Water quality and hydraulic performance of biochar amended biofilters for management of agricultural runoff

Bioretention Design Modifications Increase the Simulated Capture of Hydrophobic and Hydrophilic Trace Organic Compounds

Stormwater rapidly moves trace organic contaminants (TrOCs) from the built environment to the aquatic environment. Bioretention cells reduce loadings of some TrOCs, but they struggle with hydrophilic compounds. Herein, we assessed the potential to enhance TrOC removal via changes in bioretention system design by simulating the fate of seven high-priority stormwater TrOCs (e.g., PFOA, 6PPD-quinone, PAHs) with log KOC values between -1.5 and 6.74 in a bioretention cell. We evaluated eight design and management interventions for three illustrative use cases representing a highway, a residential area, and an airport. We suggest two metrics of performance: mass advected to the sewer network, which poses an acute risk to aquatic ecosystems, and total mass advected from the system, which poses a longer-term risk for persistent compounds. The optimized designs for each use case reduced effluent loadings of all but the most polar compound (PFOA) to <5% of influent mass. Our results suggest that having the largest possible system area allowed bioretention systems to provide benefits during larger events, which improved performance for all compounds. To improve performance for the most hydrophilic TrOCs, an amendment like biochar was necessary; field-scale research is needed to confirm this result. Our results showed that changing the design of bioretention systems can allow them to effectively capture TrOCs with a wide range of physicochemical properties, protecting human health and aquatic species from chemical impacts.

Fate of pesticides in agricultural runoff treatment systems: Occurrence, impacts and technological progress

The levels of pesticides in air, water, and soil are gradually increasing due to its inappropriate management. In particular, agricultural runoff inflicts the damages on the ecosystem and human health at massive scale. Present study summarizes 70 studies in which investigations on removal or treatment of pesticides/insecticides/herbicides are reported. A bibliometric analysis was also done to understand the recent research trends through the analysis of 2218 publications. The specific objectives of this study are as follows: i) to inventorize the characteristics details of agriculture runoff and analyzing the occurrence and impacts of pesticides, ii) analyzing the role and interaction of pesticides in different environmental segments, iii) investigating the fate of pesticides in agriculture runoff treatment systems, iv) summarizing the experiences and findings of most commonly technology deployed for pesticides remediation in agriculture runoff including target pesticide(s), specifications, configuration of technological intervention. Among the reported technologies for pesticide treatment in agriculture runoff, constructed wetland was at the top followed by algal or photobioreactor. Among various advanced oxidation processes, photo Fenton method is mainly used for pesticides remediation such as triazine, methyl parathion, fenuron and diuron. Algal bioreactors are extensively used for a wide range of pesticides treatment including 2,4-Dichlorophenoxyacetic acid, 2-methyl-4-chlorophenoxyacetic acid, alachlor, diuron, chlorpyrifos, endosulfan, and imidacloprid; especially at lower hydraulic retention time of 2-6 h. This study highlights that hybrid approaches can offers potential opportunities for effective removal of pesticides in a more viable manner.

Fixed-bed biofilter for polluted surface water treatment using chitosan impregnated-coconut husk biochar

Pelletizing biochar enables its use as a biofilter medium for polluted canal water treatment. Coconut husk biochar pellets and their modification with chitosan (CHC) were compared with conventional activated carbon pellets and gravel. The biofilter columns with these media were operated with a hydraulic loading rate of 0.1 m3/m2∙h. CHC showed the highest potential to reduce phosphate and nitrogen, via the adsorption process in the first week of filtration and later enhanced by biodegradation, to achieve removal efficiencies of 61.70 and 54.37% for these two key nutrients, respectively, over five weeks of biofilter operation. The predominant bacteria in the biofilter communities were characterized at the end of the experiments by next generation sequencing and quantitative polymerase chain reaction analysis. The biofilter communities included ammonium oxidizing, nitrite oxidizing, denitrifying, polyphosphate accumulating and denitrifying phosphate-accumulating bacteria that benefit nutrient removal. The CHC biofilter also effectively removed micropollutants, including pharmaceuticals.

Nitrogen removal mechanisms in biochar-amended sand filters treating onsite wastewater

The performance of biochar-amended sand filters treating septic tank effluent (STE) was investigated in bench-scale columns. Softwood biochar showed higher NH₄ ⁺ -N adsorption capacity (1.3 mg N g^-1 ), and its water holding capacity (0.57 g ml^-1 ) was significantly higher than sand (0.26 g ml^-1 ). Two biochar amendment ratios (10% and 30%) were selected for STE treatment in short-term (20 days) and long-term (8 months) studies. During the short-term experiment, the overall total nitrogen removal efficiency was greater in biochar-amended sand columns (94.7%-95.6%) than in 100% sand columns (71.2%) due to the additional NH₄ ⁺ -N adsorption by biochar. Greater nitrification performance was also observed in biochar-amended columns (87.1%-96.3%) than in 100% sand columns (61.4%) during long-term operation when alkalinity was insufficient. The nitrification performance in biochar-amended columns resumed more quickly (<7 days) after sufficient alkalinity was amended. The density of total biomass and nitrifying bacteria in biochar-amended columns (30%) were significantly higher at all experimental stages, suggesting biochar served as a growth media for enhanced biomass growth. The alkalinity changes and STE composition fluctuation had little impact on the nitrification performance of the 30% biochar-amended sand columns. In addition, biochar surface functional groups and zeta potential changed little after long-term STE filtration. Collectively, the results demonstrated proper biochar amendment ratio (30%) could enhance the nitrification performance of sand filters treating STE by increasing the system hydraulic retention time, providing additional alkalinity for nitrification, and serving as a growth media for enhanced biomass growth.

Removal of ammonia nitrogen, nitrate, and phosphate from aqueous solution using biochar derived from Thalia dealbata Fraser: effect of carbonization temperature

Thalia dealbata Fraser-derived biochar was prepared at different carbonization temperatures to remove nutrients in aqueous solution. Thermogravimetry/differential thermogravimetry (TG/DTG) was used to analyze the carbonization and decomposition procedure of Thalia dealbata Fraser. X-ray diffraction (XRD), scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR), zeta potential, and N₂ adsorption-desorption isotherms were employed to characterize the prepared biochar. The carbonization temperature obviously effected the physical and chemical properties of biochar. The adsorption efficiency of ammonia (NH₄⁺-N), nitrate (NO₃^--N), and phosphate (PO₄^3-) adsorption on biochar was tested. Pseudo-first-order kinetic, pseudo-second-order kinetic, and intra-particle diffusion kinetic models were used to fit adsorption kinetic. Langmuir and Freundlich models were used to fit adsorption isotherms. The theoretical adsorption capacity of NH₄⁺-N, NO₃^--N, and PO₄^3- on biochar was 5.8 mg/g, 3.8 mg/g, and 1.3 mg/g, respectively. This study provides the insights for effect of carbonization temperature on biochar preparation and application.

Performance of Various Filtering Media for the Treatment of Cow Manure from Exercise Pens—A Laboratory Study

During summer and winter months, pastures and outdoor pens represent the conventional means of providing exercise for dairy cows housed in tie-stall barns in the province of Québec, Canada. Unfortunately, outdoor pens require large spaces, and their leachates do not meet Québec’s environmental regulations. Therefore, there is a need to develop alternative approaches for these so-called wintering pens. A sustainable year-long approach could be a stand-off pad consisting of a filtering media to manage adequately water exiting the pad. Different filtering materials can be used and mixed (gravel, woodchips, biochar, sphagnum peat moss, sand, etc.). To find the best material and/or mixes, a laboratory study was carried out using 15 PVC pipes (5 cm in diameter and 50 cm long) to test five different combinations of materials over a 3-week period. Different contaminant-removal efficiencies were achieved with the alternative materials, including for chemical oxygen demand (11–38%), phosphates (8–23%), suspended solids (33–57%), and turbidity (23–58%). Alternative treatments with sand, sphagnum peat moss, and biochar improved the filtration capacity when compared to the conventional material (woodchips). However, after three weeks of experimentation, the treatment efficiency of sand gradually decreased for pollutants such as suspended solids and phosphates.

Biochar application in biofiltration systems to remove nutrients, pathogens, and pharmaceutical and personal care products from wastewater

Although conventional on-site wastewater treatment systems (OWTSs) provide only primary treatment of domestic wastewater, removal of a limited level of nutrients (N, P), pathogens, and pharmaceuticals and personal care products (PPCPs) could be achieved by such a treatment process. Biochar has the capacity to remove various contaminants and has been widely used as an ideal soil amendment in agriculture due to its persistence, superior nutrient-retention properties, low cost, and ready availability. However, few applications on the use of biochar in onsite wastewater treatment have been explored. In this review, we systematically reviewed the applications of biochar in filtration-based OWTSs for nutrient (N, P) removal and recovery as well as pathogen and PPCP removal. Although adsorption was the main mechanism for P, pathogen, and PPCP removal, biochar can also serve as the growth media for enhanced biological degradation, improves available alkalinity, and increases water holding capacity in the OWTSs. The biochar source, surface modification methods, and preparation procedures (e.g., pyrolysis temperature change) have significant effects on contaminant removal performance in biochar-amended OWTSs. Specifically, contradictory results have been reported on the effect of pyrolysis temperature change on biochar removal performance (i.e., increased, decreased, or no change) of N, P, and PPCPs. Wastewater composition and environmental pH also play important roles in the removal of nutrients, pathogens, and PPCPs. Overall, biochar holds great potential to serve as an alternative filtration material or to be amended to the current OWTS to improve system performance in removing a variety of contaminants at low cost.

Biochar-based bioretention systems for removal of chemical and microbial pollutants from stormwater: A critical review

Biochar has been increasingly used as a filter medium in engineered low impact development systems (e.g., bioretention systems) for decontamination of urban stormwater and management of hydrology. This review paper critically analyzes the performance of biochar-based biofiltration systems for removal of chemical and microbial pollutants present in urban runoff. Biochar-amended biofiltration systems efficiently remove diverse pollutants such as total nitrogen (32 - 61%), total phosphorus: (45 - 94%), heavy metals (27 - 100%), organics (54 - 100%) and microbial pollutants (log₁₀ removal: 0.78 - 4.23) from urban runoff. The variation of biofiltration performance is due to changes in biochar characteristics, the abundance of dissolved organic matter and/or stormwater chemistry. The dominant mechanisms responsible for removal of chemical pollutants are sorption, ion exchange and/or biotransformation, whereas filtration/straining is the major mechanism for bacteria removal. The pseudo-second order and Langmuir isotherm are the best models that describe the kinetics and chemical equilibrium of pollutants, respectively. This critical review provides the fundamental scientific knowledge for designing highly efficient biochar-based bioretention systems for removal of diverse pollutants from urban stormwater. The key knowledge gaps that should be addressed in future research include long-term field-scale bioretention study, development of novel methods for filter media regeneration/reuse, and dynamics of filter media microbial communities.