Description of the technology
The BioGreen Secondary Wastewater Treatment System is designed primarily to provide
domestic wastewater treatment for individual homes and small communities, but could also be used in commercial applications such as restaurants and stores. A process description is provided below and a flow diagram is shown in this figure.
The initial two compartments are settling tanks which remove sediment, debris and floating material from the influent. The first settling tank is larger than in conventional systems and provides a buffer for controlling the impact load. This is often a serious problem in conventional systems but is easily dealt with in BioGreen. The water passes from the settling tanks to the fermentation tank where sludge and approximately one half of the carbohydrates are removed by filtration.
The next stage of the treatment process is aeration. The two aeration tanks contain an array of filters. Critical flow rates to the aeration tanks are maintained by a control valve, which minimizes outside variables affecting the impact load. Air injected through specially designed draft tubes creates ideal circulation and maintains adequate DO (Dissolved Oxygen) concentration. A DO gradient from zero to saturation is created, which allows for a much longer food chain for nutrient digestion. This minimizes sludge production as compared to existing methods. The final step is the effluent holding tank which removes suspended solids before discharge. Because of the relatively long retention time (average three to five days), most of the E-Coli are killed, and therefore effluent can generally be discharged or reused with no further need for disinfecting.
Performance
The BioGreen system is designed to meet 5mg/l discharge criteria for both Biochemical Oxygen Demand (BOD) and Suspended Solids (SS). The reduction of fecal coliform bacteria occurs naturally in the system to levels below 1000 colonies/100 ml. If further reduction in fecal coliform bacteria is required, a disinfection process can be added to the system before effluent discharge.
Typical household units are designed to handle flowrates of up to 3,000 litres per day (660 gpd). Table 1 provides information on typical system performance where various parameters are measured at different points throughout the treatment process.
Table 1 – Example of System Performance (after 4 year of use)
| Â Parameter (mg/L) | Fermentation Tank | 2e Aeration Tank | Effuent (mg/L) |
| Suspended Solids |  328±263 |  6.9±9.2 |  7.7±2.7 |
| BOD |  152±51 |  6.0±4.8 |  3.9±0.5 |
| ATU-BOD |  143±69 |  2.9±1.4 |  2.2±0.2 |
| Soluble BOD |  56±8 |  1.9±1.5 |  1.3±0.4 |
| COD (Mn) |  125±50 |  12.8±4.5 |  9.8±0.5 |
| Soluble COD |  29±2 |  8.9±1.3 |  8.4±0.5 |
| Nitrogen (NO4) |  41.4±1.3 |  2.98±6.68 |  0.69±0.08 |
| Nitrogen (NO3) |  0.01±0.01 |  0.10±0.13 |  0.03±0.01 |
| Nitrogen (NO2) |  0.09±0.08 |  23.9±4.6 |  25.5±0.4 |
| Nitrogen (organic) |  13.2±11.5 |  1.31±1.04 |  1.14±0.14 |
| Total Nitrogen |  4.7±10.5 |  28.3±2.6 |  27.3±0.5 |
| Total Phosphorus |  7.32±1.91 | 4.61±0.09 |  4.83±0.04 |
Limitations
The current design is limited to domestic wastewater only, and the sizing of the BioGreen units is based on the needs of the application. As with septic tanks, the unit cannot handle large doses of household cleaning products as the operation of the unit depends upon biological reduction of the BOD in the incoming wastewater stream.
Installation and operation
The typical household installation consists of a unit with dimensions 2.9 m long X 2.0 m wide) X 2.0 m high and a design treatment capacity of 1,600 litres per day (350 gpd). The installation of the unit and proximity to the house, as well as the location of the effluent discharge, are the responsibility of the contractor or property-owner.
One of the main advantages of the BioGreen system is the reduced land requirement for effluent disposal. A large discharge field, as for a septic tank, is not required, since the wastewater treatment occurs inside the unit and not in the receiving soil. This result in reduced lot sizes for new construction. The performance of the BioGreen system is also such that it produces a high quality effluent which can be used for irrigation, or discharged to a surface water body in accordance with local regulations.
Once operational, a minimum level of operator knowledge is required. Some yearly maintenance and backwashing of the aeration chambers is required. The settling chambers also require pumping out every 5 to 10 years.
Costs
The purchase price of a typical household unit is less than $ 10,000 per household. The units are sold with all internal components installed. Operating costs are low as the only moving part that requires power is the compressor. Based on 24 hour per day running time, an approximate allowance of $8 per month should be made. In addition, a minor annual expenditure should be allowed for the above mentioned maintenance.
Additional Information
The BioGreen Secondary Wastewater Treatment System is a Japanese technology which has been imported to Canada. There are presently four demonstration units installed in Newfoundland, where research is ongoing to optimize the technology for the Canadian climate and environment.
BioGreen has invested approximately $500,000 over two years on research and development. The Industrial Research Assistantship Program (IRAP) from the National Research Council of Canada (NRCC) and the University of British Columbia (the west coast partner, Suimon Engineering Canada Limited) have been associated with the development. BioGreen (Nfld.) Limited has the right to sell the systems in Eastern Canada (i.e. Ontario, Quebec and Atlantic Provinces), USA, Caribbeans, Europe and Southeast Asia.
BioGreen(Nfld) Ltd.
M. Tom Healey, Service de la vente et de la commercialisation
48 Main Dam Road
Deer Lake, Terre-Neuve, A8A 1S2
Phone : (709) 635-5170
Fax : (709) 635-3281
Email : biogreenwastewater@hotmail.com