Use of pilot-scale geomedia-amended biofiltration system for removal of polar trace organic and inorganic contaminants from stormwater runoff

Realistic and field scale applications of biochar for water remediation: A literature review

Biochar has received increasing attention in recent years as a potentially cost-competitive adsorbent for removing various contaminants from surface water and groundwater. However, most published studies have been conducted in the laboratory on a bench scale. Laboratory conditions do not necessarily reflect the complex, heterogeneous, and dynamic field conditions of actual contaminated surface water and groundwater environments. There is a lack of comprehensive literature review regarding the performance of biochar for contaminant removal, especially under realistic field conditions and at field scale. Here, we evaluated 31 studies on realistic applications of biochar for water remediation by searching the keywords: pilot scale, field scale, and mesocosm scale combined with biochar and water remediation. Biochar was found to be incorporated into a variety of water remediation technologies for treating both inorganic and organic contaminants, such as nutrients, heavy metals, pesticides, and pharmaceuticals in polluted waters and wastewaters. Also, biochar showed the potential to be effective on a field scale or in realistic remediation technologies, although it is not always as effective as other sorbents, such as activated carbon (AC). This is partially because AC has better physicochemical characteristics such as higher surface area and more micropores. Effectiveness for contaminant removal varies according to the targeted contaminants, the type and dosage of biochar used, and the treatment technology incorporating biochar. Finally, knowledge gaps and future research areas are identified. For example, more field scale studies are needed to test the effectiveness of biochar as an adsorbent under realistic conditions to pinpoint specific characteristics suitable for target contaminants. Physicochemical characteristics of the biochar can also change over time during the treatment process due to weathering, which may negatively affect the treatment performance. The effects of scaling up production on biochar quality should therefore also be further investigated, as physicochemical characteristics can be affected by varying the synthesis conditions. Regeneration and disposal of spent biochar is another active research area to determine the overall treatment costs.

Deteriorated abatement of micropollutants in biological activated carbon filters with aged media: Key role of permeability

Biological activated carbon (BAC) filtration is vital for the abatement of micropollutants in drinking water. However, limited information is available on contaminant removal in BAC filters with aged media (e.g., >6 year) which are commonly operated at water treatment plants, and mechanistic insights into linkages among media age, microbial community, and contaminant removal still lack. In this study, the effects of media age on the abatement of eight micropollutants with various functional groups were investigated. The abatement of micropollutants decreased with increasing media age. Pseudo-first-order rate constants for contaminant removal in 6- and 15-year BAC were (0.3-3.1) × 10-3 and (0.2-2.6) × 10-3 s-1, compared to (0.9-4.3) × 10-3 s-1 in 3.5-year BAC filter. Biosorption- and biodegradation-dominated contaminant removal depended on protein and adenosine triphosphate concentrations in biofilm, respectively. Micro-computed tomography revealed the formation of biofilm-dominated clogging with rare voids and channels in 15-year BAC, resulting in low permeability. The decreased permeability led to deficient dissolved O2 and nutrient supply and thus changed microbial community assembly process, reducing community diversity and function. Core members including families of Saprospiraceae, Chitinophagaceae, Rhodocyclaceae, Comamonadaceae, and Nitrospiraceae in 3.5-year BAC were affiliated with active aerobic metabolism and contaminant biodegradation capacity. Abundances of these functional microbes and genes decreased with increasing media age. Simultaneously, protein in biofilm decreased, thereby decreasing biosorption. The findings of this study reveal the pivotal role of permeability in shaping microbial community and function and the corresponding micropollutant removal in BAC filters with aged media.

Surveillance and environmental risk of very mobile pollutants in urban stormwater and rainwater in a water-stressed city

Urban stormwater and rainwater in water-stressed cities serve as critical vectors for the transport and dispersion of pollutants, including very mobile compounds These pollutants, which can be influenced by factors such as land use, rainfall intensity, and urban infrastructure, pose significant risks to both human and environmental health. Although several priority pollutants have traditionally been detected in urban stormwater, little is known about the presence of very mobile compounds that may threaten urban drinking water supplies and pose environmental risks to aquatic species. In this study, 131 urban rain and stormwater samples were collected from three districts of Barcelona (Spain) and analysed for 26 very mobile pollutants that are often overlooked in conventional monitoring efforts. The findings reveal that stormwater and rainwater are major contributors to the spread of pollutants in water-stressed cities, with particular emphasis on substances like lifestyle products, pharmaceuticals, and industrial chemicals. Among the 23 compounds detected, 12 were reported for the first time to occur in urban stormwater with concentrations as high as 271 µg L-1. Measurements of dissolved organic carbon, electrical conductivity, and the presence of wastewater-borne pollutants within the correlation analysis, suggested the contribution of sanitary sewer overflows (SSO) to urban stormwater. Finally, an environmental risk assessment (worst-case scenario) was performed, showing a moderate risk of target analytes such as acesulfame and 1-naphthalenesulfonic acid (ERQ > 0.1). The results highlight the need for improved surveillance systems, more sustainable stormwater management practices, and strategies for mitigating the environmental risk posed by very mobile pollutants in regions facing water scarcity.

A self-sustaining effect induced by iron sulfide generation and reuse in pyrite-woodchip mixotrophic bioretention systems: An experimental and modeling study

Dual electron donor bioretention systems have emerged as a popular strategy to enhance dissolved nitrogen removal from stormwater runoff. Pyrite-woodchip mixotrophic bioretention systems showed a promoted and stabilized removal of dissolved nutrients under complex rainfall conditions, but the sulfate reduction process that can induce iron sulfide generation and reuse was overlooked. In this study, experiments and models were applied to investigate the effects of filler configuration and dissolved organic carbon (DOC) dissolution rate on treatment performance and iron sulfide generation in pyrite-woodchip bioretention systems. Key parameters govern that DOC dissolution and microbe-mediated processes were obtained by experiments. The water quality models that integrate one-dimensional constant flow, sorption and microbial transformation kinetics were used to predict the performance of bioretention systems. Results showed that the mixotrophic bioretention system with woodchip mixed in the vadose zone and pyrite in the saturated zone achieves a better performance in both nitrogen removal efficiency and by-product control. Comparably, woodchip and pyrite mixed in the saturated zone could encounter a high secondary pollution risk. The sensitivity coefficients of oxic/anoxic DOC dissolution rates to total nitrogen removal are 0.36 and -2.43 respectively. Iron sulfide generation was affected by DOC distribution and the competition between heterotrophic denitrifiers, autotrophic denitrifiers, and sulfate-reducing bacteria (SRB). DOC accumulation has an antagonistic effect on iron production and sulfate reduction. Extra DOC accumulation favors sulfate reduction while high DOC concentration inhibits pyrite-based denitrification and reduces Fe(III) production. The recycling of iron sulfide can improve the robustness and sustainability of bioretention systems.

Sustainable urban water management: Evaluating two pilot-scale advanced decentralized treatment systems for removal of organic contaminants of emerging concern in reclaimed groundwater

The rapid growth of population and the effects of climate change have placed unprecedented pressure on urban water supplies and pollution control. Consequently, it is essential to explore new local water resources in water-strained areas. To this end, this work focuses on evaluating pollutant removal effectiveness of decentralized treatment systems for groundwater reclamation. Two pilot-scale treatment trains, Treatment Line 1 (L1) and Treatment Line 2 (L2), which use membrane-free (with granulated activated carbon as the main process) or membrane-based (with reverse osmosis as the primary technology), were compared for their effectiveness in reducing concentrations of organic contaminants of emerging concern (CECs). Additionally, the effect of sodium hypochlorite addition for biofilm control on the contaminant removal performance was also examined. Results from the analysis of nearly 120 trace organic compounds (only 21 were detected in the raw water) showed that L2 significantly overperformed L1. Furthermore, the addition of a pre-chlorination step did not improve the removal performance. Regarding trace organic compounds, L1 without pre-chlorination averaged an overall good removal performance (94 ± 12%). However, Irbesartan, gemfibrozil and gabapentin showed moderate removals (50-90%) and Valsartan was poorly removed (<50%). After pre-chlorinating L1, the overall removal performance decreased (86 ± 20%). Nearly one third of the target contaminants showed moderate removal (50-90%), with Irbesartan and Valsartan exhibiting poor attenuations (<50%), highlighting that negatively-charged compounds were challenging to eliminate. In contrast, L2 exhibited very high removals (>99%) on all studied trace organic contaminants regardless of pre-chlorination. Our study also identified several indicator compounds to monitor CEC removal. Finally, considering the trade-offs between cost and final water use (non-potable), L1-based schemes with intermittent pre-chlorination could be the preferred implementation option. The results of this work will offer valuable insights into decentralized treatment systems, assisting decision-makers in choosing suitable approaches for sustainable urban water management.

Multi-media interaction improves the efficiency and stability of the bioretention system for stormwater runoff treatment

Bioretention systems are one of the most widely used stormwater control measures for urban runoff treatment. However, stable and effective dissolved nutrient treatment by bioretention systems is often challenged by complicated stormwater conditions. In this study, pyrite-only (PO), pyrite-biochar (PB), pyrite-woodchip (PW), and pyrite-woodchip-biochar mixed (M) bioretention systems were established to study the feasibility of improving both stability and efficiency in bioretention system via multi-media interaction. PB, PW, and M all showed enhanced dissolved nitrogen and/or phosphorus removal compared to PO, with M demonstrating the highest efficiency and stability under different antecedent drying durations (ADD), pollutant levels, and prolonged precipitation depth. The total dissolved nitrogen and dissolved phosphorus removal in M ranged between 64%-86% and 80%-95%, respectively, with limited organic matter and iron leaching. Pore water, microbial community, and material analysis collectively indicate that pyrite, woodchip, and biochar synergistically facilitated multiple nutrient treatment processes and protected each other against by-product leaching. Pyrite-woodchip interaction greatly increased nitrate removal by facilitating mixotrophic denitrification, while biochar further enhanced ammonium adsorption and expanded the denitrification area. The Fe3+ generated by pyrite aerobic oxidation was adsorbed on the biochar surface and potentially formed a Fe-biochar composite layer, which not only reduced Fe3+-induced pyrite excessive oxidation but also potentially increased organic matter adsorption. Fe (oxyhydr)oxides intermediate product formed by pyrite oxidation, in return, controlled the phosphorus and organic matter leaching from biochar and woodchip. Overall, this study demonstrates that multi-media interaction may enable bioretention systems to achieve stable and effective urban runoff treatment.