Wastewater Management in Kuwait (With Diagram)

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W. Al-Essa

Assistant Undersecretary & Chief Engineer Sanitary Engineering, Ministry of Public Works P.O. Box 8, 13001 Safat, Kuwait

Sanitary Master Plan of Kuwait:

In 1988, the Ministry of Public Works (MPW) commissioned consultants to assist with the preparation of a 20 years Sanitary Master Plan for Kuwait. The Kuwait Sanitary Master Plan (KSMP) was completed in July 1989.

The KSMP addressed the wastewater management needs of a community whose population was expected to increase from around 1,900,000 persons in 1990, to 2,284,000 in 2010. When development of the existing wastewater management infrastructure started in the 1960s, Kuwait’s population was less than 800,000 persons.

At the time the KSMP was commissioned, the wastewater management infrastruc­ture of Kuwait was focused on three wastewater treatment plants. They were Ardiya, serving the north-eastern part of the city including the downtown area; Jahra, serving the western part of the urban area; and Rikka, serving the southern part of the urban area.

The catchment areas of these three treatment plants are shown in Fig. 1. The collection system in the catchment areas were comprised of 4,700 km of gravity sewers, 17 major pumping stations, 57 secondary pumping stations and 1600km of pressure main. The Ardiya plant was developed through a number of expansion stages with the first stage of construction being undertaken in the mid-1960s. The Rikka and Jahra plants are of more recent construction.

In 1990, the three treatment plants had the design capacities shown in Table 1.

However, the master plan’s investigations suggested that the actual treatment capac­ity available at these plants was only about 90 per cent of the design capacity, due to underestimation’s of the strength of the wastewater to be treated.

All of the treatment plants provide tertiary treatment through sand filtration and disinfection, and use mainly extended aeration activated sludge for secondary processing.

Present Master Plant Scheme:

The long-term strategy outlined by the master plan will implement a bold program of major wastewater infrastructure development, which is expected to handle nearly 500,000 m³/d of wastewater expected to be produced in 2010. Facilities will be planned with the more distant need of 2020 and 2050 in mind.

The infrastructure in 2010 will have a wastewater collection system focused on two new wastewater treatment plants, while the existing plants in Ardiya, Rikka and Jahra will be abandoned after the new plants are commissioned.

One new plant will be constructed in Sulaibiya to the south-west of the urban area and will permit the abandoning of the existing plants in Ardiya and Jahra. The second plant will be constructed in Shuaiba to the south of the urban area and will permit the abandoning of the Rikka treatment plant. The catchment areas of the two new treatment plants are shown in Fig. 2.

Like most cities in the Gulf region, over the last three decades Kuwait has experi­enced rapid growth in population and major expansion of its urban area. As a result, the existing wastewater treatment plants, which were constructed well away from urban areas, are now very close to new residential developments.

This, coupled with the need for additional space for expanded treatment facilities, necessitates the abandoning of existing treatment plants and the construction of new treatment plants in more remote locations.

The proposed wastewater collection system serving the two new treatment plants will be a major departure from the strategies previously adopted for cities in the region. Each catchment area will be served by one or more interceptor, enabling large areas of Kuwait to be sewered without resorting to pumping stations.

The new interceptors will also allow the MPW to abandon most of the existing pumping stations by connecting their tributary sewer directly to the sewer tunnels. Inter­ceptor sewers will be connected to deeper sections of the sewer tunnels through vortex drop shafts preceded by grit removal facilities. Flow measurement, grit removal and odour control facilities will be provided at each interconnection.

The master plan’s recommendations were to be implemented in three stages; 1990- 95, 1996-2000 and 2005-10. The master plan proposes the upgrading of the existing treatment plants. This upgrading will improve these plants’ performance for the interim period until the commissioning of the proposed new plants permits the older plants’ abandonment.

Sewer Renovation Program:

Due Kuwait’s mainly flat terrain, and the resulting need to include manned pumping stations in the wastewater collection system, sewage is retained in collection for a long time before arriving at the treatment plants. This ageing of the sewage, coupled with high summer temperatures, leads to septicity and the generation of hydrogen sulphide, odours and corrosive conditions in the collection system.

Many of the sewers were constructed of asbestos cement pipes, which are particularly susceptible to deterioration from internal corrosion. This is a problem Kuwait shares with a number of cities in the region.

The MPW has initiated a 13 phase sewer renovation program, which started with initial studies and investigations in 1982. To date, consultancy service contracts have been awarded for the first 7 phases of the program. Construction started in 1984, and the renovation work has been completed in Phases I and II, while it is on-going in Phases IV and V. Phases III and VI are in preparation for starting.

To date, each phase of the sewer renovation program has involved three steps:

(1) Closed-camera television (CCTV) inspection, flow measurement and evaluation of the existing sewers, including evaluation of their hydraulic capacity relative to the long-term capacity needs;

(2) Design of renovation or replacement measures; and

(3) Implementation of the designs.

In Phase I of the program the majority of defective sewers were renovated, with 127 km of sewer being renovated with inversion linings using resin impregnated polyester fiber felt, and 33 km of sewer being renovated with slip linings. Only 15 km of defective sewer was replaced.

The aims of the renovation program now are to:

1. Improve pipe material and flow characteristics,

2. Remove blockage and odour problems,

3. Rationalise and reduce the number of pumping stations, and

4. Provide a system which will have a useful life of at least 50 years

Based on the above outlined policy goals for subsequent phases of the program, the MPW have changed the emphasis, with most defective sewers being replaced, often by micro-tunnelling. This approach is cost-effective and provides greater opportunity for re­routing sewers, abandoning pumping stations, and providing increased capacities to cater to future wastewater management needs.

Treated Effluent Reuse:

The Government of Kuwait has identified treated effluent as a valuable source of irrigation water that is able to make a significant contribution to the national policy for the beautification of Kuwait through extensive planting. This policy is commonly referred to as the Greening of Kuwait. At present, treated effluent is used for irrigation of agriculture, afforestation projects and landscaping in greenbelts.

The MPW’s plan is that all treated effluent be reused. The KSMP outlines three alternative strategies for effluent reuse, each with a different degree of emphasis on reuse for agriculture, afforestation and the beautification of motorway greenbelts. The MPW’s priority for the time being is implementing a strategy which concentrates on planting and irrigating motorway and main road greenbelts, with some new projects for the irrigation of afforestation and agriculture.

At each of the existing treatment plants, there is a local scheme for effluent reuse, but there is also a system to transfer effluent from the treatment plants at Ardiya and Rikka to the reuse storage and distribution centre at the Data Monitoring Centre (DMC) near Sulaibiya.

This concept will be continued in the future, with some treated effluent from both the Sulaibiya and Shuaiba Wastewater Treatment Plants, being conveyed to the DMC. Components of the transfer system at the existing Ardiya and Rikka Wastewater Treatment Plants will be retained after the treatment plants themselves have been abandoned.

Sludge Disposal:

The KSMP’s strategy for sludge disposal is that the primary disposal method should be land application to improve soil conditions for agriculture, afforestation and landscap­ing. Before land application, the sludge is to be stabilised by digestion, and mechanical dewatering.

Sulaibiya Wastewater Treatment Plant:

The first major KSMP’s component selected for implementation is the new Sulaibiya Wastewater Treatment Plant, together with the related wastewater conveyance system. The conveyance system includes a major pumping station at Ardiya and triple 1400 mm diameter pressure main from the new pumping station to the treatment plant at Sulaibiya.

The project’s scope includes a Central Telemetry Control System (CTCS) facility for monitoring Kuwait’s wastewater management infrastructure. From the CTCS, which will be located in Ardiya, the MPW will be able to monitor the status of both the new project’s facilities and the existing sanitary sewerage system of the major pumping stations, secondary pumping stations, lift stations and three treatment plants.

The existing facilities will be linked into the CTCS under contracts separate to that for the Sulaibiya Wastewater Treatment Plant project.

Wastewater Conveyance System:

Raw sewage will be pumped to Sulaibiya from the new Ardiya pumping station located on the site of the existing Ardiya Wastewater Treatment Plant. Three 1400 mm diameter, ductile-iron pressure mains will run for the approximately 24 km distance from Ardiya to Sulaibiya. At the pumping station, the raw sewage will be screened in four mechanically raked bar screens of the climbing type, and grit will be removed in four vortex detritors.

The pumping station will be a wet-well/dry-well type installation capable of housing 12 pumps (9 duty and 3 standby) each with a 1.3 m³/s capacity. The initial installation will involve ten pumps, each with a 1.15 m³/s capacity. The motors will be two speed units with 11 kV and 1.5 mW of power.

The maximum pumping heads will be around 100 m at ultimate flow. The pumping station’s operation will be fully automatic with a facility for remote monitoring and control.

Odour control is provided at the screening and grit removal facility, and at the wet well by ventilation through multistage, packed scrubber towers which use NaOH and NaOCI solutions. At each air valve on the pressure mains, vented gases will be passed through activated carbon canisters.

Wastewater Treatment Plant:

The site layout for the Sulaibiya Wastewater Treatment Plant is planned to permit the ultimate construction of facilities to treat the wastewater expected to be generated by communities in its catchment area through the year 2050. The first phase of facility’s development is intended to meet the wastewater treatment needs of design year 2015, which is projected to be 375,000 m³/d. A process flow diagram for the facility is shown in Fig. 4.

The expected raw sewage characteristics and design treated effluent characteristics are given in Table 2. Anticipated removal efficiencies for the various treatment process units are given in Table 3.

A further design criteria was the avoidance of odours, and this was a significant factor in the selection of specific processes, particularly the decision to omit primary sedimenta­tion and to use aerobic sludge digestion.

Primary and Secondary Treatment:

The wastewater treatment processes selected are:

1. Grit removal using four vortex detritors housed in a building with odour control facilities.

2. Pre-aeration with H₂S stripping,

3. Lime addition for alkalinity,

4. Activated sludge secondary treatment process inn 11 aeration basins, and

5. Clarification in 11 secondary clarifiers.

Although primary sedimentation is not to be provided in the initial construction of the treatment plant, the facility has been planned and laid out to permit its later addition. The decision not to use primary sedimentation was based on the belief that the primary sedimentation process will have reduced effectiveness on wastewater which has degraded in the long collection system and pre-aeration process, while there is a potential for odour generation and a consequent need for costly measures to contain and treat vented gases.

The activated sludge aeration basins are designed to operate in either the conven­tional plug-flow nitrification mode, or in a biological denitrification mode by introducing the option to use the modified Ludzack-Ettinger process.

Diffused air aeration is used in the aeration basins, with the main system being of the medium-bubble type. Some aeration/mixing are met by jet-aerators. Two blower build­ings are provided, one containing eight blowers and the other blowers (with provision to add another four). The blower are single-stage centrifugal units that are driven by 11 kV motors with 2,000 kW of power.

Tertiary Treatment:

Tertiary treatment is provided by twenty gravity sand filters of the travelling-bridge type, followed by disinfection. Ultraviolet disinfection is used for the final effluent, with the addition of chlorine to provide a chlorine residual in the treated-effluent distribution system. The chlorination system is also able to provide backup in the event of failure of the ultraviolet facility.

Sludge Treatment:

The sludge treatment processes are:

1. Thickening using gravity belt thickeners,

2. Aerobic digestion in five digester basins with low-speed mechanical aerators,

3. Dewatering using belt-filter presses, and

4. Pasteurization by the addition of lime kiln dust in a pug mill.

After dewatering and pasteurization, the sludge is matured through window storage in a covered area.

Control of the treatment plant processes will, to a large extent, be automatic.

Odour control measures are provided at the grit removal facility, the pre-aeration chamber, the primary clarifiers (if constructed) and for the first, anoxic, stage of the activated sludge process. In each case vented gases will be passed through single-stage, packed, scrubber towers.

Other facilities provided on the treatment plant side include an administration build­ing housing the operational control offices and staff amenity facilities, a laboratory and a maintenance facility equipped to provide all necessary on-site maintenance support for the plant.