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Evaluation of Onsite Preanoxic Recirculating Gravel Filter Wastewater Treatment Systems for Nitrogen Removal.

机译：现场前缺氧循环砂石滤池污水处理系统的脱氮效果评估。

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摘要

Approximately 25 percent of the United States population is served by conventional onsite wastewater treatment systems (OWTS), which consist of a septic tank followed by a soil adsorption field with subsurface effluent dispersion. OWTS have limited nitrogen removal ability, and in some locations their nitrogen loading contributes to eutrophication and impairs groundwater for potable uses. Consequently, there is a need for OWTS with improved nitrogen removal efficiency. The design of onsite nitrogen removal systems should be simple with minimal mechanical equipment and chemical addition. These systems should also require very little operating attention and provide reliable nitrogen removal performance under varying household load conditions. This study evaluated the long-term performance of two new designs intended to meet these requirements while also producing an average total nitrogen effluent concentration of less than 20 mg/L. The designs tested were modifications of recirculating gravel filters (RGF), which have been used for many years. RGFs are easy to operate and are proven to be highly effective for the removal of organic pollutants such as biochemical oxygen demand (BOD) and total suspended solids (TSS), as well as biological oxidation of ammonia to nitrate. The modified RGF systems included an anoxic zone below the normal aerobic zone in which flow from the upper zone contacted septic tank effluent flow to promote biological denitrification for nitrogen removal. The systems were considered passive nitrogen removal systems because they do not require an exogenous carbon source. The differences between the two system designs included one having a vegetated aerobic zone (Vegetated RGF) and the other having a layer of oyster shells at the top of aerobic zone, and a different anoxic zone inlet design and upflow flow pattern (Enhanced RGF) versus a horizontal anoxic zone flow pattern for the Vegetated RGF. Each system treated 480 gallon/day of domestic wastewater with a typical diurnal flow pattern. Their performance was evaluated for twelve months, which also included five stress tests that simulated extreme wash loads conditions, low loading periods, vacation interruptions, and power failure that might occur for a single home. This research evaluated and compared the performance of these systems in regards to nitrogen, BOD, TSS, total phosphorus (TP), and fecal coliform removal. Their responses to the stress tests and the effect of temperature were also assessed. The Vegetated RGF achieved high average treatment efficiencies for BOD (98%), TSS (99%), and fecal coliform (1.4 log reduction). The Enhanced RGF was equally effective at removing BOD (97%), TSS (99%), and fecal coliform (1.1 log reduction). Both systems achieved a total phosphorus removal efficiency of about 40 percent. The effluent annual average total nitrogen concentrations were 15.2 and 8.6 mg/L with 95 th percentiles of 18.5 and 12.3 mg/L for the Vegetated RGF and Enhanced RGF systems, respectively. Both the Vegetated and Enhanced RGF systems had good nitrification efficiency, but some operational clogging in the feed distribution piping did cause higher effluent ammonia concentrations. The larger aerobic volume and lower nitrogen loading to the Vegetated RGF system provided a higher nitrification efficiency compared to the Enhanced RGF. A much greater denitrification efficiency was observed for the Enhanced RGF system compared to the Vegetated RGF system due to its improved method of contacting the nitrified flow from the upper aerobic zone and the septic tank effluent.
机译：传统的现场废水处理系统（OWTS）为美国人口提供约25％的服务，该系统由化粪池组成，其后是具有地下废水扩散能力的土壤吸附场。 OWTS的脱氮能力有限，在某些地方，其氮负荷会导致富营养化并损害饮用水的饮用水。因此，需要具有改善的氮去除效率的OWTS。现场除氮系统的设计应简单，机械设备和化学药品最少。这些系统还需要很少的操作注意，并在变化的家庭负载条件下提供可靠的脱氮性能。这项研究评估了旨在满足这些要求的两种新设计的长期性能，同时还产生了小于20 mg / L的平均总氮排放浓度。测试的设计是对再循环砾石滤池（RGF）的改进，该滤池已经使用了很多年。 RGF易于操作，并被证明对去除有机污染物（例如生化需氧量（BOD）和总悬浮固体（TSS））以及将氨生物氧化为硝酸盐非常有效。改进的RGF系统在正常好氧区域下方包括一个缺氧区域，其中上部区域的流与化粪池废水流接触，以促进生物脱氮以去除氮。该系统被认为是被动除氮系统，因为它们不需要外部碳源。两种系统设计之间的区别包括：一种具有植被好氧区（Vegetated RGF），另一种在好氧区顶部具有一层牡蛎壳，以及不同的缺氧区入口设计和上流模式（增强型RGF）与植被RGF的水平缺氧区流型。每个系统以典型的日间流量模式处理480加仑/天的生活污水。他们的性能进行了为期十二个月的评估，其中还包括五项压力测试，它们模拟了单个房屋可能发生的极端洗涤负荷条件，低负荷期，休假中断和电源故障。这项研究评估并比较了这些系统在氮，BOD，TSS，总磷（TP）和粪大肠菌群去除方面的性能。还评估了他们对压力测试的响应和温度的影响。植被RGF对BOD（98％），TSS（99％）和粪大肠菌群（减少1.4 log）的平均治疗效率很高。增强型RGF在去除BOD（97％），TSS（99％）和粪便大肠菌（减少1.1 log）方面同样有效。两种系统的总除磷效率均约为40％。植被RGF和增强RGF系统的废水年平均总氮浓度分别为15.2和8.6 mg / L，第95个百分位数分别为18.5和12.3 mg / L。植被型和增强型RGF系统都具有良好的硝化效率，但是进料分配管道中的某些操作性堵塞确实会导致较高的废水氨浓度。与增强型RGF相比，较大的需氧量和较低的植物RGF系统氮负荷提供了更高的硝化效率。与改良型RGF系统相比，增强型RGF系统的反硝化效率要高得多，这是因为改进的RGF系统使来自上部好氧区和化粪池废水的硝化流接触的方法得到了改进。

著录项

  • 作者

    Wei, Stephany.;

  • 作者单位

    University of Washington.;

  • 授予单位 University of Washington.;
  • 学科 Engineering Environmental.
  • 学位 Masters
  • 年度 2013
  • 页码 95 p.
  • 总页数 95
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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