Land treatment of wastewater 417Storage
Storage of wastewater is required for any process of land treatment in order to
equalize the incoming flows, to maintain constant application rates, and in the
case of repairs or operational problem in the distribution system. Even though
SR and RI systems are capable of operating during adverse climatic conditions
storage may be required. In the case of OF system, storage is necessary to
accommodate the wastewater during rainy and winter seasons due to reduced
hydraulic loading or complete shut down, and also to accommodate stormwater
runoff. Generally 5-10 days of storage is sufficient to overcome the problems.
Distribution system
Distribution system design consists of two important components:
- selection of the type of distribution system, and
- detail design of system components.
Method of wastewater distribution varies with the type of land treatment
system. For SR system, either surface distribution system in which wastewater
is applied to the land at one end and allowed to spread over the field by gravity
(Figure 8.2 b) or sprinkler distribution system where the wastewater is spread
over the land by sprinklers (Figure 8.2 c) is suitable. In the case of RI system,
wastewater distribution is usually by surface spreading (Figure 8.3). This
method employs gravity flow from piping systems or ditches to flood the
application area. Wastewater distribution onto OF slopes can be achieved by
surface methods, low-pressure sprays and high-pressure impact sprinklers.
Choice of the appropriate system should be based on minimization of
operational difficulties such as uneven distribution onto the slope, and also the
operational cost of the system. If surface distribution method is adopted, the
land should be perfectly levelled to avoid ponding. Extreme care should be
taken when sprinkler system is used for the treatment area situated near
residential areas to avoid spreading of pathogens due to aerosols and wind
action.