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Zone planning: basis for local wastewater treatment policy

Aquafin developed a zoning methodology to define how sanitation is best organised in areas where there currently are no water treatment facilities. Our zone planning determines per treatment area or per municipal area for which percentage of houses the pollution load can best be connected to the (existing) collective sewer system and transported to a treatment plant. The zoning plan provides a solution without infringing on the local authorities’ autonomy and wishes.

According to Aquafin’s methodology, the existing built-up areas are divided into geographical clusters. The possible infrastructural elements (individual wastewater treatment installation, sewer system, connecting trunk sewers, new small-scale wastewater treatment plants, expansion of existing (small-scale) wastewater plants) required to provide complete sanitation for these remaining areas are being drawn up. Based on this data, a mathematical model considers the following three options per cluster: individual treatment per dwelling, sewer system within the cluster connected to a small-scale wastewater treatment plant, or sewer system within the cluster connected to other clusters.

The aim of the instrument is to keep the costs involved to a minimum (investment and operating costs). Water quality objectives and protected areas can be introduced as ecological pre-conditions. The end result of the model isa division of the areas with no sewer facilities into five treatment zones. Our methodology makes it possible to draft a zoning plan, which provides the local authorities with plenty of scope for their choices and what they want to focus on. The most important benefit of this exercise is a precise definition of the zone where individual treatment is recommended,  which brings clarity to everyone involved.

  • Zone 1 (dark green) covers the area already sanitized
  • Zone 2 (lighter green) needs collective treatment facilities.
  • In zones 3 and 4 (yellow and orange) collective or individual treatment are both options.
  •  In zone 5 individual treatment is the appropriate solution.