Microbial analysis of soil samples in a wastewater irrigated vegetable production site: Case study at Atonsu, Kumasi.
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Date
November, 2009
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Abstract
Though irrigation with wastewater has potential benefits of meeting water requirements as well
as providing organic matter and nutrients to soil, it may also pose health hazards to farm workers
and consumers of food products from wastewater-irrigated crop production. The soil then
becomes a reservoir of enteric pathogens and has the potential to transmit many various diseases
of enteric origin. The study was conducted on urban vegetable farming sites at Atonsu in
Kumasi, Ghana. The objective of this research was to determine the effect of irrigation with
wastewater on the microbiology of soils under vegetable cultivation by, (a) assessing the soil
contamination levels in wastewater irrigated agricultural plots in urban Kumasi, and (b) detecting
the presence of indicator organisms associated with agricultural plots. Soil samples from two
different depths (0 - 30 cm and 30 - 45 cm) were collected from fields treated with different
irrigation water sources and analysed. The treatments include plots where: (i) wastewater
irrigation practice has been going on for over a decade , (ii) piped-water (PW) irrigation practice
has been used for over a decade (control), and (iii) no recent cultivation has taken place (control).
The irrigation water sources were also sampled for analysis. Both soil and irrigation water
samples were analyzed for different physicochemical (pH, soil moisture, soil texture) and
biological parameters (Total coliforms (TC), Fecal coliforms (FC), and helminth eggs) using
standard methods. Soil samples from all three plots carried FC and helminth egg populations
ranging between 0.03 to 9.5 x 104 per 10g for FC and 0 to 30 per 10 g for helminth. A number of
different types of helminth eggs, including that of Ascaris lumbricoides, Strongiloides
stercoralis, Fasciola hepatica, Schistosoma spp. were also identified in the soil samples. All soil
samples had the following bacteria genera present in them: Escherichia, Bacillus, Staphyloccus,
Pseudomonas and Clostridium. The upper soil profile had higher counts of coliforms and
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helminth eggs than the deeper soil profile. Wastewater irrigated plots had higher numbers of
coliforms and helminth counts than those obtained from the potable water irrigated and no
irrigation plots. The study concluded that pathogenic microorganisms in soils irrigated with
wastewater may extend into lower profiles of the soil. However, factors such as the sieving effect
of soil (influenced by soil texture), higher pathogen die-off rates, lack of substrate diversity and
reduced soil moisture contributed to lower counts of coliforms and helminthes in the lower
profiles of soil.
Description
A thesis submitted to the Department of theoretical and Applied Biology, Kwame Nkrumah University of Science and Technology (KNUST), Kumasi in partial fulfilment of the requirements for the degree of Master of Science in Environmental Science.