Washing Bottom Sediment for The Removal of Arsenic from Contaminated Italian Coast

Among various forms of anthropogenic pollution, the release of toxic metals in the environment is a global concern due to the high toxicity of these metals towards living organisms. In the last 20 years, sediment washing has gained increasing attention thanks to its capability to remove toxic metals from contaminated matrices. In this paper, we propose a Response Surface Methodology method for the washing of selected marine sediments of the Bagnoli-Coroglio Bay (Campania region, Italy) polluted with arsenic and other contaminants. We focused our attention on different factors affecting the clean-up performance (i.e., liquid/solid ratio, chelating concentration, and reaction time). The highest As removal efficiency (i.e., >30 μg/g) was obtained at a liquid/solid ratio of 10:1 (v/w), a citric acid concentration of 1000 mM, and a washing time of 94.22 h. Based on these optimum results, ecotoxicological tests were performed and evaluated in two marine model species (i.e., Phaeodactylum tricornutum and Aliivibrio fischeri), which were exposed to the washing solutions. Reduced inhibition of the model species was observed after nutrient addition. Overall, this study provides an effective tool to quickly assess the optimum operating conditions to be set during the washing procedures of a broad range of marine sediments with similar physicochemical properties (i.e., grain size and type of pollution).

Response Surface Methodology for the Optimization of Zn-Contaminated Soil Remediation by Soil Washing with Water-Soluble Chitosan

Soil washing is an important method for the remediation of contaminated soil. This research presents the optimization of soil washing conditions in the remediation of Zn-contaminated soils with water-soluble chitosan (WSCS). Response surface methodology (RSM) was used to optimized the washing conditions after single factor experiments. The central composite design (CCD) with three factors and five levels was applied to the optimization of the removal efficiency of Zn from soils, and WSCS concentration, pH value, and washing time were evaluated variables in the washing process. Results indicated that the pH value (p < 0.0001) was the most significant factor which mainly affected the distribution and content of metal species in aqueous solution, ion exchange and adsorption/desorption behavior of metals, solubility of chelating agent, as well as readsorption of metal complexes. The optimal conditions for the Zn removal from soils were WSCS concentration of 1.5%, pH of 3.3, and washing time of 72 min. The removal efficiency could reach 65.4% under the optimized conditions, which was close to the predicted value of 68.3% by the response surface method. Therefore, it could be found that the response surface methodology was an effective method to determine the optimal conditions for the removal of metals from contaminated soils by soil washing.

Bioremediation of lead-contaminated soil by inorganic phosphate-solubilizing bacteria immobilized on biochar

In this study, a bio-composite (IBWS700) was prepared using inorganic phosphate-solubilizing bacteria (iPSB), which were immobilized on biochar produced from wheat straw (WS700). Further, the bio-remediation effects of the composite for lead (Pb) in soil were also investigated. The presence of different Pb species, physicochemical properties, enzyme activities, and immobilization mechanisms of Pb in soil were also evaluated. Compared to free iPSB and biochar, IBWS700 significantly decreased the lead bio-availability whereas increased the residual fraction, also affected available phosphorus (AP), cation exchange capacity (CEC), organic matter (OM) and activity of urease, alkaline phosphatase, sucrase and catalase. Interestingly, the changes in the enzyme activity, AP and OM performed twice increases with increasing Pb concentration, which was rarely reported. The reason might be attributed to the reconstruction of bacteria communities with high Pb load. Further, the immobilization mechanisms mainly included bio-adsorption and bio-precipitation. SEM revealed that the surface of IBWS700 covered with a large number of heterogeneous colonization of iPSB and white stack after Pb²⁺ adsorption. FTIR spectra showed that O-H, C-O-P, CO, and C =C could play important roles in bio-adsorption. Moreover, XRD analysis indicated that bio-precipitates were mainly Pb₅(PO₄)₃Cl. In general, the use of IBWS700 could effectively immobilize Pb²⁺ and improve soil quality.

Process Development for the Detoxification of Fermentation Inhibitors from Acid Pretreated Microalgae Hydrolysate

The aim of this study was to remove 5-hydroxymethyl furfural (5-HMF) and furfural, known as fermentation inhibitors, in acid pretreated hydrolysates (APH) obtained from Scenedesmus obliquus using activated carbon. Microwave-assisted pretreatment was used to produce APH containing glucose, xylose, and fermentation inhibitors (5-HMF, furfural). The response surface methodology was applied to optimize key detoxification variables such as temperature (16.5–58.5 °C), time (0.5–5.5 h), and solid–liquid (S-L) ratio of activated carbon (0.6–7.4 w/v%). Three variables showed significant effects on the removal of fermentation inhibitors. The optimum detoxification conditions with the maximum removal of fermentation inhibitors and the minimum loss of sugars (glucose and xylose) were as follows: temperature of 36.6 °C, extraction time of 3.86 h, and S-L ratio of 3.3 w/v%. Under these conditions, removal of 5-HMF, furfural, and sugars were 71.6, 83.1, and 2.44%, respectively, which agreed closely with the predicted values. When the APH and detoxified APH were used for ethanol fermentation by S. cerevisiae, the ethanol produced was 38.5% and 84.5% of the theoretical yields, respectively, which confirmed that detoxification using activated carbon was effective in removing fermentation inhibitors and increasing fermentation yield without significant removal of fermentable sugars.