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Pasture as a treatment system for high rate application of effluent

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Cooke, IB (1985) Pasture as a treatment system for high rate application of effluent. Unspecified thesis, University of Tasmania.

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Abstract

The basic aim of this project was to study the
effectiveness of pasture as an aerobic treatment system for high
rate piggery effluent application. Two management systems were
compared. The first was year round applicaLion of effluent and
the second employed separation of the effluent into particulate
matter and supernatant then application of the sludge to pasture
and storage of the supernatant during those months where the
pasture cannot accept extra hydraulic loading. The stored
supernatant was applied to pasture during the summer months when
the soil water levels were low.
Separating out the high BOD containing solids components
of the effluent before storage considerably reduced the oxidation
pond area required. An above ground settling tank was easy to
operate and after 24 hours settling the tank produced a
supernatant with a total solids content of 1172 mg/1 and a sludge
of 9993mg/1 total solids. An oxidation pond was chosen to store the supernatant to
keep odour problems at a minimum. The pond worked well with the
low turbidity effluent allowing good light penetration resulting
in dense algal growth and thus producing an aerobic layer that
reduced odour. Large losses of water and nutrients occurred from
the pond due to evaporation, seepage, losses in gases and
fixation by the clay forming the bottom and walls of the pond. These losses may have been compounded by difficulties in
obtaining representative samples from an unmixed pond.
Soil on the effluent treated plots showed a larger
increase in phosphorus content than potassium which would reflect
the higher phosphorus levels in the effluent applied.
Pasture growth was not adversely affected by the high
application rates. Pasture growth was greater on the effluent
treated plots than the control plots during summer due largely to
the irrigation effect.
Acceptance of effluent soiled pasture by sheep was poor
when new sheep were introduced, however, acceptance increased
with time after introduction. Runoff was measured by draining the .45 hectare plots
with levy banks and surface drains to a dumping tank situated in
a ditch at the base of each plot. The number of dumps were
automatically recorded and surface water samples taken daily
during periods of runoff. Runoff was higher in 1981 which had a
higher rainfall than 1982, 604mm compared to 453mm. Total runoff
on the stored plots was 48% and 46% of the runoff on the fresh
plots in 1981 and 1982 respectively. Even the stored treatment
showed a large increase in runoff over the control plots due to
extra hydraulic loading onto saturated soil during the winter
months. The ability of pasture to filter nutrients was very
high. Approximately 1.3% of the BOD, 4.2% of the nitrogen, .8%
of the phosphorus and 1.3% of the potassium applied to the stored
plots was lost in runoff. However the quality of the runoff was
not good enough for direct discharge into streams.
Drainage pipes were laid in the plots at a depth of
30cm. Pollutants in the drainage water were generally in low
concentrations.
Runoff predicted by a water balance model WBAL3
(Rosenthal et al, 1976) was compared to runoff actually measured
for each plot. The model accurately predicted the weeks in which
runoff occurred. It also satisfactorily predicted the volumes of
runoff although it showed a tendency to overestimate. The model
can also be used to determine when and how much effluent
irrigation could be applied throughout the year without causing
increased runoff and therefore has a place as a management aid
for high rate effluent application.

Item Type: Thesis (Unspecified)
Keywords: Organic wastes as fertilizer, Land treatment of wastewater, Sewage irrigation
Copyright Holders: The Author
Copyright Information:

Copyright 1985 the Author - The University is continuing to endeavour to trace the copyright
owner(s) and in the meantime this item has been reproduced here in good faith. We
would be pleased to hear from the copyright owner(s).

Additional Information:

Thesis (M.Agr.Sc.)--University of Tasmania, 1986. Bibliography: leaves 90-107

Date Deposited: 25 Nov 2014 00:43
Last Modified: 01 Jun 2016 01:15
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