Walnut-Shell & Media Filters

Where the final discharge or reinjection limit is tight, a deep-bed media filter — classically crushed walnut shell — polishes the water after flotation. The oleophilic media captures residual oil droplets; periodic backwash (often with scrubbing) regenerates the bed, achieving oil-in-water down to single digits.

Walnut-shell and media filters — the deep-bed polishing stage that captures residual dispersed oil to meet single-digit discharge limits.

Emulsions are the hard case — chemically or mechanically stabilised oil-in-water that will not separate by gravity — and need demulsifier chemistry, pH adjustment or thermal/electrostatic treatment to break before the physical stages can work. For reinjection, the spec flips toward solids and particle-size control to protect formation permeability, so the train is tuned to the disposal route rather than a generic standard.

Reynolds & Bauhm designs produced-water trains stage by stage against the governing discharge or reinjection spec — selecting separators, hydrocyclones, flotation and polishing media, and the demulsification chemistry that makes the physical stages perform.

Produced water is the largest waste stream in oil and gas, and its treatment is a staged de-oiling problem: free oil, dispersed oil and emulsified oil are removed in sequence because no single device handles all three economically. The target — whether for overboard discharge, reinjection or reuse — is set by regulation such as the OSPAR 30 mg/l dispersed-oil limit offshore or the US EPA effluent limitation guidelines.