Condominial Sewerage System

 

Sanitation is one of the greatest feat of mankind; sanitary facilities have saved countless lives from epidemics like cholera facilitating growth and progress of human civilization into the next frontier. London sewerage system, constructed in 1868 (started from 1859), reduced the outbursts of cholera killing as much as 6000 at once, returned glory of the Thames, and maintained London's reputation as the centre of the world during Victorian Era.   

However, this progress has not spread equally throughout the developing and underdeveloped nations. Though most houses have isolated sanitary system in form of septic tanks and soak pits, those unable to afford such construction are left without a proper sanitary system. The nature of sanitation is such that for the lack of the few, we must bear the consequences as a collective. Stinking holy rivers traversing our capital city, the 2018 spread of dengue across 43 out of 77 districts of Nepal are noteworthy instances of our mutual suffering by virtue of inadequate sanitary infrastructure.

As a response to inability of conventional sewer systems- in rapidly urbanizing Brazil- to serve the peri-urban poor of the state of Rio Grande do Norte, Brazil, Jose Carlos Melo envisioned condominial sewerage system in 1980s.

 

Condominial sewerage system can be better understood through its differences with conventional sewerage system.

Conventional sewers serve individual household as seen in figure 1 and 2. Collection lines drawn from individual homes are connected to conduits laid below the street. In contrast, in Jose Carlos Melo’s own words, “condominial systems deliver services to each housing block or any group of dwellings that could be termed a neighborhood unit or “condominium.” This is similar to the concept of providing a single connection to an apartment building, except that in this case the condominium is physically horizontal and institutionally informal.”  This approach greatly reduces length and diameter of conduits used, and slope at which they are laid out. Similarly, treatments facilities are decentralized in order to minimize the costs associated with transportation of fluid over long distances as opposed to centralized system where fluids are concentrated at a single geographical point.

Figure 1 Layout of conventional sewerage system and Condominial sewerage system (frontyard, back yard, and sidewalk respectively)

Figure 2 Layout of conventional sewerage system vs Condominial sewerage system

Conventional sewers are laid along main street as shown in figure 1. Since the conduits should not be harmed by vehicular loads, they are placed deep below generally with a minimum depth of 1 m. Placing it so deep requires costly asphalt removal, excavation of trench, dewatering of trench, backfilling of trench, and pavement of surface. These activities often account for a significant proportion , as much as 40%, of all costs of sewer construction projects. On the other hand, condominial sewers are laid along backyard, front yard, or under sidewalk. Since these places do not experience as much load, conduits can be laid as shallow as 0.3 m and rarely exceed 1 m depth.

Figure 3 Trench Excavation for conventional sewerage

Figure 4 Trench Excavation for condominial sewerage system

 

Another fundamental difference between conventional and condominial sewerage system lies in the institutional setup: construction of condominial sewerage systems are defined by the collaboration that exists between residents and engineers from the beginning of the project. First, the residents are educated about condominial sewerage system in order to increase acceptance as much as possible.  Then, layout is designed as per affordability of the residents: backyard layout has the lowest cost and under sidewalk layout has the highest cost. Operation and maintenance of public sewer lines is ensured by institution while residents are responsible for proper functioning of feeder lines; in case of under sidewalk layout, the most expensive of all, entirety of operation and maintenance responsibilites is born by responsible institution. Behemoth bureaucracy that entails with construction of conventional sewers hardly allows for such flexibility.

 

Working of Condominial sewerage system

Both conventional and condominial sewerage system are water borne systems, i.e. water carries domestic waste from higher head- a factor determined by pressure, velocity, and elevation from specific line of reference- to lower head.

Effluent is collected from individual household by conduits which confluence into a feeder line carrying domestic waste from the entire condominium; the feeder line discharges into public trunk line. Public trunk line of the condominial sewerage system is similar to that of conventional sewer. However, since feeder line does most of collection work, requirement of trunk line is greatly reduced.

Effluent is transported to a treatment facility; in most cases, these treatment facilities are also decentralized in order to minimize cost of transportation, as a single point treatment facility requires a large number of pumps, significantly larger treatment plant, and a much expensive operation and management plan.

Figure 5 A 3D diagram of condominial sewerage system

 

Similarly, for regular observation, manholes are replaced by much cheaper concrete collection boxes.

It must be noted that no condominial sewerage systems are alike; flexibility is key.

 

How cheap are these sewers?

 Both installation and operation cost of condominial sewerage systems is significantly lower in comparison to conventional sewers: condominial sewers systems were 40% cheaper than conventional sewers in Parauapebas (Melo,2005).

 As mentioned above, cost of excavation is quite low for condominial sewerage system. Similarly, diameter of conduits is also reduced: in conventional sewers, 150 mm diameter are taken as the minimum requirement, while 100 mm diameter conduits are taken as minimun, and used as much as possible, in condominial sewers. Based on 94 condominiums served Brasilia, the diameter of the minimum pipe diameter of 100 millimeters, applied to 51.2 kilometers (equivalent to 56% of the total length of the system). An additional 26.5 kilometers of the network (representing an additional 29% of its total length) were rendered in pipes 150 millimeters in diameter, while a mere 2.7 kilometers of the network utilized pipes 250 millimeters in diameter (in other words, no more than 3% of the total).

In grand scale of things, when condominial sewerage system was first installed in 1981 in northeast Brazil the cost was USD 325 per household (compared with around USD 1500 per household for conventional sewerage), with a monthly payment by each household of only USD 1.50 (Sinnatamby, 1986). Further reduction in costs were seen with increased adoption of the system: costs in Brasília were USD 200−300 per household (Maurício Luducice, Water and Sewerage Company of Brasília and the Federal District − CAESB, quoted in McCann, 2005); and in South Africa they were USD 220−260 per household in 2002 (DWAF, 2002). Costs in India, where condominial sewerage system is known as “slum networking”, are around USD 150 per household (Parikh et al., 2002). The cost of simplified sewerage in small villages (populations up to ~1000) in rural Ceará, northeast Brazil, was BRL 120 (~USD 80) per connection in 1999 (Sarmento, 2001). The monthly charge to householders was BRL 1.50 (USD 1).

 Above experiences show that condominial sewerage system can be adopted with much less cost often eliminating need for subsidy. For political reasons, water and sanitation projects are the most subsidized services in developing nations: can you believe we still pay NRs. 100 (USD 0.69) a month for water services?  However, these subsidized services unevenly distributed, often serving the rich better. Condominial sewerage system provide equitable service without putting a strain on a region’s economy.

 Are cheap sewers good?

They are.

Condominial sewerage system has been accepted throughout Brazil where it has been used for over 45 years serving millions of people. It has been successfully adopted in the haphazardly built slums of Bacia do Alto Camurujipe as well as planned neighborhoods of Brasilia. CAESB, the water and sewerage company of Brasilia and the Federal District, started implementing simplified sewerage in poor areas in 1991 and now it considers condominial sewerage as its “standard solution” for rich and poor areas alike (Mara, 2005). Surveys have shown satisfaction A survey of condominial sewerage schemes in Brazil (Sarmento, 2001) found user satisfaction levels high, even after ~20 years of operation.

 

Figure 6 Bacia do Alto Camurujipe where condominial sewerage systems are installed

Adoption of condminial sewerage system- often referred to as simplified sewerage system though the principles remain the same- in other nations are helpful in grasping efficacy of condominial sewerage systems: 

Simplified sewerage was transferred to Pakistan (Sinnatamby et al., 1985), where in early 1985 in the low-income area of Christy Nagar in Karachi The concept of simplified sewerage was embraced by the Orangi Pilot Project (Khan, 1996; Zaidi, 2001), and to Sri Lanka where there are now around 40 schemes (Mara, 2005). Simplified sewerage was used in the El Alto Pilot Project in Bolivia (Canelli, 2001) which led to development of a Bolivian standard for simplified sewerage (DGSB, 2001). Simplified sewerage has also been developed in South Africa (Brocklehurst, 2001; Anon., 2004; WRC, 2005). Community-based sewerage schemes have been developed in Indonesia (Foley et al., 2000) and “slum networking” schemes in India (Parikh et al., 2002; Kakumbi, 2005).

 

Challenges Regarding Acceptance of Condominial sewerage system

Above examples, however show that condominial sewerage systems have not been adopted beyond poor neighborhoods in most other nations.

Brazil remains a unique example. Its success can be attributed to dissemination of innovative technique among engineers, leading Brazilian sanitary engineers being its advocate, keen interest shown by authorities, and acceptance of the technique by public.  

 Regardless of the benefits, acceptance of condominial sewerage systems remains low.

This might be due to preconceived bias in public that that cheap must equate with low quality. Similarly, these are not favourable projects to construction companies as these projects have a relatively lower budget.

 Conclusion

Condominial sewerage systems, also known as simplified sewers, are excellent alternative to conventional sewers increasing access to sanitation as well as reducing cost. Along with certain changes in layout and design principle, interaction with public is the must have feature of condominial sewerage system. It is applicable in chaotically sprung up settlements as well as planned residences. Lack of awareness among the consumers, and unwillingness of planners, engineers, and policy makers are major hindrances to its widespread acceptance.