DecS - De­­co­­ding Trace Substances

The dominant input pathway of many organic trace substances of anthropogenic origin (industrial chemicals, household chemicals, pharmaceuticals, biocides, etc.) is effluents from municipal wastewater treatment plants. In addition to source-oriented measures to reduce trace substance inputs to wastewater, advanced wastewater treatment is therefore increasingly using separate elimination stages to reduce trace substance inputs from these point sources. Ozone oxidation and adsorption on activated carbon have been the main methods used to date. As of today, the elimination processes of the installed technologies are assessed exclusively by discontinuous input-output considerations. Since technologies for the continuous collection of a broad spectrum of trace substances are lacking so far, the processes for trace substance elimination are not specifically influenced in the sense of control or regulation. It is true that the surrogate measurement of the spectral absorption coefficient at a wavelength of 254 nm (SAK254), which is used in some cases, can provide continuous information on the residual organics, which allows conclusions to be drawn about the required dosing quantity of the adsorbent or oxidant. However, it is not sufficient for a targeted influencing of the dynamic processes. A sustainable further development and optimization of the purification processes with the aim of the most efficient possible use of resources with the greatest possible water pollution control has thus not yet been achieved.

The DecS project is pursuing the goal of using continuous data acquisition and data processing to make the operation of processes for removing organic trace substances from wastewater as efficient as possible by minimizing the resources required for this purpose.

With this in mind, the partners in the project have so far worked in separate projects on the development of a continuous recording system for organic trace substances, the modeling of adsorption processes for various trace substances on powdered activated carbon, and the semi-technical testing and large-scale implementation of trace substance elimination processes at municipal wastewater treatment plants. The knowledge gained in this process will be deepened within the framework of DecS and expanded to include the processes of adsorption in activated carbon filters (GAK) and oxidation with ozone.

The continuously collected measurement data will be linked to the model systems to be further developed within the framework of DecS . The simulation system SIMBA#water, which can be used to realistically model the automation technology of the plants, serves as the starting point for the networking. This can be used both to determine the sustainability potential of digitized trace substance elimination and to test and answer general questions about simulation-based process optimization at water management plants.

The large-scale applicability of the models and control strategies developed within the framework of DecS will be tested at two municipal wastewater treatment plants of the Lippeverbands (EGLV) in so-called digital real laboratories. The digital real laboratories serve as temporally and spatially limited test rooms. Here, concrete experience is to be gained in the interaction of the digital instruments used and these are to be optimized in a user-oriented manner.

In this way, the project also contributes to achieving the Sustainable Development Goals (SDGs) adopted in 2015 as part of the 2030 Agenda, in particular the subgoals "Reduce illnesses caused by hazardous chemicals" (SDG 3.9), "Improve water quality" (SDG 6.3), "Environmentally sound management of chemicals" (SDG 12.4) and "Reduce marine pollution" (SDG 14.1).

In ozonation, the chemical compounds of the trace substances are converted into less harmful reaction products by oxidation with ozone (O3). Ozonation thus depends mainly on chemical reactions and the oxidation capacity of the trace substances. In addition, like adsorption, oxidation is significantly influenced by the background DOC matrix of the individual wastewater. Ozonation produces small amounts of the carcinogenic bromate (BrO3-) even when small amounts of bromine are present. Ozone reactions with bromine will be included in the model to be developed and reaction rates will be determined using established calculation approaches.

Within the scope of WP 1, a detailed trace substance screening is carried out with the WATERTRACETM system at the wastewater treatment plants Dülmen and Bad Sassendorf. The WATERTRACETM system will be continuously calibrated by means of reference analyses accompanying the project. In parallel, concepts for automated data acquisition and evaluation are being developed. The aim is to develop an intelligent trace substance monitoring system that guarantees user-oriented and user-friendly operational data evaluation.

WP 2 comprises the further development of the already existing model approaches for powder activated carbon (PAH) adsorption to include adsorption processes on granulated activated carbon (GAH) as well as oxidation processes with ozone. For this purpose, mathematical model hypotheses from the known literature are further developed and implemented in the simulation system used. The models will be verified by using them to reproduce the results of laboratory experiments. The aim of WP 2 is to develop a web-enabled modeling system that can be used as a "digital twin" either offline for planning and optimizing wastewater treatment processes or online as a virtual measuring device and for control tasks.

In WP 3, simulation models or "digital twins" of the real laboratories (KA Dülmen with powder activated carbon dosing, KA Bad Sassendorf with ozonation) are created and various automation concepts are developed and analyzed. This will enable optimized automation solutions to be found for the trace substance elimination processes, which will ensure minimum energy input and resource consumption with the best possible compliance with the effluent requirements.

In the real laboratories (WP 4), the models and "digital twins" developed in WP 2 and WP 3 for adsorption on powdered activated carbon (KA Dülmen) and for ozonation (KA Bad Sassendorf) will be validated on a large scale and tested in practice. The reallabs are intended to help anchor the digital innovations in water management practice and to transfer findings from research to the operational practice level of a wastewater treatment plant operator.

Based on the results of the preceding work steps, a specification sheet and a functional description for a resource-efficient automation of the processes for trace substance elimination will be developed in WP 5. A catalog of requirements for all necessary components of the digitized measurement and control technology will be developed. In addition, essential technical as well as content-related specifications about the process, the necessary boundary conditions of the different process variants (PAH, GAH, ozone) as well as concrete automation concepts are set down in writing in general form. This will enable the new digital control system to be transferred to other wastewater treatment plants.

WP 6 is implemented by the University of Kassel and includes the overall project organization, project planning and project documentation as well as public relations and controlling.

The Dülmen wastewater treatment plant has a capacity of 55,000 p.e. and is equipped with a mechanical-biological wastewater treatment system with targeted nutrient elimination (nitrogen, phosphorus). Since its expansion in 1995, the Dülmen wastewater treatment plant has had a sand filter with a total of five filtration chambers. Since 2015, the structure of the filtration plant has been used for advanced wastewater treatment using powdered activated carbon in combination with flocculation filtration. Two chambers of the former sand filter serve as contact reactors for mixing in the powdered activated carbon. In the subsequent separate sedimentation basin, this is separated from the wastewater. For fine cleaning, a two-layer fixed-bed filter is installed downstream of the sedimentation tank, for which the remaining three filter chambers are used. The dosing and plant technology is located below the new activated carbon powder silo, consisting of a highly accurate dosing scale with discharge screw and a compressed air flushing system for the silo hopper.

The trace substance screening for DecS with the WATERTRACETM measuring device takes place at the Dülmen wastewater treatment plant in the inlet and outlet of the powdered activated carbon stage. The wastewater is conveyed to the measuring container via one continuously running pump each in the inlet to the lifting station and in the outlet of the fixed-bed filter, where it is analyzed with a UV spectrometer. The data obtained is transmitted via the Internet directly to the UNISENSOR headquarters in Karlsruhe.

The wastewater treatment plant Bad Sassendorf treats the wastewater of about 12,000 inhabitants. With 1,200 beds in six spa clinics, the catchment area of the wastewater treatment plant has a very high proportion of hospital wastewater, which contains an increased amount of trace substances such as X-ray contrast media or drug residues.

In October 2009, a downstream ozonation plant was therefore put into operation between the secondary clarification and the existing fining pond. The plant is designed for a water volume of 300 m³/h (corresponding to the dry-weather inflow) and flows through at a free gradient. The wastewater to be treated is fed into a covered contact reactor. During rainy weather, the excess water volume is discharged in advance via a weir sill to the wastewater treatment plant outlet. Ozone is generated in a separate generator and introduced into the wastewater through ceramic diffusers at the bottom of the basin. After ozone treatment, the wastewater is fed to the existing fining pond for biological post-treatment.

At the Bad Sassendorf wastewater treatment plant, trace substance screening is also carried out as part of DecS using the WATERTRACETM measuring device in the inlet and outlet of the ozonation process. The wastewater is conveyed to the measuring container via a continuously running pump in the inlet to the contact reactor and in the outlet of the secondary clarification, where it is analyzed with a UV spectrometer. The data obtained is transmitted directly to the UNISENSOR headquarters in Karlsruhe via the Internet.