Adjustable weir for a collection trough, a collection trough and a collection trough assembly

A wash trough assembly for a compartment of a treatment unit housing at least one layer of granular media for removing impurities from water or wastewater passing through the at least one layer of granular media, said wash trough assembly comprising:

• (a) at least one wash trough having opposing side walls, a bottom connected to and extending between a lower portion of each of the opposing side walls, a first end and a second end, said first end being configured to be operably associated with a wash trough opening formed in a wall of the compartment of the treatment unit so that a liquid collected by the at least one wash trough exits the compartment of the treatment unit through the wash trough opening;
• (b) the wash trough assembly further including at least one of the following:
• (i) an adjustable weir connected to one of said opposing side walls of the at least one wash trough, the adjustable weir having at least one screening section including a plurality of slots sized to perform a screening function in which liquid and solid particles having a size less than a predetermined size can pass through anyone of the plurality of slots of the at least one screening section and enter the at least one wash trough through a corresponding slot while solid particles having a size equal to or greater than the predetermined size cannot pass through any of the plurality of slots of the at least one screening section;
• (ii) at least one of the opposing side walls of the at least one wash trough having at least one screening section including a plurality of slots sized to perform a screening function in which liquid and solid particles less than a predetermined size can pass through any one of the plurality of slots of the at least one screening section and enter the at least one wash trough through a corresponding slot while solid particles equal to or greater than the predetermined size cannot pass through any of the plurality of slots of the at least one screening section;
• and,
• (iii) the at least one wash trough includes a first wash trough, the opposing side walls of the first wash trough each having a uniform height across a length of at least a major portion of the first wash trough, the bottom of the first wash trough having a varying width over at least a major portion of the first wash trough so that the width of a collection channel formed by the bottom and the opposing side walls varies over at least a major portion of the first wash trough.