A number of water utilities make use of reverse osmosis (RO) or (capillary) nanofiltration (NF) membranes as a component of their drinking water treatment, since these provide a good barrier for all kinds of substances (e.g., salts, pathogens, particles, organic matter).
Because RO and NF are separation processes, they generate a concentrate stream consisting of components of the feed water in concentrate form, as well as possible additives, such as antiscalants and salts. The management of these concentrate streams is of great importance given the increasing application of these advanced treatment processes.
Dealing with concentrate streams in NF/RO treatment techniques
One can clearly observe that, for a variety of reasons, the interest in the application of membrane techniques in drinking water treatment is generally increasing. For this reason, and for socio-developmental reasons, the management of the concentrate streams is becoming more and more important. It is also frequently the case that concentrate management can represent an obstacle to the application of membrane techniques. This is why it is important to survey the current situation regarding concentrate management and, if possible, recommend a joint approach for the disposal or treatment of (capillary) NF/RO concentrate streams.
The objective of the research is to provide an overview of current practices and experience with NF and RO concentrate treatment and disposal, and to recommend a future-proof approach to concentrate management.
- Survey current concentrate treatment and disposal practice
Interviews will be conducted with drinking water technologists experienced in the field of concentrate treatment and/or disposal, to gain an overview of the main challenges faced by these activities. Additional information will then be collected through an examination of the (international) literature, and/or the conduct of further interviews at Dutch Water Authorities that are active in concentrate treatment and/or disposal.
- Develop relevant conceptual scenarios for concentrate treatment and disposal
Three integrated treatment scenarios of typical treatment processes for (1) surface water, (2) aerobic groundwater and (3) anaerobic groundwater will be developed, based on a jointly agreed (I) conventional scenario and (II) a (capillary) NF/RO scenario. For these scenarios the mass balance of salts, nitrate, phosphorus, organic carbon and pollutants will be set with a view to the composition of the concentrate stream generated, and the possible impact on receiving water bodies (compared with conventional scenarios).
- Survey and analysis of possible solution paths for concentrate treatment and disposal
Any components in the concentrate stream causing problems in the different scenarios will be defined in terms of the chance of standard exceedances in receiving water bodies (depending on location). Possible solutions will then be proposed per scenario for such cases, and relevant research questions formulated for experimental research into the treatment of (capillary) NF/RO concentrate streams.
- A report containing an overview of the current situation regarding the treatment and disposal of concentrate generated by RO and NF membrane techniques.
- A recommendation for concentrate management that is collectively endorsed by the Water Authorities and Rijkswaterstaat, water distribution utilities and possibly AquaMinerals, which can be used to arrive at the best concentrate solutions in the future.
- Understanding of problem-causing components in the NF/RO concentrate stream of the three types of feed water: (1) anaerobic groundwater (RO), (2) aerobic groundwater (RO) and (3) surface water [(capillary) NF] and RO, including suggestions about the use of pre-treatment in relation to concentrate quality and/or concentrate treatment, possibly including resource recovery.