Wastewater treatment doesn’t have to be high-tech

Amplification of TOP points

Throughout the TOP, readers will find repeated references to the Design Manual for Waste Stabilization Ponds in India. The document (referred to in the TOP as the India manual) contains a detailed analysis of all aspects of WSP design, construction, operation and maintenance. These hyperlinks make it easy to hop in and out of the manual to get more information on specific points.

• Section 1: Introduction (making the case for WSP)
• Section 2: WSP applicability and usage in India
• Section 3: Wastewater treatment in WSP
• Section 4: Process design of WSP
• Section 5: Physical design of WSP
• Section 6: Operation and maintenance
• Section 7: Monitoring and evaluation
• Section 8: Rehabilitation and upgrading
• Section 9: Wastewater storage and treatment reservoirs
• Section 10: Effluent reuse

Less than 35% of cities in the developing world have their wastewater treated (Habitat, 2001). Of those that do, many use high-tech treatment processes that are proving too costly or too complex to keep in running order.

Why is it then that a technology that is simple, low-cost and highly effective is frequently ignored as a treatment option?

This Thematic Overview Paper (TOP) makes the case for much wider use of waste stabilization ponds (WSPs) to treat municipal sewage and produce effluent that can be used to irrigate crops, support fish farms, or simply control river pollution. It explains the principles of WSP design, construction and operation, to encourage planners and engineers to consider the economics of WSPs in any appraisal of wastewater treatment options.

Non-technical readers should not be put off by the complex looking formulae and Greek symbols used to provide designers with enough detail to assess the merits of WSPs. The main message is that there are well-researched methods for designing appropriate WSP systems to suit a wide range of wastewater types, climatic conditions and geographic situations. A third of all wastewater treatment plants in the USA are WSP systems. Yet in developing countries, where climatic, geographic and operational conditions very much favour WSPs, designers are predominantly choosing more expensive and operationally daunting alternatives such as activated sludge, aerated lagoons, oxidation ditches, upflow anaerobic sludge blanket (UASB) reactors or biological filtration plants. US statistics quoted in Section 1 of the India manual (see box for link) compare energy consumption for the alternative systems, based on a 1 million US gallons a day (3,780m3/d) plant. Waste stabilization ponds consume no energy; the corresponding activated sludge plant uses 10 million kWh a year.

Other countries too have been reaping the benefits of WSPs’ favourable economics and simplicity. The case studies in Section 3 of the TOP include examples from Turkey, Cyprus, Israel and Jordan in the Eastern Mediterranean; Egypt, Tunisia, Algeria and Morocco in North Africa; Portugal, Spain, France and Greece in Mediterranean Europe; as well as several sites in India. Too many others though seem to be ignoring the potential of WSPs and paying the price in high operating costs and low sustainability of other wastewater treatment methods.

Quite a few WSPs also have operating problems. A key message of the TOP is that WSPs may be simple, but they still need to be properly designed and maintained. Hence the emphasis in the TOP on design parameters, simple operating rules, and potential pitfalls.