CoRe Water – From WWTP to sustainable water factory

CoRe is an innovative treatment concept that stands for ‘Concentrate, Recover and Reuse’. In the CoRe Water concept the wastewater is first concentrated before undergoing further treatment. This allows sewage water to be treated efficiently, with the use of less energy, with greater removal efficiency (N, P and micropollutants), and with an optimal recovery of resources like nutrients, energy and, most of all, water: from a WWTP to a sustainable water factory.

Technology

This new concept’s key technology is Forward Osmosis (FO), in which the treatment process is actually reversed. The first step involves producing clean water of high quality by using a strong saline (draw) solution to extract the water from the wastewater. The waste materials remain behind in a concentrate stream at a volume that has been reduced twenty-fold. This concentrate stream can then be used for the recovery of resources and for energy production. The hypothesis is that this can be done with greater effectiveness and efficiency because the stream is concentrated.

Challenge

The main objective of the partners in this project was to further develop the CoRe Water concept into a new modular and adaptive concept for the treatment of municipal wastewater. Part of the project involved the design and construction of a CoRe pilot focused on the FO-RO combination, with a targeted capacity of 2 m3/hour, and to achieve a flux of 5 litres per m2 per hour, and a concentration factor of 20. The recovery of resources from the concentrate was not a component of the pilot studies carried out in this research. With an existing (smaller) pilot, initial experience was gained at the Wehl WWTP and at a pumping station in Leusden. This experience was important for the design and operation of the CoRe pilot. Besides the experience with the FO-RO combination in practice, the FO process was subject to laboratory research on a small scale under controlled lab conditions. This focused primarily on the options for managing the FO membrane fouling through (a combination of) air/water flushing (AWF), osmotic backwash (OBW) and chemical treatment (CIP). Desk studies provided further insight into the main critical parameters in the practical implementation of the CoRe Water concept, the key quality requirements for the produced water – as set, for example, by agriculture and industry – and the best options for the recovery of nutrients from the concentrate. The potential of biogas production from the concentrate from the CoRe Water concept was studied on a bench scale on the basis of the concentrate from the Wehl WWTP.

Results

Based on the field trials with the newly-built CoRe pilot at the WWTP in Roermond, it was concluded that the CoRe Water concept in its current form with spiral-wound FO membranes (SWFO-RO) is not technically nor economically feasible. The FO cannot be operated stably and with sufficient flux (5 L/m/m2/h) and an appropriate concentration factor (≥20). The main reason for this was a complex combination of particle fouling, organic fouling and biofouling, a consequence of the inadequate pre-treatment of the wastewater. The CoRe pilot showed however that the concept does form a robust barrier to nutrients (COD, tot-N, tot-P, NH4 and salts) and to a wide range of organic micropollutants. The quality of the water produced (RO permeate) was very good.

New perspective

The CoRe Water concept is technically feasible if the fouling and clogging can be managed. An alternative FO module design offers a potential solution to the fouling susceptibility, the high energy consumption and the high CAPEX/OPEX. The report contains a proposal for a new CoRe Water concept based on a submerged system, in which the FO membranes are implemented as submerged plates, and/or a capillary/tubular FO (cap-FO/TFO) system, in which the feed is configured to flow inside-out. A system of this kind is less susceptible to fouling, easier to clean, requires less energy, is easier to design, and the membranes are less costly than the spiral-wound FO (SWFO) ones. A patent application has been submitted for this new CoRe Water concept. It opens new perspectives for the conduct of follow-up research.