Estate Service Asset - PDO

Petroleum Development Oman
Estate Services Asset
Environmental Assessment
2002 Review and Update
The influent into MAF-STP consists of wastewater generated from all toilets and
washrooms in the office buildings and the wastewater generated from the MAF camp
kitchen. Additionally, a car wash area located at the waste management compound
discharges excess wastewater to the sewer system via a grease trap. The influent into
RAH-STP consists of wastewater generated from all the households, two restaurants
located in the RAH recreation centre and PDO school.
Both the STPs are similar in configuration and are based on the activated sludge
system. Each STP consists of the following seven unit processes.
• Screening and Maceration
The raw sewage collecting into the underground sewage sumps passes through bar
screens to remove large floating matter, then pumped into the STP by a screw lift
pump via a macerator. The macerator comminutes all coarse solids present in the
sewage into fine suspended matter. From the macerator, the homogenised sewage is
dosed with a multi-nutrient chemical (Biologic-SR2) at an approximate concentration
of 1 ppm.
• Aeration
There are three parallel aeration channels, each of 24m-length and 3m-water depth.
The middle channel is of 3m width, while the right and left channels are of 2m width.
The sewage flow is split evenly among the channels such that the hydraulic retention
time in each channel is approximately 24 hours. Brush aerators located at the inlet of
the aeration channels provide the oxygen required. These aerators are designed to
operate continuously, providing a dissolved oxygen level in the range of 1.5 to
3.25ppm. The sewage in the aeration channels is internally re-circulated to ensure
good mixing and to eliminate the settling of solids in the aeration channels. Due to
the biochemical oxidation of the sewage by the aerobic bacteria present, the biological
oxygen demand (BOD) is reduced and simultaneously, the biomass is increased.
• Clarification
The effluent from the aeration channels then flows into a sludge-blanket clarifier,
where the excess biomass is settled as sludge. The sludge blanket formed acts as a
physical filter for smaller particles, thus improving the efficiency of the clarification
process. The clarifier has a design hydraulic retention time of 4 hours. To maintain a
healthy biomass concentration (mixed liquor suspended solid concentration of 3500-
4000 mg/L), 10-20% of the settled sludge is returned to the aeration channels. The
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