Situation: | The treatment of drinking water using nanofiltration (NF) and reverse osmosis (RO) is primarily carried out to remove hardness, other inorganic components, natural organic substances as well as trace organics from water introduced by man-made activities. NF and RO processes produce different quantities of concentrate stream with a correspondingly higher concentration of the separated substances. Antiscalants (predominantly phosphates and carboxylates), which are dosed to avoid precipitation of salt, also remain in the concentrate. All disposal routes for the concentrates (direct or indirect discharge) are part of the plant authorisation and require the approval of the responsible water authorities. In recent years, the discharge of concentrates into a water body has been viewed increasingly critically by the competent licensing authorities, especially when the concentrates contain high concentrations of unnatural anthropogenic trace substances, nutrient salts and / or substances added during the treatment process. Since the refusal of a discharge permit for the concentrates is usually synonymous with withdrawal from the NF/RO process, solutions are required which secure the use of this innovative, energy efficient technology that has many advantages in drinking water treatment in the long term. |
| Methodology: | In the joint project, KonTriSol, different approaches are being investigated under 7 work packages. The DVGW-Forschungsstelle TUHH coordinates the work package “Antiscalants – assessment and alternatives”, which contains the following sub-goals: - Reliable evaluation of the effectiveness of the antiscalants in the treatment process by standardized measurement of homogeneous and heterogeneous crystallization
- Reliable declarations on the behaviour of antiscalants used in the preparation process and their evaluation, substantiated with optimised and reliable analysis
- Development, semi-technical implementation and validation of process engineering strategies for the minimisation/avoidance of antiscalants
To this end, laboratory tests on the effectiveness of antiscalants under changing boundary conditions (DOC content, yield, temperature, pH, etc.) are carried out at the DVGW-Forschungsstelle TUHH. Tests for the evaluation of homogeneous scaling in the water phase and heterogeneous scaling on membrane surfaces are applied and further developed and compared with the calculation results from software programs of various membrane and antiscalant manufacturers. The aim is to develop a reliable and compatible test to assess the efficacy of scaling-inhibiting substances (antiscalants and their ingredients), depending on the respective boundary conditions of the membrane process (pretreatment, water matrix, yield, etc.). This should serve to identify antiscalant products or product mixtures and if necessary, alternative formulations which are retained as completely as possible by the membranes, which can be used in the lowest possible concentrations with as few secondary constituents as possible and which have the least possible impact on the environment when discharged into water bodies. |
