The Bear River Solar Aquatics Sewage Treatment Plant is made up of a combination of (unit) processes:

- Screening (the removal of gross solids)
- Grit Removal (separation of inorganic solids)
- Bioaugmentation (activated sludge recirculation and bacteria addition)
- Solids Grinding (breaking up gross solids that are not removed on the screens)
- Biological Treatment in Solar Tanks
- Biological Treatment in the Solar Pond (three stages)
- Sedimentation
- Disinfection
- Activated sludge Treatment

Screening and Grit Removal are conventional primary treatment unit processes. They are applied in most municipal sewage treatment plants. A main theme in sewage treatment operations is the separation of the solid and liquid components of the waste water stream. Large solids and grit (e.g. sand) can be most effectively removed before the sewage is mixed and agitated in the biological processes. Large solids and materials like unshredded toilet paper are caught on the Bar Screen. These solids are removed, manually, by the operator on a daily basis. The materials are composted. The grit is allowed to settle in a still environment. The grit is pumped out several times per year, hauled in a "honey wagon" to an offsite lagoon and allowed to naturally neutralize before disposal in a landfill or on agricultural land.

Bioaugmentation involves the mixing of activated sludge and, occasionally, a solution of water and bacteria, with the raw, incoming sewage. The activated sludge is the material that is separated from the sewage in the "Clarifier" (the sedimentation operation carried out after the sewage passes through the Solar Pond). The purpose of the Bioaugmentation is to maintain the appropriate balance of bacteria (that consume the dissolved organic fraction of the sewage) and the organic feed stock for the bacteria. As a part of running the plant, the operator has the ability to increase and decrease the activated sludge recirculation rate and, as required, add bacteria. A critical process control factor in microbiological treatment of sewage is the food to microorganism (F:M) ratio. Simply stated, the F:M ratio is the relative proportion of the bacteria population and available food for the bacteria. If you have too many bacteria, some will starve and die, prematurely. If you have too much food (organics), the surplus will be retained in the fluid part of the waste stream and will be discharged to the receiving water, resulting in pollution.

Before the sewage is introduced to the biological treatment unit operations, it is run through a Grinder Pump. The Grinder Pumps macerate solids that have passed through the Bar Screen and that have not been removed by the Grit Separation unit process. The solids (largely organic) need to be ground so that they can be mixed more thoroughly with the fluid constituent of the waste stream and, thus, be more readily available as food stock for the plants and bacteria in the process. The Grinder Pumps also elevate the sewage to establish the energy gradient needed to keep things moving through the treatment process.

The first step in the biological treatment process occurs in the Solar Tanks. At Bear River we have four rows of Solar Tanks. Each row contains three, five foot high, six foot diameter tanks that contain sewage, bacteria, plants, snails and other aquatic life forms. The tanks contain between 10,000 and 11,000 gallons of sewage. Air is pumped into each tank. The air is added at the bottom of each Solar Tank through diffusers, connected to the air piping system. The purpose of adding air is to keep the fluids and the solids in the tank well mixed, to minimize sedimentation of solids in the tank and to maintain a sufficiently oxygen rich environment to foster the growth and development of the forms of bacteria that are necessary to sustain the process. The biological treatment process is simply the digestion and adsorption of organic materials that are both dissolved and suspended in the fluid. The organics are consumed by the various life forms in the tanks. The bacteria and other animal life forms live in the sewage. The plants are rooted in the sewage and suspended by fish netting. The fish netting is draped and anchored across the tops of the Solar Tanks. the

To help maintain the life forms in the sewage, the Solar Tanks are constructed of clear plastic sheeting (like big freezer bags), supported by plastic coated wire mesh frames.

The second part of the biological treatment process occurs in the Solar Pond. The pond is 29 feet long and 18 feet wide. It has a liquid depth of nine and one half feet and holds about 31,000 gallons of sewage.

The pond is divided into three sections, separated by suspended curtains. The sewage from the Solar Tanks flows into the first Solar Pond compartment. The sewage flows from first compartment to the second compartment and then to the third. The difference between the biological processes in the Solar Tanks and the Solar Pond is related to the species of bacterial and other life forms in the two unit processes. In fact, the three compartments in the Solar Pond each contain different microbiological life forms. The nature of the different bacteria and the dominant species found in different parts of the biological unit processes is controlled by altering the rate at which air is introduced to the different environments. Different microbiological life forms are needed to remove different organic compounds that are dissolved and suspended in the sewage. Air is introduced into the Solar Pond in the same way that it is introduced into the Solar Tanks. The dissolved oxygen (DO) concentration (related to the rate of air input) in the first Solar Pond compartment is higher than that in the second, and the DO in the second compartment is higher than in the third. As in the case of the Solar Tanks, the animal forms in the Solar Pond are suspended in the sewage. The plants are rooted in the sewage and are suspended by fish netting. The netting in the Solar Pond is supported by square raft frames built of sections of plastic piping, glued together. In theory, each Solar Pond compartment should have different plants; however, we have been unable to keep the plant growth from spreading and developing a relatively homogeneous mat.

Sewage discharged from the third Solar Pond compartment has a fluid component, a suspended solids load and a minimum of dissolved material. The sewage from the Solar Pond is discharged into a Clarifier or sedimentation unit operation. In the Clarifier, a significant portion of the suspended solids load settles out of the fluid. The Clarifier is a three foot diameter, three foot high upflow unit. The sewage is introduced near the bottom of the clarifier and forced to flow upwards through a sloping honeycomb type of passage arrangement. The solids settle out in the honeycombs. As the material accumulates on the sloping walls of the honeycombs, it becomes too heavy to remain in place and slides off, settling to the bottom of the Clarifier. Once or twice a day, at the operator's option, a valve on a pipe at the bottom of the Clarifier opens, draining the Clarifier and removing the solids. The solids (called Activated Sludge) are diverted either to the Bioaugmentation unit process or to the Sludge Digester.

Depending on the effectiveness of the biological treatment unit operations the suspended solids load in the effluent discharged from the Clarifier will vary. In order to further reduce the solids load in the effluent the sewage may, at the operator's discretion, be run through a Micro Screen.
The solids load in the effluent needs to be controlled in order to maximize the effectiveness of the Disinfection unit process that follows the Sedimentation/Micro Screening operations. At Bear River, we used a Rotary Micro Screen with a membrane filter. We have recently replaced the membrane with a cloth filter in order to optimize the operation. The membrane filter had 30 micron sized holes. The cloth filter allows 100 micron sized particles to pass. The Micro Screen is equipped with an automated washing system. The operator determines the time period between
washes, sets the timer in the backwash spray control valve and allows the system to backwash accordingly. The sewage is introduced to the inside of the Screen and flows through the Screen to the outside. Solids accumulate inside the Screen and are manually removed by the operator, daily, using a shopvac. The solids are combined with the activated sludge from the Clarifier. At Bear River, we have not made extensive use of our Micro Screen. From the time that the plant was constructed (1995) until the spring of 1998, we have had chronic water supply problems at the plant. The Micro Screen is a high water consumption unit. The water demands associated with the unit, coupled with the high solids removal rate of the membrane filter (increasing the frequency of the backwash requirement), made regular use of the Micro Screen impractical. We believe that by resolving our water supply problems (with a more reliable well) and by replacing the membrane with a filter cloth that we will be able to make more use of the Micro Screen.

The sewage effluent discharged from the Clarifier and Micro Screen contains bacteria and minimal amounts of solids and dissolved organic material. The effluent is disinfected to kill the bacteria. At Bear River, we disinfect the sewage by exposing it to a high concentration of Ultraviolet (UV) light. The UV light is generated by special lighting fixtures mounted within tubes. The effluent and bacteria are exposed to the UV light by running the effluent through the tubes containing the special bulbs. The effectiveness of the UV light in the destruction of bacteria is a function of the suspended solids load in the effluent. Suspended solids create "shaded areas" in which the bacteria are sheltered from the light. In order to achieve the highest possible bacteria kill, it is necessary to reduce the suspended solids load in the effluent.

The treated sewage effluent is discharged to the Bear River after it is disinfected. For plant management purposes, the rate of discharge from the plant is measured and recorded before the discharge occurs.

When the Clarifier is drained, the operator has the option to return the activated sludge to the treatment process (in the Bioaugmentation unit, or to waste the activated sludge to the Sludge Digesters. The Sludge Digesters are two buried tanks into which activated sludge is discharged. Air is introduced into the Sludge Digesters in much the same manner that it is introduced into the Solar Tanks and the Solar Pond, but at a much higher rate. In the Sludge Digesters, bacteria, in an oxygen rich environment, consume the organic material in the sludge. Over time, the organics are
removed, the bacteria die and are consumed by other bacteria. Periodically, the operator shuts the aeration system in the Digesters off, allowing the digested and partly digested sludge to settle. The fluid on top of the sludge is removed (decanted), consequently thickening the sludge. The decanted fluid is recirculated back to the Bioagmentation unit. After about 45 to 50 days of a Digester being filled and the sludge digested and thickened, the sludge is removed and placed on the Sludge Drying Beds. The Sludge Drying Beds are underdrained sand beds surrounded by a fence. The pipes under the Beds (the underdrains) collect residual fluid from the sludge and return it to the Bioaugmentation unit. The dried sludge looks and feels like damp coffee grounds. The digested, dried sludge, while its organic content is low, is composted.

More information about technical aspects of the project may be obtaining by contacting:

Environmental Design and Management Limited (EDM)
Suite 707
Purdy's Wharf Tower 1
1959 Water Street
Halifax, Nova Scotia, Canada
B3J 3N2
Phone: (902) 425-8899 FAX: (902) 425-7990
EMAIL: [email protected]