Membrane bioreactor technology for the treatment of greywater from a sports and leisure club

Especially in the Mediterranean region water is a scarce resource and new approaches to water supply need to be focused. An important contribution can be realised by greywater recycling in decentralised structures. This paper describes the results of a technical feasibility study to treat greywater with membrane technology in view of its reuse for applications which do not require potable water quality. A 3L-lab-scale membrane bioreactor (MBR) treating the shower effluent from a sports club in Rabat, Morocco, was operated with a hollow fibre membrane (Zeeweed, Zenon) for 137 consecutive days. Removal performance and membrane behaviour were assessed. The permeate was of excellent quality and complied with commonly proposed standards for domestic reuse except for bacterial contamination. Non-detectable levels of faecal coliform could not be continuously guaranteed due to bacterial re-growth in the permeate pipe from the open permeate storage tank.

Fig. 4. Flux, maximal TMP (=highest TMP in a cycle, i.e. after 45 min of permeation). 3.4. Flux and hydraulic retention time Stable operation was achieved at a flux of 8 L m–2 h–1 (Fig. 4) and 10 L m–2 h–1 were found to be above the critical flux. These values are at the lower end of reported literature data, because a lab-scale module was used in this study. In studies on municipal and domestic wastewater values for submerged membrane modules between 5 and 40 L m–2 h–1 are found [1]. The low flux may be explained by the fact that in the ZeeWeed membrane used in this study the hollow fibres were not flexible, and therefore not optimised for high fluxes. It gives mainly the ability to work with membrane in small batch vessels. In commercial modules fibres float in the current which creates a self-cleaning effect. Thus, working with such commercial membranes on pilot-scale would yield substantially higher fluxes. The low flux led to an HRT of 13 h in steady state operation. Membrane cleaning with a chlorine solution provided only a short term of a reduced HRT = 11.3 h, but a dramatic reduction of TMP from 250 mbar down to 100 mbar. Although not shown in Fig. 4, the value is in the same range as in the beginning of this study, which is a month before day 0. For economic reasons an increase of the flux is highly desirable. Removal performances of This study demonstrates that MBR technology can be used to treat greywater with low CODand low absolute nutrient content. With a ratio of 100:14:1.5 COD:NH3:P the relative nutrient content was high in comparison to that observed by other authors. The permeate characteristics met commonly adopted standards for recycling for toilet flushing or other household uses, which do not require potable water quality. To guarantee zero faecal coliform levels at all times, disinfection of the permeate is very likely to be necessary. The permeate was of excellent aesthetic quality and free from odours, a fact that is very important in view of public acceptance of treated water recycling. An important drawback of MBR technology remains its high investment cost. If flux cannot be increased the required membrane area and associated costs will be high. Moreover, there is a need for power supply for aeration and mixing. However, in cases of space limitation like e.g. in hotels or leisure clubs, the small footprint of the MBR can outweigh these inconveniences.