Membrane and Desalination Technologies - TCE Moodle Website

216 L.K. Wang and R. Menon
Fig. 5.7. Comparison between MBR and equivalent traditional WWTP.
comparison of the MBR and CAS systems, both designed to produce an effluent quality,
suitable for recycle/reuse within and without the production facility.
In a water shortage region, such as California, the treated effluent should be recycled for
reuse as much as possible. When water recycle is under consideration by environmental
engineers, then both capital and O&M (Operations & Maintenance) costs of an MBR system
will be much lower than that of a comparable CAS system. As shown in Table 5.1, 67% of the
MBR treated effluent will meet the water quality requirements for direct nonpotable reuse,
while the CAS treated effluent will not be suitable for recycle and reuse, unless tertiary
treatment process units, such as sand filter (SF), activated carbon filter (ACF), and disinfection,
are added for further effluent purification.
3.2.4. Waste Treatment Consideration
Finally, the average MLSS in a CAS aeration tank is around 4,000 mg/L, whereas that for
an MBR system is approximately 15,000 mg/L (10,000–20,000 mg/L range), as shown in
Fig. 5.6. Then, an MBR process system with much higher MLSS concentration is more
suitable than a CAS process system when treating a high-strength wastewater stream.
3.2.5. Summary
In summation, the following are the advantages of an MBR process system over a CAS
process system (15, 39, 40):
1. Excellent quality of treated effluent.
2. Possibility of recycle/reuse of treated effluent – better overall water economy.
3. Very compact installation: low construction costs.
4. Lower sludge production: lower sludge handling and nutrient costs.
5. Operating flexibility and simplicity; no sludge bulking problems, full automation possible.
6. Ideal preparation for the future; more stringent standards, rising costs of make-up water, etc.