Posted by adminJanuary 10, 2006General

Vacuum System

Introduction

Vacuum technology is used for collecting and conveying wastewater in domestic, commercial and industrial areas, for both outdoor and indoor systems. High groundwater table, low population density, flat terrain (lack of natural slope); unfavourable soil conditions like sandy, unstable or rocky ground are the ideal circumstances in which to use vacuum sewer systems. In areas along rivers, lakes or coasts as well as in water protection zones, vacuum sewerage is often the only choice. Moreover it offers specific advantages for residential areas where the wastewater flow is low or varies in a wide range (e.g. tourist areas). Other benefits include independence from terrain, small pipe diameters, high flexibility and low maintenance costs¹.

Figure 2²

Comparisons between vacuum and gravity systems ³

Vacuum Gravity
Light, flexible pipelines made of PE or PVC Heavy, rigid pipelines made of respectively cast iron
Small trenches (layout also beneath pavements, in narrow streets/passages) Wide, large trenches-big excavating machinery (caterpillar) in use
Shallow trenches (1.0 – 1.2m deep, frost-free layout or even nearer to the surface in frost-free areas) 

Figure 3

Deep trenches 

Figure 4²

Layout (in common trenches) together with other pipelines (even those for drinking water) possible Layout together with other pipelines not allowed
Manholes in pipeline reticulation are not required In case of changing the direction of the pipeline and at least at each 70m distance, a manhole is required
In flat terrain, the layout of pipelines for a length of several km possible-without additional pumping stations In flat terrain at appointed, regular distances pumping stations are required in order to lift the sewage to a higher level
Layout of pipelines in potable water intakes or catchment areas possible, because in case of damages no leakage of sewage can occur. Layout in ecologically sensible areas prohibited due to danger of leakage
Simple layout of pipelines in swampy ground and in areas with a high groundwater level or in areas which are often flooded Layout of pipelines in swampy ground and areas with high ground-water table is difficult and mostly impossible due to often expensive and work-intensive excavation security measures and water management
Easy crossing of obstacles (trenches, rivulets, inverted siphons, cables) over pipe bridges or beneath obstacles Crossing of obstacles is difficult and cost/work-intensive, only with lifting machinery
Cheaper layout of the sewer lined in case of difficult geological/ground conditions (swampy ground, peat soil, rocky ground, danger of movements of ground or unstable ground) Cost- and work-intensive layout in case of difficult ground conditions
Trenchless or no-dig layout possible Trenchless or no-dig layout not possible
Less construction costs Higher construction costs
Shorter construction periods Longer construction periods
Tight, odourless system Open, no odour-free system
Especially in flat terrain: Energy saving: Connection to the electrical net only in the vacuum station Several decentralized pumping works and lift stations increase the energy consumption of the total system

**Note: Vacuum Sewerage Systems (VSS) may not be the appropriate solution for every application.

Vacuum System Components 4

The vacuum sewer system consists of the vacuum valve unit, the vacuum pipeline and the vacuum station.

1. Vacuum valve unit
The sewage from the houses and buildings flows into the vacuum valve unit by gravity. When the sewage quantity reaches to a certain level, the water level controller is triggered to open the vacuum valve and the sewage is sucked into the vacuum pipeline. The vacuum valve is operated automatically by the vacuum pressure in the pipeline and electric supply is not required.

2. Vacuum pipeline
The sewage is sucked into the pipeline together with the air at the valve units. The sewage and the air are intensively mixed up in the vacuum pipeline and transferred into the vacuum station. Thus the sewage is supplied with sufficient oxygen and the generation of dangerous and harmful gas is avoided. Isolation valves are installed every approx. 400m distance for maintenance purpose in the pipeline. Maintenance manholes as in the case for the conventional gravity sewer system are not required at all. The vacuum pipeline consisting of the down grade slopes (0.3%) and the upward lifts can be positioned along the ground surface geometry and can avoid various obstacles underground.

Figure 5²

3. Vacuum station
Vacuum is generated in the vacuum station and the sewage in the pipeline is sucked into the collecting pit or tank in the vacuum station. The collected sewage is transferred by pumps to a sewage treatment plant. There are two options as for vacuum generation. The one is ejector system and the other vacuum pump. With the ejector system, the sewage in the collecting pit is recirculated by the circulation pumps through the special ejector which generates the vacuum.

EcoSan Concept 5

Vacuum technology is particularly applicable to systems designed in accordance with the EcoSan concept. Vacuum toilets and interface valve units are major components of systems where foul and grey water is to be collected and treated separately.

There are numerous examples to demonstrate this. The foul water from vacuum toilets and urinals is collected under vacuum and transported for biological treatment. During treatment biogas is produced having a large methane content together with other biodegradable residues. The biogas can be refined and used as an energy source whilst the biodegradable residues can be mixed with other green waste to produce compost. This can be used as a soil conditioner in either horticulture or agriculture closing the recycling loop.

Loops can be closed including the solid waste streams and eventually create an integrated energy concept.

Additionally, the black water can also be collected separately for urine and faeces. The reuse of urine has priority. After urine is gathered undiluted and stored for some months, it can be used as a fertilizer in agriculture. Alternatively certain ingredients (phosphates, nitrates etc.) can be isolated for a further use in the chemical industry.

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1 ROEVAC® Vacuum Sewer Systems. [Online]. Available: http://www.roevac.com/page/en/page_ID/42[2006, January 19]
2 Behnke, S.M. (2003) Vacuum Sewerage – A Modern System Aiding To Reduce The Costs of Communal Wastewater Collection. Roediger Vakuum- und Haustechnik GmbH, [email: behnke@roediger-hu.de]
3 Wong, Y.Y.L. The Sewerless Concept-Sewerage System for the Future and its Suitability in Malaysia. Sistem Vakuum Sdn. Bhd. [email: yale@pc.jaring.my]
4 Japanese Advanced Environment Equipment.[Online]. Available: http://nett21.gec.jp/JSIM_DATA/WATER/WATER_2/html/Doc_247.html [2006, January 19]
5 ROEVAC® Vacuum Sanitation Systems. [Online]. Available: http://www.roevac.com/page/en/page_ID/54 [2006, January 24]

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