Water Quality Standards Unit, Water Assessment Section, Environmental Analysis and Outcomes Division, Minnesota Pollution Control Agency, Saint Paul, Minnesota, United States of America.
Effluent Limits Unit, Water Assessment Section, Environmental Analysis and Outcomes Division, Minnesota Pollution Control Agency, Saint Paul, Minnesota, United States of America.
PLoS One. 2021 Feb 5;16(2):e0246688. doi: 10.1371/journal.pone.0246688. eCollection 2021.
Chloride is a key component of salt, used in many activities such as alkali production, water treatment, and de-icing. Chloride entering surface and groundwater is a concern due to its toxicity to aquatic life and potential to degrade drinking water sources. Minnesota being a hard-water state, has a high demand for water softening. Recent research has found that home-based water softeners contribute significantly to chloride loading at municipal wastewater treatment plants (WWTPs). Because of this, many WWTPs would now require water quality based effluent limits (WQBELs) to comply with the state's chloride water quality standards (WQS), unless they install chloride treatment technologies, which are limited and cost-prohibitive to most communities. A potential solution to this problem, is shifting from home-based water softening to a system where water is softened at drinking water plants, before reaching homes, i.e. centralized softening, analyzed in this paper based on its ability to address both chloride pollution and water softening needs, at reasonable cost. We estimate lifetime costs of three alternative solutions: centralized softening, home-based softening, and a Business as Usual (BAU) or baseline alternative, using annualized 20-year loan payments and Net Present Value (NPV), applied to 84 Minnesota cities with matching data on drinking water plants and WWTPs. We find that centralized softening using either Reverse Osmosis (RO) or lime-softening technologies is the more cost-effective solution, compared to the alternative of home-based softening with end-of-pipe chloride treatment, with a cost ratio in the range 1:3-1:4. Between the two centralized softening options, we find RO-softening to be the lower cost option, only slightly more costly (1.1 cost ratio) than the BAU option. Considering additional environmental and public health benefits, and cost savings associated with removal of home-based softeners, our results provide helpful information to multiple stakeholders interested in an effective solution to chloride pollution.
氯是盐的主要成分之一，用于许多活动，如碱生产、水处理和除冰。由于其对水生生物的毒性以及可能降低饮用水源质量，进入地表水和地下水的氯是一个令人关注的问题。明尼苏达州是一个硬水州，对水软化的需求很高。最近的研究发现，家用软水器对市政污水处理厂（WWTP）的氯负荷有很大贡献。因此，许多 WWTP 现在需要根据水质制定污水排放标准（WQBEL），以符合该州的氯水质标准（WQS），除非他们安装氯处理技术，但这些技术受到限制，且对大多数社区来说成本过高。解决这个问题的一个潜在方法是，从家用软化水转向在饮用水厂软化水的系统，即在水到达家庭之前进行软化，即集中软化，本文根据其解决氯污染和水软化需求的能力，以及在合理成本下进行了分析。我们估计了三种替代方案的终身成本：集中软化、家用软化和“照常营业”（BAU）或基线替代方案，使用年化 20 年贷款支付和净现值（NPV），适用于 84 个明尼苏达州城市，这些城市有与饮用水厂和 WWTP 相匹配的数据。我们发现，与家用软化加末端氯处理的替代方案相比，使用反渗透（RO）或石灰软化技术的集中软化是更具成本效益的解决方案，成本比为 1:3-1:4。在这两种集中软化方案中，我们发现 RO 软化是成本较低的方案，仅比 BAU 方案略高（成本比为 1.1）。考虑到额外的环境和公共卫生效益，以及与去除家用软化器相关的成本节约，我们的结果为对有效解决氯污染感兴趣的多个利益相关者提供了有帮助的信息。
