各种污水生化处理工艺流程框图.doc

各种工艺流程框图

The MLE consists of an anoxic basin upstream of an aerobic zone. An internal recycle carries nitrates created during the nitrification process in the aerobic zone along with mixed liquor to the anoxic zone for denitrification. RAS is mixed with the influent to the anoxic zone. The extent of denitrification is tied to the mixed liquor recycle flow; higher recycle rates increase denitrification. Because only recycled nitrate has the opportunity to be denitrified, the MLE alone cannot achieve extremely low final nitrogen concentrations. The maximum denitrification potential is approximately 82 percent at a 500 percent recycle rate (WEF and ASCE 2006). TN effluent concentrations typically range from 5 to 8 mg/L (Barnard 2006). Actual denitrification might be limited by other factors, such as carbon source availability, process kinetics, and anoxic or aerobic zone sizes. Furthermore, oxygen recycled from the aerobic zone can negatively affect the denitrification rate in the anoxic zone (WEF and ASCE 2006). Performance factors include limitations due to the single anoxic zone and the internal recycle rate that returns nitrates to the anoxic zone. Selection factors include the possibility of constructing walls in existing basins to create an anoxic zone; additional pumping, piping, and electricity to accommodate the internal recycle; and the possible need for an additional carbon source to promote denitrification. The modified Ludzack-Ettinger process is illustrated in Figure 2-3.

IFAS systems are hybrids that have attached growth media included in an activated-sludge basin.

Schreiber Process
The patented Schreiber countercurrent aeration process can provide nitrification and denitrification in one basin. The wastewater enters a circular basin equipped with a rotating bridge that provides mixing. Aeration is provided by fine-bubble diffusers attached to the bridge. Should sequencing between aerobic and anoxic conditions be required, the aeration can be turned off while the bridge continues to keep the tank mixed. The system footprint is approximately that of a conventional activated-sludge system but with additional equipment built in. Because it includes alternating aerobic/anoxic conditions in one tank, very low effluent TN concentrations are possible, when optimized. The performance could be further enhanced with additional anoxic zones downstream of the primary reactor. In the standard Schreiber configuration, the need for additional food is typically reduced or eliminated because everything is done in one tank. The Schreiber countercurrent aeration process is illustrated in Figure 2-12. The TN effluent concentrations for the Schreiber process in the literature evaluated as part of this study was 8.0 mg/L (see Table 2-1 in Section 2.5).

The Virginia Initiative process (VIP) is similar to the modified UCT process and is another variation of the Phoredox process. The nitrates from the aerobic zone are returned to the head of the first anoxic zone, instead of the second anoxic zone as is done with the modified UCT process. The second return is from the end of the second anoxic zone to the head of the anaerobic zone. RAS continues to enter the head of the first anoxic zone. The VIP process allows for additional denitrification and thus minimizes the introduction of nitrate to the anaerobic zone. Nitrate in the anaerobic zone would interfere with phosphorus release, and so would reduce the opportunity for subsequent phosphorus uptake in the aerobic zone. The VIP process is operated in a high-rate mode, allowing for small tank volumes, which require less space than other similar processes. This process has a medium-sized footprint and could be set up in existing basins. As with other processes in this section, no additional head is needed, but extensive piping and pumping are needed for the recycle streams. As with the other processes, if sufficient VFAs are present, no supplemental carbon sources are required. Achieving a very low phosphate concentration requires downstream chemical precipitation and filtration. The VIP is illustrated in Figure 2-26. The ranges of TN and phosphorus effluent concentrations found in the literature for the VIP were 3.0 mg/L to 10.0 mg/L in TN and 0.19 mg/L to 5.75 mg/L in TP; for the VIP with VFA addition the ranges were 5.0 mg/L to 10.0 mg/L in TN and 0.6 mg/L to 0.8 mg/L in TP (see Tables 2-1, 2-2, and 2-3 in Section 2.5 for details).

Blue Plains Process
The Blue Plains process was a retrofit to the existing nitrification activated-sludge process at the Washington, DC, facility. A new anoxic zone was created inside the aeration tank with an HRT of 0.8 hour from the nominal 3.3 hours in the total basin. The design sludge age was 13 days. The existing return activated-sludge system remained unchanged in this retrofit. Methanol was fed directly into this new anoxic zone for a target nitrogen concentration of 7.5 mg/L (Kang et al. 1992; Sadick et al. 1998). Phosphorus is removed by ferric chloride addition and tertiary filtration. The Blue Plains process is depicted in Figure 2-29. The TN and TP effluent concentrations found in the literature for the Blue Plains process were 7.5 mg/L in TN and 0.12 mg/L in TP (see Table 2-1 in Section 2.5 for details).

Westbank Process
The Westbank process is a modification of a five-stage Bardenpho, with elimination of both the second anoxic zone and the reaeration zone. The process uses a step-feed arrangement for distributing primary effluent and fermenter supernatant (VFA-enriched) to the anaerobic and anoxic zones, as shown in Figure 2-30. The process consists of a small pre-anoxic zone, followed by an anaerobic zone, an anoxic zone, and an aerobic zone. The pre-anoxic zone minimizes the DO and nitrates entering the anaerobic zone, thereby maximizing the release of phosphorus. RAS is fed to the anoxic zone. Primary effluent is divided between the preanoxic zone (to denitrify the RAS), anaerobic zone (to stimulate phosphorus release), and anoxic zone (to stimulate denitrification). The direct feeding of the primary effluent to the anoxic zone increases the denitrification rate, thereby reducing the required size of the anoxic
zone compared to that in a 5-stage Bardenpho system. The fermenter supernate, ontaining VFAs, is fed directly to the anaerobic zone. An internal recycle at a flow ratio of up to 600 percent directs the nitrates from the aerobic zone to the anoxic zone for denitrification. In the specific case of Kelowna, British Columbia, the effluent from the Westbank process is gravity filtered. The TN and TP effluent concentrations found during the case study period for the Westbank process with filtration ranged from 2.7 mg/L to 5.8 mg/L in TN, with an average of 4.4 mg/L in TN, and were 0.05 mg/L to 1.88 mg/L in TP, with an average of 0.14 mg/L TP (see Tables 2-1 and 2-2 in Section 2.5 for details).

2.5 Full-Scale Nutrient Removal Process Cases
2.5.1 Nitrogen Removal Matrix and Variability Data
The variability or reliability of nitrogen control technologies is summarized in Table 2-1. For plants for which a full year of daily nitrogen removal data were obtained, a statistical summary is presented for the annual average, maximum month, maximum week, and maximum day. These correspond to the points at 50, 92, 98, and 99.7 percent, respectively, when plotted on probability paper (based on the number of data points). This summary is the first known in the literature to compare full-scale technologies on an equal basis. Monthly, weekly, and daily maximums may be set by regulatory authorities for facilities that discharge to particularly sensitive waters. If TN effluent data were collected weekly because that was all that the permit required, the daily maximum value was not available. The performance levels shown from reported sources are documented in descending order for the technologies reported. It should be emphasized that, for this table as well as Tables 2-5 and 2-8, the performance results reflect specific operating philosophy, permit limitations, temperature, influent conditions, flow conditions, and the relative plant load compared to design. Thus, they do not necessarily represent optimum operation of the technologies presented. Most of the selected periods appeared to be typical; however, climate and weather variations could significantly affect performance. Similarly, the performance results reflected in the curves in Figures 2-31, 2-33, 2-34, 2-35, and 2-36 reflect site-specfic situations and do not necessarily represent optimum operation of the technologies.

各种变化的、可靠的脱氮控制技术，总结在表2-1。对于那些每天脱氮的数据，全年分别获得的统计结果，是提出了全年的平均，最大个月，最长一周植物，最高一天。这些对应点50，92，98和百分之99.7，分别在文件上概率的数据点数目为基础（绘制）。这是总结在文献中已知的第一个比较平等的基础上的全面技术。每月，每周，每天的最大值可以设置由监管当局设施，排放要特别敏感的水域。如果总氮污水收集资料，因为这是每周所有的许可证规定，每日最高值是不可用。 Ŧ

The annual average and the maximum month concentrations, respectively, are shown for each facility:
1 = Denitrifying activated sludge: 1.63 mg/L and 2.46 mg/L with a COV of 36 percent at Western Branch, Maryland
2 = 5-stage Bardenpho: 2.04 mg/L and 3.10 mg/L with a COV of 42 percent at the Clearwater, Florida, northeast plant
3 = Denitrification filter: 2.14 mg/L and 2.77 mg/L with a COV of 16 percent at the Central Johnston County, North Carolina, plant
4= Denitrification filter: 1.71 mg/L and 2.61 mg/L with a COV of 28 percent at the Lee County, Florida, plant
5 = 5-stage Bardenpho: 2.32 mg/L and 3.1 mg/L with a COV of 16 percent at the Clearwater, Florida, Marshall Street plant
6 = Step-feed activated sludge (AS): 2.58 mg/L and 4.30 mg/L with a COV of 57 percent at the Piscataway, Maryland, plant
7 = Concentric oxidation ditch with internal recycle: 3.0 mg/L and 4.24 mg/L with a COV of 32 percent at the Hammonton, New Jersey, plant

年平均每月的最高浓度，分别是显示每个设施：
1 =反硝化活性污泥：有百分之36的COV在西方科，马里兰1.63毫克/升和2.46毫克/升
2 = 5级Bardenpho：2.04毫克以百分之42的COV / L和3.10毫克/升的清水，佛罗里达州，东北植物
3 =脱氮过滤器：有百分之16的COV 2.14毫克/升和2.77毫克/升在中央约翰斯顿县，北卡罗莱纳州工厂
4 =脱氮过滤器：有百分之28的COV 1.71毫克/升和2.61毫克/升利县，佛罗里达，植物
5 = 5级Bardenpho：2.32 mg / L和3.1毫克/ L的百分之16的COV在佛罗里达州Clearwater，马歇尔街厂
6 =步饲料活性污泥（AS）的：2.58毫克以百分之57的COV / L和4.30毫克/升的皮斯卡塔韦，
7 =同心内部循环氧化沟：3.0毫克/升和32百分之的COV 4.24毫克/升的哈蒙顿，新泽西州，植物氧化沟
Western Branch, Maryland
This facility employs a unique denitrifying activated-sludge stage following two upstream activated-sludge stages, making a three-stage system overall. Methanol is fed upstream of the denitrifying stage. The annual average effluent concentration was 2.52 mg/L, with COV of 36 percent.
这一设施采用了独特的反硝化以下两个上游活性污泥阶段活性污泥阶段，作出了三个阶段的系统的整体。甲醇是注入到上游反硝化阶段。当百分之36的变化系数时，TN出水浓度年平均为2.52毫克/ L。