The Complete Guide To Septic Tank Filters
Filters play an essential role in the treatment of wastewater from septic tank systems. Commonly used filtration media include sand and gravel, but there are a variety of alternative materials such as recycled glass, textiles, synthetic foam, peat, and more that can be used for improved solids removal and enhanced treatment. Traditional filters work by removing suspended solids mechanically through straining or sedimentation and require aerobic conditions to work efficiently. Alternate media filters often operate similarly, with the added benefit of potentially doubling the loading rate achieved with traditional sand filters. Additionally, they usually only allow wastewater to pass through them once before being discharged.
Applications
Alternate media filters are a relatively new technology in the realm of wastewater treatment and filtration. They offer an alternative to traditional septic tank drainfields, which typically consist of multiple trenches filled with gravel and perforated plastic piping. Alternate filter media provides several benefits, such as higher loading rates, less space for installation, and the use of easier-to-obtain materials. For example, the Waterloo biofilter medium is composed of absorbent plastic foam cubes, which permits a much higher loading rate than conventional sand filters! These filters can be used in lots with size constraints or in areas where water tables or bedrock limit the depth of a drainfield. Additionally, because alternate media filters perform more successfully than traditional gravel drainfields and sand filters, many states now offer a sizing reduction allowance for these units when installing them.
Peat
Peat is an absorbent, porous material widely used to filter wastewater onsite. In the Northeast and other places where peat is abundant, research has been carried out to measure its filtering capabilities. It can remove up to 90% of BOD5, but with variations in composition depending on the natural source. To protect against these variations, manufacturers usually enclose the peat inside a fiberglass housing. Long-term data on its filtration efficacy has yet to be established, though.
Textile
Textiles are increasingly being used as an effective technique for wastewater treatment. Textile chips, sometimes referred to as “coupons,” are placed in a filter housing similar to a sand filter, and wastewater is applied by spraying it at the top. The standard loading rate of this technique is 400 liters/square meter/day (10 gallons/square foot/day). However, with certain modifications, the loading rate can be increased up to 600 liters/square meter/day (15 gallons/square foot/day). This technique produces excellent results, surpassing even those from advanced treatment standards.
Foam
Foam cube filters are an efficient and effective way to filter wastewater. The filter cube can be housed in a container as large as 1.8 meters by 1.8 meters by 1.5 meters, with 1.2 meters of media inside, or it can be placed in pre-assembled cylinders in a tank. This type of filter has been tested at 10 times the loading rate of other intermittent sand filters and can be used for wastewater treatment with great success.
Crushed Glass
The City of Roslyn, Washington, conducted a pilot project to determine the suitability of crushed recycled glass as a filtration medium in slow sand filters. A 38 cm (15 in) PVC pipe was used to contain the media, which included three types of sand and crushed glass. The media was washed and had no more than 0.10% passing a #200 mesh sieve. Wastewater was added to the filter at a rate of 0.002 m^3/min/m^2 (0.06 gal/min/sqft). Bacteriological contaminants were removed from the filter, showing that it operated like a conventional slow-rate sand filter. It is suggested that such filters would be effective for treating water sources in Roslyn, but their efficacy for other geographical areas has not been determined yet.
Advantages
Alternate media filters offer many advantages over traditional sand filters, including minimal operating costs, low energy usage, and easy maintenance. Additionally, the alternative media can provide an increased surface area, which allows for higher loading rates and better effluent quality. The stability of the filter also requires little intervention from operators. Finally, this type of filter may be a suitable option for degraded or failed septic systems if it can operate efficiently over extended periods of time.
Disadvantages
Alternate media filters may not be the most reliable option for treating septic tank effluent, as there is no long-term operating data available for crushed glass and textile media. These systems also tend to be more costly to run and maintain, and odors from open, single-pass filters may be problematic. The filter media can vary greatly from supplier to supplier or batch to batch and require additional monitoring cost. Furthermore, the performance track record of alternate filter media is not as established as that of conventional sand filters. Frequent inspection and monitoring are also necessary to ensure the proper functioning of filtration units. Ultimately, filters using alternate media have yet to demonstrate consistent results in real-world settings.
Performance
Performance evaluations of alternative filtration systems made of peat, crushed glass, and textile media are lacking in terms of long-term efficacy. The results of experiments, on the other hand, suggest that these alternative filter materials are better at cleaning water than traditional sand filters when higher loading rates are used.
Operations and Maintenance
When it comes to Operation and Maintenance (O&M) tasks such as alternate media filtering, filter surface maintenance, monitoring of both influent and effluent, and servicing of dosing equipment are all necessary. Overuse may cause clogging on the filter’s surface, which may lead to the filter being taken offline for rest or for media removal and replacement. On the other hand, buried filters can operate without O&M for their designed lives. Additionally, filters exposed to sunlight may experience algae mats, which can be controlled through shading. If used by community systems, disinfection is required prior to discharge; however, disinfectant quantity will be low due to the effluent’s efficiency.
Cost
The cost of alternate filter media used in wastewater treatment systems is largely dependent on location and availability. For example, peat moss is much more readily available and cheaper in certain areas, such as Maine, Minnesota, and Wisconsin, than it is elsewhere. Additionally, the amount of media needed can range from 10 to 20 cubic yards of crushed glass per installation, or 30 bags of peat weighing 30 pounds each. Factors like transportation costs are also important to weigh when calculating the overall cost of adopting an alternate filter media solution.
