Negative impacts of cleaning agent DEPTAL MCL® on activated sludge wastewater treatment system

DEPTAL MCL® is a professional cleaning agent approved by the Portuguese Food Regulatory Authority and is used in agro-food industries, namely in fish canning industries in the north of Portugal. Its extensive use during cleaning procedures results in potential significant negative impacts on the performance of the downstream municipal wastewater treatment plant (WWTP). A lab-scale extended areation activated sludge wastewater treatment system, continuously fed by influent collected at a municipal WWTP, was used to assess the impact of a range of DEPTAL MCL® concentrations during 72h. Despite distinct activated sludge community composition (due to its dynamic nature) and variations in real influent characteristics, a relevant impact was observed. DEPTAL MCL® effect was underscored through the use of a multivariate analysis using seventeen physicochemical operational factors and nineteen quantitative image analysis (QIA) parameters. DEPTAL MCL® exerted a severe negative impact on phosphorous (P-PO4) removal, total nitrogen (TN) removal and sludge volume index (SVI). With increasing DEPTAL MCL® concentrations, both P-PO4 and TN removal were affected and diminished proportionally. Moreover, several QIA parameters indicate defloculation when DEPTAL MCL® was present, in particular for intermediate size aggregates with significant impacts. Optical density of the effluent (Ode), displayed an increase of effluent turbidity. Percentage of area covered by small aggregates (%Areasml) was also significantly higher for the intermediate and higher DEPTAL MCL® concentrations tested. Principal component analysis exhibited 3 distinct ordenations: (i) control without addition of DEPTAL MCL®; (ii) addition of 0.03% and 0.06% and of (iii) 0.13 and 0.26% (v DEPTAL MCL®/v aeration tank). Canonical correspondence analysis (CCA) was used to correlate the physicochemical data, QIA and the filamentous bacteria species prevalence to DEPTAL MCL® concentration and incubation time. A time persistent DEPTAL MCL® effect was observed, underscoring the need of a pretreatment of wastewater containing this cleaning agent.This study was supported by the Portuguese Foundation for Science and Technology (FCT) under the scope of the strategic funding of UID/BIO/04469/2019 unit and BioTecNorte operation (NORTE-01-0145-FEDER-000004) funded by the European Regional Development Fund under the scope of Norte2020 - Programa Operacional Regional do Norte. This work was also supported by the project Innovative strategies to control filamentous overgrowth in activated sludge wastewater treatment (INOVCONTROLFIL) (PTDC/AAG-TEC/3331/2014). In addition, it was also supported Universidad de la Frontera DI21-1004, ANID/REDES 180003 and by FEDER funds through the Operational Competitiveness Program COMPETE and FCT under the projects PTDC/CTM-TEX/28295/2017 and UID/CTM/00264/2019.