Collaborative Research: Reevaluating Pre-denitrification BNR for Low Molecular Weight Dissolved Organic Nitrogen and its Impact on Phytoplankton Bloom Dynamics in Coastal Waters

沿海水域被富含营养的径流污染，这些径流刺激了植物的密集生长。藻华是这种植物生长的一种常见的破坏性形式，它导致氧气消耗和食物网的变化，威胁到这些水域的可持续性。沿海生态系统中这种富含营养物质的径流的显著减少主要是通过先进或升级的废水处理厂（WWTPs）来实现的，这些污水处理厂可以有效地去除这些污染物。然而，尽管通过污水处理厂的升级成功地减少了营养物质的释放，这些沿海系统仍然面临着同样的污染，可能是因为用于减少污水处理厂营养物质排放的工程实践导致了这些营养物质的不同形式的产生，这些营养物质仍然刺激了藻华的形成。为了验证这一假设，本研究将探讨污水排放与沿海水域藻华形成的潜在联系。这项研究意义重大，因为它可能为沿海水域持续缺氧提供解释，即使在污水处理厂排放的养分输入显著减少之后。如果成功，这项研究可以帮助制定新的污水处理厂战略，以减轻受损沿海生态系统的营养影响，更好地保护国家的水安全。本研究的目的是：1)评估预反硝化生物脱氮（BNR）工艺，这是减少污水处理厂中无机氮(N)排放的最常见方法，以形成低分子量溶解有机氮（LMW-DON）；2)更好地了解BNR过程对沿海水域悬浮藻（浮游植物）生产和组成的影响。我们的假设是：1)与传统的活性污泥系统相比，预反硝化BNR工艺容易产生大量的LMW-DON；2)与无机氮相比，LMW-DON导致浮游植物生物量产量意外增加；3) LMW-DON选择性影响浮游植物群落组成，有利于有害藻华类群。为了验证这些假设，本研究提出了四个具体目标：1)记录污水处理厂废水中的LMW-DON；2)研究预反硝化BNR中LMW-DON的生成；3)研究浮游植物群落对不同浓度LMW-DON污水的响应；4)研究阳离子强化生物絮凝对出水LMW-DON的影响。这项合作研究结合了环境工程、环境生物学和生态学的专业知识。本研究将对纽泽河河口（NC）和长岛湾（NY-CT）水域进行原位和实验室生物测定，以定性和定量地研究出水中N对浮游植物生产和群落结构的影响。本研究还将探索在废水系统中添加阳离子作为最大限度地减少废水LMW-DON产生的潜在解决方案。这项跨学科的合作研究将对理解污水处理厂驱动的LMW-DON在沿海水域富营养化和浮游植物群落结构中的作用产生深远的影响。此外，该项目将阐明特定氮输入与沿海富营养化和有害水华动态的耦合机制。这项研究的结果可以改变如何管理氮来减轻沿海水域的富营养化。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Coastal waters are contaminated by nutrient-rich run-off that stimulates the dense growth of plant life. Algal blooms, a common damaging form of this plant growth, cause oxygen depletion and food web changes that threaten the sustainability of these waters. Significant reduction of this nutrient-rich run-off in coastal ecosystems is primarily achieved by advanced or upgraded wastewater treatment plants (WWTPs) that can effectively remove these contaminants. However, despite the successful decreases in nutrient releases through WWTP upgrades, these coastal systems still face the same contamination, possibly because the engineering practices used to decrease nutrient discharge from WWTPs lead to the production of different forms of these nutrients that still stimulate algal bloom formation. To examine this hypothesis, this research will investigate the potential linkage of advanced WWTP discharge and algal bloom formation in coastal waters. This research is significant because it could potentially provide an explanation for persistent oxygen depletion in coastal waters even after significant decreases in nutrient inputs from WWTP discharges. If successful, this research could help develop new strategies for WWTPs to mitigate nutrient effects in impaired coastal ecosystems to better protect the Nation's water security.The objectives of this research are: 1) to evaluate pre-denitrification biological nutrient removal (BNR) processes, the most common way to reduce inorganic nitrogen (N) discharge from WWTPs, for the formation of low molecular weight dissolved organic N (LMW-DON); and 2) to better understand the impact of BNR processes on suspended algal (phytoplankton) production and composition in coastal waters. The hypotheses are that: 1) the pre-denitrification BNR processes are prone to produce significantly larger amounts of LMW-DON than conventional activated sludge systems; 2) LMW-DON leads to unexpectedly larger phytoplankton biomass yield compared to inorganic N; and 3) LMW-DON selectively affects phytoplankton community composition, favoring harmful bloom taxa. To test these hypotheses, this research proposes four specific aims: 1) document LMW-DON in WWTP effluents; 2) investigate the production of LMW-DON in pre-denitrification BNR; 3) investigate phytoplankton community responses to effluents laden with different level of LMW-DON; and 4) investigate the effect of cation-enhanced bioflocculation on effluent LMW-DON. This collaborative research combines expertise in Environmental Engineering with Environmental Biology and Ecology. This research will employ in situ and laboratory-based bioassays on Neuse River estuary (NC) and Long Island Sound (NY-CT) water to investigate the qualitative and quantitative effects of N in effluents on phytoplankton production and community structure. This research will also explore the addition of cations in wastewater systems as a potential solution for minimizing production of effluent LMW-DON. This interdisciplinary collaborative research will have far-reaching impacts for the understanding of the role of WWTP-driven LMW-DON in both eutrophication and structuring of phytoplankton communities in coastal waters. Furthermore, the project will shed light on mechanisms coupling specific N inputs to coastal eutrophication and harmful bloom dynamics. The results of this research can transform how N is managed to mitigate eutrophication in coastal waters.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.