BIODISK - Wastewater Treatment Systems
Wastewater treatment using a BIODISK is a natural biological process based on the principle of the rotating biological contactor (RBC). It is self regulating, a complete treatment plant and can be sized to meet your needs. The treatment process has capabilities of secondary, tertiary and advanced treatment with an additional capability of denitrification.
The BIODISK is a natural biological process for the treatment of wastewater based on the principle of rotating biological contactors (RBCs). This process has many inherent operating characteristics that make it ideally suited for the treatment of domestic wastewater.
The treatment process easily accommodates flows ranging from 0 to 100 percent of design. The biomass on the RBC media is directly proportional to the organic material received. The process is self-regulating without supervision.
Sized to Meet Your Needs
Designed specifically for small flow applications of less than 1,000,000 gallons per day (gpd). The modular design allows today’s needs to be addressed today whereas tomorrow’s needs can be addressed tomorrow.
Complete Treatment Facility
RBC facilities have primary clarification, aeration, final clarification and easily accommodate auxiliary equipment such as filtration, disinfection, chemical addition and minimal biosolids management. The treatment process can be designed for secondary, tertiary and advanced wastewater treatment.
The BIODISK has several unique properties making it a desirable system for ease of operation and maintenance such as:
- Low power consumption
- No field tests
- Long-term biosolids (sludge) storage
- No odour
- Built-in multi-stage process utilizes naturally occurring microbes
- Low operator skill requirements
- Operator intervention is limited to preventative maintenance and periodic sludge withdrawal
Low Power Consumption: The BIODISK process requires less electrical energy than other treatment processes. The installed horsepower (hp) ranges from ¼ hp to less than 10 hp. The installed hp is required for start up only. When in operation the power draw is just 60% of rated capacity. During normal operation the balanced shaft rotates effortlessly. The shaft power draw is consistent and fluctuates only when start up is required. The rotational speed of the disks is just 1 ft per min. Slow speed is naturally associated with lower power requirements.
There is no requirement to remove or treat the biosolids that are contained within the process. The internal storage of biosolids is essential to the process. Biosolids, when stored in the primary and final tanks, provide a source of heat. The sludge blanket is exothermic and static. No sludge collection devices are required. Sludge is removed once or twice each year. The BIODISK uses a recycle system that puts oxygen into the primary tank. This oxygen recycle eliminates nuisance odours from the primary tank and allows long-term biosolids storage. The recycle also ensures that a food source is available to the biological population 24 hours a day and 7 days a week.
Even accessory items have low power requirements. Phosphorous is removed with the addition of a fractional hp chemical feed pump that proportionally feeds the chemical in relation to the flow. When lower effluent qualities are required the biosolids are returned to the primary sedimentation tank by a fractional hp submersible pump. The frequency of return is only three times a day and for short periods. The control panel allows the owner/operator to adjust the frequency and duration of the biosolids return rate.
The operational cost of the BIODISK is lower than for other forms of treatment processes. The lower power requirement will also save capital if stand by power is a requirement. The low hp in the BIODISK will be reflected in the reduced size stand-by generator requirements.
No Field Tests: The BIODISK processes regulates itself. When the owner/operator becomes familiar with the system, visual inspection is all that is required. When we talk about wastewater we think of pollution. In the BIODISK, pollution is considered a food source for the biological population. The biomass is a living matt of activity that attaches itself to the slowly rotating disks. Microbes that are naturally present in the wastewater accomplish the purification. These microorganisms are often called bugs for simplicity. The bug population is directly related to the food source. If there is a lot of food the bug population will occupy a lot of disk surface area. When the flow or source of pollution is reduced, the bugs or biomass is reduced. This is a natural process that we do not need to influence.
The RBC process does not need to artificially over populate the aeration process. There is no requirement to test for mixed liquor suspended solids (MLSS). There is also no need to calculate the sludge volume index (SVI). The slow rotation of the disk provides a large wetted surface area and efficient oxygen transfer. Higher than required dissolved oxygen (DO) levels are normally present. High DO eliminates odours and does not inhibit the biological activity. Efficient plant operation is achieved without the need for measuring or adjusting DO.
The requirements for effluent testing are dependent of the environmental authority and are stated in the approval documents. It is often a requirement to periodically test the effluent for biological oxygen demand (BOD), suspended solids (SS), nutrients such as ammonia, nitrogen, phosphorous and fecal coliform. BIODISK Corporation recommends that both the influent and effluent be tested during the start up period and until the owner/operator becomes comfortable with the process. An experienced eye can visually determine effluent quality by the colour, texture and quantity of the biomass on the disks.
Long Term Biosolids (Sludge) Storage: The ability to have static and long term biosolids storage is both an advantage and a necessity. Biosolids are a source of heat and food with 90% of what is consumed going off in the form of heat. Aerobic biological activity needs DO levels of at least 2.5 mg/L in the wastewater. The BIODISK can have as much as 8 mg/L of DO in the last stage of the process and some of this liquid is recycled back to the primary clarifier to reduce odours.
Buckets are attached to the outside of the disk bank. When the disks rotate the buckets fill and discharge from the fourth stage to the primary sedimentation tank. This recycle introduces a closed loop flow pattern through the primary and all four stages of the disk system. The static sludge continues to decompose under anaerobic conditions.
Anaerobic conditions need DO levels approaching zero. The decomposition of sludge releases dissolved organics and gasses. The anaerobic gases are absorbed into the aerobic layer caused by the high DO in the recycle. The food or dissolved organic matter is transported by the closed loop recycle to the disks. The continuous source of food ensures a stable biological population on the disks. The BIODISK process is not affected by intermittent loadings or seasonal flow changes. The volume of sludge is reduced through aerobic and anaerobic activity. Aerobic activity is quicker than anaerobic activity. The recycle of high levels of DO starts the biological process in the primary tank and reduces biosolids accumulation. Research has shown that the RBC process can reduce biosolids by up to 80%.
The BIODISK does not require the artificial increase in biological population. The bug population does not have to operate in the endogenous phase of respiration. What this means is that the bug population does not have to be operated in a declining growth phase so that they are under fed and hungry. In some treatment plants the final tank influent strength can be 2,250 mg/L. In the BIODISK the final tank influent strength is about 40 mg/L. This low level of final tank influent greatly reduces the potential for excessively high organic wash out. Final tank sludge storage is reduced in volume and strength in the BIODISK. When tertiary treatment is required the biosolids are returned to the primary tank.
No Odour: The RBC process consumes odour. Henry’s Law of Equalized Pressure states that if we put a gas in the headspace of a test tube and clean water in the bottom half of the test tube, the gas will migrate freely from the headspace to the liquid. In the BIODISK the wastewater in the first stage can emit odour. As the process takes effect, the lag stages have greatly reduced substrate strength and subsequently absorb gases and consume odour. Municipal treatment plants and fish feed producers have used the RBC as an odour control device.
In some wastewater treatment processes the strength of the wastewater in the aeration chamber is increased by 10 times. Normal wastewater has a strength of 225 mg/L for biological oxygen demand (BOD). In a suspended growth system the aeration chamber wastewater strength can be 2,250 mg/L BOD. The odour is associated with waste strength. As indicated above, the BIODISK will consume any odour that is given off by higher strength stages. Surplus oxygen levels also reduce odour levels.
Within the BIODISK there is an organic scent to the air. There are no exposed anaerobic conditions or requirements for high levels of BOD. No air is pumped through the system
Naturally Occurring Microbes: There is nothing to add to the BIODISK process except a small amount of electrical energy. Mother Nature provides all that is required for efficient biological activity.
When in the disk sections, the microbes attach themselves to the disk media. With the rotation of the disks they receive the ingredient they require for their propagation. That ingredient is oxygen.
The disks are 40% submerged in the wastewater and have 60% exposure to the air. As the disks rotate the huge wetted surface area allows the oxygen to enter the wastewater and come in contact with the biomass. Simply put - the bugs breath when out of the wastewater and consume pollutants when in the wastewater. The disks revolve 3 times per minute.
The biological population is segregated. There are thousands of different bacteria that are present in the wastewater. They do not all like to live together. These microbes can be divided into two basic classes. Carbonaceous consuming microbes, bugs that eat organic material, occupy the first stages of the disk. Nitrification bacteria occupy the later stages. These microbes convert ammonia into nitrate.
The carbonaceous microbes consume all forms of organic material and prevent the nitrification microbes from getting established until the wastewater strength is less then 30 mg/L. When the strength of the wastewater is reduced to 30 mg/L there is still sufficient nitrification bacteria to establish a beneficial biomass. These bugs can be referred to as pit bulls and poodles. The pit bull is aggressive and eats everything. The poodle is smaller, not as forceful, harder to maintain and more selective in what it consumes.
The fourth stage process in the BIODISK allows different microbes to dominate in different stages. The different populations can be seen as having different textures, colour and thickness of growth. The BOD removal sections are typically dark brown and have a biomass thickness of 1/16 of an inch. The nitrification section is lighter in colour and has a much thinner biomass. An operator can look at the colour and texture of the disks and know if the plant is operating correctly.
Operator Skill Requirements: The BIODISK is a self-regulating process that looks after itself. The operator requirements are limited to preventative maintenance. The factory has permanently lubricated the drive system. The operator only has to grease the bearings twice a year and take down a few operator notes. When the biosolids accumulation exceeds requirements, the recycle begins to pick up excessive organic content. The disk colour and texture will reveal to the operator when it is time to remove biosolids. Septic haulers remove the biosolids.
The second measure of biosolids accumulation is the sludge blanket. Wastewater contains fats, oils and greases (FOG). This material will float on the surface of the primary tank. Scum accumulation (FOG) is related to the biosolids on the bottom of the primary tank. Visual inspection of the scum blanket will tell the owner/operator when it is time to remove scum and biosolids.
No tests are required to be performed. The operator does not have to determine mixed liquor suspended solids, sludge return rates, dissolved oxygen levels or sludge age. The operator only has to see if the disks are rotating and that the colour and texture of the biomass is normal.
Operator Intervention: Operator intervention is limited to preventative maintenance and periodic sludge withdrawal. Normal operations include greasing the bearings, filling any chemical tanks if required for the process, checking the disinfection device and making sure the disks are rotating. If visual inspection indicates that the biosolids need to be removed the operator contacts a pump out truck. Biosolids from the BIODISK are considered to be primary solids and must be disposed of in a suitable and safe manner.
Additional advantages in comparison to typical municipal systems such as extended aeration and sequential batch reactors. The additional advantages include:
- Small foot-print allows for cost effective architectural design
- Totally enclosed system
- Safe - no open ponds or exposed tanks
- Blends easily with surrounding community
- Easily expandable with modular design
- Addresses today's needs today and easily accommodate future designs
- Low power consumption
- Huge biomass inventory
- Segregated biomass development
- Very low noise levels
- High Resale value
- Life-cycle costs of a BIODISK facility are substantially less than for comparable treatment processes
Architecture: The small footprint allows cost effective architectural design of a totally enclosed system. Land can be expensive. It is a fact that in some locations the smaller space required for an RBC will save the owner enough space to pay for the system.
In Jakarta Indonesia, the RBC is sited in the basement car parking area. On several projects the RBC was 27 car parking spaces smaller than the competition. At $27,000 per parking space the client's revenue increased by $729,000 US and more than paid for the complete system
In most instances, just the savings in concrete or brickwork can be an advantage. A small structure is not as ominous and a small building blends in with the surrounding architecture easily. When it looks like a treatment plant, the Not In My Back Yard (NIMBY) process kicks in. When it looks like the New Horizons project in the Applications Section, it just adds elbow space to the neighbour's property. A covered treatment plant is also safer from a health perspective; there is no airborne bacteria or exposed wastewater.
The design of an RBC is based on organic loading and the disk surface area. The shafts are modular and can be duplicated easily. There is no need to build a plant for a projected 20-year life span. The design engineer can select a model that will meet the current needs plus some small expansion. When the treatment works approach the design capabilities, a second module can be placed beside the first and so on. Environmental engineers and the approval authority will always design on the safe side. A BIODISK that is overbuilt will have a better quality effluent than one operating at design. When a second shaft is necessary it will start up without process malfunctions or disruptions even when underloaded.
Low Power Consumption: The BIODISK operates at one half to one eighth of the power requirements for other forms of aeration equipment. The largest drive on the biggest BIODISK is less than 10 hp. There are no high power requirements for the supporting equipment. Phosphorous is removed with a fractional hp chemical feed pump that is flow proportioned by a flow meter. Sludge is returned from the final tank by a small hp submersible pump. Filtration and disinfection power draws are consistent with other technologies.
The low power required not only affects the daily operation of the disk but it also reduces the size of the standby generator when required. The prospective owner of a BIODISK wastewater treatment plant needs to be aware of the total installed electrical draw of the plant as compared to other installations.
Biomass Inventory: The high biomass inventory is an inherent feature of the BIODISK process. The RBC is referred to as a fixed film system. The biomass is attached and cannot be washed out. Attached growth systems (fixed film) have up to 10 times more bug population than other forms of wastewater treatment. This is important when considering the effects of shock loading. Shock loading can be biological and or hydraulic.
It is next to impossible to wash the biomass off the disks with a hydraulic surge. The biomass is like the seaweed that grows on the rocks on an ocean shoreline. The wave action cannot wash off the seaweed and hydraulic surges cannot wash off the biomass. The final clarifier is designed for a peak hydraulic load of three times its design capacity and it can be washed out. What is important about the final clarifier of an RBC is that the influent is approximately 40 mg/L BOD and SS.
A suspended growth system for other forms of treatment has a final clarifier influent of about 2,250 mg/L. Wastewater strength of this magnitude can and does cause sever pollution in surface water during washout conditions. If the process discharges to a filter bed with a strength of 2,250 mg/L, it can overwhelm the filter bed.Even a normal operating suspended growth system will periodically discharge rags and debris that end up in the filter bed. Mr.
Farley Fry has tested the response time to hydraulic upset in the RBC at Virginia Polytechnic Institute. Mr. Fry has said the RBC will recover in 24 hours for BOD and five days for nitrification. An operator has commented on how long it would take a suspended growth system to restart after a hydraulic upset and his answer was 'Six to eight weeks as long as it was not in cold climate conditions'. The RBC does not lose its biomass inventory with shock hydraulic loading.
Organic shock can also be accommodated in the BIODISK. With an inventory of 5 to 10 times more biomass the assimilation capacity is proportionally bigger. The microbes are like foragers that accumulate organic material in the shell structure for later consumption.
Segregated biomass development: Allows for more efficient treatment. The BIODISK is a self-regulating process. The operator does not have to perform tests to balance the system. There are no mixed liquor suspended solids to monitor. The process is not affected by sludge age. Dissolved oxygen is not a design parameter. The operator may have to have effluent samples tested to ensure compliance. The operator can tell if the system is operating correctly with some visual inspection of the colour and texture of the biomass, the quantity of floating materials and the odour within the process.
1. The biomass that matures on the disk is directly related to the food source. If there is 25% of the designed organics then the system will receive 25% of the food and just 25% of the disk surface area will be used. With 75% of design loading the disk will have 75% of the surface area covered by biomass.
2. The colour of the biomass indicates the system’s condition. Normal biomass will be dark brown in colour and cover the complete disk. It will then progress to a lighter brown on the succeeding stages. When the system is upset by excessive amounts of fats, oils and grease the disks will start to have grey and black patches. If the external problem is not corrected, the first and then subsequent sections of the disks will also turn grey and the process efficiency will decrease.
3. When operation is normal the odour inside the system will have an organic scent like good garden earth. Unpleasant odours are associated with organic overload, high greases, detergents, some form of biological inhibitor, or a combination of these. This biomass is a living body, which can be killed by wax strippers, antibacterial soaps or excessive use of detergents. All forms of wastewater treatment, not just BIODISK, will be adversely affected by such harsh chemicals. In the BIODISK the adverse effect of chemicals is dampened by the use of a primary sedimentation tank.
4. It is normal to have the fats, oils and greases collect along the sides of the BIOZONE. This is called scum. The system design incorporates a primary tank where the floating material can be retained. The amount of floating solids is related to the amount of biosolids that are retained on the bottom of the same primary tank. When the scum gets thick it is a visual indicator that the system needs to be cleaned out. Cleanout is required about once a year.
Noise Levels: Noise levels are very low even inside the BIODISK. The only sound is the gentle rotation of the disk in the water. The mechanical components are limited to a shaftmounted reducer and the gentle hum of the electric motor can be heard.
Resale Value: The BIODISK has resale value. Two of the school projects in the Applications section have benefited from the resale of a treatment works. It is often suggested that if the treatment works has a short life span, then use a full steel tank. Many steel tank systems have been moved from location to location successfully. Construction camps, for instance, are a good example of use and reuse of the BIODISK. If you cannot find a buyer for your system we will help. Used systems are in demand.
Life Cycle Costs:
The lower power consumption is one of the biggest life cycle cost savings of the BIODISK.
At 1/2 to 1/8 the power draw of comparable forms of treatment the electrical cost saving over the life of the works can more than cover the capital expenditure.
The small RBC footprint reduces house-cleaning time. There is no requirement to have an onsite lab to monitor the process. In some jurisdictions a lower level of operator certification helps to reduce costs.
If the process discharges to a tile field then the field will have an indefinite life. No rags or high strength wastes will be discharged to the bed.
Control panels do not have any programmed logic control (PLC) requirements. Simple mechanical timers can easily be adjusted by the operator without the need for computers or associated programs.
Sludge disposal can be labour intensive and expensive. There is less sludge to dispose of in the BIODISK process and the stored sludge does not have to be aerated or have any process requirements.