Vacuum truck

Vacuum truck.

A vacuum truck or vacuum tanker is a type of tank truck that has a pump and a tank, designed to pneumatically suck liquids, sludges (such as fecal sludge), slurries or sand/water mixtures without the contact of any mechanical equipment. They are used to transport sanitary waste (human excreta mixed with water, e.g. from septic tanks) as well as for some industrial liquids or slurries. They can be equipped with a high pressure pump if they are used to clean out sewers from sand. 

Vacuum trucks are used to transport the collected material to a treatment or disposal site, for example a sewage treatment plant.

Other names used

Vacuum waste collection vehicle. Waste suction apparatus from R98 (a municipal cleansing company in Copenhagen in Denmark). The tube on the top is connected to a connecting piece kept under the pavement, and the waste is sucked out from a tank placed in a strategic place in the neighborhood.
Vacuum tanker used to collect sewage at Tatton Park flower show, July 2009, England

Other names used for vacuum trucks: vacuum tanker, "Sucker truck" (in Australia) or "Sewer Sucker", "Hydro-vac" or "vac-trucks" (in Canada). Slang terms include: "honey truck", "honey sucker" (in India and South Africa), and "honeywagon", all (probably) derived from honey bucket.

When a vacuum truck is used to transport fecal sludge then it can also be called "fecal sludge truck".

Design and configurations

Commercial vacuum trucks which collect fecal sludge usually have a volume of 10 - 55 cubic metres.[1] However various smaller versions for specialized applications or low-resource settings can be found with tanks as small as 500 liters.[2]

Pumps

They generally use a low-volume sliding vane pump or a liquid ring pump to create a negative air pressure.[1] The use of diaphragm mud pumps is less common, but with the advantage of a simpler design and usually lower overall costs.[3] The disadvantage is that mechanical parts come into contact with the sludge, which is not the case for the more common vacuum pumps.

The truck can be configured to be a direct belt drive, or a hydraulic drive system.

There are two different ways to mount the pump: either directly on the truck with the vacuum drive powered by the truck motor, or on the trailer with an independent motor. The second option with the independent motor is more complicated and not commonly used. It has the advantage of potentially having the pump closer to the septic tank. It is also able to use the negative pressure suction side of the pump as well as the positive pressure side to pump sludge over longer distances or lift it higher into the tank.

Suction hoses

The suction hoses are typically 2 to 4 inches (5.1 to 10.2 cm) in diameter with 3" or 3 inches (7.6 cm) being the norm. The possible length depends on various factors mainly related to the lift and other pressure losses. It is usually impossible to extend it beyond 50 m.

An inherent suction limitation of all suction pumps is that they can only lift a liquid through utilizing atmospheric pressure. For pure water the theoretical maximum lift is approximately 10.3 m (33.9 feet)). [4] However, due to the viscosity of fecal sludge it is possible to mix air into it either by sucking close from the surface or by adding air with a compressor through a separate hose. Through this the overall density of the sludge/air mixture can be reduced below that of pure water and thus a higher lift (10-15 m) can be reached under optimal conditions. Other factors affecting the possible lift and total length of the suction hose are that single stage vacuum pumps only reach a 85-90% partial vacuum, and that small air leakages, pipe friction losses and the viscosity of the liquid further reduce the possible lift.

Emptying the tanker

Normally a tanker is emptied by gravity. There is a possibility to pressure up the vacuum tank in order to “pressure out” the liquid quicker or against a small difference in level. But that procedure is not good for the equipment and is therefore done only in special situations.

The regular discharge time for a tanker of 8 – 9 m³ is about 15 minutes (or 7-10 minutes to unload a tanker of 4000 liters). The outlet is typically 4 to 6 inches (10 to 15 cm) in diameter. The discharge time depends on the thickness of the sludge, the size of the outlet valve and hose, the amount of garbage in the fecal sludge and how often the driver has to stop to clean the dump screen.

Uses

Vacuum trucks are used by town, and municipal, governments, and by commercial entities around the world.[5]

Human excreta

Several types of non centralized sanitation systems are served by vacuum trucks. They are used to empty septage from cesspits, septic tanks, pit latrines and communal latrines, for street cleanup, for sewer clean out, and for individual septic systems.[6] The trucks are used in the cleaning of sanitary sewer pumping stations. Vacuum trucks are used to empty portable toilets. In commercial aviation, vacuum trucks are used to collect waste from airplane toilets.

Vacuum trucks discharge these wastes to the sewer network, to a wastewater treatment plant, or—usually illegally, for example in many developing countries—into the environment. The latter practice, called "institutionalised open defecation", is dangerous since it constitutes a public health and environmental hazard.

Industrial liquids

Vacuum trucks are used in the petroleum industry, for cleaning of storage tanks and spills. They are also an important part of drilling oil and natural gas wells, as they are located at the drilling site. Vacuum trucks are used to remove drilling mud, drilling cuttings, cement, spills, and for removal of brine water from production tanks. They dispose of this in sump pits, treatment plants or if within safe levels may be spread out in a farmer's field.

Others

Vacuum trucks are also used for exposing underground utilities. The ground is jetted with water, and the vacuum truck sucks up the muddy product. This exposes the buried utility without the possibility of damage, as would be possible if a digging machine were used (i.e. tractor backhoe, tracked or wheeled excavator, ditch witches).

Vacuum trucks can also be used for cleanup of contaminated soil.

Examples

Bangalore, India

A typical vacuum truck in India has a capacity of 3,000 litres and serves about five buildings a day. Assuming a 2-year emptying cycle one truck can cater to about 3,000 to 4,000 buildings or 15,000 to 20,000 people. Vacuum trucks are an alternative to the dangerous and humiliating practice of manual scavenging that became illegal in India with the Manual Scavenging Act of 1993. In the city of Bangalore alone, it is estimated that there were up to 200 such trucks in 2012, serving more than 3 million people.[7] These vacuum trucks are operated by private companies without the need for subsidies. The charge for emptying a septic tank is between 1,200 and 3,000 Rupees (USD 24 and 60) every two years. After three months of composting, a truckload of compost can be sold for 1,500 to 2,000 Rupees (USD 30 to 40). In the Bangalore area, compost is used primarily on banana and coconut trees.[8][9]

Compost can generate revenues since it replaces expensive fertilizer. If septage is discharged on land for composting, each vacuum truck requires one hectare of land for composting.

See also

References

  1. 1 2 Strande, L., Ronteltap, M., Brdjanovic, D. (eds.) (2014). Faecal Sludge Management (FSM) book - Systems Approach for Implementation and Operation. Page 81. IWA Publishing, UK (ISBN 9781780404738)
  2. ↑ O’Riordan, Mark (April 2009). Investigation into Methods of Pit Latrine Emptying (PDF). WRC PROJECT 1745 Management of sludge accumulation in VIP latrines. pp. 15pp. Retrieved 18 January 2017.
  3. ↑ Wastecorp Pumps. "Mud sucker diaphragm pumps" (PDF). Wastecorp. Retrieved 18 January 2017.
  4. ↑ "Hydrostatics". Composed by J. B. Calvert. 5 January 2007. Retrieved 18 January 2017.
  5. ↑ Strande, L., Ronteltap, M., Brdjanovic, D. (eds.) (2014). Faecal Sludge Management (FSM) book - Systems Approach for Implementation and Operation. IWA Publishing, UK (ISBN 9781780404738)
  6. ↑ Lloyd Kahn, John Hulls, Peter Aschwanden, The Septic System Owner's Manual Shelter Publications, Inc., 2007 ISBN 0-936070-40-4 page 49
  7. ↑ Vishwanat Srikantaiah, Biome Environmental Trust: Sanitation without pipes - The 'Honeysucker' Approach to Human Waste Management Using Vacuum Trucks, in: Water and Food Security, World Water Week in Stockholm, 2012, Abstract Volume, p. 239-240
  8. ↑ Elisabeth Kvarnström, Vectura Consulting, Inc. Joep Verhagen, IRC Mats Nilsson, MN Context Vishwanath Srikantaiah, Biome Karan Singh, Biome Shubha Ramachandran, Biome. "Honey-suckers: Sanitation without pipes. Eco-san at work?" (PDF). Retrieved 2 September 2012.
  9. ↑ Rainwaterharvesting.wordpress.com (10 November 2011). "Eliminating manual scavenging – The Honey-sucker approach". Retrieved 2 September 2012.
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