Approximately 35% of public-supply water withdrawals come from groundwater sources. One of the most common issues that water plants encounter when it comes to groundwater treatment is the removal of contaminants, including iron and manganese.
Iron and manganese aren’t considered hazardous; they fall under the EPA’s Secondary Maximum Contaminant Level (SMCL) standards. The downsides of having significant amounts of iron and manganese in drinking water are a strong metallic taste to the water, and staining once the water is exposed to oxygen.
In addition, plant equipment can be affected by a buildup of iron and manganese deposits, which can lead to reduced water quality. In public water systems, these contaminants can react to produce other substances that clog pipes and distribution lines.
Treatment Options for Removing Iron and Manganese
As with most water treatment challenges, there are several different approaches to address this issue.
One option is cation exchange. Using conventional softening resins for iron and manganese removal can be effective for treating low levels of dissolved iron. But it is not ideal for high flows or higher concentrations of iron and manganese that can inhibit the resin and cause more frequent regenerations and increase waste production.
Another method is the two-step process of oxidation-filtration, which first uses oxygen, chlorine, or potassium permanganate to oxidize and precipitate the iron and manganese. The second step is to filter the water to remove the precipitated particulates.
One challenge of the oxidation filtration approach is that if iron concentrations are high, the filter media will require more frequent back washing, which impacts the plant’s productivity.
Packaged Groundwater Treatment System Combines Aeration, Detention, and Filtration
One approach that has proven to be particularly effective for a number of municipalities is a packaged groundwater treatment system that combines aeration, detention, and filtration to remove iron and manganese.
WesTech has worked with more than 500 plants to install AERALATER® water treatment aeration systems to dramatically improve the cities’ drinking water quality. The packaged system uses a draft aerator to saturate the raw water with oxygen, a detention tank to precipitate manganese, and a filter below to capture the precipitated solids. These three processes are stacked one atop the other.
Here’s how it works:
The raw water is introduced in the top of the aerator and distributed evenly using a distributor tray. (See image.)
Target nozzles spray the water across the top of the media, eliminating the need for high-pressure spray nozzles and thereby reducing overall operating cost.
A blower moves the atmospheric air through a screened opening designed to allow air flow with minimal pressure drop. The bottom of the aerator is open to the detention tank.
A chemical oxidant is added and mixed into the influent flow prior to the detention section using the static mixer located under the aerator.
The water spends a minimum of 30 minutes in the detention tank, prior to the filter media, to allow adequate time for the oxidation and precipitation of iron.
The water from the detention section then flows through a set of integral face piping and into a four-cell filtration system. The filter uses 24 inches of treated 0.6 mm to 0.8 mm anthracite media, which removes the precipitated iron and manganese.
Filter backwashing is accomplished by closing the system effluent valve, then closing the inlet valve followed by opening the backwash waste valve for the filter cell to be backwashed.
Pressure from the water level on the detention tank forces water through the three remaining filter cells that are in service and into the common underdrain.
The treated water flows up through the filter cell being backwashed, where the backwash water is collected in an over-drain and flows out the backwash waste valve to waste.
The remaining cells are backwashed in sequence until all have been backwashed, then the entire system then is brought back into service.
Advantages and Success Stories
This approach eliminates the need for backwash supply pumps and tanks, or to bring system water back for backwashing, due to the backwash sequence that uses in-service filter cells.
In addition, the AERALATER’s filter media (Manganese ANTHRA/SAND) is more cost effective than manganese greensand, while still offering the same manganese removal capacity.
Finally, because the unit is manufactured in three primary sections (aeration, detention/filtration, filter face piping), the installation consists only of attaching the aerator section, attaching the face piping and valves, installing the filter media, and hooking up the power to the aerator blower. This minimizes the overall installation cost and reduces time spent on installation.
Recently, several city water treatment plants in states including Georgia, Iowa, and New York have gone on record to talk about their successful AERALATER installations.
When the Village of Bolivar, New York, needed to build a new water treatment plant to meet water quality requirements, they chose the combined aeration, detention, and filtration system due to its cost-effectiveness, ease of use, and low maintenance.
In Grand Junction, Iowa, the water treatment plant had been struggling to maintain a vertical pressure filtration system from the 1930s. When they decided to build a new plant, the requirements included efficient operation and minimal maintenance. The AERALATER fit neatly into those requirements and offered much improved iron reduction.
These examples show that combined aeration, detention, and filtration systems can offer efficient removal of iron, manganese, and other groundwater contaminants, as well as being low maintenance and cost-effective. These aspects make this type of system worth considering for drinking water treatment plants looking to reduce iron and manganese levels from groundwater sources.