A Wastewater RO (WWRO) is a commonly used name designated to identify reverse osmosis systems fed from a pretreated wastewater source. This takes place mostly when we manage recycle/reuse applications intended to reducing either the liquid waste to be disposed or the fresh water consumption that feeds the process water treatment plants.
So far so good, the difficulties start appearing when designing a completely brand new facility where the wastewater does not yet exist, thus it cannot be characterized. The challenge therefore becomes on how to produce a cost effective WWRO with such limited wastewater information. In some projects, process engineers will be able to gather design data from other similar facilities, from the same industry, and simulate the blending of water streams that conforms the available wastewater source to be reused. Easy to say but difficult to perform. Engineering team experience for sure will be your best allied.
There are several recommendations to consider when designing a WWRO. First of all we need to keep in mind that the Wastewater Treatment Plant (WWRO pretreatment) shall be able to produce the best water quality as possible in terms of TSS, Turbidity and SDI (Silt Density Index) but also considering this time other parameters like BOD, COD, TOC, O&G, heavy metals, etc. This is critical since the cost effectiveness in WWRO applications is highly impacted from the OPEX side due to elements that reduce the WWRO recovery rate but also other non considered contaminants that will produce fouling/scaling on RO membranes. Commonly a WWRO will require 2-3 times more frequent membranes CIP (Cleaning in Place) and probably 2 times more RO membranes replacement compared with a fresh water RO system (fed from pretreated river or well water).
Good practices when designing WWRO consider combination of the following pretreatment techniques as applicable: Biological Treatment, Advance Oxidation, Ultrafiltration, Metals Removal, Hardness Reduction, Ion Exchange, use of Biocides, etc. Also to consider: special RO membrane spacers, exhaustive Operation Monitoring and customized CIP for the specific application. In the end the key to succeed with your WWRO project is about the balance, controlling OPEX but not killing the CAPEX.
