Comparison of Ammonia and DO Aeration Control Strategies to Optimize Energy and Performance at Low Capital Cost: A Case Study
Wastewater treatment is an inherently energy-intensive process. Estimates of the energyrnconsumption on a national scale have placed municipal water and wastewater treatment at asrnhigh as 5% of the national energy consumption. Furthermore, the rising costs of energy presentrnan ever-increasing burden to each facility. In order to minimize the cost of energy, facilities havernaimed to improve the efficiency of the most energy intensive processes. Energy auditsrnperformed by the authors at over 24 municipal wastewater treatment facilities in the Midwestrnhave indicated that aeration systems can represent as much as 76% of a facility’s energy bill.rnWith permitted ammonia limits tightening, the cost of treatment is increasing. Thus, reducing thernpower required in the aeration process can produce significant energy savings for a treatmentrnfacility.rnAeration systems are composed of three major parts: blowers, diffusers, and controls. An idealrnaeration system matches the oxygen provided to the system with the real-time oxygen demand ofrnthe process. Utilities have realized significant savings by installing high-efficiency blowers andrndiffusers. However, equally significant savings can be realized by improving process controls.rnThe system that controls the process can be responsible for reducing energy consumption by asrnmuch as 30% or more in the aeration system at low- to no-capital cost to the utility. Thernobjective of this study is to determine the most operationally-effective and energy-efficientrncontrol strategy for aeration in activated sludge systems.rnCurrently, most aeration systems that use real-time control are based on dissolved oxygen (D.O.)rnmeasurements in the aeration tanks. However, as technology is improving for instrumentation,rnnew control strategies are being developed that optimize system performance and minimizernpower consumption. Of particular interest in this study is the use of predictive parameters thatrnwould allow control based on influent wastewater quality as opposed to the often slow-to-reactrnD.O. parameter. While at the time of writing, the development of in-line BOD probes is notrncomplete, real-time probes for measuring other parameters, such as ammonia, are ready forrnintegration.rnDue to the comparatively slow metabolic rates of ammonia oxidizing bacteria (AOB) versusrnorganic oxidizing bacteria, the latter outcompete AOBs. Ammonia is oxidized only when thernBOD/COD load has been mostly consumed. The residual D.O. in tanks is indicative of thernexcess oxygen provided, and therefore considered a responsive parameter. If ammonia, on thernother hand, is used to control airflow to the process, theoretically the absolute minimum oxygenrncan be provided while achieving process requirements and presumably resulting in lower oxygenrnsupplied than would be used from a typical D.O. control strategy.rnBlower power is proportional to airflow and also related to pressure and site conditions ofrnoperation. Wheaton Sanitary District in Wheaton, Illinois operates a single-stage nitrificationrnactivated sludge system comprised of five equally-sized aeration tanks running in parallel with arnnormally equal upstream flow split. Given that the operating pressure and site conditions of thisrnsystem are equal for each tank, the airflow to each tank can be used to estimate the relativernpower consumption of that tank. A common baseline was established using the design actualrnoxygen requirement (AOR) of the system. The AOR corresponds to the blower design point andrntherefore the blower output in a system with no blower control. In this study, full-scale controlrnstrategies were tested in the activated sludge system to judge the relative treatment efficiency andrnprocess stability as compared to the baseline, including the following:rn1.? Control of airflow to the tank based on a fixed airflow setpoint (previous mode ofrnoperation);rn2.? Control of airflow to the tank based on D.O. as measured at the downstream end of therntank, to maintain a D.O. setpoint of 2 mg/L;rn3.? Control of airflow to the tank based on upstream ammonia measurements such that therninfluent ammonia is used to predict the actual airflow required for oxidizing bothrnorganics as well as ammonia.rnThe study demonstrated that while fixed airflow and D.O. control modes offer energy savings asrncompared to no control, neither allows the system to respond in time to dynamic loads.rnAmmonia feed-forward control, on the other hand, resulted in 17% energy savings compared tornthe baseline or 11% energy savings compared to D.O. control. The ammonia feed-forwardrnsystem also responds faster to changes in process loadings, which can allow for tightened controlrnof aeration zones for BNR processes. As compared to other control strategies, ammonia feedforwardrnis the only one to balance both energy savings and process reliability.rnBy establishing a common baseline, the relative savings among control strategies can be used tornestimate energy savings at other facilities for funding opportunities or to justify the purchase ofrninstrumentation based on payback periods.......
【作者名称】: Amanda L. Poole
, Jason Neighbors
, David J. Green
, Sue E. Baert
, Christopher T.Sosnowski
, Derek J. Wold
【作者单位】: Baxter & Woodman, Inc. Email: firstname.lastname@example.org.
, Wheaton Sanitary District
, B&W Control Systems Integration, LLC.
, Wheaton Sanitary District
, B&W Control Systems Integration, LLC.
, Baxter & Woodman, Inc.
【关 键 词】: Energy efficiency
, wastewater treatment
, activated sludge
, feed-forward control
【会议名称】: 85th annual Water Environment Federation technical exhibition and conference
【会议地点】: New Orleans, LA(US)
【会议组织】: Baxter & Woodman, Inc. Email: email@example.com.;Wheaton Sanitary District;B&W Control Systems Integration, LLC.;Wheaton Sanitary District;B&W Control Systems Integration, LLC.;Baxter & Woodman, Inc.;
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