Resumen de Integrated assessment of wastewater treatment plants and their receiving river systems in a global change context
Fragmented environmental policies on wastewater sanitation, global change, and emerging contaminants are increasingly threatening freshwater ecosystems and human health. Given this background, an integrated approach to the management of the artificial and natural elements of the urban wastewater system is needed.
This thesis embeds a series of research studies aiming to improve our comprehension of the functioning of urban wastewater systems (UWWS), considering both natural and artificial elements, and with a special emphasis on the occurrence and fate of global changes and emerging contaminants. In the thesis, an integrated model for a UWWS in NE Iberian Peninsula has been developed and calibrated using data from an intensive and integrated survey. More specifically, the work developed in this thesis was divided into three parts. First, we investigated how an UWWS perform together in the removal of conventional contaminants and evaluated the impact of future global change scenarios. Second, we investigated the occurrence and fate of pharmaceuticals and their transformation products in the UWWS. Third, and as a continuation of this second work, we assessed the influence of the sampling strategy when estimating the loads and attenuation of emerging contaminants in UWWS.
In the first chapter, the detailed assessment of the integrated system of Puigcerdà showed that the coupled WWTP-river system contributed to the overall removal of carbon, nitrogen and phosphorus, where we can clearly see that the river is influenced by the WWTP dynamics. Whereas the WWTP could not remove nitrogen, the river had the capacity to nitrify 80% of the ammonia load coming from the catchment with just five km. An integrated model was developed and calibrated by connecting the ASM3-bioP and the RWQM nº1 models. The simulations allowed us to conclude that under future foreseen population growth and decrease in the river flow (leading to increased loads from the catchment discharged to the river and decreased dilution capacity) the chemical status of the system will turn into bad conditions as well for the last 3 km studied. Hence, actions will be needed to adapt to changing conditions.
In the second chapter, and with regards to pharmaceuticals and their transformation products, the results showed that these compounds are highly present in receiving water bodies. For the period under study, only 5 out of the 19 pharmaceuticals were reduced by more than 90% at the WWTP, while the rest were partially or non-attenuated (or released) and discharged into the receiving river. The study showed that higher attenuation efficiencies were obtained in the river compared to the WWTP, while load reductions were higher in the WWTP. We were also able to identify the routing between some pharmaceuticals and their transformation products, demonstrating that dynamic attenuation could be successfully predicted with simple first order attenuation kinetics for most modelled compounds.
In the last chapter, and as a continuation of the second chapter, we could demonstrate that sampling matters when investigating attenuation micro-contaminants in WWTPs and rivers, showing that it highly affects the uncertainty in the estimates of attenuation. The study showed that different levels of uncertainty are obtained in the estimation of loads (influent and effluent of the WWTP, upstream and downstream of the river) and in the estimation of attenuation. We identified that WWTP influent sampling is especially critical when designing sampling strategies and that compound degradability plays a significant role. Short sampling intervals and longer sampling durations are needed to obtain attenuation estimations with low uncertainty.
Overall, this thesis highlights the need for integrated approaches to better understand the performance of WWTPs and their receiving rivers, to take actions against the increase of micro-contaminants concentrations and the effects of global change.
