| Author | Siranee Sirisukhodom |
| Call Number | AIT Diss. no. SR-98-1 |
| Subject(s) | Sewage--Purification--Heavy metals removal
|
| Note | A dissertation proposal submitted in partial fulfillment of the requirements for the degree of
Doctor of Technical Science, School of Environment, Resources and Development |
| Publisher | Asian Institute of Technology |
| Abstract | Since agricultural utilization of sewage sludge is ranked as first disposal option to be
promoted in Thailand. Laboratory and greenhouse experiments were conducted to determine
movement of heavy metals (cadmium, copper, zinc, iron, and manganese) in the soils and uptake
by plant following application of sewage sludge. Sewage sludge were obtained from Sipraya
wastewater treatment plant and two major agricultural soil series, Rangsit and Thonburi, were
collected from Bangkok area for used in the studies.
The indigeneous soils contained low heavy metals (Cd = Trace; Cu= 14-27 mg/kg; and Zn
38-5 1 mg/kg) while the sludge contained higher amount of heavy metals which were in
acceptable ranges for application as plant nutrient source in agricultural soil.
Thonburi soil has higher capacity of inorganic cadmium sorption than Rangsit soil. Plough
soil layer also has higher cadmium sorption capacity than subsoil layer. Cadmium sorption capacity
of the soils decreased when ·zinc was added as a background metal and it significantly increased
when free manganese oxide and soil pH were increased. Cadmium desorption patterns of the two
soils were similar to that of sorption, however, antagonistic effect of zinc in a desorption process
was less than that in a sorption process.
As a result of soil study, application of sewage sludge could extensively increase pH of
acid soil and improve soil fertility. On contrary, it also raised up soil heavy metal levels in
proportion to the application rate. Most of studied heavy metals from applied sludge became
immobile with time. However, elevated amount of bioavailable cadmium (0.23-0.35 mg/kg),
copper (6 1.06-91.10 mg/kg), zinc (103.40-126.39 mg/kg), manganese ( 175.67-247.14 mg/kg),
and iron (5.15-17.51 mg/kg) in soil solution were still found at 12 weeks of incubation time.
As a result of greenhouse study, lettuce yield increased when soil was applied with sludge
and other amendment materials. The increased yield was high as sludge application rate was
increased. At the same time, it accumulated more heavy metals. Adding lime, zeolite, and burnt
rice hull to the soils helped decreasing accumulation of metals in the lettuce. Both soils physical
and chemical properties were improved after applied with sewage sludge which continued to
supply .plant nutrients to the soils after second crop. Plant nutrients and heavy ·metals residue were
decreased after first and second harvests.
It is recommended that, for safe practice of sewage sludge utilization, dried sludge
application rate should be below 268 ton/ha to maintain cadmium content below 0.3 mg Cd/kg
soil. This rate is suitable for providing sufficient plant nutrients to the soil and raising metals
accumulation in plant and soil residue in the acceptable concentration. It is also recommended to
adjust soil acidity with lime and reduce bioavailability of heavy metals by mixing sludge together
with soil amendments such as zeolite or burnt rice hull. |
| Year | 1998 |
| Type | Dissertation |
| School | School of Environment, Resources, and Development (SERD) |
| Department | Other Field of Studies (No Department) |
| Academic Program/FoS | Space Technology Application and Research (SR) |
| Chairperson(s) | Preeda Parkpian ;Apisit Eiumnoh; |
| Examination Committee(s) | Eckhardt, Heinz ;Reutergardh, Lars; |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 1998 |