Chongrak Polprasert

Evaluation of phosphate fertilizers for the stabilization of cadmium in highly contaminated soils.

The efficiency of three phosphate fertilizers including triple superphosphate (TSP), diammonium phosphate (DAP), and phosphate rock (PR) as stabilizing agents of cadmium-contaminated soils has been assessed in this study. Two types of assessment criteria, (a) the reduction of leachable cadmium concentration; and (b) the changes in Cd association with specific operational soil fraction based on the sequential extraction data, are used in the evaluation of stabilization performance of each fertilizer. Results of the study showed that after the 60-day stabilization, the leachable concentrations of Cd in PR-, DAP- and TSP- treated soils reduced from 306 mg/kg (the control) to 140, 34, and 12 mg/kg with the stabilization efficiency as TSP>DAP>PR. Results from the assessment of Cd speciation via sequential extraction procedure revealed that the soluble-exchangeable fraction and the surface adsorption fraction of Cd in the soils treated with PO(4) fertilizers, especially with TSP, have been reduced considerably. In addition, it is found that the reduction was correspondingly related with the increase of more stable forms of cadmium: the metal bound to manganese oxides and the metal bound to crystalline iron oxides. Treatment efficiency increased as the phosphate dose (based on the molar ratio of PO(4)/Cd) increased. In addition, it was observed that stabilization was most effective when using the molar ratio of PO(4)/Cd at 2:1 and at least 21-day and 28-day stabilization time for TSP and DAP, respectively.

Paraquat Adsorption, Degradation, and Remobilization in Tropical Soils of Thailand

Paraquat adsorption, degradation, and remobilization were investigated in representative tropical soils of Yom River Basin, Thailand. Adsorption of paraquat in eight soil samples using batch equilibration techniques indicated that adsorption depended on soil characteristics, including exchangeable basic cations and iron content. Multiple regression analysis indicated significant contribution of exchangeable calcium percentage (ECP), total iron content (TFe) and exchangeable sodium percentage (ESP) to paraquat sorption (Q). ESP and TFe were significant at all adsorption stages, whereas ESP was significant only at the initial stage of paraquat adsorption. Adsorption studies using two soils representing clay and sandy loam textures showed that paraquat adsorption followed the Freundlich model, exhibiting a nonlinear sorption curve. Paraquat adsorption was higher in the clay soil compared to the sandy loam soil with K f values of 787 and 18, respectively. Desorption was low with 0.04 to 0.17% and 0.80 to 5.83% desorbed in clay and sandy loam soil, respectively, indicating some hysteresis effect. Time-dependent paraquat adsorption fitted to the Elovich kinetic model indicated that diffusion was a rate-limiting process. Paraquat mobility and degradation studies conducted using both field and laboratory soil column experiments with clay soil showed low mobility of paraquat with accumulation only in the surface 0–5 cm layer under field conditions and in the 0–1 cm layer in a laboratory soil column experiment. Degradation of paraquat in soil was faster under field conditions than at ambient laboratory conditions. The degradation rate followed a first-order kinetic model with the DT50 at 36–46 days and DT90 around 119–152 days.

AN INTEGRATED KINETIC MODEL FOR WATER HYACINTH PONDS USED FOR WASTEWATER TREATMENT

Water hyacinth (Eichhornia crassipes) is a floating aquatic plant which has been employed for wastewater treatment in many parts of the world. By planting water hyacinth in a wastewater pond, part of the gaseous oxygen produced by photosynthetic activity of the green leaves is translocated to the stems and roots and to the water body; this oxygen is used by the aerobic and facultative bacteria in biodegrading organic matter contained in the wastewater. Two groups of bacteria normally exists in a water hyacinth pond (WHP), namely the suspended bacteria which are present in the liquid portion and the biofilm bacteria which are attached on the surfaces of the roots of the water hyacinth plants and on the side walls and bottom layers of the pond itself. Current design criteria for WHPs do not emphasize the roles of these two groups of bacteria, but they are based on either empirical relationships or first-order reaction rate and complete-mix flow condition. This study attempts to show the significance of both the suspended and biofilm bacteria and the flow hydraulics (based on dispersion number) in the reduction of organic matter in the WHP system. Kinetic coefficient of the suspended bacteria was calculated from a first-order reaction rate including the effect of organic loading rate. For the biofilm bacteria, the reaction rate was also first-order and based on the substrate flux into the biofilm. The integrated kinetic model proposed for the WHP incorporates the activities of both the suspended and biofilm bacteria and the hydraulic dispersion number. The model was found to be satisfactory in predicting biochemical oxygen demand (BOD) removal in a full-scale WHP treating an anaerobic pond effluent. Design guidelines and an operating strategy to achieve improvement in BOD removal efficiency in WHP are given.

Heavy metal pollution in the Chao Phraya River estuary, Thailand

Abstract A study on heavy metal pollution in the Chao Phraya River estuary indicated that the accumulation of Cd, Cu, Cr and Pb in water in the river mouth vicinity was significant, which may have a long term impact on the aquatic environment through precipitation of heavy metals to the bottom sediments and bio-accumulation and bio-magnification of heavy metals in various food chains. Although the seasonal and spatial variations of heavy metals in the sediments and fish did not conform to a definite pattern, the heavy metal contents of samples were higher than those previously reported in the area and in some cases were higher than the mean world concentrations. Thus, Thai people may ingest Hg and Pb in fish in the Chao Phraya River estuary at quantities more than those reported for other countries.

Influence of condensed silica fume on the properties of cement-based solidified wastes

Influence of condensed silica fume (CSF) addition as cement replacement material on the properties of cement-based solidification products was investigated. Final setting, unconfined compressive strength, and leachability of the synthetic lead and chromium hydroxides were determined. CSF was used at 0, 5, 10, and 20 wt.%. substitution for Portland cement. A water-to-solid ratio (w/s) of 0.45 was used for all mixes. Experimental results showed that the severe retardation effect on ordinary Portland cement (OPC) hydration caused by lead hydroxide has been minimized due to the pozzolanic effect and, as a result, the time to final setting has been significantly reduced. In addition, compressive strength of the solidified wastes was increased to the highest with 10% cement replacement but decreased to lower than the one without CSF at 20% replacement. Leaching of the amphoteric lead and chromium hydroxides is primarily determined by leachate pH and therefore lead was found in the leachates at higher concentration than chromium.

Assessment of metal speciation evolution in sewage sludge dewatered in vertical flow reed beds using a sequential extraction scheme

Abstract An investigation was carried out into the speciation of metals contained in an industrial sewage sludge dewatered in vertical flow reed beds as compared to conventional sand drying beds. The highly contaminated sludge was loaded for two consecutive months and the dewatered sludge layers were monitored periodically during an ageing period of 15 months. Metal speciation was assessed by means of sequential extraction. The raw sludge was characterised by high metal mobility. 445 mg kg−1 dry matter (DM) Mn (70% of total Mn), 632 mg kg−1 DM Ni (42% of total Ni), 11,246 mg kg−1 DM Fe (32% of total Fe), 2,315 mg kg−1 DM Zn (19% of total Zn) and 258 mg kg-1 DM Pb (14% of total Pb) were retrieved in the exchangeable and acid extractable fractions. Cu and Cr were less mobile, with 24 mg kg−1 DM Cu (1.2% of total Cu) and 7 mg kg−1 DM Cr (0.8% of total Cr) occuring in these fractions. Upon sludge ageing, all metals except copper, were greatly immobilised in the oxidisable, reducible and residual fractions. However, considerable amounts remained mobile, posing environmental threats upon final disposal of the dewatered sludge.

The inactivation of faecal coliforms and Ascaris ova in faeces by lime

Abstract The inactivation effects of lime, when applied to faeces on faecal coliform bacteria and Ascaris lumbricoides ova, were investigated in the laboratory. A faecal coliform inactivation of about 5 orders of magnitude could be achieved at 19 g CaO l −1 (or initial sample pH of 12) and contact times over a 3 h period, while negligible reduction of faecal coliform bacteria was obtained at 5.7 g CaO l −1 (or initial sample pH of 9) with contact times from 3 to 48 h. However, only a 26.5% reduction of Ascaris ova was observed with 19 g CaO l −1 and a contact time of 48 h. Microscopic examination of the treated samples suggested the ovicidal effects of lime upon the Ascaris ova was of a low efficiency.

Mercury emission and distribution: Potential environmental risks at a small-scale gold mining operation, Phichit Province, Thailand

Mercury (Hg) contamination was assessed in environment near an amalgamation gold recovery operation located at a small scale mining operation (Phanom Pha) in Phichit Province, Thailand. Total mercury (THg) concentrations was determined in water, sediment, bivalves in the aquatic environment and as dry deposition or atmospheric fallout on surface soil and leaves of Neem tree (Azadirachta indica Juss. var. siamensis Valeton) near the mining operation. THg in surface soil, Neem flowers (edible part) and rice grain in surrounding terrestrial habitat and with distance from the mining area were also evaluated for possible contamination. Potential environmental risks were evaluated using the hazard quotient equation. Hg analyses conducted in the aquatic habitat showed that THg in water, sediment and bivalves (Scabies cripata Gould) ranged from 0.4 to 4 μ g L− 1, 96 to 402 μ g kg− 1dry weight (dw) and 15 to 584 μ g kg− 1 wet weight (ww), respectively. High concentrations of THg in water, sediment and bivalves were observed in the receiving stream near the mining operation which was located near the Khao Chet Luk Reservoir. Whereas the THg concentration in water, sediment and bivalves from monitoring stations outside the gold mining operation (upstream and downstream), were considerably lower with the values of 0.4–0.8 μ g L− 1, 96–140 μ g kg− 1 dw and 88–658 μ g kg− 1 dw, respectively. The elevated concentration of Hg found in the sediment near the mining operation was consistent with Hg accumulation measured in bivalves. The elevated Hg levels found in living bivalves collected from highly contaminated sites suggested that the sediment bound Hg was bioavailable. THg in surface soils, brown rice grain (Jasmine rice #105) and Neem flowers of terrestrial habitats were in the range of 16 to 180 μ g kg− 1 dw, 190 to 300 μ g kg− 1 dw, and 622 to 2150 μ g kg− 1 dw, respectively. Elevated concentrations of mercury were found in Neem flowers with the concentration greater than 600 μ g kg− 1 ww, which exceeds the maximum permissible concentration reported for biota tissue (500 μ g kg− 1 ww). An evaluation of air and soil pollution near the mining operations showed high concentrations of THg in dry deposit from atmospheric fallout (139 μ g m− 2 d− 1), and in surface soil (10,564 μ g kg− 1 dw) at station near where open burning of gold ore extracts using the amalgamation process occurred. High or elevated concentration of THg (1172–1301 μ g kg− 1 dw) in leaves of Neem tree was also measured near the mining operations. A survey of Hg in surface soil showed elevated Hg concentrations near the site which corresponded to the elevated THg concentration in dry deposition. These results suggested that atmospheric fallout is a major source of Hg to the area surrounding the mining or gold ore extraction. Results also suggest that Hg emitted into the air (estimated to be 60–150 g d− 1) from the gold mining activities (over the past 10 years) contaminated air, the aquatic environment, surface soil and biota in the area surrounding the gold mining operation.

Phosphorus adsorption characteristics of oyster shells and alum sludge and their application for nutrient control in constructed wetland system.

This research aimed to evaluate the feasibility of employing some locally available oyster shells (OS) and alum sludge (AS) as the P adsorption media of constructed wetland beds. The batch and column tests were conducted with different sizes of OS and AS to observe the P adsorption characteristics and breakthrough, while P adsorption rates were determined from jar test. From the batch test, the ability to adsorb the amount of added P was different considerably between OS and AS media and sizes. At the same size, the P adsorption capacities of OS were higher than those of alum sludge. The P adsorption capacities of AS with 0.3–0.6 mm and > 0.6 mm sizes were similar, but those of 0.3–0.6 mm OS was higher than > 0.6 mm OS. Jar test results revealed the first-order P removal rates (k) to be 11.4, 4.5, 1.7 and 1.0 d− 1 for the 0.3–0.6 mm AS, > 0.6 mm AS, 0.3–0.6 mm OS, and > 0.6 mm OS, respectively. From the column tests, the adsorption capacities were found to be more than 26 and 24.5 g/kg for the OS media sizes of 0.3–0.6 and > 0.6 mm, respectively, and 12 g/kg for the AS media. The column tests revealed that AS was able to adsorb P faster than the oyster shells, but due to its low adsorption capacity, the periods of P breakthrough in the effluent of the alum sludge columns were shorter than those of the oyster shell columns. Experiments with a pilot-scale vertical-flow subsurface constructed wetland unit packed with > 0.6 mm OS media demonstrated the high P removal efficiencies of more than 96.2% during the 210 days of operation.

Hazardous waste generation and processing

Abstract A waste is considered hazardous if it exhibits one or more of the following characteristics: ignitability, corrosivity, reactivity and toxicity. This paper reviews the sources of hazardous waste generation which come mainly from industries. The major types of hazardous wastes are toxic organic compounds and heavy metals. Up to the present, the developed countries such as USA, Japan and many European countries are the major hazardous wastes generators, while increasing quantity of hazardous wastes is being generated by the newly industrialized countries (NICs). To minimize hazardous waste disposal problems, certain technologies to reduce waste quantity are recommended. These technologies include; in-plant minimization, raw material alteration, equipment redesign, improved housekeeping and product substitution. Some proven hazardous waste processing and treatment technologies are described in the paper.