Role of Colocasia esculenta L. schott in arsenic removal by a pilot-scale constructed wetland filled with laterite soil.

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.

Assessment of potential location of high arsenic contamination using fuzzy overlay and spatial anisotropy approach in iron mine surrounding area.

Fuzzy overlay approach on three raster maps including land slope, soil type, and distance to stream can be used to identify the most potential locations of high arsenic contamination in soils. Verification of high arsenic contamination was made by collection samples and analysis of arsenic content and interpolation surface by spatial anisotropic method. A total of 51 soil samples were collected at the potential contaminated location clarified by fuzzy overlay approach. At each location, soil samples were taken at the depth of 0.00-1.00 m from the surface ground level. Interpolation surface of the analysed arsenic content using spatial anisotropic would verify the potential arsenic contamination location obtained from fuzzy overlay outputs. Both outputs of the spatial surface anisotropic and the fuzzy overlay mapping were significantly spatially conformed. Three contaminated areas with arsenic concentrations of 7.19 ± 2.86, 6.60 ± 3.04, and 4.90 ± 2.67 mg/kg exceeded the arsenic content of 3.9 mg/kg, the maximum concentration level (MCL) for agricultural soils as designated by Office of National Environment Board of Thailand. It is concluded that fuzzy overlay mapping could be employed for identification of potential contamination area with the verification by surface anisotropic approach including intensive sampling and analysis of the substances of interest.

Spatial distribution of metals in the constructed wetlands.

Investigation of the spatial distribution of metals was conducted for two constructed wetlands used as tertiary treatment in Chia Nan University of Pharmacy and Science (CNU) and Metal Processing Industries (MPI) located in Tainan, Taiwan. These two distinguished sites were selected to compare the distribution of metals for constructed wetlands treating different types of wastewater. Along the distance, samples of water, sediment, and macrophytes were analyzed for metals including Al, Cd, Cr, Cu, Fe, Mn, Ni, Pb, and Zn. Additionally, measurements of water quality including temperature, pH, EC, ORP, DO, TSS, BOD, COD, and turbidity were performed. Results show that, at CNU, wastewater contained higher organic consititute (BOD 29.3 +/- 11.7 mg/, COD 46.7 +/- 33.6 mg/L) with low metals content. Wastewater at MPI contained low level of organic consititute (BOD 7.1 +/- 3.3 mg/L, and COD 66.0 +/- 56.5 mg/L) and higher metals content. Metals distribution of both sites showed similar results where metals in the sediments in the inlet zone have greater concentrations than other areas. The constructed wetlands can remove Cd, Cu, Ni, Pb, and Zn. However, there was no removal of Al, Cr, Fe, and Mn. A distance along the constructed wetlands had no effect on metal concentrations in macrophyte and water.

A feasibility study of immobilized and free mixed culture bioaugmentation for treating atrazine in infiltrate.

A feasibility study of phosphorylated-polyvinyl alcohol immobilized and free mixed bacterial culture bioaugmentation for removing atrazine in agricultural infiltrate was conducted utilizing a sand column setup. The effects of bacterial cell loading and infiltration rate on atrazine degradation were investigated by short-term tests in which the amount of synthetic infiltrate fed through was five times of the void volume (five pore volumes) of the sand column. In addition, the loss of the inoculated atrazine-degrading cultures and the change of bacterial community were determined. Selected tests were continued for monitoring a long-term performance of the system (50 pore volumes of the sand column). The results indicated that the inoculated cells removed 42-80% of the atrazine. The infiltration rate and cell loading significantly affected the atrazine removal. In the short-term tests, the immobilized and free cells provided similar atrazine removal; however, leaching of the free cells was much greater than that of the immobilized cells. For the long-term performance, only the immobilized cells provided consistent atrazine removal efficiency throughout the test. Both immobilized and free cell systems exhibited a significant change in bacterial community structure during the atrazine degradation experiments. The infiltration rate was a significant factor for the change.

Atrazine removal in agricultural infiltrate by bioaugmented polyvinyl alcohol immobilized and free Agrobacterium radiobacter J14a: a sand column study.

Bench-scale sand column breakthrough experiments were conducted to examine atrazine removal in agricultural infiltrate by Agrobacterium radiobacter J14a (J14a) immobilized in phosphorylated-polyvinyl alcohol compared to free J14a cells. The effects of cell loading and infiltration rate on atrazine degradation and the loss of J14a were investigated. Four sets of experiments, (i) tracers, (ii) immobilized dead cells, (iii) immobilized cells, and (iv) free cells, were performed. The atrazine biodegradation at the cell loadings of 300, 600, and 900 mg dry cells L(-1) and the infiltration rates of 1, 3, and 6 cm d(-1) were tested for 5 column pore volumes (PV). The atrazine breakthrough results indicated that the immobilized dead cells significantly retarded atrazine transport. The atrazine removal efficiencies at the infiltration rates of 1, 3, and 6 cm d(-1) were 100%, 80-97%, and 50-70%, respectively. Atrazine degradation capacity for the immobilized cells was not significantly different from the free cells. Both infiltration rate and cell loading significantly affected atrazine removal for both cell systems. The bacterial loss from the immobilized cell system was 10-100 times less than that from the free cell system. For long-term tests at 50 PV, the immobilized cell system provided consistent atrazine removal efficiency while the atrazine removal by the free cells declined gradually because of the cell loss.

Effects of iron type in Fenton reaction on mineralization and biodegradability enhancement of hazardous organic compounds.

The mineralization and biodegradability increase and their combination of two traditional and two relatively new organic contaminants by Fenton reagents with three different types of iron, Fe(2+), Fe(3+), and Fe(0) were investigated. The traditional contaminants examined were trichloroethene (TCE) and 2,4-dichlorophenol (2,4-DCP) while 1,4-dioxane (1,4-D) and 1,2,3-trichloropropane (TCP) were studied for the relatively new contaminants. The mineralization and biodegradability were represented by dissolved organic carbon (DOC) reduction and the ratio of biodegradable dissolved organic carbon and DOC, respectively. For all four contaminants, Fenton reagent using Fe(2+) was more effective in the DOC reduction than Fenton reagents using Fe(3+) and Fe(0) in most cases. The types of Fe that provided maximum biodegradability increase were not the same for all four compounds, Fe(3+) for TCE, Fe(0) for 2,4-DCP, Fe(2+) for 1,4-D, and Fe(3+) for TCP. When the combination of DOC elimination and biodegradability increase (least refractory fraction) was considered, Fe(2+) was the best choice except for 2,4-DCP which was susceptible to Fe(0) catalyzed Fenton reagent the most. The least refractory fractions remaining after 120 min of reaction were 20-25% for TCE, 2,4-DCP, and TCP and 30-40% for 1,4-D. The iron type in Fenton reaction also affected the type of mineralization kinetics of TCE, 2,4-DCP, and TCP as well as the types of degradation by-products of these contaminants. Some of the by-products found, such as isopropanol and propionic aldehyde, which were produced from Fe(0) catalyzed Fenton degradation of TCP, have not been previously reported.

Atrazine remediation in agricultural infiltrate by bioaugmented polyvinyl alcohol immobilized and free Agrobacterium radiobacter J14a.

Bench-scale sand column breakthrough experiments were conducted to examine atrazine remediation in agricultural infiltrate by Agrobacterium radiobacter J14a (J14a) immobilized in phosphorylated-polyvinyl alcohol compared to free J14a cells. The effects of cell loading and infiltration rate on atrazine degradation and the loss of J14a were investigated. Four sets of experiments, i) tracers, ii) immobilized dead cells, iii) immobilized cells, and iv) free cells, were performed. The atrazine bioremediation at the cell loadings of 300, 600, and 900 mg dry cells l(-1) and the infiltration rates of 1, 3, and 6 cm d(-1) were tested for 5 column pore volumes (PV). The atrazine breakthrough results indicated that the immobilized dead cells significantly retarded atrazine transport. The atrazine removal efficiencies at the infiltration rates of 1, 3, and 6 cm d(-1) were 100%, 80-97%, and 50-70% respectively. Atrazine remediation capacity for the immobilized cells was not significantly different from the free cells. Both infiltration rate and cell loading significantly affected atrazine removal for both cell systems. The bacterial loss from the immobilized cell system was 10 to 100 times less than that from the free cell system. For long-term tests at 50 PV, the immobilized cell system provided consistent atrazine removal efficiency while the atrazine removal by the free cells declined gradually because of the cell loss.

Soil erosion and its impacts on water treatment in the northeastern provinces of Thailand.

The economy of Northeast Thailand is mainly based on agriculture. The transformation of forestlands to agricultural areas and the encroachment of riverbanks within the Phong watershed have caused severe soil erosion. Strong storms in rainy season exacerbate the problem of soil erosion. Difficulty in getting water drives people in the upstream region to live on riverbanks. Soil erosion affects water utility by increasing the turbidity in the Phong River and also by decreasing the water storage capacity of small reservoirs for the upstream residents, as well as that of the Ubolratana Dam. The rate of siltation in the Ubolratana Dam was estimated to be 1.5 million tons/year during 1965-1990. The main source of water supply is surface water in the Phong watershed, and fluctuating turbidity makes water treatment difficult. The maximum turbidity in the upstream Phong River exceeds 5000 NTU, whereas it is reduced to be about 300 NTU at the intake point of Khon Kaen Municipal Water Treatment Plant because the Ubolratana Dam works as a huge clarifier. Khon Kaen Municipal Waterworks has a daily water supply of 72,960 m3/day. The average amounts of alum used in the wet (May-October) and dry (November-April) periods are 42.33 g/m3 and 28.46 g/m3, respectively. The average costs of the amounts of alum used are 0.213 and 0.143 Bahts/m3 during the wet and dry periods, respectively. Fluctuation of turbidity in raw water makes it difficult to adjust alum dose, resulting in treated water quality unstable, and handling of sludge disposal difficult.

Degradation and detoxification of formaline wastewater by advanced oxidation processes.

In this study, advanced oxidation processes (AOPs) utilizing the combinations of UV/H(2)O(2), Fenton, photo-Fenton and the combination of Fenton/photo-Fenton reactions were investigated in lab-scale experiments for the degradation of formaline wastewater. The studied toxic chemicals were formaldehyde and methanol in mixture solution, so-called formalin, which is the embalming agent in mortuaries. The experimental results showed that the photo-Fenton process was the most effective treatment process among the studied AOPs. Pseudo-first-order degradation rate constants of formaldehyde and methanol were obtained from batch experimental data. In the combination of Fenton/photo-Fenton reactions, the results show that applying UV light at an early stage of the reaction might not be necessary for a speedy oxidation reaction of the Fenton process. With Fenton and photo-Fenton processes, mineralization of formaline wastewater can be achieved, as no residual TOC is detected in the effluent after the reaction period. It is suggested that Fenton and photo-Fenton processes are viable techniques for the formaline wastewater treatment as they were able to provide high degradation of formaldehyde and methanol with relatively low toxicity of the by-products in the effluent.