Standards Development

Scope

The proposed work item aims to set out the general principles for, and provides guidance on, the quantitative characterization of life cycle cost of a complete wastewater management system, including collection, treatment and reuse in order to enable consideration of different degrees of distribution. This methodology is applicable to urban areas wherein several smaller plants might provide a lower cost solution than a single centralized plant. It may also be applied to rural areas wherein a treatment and reuse facility in each location might provide a lower cost than a central plant treating several settlements of any size.

Although primarily intended and prepared for comparison of different degrees of distribution for wastewater treatment and reuse systems, the same methodology may also be applied for comparing and selecting other treatment systems that might be either distributed or centralized, such as sludges and wastes management.

The proposed document will include:

- A definition of the elements and components included in the life cycle cost of the different degrees of distribution in wastewater management systems. These will include:

a. investment costs such as the part of the collection system piping that should be included and the part to be excluded, pumping stations, wastewater treatment plants construction, reuse infrastructure and facilities;

b. operational costs such as electricity, labor, maintenance, sludge handling; compliance analyses etc.)

- Guidance on steps for the calculations, including consideration of term and interest; including operating and maintenance, replacement parts, life expectancy of equipment; also including the value of water for reuse.

- To define metrics for reporting on the results, including the cost per unit, scope, term and interest. It is emphasized that the proposed work item does not aim to quantify and consider the social impact factors nor the environmental risks and impacts.

Purpose

Centralized wastewater treatment is commonly the default planning scheme. However, the long distance piping and pumping for centralized design is associated with high investment cost which is sometimes hard to bear for low population densities. One of the barriers to considering an alternative design based on a network of decentralized wastewater treatment facilities, is accessible and accepted means compare the cost as basis for a decision. In many cases such optimization will reduce any of the investment and operating cost of the entire system. The distributed planning alternative has recently become viable due to developments in automation and telecommunication, as well as advanced biological wastewater treatment processes.

The economic optimization of the entire system is influenced by the serviced population density as well as topography and local cost parameters. Each of these might have a critical influence on the real cost of different design alternatives.

Therefore, this document aims to define cost evaluation criteria over the life cycle of a wastewater management system, where currently there are no unified guidelines, including regarding the following topics:

- The scope of the system to be considered in cost calculations – the collection system, pumping stations, treatment plant, reuse facilities, distribution system and other

- operating cost items to be considered in cost calculations – electricity, lab, sludge treatment, labor and other

- The term and interest rate for the calculation

- What should be reported as part of the results – the scope, the economic parameters, others.