Conclusions
- Although land application is better suited to land
reclamation and forest application, agriculture is the
largest use. This is unfortunate because the
negative aspects of land application have more of an
impact on agricultural land.
- Mineralization rates decrease with time which means that
in order to apply enough nutrients to meet a crops needs
excesses will be added
- Unbalanced nutrients means that some excesses will be
added in order to get enough of others
- Phosphates accumulate in soil and move into surface water
by erosion leading to eutrophication
- There are trace elements in sludge that are toxic to
humans as well as plants and animals. Some of these
are amplified in the food chain. (Rachel Carson)
These elements are attached to soil particles and
considered removed from the soil-water system when they
are still in the soil and can be released when conditions
change (inevitable)
- New legislation (40 CFR part 503) greatly increased the
cumulative loadings of most trace elements, including
toxic and heavy metals, in order to encourage this method
of recycling and not to protect public health.
- Organics in the sludge are degraded very slowly in the
soil and many of there decay products are just as
harmful. These chemicals are usually toxic.
- Organics have unpredictable chemical reactions in the
soil and there concentrations are too variable to
estimate well.
- Pathogens are not sufficiently destroyed in most current
application programs
- Most communities are not willing to locate waste
treatment plants in their communities. The majority
of the systems are located in poor, rural communities
with little political power.
- With current technologies, the waste treatment process is
too expensive. The common solution is to short cut
the system resulting in less than desired treatment.
- Extremely large development costs initially is one of
main drawbacks to land based waste treatement. Most
communities would rather landfill today than land apply
for future.
- Trace metals are phototoxic in very small amounts to
plants and animals. The wastestreams in larger
urban areas are extremely variable. Industrial
wastes are a major problem in most urban waste streams.
- summary: Good technology but dangerous when
improperly managed as is currently done.