Inorganic and Organic Silicon Fouling of Nanofiltration Membranes during Pilot-Scale Direct Potable Reuse

Abstract

Fouled nanofiltration membranes from lead and lag positions of a 2-stage pilot-scale direct potable reuse plant treating secondary municipal wastewater effluent in El Paso, Texas were thoroughly characterized after 9 months of operation to elucidate the role of silicon moieties on fouling. X-ray photoelectron (XPS), energy dispersive X-ray (EDS), and Fourier transform infrared (FTIR) spectroscopies identified silicon oxides/ silica as dominant foulants, especially on the lag element. Gas chromatography/mass spectroscopy also identified organosilicon moieties such as linear-and cyclosiloxanes on the lead element. Extensive siliceous fouling was accompanied by calcium, aluminum, and magnesium scaling as well as deposition of bioorganic materials thereby modifying membrane surfaces that resulted in irreversible productivity loss. None of the three selected cleaning agents (sodium dodecyl sulfate and NaOH, EDTA and NaOH, and HCl), either singly or in combination satisfactorily restored water permeability of the membrane. EDTA performed better in the lead element (where bioorganic fouling prevailed), and HCl was more effective in the lag element (where mineral scaling accompanied silicon oxides). This suggests the express need for novel antiscalants to reduce organosilicon/silicon oxide deposition and the necessity of harsher cleaning agents/ regimens specifically targeting silicon (e.g., hydrofluoric acid or ammonium bifluoride).

Performance Restoration of Iron Electrodes by Polarity Reversal after Long-Term Surface Fouling in Wastewater Electrocoagulation

“…A flow-through pH meter was used to simultaneously monitor the solution pH at the exit of the EC cell during the operation. The system was run with the same synthetic wastewater secondary effluent , as described in Table S1 [Supporting Information, SI], at pH 7.0 ± 0.2, with the overall potential, conductivity, and solution pH continuously monitored. Air was continuously sparged to increase the dissolved oxygen (DO) concentration to levels above 9 mg/L at the beginning of EC.…”

“…Silica and hardness removal is an important function of many raw and process water treatment trains. Irreversible membrane fouling, such as mineral scaling, which limits the degree of water recovery under high pressure, and the high operational cost are the primary drawbacks of membrane technologies. , Recent studies show that EC has high potential for silica and hardness removal from various waters (e.g., groundwater, cooling tower blowdown water, and oil-sand produced water), ,, so it can serve as a pretreatment step prior to membrane separation, within the overall water treatment train . Integrating EC with membrane filtration can further improve the quality of the discharged water .…”

Tuning of polymeric membranes to mitigate fouling and removal of dissolved compounds for wastewater treatment: a Review

“…Fouling of NF membranes by silica, linear, and cyclic siloxanes was observed, along with mineral scaling and organic fouling, which led to the irreversibility of fouling. This integrated fouling situation led to a rapid decline in NF productivity and showed the current need for serious novel antiscalants for fouling issues (Abada et al, 2023;Guo et al, 2020 have demonstrated in their work that fouling due to interactive organic molecules (polysaccharides, proteins, and fulvic acid) was more significant than individual organic molecules. Mixed matrix membrane embedded with 1.0 wt% aminefunctionalized boron nitride (AFBN) showed the highest Reactive Blue 19 rejection (99.7%), the lowest contact angle (51.7 °), the highest degree of fouling (FRR of 90.4%), and the highest dye solution permeability (48 L m −2 .…”