Cost-effective solutions for sewage treatment in developing countries - the case of Brazil

Abstract

Cost-effective solutions are a must in developing countries, not only regarding investment costs, but also in respect to technology and operating practices. With these two goals in mind, in Brazil a particular effort has been directed for the development and application of the Chemical Enhanced Primary Treatment (CEPT) process and of the Upflow Anaerobic Sludge Blanket (UASB) process, both followed by complementary secondary treatment. Both technologies are under current expansion in Brazil. Large CEPT plants have been designed and built, up to 3.7 m3/s average design flow, as well as large UASB reactors, up to 3.0 m3/s average design flow. The applied technologies are cost-effective: they present low investment and efficiencies of BOD removal of up to 50% to 70%. They allow the plant construction in steps, an initial phase with efficiency over the usual primary treatment, and in order to achieve best effluent quality and meet legal water quality standards, a logic upgrade post-treatment can later on be implemented. The higher initial reduction of BOD and TSS also permits savings in construction and operational costs of secondary treatment, due to lower organic load and lower energy consumption. Sludge represents a particular point of attention: in the cases when the CEPT was used, Chemical Stabilisation of the Sludge (CSS) has also been practiced, eliminating the high construction costs of the digesters, all the plant staying chemically operated. In the cases when the UASB is used preceding secondary treatment, sludge can easily return to the anaerobic vessel, the costly sludge digestion unit being avoided. UASB reactors have practically no equipment in the anaerobic vessel, no energy consumption, low sludge production, and when applied in hot climates as in Brazil, heating devices are not required. The Brazilian experience, some particular cases, special comments on design and different secondary treatment processes are presented in this paper, as a contribution to the discussion of cost and benefits, a prime point to be considered.

Occurrence of anionic surfactants in treated sewage: Risk assessment to aquatic environment

“…However, from economic point of view, biological processes still appear to be ideal option. Most investigated biological processes are [41,42]: (i) biofilm processes (downflow hanging sponge, rotating biological contactor, trickling filter, submerged biofilter, anaerobic filter), (ii) pond processes, (iii) activated sludge process, and (iv) soil/plant processes (rapid infiltration, superficial irrigation, overland flow, constructed wetlands). A research programme on feasible technologies for UASBR post-treatment was carried out by a network of 15 Brazilian Universities.…”

“…A research programme on feasible technologies for UASBR post-treatment was carried out by a network of 15 Brazilian Universities. Design values for different post-treatment units such as trickling filter (TF), aerated submerged filter, dissolved air flotation, aerated ponds and activated sludge have been suggested [42]. However, research has been mainly restricted to the use at either laboratory-scale or pilot scale using natural or synthetic wastewaters.…”

Chemically enhanced primary treatment (CEPT) for removal of carbon and nutrients from municipal wastewater treatment plants: a case study of Shanghai

“…CEPT was believed to be a costeffective method for wastewater treatment in developing countries (Harleman & Murcott 1999). CEPT possesses some advantages in wastewater treatment, such as saving footprint (Aiyuk et al 2004a), small investment and efficient removal of some pollutants such as phosphate (Jiang & Graham 1998), low energy requirement (De Feo et al 2008), easy to operate and maintain (Jordao & Volschan 2004), and so on. For these reasons, CEPT has been widely used over the last twenty years, not only in municipal wastewater treatment (Ho et al 2008), but also in industrial wastewater treatment (Haydar & Aziz 2009).…”

Activated Sludge – 100 Years and Counting

“…downflow hanging sponge (Machdar et al, 2000)), can be economically compared to an AS system. Indeed these two-stage systems have particularly low energy, sludge disposal and maintenance costs for similar carbon removal and nitrification efficiencies (Tandukar et al, 2005(Tandukar et al, , 2007Sato et al, 2007;Jordão & Volschan, 2004). However, N removal is usually less efficient than in AS systems.…”