Environmental Engineering Reference
In-Depth Information
3.1.2 Results and discussion
During the period March 2002 to March 2003 the effluent and sludge flow rates averaged
23,020 m
3
/d and 1033 m
3
/d respectively. The monthly variation is shown in Figure 9.5.
The average value is about 15% higher than the flows pumped to the farm during 1998-
1999 (Chapter 8). The variations of the flow to the farm relate primarily to fluctuations of
the inflow rate to CSTW.
The trickling filters line and the holding ponds receive the majority of any incoming
excess flow (the BNR plant works at a load, close to its design capacity). The highest
figures are recorded during the wet season and are attributed to the infiltration of run-off
into the sewer system and recharge to portions of the sewer system from groundwater in
saturated areas. On some occasions of very intensive storms, part of the pond effluent is
discharged from the ponds to the Marimba River.
A water balance of incoming and out-coming flows during the period of study, based
on the total active farm area is presented on Figure 9.6. It shows that the SEM hydraulic
load to the farm exceeds the evapo-transpiration rate based on average annual loads and
the assumption that the total active pasture area is used. During the wet season, the farm
area is hydraulically overloaded. However, the actual hydraulic load, calculated based on
the annual average daily flow rate and the area of three paddocks, which are used for
irrigation most often, is 47 mm/d. This shows a significant hydraulic overloading due to
an inadequate operational practice, which is reflected in ponding and the creation of
anaerobic conditions on selected portions of the farm area. The under drain system could
alleviate this problem in the portions, where soils are more permeable (the southern lower
part of the pasture). However, due to the long period of exploitation, the under drain
system might be blocked. All these factors reflect in a very irregular hydraulic loading
pattern along the pasture.
