poly(dimethylamine-co-epichlorohydrin-co-ethylenediamine) in Cu2+ removal from wastewaters by polymer-assisted ultrafiltration

Some results on metal ions removal from wastewaters using water-soluble polymers such as polyethylenimine (PEI), polyacrylic acid (PAA), polyacrylic acid sodium salt (PAASS) and poly(dimethylamine-co-epichlorohydrin-coethylene-diamine) (PDEHED) as chelating agents and the Cu2+ ion as the model in combination with a polymer-assisted ultrafiltration process (PAUF) are reported. In particular, the performances of these polymers in Cu2+ removal from wastewaters were compared. Tests of bonding capacity and best operating conditions of the process showed that complexation conditions depend on pH; indeed, copper ions are complexed by PEI, PAA, PAASS and PDEHED at pHs higher than 6, 4.6, 4.6 and 8, respectively. The decomplexation reactions took place at pH <3. Bonding capacity was 0.333 mg Cu2+/mg polymer, meaning a ratio of polymer/Cu2+ = 3 (w/w) for PEI, PAA and PAASS. For the chelating agent PDEHED, a ratio of PDEHED/Cu2+ = 0.5 (w/w) was determined. UF tests, realized at two transmembrane pressures (2 and 4 bar) by using five different flat-sheet membranes, showed that the PAA polymer and the PAN GKSS HV2/T membrane can be used when the objective of the purification process is to decrease metal concentration not lower than a certain value. The PDEHED polymer is useful if the objective of wastewater treatment is to obtain complete copper removal. Simple washings with tap water were enough for regeneration and reuse of the membranes.

The objective of this work was to compare the performances of the water-soluble polymers PEI, PAA, PAASS and PDEHED in copper(II) removal from wastewater by means of the PAUF process. The results showed that copper removal from wastewaters can be achieved with this process, even with a potential pollution load of 50 mg/l metal concentration. Experimental data showed that: C It is better operate at P = 2 bar rather than at 4 bar; indeed, the small increase of steady-state permeate fluxes registered for PEI and PAA polymers do not justify the elevated costs (e.g., electrical and cooling ones) due to a higher transmembrane operating pressure. Probably this is due to cake compaction at increasing normal stress, meaning also a rejection decrease. C The PDEHED polymer is useful if the objective of wastewater treatment is to obtain complete copper removal. C The PAA polymer with the PAN GKSS HV2/T membrane can be used when metal concentration below a certain value for the water purification process is required (water reuse or fixed by water laws for discharge). In fact, it gave best rejection (99.6%) and permeate flux (275 l/h@m2). C Regarding the possibility of membrane regeneration (by washing) and reuse, PAUF tests in series showed that after a flux decrease observed with respect to new membranes, their performance remained practically constant. In view of PDEHED usage, a proper membrane choice and the optimisation of fluid dynamics conditions could enhance permeate fluxes. Bearing in mind that the PAUF technique is relatively new, an accurate approach to the fluid dynamics and to the chemistry of the process, with a specific study on polymer regeneration, might improve PAUF performances. Thus, this separation technique could be used in the future on a large scale in industrial applications for metal removal and/or recovery, becoming technically and economically feasible.