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The sewage system without solids is also known as small-diameter sewage or settled sewage networks. The system was originally conceived in the Department of Agriculture of the United States in the decade of the seventies to address problems of infiltration in areas with little capacity to absorb effluent from septic tanks.
In the system of settled sewage networks (RAD), these are decanted or settle before being taken to the networks in order to retain the solid, the liquid flows into the collectors.
The process of settling of solids takes place in interceptor tanks septic tanks or a single camera and can receive wastewater from one or several homes.
· Advantages and disadvantages
The main advantage is the reduction of costs:
· Excavations since the absence of solids in the system it is necessary to ensure minimum flow velocities self-cleaning, which decreases the slope of the collectors.
· Pipes, used for small diameter collectors.
· Ancillary works, because pits are replaced by structures more simple record such as check boxes and cleaning and inspection records.
· Sewage treatment because primary treatment takes place in the septic tanks, and is no longer necessary to plan this process in the treatment units.
The main drawback of the system is in the septic tank maintenance requires periodic removal and disposal of solids accumulated there. For this reason, the sewer must be constructed opted only when there is an organization that ensures the maintenance.
This organization should carry out a strict control to prevent illegal connections to which they may be missing or have interceptor tank erroneous connections that would enable the introduction of solids or rain water that would cause serious problems in operation and maintenance.
· The system components sewer opted consist of the following parts:
Cleaning and inspection records and check boxes
a. Household connection: This connection is placed at the entrance of the interceptor tank. Entering the system for it all household waste; be excluded stormwater and solid waste. The diameter of these collectors is 75-100 mm.
b. Interceptor tank: A septic tank and essential component. This tank should be adapted and easily constructed; should remove floating and settleable solids. Has inlet and outlet pipes, the latter is connected to the system through a tee and an elbow and may have a smaller diameter than the inlet pipe.
c. Collectors Collectors are polyvinyl chloride pipe (PVC) of small diameter (minimum 50 mm) that are buried deep enough to collect sedimented water. Unlike conventional collectors, these are not necessarily placed on a uniform gradient with straight alignment between the cleaning and inspection records.
As no solid carry, allows for sections of pipe work properly even under pressure, positive or negative slopes, provided that the pressure in the pipes does not cause the backflow of sewage into septic tanks are connected. It is not necessary to consider the slope and minimum and maximum speed because the liquid is free of solids, therefore, the pipes can follow the topography, maximizing the energy resulting from the difference in height between the upstream and downstream. The list can be drawn by green and pedestrian areas, to reduce the risks of live loads due to vehicular traffic, thereby decreasing the excavations.
d. Cleaning and inspection records and check boxes cleaning records and inspection and check boxes allow access to sewers for inspection and maintenance. In many instances the records are preferred cleanup before check boxes because they cost less and can be sealed hermetically and avoided most of the infiltration and sand that commonly enter through the walls and caps check boxes. Check boxes are recommended in the main meetings of collectors in very abrupt changes of direction, or in places where it is difficult to build a record, having very deep pipeline. See Figures 1 and 2 (Ref.)
Records of inspection and cleaning should be arranged in the headwaters of the network, at the junction of two or more collectors in very abrupt changes of direction, at high points to avoid the accumulation of gases and straight every 200 m. See Figures 3 and 4 (Ref.)
· Conditions for installation: The unsettled sewage network is a system that is best suited to small communities, outlying areas of low population density, high water table, coastal villages, isolated groups of houses and rural settlements.
· Costs: Construction costs represent about one fifth of conventional sewerage, plus the system provides primary treatment of domestic wastewater. In places with relatively large financial resources is possible the acquisition of mechanical equipment for vacuum cleaning of the interceptor tanks. For small communities, cleaning should be performed by users, under the supervision of an entity experienced in this field.
Simplified sewerage networks (SAN) are formed by a set of pipes and fittings that are designed to collect and transport the wastewater for disposal. The RAS differ from conventional sewerage in simplifying and minimizing the use of materials and construction criteria. The main differences in the RAS with conventional sewers are:
They are designed from house connections.
His depth of excavation is reduced. For this reason, the pipes are projected through pedestrian areas or to prevent vehicular areas require protection against mechanical shock tube. In some cases, networks projected double.
Its design period is shorter and can be built in stages.
Are sized according to the per-capita consumption and socioeconomic conditions of the population.
It controls the sedimentation in the pipes, with the concept of drag force, which is more practical to control the sedimentation through the criterion of a minimum speed rating.
Requires fewer manholes and the cost of building these structures is reduced.
Elastic jointed pipe used to reduce infiltration.
The tie ratio (h / d) should be less than or equal to 0.8 in order not to increase the diameter of the pipe and allow free movement of gases.
Accept a minimum diameter of 100 mm.
· Design Innovations
a. Driving voltage
Drag tension (O) is the unit tangential force exerted by the liquid on the collector and on the deposited material. It is also considered as the drag force divided by the area over which it operates.
The drag force is the tangential component of the weight of liquid that moves in an inclined plane. To consider the portion of the liquid in a section of length L, we apply the following formula:
Formula to determine the drag force
F = y * A * L
F weight of liquid, kg
Ft tangential force, kg
Ft = Y * A * L * sin or
Or pulling force, kg/m2
O angle of inclination
o = Y * A * L * sin o / P * L
Section length, m
A wet area m2 section
o = Y * Rh * sen or
Cartago within p / <>
And specific weight, kg/m3
Rh hydraulic radius, m
P wet perimeter, m
o = 1000 * Rh * I
I slope of the collector, m / m
It is important to note that the hydraulic radius hydraulic radius must be real and not corresponding to the nominal or full pipe flow.
This is not to sedimentation in the pipes the value of the tensile force is 0.15 kg/m2 for the removal of particulates down to 2.0 mm in diameter.
When you do not want to design the drag force approach can be avoided by controlling sedimentation real flow velocity and not the rated speed or full pipe, this speed can be set to a value greater than 0.3 m / s, because according to studies in Brazil, with values â€‹â€‹of 0.3 m / s the collectors did not suffer any damage.
b. Inspection and cleaning devices
In conventional sewers is necessary to project a manhole in spurts, slope change, changes in diameter or address, at the intersection of two or more collectors and straight with lengths exceeding 100 m. The model of these wells is similar for each of these conditions while the simplified sewerage using different models for each case. The proposed solutions are:
Inspection and cleaning devices
Initial stretch or tear
Change of slope or diameter
S long straight Collector
Vertical tube inspection.
The alternative proposed structures are simpler and less expensive, with new mechanical equipment for cleaning sewers, it is not necessary that a worker down a manhole for inspection. It is necessary that a sewer project including a description of these teams with their technical specifications to perform maintenance.
Construction costs of simplified sewerage networks are 30% or 40% less than the cost of a conventional sewerage, not including the cost savings from pumping and treating sewage.
This system consists of sewer networks condos within a block, in other words, the networks in condominiums are planned for the lots or backyards of homes, in order to reduce the maximum length of nets internal (inside the house) and external.
The basic system of collection is designed as a simplified sewerage networks. The derivation in condominiums within each block consists of a surface line of t 100 mm and usually with a minimum slope of more than 1%.
As the sewer system within a condominium block is built over successive private property, you must have prior consent of the owners. It is therefore essential to carry out health education, personal hygiene and community participation to promote the project, explain the system, to convince stakeholders and ensuring community participation in the construction, maintenance and operation of the system .
Easy construction and lower cost of connections indoors.
Minor extension of main sewers.
Increased community participation.
Low cost of construction and operation of the entire system
Installation depends on the architectural layout of the houses, health services should be located in the back of these and having free zones for expanding networks.
Legal issues may arise as the managing entity must have legal authorization to inspect and repair the system, plus the owners can not build on the pipes.
In other cases it may be prohibited from the drain of a property is discharged into the neighbor's land.
Some users may abuse the connection, dumping solid waste or storm water that would cause serious damage to the system.
The risks can find the personnel performing the cleaning in the toilet, can be:
Burns âž use of corrosive chemicals.
âž poisoning, suffocation (places with little ventilation, inadequate mixing of substances, ...)
âž Biological hazards from bacteria, fungi, etc.
âž Punctures, cuts, etc..
The cleaning staff of health centers will be exposed to the following risks:
âž infections in contact with biological contaminants.
âž Tuberculosis, chicken pox, influenza, tetanus, rubella, hepatitis B and C, HIV, ...
The cleaning staff does its work in pits, tanks, confined spaces, are exposed to:
âž Falls at different level within the trench.
âž wounds, punctures in the hands or feet.
âž Projection of fragments and particles on the eyes
âž Projection liquid eyes, face, etc, whose consequences will burn.
Risk âž electric metal walls, humidity, etc
âž Inhalation of vapors that could eventually lead to suffocation, poisoning, etc..
The janitors of the schools will be exposed to risk for infectious diseases, fungi, bacteria, etc.
A very high percentage which is the sector are women. Recent studies have indicated that the cleaning women (especially those working in the cleaning of hospitals and health centers) suffer up to three times more than your health problems than women who do not perform this type of work, increasing the risk of asthma and bronchitis. A recent study of women engaged in cleaning work, published in the journal "European Respiratory Journal, has seen a worsening of symptoms of asthma and chronic bronchitis due to the use of certain products, like bleach or some aerosols . As explained in the study, the researcher Jan Paul Zock of the Centre for Research in Environmental Epidemiology (CREAL), Municipal Institute of Medical Research (IMIM) in Barcelona, â€‹â€‹you should be aware of this disease in this type of workers - most are women, and carry out a series of recommendations:
âž Avoid harmful products for asthma and chronic bronchitis as-spray-especially since it facilitates inhalation.
âž Leave the room then have been applied to these substances.
âž properly ventilated rooms
âž Adequate disease control through monitoring of medication (help control symptoms.)
The chemicals are a risk on health and the environment, which should be made known to avoid the risk, while enabling workers to intervene with that risk, being of vital importance to identify risk, understand the alternative products and practices.
In case of accidental ingestion, call a poison control tel: 915 620 420 Some of the environmental damage caused should be mentioned water pollution with persistent chemicals, endocrine disruptors, or phosphates, air pollution with volatile organic compounds, destruction ozone layer, generating large amounts of packaging waste, etc.
Chemicals can be harmful to workers and the environment
Used in cleaning a wide variety and quantity of substances that can produce from acute to chronic effects in the body of the worker. A large number of these products are irritating and also many of these chemicals are corrosive, and the most worrisome long-term effects (Table 2), which is more difficult to protect. These include the sensitization, asthma, but also used some products that are carcinogenic, neurotoxic, which may affect the endocrine system, reproductive, muscular, etc.
This labor, because their work is in contact with chemicals, and a large percentage of cases, there is a series of factors predisposing to accidents at work:
âž Rhythms of overwork, layoffs, non-compliance in health and safety, stress, lack of means to do the job safely and professionally.
âž Loss of job: part-time work, high turnover, low wage levels.
âž lack of studies on specific occupational risks in the sector.
âž deficient training of employers, workers, ... on the prevention of occupational hazards.
âž Subcontracts: workers are directly affected by the conditions of work of the user enterprise, without possibility to negotiate better working conditions.
These new technologies of sewage are simple, practical and economic. Should be implemented to increase coverage of sewerage services, thereby reducing the morbidity rates of waterborne diseases.
This new technology should be promoted together with the use of low flush toilets (4 or 6 liters), showers and mixers, low power consumption, thus significantly reducing per capita consumption of water and, therefore, the volume of wastewater.
(Documents available at the library of CEPIS)
Otis, Richard J. Mara, D. Duncan Sewerage design of small diameter. Washington, DC, World Bank, 1985.(TAG Technical Note, 14).
Rizo Pombo, JE handles, a new sanitation solution. Acodal, 28 (124) :441-68, May-Aug. 1985.
Guimaraes, Augusto Sergio Pinto. Technological alternatives to baixo custo. Papers presented at the Regional Research Seminar on Alternative Technology's Low Cost Sanitation marginalized urban areas.Lima, 1985.
. Brazil. Ministry de Desenvolvimento Urbano e Meio Ambiente. Simplified sewerage networks (SAN). Lima, CEPIS, 1987. Technical Manual, 1.
Vines, Marus, Reed, Bob. Low-cost Sewerage unconventional. Waterlines: Journal of Appropriate Water Supply and Sanitation Technologies, 9 (1) :26-29, July. 1990.
Azevedo Netto, Jose Martiniano de. Esgotamento health; Soluções appropriately. Sao Paulo, sn, 1986.
Note: - This Technical Disclosure Sheet has been prepared by Mr. Roberto Mejia, University of Antioquia (Colombia), during her internship as a participant in the CEPIS Continuing Education Program for University Teachers Convention Latin GTZ / OPS / CEPIS. We thank the technical review of Mr. Ricardo Torres, CORPOSANA, Asuncion, Paraguay.