Sewage sludge amendment for acid sulfate soils | |
| Author | Katerachada Klankrong |
| Call Number | AIT Diss no.EV-02-04 |
| Subject(s) | Sewage sludge Acid sulphate soils |
| Note | A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Engineering, School of Environment, Resources and Development |
| Publisher | Asian Institute of Technology |
| Abstract | The potential leachability of metals from sewage sludge amended soil is of great importance in enhancing contamination of the metals to groundwater. Evaluation of those potential leachability, bioavailability and accumulation following sludge applied to agricultural soil would be focused in this study. In addition, geochemical forms of sludgeamended soil were also subjected to fractionate using a sequential extraction procedure to better understanding of their potential remobilization. The potential leachability was obtained by soil column leaching test technique from reconstructed soil profile where dewatered sewage sludge was incorporated into the 10-cm soil depth. Two-sludge application rates; 150 and 300 kgN/ha, were applied to two typical types of agricultural clay soil in Thailand; Rangsit soil (acid soil) and Thonburi soil (neutral to slightly alkaline soil). These soil columns were leached with 32 liters equivalent to 600 mm by different leachants in the range of pH 3 - 6.5. Mn leachability was the highest in both sludge application rates from sludge amended Rangsit soil. With Thonburi soil, Cd had the highest leachability at both rates. Results from the experiments indicated that varied pH (3 - 6.5) of leaching solution had much less effect on potential leachability. Leachability of elements from soil column depends on a rate of sludge applied, element itself, linkage forms of metals associated with soil constituents and soil properties such as organic matter, CEC, soil pH and minerals in soil, which have led to high buffering capacity of soils. Focusing on Cu and Zn in soil column found that close to 100% of the added metals from sludge was recovered within 10 cm depth at both application rates. As a result of lysirneter experiment ( 40-cm soil depth), Chinese kale grown in sewage sludge treatment at the rate of 150 kgN/ha gave a yield equivalent to 94 kgN/ha of chemical fertilizer treatment. Soil pH is considered as a main effect responsible for metal solubility and availability for plant uptake and growth. Yields of plant increase with increasing soil pH. Therefore, Rangsit soil (soil pH 4.5) crop yield was lower than Thonburi soil (soil pH 8.3) crop yield in every treatment from this experiment. Precaution should be made that sewage sludge from Bangkok applied to acid sulfate soil for agriculture at a rate equivalent to 150 kgN/ha (4-ton dry wt.Iha of sludge) is the awareness rate concerning on heavy metal toxicity in soil. Balancing Cu and Zn from lysimeter experiment data indicated that Cu and Zn from sewage sludge were mainly accumulated in both soils over 99%. Cu was presented in exchangeable form in Rangsit soil more than in Thonburi soil; therefore, such an easily soluble form of Cu is phytotoxic in Rangsit soil. In addition, Zn was also toxic to plant higher in acidic soil than neutral soil. However, Zn toxicity in any plant depends not only on the bioavailable fractions of Zn in the soil such as exchangeable form but also the plant itself and some other environmental fractions. The selected sludge application rate of 150 kgN/ha, according to AIT recommendations (1998) for sludge reuse in agricultural land, was found to be safe for application in neutral or slightly alkaline soil, but not in acidic soil. This study showed that plants grown in Rangsit soil assimilated more metals resulting in yields suppressed. Therefore, the soil pH of acid soil should be raised up to at least 6.0 or above before sludge application. For tropical soils as Rangsit and Thonburi soil series with heavy texture types, there is no doubt that the soils initially provide a strong protection against metal leachability as leachant pH is in the range of 3 - 6.5; it is likely that the nature of the major inorganic constitutes in soils (Fe, Al, Ca or P) as well as the native properties of the sludge applied to the soils have a profound effect over the solubility of heavy metals. Thus, metal remobilization becomes restricted only in the top few centimeters near the soil surface. Since there was no lateral movement observed from the lysimeter experiments, therefore, metal losses by runoff and erosion were not examined. However, metal transport with water by rainfall and irrigation in lateral movement might possibly less occurred due to small slope (less than 0.1 %) of the potential target areas. Most water will be moved down through a soil profile as downward movement. Nevertheless, the potential for metal movement both in the vertical and horizon directions, resulting from land application can be minimized if good management practices are followed accordingly. Based on the results obtained from this study, the incorporation of sewage sludge within 10 cm of soil depth at the recommended rates should be operated before starting of rainy season to protect leaching of metal to groundwater or transport with surface waters. Application of sewage sludge in dry season is recommended to stabilize metals contained in sludge with soil minerals, which metals' forms will be further transformed into non - easily water soluble forms. |
| Year | 2002 |
| Type | Dissertation |
| School | School of Environment, Resources, and Development (SERD) |
| Department | Department of Energy and Climate Change (Former title: Department of Energy, Environment, and Climate Change (DEECC)) |
| Academic Program/FoS | Environmental Engineering and Management (EV) |
| Chairperson(s) | Preeda Parkpian; |
| Examination Committee(s) | Chongrak Polprasert;Apisit Eiumnoh;Trankler, Josef;Reddy, K. Ramesh ; |
| Scholarship Donor(s) | Royal Thai Government; |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 2002 |