The Suitability of the sewage effluent from Unayzah City (Central Region of
Saudi Arabia) wastewater plant for irrigation purposes was assessed during three
consecutive years (1999/2000. 2000/2001, and 200112002) by considering some of its
biochemical, physiochemical and microbiological characteristics. Processing of the
available data and thereafter comparing them with the locally and the internationally
acceptable standards for unrestricted and restricted irrigation revealed that: 1) the
expected yearly average volume of treated sewage effluent varied from 10.9X10s to
38.3X105 m3 which raises a high concern to' the authorities regarding its disposal. 2)
The effluent under the study is unacceptable for irrigation reuse in respect to the
following: a) The mean BOD (range 25-34 mgL'\ in spite of a relatively high BOD
removal efficiency (range 83-87%), b) The mean COD level, which varied from 115 to
135 mgL", c) The mean alkalinity level (range 290 • 298 mgL'\ d) The mean total •
suspended solid contents (range 42 • 135 rnql,"), 3) The mean electric conductivity
(EC mmhose Cm-l) (range 1.65-1.85) and the mean pH value (7.3) of the effluent,
however, are within the acceptable recommended quality limits for restricted irrigation.
4) The high fecal coliform count (ran~e 1.6X103• 1.2X104 MPN 100 rnt') and the high
total coliform count (range 2.2X10 - 101X104 MPN 100 rnl") were evident thus
indicating low efficiency of and incomplete microbial removal which renders the
effluent unacceptable for restricted and unrestricted irrigation because of
environmental and public health concern.