Wash-water effluent product recovery
BACKGROUND
PCI Membranes was contacted by a multinational consumer goods company that specialises in producing a wide range of hygiene and personal care products, to evaluate the feasibility of using a tubular membrane system for the treatment of a laundry detergent wash-water resulting from one of their global manufacturing sites, with a target to concentrate the wash-water to a satisfactory level whilst generating a permeate stream that is good enough for disposal into the local sewer network.
Following the chemical and physical evaluation of the wash-water, PCI Membranes selected the appropriate tubular membrane type and, using one of PCI Membranes’pilot units configured with a 4ft B1 type module with series flow end caps and instrumentation, completed an extensive trial on the wash-water and collected sufficient design data and samples for laboratory analysis.
THE CHALLENGE
Depending on the location of the manufacturing facility, the acceptable level of pollutants in the permeate stream vary; with the major concern mostly related to the amount of chemical and biological oxygen demand (COD & BOD) and followed by the concentration of total dissolved or suspended solids, oil & grease, dissolved sulphates and total nitrogen.
TEST PROCEDURE AND PROCESS OUTPUT
PCI’s reverse osmosis membrane: AFC99, a polyamide thin film composite membrane with 99% sodium chloride retention characteristic was used for the test and all tests conducted in the trials. The membrane suitability with the process fluid was confirmed with the membrane clean water flux recovered post cleaning in place. Cleaning chemical used is either Ultrasil 11, NaOH or Nitric acid and a mechanical clean with a bespoke foam ball – which gave an insight about the membrane fouling characteristic. Samples collected during the trial have been tested for COD, BOD, pH, conductivity, TDS, total nitrogen, total sulphur, dry matter and concentration of organic matter.
For every single dilution range: 10%, 30% and 50%, the following steps were completed: a pressure scan (to quantify flux variation with pressure and determine the optimal operating pressure for the system), temperature scan (analyse flux variation with temperature at fixed pressure and the impact on solute passage to the permeate stream), concentration scan (define flux variation with the volumetric concentration factor) and process run (to outline a detailed variation of the process flux with concentration).
The same set of AFC99 membrane has been used across the duration of this extensive trial and by using a combination of chemical (Ultrasil 11, NaOH or nitric acid) and/or mechanical cleaning (foam ball) across the process stage, the clean water recovery efficiency of the membrane would stabilise around the 40% range. Considering the nature of the fluid being highly viscous/concentrated and the final concentration factor achieved, the membrane recovery efficiency does not suggest any irrecoverable fouling.
CLIENT BENEFITS
The application of a tubular reverse osmosis membrane AFC99 for the treatment of the laundry detergent wash-water stream has been proven practicable and suitable for achieving the required permeate quality specification.
- The specific site overall permeate quality requirement can be satisfied by simply implementing a one-stage tubular reverse osmosis system (and/or if needed, a 2-stage reverse osmosis system can be used to polish the permeate stream further).
- The ability to reuse the filtrate/permeate stream generated from the process to replenish a part of the water usage requirement on site.
- Save on disposal cost (both in relation to the quantity of water to be disposed of and the pollutants content of the stream).
- The ability to reuse or sale the resulting concentrated product on aftermarkets.
