This chapter focuses on a new set of technologies that to some extent use the batch-type technology for the treatment of septic wastes. Batch technology, as its name implies, treats sewage in "batches". This type of technology can be contrasted with the majority of alternative technologies covered in this newsletter up to now, that treat septic tank effluent in a continuous stream that passes over or through a media for the nitrification step of the process (conversion of ammonia to nitrate) and then returns to an anaerobic part of the system (sometimes the septic tank) for the denitrification step (the conversion of nitrate to nitrogen gas). Batch technologies covered in this issue of the newsletter are ones that alternately supply and deprive batches of effluent with air so that the nitrification/denitrification steps can occur, even in the same vessel.
Batch technology is most commonly employed in larger treatment systems that have the ability to control the flows through the treatment plant by various valves, pumps and storage tanks. The advantage of batch technology is better process control. By this we mean that operational details such as dissolved oxygen necessary for nitrification, and exact times needed for denitrification, can be better controlled by the use of timers, fluid pumps, valves, and air blowers. Although at the outset these systems may seem complicated, their advanced treatment, well proven on the large scale, holds promise that the right recipe can be found to remove contaminants of choice - in our case nitrogen ! The challenge for these technologies will be to provide a cost effective way to treat sewage onsite, amidst some stiff competition. Although it is still too early to tell what "niche" in the overall onsite treatment world batch technology will fill, it seems evident that at flows slightly above the single family use (small collective systems in cottage colonies, trailer parks, small clusters of homes, etc.), these systems may find their cost effectiveness optimum.
New to onsite treatment, but certainly not new to municipal waste treatment, Tetra Technologies, Inc., through its affiliate FR Mahoney & Associates, Inc, of Rockland, Massachusetts is developing and introducing the Amphidrome system. This system merges two proprietary technologies, the ColOX® System for the nitrification of the waste, and Denite® for the denitrification of the waste. One system was installed and is undergoing monthly testing as part of the Waquoit Bay National Onsite Demonstration Project. This installation is the only single-family residential system to date.
ColOX® can best be described as a process where microorganisms, growing on the surface and in the voids between a solid media in a reactor vessel (see the Amphidrome Reactor illustrated on the next page), are supplied air by use of a blower. The microorganisms subsequently process waste and remove BOD and suspended solids. In addition, the high efficiency of oxygen transfer results in high rates of ammonium nitrification. Remember, the conversion of ammonium to nitrate (called nitrification) is the first series of steps necessary for the ultimate denitrification or transformation to nitrogen gas (called denitrification). The Denite® process uses the same reactor vessel and media as the ColOX® process to denitrify waste, again using a fixed film.
"Amphidrome" refers to the linking of the ColOX® and Denite® technologies such that a single reactor vessel serves both technologies in a rhythmic pattern analogous to a tidal cycle in a bay. The effluent passes back and forth through the reactor vessel, alternately being supplied with and deprived of air, for enough cycles to process the waste to a predetermined level.
An Amphidrome system has recently been installed at Stuart's Mall in Swansea, and another has been installed a little closer to home at a location in Mashpee. These latter systems purport to produce an effluent total nitrogen of less than 5 mg/l. Well, they say a picture is worth a thousand words, so, turn the page and follow the proposed sequence of flow through the Amphidrome system as it is being operated at the Waquoit Bay system. The first illustration is a detailed and labeled plan view. Despite the more extensive appearance of the system, it can easily fit almost anywhere a standard system can fit since the reactor vessel is only two feet across and the clearwell can be sized less than 500 gallons.
STEP 1. At 3:30 AM each day, the system discharges to the leaching facility using discharge pump until the low water float is activated.
STEP 2. Flow begins to enter the system causing sewage to flow into the Amphidrome Reactor and equalize elevation in the clearwell. Process air is bubbling up through the chamber, opposite the liquid flow direction. This a nitrification stage.
STEP 3. Recirculation pump activates and pumps clearwell liquid back trough the Amphidrome Reactor, forcing the liquid level up to the return line. Again, process air is still entering the lower part of the unit and bubbling up through the effluent, continuing to create conditions for nitrification.
STEP 4. Liquid from the treatment unit beginning to flow back to the septic tank via the return line, and mixes with fresh sewage coming in. The now-nitrified effluent enters the anoxic conditions of the septic tank and begins to denitrify using the sewage as a carbon-food source.
Step 4 - The recirculation pump in the clearwell goes off and allows the septic tank and clearwell to once again equilibrate liquid elevations. Since the process air is not applied during the passage through the Amphidrome Reactor, anoxic conditions result in denitrification (Denite®) (10AM-11:30AM).
STEP 5 - At 11:30 AM, is a repetition of STEP 3 - process air
on (reverse ColOX® )
STEP 6. - At 12:00 noon, is a repetition of STEP 4 with process
air on (forward ColOX® )
STEP 7 - At 3:00 PM, is a repetition of STEP 3 - process air on
(reverse ColOX® )
STEP 8 - At 3:30 PM, is a repetition of STEP 4 - process air off
( Denite®)
STEP 9 - At 4:30 PM, is a repetition of STEP 3 - process air on
(reverse ColOX® )
STEP 10 - At 5:00 PM, is a repetition of STEP 4 with process air
on (forward ColOX® )
STEP 11 - At 7:30 PM, is a repetition of STEP 3 - process air on
(reverse ColOX® )
STEP 12 - At 8:00 PM, is a repetition of STEP 4 with process air
on (forward ColOX® )
STEP 13 - At 11:00 PM, is a repetition of STEP 3, with higher air
input for the purpose of scouring media, dislodging sludge and allowing
it to recycle to the septic tank (BACKWASH).
STEP 14 - At 11:30 PM, is a repetition of STEP 4 - process air off(
Denite®)
STEP 15 - Is a repetition of STEP 1
Whew !. Before you begin to think about how complicated this all is, you should remember that even a recirculating sand filter activates a pump every half hour by timer. Performance? Theoretically, the Amphidrome should be able to achieve a discharge concentration of nitrogen at less than 10 PPM, but at this point we can only wait and see. As more of these systems are proposed and installed, DEP will at some point assign a reduction credit. Costs? Still undetermined. We will know more after the Waquoit installation, but as you can see, the costs above and beyond the Title 5 components would be the reactor chamber (actually only concrete piping sections filled with media), air blower, recirculation pump, discharge pump, and control panel including a programmable timer. The operational costs per year would likely be less than $ 100.00 for electricity. We do not yet have information on a maintenance contract or monitoring. If you want further information on the system, Contact Keith Dobie at F.R. Mahoney & Associates, 617-982-9300.
The Cromaglass® wastewater treatment system is another type of sequencing batch reactor. It is designed to operate as a continuously fed activated sludge process with clarifiers that are operated on a batch basis. Treatment operations occur in a single tank module which is divided into three treatment sections. Treatment is accomplished by turbulent aeration of incoming waste in the first compartment and batch treatment of sewage in separate aeration and settling chambers. The treatment process operates as follows:
FILL AND AERATION: Flow enters the solids retention section which is separated from the aeration section by a screen. Inorganic solids are retained behind the half inch mesh screen. Organic solids are broken by turbulence created when mixed liquor from the aeration section is forced through the screen by submersible aeration pumps. Liquid and small organic solids pass through the screen into the aeration section of the tank.
AERATION AND OPTIONAL DENITRIFICATION: In the aeration section of the tank submerged pumps with venturi aspirators provide continuous air, mixing and heat. The pumps receive air through pipe intakes from the atmosphere. Aeration proceeds for several hours mixing new inflow with the existing activated sludge that is maintained in the tank. Operating time of the aeration pumps is automatically adjusted to control dissolved oxygen at proper levels suited to the organic loading and treatment requirements of the wastewater
The system can also be configured to achieve denitrification. This is accomplished by providing a time interval during which the air intakes of the venturi aspirators are closed by electric valves. This stops aeration allowing the system to go anoxic so that denitrification can proceed. The pumps continue to mix the sewage in the tank during the anoxic period .
TRANSFER/SETTLE: The treated mixed liquor is transferred by pumps to the clarification section where solids separate and settle under quiescent conditions.
DISCHARGE: After settling, a selected portion of the effluent is pumped out of the clarifier for discharge. Sludge remaining in the clarifier is pumped back in to the aeration area for further aeration and breakdown, or can be wasted to a sludge collection tank.
As with other small sequencing batch reactors, the Cromaglass unit is able to accommodate continuous inflow of new sewage. This new inflow is slowly added to the sewage in the aeration compartment where it begins the treatment cycle. One to six aeration/settling cycles per day are typical for a small residential Cromaglass system depending upon sewage flow.
The Cromaglass system is housed in a single fiberglass tank. The system is sold as a module consisting of tank, internal pumping and sensor equipment and electrical control panel. Five different size modules are available with daily flow capacities from 300-12,000 gpd. Additional modules can be added to a previously installed system if design flows increase. For example, a condominium project with a phased build-out might install 1 or 2 modules initially, and add modules as development proceeds. Because the modules are completely self-contained they can be placed in multiple locations saving additional piping and pumping costs.
The home-sized modules contains 2 pumps: one for aeration and transfer, and the other for discharge of the effluent to the leaching area. The largest modules (7000-12,000 gpd) contain 9 pumps: two main aeration pumps, two transfer/aeration pumps between the two tanks, two transfer to clarifier pumps, two discharge pumps, and one sludge removal or wasting pump.
The manufacturer claims that the system is capable of reducing BOD and TSS by over 90%. Influent BOD in the range of 250-400 mg/L was consistently reduced to <20 mg/L in finished effluent. Limited data from one system configured for total nitrogen removal also shows significant nitrogen reduction. Inflow total nitrogen of 24.4 mg/L was reduced to 4.9 mg/L in finished effluent.
A basic residential system, which can treat up to 800 gpd, costs $6800 for the module plus $750-1000 in additional installation costs. The distributor estimates a yearly electricity cost to operate the system of about $30 per user. The system requires regular maintenance. Analytical Systems, Inc., the local distributor, offers a maintenance contract at a yearly cost of $240 for residential systems. This includes quarterly maintenance and 24 hour alarm monitoring. The New England version of the Cromaglass system is designed with internal sensors connected to the system control panel so that operations in the system can be remotely monitored and adjusted.
The Cromaglass system has received general use approval from DEP for use in place of a septic tank. It has also received piloting use approval for 80% nitrogen reduction (final effluent <10 mg/L) and for a 67% reduced size leaching facility. A 550 gpd residential Cromaglass system has recently been installed in Cohasset. A unit has also been recently installed in the "99" Restaurant in Yarmouth. There are also numerous Cromaglass installations in Pennsylvania, New York, and Maine. Local distributor of the system is Analytical Systems, Inc., PO Box 720, 11 School St., Sandwich, MA. (508) 833-8856.