Bioreactor-biochar (B2) treatment system: A novel design for efficient water pollution control from agri-drainage
As part of modern agriculture, agricultural subsurface drainage plays a significant role in enhancing crop productivity, but there have been adverse environmental and health consequences associated with the use of the systems. Previous studies encourage adopting conservation practices or best management practices to overcome environmental impacts of drainage, such as denitrifying woodchip bioreactor and phosphate removal structure. The research presented in this dissertation aims to introduce and design an innovative edge-of-field technology that enables the control of water pollution from tile drainage using woodchip bioreactor and biochar systems. In this study, the engineering potential of designer biochar pellets for dissolved reactive phosphorus (DRP)loss reduction from an intensified tile-drain agroecosystem was first evaluated. The performance of two types of designer biochar pellets on reducing agricultural diffuse DRP losses from tile drainages was investigated: Phase I - biochar pellets size 2~3 cm (operated for 170 days) vs Phase II - biochar pellets size <1 cm (operated for 250 days). The field demonstration indicated that multi-factors can co-affect the DRP loss reduction performance using designer biochar pellets, including pellet size, influent phosphorus load/concentrations, crop management, and temperature, especially pellet particle size. Techno-economic analysis revealed that designer biochar pellets economically remove DRP with an average unit production cost of $412.6/ton biochar and unit removal cost of $402.3 per kg DRP under wide economic and system design parameters. The results verified the use of biochar in the environmental management of tile drainage, allowing us to further design advanced systems for maximizing benefits. Following up this study, the possibility of a novel treatment system that combines woodchip bioreactor and designer biochar (B2) system was investigated to reduce both nitrogen and phosphorus loss from tile drainage at the field scale. The results indicated that more than 83% of nitrate and 25% of ammonia (NH3 -N) was removed by the B2 systems. However, the woodchip bioreactor released significant amounts of byproducts (total P and DRP) while the two-stage biochar-sorption channel removed total P and DRP from upstream woodchip bioreactor effluent. These results underscored the importance of mitigating the environmental impact of woodchip bioreactors when using them as a conservation practice. Further, the impact of different configurations of woodchip bioreactor and biochar on the treatment performance was assessed to provide guidance for B2 system adoption, including a common design (biochar-woodchip mixture bioreactor, single-stage W&B) and two emerging treatment train designs (WBRs followed by biochar systems, W-B, and biochar systems equipped with secondary WBRs, B-W). The results demonstrated that all B2 systems exhibited synergistic removal of nitrate and DRP. Single-stage W&B systems achieved the highest reductions in DRP and nitrate but had the drawback of generating the highest amounts of byproduct (organic matter). Meanwhile, W-B systems effectively mitigated byproduct leaching while maintaining stable nitrate removal. Microbial analysis revealed that the interaction between biochar and woodchip amendment selectively supported the growth of microbes that facilitate denitrification and organic matter decomposition. Furthermore, the techno-economic analysis identified W-B systems as optimal for maximizing nutrient removal per unit cost at field-scale application scenarios, achieving $187.9 ± 160.0/kg DRP and $5.5 ± 1.7kg nitrate per year. Overall, the findings highlight the importance of media interaction for designing B2 systems in water quality management. Finally, the possibility of B2 treatment systems to simultaneously remove excess nutrients and PPCP contaminants was examined to extend the applicability. The results found that longer hydraulic retention times and smaller biochar particles could enhance the removal efficiencies of targeted contaminants. Average contaminant removals were 77.3%, 99.0%, 69.5%, 73.7%, 91.1%, and 96.9% for nitrate, DRP, ibuprofen, naproxen, sitagliptin, and estrone, respectively. The presence of PPCPs in the woodchip bioreactors promoted the enrichment of certain species, like Methylophilus (69.6%), while inhibiting other microorganisms, leading to a decrease in microbial community diversity. Nevertheless, PPCPs also increased positive interactions among functional microorganisms, potentially enhancing the complexity of the microbial community. Overall, through a series of laboratory-scale experiments, field-scale demonstrations, and sustainability assessment, this dissertation suggests that the combination of a woodchip bioreactor and biochar system to construct B2 system offers a promising solution for combating emerging and conventional contaminants from tile drainage and beyond in modern agriculture.
Biochar, Drainage, Woodchip Bioreactor, Sustainability
University of Illinois - Urbana-Champaign
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University of Illinois at Urbana-Champaign