Methanogenic leachate

Table 3. Composition of the methanogenic leachate and freshwater used in the experiments...

In summary, signihcant numbers of bacteria, detected with several different approaches, are present in landhll leachate plumes. Methanogens, sulfate reducers, iron reducers, manganese reducers, and denitrihers are believed to be widespread in leachate plumes. Microbial activity seems to occur throughout leachate plumes, although the actual activity (as measured by ATP, PLFA, and redox processes) is low compared to activity in topsoil. Several redox processes can take place in the same samples adding additional diversity to the concept of redox zones illustrated in Figure 3. 

Albrechtsen H.-J., Bjerg P. L., Ludvigsen L., Rilgge K., and Christensen T. H. (1999) An anaerobic field injection experiment in a landfill leachate plume (Grindsted, Denmark) 2. Deduction of anaerobic (methanogenic, sulfate and Ee(lll)reducing) redox conditions. Water Resour. Res. 35, 1247-1256. 

Once established, the methanogenic bacteria will help to control the pH at or near neutrality such that acetogenic phases (pH S - 6) and methanogenic phases (pH 6 - 8) of landfill can be cleariy discerned. At this stage, landfill gas production will increase as a result of the bacterial activity, with the result that carbon compounds that might otherwise contribute to leadiate TOC may be converted to landfill gas with a resultant decrease in this parameter within the MSW leachate (Table 6). The leachate hazard will therefore be reduced with a consequent increase in the landfill gas hazard. 

The composition of landfill leachate may be expected to vary with time, and from site to site, as a consequence of variable water infiltration rates and amounts, differing ages of sites, differing waste composition and local environmental conditions. The processes of leachate generation within the site have already been discussed, and the change in leachate composition as the waste moves from the acetogenic phase to the methanogenic phase have been described briefly. 

It is difficult, because of the above, to describe a typical landfill leachate, although most leachates will contain characteristic components which change as the waste moves from the acetogenic phase to the methanogenic phase. However the data in Table 6 are. within the confines of the above, considered to be typical... 

Ammoniacal nitrogen is probably the most important inorganic component and will often be present at high levels even in methanogenic waste, and because of this, it is often necessary for leachate to be treated off-site before discharge to sewer. Once released within a landfill, there is no significant biochemical pathway whereby ammonia can leave the waste (Robinson and Gronow, 1992), and thus controlled treatment is required to remove this component. 

Table 11.3. Leachate composition in terms of average values and ranges for parameters with differences between acid and methanogenic phase (Ehrig 1988) and average values for parameters with no observed differences between acid and methanogenic phase (Ehrig 1983)...

Many years of observation showed that phases that take place in the mass of deposited waste are related with the age of landfill, which is understood as the time elapsed since the deposition of the waste or the appearance of leachate (Andreottola Cannas, 1992). Due to the age, the landfills are divided into young—operated for less than five years, the medium— from 5 to 10 years and old (mature)—over 10 years (Chian De Walle, 1976). The young landfills are in a phase prior to the methanogenic one or in the early unstable methanogen-esis. The medium landfills are characterized by stable methanogenesis, whereas the process of maturation begins on the old landfills. 

---