The filter bed of the MEL-BF meets the standards and guidelines for slow sand filters, in EVERY known regulatory jurisdiction, before and after cleaning using the backwash procedure. In most jurisdictions freshly cleaned traditional slow sand filters (scraped filters) are put back into production after a filter-to-waste procedure (after the turbidity of the filtered water is less than 1 NTU). This filter-to-waste procedure is identical to that recommended when using the MEL-BF when cleaned using a backwash procedure. After backwashing the MEL-BF meets ALL the specifications for a slow sand filter as stated in AWWA Guidelines.
In cold regions the media bed of slow sand filters will become air bound. Cleaning using scraping or harrowing will not eliminate the problem. It is necessary to degas the media bed using a backwash procedure (at the minimum a reverse flow that does not fluidize the media) using filtered unchlorinated water to eliminate the trapped gases. Any disturbance of the filter bed, including a degassing procedure, will require a filter-to-waste procedure.
Demand operation of slow sand filters has been thoroughly evaluated and proven not to degrade filter ability to remove pathogens. The obvious advantage of demand operation is the elimination of the need to operate a slow sand filter once treated water storage is full and production is wasted. However, the use of the MEL-BF technology does not require use of demand operation. MEL-BFs may be operated in exactly the same manner as traditional slow sand filtration.
Practical use of slow sand filtration is limited by the concentration of suspended solids in the water being treated and the method used to clean the filter. Traditional slow sand filters are limited to treating water with very low concentration of suspended solids (turbidity less than 20 NTU and preferably less than 5 NTU). MEL-BFs cleaned using a backwash procedure may treat water with significant concentration of suspended solids (greater than 5 mg/L) with application limited only by the practical considerations associated with frequency of cleaning. It is recommended that pilot studies be conducted to determine the effectiveness and practicality of the technology if the application seems extreme.
Similar to MEL-PF, MEL-BF performance may be enhanced if water is pre treated with coagulants and cleaned using backwash (subject to pilot testing and regulatory approval).