Metro - ECCV Zero Liquid Discharge Pilot Study_Application

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The AC for many receiving waters around populated or otherwise impacted areas is low or non-existent, making it difficult to discharge high concentrations/volumes of pollutants. Discharqe to Irriqation Canals: This may be a viable disposal option for some discharges. Regulatory requirements include narrative and numeric standards in Regulation Nos. 31,41, 42 and 62. Due to the irregular flow regimes in irrigation ditches, AC is not available, resulting in end of pipe limits. This discharge is also subject to the approval of the ditch owner/operator, who may also add additional requirements. Discharqe to a Publiclv Owned Treatment Works (POTW): Discharges to a POTW, or blending with wastewater effluent just prior to an outfall may be authorized subject to a POTW's pretreatment program and/or the pretreatment regulations in Regulation No. 63. POTWs need to be willing to accept the waste, must consider impacts to its operations, may impose additional limitations, and may need to have its own permit amended. Deep Welllniection: This disposal method is subject to issuance of an Underground Injection Control permit from EPA Region VIII. The ability to use deep well injection is limited in Colorado, principally due to site-specific hydrogeologic conditions. Evaporation: Evaporation of RO/NF concentrate does not require a discharge permit if the evaporation pond meets the state required infiltration rate found in Regulation No. 61. Due to land requirements, this option may be limited to smaller facilities. Discharqe to Groundwater: Groundwater discharges are subject to Regulation Nos. 41, 42, 61 and 62. The amount of land area needed and lack of AC in groundwater for this type of discharge are potentially the key limiting factors. Pollutant Tradinq: Trading of "pollutant credits" is a tool available through Regulation No. 61, the Colorado Pollutant Trading Policy, and other Division accepted trading programs. In essence, removing or reducing an existing contaminant load would "free up" AC that could then be assigned to another source. Zero Liquid Discharqe: ZLD refers to technologies that process the concentrate to a point where there is no liquid to discharge. ZLD does not require a discharge permit but the remaining solid waste would require disposal in accordance with solid waste and other applicable regulations. Relative to other disposal options, ZLD is an expensive, complex process with large energy requirements that could include using alternative energy sources to aid in sustainability and cost control. ZLD technologies have not been used in drinking water treatment plants of any significant size (> 1 mgd). Cost-effective and energy-efficient ZLD, including alternative energy sources, will require well funded research and development efforts. Conclusion and Recommendations To assure an adequate supply of high-quality water protective of human health and in support of Colorado's economy, the State of Colorado needs to take a leadership role in developing cost effective and energy efficient ZLD technologies and demonstrating their use in sustainable RO/NF concentrate management. This includes providing active political and financial support, in conjunction with private interests, for the development and operation of pilot testing programs. 2