Process auditing and performance improvement in a mixed wastewater–aqueous waste treatment plant Maria Cristina Collivignarelli, Giorgio Bertanza, Alessandro Abbà and Silvestro Damiani ABSTRACT The wastewater treatment process is based on complex chemical, physical and biological mechanisms that are closely interconnected. The efficiency of the system (which depends on compliance with national regulations on wastewater quality) can be achieved through the use of tools such as monitoring, that is the detection of parameters that allow the continuous interpretation of the current situation, and experimental tests, which allow the measurement of real performance (of a sector, a single treatment or equipment) and comparison with the following ones. Experimental tests have a particular relevance in the case of municipal wastewater treatment plants fed with a strong industrial component and especially in the case of plants authorized to treat aqueous waste. In this paper a case study is presented where the application of management tools such as careful monitoring and experimental tests led to the technical and economic optimization of the plant: the main results obtained were the reduction of sludge production (from 4,000 t/year w.w. (wet weight) to about 2,200 t/year w.w.) and operating costs (e.g. from 600,000 €/year down to about 350,000 €/year for reagents), the increase of resource recovery and the improvement of the overall process performance. Maria Cristina Collivignarelli Alessandro Abbà Silvestro Damiani (corresponding author) Department of Civil and Architectural Engineering, University of Pavia, via Ferrata 1, 27100 Pavia, Italy E-mail: silvestro.damiani01@universitadipavia.it Giorgio Bertanza Department of Civil, Environmental, Architectural Engineering and Mathematics, University of Brescia, via Branze 43, 25123 Brescia, Italy Key words | cost saving, experimental tests, management, monitoring, process optimization INTRODUCTION The performance of wastewater treatment plants (WWTPs) is often a significant issue, mainly due to technical and operational deficiencies. In many cases, structural upgrades are applied in order to solve plant problems: this approach often involves high capital costs, sometimes without effect. However, it is important to provide management actions, firstly through intensive monitoring aimed at: (i) complying with the effluent discharge limits, (ii) calculating the removal yields of pollutants, (iii) providing information on the health of the biomass, (iv) maintaining the correct operating par- ameters. Afterwards, experimental tests (both at laboratory and in-situ scales) should be conducted with the aim of iden- tifying any weaknesses and optimizing the process. In this regard, the methodological approach reported by Sorlini et al. () for drinking water treatment facilities may also be suggested for WWTP performance optimization, thus lead- ing to increasing the pollutant removal efficiency and simultaneously reducing the operating costs. This approach is particularly important in the case of municipal WWTPs with a significant industrial input. The characteristics of industrial wastewater change not only according to the manufacturing sector, but also within the same sector. This aspect is more pronounced for industrial than municipal wastewater, that usually maintains qualitat- ive and quantitative homogeneous characteristics (Oller et al. ). Moreover, in the case of plants that receive an additional load of aqueous waste, this aspect is even more crucial. Aqueous waste can be treated in typical WWTPs (Renou et al. ), or in dedicated plants, typically after a series of chemical-physical pre-treatments, such as coagu- lation, flocculation, neutralization and advanced chemical oxidation (De et al. ; Gonzàles et al. ; Martins et al. ; Covinich et al. ; Hermosilla et al. ; Moha- patra et al. ; Muruganandham et al. ; Collivignarelli et al. a, b). Also, the plants that treat aqueous waste clearly differ from conventional systems in that they 891 © IWA Publishing 2018 Water Science & Technology | 77.4 | 2018 doi: 10.2166/wst.2017.605 Downloaded from http://iwaponline.com/wst/article-pdf/77/4/891/674590/wst077040891.pdf by guest on 13 December 2021