Water pollution caused by human activities is a major issue and the problem of wastewater contamination by dangerous heavy metals is an important environmental concern in the world (Garba et al., 2019). Different industrial activities such as mining, textile production, tannery, steel production, etc, can pollute the water resources with heavy metals.
Heavy metals have a high solubility in water and can be stored in biological cells (Shrestha et al., 2021). Heavy metals can cause problems for humans directly through the use of contaminated water or indirectly by the food chain through the use of contaminated products. Using resources that are polluted with heavy metals can cause health problems for humans or other living beings such as nausea, kidney problems, cancer, nervous system problem, pulmonary problems, skin sensitivity, bone problems, sleep problems, liver problems, etc (Fu and Wang, 2011; Shrestha et al., 2021).
It is necessary to remove heavy metals from mine drainage and industrial wastewater to prevent the pollution of water resources, prevent potential harm to plants, animals, and humans, and confirm the effluent guidelines. Also, many heavy metals have high value, and recovering them can be economically efficient.
Copper is a valuable heavy metal. Copper with high concentration is found in wastewater from some industries such as metal finishing, electroplating, plastics, and etching (Al-Saydeh et al., 2017). In the copper mine drainage can be a large amount of copper that as a result of removing and recovering it, environmental pollution can be prevented and also can bring some economic income.
Copper is a toxic metal in low concentrations. High concentrations of copper in drinking water can cause several problems such as gastrointestinal effects, carriers of the gene for Wilson disease, and metabolic disorder of copper homeostasis (Shrestha et al., 2021). Also, copper-containing solutions are toxic for plants because they can prevent photosynthesis, plant growth, and plant reproduction (Singh et al., 2011) and even it is harmful to aquatic organisms (Simate and Ndlovu, 2014). So it is necessary to remove copper from effluents that are discharged into the water resources.
Different methods have been used for removing heavy metals from aqueous solutions such as sorption, precipitation, ion exchange, electrochemical techniques, photocatalysis, and membrane filtration. Membrane filtration needs relatively less time for removing copper compared with other methods. Ultrafiltration (UF) needs less applied pressure than reverse osmosis (RO) and nanofiltration (NF) and membrane fouling in UF occurs less than in RO and NF due to the bigger size of membrane pores. Polymer-enhanced ultrafiltration (PEUF) method is able to remove a percentage of heavy metals from aqueous solutions. Using water-soluble polymers that have a low price in addition to effectiveness can make UF process economically more favorable.
UF membranes have relatively big pores in their structure and have a relatively high permeability that alone is thought to be unable to remove heavy metals efficiently (Bhattacharjee et al., 2016; Zhu et al., 2019). Commercial UF membranes such as polyethylene, polypropylene, and polyvinylidene fluoride are made of hydrophobic membranes and others such as polysulfone and polyethersulfone are less hydrophobic (Huang and Feng, 2019). The applied pressure needed for UF is about 2 to 5 bar (Singh and Hankins, 2016). UF can separate dissolved molecules that are about 100 nanometers or larger. Bacteria, colloids, and macromolecules with a molecular weight of about 1 to 300 kiloDalton (kDa) can be separated by UF membrane. In order to remove heavy metals by UF, this method can be enhanced by the addition of surfactants or polymers (Fu and Wang, 2011; Saleh et al., 2022).
Micellar-enhanced ultrafiltration (MEUF) was first introduced by Scamehorn et al in the 1980s for removing dissolved organic compounds and multivalent metal ions from water flows (Fu and Wang, 2011; Landaburu-Aguirre et al., 2009). This method uses cationic or anionic surfactants as micelle agents for complexation with heavy metals. Polymer-enhanced ultrafiltration (PEUF) is another enhanced ultrafiltration method. In this method, water-soluble polymers with a relatively high molecular weight that has functional group are added to the aqueous solution and these polymers catch small dissolved pollutants in water using interactions between them and make the dissolved pollutants bigger so they could be separated from the aqueous solution by UF (Huang and Feng, 2019). Actually, heavy metal ions make large complexes that have a molecular weight greater than the MWCO of the membrane (Al-Saydeh et al., 2017).
In this research removing copper by PEUF using polyacrylic acid and polyvinyl alcohol polymers was studied and the effect of parameters such as concentration of copper in influent solution, pH, polymer-to-metal ratio (P/M) (polymer dosage), type of polymer, applied pressure, and ionic strength of the aqueous solution was investigated. Also, the simultaneous effect of two parameters on removing copper by PEUF was examined by Design Expert v.7 software. The aim of this study is to remove copper from an aqueous solution using the PEUF method.