A wastewater trickle tower has at least one biomedia grate including pairs of upper hanger bars, pairs of lower hanger bars, and spaced-apart rows of biomedia strands, preferably looped cord strands, connecting the upper and lower hanger bars. Upper ends of the strands are secured between pairs of the upper hanger bars, and lower ends of the strands are secured between pairs of the lower hanger bars. A base receptacle to collect wastewater is disposed below the grate. The upper hanger bars are secured together as a unit, the lower hanger bars are secured together as a unit, and a tensioning arrangement is provide for tensioning the strands by influencing the upper and lower hanger bars apart. The grate may be mounted in and surrounded by a rigid casing so forming a self-supporting filter unit. Two or more such casings may be stackable one upon the other to form a trickle tower two of more filter units high.