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In this study, humic substances were extracted from lignite of Zarand coalfields, Kerman, Iran, using a stirred batch reactor. A membrane ultrafiltration system was used to purify humic acids (HAs) from lignitederived alkaline extracts obtained from the reactor. Gravimetric analysis along with several analytical methods including CHNOS, UV-Vis, FT-IR, ICP-OES and SEM were utilized to investigate the characteristics of the purified HAs. Gravimetric analysis showed that the purity of HA purified from membrane concentrated humates was higher than 95 %. CHNOS elemental analysis indicated the higher stability and condensation degree of the purified HA compared to the commercially available HAs. The ratios of E 4 /E 6 , E 2 /E 3 , and ΔlogK obtained from UV-Visible spectroscopy revealed that a purified HA had a higher molecular weight, aromaticity, and humification degree in comparison with commercial HAs. Furthermore, the peaks observed in the FT-IR analysis showed that HA had an aromatic structure. The very low concentrations of heavy metals and inorganic element contaminants observed by ICP-OES spectrometry showed a proper performance of the HA membrane purification. These results along with the results of SEM analysis showed the acceptable characteristics of purified HA from the lignite coal for agricultural and industrial applications.

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Membrane fouling is an important drawback of membrane‐based separation processes. After clarification of pomegranate juice by 0.22 µm polyvinylidene fluoride membrane, analysis of the FTIR spectra of formed‐cake showed that polyphenols are the main components of blocking materials. Various solutions including water (with 0.5, 1, and 1.5% NaOH or 0.1% hydrochloric acid), ethanol (with 77% and 96% purity), and mixture of ethanol (77%) with acetic acid (96%) with 99:01 ratio were used to clean membranes with different washing time of 10–30 min. The permeate flux recovery was calculated to determine the efficiency of cleaning protocols. The results showed that the cake layer was dominant because the blocking index was between 0 and 0.5. Overall, the ethanol 77% had the best performance among different solutions for cleaning (mainly due to its positive effects on membrane hydrophilicity) and the initial permeate fluxes of pomegranate juice and pure water did not change significantly after using this protocol. Practical applications Membrane technology is widely used in industrial juice clarification processes. The main problem with this process is the formation of fouling on the membrane surface, which minimizes its use in the fruit juice industry. This affects the lifetime of the membrane, the number of times the membrane is cleaned, the size of the membrane required, and ultimately the operation costs. In fact, cleaning costs make up 5%–20% of operating budgets, so more research is needed. The main method in regenerating a fouled membrane is its chemical cleaning, and the first step in this method is to find the best chemical detergent, which is determined according to the type of food, the type of membrane, and the nature of the deposition.