A city in the midwestern United States needed a new groundwater treatment system to replace an aging system that relied on reverse osmosis (RO) to remove radium, a primary drinking water contaminant. This project used a design-build, collaborative delivery approach, and Tonka Water, a Kurita brand, partnered with a consulting engineer and a local contractor to help design a high-efficiency system that met the city’s needs. An integrated system using hydrous manganese oxide (HMO) technology was ultimately selected after evaluations showed benefits on waste volume, life cycle cost, and operation and maintenance (O&M) burden. Tonka Water also provided a packed aerator, horizontal pressure filter, RO membrane system, and full plant controls for the new system.
Treatment begins at the packed aerator to remove hydrogen sulfide (H2S), which imparts a “rotten egg” smell to water. H2S also reacts readily with large amounts of chlorine, a common treatment chemical used for oxidation and disinfection. In the aerator, water is sprayed over a depth of loose-fill packing and flows downward as air is blown through the unit. Concentration gradients drive the mass transfer of dissolved gases, like H2S, across the water’s surface. As H2S leaves the water, oxygen dissolves into the water and causes natural oxidation of iron. Water flows by gravity into a detention tank, where any remaining dissolved sulfur compounds and iron are oxidized with chlorine to form precipitated solids that will be removed by the downstream media filter. The natural aeration/degasification process decreases the amount of treatment chemicals required to operate the system.
Following detention, HMO is fed for the treatment of radium. HMO consists of suspended manganese oxide particles, which are large enough to be removed by conventional media filtration. Because manganese oxide has a high affinity for radium adsorption, radium affixes to the HMO and is removed in the subsequent media filter along with any iron and sulfur particles.
Media filtration is implemented in a horizontal pressure filter with isolated cells. The filter cells are completely separated from one another above and below the underdrain with the ability to take one or more off-line while the others remain in service. This means that the system operates identically to one of multiple vertical pressure filters, providing redundancy and operator flexibility within a single vessel, minimizing system footprint.
The media filter uses Kurita America’s IMAR™ media to minimize radium accumulation within the vessel. IMAR™ has a relatively low affinity for radium adsorption, so radium stays attached to the HMO solids and is purged from the filter during the backwash process. Accumulation is minimized further with Kurita America’s Simul-Wash™ back method, which uses air and water simultaneously to maximize media cleansing while using half the water of conventional backwash methods.
The final treatment step uses a reverse osmosis (RO) membrane system to lower hardness and total dissolved solids (TDS) in the finished water. The RO process removes nearly all hardness and TDS, which is more than necessary and generally undesirable for drinking water. For this reason, only a smaller flow of water is treated through RO, and some water is bypassed around the RO system to blend with the permeate and create a desirable concentration. Blending also reduces the size of the RO system, saving money on capital and operational costs; however, the previous system’s ability to blend was limited to ensure that the RO system removed enough radium to meet safe drinking water needs. The new treatment system removes radium during the media filtration step, prior to RO, which allowed for a smaller RO system designed specifically for meeting the goals around hardness and TDS.
Tonka Water, a Kurita brand, delivered a robust drinking water treatment solution with guaranteed performance from raw source to finished water. The collaborative delivery approach ensured that the city’s new system was customized to their specific needs using integrated treatment equipment from a single responsible manufacturer. This resulted in an optimized solution that reduces costs, increases efficiency, and minimizes waste.
Org. 2017/ Rev. November 2022