Porous Anion Exchange Membrane for Effective Acid Recovery by Diffusion Dialysis

Diffusion dialysis (DD) employing anion exchange membranes (AEMs) presents an attractive opportunity for acid recovery from acidic wastewater. However, challenges exist to make highly acid permeable AEMs due to their low acid dialysis coefficient (Uacid). Here, a series of porous and highly acid permeable AEMs fabricated based on chloromethyl polyethersulfone (CMPES) porous membrane substrate with crosslinking and quaternization treatments is reported. Such porous AEMs show high Uacid because of the large free volume as well as the significantly reduced ion transport resistance relative to the dense AEMs. Compared with the commercial dense DF-120 AEM, our optimal porous AEM show simultaneous 466.7% higher Uacid and 75.7% higher acid/salt separation factor (Sacid/salt) when applied to acid recovery at the same condition. Further, considering the simple and efficient fabrication process as well as the low cost, our membranes show great prospects for practical acid recovery from industrial acidic wastewater.

Unsaturated fatty acid salts remove biofilms on dentures

Candidiasis-causing Candida sp. forms biofilms with various oral bacteria in the dentures of the elderly, making it harder to kill and remove the microorganism due to the extracellular polymeric substances. We found that biofilms on dentures can effectively be removed by immersion in an unsaturated fatty acid salt solution. Using optical coherence tomography to observe the progression of biofilm removal by the fatty acid salt solution, we were able to determine that the removal was accompanied by the production of gaps at the interface between the biofilm and denture resin. Furthermore, microstructural electron microscopy observations and time-of-flight secondary ion mass spectrometry elucidated the site of action, revealing that localization of the fatty acid salt at the biofilm/denture-resin interface is an important factor.

Degradation Behaviour of Deteriorated RC Beams Strengthened with CFRP under the Compound Effects of Acid-Salt Mist and Carbon Dioxide

The reinforcement effect and durability of carbon fibre-reinforced polymer (CFRP) sheets are important indicators that affect its promotion and application. This study conducted an experimental investigation of the degradation behavior of reinforced concrete (RC) beams strengthened with CFRP. The RC beams were deteriorated under the compound effects of acid-salt mist and carbon dioxide for a time period t1i, then strengthened with one or two layers of CFRP sheets, and placed in the same deterioration environment for an additional time period t2i. The failure modes, load-deflection curves, rigidity, and flexural carrying capacity changes were studied after the deteriorated RC beams were loaded to failure. Three combinations of deterioration periods were considered in this study: different t1i and same t2i, same t1i and different t2i, and same total time (t1i + t2i). This study found that the U-shaped hoops and the side concrete peeled off gradually as the CFRP-strengthened RC beams were deteriorated again with time. Under the ultimate load, the strengthening layer in the tension zone stripped. The strengthened layer, which consisted of CFRP, a binder, and the concrete cover, was stripped from the RC beam during loading. The deflection of the strengthened layer behaved differently from the other part; this disharmony prevented the mobilization of the tensile advantage of CFRP. The mechanism of RC beam’s mechanical behaviour was analyzed in terms of the degrees of deterioration of RC beams and CFRP and their coupled effects. The conclusions of this study can be used as references in the prediction of strength changing and service life of strengthened RC beams.

Synthesis and Characterisation of Activated Carbon Obtained from Marula (Sclerocarya birrea) Nutshell

Globally, a ninth of people use polluted water sources because an estimated 300–400 Mt of waste and 90% of sewage are discharged into water bodies from industries and developing countries, respectively. The utilisation of indigenous fruit pits in producing novel adsorbents will greatly benefit in wastewater treatment. In most underdeveloped countries, activated carbon (AC) is imported at a high cost. The study was aimed at synthesising and characterisation of AC obtained from Marula nutshell. Carbonization of organic matter from Marula nutshell was carried out at 200°C, 400°C, 500°C, and 600°C. Sulphuric (H2SO4) and phosphoric (H3PO4) acids were used as activating agents at concentrations of 20–60% ( v / v ). Physicochemical characteristics of the AC, such as bulk density, moisture, ash, pH, and iodine number, were analyzed using standard methods. Functional groups and total carbon content were determined using the FTIR spectroscopy and Nitrogen Carbon Sulphur (NCS) analyzer, respectively. The values of carbon yield and total carbon in activated samples with H2SO4 and H3PO4 were 32.2–93.2%, 26.9–95.8%, and 46–79%, 20.8–69.8%, respectively. The pH, ash, moisture, and bulk density of activated high carbon samples with H2SO4 ranged from 2.4–6.1, 0.65–3.49%, 1.3–8.4%, and 0.42–0.62 gcm−3, respectively. Activated high carbon samples with H3PO4 had 2.7–3.2, 11.3–29.8%, 4.7–14.6%, and 0.39–0.54 gcm−3 pH, ash, moisture, and bulk density, respectively. The synthesised AC samples with 40% H3PO4 at 500°C had the highest iodine value of 1075.7 mg/g. FTIR results showed the presence of aliphatic carboxylic acid salt, inorganic nitrate (NO3−), and phosphate groups in the synthesised AC and were not significantly different ( p < 0.05 ) from commercial AC. The untreated Marula nutshell had some aliphatic hydrocarbon (alkanes), inorganic phosphate ( PO 4 3 − ), aliphatic ester (–COO), and aliphatic carboxylic acid salt (–C(=O)O–) groups. A novel adsorbent, AC was produced from Marula nutshell with the potential to be used in water treatment.