Tertiary Partial Denitrification-Anammox (PdNA) Filters for Sustainable Nitrogen Removal: Pilot Scale Filter Results

Concentrated discharges of nitrogen into our waterways have led to seriousenvironmental impacts, such as eutrophication and algae blooms. Due to these discharges,stringent total nitrogen (TN) discharge limits have been placed on Water Reclamation Facilities(WRFs). Mainstream deammonification offers a novel approach for improving nitrogen removalat these facilities by harnessing anaerobic ammonia oxidizing bacteria (Anammox). However,the success of this process has been limited. Previous research at NC State explored theconversion of tertiary filters to mainstream deammonification filters which were shown to becapable of an average total inorganic nitrogen (TIN) removal rate of 91%, with effluent TINreaching below 2 mg/L-N. However, this research suggested that nitrate loading concentrationswere the limiting factor in meeting 2 mg/L-N TIN effluent limits. Incorporating partialdenitrification (PdN), the conversion of nitrate to nitrite for subsequent use in Anammox, offers apromising solution. The goal of this research was to explore the TIN removal capability andfeasibility of a PdN-Anammox (PdNA) filter under typical filter loading conditions, incomparison to a conventional denitrification (FdN) filter.Different carbon loading strategies in pilot scale filters confirmed that maintaining anitrate residual of >1.5 mg-N/L allowed for the highest PdN conversion efficiencies and in turnincreased Anammox activity. Furthermore, the carbon requirement (C/N ratio) of 5.1 g COD/gTIN in pilot scale FdN was higher than the 2.08 g COD/g TIN achieved in the PdNA filters,demonstrating the cost benefits associated with mainstream deammonification and theapplication of PdNA. In addition to greater than 50% reduction in supplemental carbon, otherbenefits include nearly 38% reduction in oxygen demand and reduction in excess sludge incomparison to conventional BNR processes. Through this pilot study, PdNA was demonstratedto provide TIN removal efficiencies of greater than 80%. With further research, stable TNremoval at WRFs at typical filter loading rates can be achieved, and with that, the possibility forsubstantial operational expenditure (OPEX) savings.

氮污染物的集中排入水体已引发严重的环境影响，例如富营养化与藻华暴发。受此类排放影响，水务回收设施（Water Reclamation Facilities, WRFs）被施加了严格的总氮（total nitrogen, TN）排放限值。主流脱氨工艺通过驯化利用厌氧氨氧化细菌（anaerobic ammonia oxidizing bacteria, Anammox），为提升此类设施的脱氮效能提供了全新路径，但该工艺的实际应用仍存在诸多限制。此前北卡罗来纳州立大学的研究团队开展了将三级滤池改造为主流脱氨滤池的试验，结果显示，改造后的滤池平均总无机氮（total inorganic nitrogen, TIN）去除率可达91%，出水总无机氮浓度可降至2 mg/L-N以下。但该研究同时指出，硝酸盐负荷浓度是达成2 mg/L-N总无机氮出水限值的核心限制性因素。引入部分反硝化（partial denitrification, PdN）工艺——即通过将硝酸盐转化为亚硝酸盐，为厌氧氨氧化细菌提供反应底物——可为该瓶颈问题提供极具前景的解决方案。本研究的核心目标为：在典型滤池负荷条件下，对比分析部分反硝化-厌氧氨氧化（PdN-Anammox, PdNA）滤池与传统反硝化（conventional denitrification, FdN）滤池的总无机氮去除效能与应用可行性。

中试滤池的多组碳源投加策略试验证实，维持硝酸盐残留量>1.5 mg-N/L时，可实现最高的部分反硝化转化效率，进而提升厌氧氨氧化细菌的代谢活性。此外，中试传统反硝化滤池的碳需求（碳氮比，即C/N比）为5.1 g 化学需氧量（Chemical Oxygen Demand, COD）/g TIN，高于部分反硝化-厌氧氨氧化滤池的2.08 g COD/g TIN，这一结果体现了主流脱氨工艺及部分反硝化-厌氧氨氧化工艺的成本优势。相较于传统生物脱氮除磷（Biological Nutrient Removal, BNR）工艺，该工艺不仅可减少50%以上的补充碳源投加量，还可降低近38%的需氧量，同时减少剩余污泥的产生量。

通过本次中试研究，已证实部分反硝化-厌氧氨氧化工艺的总无机氮去除效率可达80%以上。若开展后续深化研究，即可在水务回收设施的典型滤池负荷条件下实现稳定的总氮去除，进而大幅节约运营支出（operational expenditure, OPEX）。