Effects of fly ash application on soil properties, nutrient status and environment in Northern Thailand

Transcription

1 Symposium no. 4 Paper no. 49 Presentation: poster Effects of fly ash application on soil properties, nutrient status and environment in Northern Thailand INTHASAN J. (), HIRUNBURANA N. (), HERRMANN L. () and STAHR K. () () Department of Soils and Fertilisers, Faculty of Agricultural Production, Maejo University, Chiang Mai, Thailand () Department of Soil Science and Conservation, Faculty of Agriculture, Chiang Mai University, Thailand () Institute of Soil Science and Land Evaluation, Hohenheim University, Stuttgart, Germany Abstract Fly ash is a waste product of the electrical power plant at Mae Mau in Lampang province, northern Thailand. This experiment was conducted in order to study the responses of selected soil types on fly ash applications with respect to chemical properties. The experiment was based on soil samples from two depths, 0-0. m. and 0.- m. depths of three soil series developed on different substrate: Doi Pui (Dp, granite), Ubon (Ub, sandstone) and Takhli (Tk, limestone). Soil samples were mixed with fly ash at rates of 0,.5 and.0 t ha - and incubated for a month at field capacity. Soil reaction ( ph ) was slightly increased in Dp and Ub but decreased in Tk topsoil from 6. to 5.9 with fly ash application. The concentrations of available P and exchangeable K and Na were increased. Calcium and magnesium increased especially in Dp and Ub soil series with low initial amounts and coarser textures. Fly ash application had an influence on the DTPA extractable amount of trace elements. As a general trend, Fe, Mn, Cu and Zn decreased, probably due to a pheffect. A benefit is expected using fly ash as soil amendment in boron deficient soils of Thailand due to a boron content in the fly ash of more than 0 mg kg -. With respect to heavy metals, no consistent effect could be detected since background values a partly higher than concentrations in the fly ash. Usually, at the rate of.5 t ha - fly ash application, an increase of - mg kg - of As, Ni and Co can be expected in the Dp and Tk soil series, whereas Cd and Cr responses were out of the detection limit. As will be the element which restricts fly ash application and should be carefully monitored. Keywords: lignite fly ash, heavy metals, soil amendment, plant nutrition. Introduction Fly ash is a waste product of the electrical power at Mae Mau in Lampang province of northern Thailand. The capacity of electricity produced by this plant is nearly a quarter of the country s need. The lignite-fired power station releases about 0,700 t d - which means 85 % of the total waste output of the electrical power plant Based on information of Electricity Generating Authority of Thailand (EGAT), fly ash is used for brick production, rural road and dam construction. However, the total use 49-

2 7 th WCSS, 4- August 00, Thailand of lignite-fly ash today is still a small proportion compared with the gigantic stock. EGAT is looking for new applications for fly ash without harmful side effects to the environment including animals and mankind. Agricultural use could be a possibility due to nutrient and trace element in the fly ash. But intensive research is required along with field and laboratory experiments in order to identify side effect of fly ash application like heavy metal pollution. Kunavanakrit (99) reported that fly ash contained high amounts of Ca and Mg with a high ph () and a high cation exchange capacity (CEC). Ratanasthien et al. (996) analysed average element concentrations of the fly ash and found: 7% Si, % Fe, 9.8% Al, 6.4% Ca,.4% K,.% Mg and % Na. The concentration of trace elements and heavy metals were also reported with 58 mg kg - Mn, 5 mg kg - Ni, 4 mg kg - Co, 67 mg kg - Cr and 0 mg kg - Mo. According to these results, fly ash can be valuable as fertiliser in agricultural fields. However, the reports on practical use and effects of fly ash on agricultural products and environment are very scarce. Especially, the fate of fly ash heavy metals in the environment i.e. natural water resource contamination including ground water and crop uptake are unknown. The objective of this study is to gather basic information on chemical effects of lignite-fly ash application to various soils. Method and materials Three soils varying in mineral composition were selected from granite, limestone and sandstone landscapes. For the laboratory experiment, fly ash from the lignite deposit at Mae Mau, Lampang province in North-Thailand was used because it represents the largest reserve and is presently used for electricity production. The Doi Pui series (Dp) is characterised by reddish brown soils developed from granite and gneiss rocks in the rolling areas of Pong Yang, Mae Rim district, about 5 km north of Chiang Mai. The Takhli series (Tk) occurs on limestone near Ban Tan about 40 km north-east of the Mae Mau electrical power plant. Slopes are undulating to rolling. The Ubon series (Ub) is developed from alluvial sand on the nearly flat higher parts of the semi-recent terraces. Samples of Ubon soils are from the eastern slope of the Chiang Mai valley near Doi Saket district. Some chemical properties of the untreated soil samples are presented in Table. Table Chemical properties of original soil samples prior to the experiment. Soil series ph OM P K Na Ca Mg Fe Mn Zn Cu HO Bray exchangeable DTPA-extractable--- % mg kg Doi Pui (Dp) 0-0 cm 0-5 cm Takhil (Tk) 0-0 cm 0-5 cm Ubon (Ub) 0-0 cm 0-5 cm

3 7 th WCSS, 4- August 00, Thailand All soils were sampled at depths of 0-0. m and 0.- m. Samples were air-dried and passed through a mm sieve. Topsoil and subsoil samples were mixed with fly ash at rates of 0,.5 and.0 t ha - (0, and 0. gram fly ash * 00 g soil - ). The moisture was adjusted to field capacity and one month incubation followed before soil chemical parameters were determined as followed:. Soil reaction (ph) was registered in water suspension at the ratio soil:h O, :.. Extractable P was determined using Bray II and the concentration measured by spectrophotometer (Watanabe and Olsen, 96).. NH 4 OAc N, ph 7. was used for exchangeable K, Na, Ca and Mg while DTPA, ph 7. (Lindsay and Norvell, 969) was applied for Fe, Mn, Zn and Cu. All these elements were determined by flame AAS. 4. Heavy metals (Pb, As, Ni, Co, Cd and Cr) were extracted by HNO (70%) and HCl (0%) and read by furnace AAS. Results and Discussion Soil reaction and nutrients An increase of soil ph was detected with Doi Pui and Ubon samples which had low initial values and a coarser texture. The effect is more pronounced in the topsoil (Table ). Similar results were reported by Ungsatjaworng (996) applying fly ash in the same region. However, the ph decreased with the limestone Takhli samples, where the topsoil ph dropped from 6.06 to 5.90 and 5.87 with 0,.5 and.0 t ha - of fly ash application. There is no explanation for this fact at present. Available P and exchangeable cations A small but consistent positive effect of fly ash application on available P and exchangeable K and Na can be registered. Similar results were obtained by Fox et al. (967) applying fly ash to sugarcane in Hawaii. Exchangeable Ca and Mg concentrations clearly increased in the soil samples of the primarily poor substrates (Doi Pui and Ubon series), whereas there was no response detected for Ca in the limestone series (Thakli). DTPA extractable elements Even though the fly ash contains high amounts of certain trace nutrients such as Fe (%), Mn (58 mg kg - ) (Ratanasthien et al., 996),its application did not positively affect the availability as measured by DTPA-extraction. Instead, at an application rate of.0 t ha - the fraction dropped by about, 7 and 57% for Fe, Mn and Zn in the sandy Ubon soils respectively. This might be due to ph-effects and should be considered for future applications on certain soil types. In addition fly ash can also lower Mn availability which might be a positive side effect in soils potentially affected by Mn toxicity in northern Thailand. A positive effect can be expected by the boron content of more than 0 mg kg - found in the fly ash from Mae Mau electrical power plant in Lampang province (Hiranburana, unpublished) as measured by hot water extract since most soils of Thailand are low in boron in general. But it has to be considered that the concentration of B in fly ash may vary up to several 00 mg kg - (Dudas, 98; James et al., 98). So before application, the boron content should be determined. 49-

4 7 th WCSS, 4- August 00, Thailand Table Soil chemical properties after fly ash application and one month incubation. Soil series Treatment ph P K Na Ca Mg Fe Zn Mn Cu HO Bray exchangeable DTPA extractable mg kg Doi Pui (Dp) 0-0 cm cm Takhli (Tk) 0-0 cm cm Ubon (Ub) 0-0 cm cm Treatment = 0 t ha - fly ash, Trt =.5 t ha -, Trt =.0 t ha - In order to determine the effects of fly ash application on plant nutrients, experiments should be conducted on on-farm level concentrating on nutrient availability over time. Effect of fly ash on the amounts of heavy metals. Doi Pui and Takhli soils contain a high background concentration of Pb and As and moderate ones of Ni and Co (Table ). The Ubon series has naturally very low heavy metal concentrations. It contains only.5,, 0. and 0. mg kg - Pb, As, Ni and Co respectively. All selected soils show low concentrations of Cd and Cr (<0. mg kg - ). The concentration of Pb in the fly ash is not very high (6.4 mg kg - ). With the given low application rate of.5 to.0 t ha -, the effect on the surface soils is negligible if ph-conditions are maintained. The same is true for most of the other heavy metals. Though the used extraction should represent nearly the total heavy metal concentrations in the samples, no consistent increase could be detected. This might partly be due to the detection limits of our equipment. A hazardous component of the fly ash is As. The lignite fly ash from Mae Mau contains mg kg - (Ratanasthien et al., 996). With fly ash application, an As concentration increase of - mg kg - was detected in Doi Pui and Takhli soils. With repeated applications, the already high background values would exceed acceptable limits. 49-4

5 7 th WCSS, 4- August 00, Thailand Table The amounts of nitric and hydrochloric acid extractable heavy metals after fly ash application. Soil series Treatment Pb As Ni Co Cd Cr Doi Pui (Dp) 0-0 cm mg kg cm Takhil (Tk) 0-0 cm cm Ubon (Ub) 0-0 cm cm Treatment = 0 t ha - fly ash, Trt =.5 t ha -, Trt =.0 t ha Conclusion Lignite fly ash application from the Mae Mau power plant increases the available stock of Ca, Mg, K and P in all examined soils in Northern Thailand. Especially the potential of the fly ash as boron fertiliser should be examined in the future. A consistent positive ph-effects occurs, which leads on the examined soils to a decrease of certain trace nutrients. This effect must be considered on trace element poor sites. The duration of the ph-effect should be addressed in future studies. The major argument against the use of the examined fly ash is the concentration of As. The content of As and B should be determined before any kind of use in agriculture. Acknowledgement The financial support by DAAD, Germany is gratefully acknowledged. References Dudas, M.J. 98. Long-term leachability of selected elements from fly ash. Environ. Sci. Technol. 5: Fox, R.L., J.A Silva, O.R. Younge, D.L. Plucknett and G.D. Sherman Soil and plant silicon and silicate response by sugarcane. Soil Sci. Soc. Am. Proc. : James, W.D., C.C. Graham, M.D. Glascock and A.G. Hanna. 98. Water-leachable boron from coal ashes. Environ. Sci. Technol. 6:

6 7 th WCSS, 4- August 00, Thailand Kunavanakrit, W. 99. General properties of lignite fly ash, pp. -5. In Conference on the Potential of Lignite Fly Ash Utilization. EGAT, Thailand. Lindsay, W.L. and W.A. Norvell Development of a DTPA micronutrient soil test. Agron. Abstracts p. 84: Equilibrium relationships of Zn +, Fe +, Ca +, and H + with EDTA and DTPA in soil. Soil Sci. Soc. Am. Proc. :6-68. Ratanasthien, B., W.S. Fyfe and N.S. McIntyre Element separation in lignite fly ash burning in Mae Moh power plant. Unpublished data, CMU, Chiang Mai, Thailand. Rausch, H., Rozsa Fliszar-Baramyai, Szvetlana Sandor, Ibolya Laszlo-Sziklai, Szabina Torok and Eva Papp-Zenplen. 99. Distribution of toxic elements in fly ash particulate. The Science of the Total Environment. 0/:7-0. Ungsatjaworng, T The effects of fly ash applications on certain properties of soil. Dept. of Soil Science, CMU, Chiang Mai. Thailand. 5 p. Watanabe, F.S. and S.R. Olsen. 96. Calorimetric determination of phosphorus in water extracts of soil. Soil Sci. 9: