The Cromaglass CA-5 aerobic treatment unit by Cromaglass Corp. uses a four-step treatment process to reduce BOD and TSS in septic tank effluent.
The unit is described as an activated sludge sequencing batch reactor. A denitrification step can be added to reduce nitrogen for discharge to sensitive environments, and disinfection can be added to reduce fecal coliform. The CA-5, introduced in the 1960s, is among the older ATUs for residential and small commercial applications.
Site conditions
The Cromaglass CA-5 is designed generally for sites that are otherwise unsuitable for traditional trench-and-gravel septic systems. The unit processes septic tank effluent in fiberglass tanks. The manufacturer recommends that the unit be installed upon and tied down to a 9-inch-thick concrete slab.
On sites with high seasonal water tables, anti-flotation measures are required. The tank can be installed virtually anywhere the water table is not above the closed, but unsealed, top access port. It can be installed below prevailing grade and then backfilled, or the tanks may be installed at grade. In the latter case, the tanks may be enclosed with mounded berm material.
Backfilling or berming add stability and protect the tanks from external forces. In either case, locations subject to flooding should be avoided. The unit’s access panel must be above grade and unobstructed. The system can discharge to a soil absorption system, or directly to a stream if allowed by the local permitting authority.
Treatment process
The Cromaglass CA-5 treatment process has four steps:
Fill. Septic tank effluent enters the unit’s first (solids retention) section. A non-corrosive screen separates this section from the second (aeration) section. The screen retains inorganic solids, which settle in the solids retention section. Organic solids are broken down by turbulence created when the liquid and the suspended particles are drawn through the screen by a submersed pump into the aeration section. This eliminates the need for mechanical comminution (grinding).
Aeration. In the aeration section, air is introduced by venturi aspirators. As water is forced across the aspirators, it incorporates a stream of air supplied through an intake pipe from the atmosphere. This dual-action process — movement of the water, plus biological activity enabled by increased oxygen — stirs the material into a homogeneous liquid.
Transfer/settling. After the aeration step, the pump discharges the liquid to the third (clarification) section. This process delivers more liquid to the clarifier than the compartment’s capacity. The excess liquid spills through an overflow weir back to the aeration section. When overflow is achieved, the transfer stops, and the liquid in the clarifier is isolated. With all pumps shut off, tranquil conditions enable even the smallest solids particles to fall out of suspension and settle on the bottom.
Discharge. The final pump in the system discharges the treated effluent to the soil absorption system or other final destination.
If a denitrification option is added to the system design, then at the end of the aeration process, air introduction is stopped. However, the pump continues to mix the material throughout the first and second compartments.
Performance
The manufacturer states that the Cromaglass CA-5 reduces CBOD to 25 mg/l and TSS to 30 mg/l. If denitrification is added, the manufacturer says the treated effluent will have less than 10 ppm total nitrogen and less than 30 ppm TKN. A disinfection unit may be added in the form of a chlorine introduction device and contact tank, or a small tank to house a UV light downstream of the discharge pump.
Advanced control settings using timers and floats allow the treatment system to change the number and extent of aeration and settling times, depending on flow. For example, a standby mode is enabled when there is an insufficient wastewater volume in the discharge tank.
The Cromaglass CA-5 was introduced before NSF established performance evaluation protocols. NSF has issued an “equivalency status” for the system. Cromaglass offers treatment units in essentially the same design that can process flows up to 200,000 gpd.
Costs
Specific system costs must be determined on a site-by-site basis. The CA-5 unit is priced at $5,000, and installation costs approximately $5,000 more, not counting the cost of a drainfield. Denitrification or disinfection will add to the cost.
The system requires electricity, projected by the manufacturer at 8 kilowatt-hours per day, or about $290 per year (local electric rates vary). The system also requires operation and maintenance that entails four site visits per year (price based on prevailing local rates). And, like all treatment tanks, the settled solids must be periodically pumped out.
Comments
As with most ATUs, the CA-5 system requires electricity (although Cromaglass Corp. reports that at one installation, solar energy has been harvested to meet the system’s energy needs. The system also requires an operation and maintenance contract. Regulators often require landowners to document that they have a service contract, and to show proof that the system is regularly serviced. Educated and committed homeowners will want to maintain their systems’ performance by contracting for all necessary service and maintenance.
