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Dissolved oxygen (DO) in Lam Takhong River gradually reaches zero value during the dry season on several occasions in the past decade causing the unsuitable quality for use as the raw water for Nakhon Ratchasima Town. Discharges of point sources and diffuse sources containing pollutants with organics and nutrients are the major cause of water quality deterioration in the river. To find the sources of impact on the water quality in the river, a one- dimensional steady-flow systems river water quality model, QUAL2Kw, was constructed and simulated. The model was calibrated and validated using the water quality data from 2008 to 2017 for the Lam Takhong River by seven monitoring stations. The modelling was applied to simulate various water quality parameters during the critical period to compare to the designated surface water quality criteria third class in Thailand (minimum dissolved oxygen at or above 4 mg/L; maximum biochemical oxygen demand (BOD), nitrate-nitrogen, and ammonia-nitrogen at or below 2.0, 5.0 and 0.5 mg/L, respectively). The study reach of the river flows 122 km from Lam Takhong Dam to the Mun River at Chaloem Phra Kiat district through the urban central area. Several segments of the river have been alarmed for many constituents with the dissolved oxygen impairment is the focus of the study. The scenarios of loads and upstream dissolved oxygen modification were conducted to assess the change of dissolved oxygen concentration. The result of the QUAL2Kw model showed that the decomposition of organic matter and a poor reaeration were the primary cause of the impairment. The local oxygenation causes fluctuations in dissolved oxygen levels along the river and the dissolved oxygen concentration decreases downstream of the river with some values fell the meet the fourth class of surface water quality criteria in Thailand (DO above 2 mg/L and BOD5

Arsenic-polluted water is a global concern and puts millions of people at risk of developing cancer. The improvement of aqueous solution coexisting with arsenite and arsenate using iron mixed porous clay pellets was investigated in batch and fixed-bed column systems. Batch studies showed that the removal rate occurred in two main phases with an equilibrium time of 52 h. The pseudo-second-order model well described the experimental data. Isotherm data were well fitted by the Langmuir–Freundlich model. The removal efficiency was significantly reduced in alkaline solution and the presence of phosphate ions. The column study revealed that the breakthrough time and saturation time increased with lower feeding flow rate, higher bed height, and lower initial adsorbate concentration. The Thomas model provided good performance for predicting the column experimental data.

Naresuan University Journal: Science and Technology, 29, 3, 78-95

This research aims to identify the role of natural wetlands in arsenic (As) removal. Phu Lek wetland in Loei Province, Thailand, was selected as the study area. Monthly samples of water (144), plant (360), and sediment (144) were collected from the wetland for 24 months. As concentration in the surface water at the wetland inlet was 0.85±0.26 mg L-1, and 0.02±0.01 mg L-1 at the wetland outlet. It was observed that the As level in water decreased significantly along its flow path, with an As removal efficiency of 98 %. As concentration in the sediment was 89.53-356.22 mg kg-1 at the inlet of wetland, but decreased gradually downstream of the water flow. Three dominant emergent plant species were observed in this wetland. As accumulation (0.02-2.37 mg kg-1) was noted in all the parts of the three plant species. As content was the highest in the rootlet (0.00-1.27 mg kg-1) compared to that in foliage (0.00-0.84 mg kg-1), leaf stalk (0.00-1.86 mg kg-1), and rhizome (0.00-2.64 mg kg-1). The level of As in the different vegetation species was in the order Diplazium esculentum > Colocasia esculenta > Lasia spinose. Further, As entrapment in the different plant plants followed the order rootlet > rhizome > foliage > leaf stalk. All the three plant species showed high bioconcentrationfactors, with values of 0.03-1.28, 0.02-0.93, 0.00-0.84, and 0.00-0.38at the rootlet, rhizome, foliage, and leaf stalk, respectively, but had low translocation factors (foliage/rootlet: 0.02-0.90 and leaf stalk/rootlet: 0.00-0.44). In summary, As present in the surface water could be effectively removed by the wetland system.

Many people in Cambodia consume groundwater with arsenic concentrations above the WHO guideline. In this study, an iron-mixed porous pellet adsorbent was put into a lightweight bio-sand filter to treat arsenic. The filter was intermittently charged daily with 30 L influent water until the effluent arsenic concentration exceeded 10 μg/L. The results indicated that the Morrill Dispersion Index was less than 2.0, implying that the filter had preferential plug flow. Head loss accumulation led to flow rate reduction over a period of 30 days. Arsenic removal efficiency was between 97 and 99% for the influent concentration, being in the range 355 to 587 μg/L. No significant leaching of iron or organic carbon was observed. The high dissolved oxygen concentration is likely to have contributed to the aerobic conditions in the filter bed. The filter removed arsenic more efficiently than was achieved in some previous studies and might be suitable to provide household-scale, arsenic-safe drinking water.

Water pollution is largely associated with the growth of agriculture, urbanization, and industrialization. By the year 2016, the quality of significant surface water sources in Thailand has been evaluated and categorized as 34% good quality, 46% fair quality and 20% poor quality. According to the Pollution Control Department of Thailand, the lower Lam Takong river, one of the critical watersheds of Thailand, is considered to have a poor water quality. In Lam Takong watershed, non-point sources area approximately covered 89% of the total area, those sources became the significant contributors of water pollutants, particularly nutrients to the Lam Takong watershed. Plus, water quality researches of the watershed were carried out with many different watershed models, but the SWAT model has not been applied to allot the pollutant loading from diffuse sources. Therefore, the main objective of this study is to apply the SWAT model to simulate flow and nitrate from 2007 to 2017, and allocate NO3- loading in upstream is lower than downstream of the Lam Takong watershed. The R2 values are 0.69 in upstream and 0.64 in downstream of Lam Takong. The results of the study can be a useful tool for the management of surface water resources in the Lam Takong watershed.

The role of plant Colocasia esculenta L. schott (C. esculenta) in arsenic removal was investigated in a pilot-scale constructed wetland (PCW), which was filled with laterite soil (19.90–28.25% iron by weight). This PCW consists of 2 sets of flow systems in parallel, with C. esculenta planted at a density of 20 plants/m2 in one system and the other without any plants. The synthetic water containing arsenic concentration of 0.50 mg/l, with its pH controlled at 7.0 and influent flow at 1.5 m3/day. With C. esculenta, the arsenic in water decreased from 0.485 mg/l to 0.054 mg/l (89% removal), whereas, without C. esculenta, the arsenic decreased from 0.485 mg/l to 0.233 mg/l (52% removal). As for the fate of the influent arsenic, the C. esculenta was responsible for 65% of arsenic accumulation. Note that the arsenic was found mostly within the root zone depth (20–40 cm). It appears that such a high capacity of arsenic removal was enhanced both by the plants through rhizostabilization and by the iron-adsorbed process within the laterite soil bed. In addition, the arsenic removal was observed to increase along with the time from 30 to 90 days, and it reached to a maximum removal around 90 days, and then decreased after 122 days. Thus, the arsenic removal efficiency including mechanisms founded can then be applied in designing of constructed wetland for arsenic treatment from gold mine drainage with similar site/soil characteristic.

EnvironmentAsia, 12, special, 64-73

The role of plant Colocasia esculenta L. schott (C. esculenta) in arsenic removal was investigated in a pilot-scale constructed wetland (PCW), which was filled with laterite soil (19.90–28.25% iron by weight). This PCW consists of 2 sets of flow systems in parallel, with C. esculenta planted at a density of 20 plants/m2 in one system and the other without any plants. The synthetic water containing arsenic concentration of 0.50 mg/l, with its pH controlled at 7.0 and influent flow at 1.5 m3/day. With C. esculenta, the arsenic in water decreased from 0.485 mg/l to 0.054 mg/l (89% removal), whereas, without C. esculenta, the arsenic decreased from 0.485 mg/l to 0.233 mg/l (52% removal). As for the fate of the influent arsenic, the C. esculenta was responsible for 65% of arsenic accumulation. Note that the arsenic was found mostly within the root zone depth (20–40 cm). It appears that such a high capacity of arsenic removal was enhanced both by the plants through rhizostabilization and by the iron-adsorbed process within the laterite soil bed. In addition, the arsenic removal was observed to increase along with the time from 30 to 90 days, and it reached to a maximum removal around 90 days, and then decreased after 122 days. Thus, the arsenic removal efficiency including mechanisms founded can then be applied in designing of constructed wetland for arsenic treatment from gold mine drainage with similar site/soil characteristic.

Natural clay combing with iron oxide and iron particle was developed to be iron-mixed mesoporous pellet that was packed in a fixed-bed column for removing arsenic from water. The performance of the column in terms of breakthrough curve analysis was investigated with the variations of influent flow rate, adsorbent bed height, initial solution pH, and initial adsorbate concentration. The results indicated that increasing in the flow rate decreased the removal capacities of the adsorbent. A relatively low bed height provided a better and beneficial performance. Higher adsorption capacity was observed with an increase of initial adsorbate concentration. At higher initial solution pH, the repulsive process occurred between adsorbate species and the surface charge of the adsorbent, resulting in a poor performance of the column. The Thomas model fitted very well to the experimental data for all cases. Estimated from the model, the highest adsorption capacity for arsenite and arsenate was found to be about 509 and 430 μg/g, respectively. The Adam-Bohart model provided only a relatively satisfactory fit to the initial part of the experimental data. From a practical view, the new developed pellet could be used as the effective and efficient adsorbent to treat elevated arsenic contaminated groundwater.

In this study, natural clay, iron oxide, and iron powder were combined to develop low-cost iron mixed porous pellet adsorbent for arsenate and arsenite removal from aqueous solution in batch experiments. The augmented simplex centroid mixture design was applied to obtain the optimum proportion of each constituent. Higher correlation coefficient of the models (R2 > 0.95), good distribution of residuals, and lower values of p value ( 9). Kinetic and isotherm experimental data of both arsenate and arsenite were well described by the pseudo-second order and Sips models, respectively. The maximum adsorption capacity of arsenate and arsenite derived from Sips model were 13.33 and 19.06 mg/g, respectively. The separation and heterogeneity factors showed that both arsenate and arsenite were favorably adsorbed. Among coexisting anions, phosphate significantly showed negative effect on the adsorption of either arsenate or arsenite. The adsorbent could be effectively reused for several times after its regeneration and was considered as non-hazardous material after adsorption.

Millions of people in more than 70 countries are at risk of developing arsenicosis and otherhealth issues due to consuming elevated arsenic contaminated water. The present study aimed to use naturalclays heated at high temperature and treated with ferrous and ferric solutions through a simple coatingtechnique enhanced by moderate temperature for arsenate uptake from water. BET, XRF, XRD and SEMmethods were applied for the adsorbent characterization. Adsorption experiments were conducted in a seriesof batch systems in terms of contact time, solution pH, initial concentration and the presence of coexistinganions. The results indicated that the adsorption kinetics was better described by the pseudo-second order ratemodel for all adsorbents. All adsorbents exhibited higher arsenate uptake efficiency in the acidic condition.Langmuir model provided the maximum arsenate adsorption capacity of 250µg/g, 429.74µg/g and747.38µg/g for calcined clay (MC), ferric calcined clay (MC-FeIII) and ferrous calcined clay (MC-FeII),respectively. Among added coexisting anions, phosphate (PO3-) significantly decreased the arsenateadsorption capacity of all adsorbents. Overall, regarded to a wide availability of raw materials, simplicity ofthe modification and improvement of arsenate adsorption capacity, modified natural clay adsorbents,especially MC-FeII, could be considered to be effective and low-cost to remove arsenate from water.

This study evaluated environmental factors affecting on sediment and nutrient loads in Lam Takong River basin, Northeastern region of Thailand, using the results of SWAT (Soil and Water Assessment Tool) model. The simulation from 2007-2009 showed that mean annual sediment, NO3-N and TP at the outlet were 8.134 t/ha, 0.879 kg/ha and 1.213 kg/ha, respectively. Seven factors were significantly related to soil erosion including slope, elevation, agriculture, wetland, deciduous forest, evergreen forest and orchard. In addition, two factors were significantly related to NO3-N including surface runoff and urban area. Finally, four factors were significantly related to TP including surface runoff, elevation, deciduous forest and orchard. Modification of these factors can reduce sediment and nutrient loads in this basin.

Broken mesoporous ceramic filter was reutilized by coating with ferric solution through a simple loading method enhanced with heating at a moderate temperature for arsenate uptake from aqueous solution. BET, XRF, XRD, and SEM methods were applied for the adsorbent characterization. The adsorption study was conducted in a batch mode to investigate kinetics, isotherms, and the effect of solution pH and co-existing anions. The pseudo-second order kinetic model well fitted the experimental data (R2 = 0.9997). The maximum arsenate adsorption capacity (2.27 mg/g) was derived from the better described Langmuir isotherm model (R2 = 0.9992). The adsorbent expressed high arsenate adsorption capacity over a pH range of 4-10. The uptake behavior is a favorable and physical adsorption process based on the value of separation factor and mean sorption energy. The presence of co-existing anions decreased the arsenate adsorption capacity in the following order: NO3-< SO42- < PO43-. The new ferric-coated mesoporous ceramic adsorbent could be an effective and low-cost adsorbent for arsenate removal from water.