INDIRECT POTABLE REUSE VERSUS POTABLE REUSE - WHAT'S THE DIFFERENCE?

摘要

The practice of reusing wastewater started as a way to discharge treated sewage. Governments began requiring that cities and local agencies implement wastewater treatment plants to protect public health by reducing pollution of rivers and lakes. Over time, the regulations were tightened and technology increased to make the water quality of the treated wastewater increasingly better, to a point where its quality was almost as good as potable water. Many wastewater plants implemented tertiary treatment, consisting primarily of media filtration, to allow the treated wastewater to be used in agriculture, industry and landscape irrigation. In 1976, the Orange County Water District (OCWD) in California took wastewater treatment one step further, by pioneering advanced recycled water treatment with the implementation of Water Factory 21. Since then, indirect potable reuse projects have become more common, with municipal-size recycled water projects in the U.S. (California, Arizona, Texas and Florida), Singapore, Australia and the Middle East. The process design for an advanced recycled water facility (AWTF) for indirect potable reuse is now fairly standard, although there are some variations from facility to facility. Current AWTF processes typically include membrane filtration (MF) pretreatment using microfiltration or ultrafiltration followed by reverse osmosis (RO) for removal of organics, contaminants and viruses. The final step is ultraviolet light (UV) with advanced oxidation (UV-A) for disinfection and destruction of any remaining contaminants that make it through the RO membranes. Advanced treated water has been percolated or injected into the ground to be pulled out later through extraction wells and used in the potable water distribution system, hence indirect potable reuse (IPR). This water is often used as drinking water without additional treatment. While not all projects have been successful due to funding, local politics, or public aversion to using advanced recycled water, enough AWTFs have now been implemented to develop a reputation as being a viable new source of water, created from a waste product that was previously unused. As IPR becomes more common, there is now some discussion of eliminating the extra percolation or injection step and progressing to direct potable reuse (DPR).