Reverse Osmosis for Wastewater Recycling

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Reverse Osmosis For Wastewater Recycling
Reusing treated wastewater for beneficial purposes, such as agricultural and landscape irrigation, industrial processes, toilet flushing, or groundwater basin replenishment, is growing in response to environmental and economic concerns.
One of the key factors involved in recycling wastewater treatment plant (WWTP) effluent for another use is the need to reduce total dissolved solids (TDS). This is often done by using a reverse osmosis (RO) system, which relies on pressure differential to force a solution (in this case, water) through a membrane that retains the solute on one side and allows the pure solvent to pass to the other side.
While extremely effective on biologically treated
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However, upsets in the secondary clarifier can lead to effluent with higher levels of TSS and BOD, causing plugging of the brine spacer with suspended solids and organic fouling. Also, power consumption for RO systems with this type of pretreatment tends to be high, and membrane life is often quite short.
Lime-softening has been somewhat more successful in protecting the RO membranes, but this increases operating costs and does not totally prevent fouling of RO membranes. |

Ultrafiltration Improves Suspended Solids Removal As RO Pretreatment
Many of today’s water reuse systems use an ultrafiltration (UF) pretreatment step to remove suspended solids. These systems typically use hollow fiber UF membranes, which do an excellent job of providing water with low suspended solids to feed the RO system. However, the UF system is an extra treatment step, requiring additional footprint, and adding to operating costs. The UF system may also be susceptible to upsets from a conventional WWTP, which can further increase its operating costs.
Membrane Bioreactor As RO Pretreatment
With an MBR, the UF membranes are submerged in the activated sludge to combine the biological step and the solid-liquid separation into a single process. The membrane acts as a barrier, which improves the effluent quality. The MBR eliminates the secondary clarifier and does not rely on gravity for liquid-solids separation and so allows the activated sludge to operate with a
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