A Case Study - VACUUM SEWER SYSTEMS

INTRODUCTION:

During the latter days in the field of Sewerage System, a lot of alternatives were gauged and had passed through environmental requirements. Today, promotions of the advanced technology have resulted to a challenging scope of work that Corodex Electromechanic, a part of Concorde-Corodex Group (CCG), seized through the stiff competition in the market. Thus, winning the prestigious project for the Palm Island in 2000 has been CCG’s greatest conviction toward success.

The Palm Jumeirah Island holds its pride for being lucrative, while remarkably distinguished by the whole world as one of its wonders. The system has supported approximately 2,000 villas, having 900 collection chambers and 40 km of vacuum sewer line to a central Roevac vacuum station, which is installed underground inside the sewage treatment plant.

The design of the vacuum sewerage system conforms with European Standard EN 1091 and the design guidelines of the German Wastewater Association.

SCOPE OF WORK:

This method statement covers the Installation & vacuum testing of vacuum sewer line, assembling & installation of collection chamber & installation of vacuum.

SYSTEM GENERAL INFORMATION:

Vacuum sewer systems are wastewater collection systems. An air stream generated by differential air pressure drives the wastewater toward a vacuum station.

A vacuum sewer system is consisted of: a vacuum station, where the vacuum is generated, the wastewater is collected, then pumped to a wastewater treatment facility, a vacuum pipeline system, typically consisting of a branched network of vacuum sewer pipe, and collection chambers with sumps and interface valve units.

Wastewater flows by gravity from a house/villa into a collection chamber’s sump. After a given quantity (batch) of wastewater accumulates in the sump, an interface valve automatically opens.

The batch volume plus an additional volume of air flows through the open valve and is transported to a centralized vacuum station.

Vacuum sewer pipe is arranged with high and low points in a specific elevation profile. Batches of wastewater come to rest at low points in the pipe. When air is introduced through an upstream interface valve, the wastewater is pushed plug-wise over subsequent high points toward the vacuum station.

Wastewater and air are driven to a collection tank (vacuum tank) at the vacuum station. Vacuum generators (vacuum pumps) maintain vacuum in the tank and sewer pipe.

Conventional sewage pumps forward collected wastewater from the collection tank through a force main to wastewater treatment plant.

SPECIFICATIONS:

VACUUM SEWER LINES:

§ Comprised of HDPS High Density Polyethylene SDR 11 & uPVC PN10 pipes.

§ Polyethylene pipes are electro-fusion-welded to ensure airtight conditions.

§ Pipe diameters- from 90 mm up to 250 mm.

§ Outside diameter- 75 mm or 90 mm for the vacuum sewer main line.

§ Division valves are capable of sustaining a vacuum of 80 KPa.

§ Valves are made from ductile iron with internal & external epoxy coating.

VACUUM COLLECTION CHAMBERS:

§ Made of PE or fiberglass material with a wall thickness on the least 6mm.

§ Insulation layer of styrofoam in the valve chamber protects the interface valve unit from extreme (hot & cold) temperature.

VACUUM INTERFACE VALVES:

§ The interface valve body is made of ABS or material with similar characteristic.

§ These valves are membrane/diaphragm type which ensure total closing or complete opening of the valve even under unstable pressure conditions.

§ Minimum size of 65 mm diameter.

§ Capable of passing solids with a minimum size of 55 mm diameter.

§ The interface valves are complete with controller, rubber coupling, plastic tubing, sensor piping connections, and monitoring connections.

§ Valve opening times are adjustable.

§ Watertight

§ Activated pneumatically without any need of energy/electricity at each valve.

CONTROLLERS:

§ Open the interface valve only if there is a minimum vacuum of 22 kPa available.

§ Maintain the valve fully open for an adjustable time period or until the sump has been fully emptied.

§ Made of polyamide or equal material with similar characteristics.

§ Slide-attached to the valve body and exchangeable within 1 minute.

§ The air-admission time is adjustable in a wide range (up to 15 seconds) by turning of a screw or similar method.

VACUUM STATION:

§ Comprise all civil works; mechanical and electrical works including pipework, vacuum vessel, vacuum pumps, sewage discharge pumps, control panel, odor control equipment, ventilation, air-conditioning and lighting.

§ The vacuum station building is of cavity wall construction.

§ Includes one or two vacuum tanks, several non-clog sewage pumps, and a control panel.

§ A supplementary vacuum reservoir tank, standby generator, or biofilter for the exhaust air can be provided as required.

VACUUM VESSEL:

§ Manufactured of steel with internal and external epoxy coating.

§ Equipped with lifting lugs and all required process connections.

§ Vacuum vessels that are installed underground are protected against flotation and setting.

§ Constructed from not less than 9mm thick steel plate; thus, it provides flanged manhole access of minimum 600mm diameter to permit man entry for inspection and maintenance.

§ The minimum vessel capacity is calculated under consideration of the maximum switch-on-frequency of the aggregates of 12 to 15 times per hour.

VACUUM PUMPS:

§ Liquid ring pumps are not applied due to high service and maintenance requirements.

§ Minimum one duty and one stand-by vacuum pumps are installed.

§ The pump controls incorporate auto and manual duty changeover facilities.

§ Operated by pressure switches attached to the vacuum vessel.

§ Interlocked with an emergency floating switch inside the vacuum vessel to prevent sewage from being drawn into the vacuum pumps.

SEWAGE DISCHARGE PUMPS:

§ Minimum one duty and one stand-by sewage pumps were installed.

§ Suitable for operation under negative pressure without cavitation.

§ Pumps are dry pit, centrifugal impeller type capable of passing solids of a minimum shere size 65 mm diameter.

§ Controlled by analog capacitive level measurement installed inside the vacuum vessel.

ELECTRICAL CONTROL PANEL:

§ The operation of all pumps is controlled by programmable logic controller.

§ Simultaneous starting of vacuum and sewage pumps is prevented by the programme to prevent surges.

§ The vacuum pumps are controlled by monitoring the vacuum inside the vacuum vessel with adjustable pressure switches.

§ The sewage pumps are controlled by capacitive level measurement in the vacuum vessel. Telemetry:

GENERAL ADVANTAGES OF VSS:

Construction & Installation:

§ Small diameter plastic pipes (PVC or HDPE)

§ Shallow & narrow trenching

§ Uphill transportation possibility.

§ No need for manholes or lift stations.

§ Easy change of direction, crossing over or under obstacles (flexible pipeline construction).

§ Vacuum sewer may cross water protection areas because exfiltration cannot occur.

§ No need for electrical power at collection chambers.

§ Fast construction, minimal traffic disturbance and environmental impact.

§ Low construction costs.

Operation & Maintenance:

§ No line flushing because of self-scouring flow velocity.

§ No operator contact with wastewater.

§ No exfiltration & wastewater.

§ No infiltration & ground water, vacuum sewers are tightness tested.

§ No septicity because the wastewater in vacuum sewers is continuously aerated.

§ Pinpoint leak detection.

§ Reliable, durable components that are easy to service.

§ Low operation & maintenance costs.

FEATURES:

§ Complete disassembly and re-assembly of an interface valve is easily completed in less than three minutes.

§ Unique pulsed-flow controllers facilitate intermittent evacuation of small batches of water and air to keep the air/ liquid ratio (ALR) constant.

§ Automatic air admission controllers used for flushing lines with air are available. Air admission is either controlled by vacuum strength or by a timer. These controllers are used to prevent excessive hydrostatic head loss, or to increase flow velocity during low flow periods.

§ Controllers automatically adjust the ALR (air to liquid ratio) with changing vacuum levels, i.e. the lower the vacuum strength the smaller the wastewater’s batch volume.

§ Roediger designs sewer pipe profiles based on flow, line length, topography, pipeline material and ground stability. Our unique wave profile requires no lift fittings. Our saw-tooth profile provides excellent momentum transfer from air to water.

§ Inspection pipes along vacuum sewers permit manual aeration, connection of pressure gauges and isolation by introduction of an inflatable ball.

§ Vacuum stations are custom designed. Typically, the equipment is supplied as skid mounted system to be placed in a vacuum station building.

§ There is no steel, stainless, or metallic component in contact with wastewater or ground water. The only metallic compo9nents are stainless steel quick release clamps and hose clamps that are located in our watertight valve chamber.

§ Our atmospheric, passenger load chambers neither need breather lines for ventilation of valves and controllers nor air inlets on the gravity lines. The plastic covers are provided with a locking mechanism with a special key.

§ Flood-proof, light traffic chambers are provided with a sealing plastic cover and an additional cast iron lid above.

§ Flood-proof, heavy traffic chambers are provided with plastic covers and cast iron frames and covers on top of concrete support rings.

~ scribbled for CCG