Fate of mercury and its potential bioavailability in sludge amended agricultural soil | |
| Author | Gupta, Chetna |
| Call Number | AIT Thesis no.EV-99-1 |
| Subject(s) | Sewage sludge Mercury wastes |
| Note | A thesis submitted in partial fulfillment of the requirement for the degree of Master of Engineering, School of Environment, Resources and Development |
| Publisher | Asian Institute of Technology |
| Abstract | Sludge applied to land provides major plant macro-nutrients such as nitrogen, phosphorus and potassium and micro-nutrients such as copper, iron and zinc and organic matter. In addition to nutrients, sludge to be applied to the land also contains heavy metals such as cadmium, nickel, chromium, lead, mercury etc.; trace organic compounds such as PCBs, dioxins, furans and pathogens such as bacteria, vi.ruses and ascaris. These are undesirable to the soil or the plants and may pose toxic effects to the plants and human being by contaminating soil, surface water or ground waters if application rate is very high. However some of the toxic heavy metals such as mercury, nickel and lead existing in the sludge might have posed some phytotoxicity and soil health impacts, if reused in agriculture. In the present study, anerobically digested sewage sludge was used to incubate the soil (acid sulfate). Soils were applied by various rates of sewage sludge (depending on the carbon percentage from sludge applied to soil of 0.25, 0.50, 0.75 and 2 %) and incubated for 1, 4, 8 and 12 weeks. Incubated samples were analyzed for bioavailable heavy metal content, different speciation of heavy metals (using sequential extraction) and effect of heavy metal concentration on soil health. Results of the mercury analysis shows that the amount of bioavailable mercury is increasing with incubation time and the results are consistent for all four % Carbon. At 0.25% C rate the bioavailable mercury concentration varied from 23 µg/kg (1 week) to 115 µg/kg (12 weeks). Similarly at 2.00% C the Hg concentration varied from 66 µg/kg (1 week) to 88 µg/kg (12 weeks). Sequential extraction results after 4 weeks incubation shows that residual fraction is around 52% and the organic fraction is 23%. Similarly after 12 weeks of incubation the residual fraction is 86% and organic fraction is 5.5%. These results shows that mercury is mainly associated with the residual and organic fractions and percentage of residul fraction is increasing with the incubation time. Available Zn, Fe was found to gradually decrease upon time. Available Cu and Mn concentration increased slightly over time till the end of the incubation period. Cr concentration tended to decrease very little throughout the incubation time. Pb concentration of sludge amended soils showed some decreases until four weeks and then increase again. Available Cd increased proportionally to sludge application rate. Results of the microbial analysis shows that the no. of microorganisms and coliform bacteria increased with increasing incubation time and carbon percent. Amount of nitrogen increased with increase in the incubation time and carbon percent but, amount of phosphorus increased up to 4 weeks and then it tend to level off. So, it can be inferred that the heavy metal concentration including Hg is not effecting the soil health since most of the metal is present in the residual form which is not available for the plant and the microorganisms. However, steps should be taken to reduce the bioavailability of the heavy metals and the most efficient method is by liming the soil to a pH-value of 6.5 - 7 which can reduce the mobile fraction of most of the heavy metals in the soil. |
| Year | 1999 |
| Type | Thesis |
| 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 (EV) |
| Chairperson(s) | Preeda Parkpian ;Takizawa, Satoshi; |
| Examination Committee(s) | Nguyen Cong Thanh ;Apisit Eiumnoh; |
| Degree | Thesis (M.Eng.) - Asian Institute of Technology, 1999 |