State-of-the-art review of the membrane bioreactor processes for urban and industrial wastewater treatment and reuse
Effluents from urban and industrial wastewater treatment plants contain organic (e.g., COD, BOD, total suspended solids, endocrine disrupting compounds), inorganic (e.g., phosphorus, ammonia nitrogen, nitrites and nitrates, metals) and microbial pollutants (e.g., bacteria, viruses, parasites), which are either directly discharged into the environment or reused for agricultural purposes. These wastewaters are often responsible for pollution of surface and groundwater (increasing the COD, colour and eutrophication of water, for example). In the context of finding solutions for water shortages, wastewaters are more and more frequently subjected to tertiary treatment for water reuse. The treatment of wastewater for reuse must yield water that meets specific quality criteria and is adapted to be reused as washing water, cooling water, process water, irrigation water or sprinkling water, among other uses. Conventional processes can be inappropriate, notably because of their inability to provide a consistently good quality of treated-water and because of the associated risk of microbial contamination. An alternate method can be the application of membrane bioreactors (MBR) for wastewater treatment and reuse. MBR are characterized by ease of operation, ease of automation, negligible equipment requirements for adding chemicals and their capacity to remove simultaneously organic, inorganic and microbial pollutants in the same reactor. This technology offers the possibility to simultaneously clarify and disinfect wastewaters without any risk of forming organochlorinated compounds. In this paper, MBR are first compared to conventional biological treatments, followed by a particular emphasis on the present state of knowledge about MBR, criteria of application and operating conditions that greatly influence the performance of these technologies. Recent developments in the modelling of the operating process and membrane fouling are also presented. Finally, industrial applications and operating and implementation costs are briefly discussed.