On the Centralization of Wastewater Treatment Facilities1

Abstract

ABSTRACT. Two factors affecting the centralization of wastewater treatment facilities were investigated; the cost of collection and treatment systems and the performance of treatment plants. Based on computer‐generated minimum cost designs, wastewater collection networks were found to be characterized by diseconomies of scale of magnitude similar to the reported economies of scale for wastewater treatment works. The combined costs of collection and treatment are U‐shaped functions from which the least cost size of collection and treatment systems were found for particular values of population density. Examination of the day‐to‐day performance of five metropoitan‐area waste‐water treatment plants revealed that, for time series shorter than one month, the day‐to‐day variation in effluent quality was random, although the variation in quantity discharged was distinctly non‐random. The performances of all five plants on any given day showed little correlation. This suggests that the decentralization of treatment facilities can produce benefits both through the reduction in quantities of waste discharged at a given point and through in‐stream averaging of the varying performances of several treatment plants. Since the cost function of collection and treatment combined is generally flat in the region of the minimum‐cost size, little penalty is invoked to gain the potential benefits of treatment plant decentralization.

Factors affecting economies of scale in combined sewer systems

“…Figure decrease with density, due to the more efficient utilization of pipes and the decreasing length of pipe required per capita, which corresponds well with the findings in Figure 4 (Case 4). Adams et al (1972) presented a more general approach that considers the area size and population density. They conclude that in "high-density developments…”

ANALYZING THE IMPACT OF LAND USE ON SEWER SERVICE AREA PLANNING1

“…In a later study Adams, Dajani, and Gemmell (1972) examined the costs of different service area sizes assuming uniformly distributed populations. In order to generate collection costs, they also synthesized costs for different subdivisions at selected densities.…”

Screening European market potentials for small modular wastewater treatment systems – an inroad to sustainability transitions in urban water management?

“…Hence, the economic efficiency of network-based infrastructures in particularly is closely linked to population density (McKinsey, 2014;Prieto, Zofío and Álvarez, 2014). Specifically with respect to wastewater management, there is general agreement about various cost effects based on (population)-densities: the most common argument is that capital costs decrease if more people are connected to a system within a catchment because of economies of scale in wastewater treatment and shorter per capita sewer transportation distances (inter alia Adams et al, 1972;O'Flaherty, 2005). However, the cost effects are not limited to capital but include operation costs.…”