A filter system and filter suitable for water treatment includes a filter having a housing with a water inlet and an outlet, the housing defining a filtration chamber therein. The filtration chamber has filter media therein having a plurality of at least partially porous filtration beads and a pump for pumping water to the inlet. Such a filtration system enables high nutrient removal thus minimising the food source for algae.

Provided herein is a method for the purification of substrate-containing wastewater in a continuous flow-through aerobic biologically activated sludge reactor B, in which at least part of biological sludge 6 is conditioned in a selector under anaerobic or anoxic conditions with at least part of the substrate-containing, to-be-purified wastewater, optionally after a pre-treatment step of the supplied wastewater, such that at least 20 wt % of the sludge in the selector has a residence time in the selector which is at least 20% greater than the hydraulic residence time of the sludge/water mixture in the selector, after which the thus conditioned sludge/water mixture, optionally after an additional anaerobic or anoxic contact step, is fed to the aerobic purification reactor and subjected to aerobic treatment, in which the treated wastewater after aerobic treatment is optionally separated from the sludge by settling, flotation or mechanical separation, and in which at least a portion of the sludge separated from the aerobically treated wastewater is returned to the selector as return sludge.

The present invention relates to methods for biological wastewater treatment for Se control in Se-laden wastewater. The Se contaminants in the wastewater include the Se oxyanions selenate (SeO.sub.4.sup.2) and selenite (HSeO.sub.3.sup.), which are biochemically reduced and transformed to elemental selenium (Se.sup.0) by microorganisms through anaerobic biological reduction. The resulting Se.sup.0 is entrained in the biomass, which is further processed to enable the efficient recovery of concentrated Se.sup.0.