A photobioreactor for treatment of waste water that includes contaminants, the photobioreactor comprising: a treatment chamber having a base and one or more chamber walls extending from the base , and a longitudinal axis, the treatment chamber arranged for receiving a culture of algae having a biomass; a water inlet arranged for supply of waste water to said treatment chamber ; at least one light source provided within said treatment chamber , the or each light source being operable to provide light to such a culture contained within the treatment chamber ; a gas diffuser located across the full base of the treatment chamber , and operable to provide a diffused air stream into the treatment chamber ; a first one water outlet arranged for removal of treated water from the treatment chamber , wherein the at least one water outlet is further arranged for selective removal of a proportion of such biomass of the algal culture produced within said treatment chamber , when such biomass reaches a predetermined maximum level so as to maintain a continuous or substantially continuous culture of algae within said treatment chamber ; a second water outlet arranged for selective removal of a proportion of the biomass of the culture of algae produced within said chamber when said biomass reaches a predetermined maximum level so as to maintain the biomass of the culture of algae within a predetermined maximum level within said treatment chamber; and at least one membrane located within the chamber, wherein the at least one membrane has a periphery, and the entire periphery of the membrane is in contact with the one or more chamber walls, and wherein the at least one membrane is arranged between the first and second outlets so as to retain said culture of algae within the chamber while allowing treated water to be removed by said first water outlet. a treatment chamber having a base and one or more chamber walls extending from the base , and a longitudinal axis, the treatment chamber arranged for receiving a culture of algae having a biomass; a water inlet arranged for supply of waste water to said treatment chamber ; at least one light source provided within said treatment chamber , the or each light source being operable to provide light to such a culture contained within the treatment chamber ; a gas diffuser located across the full base of the treatment chamber , and operable to provide a diffused air stream into the treatment chamber ; a first one water outlet arranged for removal of treated water from the treatment chamber , wherein the at least one water outlet is further arranged for selective removal of a proportion of such biomass of the algal culture produced within said treatment chamber , when such biomass reaches a predetermined maximum level so as to maintain a continuous or substantially continuous culture of algae within said treatment chamber ; a second water outlet arranged for selective removal of a proportion of the biomass of the culture of algae produced within said chamber when said biomass reaches a predetermined maximum level so as to maintain the biomass of the culture of algae within a predetermined maximum level within said treatment chamber; and at least one membrane located within the chamber, wherein the at least one membrane has a periphery, and the entire periphery of the membrane is in contact with the one or more chamber walls, and wherein the at least one membrane is arranged between the first and second outlets so as to retain said culture of algae within the chamber while allowing treated water to be removed by said first water outlet. <EOS>