ZLD (zero liquid discharge) wastewater treatment

A method of wastewater treatment that yields zero liquid discharge (ZLD), the method comprising:

• pre-treating provided wastewater to remove heavy metals and suspended and/or colloidal solids to provide pre-treated wastewater,
• ultra-filtering the pre-treated wastewater to remove suspended and colloidal solids,
• nano-filtering the ultra-filtered wastewater to yield treated water and a concentrate, wherein the treated water comprises monovalent ions,
• treating the concentrate to remove di- and tri-valent elements and other compounds from the concentrate, and to reduce a level of sulfates to a specified level which is above a solubility level of sulfates—to yield returned water having a level of sulfates that is above a solubility level of sulfates, and sludge,
• mixing the returned water having a level of sulfates that is above a solubility level of sulfates with the provided wastewater before or at the first treatment stage and/or with the pre-treated wastewater before the ultrafiltration, and
• removing residual water from the sludge to yield removed solids with ZLD,
• wherein the treating of the concentrate comprises using calcium, calcium compounds and/or sodium compounds to reduce at least the level of sulfates,
• further comprising treating the concentrate with a fluid bed reactor (FBR), and further comprising utilizing used FBR substrate for the pre-treatment of the provided wastewater.

A system for wastewater treatment that yields zero liquid discharge (ZLD), the system comprising:

• a first treatment stage comprising:
• a first-stage treatment unit configured to remove heavy metals and suspended and/or colloidal solids from provided wastewater to provide pre-treated wastewater, and
• a filtration unit comprising:
• at least one ultra-filtration unit configured to remove suspended and colloidal solids from the pre-treated wastewater, and
• at least one nano-filtration unit configured to nano-filter the ultra-filtered wastewater to yield treated water and a concentrate, wherein the treated water comprises monovalent ions;
• a second treatment stage comprising:
• a second-stage treatment unit configured to remove di- and tri-valent elements and other compounds from the concentrate, the second-stage treatment unit comprising added sulfate removal compounds, the added sulfate removal compounds consisting of CaO, Ca(OH)2 and/or CaCO3 thereby reducing a level of sulfates to a specified level which is above a solubility level of sulfates—to yield returned water having a level of sulfates above the solubility level of sulfates, and sludge, and
• a final unit configured to remove residual water from the sludge to yield removed solids with ZLD, wherein no concentrate or brine is discharged from the system,
• a controller configured to control levels of compounds in the treated water to maintain continuous operation of the system, and
• pipework configured to mix the returned water having a level of sulfates above the solubility level of sulfates, at the first treatment stage, with the provided wastewater and/or with the pre-treated wastewater.