Thesis - faculty.ait.ac.th - Asian Institute of Technology

Table 2.3 presents the general leachate characteristics with age and suitability of
treatment options in terms of biodegradable, intermediate and stabilized landfill leachate.
As the young landfill is rich in organic, biological treatment is more appropriate than
physico-chemical which is suitable for the old landfill. However, effectiveness of
combined treatment process for the treatment of a leachate produced at specific landfill age
has not been considered. Individual treatment options cannot be a long-term solution for
leachate treatment as they are not effective in treating leachate generated at different period
of time and do not adapt to changing leachate characteristics.
Table 2.3 Relation between Landfill Age, Leachate Characteristics and Treatments
(Amokrane, et al., 1997)
Landfill Age (years) < 5 (young) 5 to 10 (medium) > 10 (old)
Leachate Type I (biodegradable) II (intermediate) III (stabilized)
pH < 6.5 6.5 to 7.5 > 7.5
COD (mg/L) > 10,000 < 10,000 < 5,000
COD/TOC < 2.7 2.0 to 2.7 > 2.0
BOD5/COD < 0.5 0.1 to 0.5 < 0.1
VFA (% TOC) > 70 5 to 30 < 5
Process Treatment Efficiency
Biological Treatment Good Fair Poor
Chemical Oxidation Fair-poor Fair Fair
Chemical Precipitation Fair-poor Fair Poor
Activated Carbon Fair-poor Good-fair Good
Coagulation-flocculation Fair-poor Good-fair Good
Reverse Osmosis Fair Good Good
2.6 Molecular Weight Distribution in Landfill Leachate
Ultrafiltration (UF) is demonstrated to be an effective method for characterizing
leachate on the basis of molecular weight (MW) distribution (Gourdon, et al., 1989; Tsai,
et al., 1997; Yoon, et al., 1998; Kang, et al., 2002). The UF cell is operated in a batch
mode with nitrogen gas applied to pressurize the system, producing a driving force for
leachate to permeate through the membranes.
The organic components of leachate are mainly composed of water soluble
substances. The suspended solid content of leachate is generally very low. Organic matter
is dependent on the waste composition and degree of degradation. The predominant
substances in each fraction are given in Table 2.4.
Low molecular weight organics are composed mainly of easily degradable volatile
fatty acids, which contribute to 90 % of this fraction. The most frequently occurring fatty
acids are: acetic, propionic and butanic acids.
Medium molecular weight compounds with molecular weight between 500 and
10,000 Da are characteristic of fulvic acid and humic fraction present in leachate. This
group is dominated by carboxylic and hydroxylic groups and are difficult to degrade, thus
termed refractory compounds. The high molecular weight organic fraction varies from 0.5
% in methanogenic landfill leachate to 5 % in acidogenic landfill leachate. These
compounds are more stable and possibly originate from cellulose or lignin.
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