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The amount of waste water has decreased by 2.2 times in comparison
to the amounts in 1990, resulting in a decrease in the amount of
sewage sludge produced in waste water treatment. Assuming that
100-120 g of sludge are produced in treatment of 1m3 of waste
water, then in 2000, a total of 20,000 t of dry sludge was
produced in Latvia. In Rīga, about 15-18 kg dry sludge is
produced per resident annually.
The heavy metal concentrations in sludge produced in large
cities (cadmium in Rīga, chromium in Liepāja, Jelgava, and
others) sometimes exceed the maximum allowed concentrations for
application of sludge as soil fertilizer. About 29% (5,800 t) of
the produced dry sludge was used agriculturally for fertilization
in 2000.
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