Reverse Osmosis Reject Disposal Options

While there may be many options to deal with RO reject, each one has advantages and limitations. Some offer cost savings, while others may increase costs, but eliminate the need to dispose of a relatively large waste stream. Reject is considered non-hazardous, and contains only those constituents that were present in the feed water (only more concentrated, which can be a problem) and any antisealants, biocides (such as DBNPA—see Chapter 8.2.5.2), or any other chemical added as pretreatment. Disposal techniques over the years have included  

The three most common techniques for dealing with RO reject 

Surface water discharge Land application Sewer 

Deep well injection Evaporation pond Zero-liquid discharge 

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Recommcndation 4-1. To avoid the possibility of unanticipated disposal problems, the PMACWA and the BGCAPP contractor should characterize and consider waste management options for reverse osmosis rejectate brine, supercritical water oxidation (SCWO) filtrate solid waste, SCWO titanium tank liners, venturi scrubber particulate filters, and energetics offgas treatment system filters before submitting the waste analysis plan required by RCRA. The PMACWA should also look carefully for any as-yet-unidentified secondary waste streams from BGCAPP or PCAPP. 

Options 8 and 9. Other Effluent Treatments. Reverse osmosis is a physical process by which the majority of the effluent water is cleansed of polluting ions. However, a highly polluted reject-water stream also is produced. This reject stream is normally sent to evaporation ponds for further concentration and ultimate disposal of the pollutant solids. Ion exchange is a physiochemical process that similarly produces a pure-water stream and a lower volume stream of concentrated waste that must be evaporated. Both processes are more expensive than is Option 7, have the same general drawbacks, and have the additional problem of disposing their concentrated waste streams. 

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