Law Ji Yeow, Slade Alexis, Hoover Natasha, Feyereisen Gary, Soupir Michelle
Dep. of Agricultural and Biosystems Engineering, Iowa State University, 605 Bissell Rd, Ames IA, 50011, USA.
Dep. of Agricultural and Biosystems Engineering, Iowa State University, 605 Bissell Rd, Ames IA, 50011, USA; Dep. of Civil and Environmental Engineering, University of Iowa, 4231 Seamans Center, Iowa City IA, 52242, USA.
J Environ Manage. 2023 Mar 15;330:117135. doi: 10.1016/j.jenvman.2022.117135. Epub 2022 Dec 28.
Woodchip denitrification bioreactors are an effective agricultural practice to reduce nitrogen (N) export from subsurface drainage via the conversion of nitrate (NO) to nitrogen gas (N), but there are challenges associated with limited woodchip supplies and increasing prices. Previous lab studies indicate that corncobs could be a promising woodchip alternative from the perspectives of N removal rate and cost. This field study aimed to provide early performance and cost assessment of denitrification bioreactors with two woodchip-corncob treatments. The objectives were to i) compare N removal rates of bioreactors with different carbon and hydraulic retention time (HRT) treatments, ii) compare bioreactor N removal costs, and iii) conduct sensitivity analysis on full-scale bioreactors (FBR) N removal costs with varying corncob lifespans and prices. Nine replicated field pilot-scale bioreactors (PBRs) using three carbon treatments and three HRTs were assessed for N removal efficiency. The carbon treatments were woodchip-only (WC100), 25% (by vol.) corncobs + 75% woodchips media (CC25) in series, and 75% corncobs + 25% woodchips (CC75) in series set at HRTs of 2, 8, and 16 h. N concentrations were monitored at each PBR inlet and outlet, and the PBR N removal efficiencies were used to estimate FBR N removal rates and costs. At respective HRTs, the estimated N removal rates of CC75 were 1.6- to 10.1-fold higher than WC100, but CC25 exhibited 0.9-fold lower (at 8-hr HRT) to 2.8-fold higher than WC100. A 15-yr cost assessment indicated CC75 ($10.56 to $13.89 kg N) was the most cost-efficient treatment, followed by WC100 ($13.30 to $88.11 kg N) and CC25 ($22.41 to $60.13 kg N). This assessment showed CC75 as a promising alternative to WC100 in terms of N removal rate and cost, but CC25 did not provide sufficient N removal rate increase for it to be a cost-efficient option. Nonetheless, using corncobs as a bioreactor medium is a relatively new approach, and we encourage more field studies to explore the long-term opportunities and challenges.
木片反硝化生物反应器是一种有效的农业实践方法，可通过将硝酸盐（NO）转化为氮气（N₂）来减少地下排水中的氮（N）排放，但木片供应有限和价格上涨带来了挑战。先前的实验室研究表明，从氮去除率和成本的角度来看，玉米芯可能是一种有前景的木片替代品。本田间研究旨在对两种木片 - 玉米芯处理的反硝化生物反应器进行早期性能和成本评估。目标是：i）比较不同碳源和水力停留时间（HRT）处理的生物反应器的氮去除率；ii）比较生物反应器的氮去除成本；iii）对不同玉米芯寿命和价格的全尺寸生物反应器（FBR）的氮去除成本进行敏感性分析。评估了九个重复的田间中试规模生物反应器（PBR），采用三种碳源处理和三种HRT，以测定氮去除效率。碳源处理分别为纯木片（WC100）、串联的25%（体积）玉米芯 + 75%木片介质（CC25）以及串联的75%玉米芯 + 25%木片（CC75），HRT分别设置为2小时、8小时和16小时。在每个PBR的入口和出口监测氮浓度，并使用PBR的氮去除效率来估计FBR的氮去除率和成本。在各自的HRT下，CC75的估计氮去除率比WC100高1.6至10.1倍，但CC25比WC100低0.9倍（在8小时HRT时）至高2.8倍。一项为期15年的成本评估表明，CC75（每千克氮10.56至13.89美元）是最具成本效益的处理方式，其次是WC100（每千克氮13.30至88.11美元）和CC25（每千克氮22.41至60.13美元）。该评估表明，在氮去除率和成本方面，CC75是WC100的一个有前景的替代品，但CC25没有提供足够的氮去除率提升，使其成为一个具有成本效益的选择。尽管如此，使用玉米芯作为生物反应器介质是一种相对较新的方法，我们鼓励更多的田间研究来探索长期的机遇和挑战。
