This study was conducted to assess the removal of arsenic (As) and heavy metals from mining wastewater by the combination of adsorption, using modified iron-ore drainage sludge, and horizontal-subsurface-flow constructed wetland with common reed (Phragmites australis). The pilot-scale experiment with a constant flow rate of 5 m³/day was operated for four months using real wastewater from a Pb–Zn mine in northern Vietnam. Atomic absorption spectroscopy was used for elemental analysis in wastewater and plant. X-ray diffraction (XRD), surface charge measurements (by a particle charge detector (PCD)), Fourier-transform infrared (FTIR), and surface area Brunauer–Emmet–Teller (BET) measurements were performed to determine the characteristics of the adsorbent. The results showed that the average removals of As, Mn, Cd, Zn, and Pb by the combined system with limestone substrate during four months were 80.3%, 96.9%, 79.6%, 52.9%, and 38.7%, respectively. The use of another constructed wetland substrate, laterite, demonstrated better removal efficiency of As than limestone. The concentrations of As and heavy metals in the effluent were lower than the limits established by the QCVN 40:2011/BTNMT for industrial wastewater, which indicated the feasibility of combining adsorption and constructed wetland for the treatment of mining wastewater.

Brilliant green (BG), a basic dye, is toxic to lung, eye, and skin. This study examines BG biosorption from aqueous solution using soybean milk residue (okara). A series of batch tests were conducted to explore influential factors including pH, biosorbent dose, initial BG concentration, contact time, and temperature. The isotherm data were fitted with Langmuir and Freundlich models. The kinetic data of BG biosorption by okara were analyzed using pseudo-first order and pseudo-second order models. The BG removal efficiency was enhanced at a higher biosorbent dose, contact time, and temperature. Contrarily, the greater BG initial concentration resulted in a decline in BG removal efficacy. In the pH range that BG dye was stable, the highest BG removal was attained at pH 5. The maximum BG adsorption capacity of okara was 64.33 mg/g. Langmuir model (R2 = 0.98) was more appropriate than Freundlich model (R2 = 0.93) in describing isotherm data. Kinetic data was well fitted with Pseudo-second order model (R2 = 0.99). Thermodynamic results suggest the spontaneous and endothermic nature of the GB biosorption. The use of okara as a novel BG biosorbent can help not only wastewater decontamination but also recycling of okara in a green way.

Recently, there is a new trend to consider wastewater as a precious resource. Since phosphorus is a limited non-renewable element, and MAP (Magnesium Ammonium Phosphate - MgNH₄PO₄.6H₂O) is a valuable slow-release fertilizer, the recovery of phosphorous as MAP has received special attention from scientists all over the world. However, the application of this process with municipal wastewater is still a challenge, due to low concentration of phosphorus and high volume of municipal wastewater. This study investigates the potential of reclaiming MAP from municipal wastewater by combination of adsorption and crystallization. Soybean milk residue (okara) was loaded with Zirconium (Zr) to prepare the adsorbent (ZLO). Adsorption and desorption experiments were conducted in a semi-pilot scale ZLO packed colum system. Effects of P: N: Mg molar ratios, chemical sources and temperature on the formation of MAP were examined in an attempt to identify the optimal crystallization conditions. The attained precipitate was characterized using XRD, SEM, FTIR techniques. It was found that the ZLO packed column adsorption-desorption system could pre-concentrate phosphorus from municipal wastewater up to 28.36 times, fitting well the minimum requirement (50 mg P/L) for the economical MAP recovery. Up to 95.19% of dissolved phosphorus in desorption solution was recovered at pH = 9, Mg: N: P molar ratio = 2:2:1, using a combination of MgCl₂.6H₂O and NH₄Cl. The harvested MAP exhibited high purity (92.59%), high P-availability (89% by mass), and extremely low levels of heavy metals. The results prove that it is viable to recover MAP from municipal wastewater by employing ZLO as adsorbent, followed by crystallization. This paves the way for mining phosphorus from municipal wastewater and reducing okara as an agricultural byproduct in a green way.

The Direct Blue 71 (DB71) dye can pose risks to the life of aquatic flora, fauna, and human beings, owing to its toxic, carcinogenic, and mutagenic nature. Hence, this study fabricated and applied acid-activated shrimp shell-derived hydrochar (A-WSH) for the adsorptive removal of anionic DB71 from aqueous solutions. The effects of adsorption conditions on DB71 sequestration by A-WSH were evaluated. Characterization and modeling methods were utilized to elucidate the DB71 adsorption behaviors and mechanisms of A-WSH. Results showed that DB71 adsorption by A-WSH was optimized at pH 6.78, contact time of 4 h, adsorbent dose of 1 g/L, room temperature of 300 K, and shaking speed of 120 rpm. The isotherm data were best described by the Langmuir model with the DB71 maximum adsorption capacity of 156.25 mg/g. The kinetic data were more satisfactorily represented by Pseudo-second-order model than the Pseudo-first-order model. Thermodynamic and characterization results revealed that DB71 adsorption by A-WSH was endothermic and chemisorption. The A-WSH can be a promising DB71 adsorbent, thanks to high adsorption capacity, short equilibrium time, and no pH adjustment requirement. This study has opened up a novel pathway for the valorization of shrimp shells and remediation of DB71-contaminated aqueous solutions.

Due to a growing concern about antibiotic pollution and resistance, there is an urgent need to seek cost-effective and eco-friendly antibiotic treatment technologies. This book chapter provides a comprehensive overview of constructed wetlands (CWs) as a promising solution for antibiotic abatement in wastewater. It commences by comparing various antibiotic pollution sources and treatment technologies. The focus is placed on evaluating the antibiotic removal in CWs, considering simultaneous effects of multiple influential factors, including antibiotic properties, wastewater characteristics, as well as CWs design and operation parameters. Moreover, it offers insights on antibiotic removal mechanisms. Finally, present obstacles and future perspectives associated with antibiotic removal by CWs are discussed. It was found that livestock was the major source of antibiotic pollution. The antibiotic removal efficacy of CWs can vary, relying on antibiotic properties, CW design and operation parameters. Among various removal pathways of antibiotics in CWs, biodegradation plays a key role, followed by substrate adsorption, plant uptake, and other processes. However, the widespread application of CWs for antibiotic decontamination from wastewater is currently facing challenges, such as poor efficacy of conventional media, excessive cost of emerging substrates, low intolerance of plants to antibiotic-rich wastewater, and limited application of full-scale CWs with real wastewater. Key strategies for boosting antibiotic treatment in CWs include substrate renovation, microbial augmentation, and integration of grey and green technologies. This book chapter aims to facilitate the development of CWs as a viable, affordable, and sustainable technology for intensified purification of antibiotic contaminated wastewater.