Adsorptive removal of Pb (II) by means of hydroxyapatite/chitosan nanocomposite hybrid nanoadsorbent: ANFIS modeling and experimental study.

In the current study, the prediction efficiency of lead adsorption by highly functional nanocomposite adsorbent of hydroxyapatite (HAp)/chitosan using ANFIS system was investigated. In this regard, the nanocomposite was applied in order to investigate the lead adsorption capacity. The operational conditions were pH (2-6), contact time between lead ions and adsorbent (15-360 min), shaker velocity (80-400 rpm), temperature (25-55 °C), amount of adsorbent (0.01-1.5 g), lead initial concentration (0-5000 ppm) and HAp concentration (10-75%). The effect of each parameter was investigated, and then the ANFIS was employed to model the adsorption process using the obtained experimental results. The ANFIS modeled the results with total average error and total average of absolute error less than 0.0646% and 4.2428%, respectively, for training data. Moreover, the coefficient of determination for training data and testing data were found to be 0.9999 and 0.9823, respectively. In addition, granular chitosan and HAp nanoparticles adsorption capabilities were compared with nanocomposite of HAp (20%wt)/chitosan adsorbent. It was found that nanocomposite adsorbent had a higher adsorption capability than other adsorbents.

Influence of microbial weathering on the partitioning of per- and polyfluoroalkyl substances (PFAS) in biosolids.

Per- and polyfluoroalkyl substances (PFAS) are a large group of man-made fluorinated organic chemicals that can accumulate in the environment. In water resource recovery facilities (WRRFs), some commonly detected PFAS tend to partition to and concentrate in biosolids where they can act as a source to ecological receptors and may leach to groundwater when land-applied. Although biosolids undergo some stabilization to reduce pathogens before land application, they still contain many microorganisms, contributing to the eventual decomposition of different components of the biosolids. This work demonstrates ways in which microbial weathering can influence biosolids decomposition, degrade PFAS, and impact PFAS partitioning in small-scale, controlled laboratory experiments. In the microbial weathering experiments, compound-specific PFAS biosolids-water partitioning coefficients (Kd) were demonstrated to decrease, on average, 0.4 logs over the course of the 91 day study, with the most rapid changes occurring during the first 10 days. Additionally, the highest rates of lipid, protein, and organic matter removal occurred during the same time. Among the evaluated independent variables, statistical analyses demonstrated that the most significant solids characteristics that impacted PFAS partitioning were organic matter, proteins, lipids, and molecular weight of organics. A multiple linear regression model was built to predict PFAS partitioning behavior in biosolids based on solid characteristics of the biosolids and PFAS characteristics with a R2 value of 0.7391 when plotting predicted and measured log Kd. The findings from this work reveal that microbial weathering can play a significant role in the eventual fate and transport of PFAS and their precursors from biosolids.

Linking PFAS partitioning behavior in sewage solids to the solid characteristics, solution chemistry, and treatment processes.

Per- and polyfluoroalkyl substances (PFAS) have gained increasing attention due to the potential health risks that they present. Secondary sludge and biosolids are known as notable PFAS emission routes to the environment. In this study, partitioning behavior of 14 PFAS were investigated across four secondary wastewater treatment types (activated sludge, trickling filter, biological nutrient removal, and rotating biological contactor; n = 10) and three sludge stabilization methods (composting, aerobic digestion, and anaerobic digestion; n = 6). Batch experiments were conducted to evaluate how PFAS sorption to secondary sludge and biosolid was affected by various treatment methods, solid properties, and solution chemistry parameters. Insignificant differences in compound-specific partitioning coefficients (Kd) were observed among the four secondary treatment methods. However, sludge stabilization resulted in significantly different partitioning behavior among biosolid samples, in which anaerobically digested biosolids generally had significantly higher Kd values compared to aerobically digested and composted biosolids (anaerobic digestion > aerobic digestion > composting). Multiple linear regression models were developed to explain analyte-specific Kd values across the biosolid samples and identified that solid-specific property significance was as follows: protein fraction > organic matter fraction > lipid fraction. Stabilization generally decreased the PFAS sorption capacity relative to the secondary sludge samples. Furthermore, PFAS Kd increased with elevated calcium concentrations and ionic strengths and decreased with increasing pH values in sludge and biosolid samples. These findings could inform the decision-making process to reduce the release of PFAS to the environment.