Capacity: 2,000-10,000 gallon per day (These are not used for individual homes.)
 Procedures & Schedules |
Operational Problems |
| Personnel & Contracted Work |
Operation & Maintenance Requirements |
| Parts, Supplies and Equipment |
Comparison to Past Work |
| Example Annual Costs Per Home |
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1. Daily:
a) Visually check color and appearance for proper aeration and mixing. Check for proper odor. Clean air diffusers as necessary. Record.
b) Remove scum with net and dispose of.
c) If hand-raked influent screens, clean and dispose of screenings.
d) If comminutor, clean and dispose of large objects.
e) Chemical analysis (and record keeping):
- mixed liquor and effluent settleable solids (half hour cylinder settlement test)
- mixed liquor dissolved oxygen (DO)
f) Adjust aeration (and sludge return) as indicated by a) and e)
2. Weekly:
a) Brush or hose down all parts of tanks
b) Inspect compressor/blower for proper lubrication, V-belt tension and wear. Fill with oil, grease bearings, clean or replace air filter.
c) Check pH and temperature of influent, clarifier, and aeration chamber. Record.
d) If comminutor, lubricate.
3. Monthly:
a) Clean air diffusers.
b) If comminutor, sharpen or replace teeth.
4. Quarterly:
a) Change oil in blower gear cases.
b) If surface discharge, measure effluent biochemical oxygen demand, suspended solids, total coliforms (FC), pH and flow. Record.
5. Other:
a) Building and grounds maintenance, painting.
b) Pump sludge and scum every 2-12 months as necessary.
c) Non-routine service and repairs.
Operation:
- trained, licensed operator
- 400 man-hrs/plant/year, $10/man-hr
Chemical analysis for surface discharging plants (BOD5, SS, FC):
- contract 4 samples/plant/year
- $3l/sample
Solids Pumping for plants without digester or land disposal:
- 1 pumping/plant/year
- $90/pumping
Parts and Supplies:
| Lab supplies: (chemicals, equipment maintenance, pencils, paper) | $ 20/yr. |
| Lubricant: | $ 25/yr. |
| Replacement parts: blower, belts, valves, alternator | $225/yr. |
| Touch up and paint: | $ 70/yr. |
| Total: | $340/plant/yr. |
Equipment: (Treatment plant enclosure if freezing climate) (Lab space with hot water, storage for chemicals)
| Test kits: DO, pH, settleable solids | $119/4 yrs |
| Garden hose | $ 20/2 yrs |
| Plastic garbage can | $ 20/2 yrs |
| Grease gun | $ 13/5 yrs |
| Stiff bristle push broom | $ 13/1 yr. |
| Small skimmer net | $ 8/1 yr. |
| Short handled brush | $ 3/1 yr. |
| Large skimmer net | $ 15/1 yr. |
| Total: | $ 91/1 yr. |
Power:
| 2.5 hp | * | 333 gpd | * | 24 hr | * | 0.746 kw | = | 3.0 kwh/day |
| 5000 gpd | home | day | hp | home |
| Labor: | 400 man-hrs/plant * $10/man-hr * 1 plants / 30 homes = | $133.33 |
| Parts and Supplies: | $340/plant * 1 plants / 30 homes = | $ 11.33 |
| Power: | 3 kwh/day/home* 365.00 days * $0.07/kwh = | $ 76.65 |
| Equipment: | $91/plant * 1 plants / 30 homes = | $ 3.03 |
| Vehicle: | 365 serv * 4 mile/serv * $.38/mile* 1 plt / 30 home = | $ 18.49 |
| Chemical Analysis: | 4 sample/plt * $31/sample * 1 surf. disc. plt / 30 home = | $ 4.13 |
| Total: | (First Quarter 1982) = | $246.98 |
| Updated Total: | Total | OMR | 1982 OMR | |
| $246.98 | * 3.49 | / 3.44 | $250.57 |
The extended aeration process is somewhat less expensive to operate in multiple home applications. Systems studied include those servicing up to 30 homes, or 10,000 gpd design flow. These systems sometimes include comminutors and/or sludge digesters. System descriptions are found in EPA (1977) and Laak (1980). Chlorinators are treated separately.
These plants are mechanically complex and relatively labor intensive. Proper aeration, again, is critical to the process. These larger systems will generally provide more operational control, such as aerator timers and valves. Plugged air diffusers can be a problem, as can flow or chemical shocks, rising sludge, foaming, and mechanical failures. Solids accumulate as in other systems and must be removed periodically. A representative list of problems and remedies has been provided by one manufacturer.
Summary of extended aeration operational problems
Secondary Treatment Process Problems:
1) Rising sludge due to denitrification.
2) Bulking sludge due to various imbalance conditions between the three variables biological oxygen demand (BOD5), suspended solids (SS) and the level of dissolved oxygen (DO) maintained.
3) Frothing, often due to the introduction of synthetic detergents.
Mechanical Problems:
1) Blower failure due to wear, improper lubrication, improper belt tension, dirty oil or air filters, clogged or leaky air lines, scale build-up on impellers or casing, etc.
2) Pump failure due to damaged impeller, electrical problems, etc.
3) Electrical problems (numerous).
Miscellaneous:
1) Clogged diffusers.
A brief summary of recommended O&M procedures, compiled from many sources has been developed. Recommendations vary somewhat from system to system. Manufacturer's literature must be consulted for any particular system.
This type of sewage plant requires a minimum of 400 man-hours per plant per year for effective operation and acceptable effluent quality. A licensed operator is legally required, as is effluent monitoring when effluent is discharged to surface water. Accumulated solids must be removed periodically, varying from every two months to every five years.
If a sludge digester is not provided, and land disposal is unavailable, septage pumping may be contracted for slightly more than the cost of septic tank pumping.
A list of the necessary parts and supplies has also been developed that includes a list of common operational tools. Average power requirement for a typical plant of this size may also be calculated.
The example annual cost calculations are for one subsurface discharging plant with septage disposal facilities, servicing 30 homes.
An average of four miles per daily service is assumed.
Guo et al. (1981) presents O&M costs for eight package plants of the size treated here. When updated with the EPA OMR index, the average annual costs per home is $78 for labor and $35 for parts, supplies, power, and chemicals. The respective costs as estimated for 20 homes, in the example, are $200 (based on author's minimum recommendation of 400 man-hrs per year per unit), and $97 ($77 for power alone). Michel et al., 1969 and EPA, 1977, indicate total O&M costs of $130 for 100 persons (30 homes). For 30 homes, a total cost of $230 is obtained from the example. Using a more typical 200 man-hrs per unit, $164 is obtained.
The total costs obtained here, therefore, represent a maximum due to the accumulation of conservatively biased components. This makes the results more applicable where only a few units are utilized. This would often be the case for a small community, since each of these units services multiple homes.