Aminophosphonates in Nanofiltration and Reverse Osmosis Permeates.

Ramona Kuhn,Marion Martienssen,Volker Preuß,Isaac Mbir Bryant,Carsten Vornholt

doi:10.3390/membranes11060446

Ramona Kuhn, Marion Martienssen + Show 3 more

Open Access

https://doi.org/10.3390/membranes11060446

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Abstract

Aminophosphonates such as aminotris(methylenephosphonic acid) (ATMP) are common constituents of antiscalants. In nanofiltration (NF) and reverse osmosis (RO) processes, ATMP prevents inorganic scaling leading to more stable membrane performance. So far, little attention has been paid to the possible permeation of aminophosphonates through NF and RO membranes. We have investigated the permeability of these membrane types for ATMP and its potential metabolites iminodi(methylenephosphonic acid) (IDMP) and amino(methylenephosphonic acid) (AMPA) with two different NF membranes (TS40 and TS80) and one RO membrane (ACM2) and three different water compositions (ultra-pure water, synthetic tap water and local tap water). We found traces of phosphonates in all investigated permeates. The highest phosphonate rejection occurred with local tap water for all three membranes investigated. Filtration experiments with a technical antiscalant formulation containing ATMP indicated similar trends of phosphonate permeability through all three membranes. We assume that the separation mechanisms of the membranes are the results of a very complex relationship between physico-chemical properties such as Donnan exclusion, feed pH, feed ionic strength and feed concentration, as well as solute–solute interactions.

Highlights

Nanofiltration (NF) and reverse osmosis (RO) processes are well-established applications in softening water and desalination for drinking water production [1]
We investigated the rejection of amino(methylenephosphonic acid) (AMPA), iminodi(methylenephosphonic acid) (IDMP) and ATMP during NF and RO processes
Our results clearly demonstrate that none of the investigated membranes, neither NF nor RO rejected AMPA, IDMP or ATMP completely (Figure 2A–C)

Summary

Introduction

Nanofiltration (NF) and reverse osmosis (RO) processes are well-established applications in softening water and desalination for drinking water production [1]. Their high process stability is an important prerequisite for ensuring sufficient efficiency. Antiscalants comprise a group of synthetic organic polymers such as polyacrylic acids, carboxylic acids, polymaleic acids, polyphosphates, anionic polymers and phosphonates [4]. The latter, such as aminotris(methylenephosphonic acid) (ATMP), is well-known to prevent the scaling of calcium salts at the early stages of the crystallisation process. The required concentration of antiscalants using phosphonates is often lower compared to other antiscalants

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