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

leachate in municipal wastewater treatment plants. A combined treatment may provide a
better effluent quality as a result of the maintenance of a more heterogeneous population,
increased availability of nutrient and possible dilution of potential inhibitors. Another
advantage of co-treatment of leachate with domestic sewage is that leachate contains
excess of nitrogen while sewage contains excess of phosphorus which eliminates the need
for addition of nutrients. However, the main disadvantage is the high concentrations of
organic and inorganic components contributed by both young and old leachate.
To review the of co-treatment of leachate in MWW plants, Qasim and Chiang (1994)
summarized research conducted by various researchers (Chian and DeWalle, 1977; Henry,
1985; Raina and Mavinic, 1985). From the review, it was evident that a disagreement arose
as to whether this option was viable and under what conditions. Whilst Raina and Mavinic
(1985) successfully treated leachate-MWW combinations of 20 to 40 %, Henry (1985),
Chian and DeWalle (1977) and others reported poor performance in the co-treatment for
leachate to MWW a ratio of less as 10 %. Since, there are contradicting results from
various researchers, it is unknown whether this treatment option is suitable under practical
application. Although BOD5, COD and heavy metal reduction is well established, the
relative proportions of leachate effectively treated is effected by ammonia conversions,
temperature, sludge production, foaming, poor solids settleability, heavy metal
accumulation and precipitate formation.
2.9 Combined Treatment Facility
A single treatment technology is not efficient in the leachate treatment due to the
complexity involved in treating leachate having a varied composition and characteristic.
Leachate treatment entails the integration of several treatment processes. The coupling of
units for the development of treatment sequences should be modular to allow maximum
flexibility in order to vary the order of arrangement and for addition/removal of unit
operations. This effectively creates different treatment lines and thus better adapted to the
changing qualitative conditions of the leachate (Qasim and Chiang, 1994; Bressi and
Favali, 1997).
Physical-chemical treatment processes for leachate from young landfills are not as
effective as biological processes, whereas they are extremely efficient for stabilized
leachate. COD/TOC and BOD/COD ratios, absolute COD concentration and age of the
landfill are necessary determinants in the leachate characteristics for selection of
appropriate treatment system. In treating leachate, the treatment sequence should be able to
meet either the standards for discharge in receiving water bodies or an acceptable limit for
discharge into water treatment works. To review the treatment sequences prior to
development of optimum treatment sequence, few treatment combinations have been
reviewed.
2.9.1 Biological Treatment and Reverse Osmosis
A treatment sequence that is capable of removing mineralized material should
include anaerobic digestion, suspended growth biological waste treatment, partial softening,
filtration and reverse osmosis (RO). The anaerobic digester stabilizes the waste while the
aeration system degrades the biological matter. The effluent could be polished in a gravity
filter and demineralised in a RO unit, thus achieving an effluent devoid of dissolved salts
and low in organics. The process train is as shown in Figure 2.7(a). With increase in age,
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