Operation and Maintenance of Alternative Systems
(Sand Filters, Aerobic Treatment Units, Spray and Drip Irrigation)
Bill Patrakis, R.S.
Guilford County Health Department
201 S. Eugene St.
Greensboro, NC 27402
The purpose of scheduled maintenance of alternative wastewater systems is primarily to prevent a chronic or acute malfunction of the system. Nonetheless, the operator may get an emergency call from the resident or homeowner even though a regimen of regular inspections has been followed. this may occur usually during or after a significant weather event. Heavy rains or power outages can wreck havoc on alternative systems. In addition, careful questioning of the water usage habits of the resident may give valuable information to the reason for the malfunction. Visual or audible alarms will indicate high water in pump tanks. There may be one or more reasons for the high water failure. I and I – infiltration and inflow- form heavily leaking tanks, failing pumps, or clogged spray nozzles are just few of the possible causes. The operator’s intimate knowledge of the system in question in integral to solving the problem. Previous maintenance visits by the operator, observations and data (drawdowns are a valuable tool in troubleshooting) gathered by him during all types of weather conditions will clue him as to the cause to the trouble. Some detailed logs of what maintenance procedures were done and when is also of great value. A log may clue the operator as to what had previously been overlooked and if the system had been maintained by a previous operator, the new operator will gain great insight into the functioning of the system.
New systems may need tweaking in the first few months of operation until the system operates properly under all or most weather and seasonal conditions. Careful observation of all parts of the wastewater treatment system in the first few months of operation will give hints as to sites of future problems. dosing frequencies and dose amounts are often variables that can be adjusted by the operator to help in good operation. The addition of effluent filters may be helpful in reducing the amounts of solids entering the more delicate parts of some systems. the operator should keep in mind at all times to stay within the permit parameters. Conscientious installation is paramount to a properly functioning system. Improperly grouted tanks or poor pipe connections will require expensive retrofitting.
I. Sand filters – advantages – provides for efficient secondary treatment of effluent with good reduction in suspended and dissolved solids. Highly recommended as pretreatment for drip and spray irrigation systems. Keypoint to remember – evenly distributed flow over sand medium is very important. Unevenly distributed flow will cause localized clogging of sand filter medium resulting in short circuiting of system and shortening of life of the medium.
Diagnosis – ponding of effluent in sand bed, black and/or green spot in bed. This is usually caused by clogging of nozzles and holes in distribution system as a result of biological growths and debris. A septic odor in the pump tank may also be a symptom, although this may also be caused by insufficient dosing frequency.
Solution – frequent flushing of distribution system will prevent excessive clogging. Open the cleanouts one at a time and throttle the pump to full. Let the pump run 10-20 minutes. Reset the pressure head with a stand pipe.
II. Aerobic Treatment Units – advantages – provides good primary and secondary treatment for subsurface disposal systems. Actus are essentially mini-waste treatment plants treating raw sewage with an aerated mico-faun and final clarifying.
Keypoints to remember – keep the Mixed-Liquor Suspended Solids well aerated. Make sure all seals are tight to prevent short circuiting of system. Keep solids pumped out of the aeration chamber. Use the settleable solids test to determine if this needs to be done. The time frame for this will depend on size of unit and number of person it serves. Fill a one liter container by scooping out some of the MLSS while the unit is in operation. Let the liquid settle for about 30 minutes then measure the amount of supernatant. If the supernatant is less that 50 percent of the total volume of the one liter container (50% or more of settleable solids) then have the aeration chamber pumped out. Remember not to scrub the unit clean so as to “seed” it for continued service.
Diagnosis – septic, foul smell to MLSS. In some unit designs this may take several days to manifest itself if decreased aeration is not obvious. Generally, the MLSS should not have an offensive odor, but should be somewhat like humus or fresh earth. Floating solids in the clarifying area is a clue to probably short-circuiting. Check for worn seals or debris which may be causing the problem. Filtering media may also need to be serviced in some unit designs.
Solution – the most common problem may be clogged air intake hose or malfunctioning air pump or impeller. Clear hose and/or replace the pump or impeller.
III. Spray Irrigation – advantages – good final disposal strategy for areas with poorly drained soils – provided there is ample space.
Keypoints to remember – clogging of spray heads and distribution lines are the most common problem due to debris entering the pump tank. It may also be caused by inefficient primary of secondary treatment.
Diagnosis – one or more spray heads may spray erratically or not at all. If the spray system is on a timed schedule – high water alarm may signify inadequate dosing amount and accumulation of water in the pump tank. In any case, run the system and observe the operation of the spray heads.
Solution – clean or replace the spray heads and reset the pressure head if necessary.
IV. Drip Irrigation/Pumped Subsurface Disposal – advantages – a final disposal strategy for areas with limited space and/or limited soil depth.
Keypoints to remember – some hi-tech system may be too complicated for the average operator without special training. Clogging of drip lines without proper pretreatment may occur or may be caused by biological growth in distribution lines.
Diagnosis – accumulation of water in pump tanks (especially if the system is on a timed dosed schedule). Comparing the drawdown from previous drawdowns indicated decreased efficiency of the system due to pump wear or clogging of the distribution system. Ponding of water in one or more areas of the disposal field will indicate where excess water is being emitted by pipes which are not clogged. Solution frequent maintenance of the system by flushing out distribution lines as in the sand filter systems.