Management of Wastewater Treatment Plants (WWTPs) is a complex process, not only from a technical point of view but also from an economic point of view. There are several factors that influence the wastewater treatment process and can cause an increase in management costs. One of these factors is the treatment capacity, in particular the WWTPs’ oversizing problem. The difference between the design population equivalent (p.e.) and the actual p.e. treated generates imbalances in the wastewater treatment process costs. This paper analyses the influence that oversizing has on the maintenance costs for WWTPs in the Valencia region (Spain). Through an econometric approach, the behaviour of WWTPs including the oversizing variable has been modelled. Specifically, maintenance cost functions have been obtained to model the variability of maintenance costs according to oversizing influence. To date, this approach has not been considered in the published literature, reinforcing the novelty of this work. Results verify the significant influence of oversizing on maintenance costs in WWTPs. Modelling proposed in this work acts as an effective tool for WWTP managers to identify both the maintenance cost trend and how far the WWTP is from the design p.e. Likewise, results confirm the fact that WWTPs should work close to their design p.e. to improve the efficiency of the wastewater treatment process, reducing WWTPs’ costs.

废水处理厂（WWTP）的管理是一个复杂的过程，不仅从技术角度而且从经济角度来看。有几个因素会影响废水处理过程，并可能导致管理成本增加。这些因素之一是处理能力，特别是污水处理厂的规模过大问题。设计种群当量（pe）与实际处理的pe之间的差异会导致废水处理过程成本的不平衡。本文分析了规模过大对瓦伦西亚地区（西班牙）污水处理厂维护成本的影响。通过计量经济学方法，对污水处理厂的行为（包括规模过大的变量）进行了建模。特别，已获得维护成本函数，以根据规模过大的影响对维护成本的变化进行建模。迄今为止，已发表的文献中尚未考虑这种方法，这增强了这项工作的新颖性。结果证明了规模过大对污水处理厂维护成本的重大影响。这项工作中提出的模型是污水处理厂管理者识别维护成本趋势以及污水处理厂距设计指标有多大的有效工具。同样，结果证实了污水处理厂应与其设计指标接近以提高维修效率的事实。废水处理过程，降低了污水处理厂的成本。结果证明了规模过大对污水处理厂维护成本的重大影响。这项工作中提出的模型是污水处理厂管理者识别维护成本趋势以及污水处理厂距设计指标有多大的有效工具。同样，结果证实了污水处理厂应与其设计指标接近以提高维修效率的事实。废水处理过程，降低了污水处理厂的成本。结果证明了规模过大对污水处理厂维护成本的重大影响。这项工作中提出的模型是污水处理厂管理者识别维护成本趋势以及污水处理厂距设计指标有多大的有效工具。同样，结果证实了污水处理厂应与其设计指标接近以提高维修效率的事实。废水处理过程，降低了污水处理厂的成本。