QUANTIFICATION OF METHANE AND HEAVY METALS LEVELS IN LEACHATE. A CASE STUDY OF DANDORA DUMPSITE, NAIROBI, KENYA

ABSTRACT

 

Increased rate of urbanization in Kenya influences solid and liquid waste generation and
management and other environmental impacts. This has increased use of dump sites to
manage wastes and reduce pollution. However, researchers have cited dump sites to be one
of contributing sources of methane, a greenhouse gas whose level has increased in the
atmosphere. It has been noted since 2007 that there is an increase in greenhouse methane
attributing to extreme weather and climate change. Methane is a potent environmental
pollutant due to its activity as asphyxiate and its explosive nature. Basing on these
characteristics and the global concerns about rising levels, the study sought to quantify the
emission levels of methane from Dandora dumpsite in Nairobi County.
Head space chambers were used for sampling methane from twenty sites in two weeks. Gas
chromatography with flame ionization detector (FID) was used for methane analysis.
Methane was highest at the sampling point where wet waste was disposed. The levels of
methane ranged from below detectable level (BDL) at five points to as high as 3779.87 ppm
at point P17. Methane flux ranged from zero to 48869.05 µg C m-2 h-1 at point P12. The part
of dumpsite covered by vegetation, bear dry ground or/and the inactive site had BDL
(0≥level of methane). Considering the highest flux from the dump site, it was found that
1.14 x1011 mgCy-1 (114 tonnes of carbon/year) methane is emitted.
Dump sites contain leachates which can seep into ground water. Leachate may contain
heavy metals that pollute the groundwater supplies. Because of their environmental and
health implications, the study also quantified levels of some selected heavy metals i.e. lead,
copper, zinc, nickel, chromium and cadmium in the leachate. Sampling was done for six
months; during dry, short rain and wet periods. Leachate was scooped from ten sampling
trenches in Dandora dumpsite to analyse level of heavy metals using AAS technique. This
that the levels of lead metal ions were highest, 4.65 ppm in November and lowest, 0.96 ppm
in April. Levels of copper metal ions were highest, 1.61 ppm in November and lowest, 0.56
ppm in April. Zinc metal ions concentration was highest, 35.84 ppm in November and 4.60
ppm in April. Levels of nickel metal ions ranged from 0.12 ppm in April to 0.79 ppm in
November. Chromium metal ions levels were between 0.70 ppm in March and 1.43 ppm in
November. Cadmium metal ions were found at three sampling points during the month of
December only. Their mean concentration was 0.009 ppm for the month.
There was significant relationship between the month of data collection and individual

 

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