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

沿海水域受到营养丰富的径流的污染，这种径流刺激了植物生命的密集生长。藻类水华是这种植物生长的一种常见的破坏性形式，会导致氧气枯竭和食物链变化，威胁到这些水域的可持续性。沿海生态系统中这种营养丰富的径流的显著减少主要是通过先进或升级的污水处理厂(WWTP)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升级成功地减少了营养物质的释放，但这些沿海系统仍然面临同样的污染，这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藻类水华的形成。为了验证这一假设，这项研究将调查高级污水处理厂排放和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的氧气枯竭提供解释，即使在污水处理厂排放的营养物质输入显著减少之后也是如此。如果成功，这项研究将有助于为污水处理厂开发新的策略，以减轻受损沿海生态系统的营养物质影响，以更好地保护国家的水安全。本研究的目的是：1)评估预反硝化生物养分去除(BNR)过程，这是减少污水处理厂无机氮(N)排放的最常见方法，以形成低分子溶解有机N(LMW-DON)；以及2)更好地了解BNR过程对沿海水域悬浮藻类(浮游植物)产量和组成的影响。假设如下：1)预反硝化BNR工艺容易产生比常规活性污泥系统大得多的LMW-DON；2)LMW-DON导致浮游植物的生物量比无机N意外地大；3)LMW-DON选择性地影响浮游植物群落组成，有利于有害的水华类群。为了验证这些假设，本研究提出了四个具体目标：1)记录污水处理厂出水中的LMW-DON；2)调查预反硝化BNR中LMW-DON的产生；3)调查浮游植物群落对不同水平的LMW-DON的响应；以及4)调查阳离子强化生物絮凝对出水LMW-DON的影响。这项合作研究将环境工程方面的专业知识与环境生物学和生态学结合起来。本研究将在纽兹河河口(NC)和长岛海湾(NY-CT)水域采用现场和实验室生物测定方法，研究污水中氮对浮游植物产量和群落结构的定性和定量影响。这项研究还将探索在废水系统中添加阳离子作为一种潜在的解决方案，以最大限度地减少出水LMW-DON的产生。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，该项目将阐明将特定N输入与沿海富营养化和有害水华动态相结合的机制。这项研究的结果可以改变氮的管理方式，以缓解沿海水域的富营养化。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.