Continuous treatment of non-sterile hospital wastewater by Trametes versicolor: How to increase fungal viability by means of operational strategies and pretreatments

Highlights

• Non-sterile hospital wastewater was treated for 28 days in a fungal bioreactor.

• Concentration of native microorganisms affects the longevity of the treatment.

• Coagulation-flocculation pretreatment extended the fungal treatment.

• UV-radiation negatively affected the longevity of the treatment.

Abstract

Hospital wastewaters have a high load of pharmaceutical active compounds (PhACs). Fungal treatments could be appropriate for source treatment of such effluents but the transition to non-sterile conditions proved to be difficult due to competition with indigenous microorganisms, resulting in very short-duration operations. In this article, coagulation-flocculation and UV-radiation processes were studied as pretreatments to a fungal reactor treating non-sterile hospital wastewater in sequential batch operation and continuous operation modes. The influent was spiked with ibuprofen and ketoprofen, and both compounds were successfully degraded by over 80%. UV pretreatment did not extent the fungal activity after coagulation-flocculation measured as laccase production and pellet integrity. Sequential batch operation did not reduce bacteria competition during fungal treatment. The best strategy was the addition of a coagulation-flocculation pretreatment to a continuous reactor, which led to an operation of 28 days without biomass renovation.

Introduction

There is a growing concern among regulatory agencies and in the scientific community about pharmaceutical active compounds (PhACs) occurring in environmental water bodies. Although healthcare waste management is imperative, hospital wastewater (HWW), with similar pollutant load as urban wastewater but much higher concentrations of PhACs, is still commonly discharged into public sewage systems [1]. HWW constitutes the main source of PhACs in the influent of wastewater treatment plants (WWTP), which are not designed to remove these pollutants [2], [3]. Consequently, these effluents could be a vector to introduce PhACs in the environment through wastewater reuse purposes such as irrigation, landscape and surface or groundwater replenishment [4]. Therefore, a specific HWW treatment step before the HWW is mixed with urban wastewater would prevent PhAC contamination of the WWTP influent. Among the potential technologies for removing recalcitrant organic pollutants in wastewater, fungal treatment is a particularly promising strategy to biodegrade those pollutants due to their unspecific enzymatic systems. Several studies have reported the capacity of white rot fungi (and particularly Trametes versicolor) in degrading a wide range of emerging pollutants including PhACs [5], [6]. These studies have been carried out at different scales, from within Erlenmeyer flasks to bench bioreactors, and they have been conducted mainly in sterile conditions to best monitor the fungal degradation during the batch process. The studied pollutant concentrations are on the order of a few mg L⁻¹, but the typical concentrations in wastewater are on the order of 1 ng L⁻¹ [7], [8].

Moreover, the long-term operation of fungal biodegradation processes during a continuous fungal treatment of a synthetic textile wastewater, in sterile conditions, was demonstrated with a cellular retention time (CRT) of 21 days [9]. The biomass was retained in the reactor but periodic partial biomass removals were performed to limit the aging of the biomass and consequently to guarantee that metabolic activity occurred under growth-limiting conditions. However, the partial biomass renovation strategy was not enough to maintain fungus viability during the treatment of HWW under non-sterile conditions [8]. Few other references can be found that investigate the treatment of non-sterile wastewater by fungi in a continuous mode. The non-favorable competition between the inoculated fungus and the microorganisms in the real wastewater demonstrated the difficulty of developing an efficient treatment on an industrial scale due to the relatively short fungal viability time [10], [11], [12], [13].

A novel strategy to extend the fungal viability period has not yet been established and is essential to guarantee the long-term operation for the continuous treatment of HWW, which may be achieved through a continuous pumping of the influent or by sequential batch reactor (SBR) operation. In both strategies the biomass is retained in the bioreactor. In addition, a pretreatment for the HWW may reduce the bacteria level in the influent of the fungal bioreactor and consequently extend its viability. These processes include coagulation-flocculation and UV radiation, both methods widely used in WWTP [14], [15]. Their technology can be readily applied, but none of the methods have been used as pretreatments before.

Therefore, the main objective of this study is to increase the T. versicolor viability inside the reactor during a continuous treatment of non-sterile HWW. To achieve this, the following two approaches have been examined: first, the addition of two pretreatments, a coagulation-flocculation step and a UV irradiation step, and second, the continuous operation of the reactor and a SBR. The influence of both strategies on the viability period has been studied. The HWW was spiked with ibuprofen (IBU) and ketoprofen (KETO) for analytical purposes.