Alternative collection systems for decentralized wastewater management: an overview and case study of the vacuum collection system in Eretria town, Greece

In small and rural communities, the installation cost of conventional gravity-flow collection systems is often very expensive due to the presence of rocky terrain, high water table, unstable soils, extremely flat terrain, which may impose substantial difficulties in construction. Pressure, vacuum and septic tank effluent gravity collection systems are among the alternatives sewers used most commonly. As these systems are designed to be watertight, design allowances for infiltration and inflow are not required. Moreover, exfiltration does not occur in these systems, thus eliminating the risk for soil or underground water contamination. The installation cost of the alternative wastewater collection systems is often significantly lower by as much as 20–50%, compared to conventional gravity-flow collection systems. In general, alternative collection systems are suitable for communities of 10,000 people or less. In this paper, alternative wastewater collection systems are described and their benefits, costs and drawbacks are compared to conventional gravity-flow collection systems. Eretria, a relatively flat littoral town in Greece, with many shallow archaeological ruins has been selected to illustrate the optimal selection of a sewer system. Using multi-criteria analysis, the vacuum sewer system has been selected as being the most advantageous, both in terms of financial and technical considerations.