Last month I explained how ATUs operate and different categories of the units. Now we’ll talk about general information covering all ATUs.

Specific units require additional training provided by the manufacturer, but a service provider is going to encounter systems of various types and ages and needs to be able to evaluate the units to determine the next steps. Several years ago, the Consortium of Institutes for Decentralized Wastewater Treatment put together good materials on operation and maintenance. The materials included an extensive manual and a series of checklists used to evaluate different systems.

The first step is to assess the general operation and site, which involves three areas.

If odors are present, you need to locate the odors and determine if there is foaming or other evidence of bulking to the surface. There should not be odors around the site; they indicate some type of problem. It could be lack of proper venting or hydraulic or organic overloading. Some units have an active foaming process as a part of the aeration, but in general it’s not normal to find material foaming or residues indicating foaming outside of the unit.

ACCESS IS KEY

Basic questions will determine access to the unit. If you cannot access parts of the units to service them, this is a problem in terms of the unit’s long-term operability, particularly if the unit has been installed as a “best management practice.”

Access to lids and risers is important. If buried, one of the first upgrades you suggest to the homeowner may be to bring risers to the surface. Also, you want to make sure risers are watertight. If they are not, surface water may enter the unit, causing improper operation. Watch that water does not pond around the risers and increase the potential for infiltration. Lids should be securely fastened to restrict access and the lids should be in an operable condition. 

Check the air supply. There are four ways to supply air to the ATU: using an aspirator, a compressor, a blower or free air. If maintenance is performed, the specific manufacturer’s guide should be consulted.

Most units require continuous airflow. The exceptions are units that use a timer or require turning the unit on and off. The service provider needs to see whether the unit is operating properly. If it is off, the provider needs to determine if it’s because it is in the off mode or it doesn’t operate at all.

AIRFLOW SYSTEMS VARY

Distribution of air into the aeration chamber can be achieved through several different approaches, specific to each manufacturer. In general, piping carries air to the distribution point in the chamber. This point may be either aspirators in the aeration chamber drawing air into the chamber, a diffuser in the chamber, or an orifice. The piping for the aspirators needs to be cleaned to remove materials accumulating on the inside. Diffusers may need to be cleaned or replaced periodically to maintain airflow.

Operating pressure or vacuum can be used as a means to estimate the airflow through the system.  The service provider can check the operating pressure and track it over time to indicate changes in the air supply. The measurement is usually taken close to the unit. A Schrader valve, which looks like a stem on a tire, can be placed in the piping network to check the pressure. A pressure gage is attached to the valve to obtain the reading. A vacuum gauge can measure the draw of air into the system.

Maintenance of the airflow system is necessary. The airflow system begins at the inlet and stops where air exits the treatment system. The entry to the air pump can be protected by filters, screens or vents, which prevent debris from entering the system. The type of inlet device depends on the air pump and its ability to handle solids. The debris must be removed from the device during the maintenance visit. Filters can be washed, but must be dry before installation.

VENTING SYSTEMS

Once air enters the system, it must come out somewhere. This requires venting. The service provider must check to see that air can flow into and out of the system. You don’t want a situation where someone has solved an odor problem by simply plugging the system. The units will vent in different ways. Some allow venting back through the house plumbing. The unit will either have a special vent, or will have a riser that comes up with a vent cap. Some units will have a biofilter that scrubs the air coming off of the unit to remove a musty odor. Biofilters are especially useful when treating high-strength waste.

Next month we will explore evaluation of the ATU aeration chamber as well as additional concerns about overall ATU operation.