Sustainable Odor Control at the Hyperion Water Reclamation Plant

Abstract
In 2014, the City of Los Angeles Bureau of Engineering and LA Sanitation began the development of two projects to not only eliminate odors at and around the Hyperion Water Reclamation Plant (HWRP), but do so without the conventional use of caustic chemicals. The two projects accomplished this through the use of biological treatment technologies to remove contaminants of concern, primarily Hydrogen Sulfide gas (H2S), ammonia and volatile organic compounds (VOCs). The projects had to be developed around many constraints and meet or exceed H2S removal requirements set forth by the California Air Quality Management District -- specifically maintaining effluent air stream concentration of H2S under 1 ppm. The new systems will achieve greater than 99% removal efficiency by the use of a Biotrickling Filter (BTF) system and a second activated carbon polishing stage, effectively eliminating the use of caustic chemicals. The HWRP is one of the largest water reclamation plants on the west coast of the United States with average treatment of over 275 million gallons per day . The plant currently uses chemical scrubbers to treat foul air, requiring the use of sodium hydroxide, sodium hypochlorite, and considerable quantities of fresh water on a continuous basis. The use of chemicals and fresh water is a costly operational expense for the HWRP. The use of BTFs for odor control at the HWRP will significantly reduce the need to transport and use the aforementioned costly hazardous chemicals, as BTFs only require the use of non-potable water sources and trace nutrient compounds to sustainably operate. In addition to savings on chemicals and freshwater, the biological treatment of foul air also presents other cost savings from reduced maintenance (for example, no acid washing of air handling vessels) and improved safety by eliminating the risk of exposure to caustic scrubbing chemicals. The Biotrickling filter utilizes bacteria to break down odorous compounds in the wastewater treatment process airstream, but is just one unit process in a series. Foul air is first collected and passed through a degreaser. It then enters the BTF where it is scrubbed via induced flow through engineered plastic mesh media impregnated with biofilms. The foul air interfaces with the biofilm and microorganisms oxidize the H2S to generate energy for growth and reproduction. The sulfuric acid byproduct lowers the pH of the system. For optimal conditions, pH must be maintained between 1.5 - 2. Thus, a pH meter is installed and used as a process set point, and interlocked with a make-up water system to maintain a constant pH. Further presentation of the projects will detail the use of process automation to remotely monitor and control the system. Nutrients required for microbial growth in the BTF are delivered through recirculating water piping and spray nozzles to maintain moisture and nutrient levels for bacterial growth. A two-level water distribution system is installed with an option to use the top layer for VOC removal. Once the foul air is treated in the BTF, it is piped to carbon adsorber vessels for polishing and then exhausted to the atmosphere as treated air. The carbon adsorber vessels can also be used as a backup means of odor control for planned maintenance of the BTFs, in order to ensure continued odor control. Several constraints in the implementation of the new facilities were considered in the design and construction. The BTFs microorganisms require time to fully establish and reach maximum treatment capacity. During this initial growth period, the carbon scrubber, which in normal operation is a polishing step, is utilized as the primary form of treatment to maintain AQMD-permitted requirements. The HWRP operates 24 hours a day and thus, during construction, the existing chemical scrubbers were kept online to treat the air until the new facility became operational. A detailed presentation of the projects will discuss at length how the projects were designed to manage the constraints of available footprint, continued AQMD permit compliance during construction and startup, and maintenance considerations. Although these projects have a significant initial capital cost, the complete life cycle costs of four alternative solutions for these projects were analyzed and the most efficient alternative, with the lowest relative lifecycle cost was chosen. These projects, once completed, will eliminate the use of caustic chemicals for treating foul air at the Plant, thus providing a safer work environment to the HWRP maintenance and operations staff. The Headworks Odor Control Upgrades and the IPS Odor Control Upgrades are the two projects currently implementing the use of BTF for odor control at HWRP, with a combined odorous air handling capacity of over 100,000 standard cubic feet per minute. The ultimate vision for Hyperion is to treat 100% of odors generated at the plant using similar means. Upon the successful completion of these two projects, another series of systems will be designed and constructed for the treatment of additional odor sources, amounting to the entirety of the HWRP's primary wastewater treatment process. This will complete the conversion of the HWRP's odor control infrastructure to a more sustainable and environmentally conscious process. The City of Los Angeles' LA Sanitation (LASAN) is the owner/ operator of the Hyperion Water Reclamation Plant. LASAN developed the concept reports supporting the aforementioned projects while the City of Los Angeles, Bureau of Engineering, Environmental Engineering Division (EED) currently leads the preliminary design, design, procurement, construction and commissioning efforts. Once the projects are completed, they are turned over to LASAN to operate and maintain. A detailed presentation of the above HWRP BTF facilities will discuss in detail several aspects of the projects, including but not limited to: the cost-benefit analysis that demonstrates the lifecycle costs and capital recovery time, removal efficiency for criteria pollutants, day-to-day operations and systems for remote monitoring and control, the design constraints including how to meet AQMD standards throughout the construction and startup of the new facility.