§ 18.21.200. Design standards for aerobic sewerage plants.

A.

Introduction. A number of small (up to one thousand five hundred gallons per day) aerobic wastewater disposal systems have been designed and marketed for the on-site treatment of sewage. The design standards in this section govern the installation and use of on-site aerobic sewerage plants for private residences, small businesses, and institutions that will not treat more than one thousand five hundred gallons per day. Sewerage plants designed to treat more than one thousand five hundred gallons per day must meet the design criteria for sewerage systems, published by the department and the commission.

B.

Appropriate Usage. The installation and use of aerobic individual wastewater disposal units, other than septic systems, are acceptable to the licensing authority provided they meet the requirements of this section.

Table 18.21.190
Individual Usage Rates in Businesses/Institutions

This table may be used for estimating gallons of daily sewage flow per person to determine minimum tank capacity requirements, unless actual water usage data is available and has been carefully checked by the designer of the proposed system.

Type of Establishment	Gallons/ Person/ Day
Airports (per passenger) .....	5
Apartment houses .....	50
Boarding schools .....	50
Churches (per member) .....	5
Country clubs (per resident member) .....	100
Country clubs (per nonresident member present) .....	25
Day care centers (without kitchen) .....	15
Day care centers (with kitchen) .....	25
Drive-in theaters (per car space) .....	5
Factories (gallons per person per shift, exclusive of industrial wastes) .....	20
Hospitals .....	200
Hotels .....	80
Institutions other than hospitals .....	100
Laundries, self-service (gallons per wash, i.e., per customer) .....	50
Lounges (bar & tables) .....	10
Mobile homes .....	75
Motels .....	50
Movie theaters (per auditorium seat) .....	5
Office buildings* .....	15
Parks (without bathhouse) .....	5
Parks (with bathhouse) .....	15
Restaurants (24-hour full service) .....	70/seat/day
Restaurants (breakfast/lunch or lunch/dinner) .....	35/seat/day
Restaurants (fast food—paper plate service) .....	15/seat/day
Schools without cafeterias, gymnasiums or showers .....	15
Schools with cafeterias, but no gymnasiums or showers .....	20
Schools with cafeterias, gymnasiums and showers .....	25
Service stations (per vehicle served) .....	10
Stores (total per day per washroom) .....	400
Swimming pools and bathhouses .....	10
Townhouses (with clothes washer) .....	50
Travel trailer/RV parks .....	50
Vet clinics (per animal) .....	10
Work or construction camps (semi-permanent) .....	50
Youth camps (no showers or meals served) .....	15
_____
* Note: Offices without food service or bathing facilities, with restrooms equipped with toilets requiring 1.5 gallon per flush or less, and automatic cutoff faucets: .....	6

 

C.

Effluent Disposal Practice. The effluent from an individual small aerobic wastewater disposal unit must be discharged into properly designed and constructed subsurface sewerage system. No discharges to or above the ground surface or into the waters of the state are authorized by the department. No local regulatory program has been established to permit such practices.

D.

Operation and Maintenance Responsibility. Companies distributing aerobic individual small waste disposal systems shall provide an inspection and repair service.

E.

Emergency Operation. The principal structure or containing vessel of an individual small wastewater unit is designed to provide treatment to a predetermined amount of daily incoming sewage. In the event of more than one day's failure of mechanical or electrical devices, anaerobic conditions will prevail when aeration equipment is inoperable. The unit's owner shall be prepared for emergencies by contractual arrangement with the plant's seller, by stocking spare parts, by hiring a licensed sewage pumping and hauling company, or by preventing the generation of more sewage until the emergency is eliminated.

F.

National Sanitation Foundation Criteria. Individual small aerobic wastewater disposal units shall have a National Sanitation Foundation Seal indicating the unit meets the Foundation's standard 40. Units not having a NSF approval rating must be approved through the procedure of Section 18.21.080.

G.

Treatment Limitations. The prospective user should be aware that small aerobic treatment plants treat sewage differently than septic tanks. Aerobic treatment plants operate by mixing raw sewage together with air and masses of bacteria. Several kinds of bacteria consume the sewage and air, changing it to nitrogen, carbon dioxide and water, all of which are used by plant life. Treated clear effluent still contains microscopic bacteria and viruses that were in the raw sewage so it must be kept out of contact with the general public as much as possible. It is possible to disinfect treated sewage with chlorine, bromine, ultraviolet light, ozone, or other commercially available products. However, nothing will make aerobically treated sewage safe enough to use as fresh water. Disposal systems for aerobic plant effluent shall be the same as for septic tank effluents.

H.

Siting Considerations. Most aerobic treatment plants sized for single home or small commercial shop use are usually only slightly larger than a septic tank but may not be installed as deeply. The organic loading, of commercial or institutional applications may require individual design considerations. Its inspection access is exposed to the surface, unlike a septic tank which is usually covered over with a layer of gravel or grass sod. The unit is generally one piece construction using concrete or fiberglass.

I.

Solids Accumulations. Most aerobic treatment plants operate by applying air from an air compressor into the bottom of the tank that first accepts raw sewage. As the air bubbles rise to the surface the sewage mixes with a mass of brownish gray bacteria called activated sludge. Several baffles or compartments are required within the single unit so that several different activities can be done at the same time. These include mixing the air, sewage, and bacteria together, then allowing the bacteria to settle while the treated effluent is drained off the top. Solid materials that the bacteria cannot consume will accumulate in a sludge holding compartment along with grease, oil, and other undigested floating wastes. The sludge and floating wastes will have to be removed occasionally by a sludge hauling company. How often sludge has to be removed depends upon the type and amount of waste the owner applies to the system.

(Ord. 9448 (part), 1988)