Application of a membrane bioreactor for the treatment of low loaded domestic wastewater for water reuse

The paper concerns the demonstrative scale application of a Membrane Biological Reactor (MBR) for low loaded domestic wastewater with low attitude to biological treatment (Carbon/Nitrogen similar to 5). The biological process was managed by the automatically controlled alternate cycles allowing for the reuse purpose with a remarkable reduction of the operational costs. The global process evaluation revealed the system capability of obtaining high nitrogen removal (Effective nitrogen removal of 69%) thanks to its high flexibility related to the hourly loading fluctuation. Moreover high removal of heavy metals and polycyclic aromatic hydrocarbons (PAH) was obtained thanks to the perfect retention capability of the membranes. In depth studies were conducted to know the process behaviour for activated sludge over aeration and with addiction of exogenous carbon. Limitation of sludge over aeration and energy savings were observed with a gradient air supplying method. The addiction of exogenous carbon (acetic acid up to Carbon/Nitrogen similar to 9) led to the quite complete nitrogen removal (Ed=96%) and permitted the biological phosphorus luxury uptake. As a conclusion, it has been found that the coupled process alternated cycles-MBR has the capacity to remove COD, BOD, N, P and suspended solids as well as heavy metals and organic micropollutants, so to obtain an effluent suitable to reuse purpose with high quality standard.