WASTEWATER ODOR CONTROL USING ADVANCED DOSING CONTROLLER IN SANTA CRUZ, CALIFORNIA

The County of Santa Cruz, like most metropolitan areas, centralized its sewage treatment systems in the late 1970's. Four small, local sewage plants were combined into one large regional plant at the City of Santa Cruz. At face value this was a good idea, allowing the County to centralize its sewage treatment at one site and minimizing the required number of operators required and maximizing treatment plant efficiencies. In reality, the negatives appear to have outweighed the positives. That is, the result is many miles of sewage force mains connected to very large and complex pretreatment systems, most often called pump stations. Each one of these pump stations has to include, along with their large pumping and control systems, additional liquid and/or gas phase odor control systems to mitigate the low dissolved oxygen condition that results in decentralizing a regions sewer infrastructure. In effect, creating a long, dynamic septic system. After analyzing a number of options, the County of Santa Cruz has set up a unique liquid and gaseous phase odor and corrosion control system. A number of pump stations dose Bioxide®, an oxygen containing nitrate compound from outlying points in the County to assure two things: 1. Existing force mains do not degrade due to H2S and Sulfuric Acid attach and 2. The sewage does not become septic, causing noxious odors and gases. The final and main pump station provides the majority of liquid product to protect the City Wastewater Treatment Plant. To accomplish this last goal, a “Dosing Controller” provided by the odor control vendor (USFilter Davis Products) has the ability to control dosing pumps to optimize the amount of liquid product being used. Results of this process are continuously monitored downstream at the City Plant by a dissolved sulfide liquid analyzer. This paper provides a description of the Dosing Controller technology used and provides case history data from the Santa Cruz application showing improved treatment and/or lower cost treatment through the use of this technology.Required application rates of Santa Cruz odor control product (Bioxide®) typically vary with changes in wastewater flow rate, temperature, and system usage. Conventional technology attempts to model these changes and adjust application rates via timers and/or seasonal adjustments. The Dosing Controller discussed in this paper provides real-time control of application rates by monitoring these parameters and controlling the product dosing dynamically based on the ever-changing conditions. The downstream dissolved sulfide analyzer is used to continually monitor the results of the dynamic dosing model. This advanced control eliminates the feeding of excess product during rain events or fluctuations in temperature.The Dosing Controller is also designed to be a data logger which, in conjunction with a modem, allows for easy downloading from any location. Parameters within the Controller can be changed via modem as well. The controller also allows for serial port communication directly to an external computer. Remote access is also possible to the downstream sulfide analyzer via modem. Data from the analyzer is polled and compared to the dosing curve from the Dosing Controller for fine-tuning of the odor controlling process.By utilizing this technology, downstream operational problems are eliminated and odor control costs are reduced by optimizing the product dosing. A detailed review of the Santa Cruz wastewater collection system and treatment plant results using the advanced Dosing Controllers is presented in the paper.