Wastewater heat recovery systems

A heat exchanger tray comprising:

• a base comprising a cutout, the base including a bottom portion with a plurality of sidewalls forming a serpentine path for wastewater;
• a cover positioned within the cutout of the base to create a vertical space between the plurality of sidewalls and the cover, the cover including a plurality of flow-directing features positioned above the plurality of sidewalls of the bottom portion of the base, wherein each flow-directing feature engages a respective sidewall to at least partially block the vertical space between the respective sidewall and the cover;
• and
• a heat exchange coil positioned in and along at least a portion of the serpentine path between the base and the cover;
• wherein fresh water flows through the heat exchange coil;
• and
• wherein the plurality of sidewalls and the plurality of flow-directing features cooperate to direct the wastewater to flow through the serpentine path between the base and the cover, such that the wastewater heats the fresh water flowing through the heat exchange coil;
• and
• wherein the plurality of sidewalls are spaced apart from one another in a first direction and the plurality of flow-directing features are spaced apart from one another in the first direction and each flow-directing feature extends in a discontinuous manner in a second direction perpendicular to the first direction.