58% (AHTN) were found for four musks in the STPs. The total emission of Σ4musks and Σ9UV-filters were estimated to be up to 16.7 mg/person/day and 0.28 mg/person/day by the STPs. Three synthetic musks and seven UV-filters were detected in fish from the receiving river. Concentration and emission of musks and UV filters found in this study from Thailand were much higher than those reported in many other countries worldwide. The preliminary ecological risk assessment showed that Musk xylene, 4-MBC and OC may pose high risk to aquatic organisms in the riverine and estuarine environment in Thailand.

Occurrence, fate and risk assessment of biocides in wastewater treatment plants and aquatic environments in Thailand.

This study investigated the occurrence and fate of 19 biocides in 8 wastewater treatment plants and receiving aquatic environments (both freshwater and estuarine systems) in Thailand. The predominant compound in wastewater and surface water was methylparaben with the maximum concentration of 15.2 µg/L detected in the receiving river, while in sludge and sediment was triclocarban with the maximum concentration of 8.47 µg/g in sludge. Triclosan was the main contaminants in the fish samples with the maximum concentration of 1.20 µg/g. Similar results of biocides were found in the estuarine system in Pattaya city, with the maximum concentration of 185 ng/L in sea water for methylparaben, and 242 ng/g in estuarine sediment for triclocarban. The aqueous removal rates for the biocides ranged from 15% to 95% in average. The back estimated-usage and total estimated emission of Æ©19 biocides in Thailand was 279 and 202 tons/year, respectively. Preliminary ecological risk assessment showed that clotrimazole and triclosan could pose high risks to aquatic organisms in the receiving aquatic environments.

Inhibition kinetics of salt-affected wetland for municipal wastewater treatment.

A mathematical model was developed in order to describe the system behavior and performance of a constructed wetland (CW) treatment under salt-affected conditions. The rate of biodegradation of organic wastes was modeled using the first-order kinetics while the effect of salt concentrations was accounted by growth inhibition. Experimental data were used to determine model constants of the mathematical model. The experimental units were planted with cattail (Typha angustifolia) and fed with spiked municipal wastewater. The hydraulic retention time varied from 12 to 120 h and wastewater conductivity was in the range of 4-32 mS/cm. At specified conditions the model was found to well describe the trend of the experimental data in terms of BOD removal with the Pearson correlation of 0.872. The model also permits construction of a nomograph which can be used to aid the design and prediction of CW treatment under salt-affected conditions.

Constructed treatment wetland: a study of eight plant species under saline conditions.

A series of investigations was conducted to evaluate the feasibility of using constructed treatment wetlands to remove pollutants from saline wastewater. Eight emergent plants; cattail, sedge, water grass, Asia crabgrass, salt meadow cordgrass, kallar grass, vetiver grass and Amazon, were planted in experimental plots and fed with municipal wastewater that was spiked with sodium chloride (NaCl) to simulate a saline concentration of approximately 14-16 mScm-1. All macrophytes were found tolerant under the tested conditions except Amazon and vetiver grass. Nutrient assimilation of salt tolerant species was in the range of 0.006-0.061 and 0.0002-0.0024 gm-2d-1 for nitrogen and phosphorus, respectively. Treatment performances of planted units were found to be 72.4-78.9% for BOD5, 43.2-56.0% for SS, 67.4-76.5% for NH3-N and 28.9-44.9% for TP. The most satisfactory plant growth and nitrogen assimilation were found for cattail (Typha angustifolia) though the plant growth was limited, whereas Asia crabgrass (Digitaria bicornis) was superior for BOD5 removal. Both were evaluated again in a continuous flow constructed wetland system receiving saline feed processing wastewater. A high removal rate regularly occurred in long-term operating conditions. The reduction in BOD5, SS, NH3-N and TP was in the range of 44.4-67.9%, 41.4-70.4%, 18.0-65.3% and 12.2-40.5%, respectively. Asia crabgrass often provided higher removal especially for BOD5 and SS removal. Nutrient enriched wastewater promoted flourishing growth of algae and plankton in the surface flow system, which tended to reduce treatment performance.