Biocementation of soils of different surface chemistries via enzyme induced carbonate precipitation (EICP): An integrated laboratory and molecular dynamics study

Influence of biofilm and calcium carbonate scaling on lead transport in plastic potable water pipes: A laboratory and molecular dynamics study

This study investigated lead (Pb) transport through new, biofilm-laden, and calcium carbonate-scaled crosslinked polyethylene (PEX-A) and high-density polyethylene (HDPE) potable water pipes. The research focused on Pb accumulation through short-term exposure incidents (6 h) and Pb release for a longer duration (5 d). A mechanistic investigation of the surface morphology variations of plastic pipes following biofilm and scale formation has been conducted. The nanoscale surface asperities in new PEX-A pipes and microscale roughness features in new HDPE pipes supported the differences in biofilm abundance, scale formation, and metal uptake results between these two pipes. Biomass analysis and dissolved organic matter (DOM) quantification using three-dimensional excitation emission spectroscopy revealed a greater release of biofilm biomass during the Pb accumulation and release experiments from biofilm-laden HDPE pipes. Both biofilm-laden plastic pipes accumulated a significantly greater level of Pb compared to the new and scaled pipes. However, scaled pipes showed the highest Pb release, while biofilm-laden pipes released the least. Additionally, investigation of Pb2+ exchange from the pipe surface in the presence of Ca2+ in the solution indicated that divalent cations in water can trigger further Pb release from the pipe surface. Furthermore, the molecular dynamics simulation provided valuable insights into the interaction between different pipe surfaces with Pb with respect to affinity and binding energy.

Flowing-water remediation simulation experiments of lead-contaminated soil using UCB technology

The flowing-water remediation of contaminated soil was investigated. Urease combined with biochar (UCB) technology was used to handle the Pb2+-contaminated sand column. The results showed that with the continuous increase of pore volume, the concentration of Pb2+ in the leachate undergoes three stages: slow growth, rapid growth, and steady state. With increasing seepage velocity, the concentration of Pb2+ in leachate increased slightly. The residual amount of each section of the sand column gradually decreased with increasing migration distance. The comparative results indicated that the UCB technology had a good solidification effect on Pb2+. This was due to urease-induced CaCO3 precipitation, cementation, and adsorption of Pb2+. Biochar provided more nucleation sites for urease, and some Pb2+ was adsorbed on its surface or diffused into the pores of biochar, or ions exchanged with functional groups on the surface of biochar, which effectively stabilized the free Pb2+.

Evaluation of dust fixation effect of urease-based biological dust suppressant and its field application

Widespread mining of open-pit coal mines has led to severe dust pollution, which degrades air quality and affects human health. Due to the drawbacks of existing dust suppression methods, there is an urgent need to develop a biological dust suppressant, which is based on urease-induced carbonate precipitation and has excellent potential for application in the field of dust management. The research developed a biological dust suppressant based on urease-induced carbonate precipitation technology. By using biological dust suppressant with different ureases, the dust suppression effect was determined and field applications were conducted. The optimal formulation of the dust suppressant was identified through experiments, and the evaluation of erosion resistance, calcium carbonate yield, hardness, permeability resistance, and crust thickness was conducted, elucidating the consolidation mechanism. After synthesizing the economic benefits and treatment effects of field use, it was found that the optimal ratios of the dust suppressant were 1.0 mol/L for urea and calcium chloride, 100 g/L for soybean flour, and the ratio of urease solution and cementing solution was 1:1 when used; the calcium carbonate yield of the specimen treated by EICP (SCU) was as high as 7.49 %. In an alternative phrasing, after undergoing tests for resistance to wind and rain erosion, the mass loss rates were recorded at 0.24 g m-2·min-1 and 156.51 g m-2·min-1. When compared to the treatment with pure urease, there was a significant improvement in wind erosion resistance by 90 % and in rain erosion resistance by 25.53 %. Field applications have revealed that the distribution of calcium carbonate is uneven and exhibits a positive correlation with hardness, penetration resistance, and the thickness of the crusts formed. This is due to the macromolecular organic matter in crude urease, which not only can form a spatial mesh structure and play a bonding role, but also can provide nucleation sites for urease-induced production of calcium carbonate, promoting the precipitation and aggregation of calcium carbonate, so that the strength is improved.

Soil amended with Algal Biochar Reduces Mobility of deicing salt contaminants in the environment: An atomistic insight

Soil-based filter media in green infrastructure buffers only a minor portion of deicing salt in surface water, allowing most of that to infiltrate into groundwater, thus negatively impacting drinking water and the aquatic ecosystem. The capacity of the filter medium to adsorb and fixate sodium (Na⁺) and chloride (Cl^-) ions has been shown to improve by biochar amendment. The extent of improvement, however, depends on the type and density of functional groups on the biochar surface. Here, we use density functional theory (DFT) and molecular dynamics (MD) simulations to show the merits of biochar grafted by nitrogenous functional groups to adsorb Cl^-. Our group has shown that such functional groups are abundant in biochar made from protein-rich algae feedstock. DFT is used to model algal biochar surface and its possible interactions with Cl^- through two possible mechanisms: direct adsorption and cation (Na⁺)-bridging. Our DFT calculations reveal strong adsorption of Cl^- to the biochar surface through hydrogen bonding and electrostatic attractions between the ions and active sites on biochar. MD results indicate the efficacy of algal biochar in delaying chloride diffusion. This study demonstrates the potential of amending soils with algal biochar as a dual-targeting strategy to sequestrate carbon and prevent deicing salt contaminants from leaching into water bodies.