Frontiers of Environmental Science & Engineering

Sulfonamides (SAs) are one class of the most widely used antibiotics around the world. Their fate and transport in the aquatic environment is of great concern. In this study, adsorption of four SAs—sulfadiazine (SD), sulfamethoxazole (SMZ), sulfadimethoxine (SDM) and sulfamethazine (SM2)—in single-solute and multi-solute systems on sediments of Dianchi (DC) Lake and Taihu (TH) Lake, China was investigated with batch experiments. In the single-solute adsorption system, the Langmuir model and the dual-mode model described the adsorption process better than the Freundlich model. Model fitness was better on DC sediment than on TH sediment. The order of adsorption capacity approximately followed a decreasing order of SDM>SD>SM2>SMZ on both sediments, which was likely attributed to the distinctly different water solubility of the four SAs. In the multi-solute system, the order of adsorption capacity was SM2>SDM>SD>SMZ, which was probably related to the compound speciation caused by the pH values of the experimental solution. In the multi-solute system, both competitive and cooperative adsorption played important roles in the adsorption of sulfonamides on sediments.

Mesoporous silica nanoparticles (MSN), with higher water permeability than NaA zeolite, were used to fabricate thin-film nanocomposite (TFN) reverse osmosis (RO) membranes. However, only aminoalkyl-modified MSN and low-pressure (less than 2.1 MPa) RO membrane were investigated. In this study, aminophenyl-modified MSN (AMSN) were synthesized and used to fabricate high-pressure (5.52 MPa) RO membranes. With the increasing of AMSN dosage, the crosslinking degree of the aromatic polyamide decreased, while the hydrophilicity of the membranes increased. The membrane morphology was maintained to show a ridge-and-valley structure, with only a slight increase in membrane surface roughness. At the optimum conditions (AMSN dosage of 0.25 g/L), when compared with the pure polyamide RO membrane, the water flux of the TFN RO membrane (55.67 L/m2/h) was increased by about 21.6%, while NaCl rejection (98.97%) was slightly decreased by only 0.29%. However, the water flux of the membranes was much lower than expected. We considered that the enhancement of RO membrane permeability is attributed to the reduction of the effective thickness of the PA layer.

The widespread production and use of zinc oxide nanoparticles (ZnO-NPs) in recent years have posed potential threat to the ecosystem. This study aimed to investigate the ecotoxicological effect of ZnO-NPs on soil microorganisms using laboratory microcosm test. Respiration, ammonification, dehydrogenase (DH) activity, and fluorescent diacetate hydrolase (FDAH) activity were used as ecotoxicological parameters. The results showed that in the neutral soil treated with 1 mg ZnO-NPs per g soil (fresh, neutral), ammonification was significantly inhibited during the study period of three months, but the inhibition rate decreased over increasing time. Inhibition in respiration was observed in the first month of the test. In various ZnO-NPs treatments (1 mg, 5 mg, and 10 mg ZnO-NPs per g soil), DH activity and FDAH activity were inhibited during the study period of one month. For both enzyme activities, there were positive dose–response relationships between the concentration of ZnO-NPs and the inhibition rates, but the curves changed over time due to changes of ZnO-NPs toxicity. Soil type affected the toxicity of ZnONPs in soil. The toxicity was highest in the acid soil, followed by the neutral soil. The toxicity was relatively low in the alkaline soil. The toxicity was not accounted for by the Zn2+ released from the ZnO-NPs. Direct interaction of ZnO-NPs with biologic targets might be one of the reasons. The adverse effect of ZnO-NPs on soil microorganisms in neutral and acid soils is worthy of attention.

The environmentally sustainable disposal and recycling of ever increasing volumes of electronic waste has become a global waste management issue. The addition of up to 25% polymeric waste PCBs (printed circuit boards) as fillers in polypropylene (PP) composites was partially successful: while the tensile modulus, flexural strength and flexural modulus of composites were enhanced, the tensile and impact strengths were found to decrease. As a lowering of impact strength can significantly limit the application of PP based composites, it is necessary to incorporate impact modifying polymers such as rubbery particles in the mix. We report on a novel investigation on the simultaneous utilization of electronic and automotive rubber waste as fillers in PP composites. These composites were prepared by using 25 wt.% polymeric PCB powder, up to 9% of ethylene propylene rubber (EPR), and PP: balance. The influence of EPR on the structural, thermal, mechanical and rheological properties of PP/PCB/ EPR composites was investigated. While the addition of EPR caused the nucleation of the β crystalline phase of PP, the onset temperature for thermal degradation was found to decrease by 8%. The tensile modulus and strength decreased by 16% and 19%, respectively; and the elongation at break increased by ~71%. The impact strength showed a maximum increase of ~18% at 7 wt.%–9 wt.% EPR content. Various rheological properties were found to be well within the range of processing limits. This novel eco-friendly approach could help utilize significant amounts of polymeric electronic and automotive waste for fabricating valuable polymer composites.

The water quality and energy consumption of wastewater treatment plants (WWTPs) in Taihu Basin were evaluated on the basis of the operation data from 204 municipal WWTPs in the basin by using various statistical methods. The influent ammonia nitrogen (NH3-N) and total nitrogen (TN) of WWTPs in Taihu Basin showed normal distribution, whereas chemical oxygen demand (COD), biochemical oxygen demand (BOD5), suspended solid (SS), and total phosphorus (TP) showed positively skewed distribution. The influent BOD5/COD was 0.4%–0.6%, only 39.2% SS/BOD5 exceeded the standard by 36.3%, the average BOD5/TN was 3.82, and the probability of influent BOD5/TP>20 was 82.8%. The average energy consumption of WWTPs in Taihu Basin in 2017 was 0.458 kWh/m3. The specific energy consumption of WWTPs with a daily treatment capacity of more than 5 × 104 m3 in Taihu Basin was stable at 0.33 kWh/m3. A power function relationship was observed between the reduction in COD and NH3-N and the specific energy consumption of pollutant reduction, and the higher the pollutant reduction is, the lower the specific energy consumption of pollutant reduction presents. In addition, a linear relationship existed between the energy consumption of WWTPs and the specific energy consumption of influent volume and pollutant reduction. Therefore, upgrading and operation with less energy consumption of WWTPs is imperative and the suggestions for Taihu WWTPs based on stringent discharge standard are proposed in detail.

A novel method was applied to co-recover proteins and humic acid from the dewatered sewage sludge for liquid fertilizer and animal feed. The proteins in sewage sludge were first extracted using the processes of ultrasonication and acid precipitation, and then the humic acid was recovered via membrane filtration. The extraction efficiency was 125.9 mg humic acid·g−1VSS volatile suspended solids (VSS) and 123.9 mg proteins·g−1 VSS at the optimal ultrasonic density of 1.5W·mL−1. FT-IR spectrum results indicated that the recovered proteins and humic acid showed similar chemical characteristic to the natural proteins and humic acid. The acidic solution (pH 2) could be recycled and used more than 10 times during the co-recovery processes. In addition, the dewatered sludge could be easily biodegraded when the humic acid and proteins are extracted, which was essential for further utilization. These findings are of great significance for recovering valuable nutrient from sewage sludge.

Various pretreatments methods including sonication and grinding were performed on red seaweed Gelidium amansii for the subsequent extraction of agarose. The agarose products are usually extracted from agar powder products from seaweeds. In this study, the agarose was extracted using a direct polyethylene glycol (PEG) method without the need to first process the agar from seaweed. The agar extract was frozen then thawed and mixed directly with PEG solution to precipitate the agarose. The quality of agarose obtained was evaluated through physico-chemical properties analysis which includes spectral technique (FTIR), melting and boiling point, gel strength and sulfate content. These properties were compared with a non-pretreated sample and it was found that the addition of pretreatment steps improved the quality of agarose but gave a slightly lower yield. The gel strength of pretreated samples was much higher and the sulfate content was lower compared to non-pretreated samples. The best pretreatment method was sonication which gave gel strength of 742 g cm-2 and sulfate content of 0.63%. The extraction of agarose can be further improved with the use of different neutralizing agents. Pretreating the seaweed shows potential in improving the quality of agarose from seaweed and can be applied for future extraction of the agarose.