The trickling filter is a technology that can generally be described as the “trickling” of liquid over a media to achieve treatment. The media can be a wide variety of materials ranging from pieces of cylindrical plastic to stones or foam blocks. The technology can be used to provide a final “polish” to the effluent, or it can be the intermediate step in an overall process. As applied to onsite septic systems, trickling filters receive septic tank effluent. As the effluent passes or trickles over the media, available oxygen (as these systems are usually well ventilated to supply fresh air), is used by nitrifying bacteria to convert the ammonia in the effluent to nitrate and the BOD is reduced. After passing over the filter media, the effluent is sometimes discharged to the soil absorption system or leaching facility. If denitrification is desired, a portion of the filtrate is recycled back to an anaerobic chamber such as the septic tank. It should also be noted that, in many cases, the growth on the filter media thickens to the point where there are some anaerobic microzones in the media in which denitrification can take place.
If you haven’t seen the parallel already, review the chapter on recirculating sand filters. Can you see that the RSF is really a trickling filter? The difference is that media in trickling filters generally is much more open (contains relatively large pore spaces compared with the sand filter), and the residence time in the media is comparatively shorter than a sand filter.
In this chapter, we discuss three trickling filters, the Ekofinn Bioclere (which is the most popular in Massachusetts due to its approval status), the Waterloo Biofilter, and the Orenco Trickle Filter. These latter two are being variously tested in demonstration projects in Barnstable County.
Ekofinn Bioclere
Figure 1. The Ekofinn Bioclere unit in relation to septic system components.
The Bioclere is a modified trickling filter which utilizes a stable fixed film process for simultaneous nitrification/denitrification. The unit can also be designed to incorporate recirculation of wastewater to the anaerobic zone in the septic tank for more complete denitrification. The Bioclere unit is purchased as a module which is installed in the ground between the septic tank and the leach field. The placement of the Bioclere unit in relation to other system components is illustrated in Figure 1. The unit itself is illustrated in Figure 2.
The treatment process is as follows: wastewater first flows to a conventional septic tank where primary settling occurs. Effluent from the septic tank then passes to the Bioclere unit and is received in the baffled sump portion of the Bioclere. A dosing pump distributes this effluent up and over a synthetic media bed at varying recirculation rates. Oxygen is introduced to the media chamber through the use of a small fan. Nitrifying bacteria form a biomass in the aerobic environment of the media bed and this is the site of nitrification. As the biomass thickens, it forms anoxic and anaerobic zones which establishes the conditions for simultaneous denitrification. Approximately 20% of the total nitrogen can be lost through this process. After flowing over the media bed, wastewater returns to the sump portion and is further recirculated over the media. In systems designed for more complete denitrification, a portion of the water in the sump can also be shunted back to the septic tank through the use of a second pump located in the sump portion of the Bioclere. Recirculation of effluent to the septic tank where anaerobic conditions and high nutrient levels prevail allows efficient and more complete denitrification to occur.
Figure 2. Schematic representation of the Bioclere unit.
DEP, in its Provisional Approval for the Ekofinn Bioclere unit, recognizes that the unit is capable of producing finished effluent with total nitrogen content of 19 mg N/L. The Bioclere unit is also capable of 90-95% removal of BOD and total suspended solids and meets or exceeds secondary treatment standards for these parameters. BOD and total suspended solids in finished effluent are both consistently less than 30 mg/L. National Sanitation Foundation testing data show that the unit also appears capable of 1-log reductions in both total and fecal coliform.
When designed for full denitrification, the unit operates with two pumps, a fan, and a timer. Routine operation and maintenance by a qualified technician is necessary. The septic tank must also be pumped at normal 2-3 year intervals. DEP requires that all Bioclere systems be under a maintenance agreement and that a Massachusetts Certified Wastewater Operator will be responsible to oversee operation of the system. AWT Engineering Inc., the distributors of the Bioclere system, will provide a contract for operation and maintenance. DEP also requires that influent and effluent from the system be monitored monthly for the first six months and quarterly thereafter for the following parameters: pH, BOD, TSS, TKN, nitrate and ammonia.
The cost of a residential Bioclere unit, which can treat up to 1000 gpd, is approximately $4600.00. The system also requires a septic tank; a precast concrete 1500 gallon tank costs approximately $1000. There are also additional labor costs for installation of the unit and the cost of a conventional Title 5 leaching field. For the installation “credits” as of June, 1997, see the chapter on DEP Approval Process for Alternative Onsite Septic Systems. The system is becoming increasingly popular in Barnstable County.
The state of Massachusetts recognizes use of Bioclere systems for flows from a single residence to 10,000 gpd with varying strengths of wastewater. Installations include schools, nursing homes, supermarkets, health clubs and restaurants. A number of Bioclere units have been installed on Cape Cod in the towns of Yarmouth, Falmouth, Dennis, Harwich, and Chatham. (Issue 3 of this newsletter provides a review of many of these systems). Health Agents in these towns may be contacted for information on how these systems are performing.
AWT Environmental Inc., BOX 50120, 214 Duchaine Blvd., New Bedford, MA. 02745, (508) 998-7577, are the distributors of the Bioclere in Massachusetts. Mark Lubbers is the contact person.
Waterloo Biofilter
Figure 3. Waterloo Biofilter in standard application.
For many of you history buffs, Waterloo is that Belgian city where Napoleon finally took his hand out of his jacket and was defeated in 1815 (or was it 1816?). But to alternative septic system aficionados, “Waterloo” references the University of Waterloo in Ontario where researchers have been developing some interesting designs for treating septic wastes. One such design is the Waterloo Biofilter. The filter is basically a box filled with foam-block media. Yes, foam blocks, approximately 2″x2″! The septic tank effluent is distributed over the top of a 6′ square by 4′ high bed of these blocks to encourage the highly aerobic breakdown of the wastes. Increased ventilation of the system is achieved by using a small fan to draw air through the unit. The high surface area of the foam bed has achieved impressive results in Gloucester and other areas. The schematic for this system is shown in Figure 3. Pretty simple eh?
Figure 4. Waterloo Biofilter configured for denitrification.
To give you an idea of the performance, the table on the next page was compiled from data sent to us from Anish Jantrania, the Engineering Consultant up in Gloucester and are for their unit from January – March, 1995. What about nitrogen and the Waterloo ? As you can see, the nitrogen removal in the biofilter as it was configured is not terribly impressive. However Gloucester changed the piping this spring to divert some of the flow from the biofilter back to the septic tank, where anaerobic conditions might enhance the denitrification process. Figure 4 shows the configuration of two Waterloo units (one in the Waquoit Bay Demonstration Project, and another in the Wellfleet Harbor Demonstration Project) configured specifically for nitrogen reduction. Results from this modification will be presented in upcoming newsletters. Another exciting prospect for this filter is the development of a phosphorus removal module. Our department may be installing and testing this unit in the coming year under a DEP grant. Costs ? We are not yet sure what the costs of this unit will be. Much will depend on the housing unit, and whether it is placed above grade on a foundation or whether it is sunk below grade. But keep an eye on future issues of this newsletter for the latest developments.
National Onsite Demonstration Project Results – WATERLOO BIOLFILTER – January – March, 1995
ORENCO TRICKLING FILTER
Figure 5. Orenco Trickle Filter
Orenco Systems, Inc., a name well known in the western United States is making inroads in Massachusetts. Their Low-rate Intermittent Sand Filter has certification for general use in Massachusetts, and one installation has been made in Gloucester. Among the variety of other products produced by Orenco is the “trickling filter”. This filter uses urethane foam, like the Waterloo Biofilter, in a 30-inch diameter, 48-inch high cylindrical structure that sits atop the septic tank. We now understand, however, that they may be experimenting with various media. The principle is fairly simple. A pump within the septic tank pumps effluent to the top of the filter media, where presumably the first step in the nitrogen-removing process (nitrification or the conversion of ammonium to nitrate) takes place. The filter bed drains back into the septic tank, where the second step in the nitrogen-removing process (the conversion of nitrate to nitrogen gas) takes place. The actual pumping to the filter is based on a timer (Figure 5).
Again, Gloucester has been first to pioneer the use of the trickling filter, however one has been installed in Wellfleet and is undergoing testing. The Buzzards Bay Project also planning an installation of this type of system, coupled with a constructed wetland for final effluent polishing. That system is scheduled to be installed in June, 1997. Two additional units may be installed in Wellfleet in the summer of 1997.
To date , the results of the Gloucester installation have been pretty impressive. The table on the next page is a summary of results from Gloucester from January – March, 1995.
National Onsite Demonstration Project Results – ORENCO TRICKLING FILTER January – March, 1995
Costs?
It’s difficult to know how the costs will shake out, the trickle filter itself will come in at around $2,500. This includes the filter unit, two pumps and the control panel. We can not really comment on the installation costs yet, but Anish Jantrania in Gloucester says that it’s fairly simple. As you might guess, if you want the covers for the system to be at grade, a variance to the maximum -three-feet-below-grade requirement of 310 CMR 15.221:(7) will be needed.