Modification of used commercial reverse osmosis membranes to nanofiltration modules for the production of mineral-rich packaged drinking water

Abstract

Global supply of commercial reverse osmosis (RO) membranes is growing exponentially due to rapid population growth, industrialization, and urbanization. The continuous demand for enormous quantity of drinking water has brought about process improvements and technological advancements in membrane preparation. The transformation of used RO membranes into nanofiltration (NF) and ultrafiltration membranes by opening up the pores using chemical treatment by inexpensive oxidizing agents could be one of the cost-effective options. The present study investigates the chemical oxidation of the indigenously synthesized RO membrane using aqueous sodium hypochlorite (NaOCl). The performance of the membrane was evaluated by conducting experiments under varying operating conditions of operating time, feed pressure, and total dissolved solids (TDS) in raw water for calculation of flux and salt rejection (%). From an initial flux of 25.2 L/m2 h and TDS rejection of 97.5% for original RO membrane, the values reached 80 L/m2 h and 25.5%, which is in NF range, after a reaction time of 780 min with 4000 ppm concentration of NaOCl oxidizing agent. Further extension of treatment time to 900 min enhanced the flux to 130 L/m2 h with salt rejection lowering to 5.67%. Membrane cleaning was performed efficiently using an advanced technique in which chlorine dioxide (ClO2) was used in combination with citric acid. This combination ensured rapid cleaning with restoration of water flux and % salt rejection. The process was scaled up to pilot plant level using RO membranes modified to NF range of pore size. Permeate water enriched with minerals was further packed using an indigenously designed semi-automatic bottling unit. The studies revealed that the indigenously developed RO membranes are easy to alter into high-performance NF membranes. Overall, the process for production of packaged drinking water was cost-effective, easy to operate, and environmentally friendly.

WITHDRAWN: An integrated process of methanol coagulation and side-stream membrane bioreactor for the treatment of rice gruel wastewater

“…In the present study, the chemical cleaning was carried out by a combination of 1% citric acid, followed by water wash, then by 1% NaOH + 0.5% EDTA + 0.1% SLS (w/v) and again water wash for durations of 15 min each. After wash, the membrane was stored in 0.5% (w/v) SMBS aqueous solution to avoid any biological fouling and extend membrane life [32,33].…”

A prototype system for the removal of 137 Cs from liquid radioactive waste using reverse osmosis membrane

“…4. The primary and secondary amines associated with the terminal amine groups are responsible for the -CH stretching vibration of the peak, which is observable at 2876 cm -1 , and the equivalent -NH stretching vibration, which occurs at 3446.91 cm -1 (Govardhan et al, 2020). The -C=O group, amide I and II, and the bending and stretching vibrations of the carbonyl amide groups are represented by the peaks detected at 1745.64, 1672.32, and 1535.39 cm -1 , respectively (Mostafa and El-Aassar, 2012;Porubská et al, 2012).…”

“…4e), which indicates the degradation of the amide group after soaking in stearic acid. The PA skin layer's chain structure is altered and deformed as a result of this reaction, which leads to flaws in the membrane's structure and higher permeability but lower selectivity or rejection (Govardhan et al, 2020). Finally, the effect of adding different acids may be a combined effect that gives rise to enhance sorption of 137 Cs on the membrane and cannot be induced using a single acid.…”

Study for Recycling Water Treatment Membranes and Compnents towards a Circular Economy—Case of Macaronesia Area

“…Regarding membrane recycling in the Atlantic Islands, in the Canary Islands, there are 330 desalination plants in operation, concentrated on the islands of Gran Canaria, Tenerife, Fuerteventura and Lanzarote, where 291 desalination plants use RO technology ( Table 1 ) [ 5 , 20 , 21 , 22 , 23 , 24 ].…”