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This study explored the effects of peanut shell biochar (PSB) on the adsorption capacities of fungicides with and without successive chemical modifications, using KMnO4 and KOH (PSBOX-A), in order to provide a valuable understanding of their adsorption mechanisms and behaviors. To this end, the physicochemical properties of PSB and PSBOX-A were examined by using the Brunauer–Emmett–Teller method, Fourier transform infrared spectroscopy, and scanning electron microscopy with an energy dispersive X-ray spectrometer. The effects of temperature, ionic strength, and humic acids on the adsorption of fungicides, using PSB and PSBOX-A, were estimated through batch experiments. Furthermore, adsorption kinetics, isotherms, and thermodynamics were studied. The maximum adsorption capacities of fungicides by PSBOX-A were estimated to be more notable (Qmax of carbendazim = 531.2 μmol g−1, Qmax of pyrimethanil = 467.7 μmol g−1, and Qmax of tebuconazole = 495.1 μmol g−1) than PSB (Qmax of carbendazim = 92.6 μmol g−1, Qmax of pyrimethanil = 61.7 μmol g−1, and Qmax of tebuconazole = 66.7 μmol g−1). These findings suggest that successive chemical modification using KMnO4 and KOH could potentially be used to effectively fabricate PSB to remove fungicides in water-treatment processes.

Membrane fouling in seawater reverse osmosis (SWRO) occurs on the membrane surface to reduce the membrane performance. In particular, biofouling, silica scale, and calcium deposition are hardened with time and not easily removed because SWRO is continuously operated without shutdown. This study aimed to evaluate the performance of the SWRO membrane process by periodically applying forward osmotic backwashing (FOB) which is one of the physical cleaning methods. Dissolved organic carbon (DOC), UV254, and fluorescence excitation-emission matrix (FEEM) were analyzed by sampling the circulating water before and after FOB. As a result, when sodium alginate (SA) as a hydrophilic substance was fouled, its cleaning efficiency was superior to that of humic acid (HA) as a hydrophobic material. This is because SA was effectively removed due to its low adhesion force between organic matter and membrane. In addition, FEEM of cleaning wastewater was analyzed after performing clean-in-place (CIP) of the membranes with and without FOB. The peak intensity with FOB was lower than that without FOB, and SA showed relatively large differences in the peak intensity with and without FOB. The effect of FOB on SA was larger than the cleaning efficiency for HA. In conclusion, FOB can extend the CIP cycle of SWRO. In particular, although the adhesion force between organic matter is high, FOB can mitigate membrane fouling by SA with small adhesion force with membranes. [ABSTRACT FROM AUTHOR]

It is difficult to evaluate membrane fouling of seawater reverse osmosis (SWRO) membrane because fouling and concentration polarization occur at the same time. In particular, it becomes harder to distinguish the effects of fouling from those of osmotic pressure in full-scale SWRO membranes because six to eight elements are connected in series in one vessel and osmotic pressure increases more. Therefore, this study aimed to evaluate the applicability as an indicator of membrane fouling by monitoring permeation coefficient and concentration polarization factor with the progression of membrane fouling in a pilot plant with a capacity of 185 m³/d operated by the constant flow method and by comparing them before and after maintenance chemical cleaning (MCC). Permeation coefficient and concentration polarization factor decreased with the progression of membrane fouling. However, after MCC, they increased because membrane foulants were removed by MCC. The cleaning efficiency of MCC by acid was superior to that by alkali because the increasing rates of permeation coefficient and concentration polarization factor in acid cleaning were higher than in alkaline cleaning. This is because the probability of forming scale by inorganic matter increased more than membrane fouling by organic matter without injecting antiscalants in order to realize chemical-free operation. In general, it is difficult to evaluate fouling because differential pressure (DP) monitoring RO membrane fouling did not change much. Conversely, the results showed that permeation coefficient and concentration polarization factor are highly applicable as a simple tool for evaluating membrane fouling because there was a clear tendency in fouling evaluation through them. [ABSTRACT FROM AUTHOR]

It is difficult to evaluate fouling of high-pressure membranes such as seawater reverse osmosis (SWRO) membranes, although the fouling of low-pressure membranes such as microfiltration (MF) and ultrafiltration (UF) membranes can be evaluated by monitoring the decrease in flux or the increase in trans-membrane pressure (TMP). In particular, it is more difficult to evaluate membrane fouling of SWRO membrane in actually plant because SWRO membranes are connected in series of six to eight elements in one vessel and fouling and concentration polarization occur at the same time. This study aimed to distinguish concentration polarization from membrane fouling by calculating the permeation coefficient and concentration polarization factor with the progression of membrane fouling. As fouling was progressed by organic matters, the permeation coefficient and concentration polarization factor decreased. Fouling layers by organic matters reduce the concentration polarization factor because fouling layers reduce the permeation coefficient by increasing the filtration resistance and cause cake reduced concentration polarization (CRCP) by interrupting the convection of salt. Furthermore, membranes with forward osmotic backwashing (FOB) are effective in controlling membrane fouling because FOB alleviate the decreasing rate of the permeation coefficient and concentration polarization factor compared to membranes without FOB. Therefore, it was possible to evaluate the degree of membrane fouling in SWRO membranes by analyzing changes in the permeation coefficient and concentration polarization factor with the progression of membrane fouling and to evaluate cleaning efficiency by comparing them before and after FOB. This made it possible to use permeation coefficient and concentration polarization factor as an indicator to determine the timing of cleaning-in-place (CIP) or physical cleaning such as FOB. [ABSTRACT FROM AUTHOR]

Membrane separation processes are widely used in wastewater reuse systems. However, membrane fouling is a challenging issue because it leads to high energy consumption and decreases separation efficiency. In this study, we investigated measures to control the membrane fouling arising from the deposition of foulants such as particles, colloids, and effluent organic matter onto the membrane surface during secondary wastewater management. Preozonation and coagulation/flocculation pretreatments were tested as measures to reduce membrane fouling. Filtration resistance was notably high in the absence of preozonation and coagulation/flocculation pretreatments; in contrast, both preozonation and coagulation/flocculation facilitated the removal of organic foulants by decreasing the irreversible fouling during filtration. The optimal ozone contact time for preozonation was found to be 120 s, in terms of improving the permeate water flux. In addition, the use of iron(III) chloride (FeCl³ ; dosage 25 mg Fe/L) with preozonation was required to depolarize foulants from the membrane surface. These findings suggest that irreversible resistance can be controlled by using preozonation and coagulation/flocculation pretreatments after eliminating the reversible phase. Therefore, the combined application of ozone and coagulant can play a key role in stable operation of the membrane separation process for wastewater reuse. [ABSTRACT FROM AUTHOR]