416 Organic waste reuse and recycling: technology and management
Pre-application treatment
Pre-application treatment of wastewater to be used for land treatment is
necessary to:
- Inactivate the entero-pathogenic organisms to an acceptable levels
so that public health risks to the workers, grazing animals or human
beings who consume those irrigated crops are minimized (see
section 8.7), - Minimize operational problems in distribution systems such as
clogging of the spray nozzles and distribution pipes, etc., - Lengthen the working life of land treatment sites as clogging of the
soil pores will be less when pre-treated wastewater is applied, - Prevent nuisance conditions during wastewater storage prior to
being applied to land.
Screening, screening with comminution, aeration, ponding, and disinfection
are the common types of pre-treatment facilities used. In case of industrial
wastewaters containing some toxic compounds, other pre-application treatment
such as chemical precipitation and flocculation/sedimentation might be
necessary. Where concern is on nitrate contamination to groundwater aquifers,
pre-application treatment may include ammonia stripping, water hyacinth pond
treatment, or storage ponds having a long detention time, to reduce the nitrogen
content.
The level of pre-application treatment provided should be the minimum
necessary to achieve objectives stated above. Any additional treatment will, in
most cases, only increase cost and energy use.
Crop selection
Crop selection is an important factor in SR and OF processes. Presence of
suitable crops on the application area will reduce the erosion, provide support
media for microorganisms, remove the wastewater nutrients by plant uptake and
produce revenue where markets for these crops exist. Nutrient uptake capacity
(see Table 8.7), tolerance to high soil moisture conditions, consumptive use of
water and irrigation requirements and revenue potential should be considered
when selecting a crop for SR and OF systems. In SR system, presence of crop
will maintain or increase the soil infiltration rate. In OF system, a mixture of
grasses is generally preferred over a single species. Corn and paddy are also
suitable crops to be used but the public health aspects should be studied in detail
as the public consumes these crops.