Striking the Balance Between Nutrient Removal in Wastewater Treatment and Sustainability
Striking the Balance Between Nutrient Removal in Wastewater Treatment and Sustainability
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在废水处理中的营养物去除与可持续发展之间取得平衡
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发表时间：
2012
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通讯作者：
D. Reardon
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作者：
M. Falk;J. Neethling;D. Reardon
本研究重点关注废水处理厂实施处理技术以满足日益严格的营养物限制时的可持续性影响。目标是确定是否达到“收益递减”点，即增加营养物去除水平的可持续性影响超过改善水质的好处。
开发了标称 10 mgd 流量的五种不同的假设处理序列，以满足从 cBOD 模式（1 级）到四种不同营养物去除目标的处理目标。营养物去除目标范围为 8 mg N/L； 1 mg P/L（2 级）至最严格的 <2 mg N/L； <0.02 mg P/L（5 级）。
鉴于可持续发展是一个广泛的术语，对行业公认的可持续发展三大支柱进行了评估和讨论，并特别强调了环境和经济支柱。以下变量受到最多关注：温室气体 (GHG) 排放、反映潜在藻类生长的水质替代指标、资本和运营成本、能源需求以及化学品、天然气、柴油等消耗品。
温室气体排放指标的结果如下所示。请注意，沼气热电联产用负值表示，因为沼气生产可用于抵消能源需求。一氧化二氮 (N2O) 排放值基于 Ahn 等人在美国全国调查中评估的平均生物养分去除 (BNR) 和非 BNR 工厂。 （2010b）。误差线代表全国调查的数据范围。
温室气体排放结果表明，4 级时达到收益递减点（3 mg N/L；0.1 mg P/L）。温室气体排放量从 1 级到 4 级稳步增加，从 4 级到 5 级则增加 65%。尽管温室气体增加了 70%，但从 4 级到 5 级，排放的养分负荷仅减少了 1%。温室气体排放的主要贡献者是与能源相关的（曝气、泵送、混合）。为了实现更严格的营养目标，除了生物营养去除之外还需要化学处理，与化学品使用相关的温室气体排放量增加。
在成本方面，从 1 级更改为 2 级时，项目总资本成本增加了约三分之一，从 930 万美元增加到 1,270 万美元，而从 1 级更改为 5 级时，成本增加了一倍多。本报告中的项目总资本成本适用于新建工厂。级别之间的运营成本增加比项目总资本成本更明显，从 1 级到 5 级增加了五倍多（分别为 250 美元/MG 至 1,370 美元/MG）。
本报告重点关注厂内（点源）养分去除方案及其对成本和可持续性的影响。可以在评估中添加其他方法，例如解决非点源问题。与严格关注点源排放者和要求 4 级或 5 级处理不同，3 级或 4 级处理辅以非点源的最佳管理实践可能是实现可比水质的更可持续的方法。
本标题属于WERF研究报告系列。
ISBN: 9781780400433（印刷版）
ISBN：9781780403298（电子书）
This study focuses on sustainability impacts as wastewater treatment plants implement treatment technologies to meet increasingly stringent nutrient limits. The objective is to determine if a point of “diminishing returns” is reached where the sustainability impacts of increased levels of nutrient removal outweigh the benefits of better water quality.
Five different hypothetical treatment trains at a nominal 10 mgd flow were developed to meet treatment targets that ranged from cBOD mode (Level 1) to four different nutrient removal targets. The nutrient removal targets ranged from 8 mg N/L; 1 mg P/L (Level 2) to the most stringent at <2 mg N/L; <0.02 mg P/L (Level 5).
Given that sustainability is a broad term, the industry-accepted three pillars of sustainability were evaluated and discussed, and particular emphasis was placed on the environmental and economic pillars. The following variables received the most attention: greenhouse gas (GHG) emissions, a water quality surrogate that reflects potential algal growth, capital and operational costs, energy demand, and consumables such as chemicals, gas, diesel, etc.
The results from the GHG emissions metric are shown below. Note that biogas cogeneration is represented by negative values as biogas production can be used to offset energy demands. The nitrous oxide (N2O) emissions values are based on the average biological nutrient removal (BNR) and non-BNR plants evaluated in the United States national survey by Ahn et al. (2010b). The error bars represent the data range of the national survey.
The GHG emissions results suggest that a point of diminishing return is reached at Level 4 (3 mg N/L; 0.1 mg P/L). The GHG emissions show a steady increase from Levels 1 to 4, followed by a 65% increase when moving from Level 4 to 5. Despite a 70% increase in GHGs, the discharged nutrient load only decreases by 1% by going from Level 4 to 5. The primary contributors to GHG emissions are energy related (aeration, pumping, mixing). The GHG emissions associated with chemical use increases for the more stringent nutrient targets that required chemical treatment in addition to biological nutrient removal.
In terms of cost, the total project capital cost increases approximately one-third from $9.3 million to $12.7 million for changing from Level 1 to 2, followed by a more than doubling in cost when changing from Level 1 to 5. Total project capital costs in this report are for a Greenfield plant. The operational cost increase between levels is more pronounced than total project capital cost with more than five-times increase from Level 1 to 5 ($250/MG treated to $1,370/MG treated, respectively).
This report focused on in-plant (point source) options for nutrient removal and the implications for cost and sustainability. Other approaches, such as addressing non-point sources, could be added to the assessment. Rather than focusing strictly on point source dischargers and requiring Level 4 or 5 treatments, Level 3 or 4 treatments complimented with best management practices of non-point sources might be a more sustainable approach at achieving comparable water quality.
This title belongs to WERF Research Report Series .
ISBN: 9781780400433 (Print)
ISBN: 9781780403298 (eBook)