Organics removal and microbial interaction attributes of zeolite and ceramsite assisted bioretention system in copper-contaminated stormwater treatment

Reduction of methane and nitrous oxide emissions from stormwater bioretention cells through microbial electrolytic cells

This study investigated the reduction of methane (CH4) and nitrous oxide (N2O) emissions from stormwater bioretention cells through microbial electrolytic cell (MEC), showing the largest reduction of 32.21 % (CH4) at 9.2 μA/m2 of current density and 56.16 % (N2O) at 3.5 μA/m2 of current density, compared with the corresponding in the control (0 μA/m2 of current density). Kinetic of CH4 and N2O emissions could be well fitted by Logistic model with high correlation coefficient (R2 > 0.9500) and model efficiency (ME > 0.95) but low relative root mean square error (RRMSE < 7.88). The increase of pmoA and polysaccharide (PS) were responsible for CH4 reduction, while N2O reduction was attributed to the decrease of nirS and the increase for nosZ and protein (PN), which could explain the lowest GWPd (10.67 mgCO2-eq/m2/h) at 3.5 μA/m2 of current density, suggesting that MEC could be promising for the reduction of CH4 and N2O emissions from bioretention cells.

Elucidating distinct roles of chemical reduction and autotrophic denitrification driven by three iron-based materials in nitrate removal from low carbon-to-nitrogen ratio wastewater

Effective nitrate removal is a key challenge when treating low carbon-to-nitrogen ratio wastewater. How to select an effective inorganic electron donor to improve the autotrophic denitrification of nitrate nitrogen has become an area of intense research. In this study, the nitrate removal mechanism of three iron-based materials in the presence and absence of microorganisms was investigated with Fe2+/Fe0 as an electron donor and nitrate as an electron acceptor, and the relationship between the iron materials and denitrifying microorganisms was explored. The results indicated that the nitrogen removal efficiency of each iron-based material coupled sludge systems was higher than that of iron-based material. Furthermore, compared with the sponge iron coupled sludge system (60.6%-70.4%) and magnetite coupled sludge (56.1%-65.3%), the pyrite coupled sludge system had the highest removal efficiency of TN, and the removal efficiency increased from 62.5% to 82.1% with time. The test results of scanning electron microscope, X-ray photoelectron spectroscopy and X-ray diffraction indicated that iron-based materials promoted the attachment of microorganisms and the chemical reduction of nitrate in three iron-based material coupled sludge systems. Furthermore, the pyrite coupled sludge system had the highest nitrite reductase activity and can induce microorganisms to secrete more extracellular polymer substances. Combined with high-throughput sequencing and PICRUSt2 functional predictive analysis software, the total relative abundance of the dominant bacterial in pyrite coupled sludge system was the highest (72.06%) compared with the other iron-based material systems, and the abundance of Blastocatellaceae was relatively high. Overall, these results suggest that the pyrite coupled sludge system was more conducive to long-term stable nitrate removal.

Enhancing bioretention efficiency for pollutant mitigation in stormwater runoff: Exploring ecosystem cycling dynamics amidst temporal variability

In this study, three distinct bioretention setups incorporating fillers, plants, and earthworms were established to evaluate the operational efficiency under an ecosystem concept across varying time scales. The results revealed that under short-term operating conditions, extending the drying period led to a notable increase in the removal of NO3--N, total phosphorus (TP), and chemical oxygen demand (COD) by 5 %-7%, 4 %-12 %, and 5 %-10 %, respectively. Conversely, under long-time operating conditions, the introduction of plants resulted in a significant boost in COD removal by 10 %-20 %, while the inclusion of earthworms improved NH4+-N and NO3--N removal, especially TP removal by 9 %-16 %. Microbial community analysis further indicated the favorable impact of the bioretention system on biological nitrogen and phosphorus metabolism, particularly with the incorporation of plants and earthworms. This study provides a reference for the operational performance of bioretention systems on different time scales.

Effects of biochar layer position on treatment performance and microbial community in subsurface flow constructed wetlands for removal of cadmium and lead

Levels of cadmium (Cd) and lead (Pb) correspond to common composition in acid mine wastewater of Hunan Province of China. The removal path of Cd and Pb and the structure of microbial community were investigated by developing constructed wetlands (CWs) with different layer positions of biochar. The biochar as a layer at the bottom of CW (BCW) system exhibited maximum Cd and Pb removal efficiencies of 96.6-98.6% and 97.2-98.9%, respectively. Compared with original soil, BCW increased the relative proportions of Proteobacteria, Firmicutes, Acidobacteriota, Verrucomicrobiota, Desulfobacterota, Armatimonadota, Bacteroidota, Patescibacteria, Basidiomycota (phylum level) and Burkholderia-Caballeronia-Paraburkholderia, Citrifermentans, Chthonomonadales, Cellulomonas, Geothrix, Terracidiphilus, Gallionellaceae, Microbacterium, Vanrija, Apiotrichum, Saitozyma, Fusarium (genus level). The concentrations of Cd and Pb were positively correlated with the abundance of Verrucomicrobiota, Basidiomycota (phylum level), and Methylacidiphilaceae, Meyerozyma, Vanrija (genus level). This study demonstrates that BCW system can improve removal performance toward Cd and Pb, as well as alter microbial community.

Pollutant accumulation and microbial community evolution in rain gardens with different drainage types at field scale

Rain gardens play a key role in urban non-point source pollution control. The drainage type affects the infiltration processes of runoff pollutants. The soil properties and microbial community structures were studied to reveal the stability of the ecosystem in rain gardens with different drainage types under long-term operation. The results showed that the soil water content and total organic carbon in the drained rain gardens were always higher than that of the infiltrated ones. With the increase in running time, the contents of heavy metals in rain gardens showed significant accumulation phenomena, especially the contents of Zn and Pb in drained rain gardens were higher than that in infiltrated ones. The accumulation of pollutants resulted in lower microbial diversity in drained rain gardens than in infiltrated rain gardens, but the microbial community structures were the same in all rain gardens. The effects of drainage type on microbial community evolution were not significant, only the accumulation of heavy metals led to changes in the abundance of dominant microorganisms. There were differences in the soil environment of rain gardens with different drainage types. The long-term operation of rain gardens led to fluctuations in the soil ecosystem, while the internal micro-ecosystems of the drained rain gardens were in unstable states.

Corncob-pyrite bioretention system for enhanced dissolved nutrient treatment: Carbon source release and mixotrophic denitrification

Solid biomass waste amendment and substrates modification in bioretention systems have been increasingly used to achieve effective dissolved nutrients pollution control in stormwater runoff. However, the risk of excess chemical oxygen demand (COD) leaching from organic carbon sources is often overlooked on most occasions. Pyrite is an efficient electron donor for autotrophic denitrification, but little is known about the efficacy of autotrophic-heterotrophic synergistic effect between additional carbon source and pyrite in bioretention. Here, four bioretention columns (i.e., corncob column (C), pyrite column (P), the corncob-pyrite layered column (L-CP), and the corncob-pyrite mixed column (M-CP)) were designed and filled with soil, quartz sand, and modified media to reveal the synergistic effects. The results showed that the corncob-pyrite layered bioretention could maintain low COD effluent concentration with high stability and efficiency in treating dissolved nutrients. When the influent nitrogen and phosphorus concentrations were 8.46 mg/L and 0.94 mg/L, the average removal rates of ammonia nitrogen, total inorganic nitrogen, and phosphate were 83.6%, 70.52%, and 76.35%, respectively. The scouring experiment showed that placing the corncob in the mulch layer was beneficial to the sustained release of dissolved organic carbon (DOC). Erosion pits were found in the SEM images of used pyrite, indicating that autotrophic denitrifying bacteria in the bioretention could react with pyrite as an electron donor. The relative abundance of Thiobacillus in the submerged zone of the corncob-pyrite layered bioretention reached 38.39%, indicating that the carbon source in the mulch layer increased the relative abundance of Thiobacillus. Coexisting heterotrophic and autotrophic denitrification in this bioretention created a more abundant microbial community structure in the submerged zone. Overall, the corncob-pyrite layered bioretention is highly promising for stormwater runoff treatment, with effective pollution removal and minimal COD emission.

Coal gangue modified bioretention system for runoff pollutants removal and the biological characteristics

In this study, coal gangue (CG) was applied as media in bioretention system to remove runoff pollutant. CG modified bioretention systems show good removal efficiency towards runoff pollutant due to the high adsorption capacity of CG. The removal of total phosphorus (TP), total nitrogen (TN), ammonia (NH₄⁺-N) and chemical oxygen demand (COD) by CG modified bioretention systems was influenced by diverse rainfall conditions including rainfall concentration, recurrence period and drying period, and their removal rate ranged 94-99%, 30-70%, 83-97% and 33-86%, respectively. The effluent concentration of Zn, Pb and Cu was as low as 3.14-10.99 μg/L, 0.66-2.56 μg/L and 0.60-3.15 μg/L, respectively. In addition, CG could promote the plant heavy metal uptake and thus decrease their accumulation in soil to a certain extent. Meanwhile, Malondialdehyde (MDA) content and peroxidases (POD) activities of plants in CG modified bioretention were lower than that in tradition bioretention, indicating that CG could help plants recovery and lessened the oxidative stress for the negative impact of high heavy metals accumulation. CG-based media alleviated the inhibitory effect of rainwater runoff pollutant accumulation (especially heavy metals) on microbial diversity and the enhancement of the dominant bacteria (such as Proteobacteria and Bacteroidota) could conduce the nutrients removal in the bioretention systems. In overall, this study demonstrated that the CG modified bioretention systems show an excellent removal performance combine with biological effects.

Optimizing the added ratio of mixed auxiliary packings for enhancing the biological vanadium (V) removal

Developing sustainable and low-cost bio-reduction technologies is essential for vanadium (V) bioremediation in groundwater. With both agricultural waste (wheat stalk) being a solid carbon source and ceramsite and medical stone being auxiliary packings, V(V) removal was confirmed and optimized in this study. The ratio of ceramsite to medical stone was maintained at 1:3 in Group I, which accomplished a V(V) removal efficiency up to 97.5% within 120 h and an average removal rate was around 0.305 mg/(L·h). The dissolution and utilization of carbon and trace elements (Mg, Fe, Mo and Ni) by microbes also contributed to the V(V) bio-reduction enhancement. The main components of DOM (tryptophan and humic acid-like substances) were vital in the V(V) binding and electron transfer processes. This study could promote the current knowledge on the sustainable V(V) bioremediation by using agricultural waste and auxiliary packings.

A review on plant-microbial interactions, functions, mechanisms and emerging trends in bioretention system to improve multi-contaminated stormwater treatment

Management and treatment of multi-polluted stormwater in bioretention system have gained significant attraction recently. Besides nutrients, recent source appointment studies found elevated levels of Potentially toxic metal(loid)s (PTMs) and contaminants of emerging concern (CECs) in stormwater that highlighted many limitations in conventional media adsorption-based pollutant removal bioretention strategies. The substantial new studies include biological treatment approaches to strengthen pollutants degradation and adsorption capacity of bioretention. The knowledge on characteristics of plants and their corresponding mechanisms in various functions, e.g., rainwater interception, retention, infiltration, media clogging prevention, evapotranspiration and phytoremediation, is scattered. The microorganisms' role in facilitating vegetation and media, plant-microorganism interactions and relative performance over different functions in bioretention is still unreviewed. To uncover the underneath, it was summarised plant and microbial studies and their functionality in hydrogeochemical cycles in the bioretention system in this review, contributing to finding their interconnections and developing a more efficient bioretention system. Additionally, source characteristics of stormwater and fate of associated pollutants in the environment, the potential of genetical engineered plants, algae and fungi in bioretention system as well as performance assessment of plants and microorganisms in non-bioretention studies to propose the possible solution of un-addressed problems in bioretention system have been put forward in this review. The present review can be used as an imperative reference to enlighten the advantages of adopting multidisciplinary approaches for the environment sustainability and pollution control.

Biological nitrogen removal from stormwater in bioretention cells: a critical review

Excess nitrogen in stormwater degrades surface water quality via eutrophication and related processes. Bioretention has been recognized as a highly effective low-impact development (LID) technology for the management of high runoff volumes and reduction of nitrogen (N) pollutants through various mechanisms. This paper provides a comprehensive and critical review of recent developments on the biological N removal processes occurring in bioretention systems. The key plant- and microbe-mediated N transformation processes include assimilation (N uptake by plants and microbes), nitrification, denitrification, and anammox (anaerobic ammonia oxidation), but denitrification is the major pathway of permanent N removal. Overall, both laboratory- and field-scale bioretention systems have demonstrated promising N removal performance (TN: >70%). The phyla Bacteroidetes and Proteobacteria are the most abundant microbial communities found to be enriched in biofilter media. Furthermore, the denitrifying communities contain several functional genes (e.g., nirK/nirS, and nosZ), and their concentrations increase near the surface of media depth. The N removal effectiveness of bioretention systems is largely impacted by the hydraulics and environmental factors. When a bioretention system operates at: low hydraulic/N loading rate, containing a saturation zone, vegetated with native plants, having deeper and multilayer biofilter media with warm climate temperature and wet storm events periods, the N removal efficiency can be high. This review highlights shortcomings and current knowledge gaps in the area of total nitrogen removal using bioretention systems, as well as identifies future research directions on this topic.