M. Juanico et G. Shelef, DESIGN, OPERATION AND PERFORMANCE OF STABILIZATION RESERVOIRS FOR WASTE-WATER IRRIGATION IN ISRAEL, Water research, 28(1), 1994, pp. 175-186
Stabilization reservoirs are used for the seasonal storage and treatme
nt of wastewater for irrigation. These reservoirs are not steady-state
flow reactors, but rather accumulative batch ones with a relatively a
brupt discharge. A new parameter, the percentage of fresh effluents wi
thin the reservoir (PFE) is proposed as a tool to analyze the age dist
ribution of effluents in this kind of reactor. The equations to calcul
ate the mean residence time (MRT) and the surface organic loading are
also provided. The relatively small fraction of fresh effluents repres
ented by PFE and not the whole age distribution of the effluents (MRT)
determines the removal percentages of COD and BOD in the reservoir an
d the quality of the effluents released for irrigation. The effect of
environmental parameters such as water temperature and solar radiation
are overridden by the operational parameters (PFE). In steady-state f
low reactors MRT can substitute PFE to evaluate the reactor performanc
e because the ratio PFE/MRT is constant in this particular case. A val
ue of 30-40 kg BOD/ha/day is recommended as the maximum allowable surf
ace organic loading of stabilization reservoirs. The seasonal storage
of wastewater in reservoirs reduces BOD, COD, TSS and detergents by 50
-80%, and total coliforms by 90%, in terms of annual means. The qualit
y of the effluents is maximal at the beginning of the irrigation seaso
n when the reservoir is full of old effluents, but sharply deteriorate
s when water level drops and new wastewater is pumped into the reservo
ir. Design and operational alternatives to overcome this problem can a
ssure removals of at least 1 order of magnitude for chemical component
s, and of at least 3-4 orders of magnitude for total coliforms. These
alternatives are based on a change from seasonal to multi-seasonal sto
rage of wastewater, and/or a change from single reservoir to two or mo
re reservoirs supplying effluents of different quality.