Motorised Emptying and Transport

In the absence of a sewer system and where toilet products can not be reused on-site, faecal sludge from pit latrines, septic tanks, biogas settlers and other water-reliant on-site sanitation systems need to be emptied regularly. This can be done either human powered or by a truck. 

A truck is fitted with a pump which is connected to a hose that is lowered down into a tank (e.g., Septic Tank) or pit, and the sludge is pumped up into the holding tank on the vehicle. This type of design is often referred to as a vacuum truck. Generally, the storage capacity of a vacuum truck ranges between 3 and 12m3 (TILLEY et al. 2014).

Depending on the toilet system, the material to be pumped out can sometimes become very compacted that it cannot easily be removed (TILLEY et al. 2008). In these situations, the solids have to be liquefied with water in order to flow more easily (TILLEY et al. 2008). If water is not available, the waste will have to be removed manually. Faecal sludge collection and haulage are particularly challenging in metropolitan centres with their often large and very densely built-up, low-income districts. Large trucks often have difficulty accessing the latrines or septic tanks in areas with narrow or inaccessible roads (EAWAG/SANDEC, 2008). If there is no access for trucks, other techniques such as human powered pump and vehicle will have to be used. Alternative motorized vehicles or machines have been developed for densely populated areas with limited access. Designs such as the Vacutug, Dung Beetle, Molsta or Kedoteng carry a small sludge tank and a pump and can negotiate narrow pathways.

All vacuum tanker systems use a pump to create a vacuum in the tank and suction hose. The vacuum then lifts the sludge into the tanker. If the bottom layers of sludge are compacted, they can be broken up with a long spade, or jetted with a water hose, before being pumped out. Water hoses (with their own water tanks) are often fitted to the tankers. Some tankers have high-powered vacuum pumps and an air stream into the suction hose that acts as a transport medium for the sludge (“air drag” or “plug and drag” techniques; BRIKKE & BREDERO 2003). These tankers can deal with heavy sludge in pit latrines (especially at the bottom where solids have settled out and organic material has broken down). A small amount of sludge should always be left in the pit to ensure that decomposition continues rapidly (see also septic tanks). Vacuum tankers can be emptied by pressure discharge or by tipping the tank (BRIKKE & BREDERO 2003).

The vacuum truck service and its O&M are usually organised and executed by a professional organisation, normally under the responsibility of the municipality. User fees for the service are usually set officially (and often heavily subsidised), either by the organisation or the government. There is very little involvement of the households being served. Management and supervision of the services are often ineffective. In many areas, for example, the lack of vacuum tankers results in poor service (BRIKKE & BREDERO 2003).

Generally, the storage capacity of a vacuum truck is between 3 and 12 m3. Local trucks are commonly adapted for sludge transport by equipping them with holding tanks and vacuums. Modified pick-ups and tractor trailers can transport around 1.5 m3, but capacities vary. Smaller vehicles for densely populated areas have capacities of 500 to 800 L. These vehicles use, for example, two-wheel tractor or motorcycle based drives and can reach speeds of up to 12 km/h. Pumps can usually only suck down to a depth of 2 to 3 m (depending on the strength of the pump) and must be located within 30 m of the pit. In general, the closer the vacuum pump can be to the pit, the easier it is to empty.

One of those vehicles to empty pit latrines and septic tanks in areas of difficult access is the Vacutug. The UN-HABITAT Vacutug Project was conceived in 1995 with the goal of developing “fully sustainable system for emptying pit latrines in unplanned, peri-urban areas and refugee camps in the developing countries” (see also UN-HABITAT n.y.). The Vacutug consists of a 0.5 m³ steel vacuum tank connected to vacuum pump which is connected to a gasoline engine. On level ground, the vehicle is capable of around 5 km/h. The waste sludge can be discharged under gravity or by slight pressurisation from the pump (TILLEY et al. 2008). 

Another possibility is to combine small and large equipment. In this way nearly 100% of the houses can be covered. The pit latrines or septic tanks are emptied by a Vacutug and collected in a storage tank, which can be hook-lifted and hauled away by a vacuum truck (STRAUSS et al. 2002).

The use of a vacuum truck presents a significant health improvement over manual emptying  which is quite unsafe and unhygienic and helps to maintain the Collection and Storage technology. Still, truck operators are not always accepted by the community and may face difficulties with finding appropriate locations to dump and transfer the collected sludge.

Another problem could be the discharge of collected faecal sludge. Managing the faecal sludges collected from on-site sanitation systems is a crucial element in public health protection and key to successful water and sanitation projects, especially since one vacuum truck dumping sludge indiscriminately is equivalent to the open defecation of 5000 people (KONE et al. 2007).

Most pump trucks are manufactured in North America or Europe. As such, it is difficult to locate spare truck parts and a local mechanic to repair broken pumps and trucks. New trucks are difficult to obtain, very expensive and thus rarely purchased. Local trucks are commonly adapted to serve as vacuum trucks by equipping them with holding tanks and vacuums (TILLEY et al. 2008).

Maintenance accounts for at least one quarter of the costs incurred by the operator of a vacuum truck. Fuel and oil account for another quarter of the total operating costs. Owners/operators must be conscientious to save money for the purchase of expensive replacement parts, tires and equipment. The replacement could be essential to the working of the vacuum truck (TILLEY et al. 2008).

Initial costs of a vacuum truck can vary enormously and depend on the manufacturer, the condition of the equipment, the country of use, etc. Prices can vary from US$ 20 000–100 000 or more (BRIKKE and BREDERO 2003).

However, the small Vacutug is more economical. Recent results indicate that under certain circumstances (constant number of pits, transfer station, short transfer distance, etc.) the Vacutug can be sustainable and cover its operating and maintenance costs (TILLEY et al. 2008).

Most pump trucks are manufactured in North America, Asia or Europe. Thus, in some regions it is difficult to locate spare parts and a mechanic to repair broken pumps or trucks. New trucks are very expensive and sometimes difficult to obtain. Therefore, older trucks are often used, but the savings are offset by the resulting high maintenance and fuel costs that can account for more than two thirds of the total costs incurred by a truck operator. Truck owners must be conscientious to save money for the purchase of expensive replacement parts, tires and equipment. The lack of preventive maintenance is often the cause for major repairs. The most important checks, especially for vacuum trucks, are listed below (adapted from BRIKKE and BREDERO 2003):

Daily Checks before Work

• the oil levels in the vacuum pump, oil-cooling tank, hydraulic tank and tanker engine
• the tanker fuel level
• the water levels in the tanker engine, the windscreen water bottle, the wash tank, and the water tank for the vacuum pump
• are all the necessary materials present
• the cooling radiator for the hydraulic oil and pump oil
• is the rear door closed and secured

Daily Operation after Work

• drain the sludge and oil separators

Weekly Checks

• tyre pressures, lights, indicators, horns
• valves that prevent the tank from being overfilled
• contacts between gaskets and seats, and performance steel balls;
• leaks in the hydraulic system (tighten couplings), and power take-off shafts (depending on type)

The addition of chemical additives for desludging is not recommended because they tend to corrode the sludge tank.