Funktionalisierte Polyacrylnitril-Ultrafiltrationsmembranen für Ionenaustausch in der Trinkwasseraufbereitung

Project Acronym
Project Title
SMART PAN-UF Membranes for DW Treatment
Principal Investigator
Funding Organization
Project Abstract
Global demand for drinking water has risen continuously by about 1% per year over the past 30 years. According to conservative estimates, this growth will continue into 2050. In parallel, about 30% of the world's population will not have safe access to clean drinking water in 2019, but safe drinking water and sanitation are recognized as basic human rights. The reasons for the poor drinking water supply situation worldwide are diverse: Raw water availability is often insufficient due to inadequate water management; climate change contributes to further aggravation; raw waters are contaminated by geogenic contaminants (e.g., arsenic or chromium) or by inadequate treatment of wastewater (e.g., patogenic microorganisms); effective technologies for safe drinking water treatment are not available or are too energy and cost intensive.
This is where the proposed innovation project comes in. Based on an interdisciplinary cooperation between the TUHH Institute "Water Resources and Water Supply" and the Institute of Polymer Research of the Helmholtz-Zentrum Geesthacht (HZG), the aim of the project is to develop a drinking water treatment system using a novel functionalized polyacrylonitrile membrane (PAN), which can be used to remove microbiologically safe drinking water and, at the same time, frequently occurring problematic substances in drinking water treatment (arsenic, chromium). Arsenic is a carcinogenic substance and is one of the 10 highest priority public health chemicals identified by the World Health Organization (WHO). High concentrations of arsenic in groundwater pose a high health risk to more than 300 million people in about 100 countries. Arsenic is absorbed through drinking water in the neutral pH range as arsenate (As(V)) or oxyanion [HAsO42-]. The WHO recommends a guideline value of 10 μg/L As, which is exceeded by orders of magnitude in affected areas.

Another problem substance in the global drinking water supply is chromium. In addition to contamination from industrial activities, leaching from chromium-containing rocks plays a major role regionally. In aqueous solutions, chromium is present in the neutral pH range in trivalent (Cr(III)) or hexavalent form (Cr(VI)). While Cr(III) compounds in small amounts are essential for certain metabolic processes in humans, Cr(VI) compounds are considered very problematic because they are carcinogenic. Frequently, chromium is also geogenically associated with arsenic; it then also occurs as an oxyanion (CrO42-). For both target substances (As, Cr), treatment technologies for removal exist. However, these require chemical additions (e.g. Fe (II)/Fe (III); Al salts) on the one hand, and further downstream processing steps such as filtration for particle separation on the other. In corresponding coagulation processes, highly toxic arsenic- or chromium-laden sludge is then produced [2,4]. Adsorptive technologies also exist for arsenate removal, but these are interfered with by other water constituents (particulate, ortho-phosphate, silicate) and also by dissolved organic matter. Moreover, corresponding adsorbents based on iron hydroxide or aluminum, which cannot be regenerated, are very cost-intensive. The new proposed process "Smart PAN-UF" is now intended to develop a single-stage treatment system that operates at low operating pressures (max. 0.3 bar transmembrane pressure) and that ensures complete particle retention through PAN membrane pores of approx. 10-30 nm in size. On the other hand, the membrane material should be modified by chemical post-treatment with appropriate ion exchange functionalities, allowing selective removal of the oxyanions arsenate or chromate in a single treatment step. Such a single-step process is highly innovative and, of course, attractive to the market. Complete particle filtration through the ultrafiltration membrane (UF) represents the perfect pretreatment for the downstream ion exchange for arsenate or chromate. The permeate is free of pathogenic bacteria and thus microbiologically safe. To achieve high yields, operation is in dead-end mode. Therefore, the PAN ultrafiltration membrane (UF) must be backwashed regularly. In this way, the regeneration of the introduced ion exchange groups can take place. The regeneration can be done with neutral salts (e.g. NaCl) or by saturated CO2 solution (carbonic acid via H+ or HCO3-).