Russell et al. (1993) reported that the rate of N20
release from pasture and forest irrigated with effluent
rose markedly immediately following irrigation,
but fell back to base emission rates within 24 h of
irrigation ceasing. Emission was affected by the type
of wastewater and temperature. Both N20 emission
and denitrification were minimal at temperatures
below 12°C (Russell et al., 1993).
A further concern for the management of slaughterhouse-
wastewater irrigation systems is human
exposure to potentially pathogen-contaminated
aerosols. Sprinkler irrigation systems lead to the
aerosolisation of 0.1-1% of the sprayed water.
Shuval et al. (1984) found that irrigation workers
exposed to aerosol-forming (sprinkler) irrigation
were three times more likely to be carrying antibodies
to Legionella pneumophila, the causative
agent of Legionnaires disease, than the normal
population, regardless of whether the water was
clean or treated-wastewater. Oxidation-pond water,
in particular, may be a natural habitat of this bacterium
and aerosol irrigation of such water may pose
an occupational risk to exposed workers. It must be
noted, however, that this finding was only preliminary
and the authors suggest a more detailed study
is required. Clearly, irrigation with slaughterhouse
wastewater should preferably be by non-aerosolforming
techniques.