KEE RBC replacing expired Sewage Treatment Facility under Section 101a of the Water Industry Act
The picturesque village of Walton is located within the heart of Warwickshire adjacent to the River Dene. The existing privately owned sewage treatment facility located on the bank of the River Dene was life expired and would often flood, resulting in pollution to the river. An application was made to Severn Trent under Section 101a of the Water Industry Act to provide a first-time sewage connection for all 20 properties in Walton village with a population of approximately 70 people. Due to the remote location of the village, a connection onto the existing Severn Trent sewer network, either gravity sewer or a pumped solution, was not deemed feasible. Therefore, the proposal was for the installation of a new rotating biological contactor (RBC) to replace the existing treatment facility.
The wastewater treatment plant at the village of Keith in Aberdeenshire treats municipal wastewater from the village and effluent from a famous branded Whisky Distillery nearby.
The overall process on site includes inlet works with a grit chamber and screen for municipal wastewater. After this preliminary treatment, the municipal wastewater stream is mixed with the Distillery effluent and is processed through the first-stage high-rate biofilter tower. The effluent from the biofilter tower is then processed through radial flow-scraped primary settlement tanks and the settled effluent is discharged into a two-stage activated sludge basin consisting of two tanks of 7.92m x 7.92m x 4.65m deep (water depth 3.65m). The mixed liquor from the activated sludge plant is discharged through to three radial flow-scraped final settlement tanks and the settled effluent is discharged to a watercourse. The settled sludge is returned (RAS) to the activated sludge basin with excess sent to sludge storage. Finally, supernatant from the sludge storage tank is returned to the feed for the high rate filter tower.
The aeration system for the activated sludge basin consists of two surface-mounted aerators driven by a 20kW common-geared motor through a propshaft delivering approximately 30kg/hour of dissolved oxygen.
EXISTING AERATION SYSTEM – ONLY ONE SURFACE AERATOR OPERATING
The total BOD load to the plant from municipal and industrial sources is 570 kg/day and approximately 285kg of this is reduced through the high rate biofilter and the remaining 285kg/day is required to be treated through the activated sludge plant. The aeration tank capacity is 230m3 each and is normally operated at MLSS concentration of approximately 2000mg/l. One of the surface aerators in the existing aeration system had failed and a temporary venturi aeration system was installed to assist in oxygen supply.
KEE were requested to visit the site, analyse the situation and evaluate the process requirements to make a proposal to upgrade the aeration system. The factors to be taken into account included the need to upgrade the aeration system whilst the plant continued to operate (without decommissioning the plant) and to ensure that the new aeration device produced less than 60dB noise. KEE evaluated the existing process parameters and concluded that the plant could be operated at a higher MLSS concentration of up to 4000 mg/l at a substrate loading rate of 0.15g BOD/g MLSS. The estimated dissolved oxygen demand on this basis would be approximately 33kg/hour.
KEE proposed to install four 5.6kW dual mode Triton processors to provide complete mixing of both the aeration basins and to supply up to 40kg/hour of dissolved oxygen. The Triton dual mode processor is an efficient aeration device which provides total (horizontal and vertical) mixing of the whole basin. It can be mounted from a wall or a bridge or can be supported from floats. The Triton can mix up to a depth of 10m and therefore is also ideal for upgrading existing aeration systems for total replacement or supplemental aeration. The Triton uses a low-power regenerative blower for air supply and a direct-coupled electric motor to generate a plume of fine bubble aeration which is able to penetrate through to the bottom of the tank. This air/water mixer provides a long retention period for air bubbles and the resulting high efficiency oxygen transfer into the mixed liquor. By EPA definition the Triton is a fine bubble aerator.
KEE TRITON® AERATION IN OPERATION
The four Tritons were mounted from the side walls of the existing tanks and, once all the installation work was completed over two days, the electrical cabling was finalised. The blowers supplying air into the Triton were controlled through D.O. probes located in the aeration basin. Once all the electro mechanical work was complete the Tritons were switched on and the old aeration system switched off. The plant aeration system upgrade was achieved in less than one week’s time on site and without any downtime on the existing treatment process. There was no need to hire temporary plants to relieve activated sludge plant. Apart from large savings in capital and operating costs, the biggest benefit was that all the logistics and space problems associated with installing a temporary plant were avoided. The noise emitted by the new aeration system is much lower than specified and definitely lower than the previous system. The process performance of the plant has improved and the plant is able to meet its specified process objectives and has continued to do so for over twelve months.
KEE seeks to identify and satisfy the needs of their customers by providing quality engineered solutions priced to offer value for money. KEE has over 60 years’ experience in wastewater treatment, process engineering, servicing and operation with over 350,000 installations worldwide.
The technologies and services offered by the KEE Group of companies are listed below:
Anaerobic Reactors – The KEE Group offer design, installation and operation of on-site treatment plants. Their technologies include anaerobic digestion, aerobic processes including RBC and Submerged Aerated fixed film systems, extended aeration and SBR activated sludge processes, complemented with physical and physio-chemical processes. KEE also have a team of experienced process engineers and project engineers capable of delivering solutions to suit
pre-treatment of industrial and food processing wastewater
KEE Microfloat® – Dispersed Air Floatation Technology, for pre-treatment of industrial and food processing wastewater to reduce FOG, BOD, COD & SS. The KEE Microfloat system achieves the same result as conventional DAF systems without the need to use a high-pressure pump and venturi. It incorporates a system to produces extremely fine bubbles 10 to 50 micron air bubbles into the water to float the light fractions
KEE – FINE BUBBLE AERATION SYSTEM WITH BUILT-IN MIXER
The patented new Dual Mode Processor called the Triton Aerator/Mixer.
This new technology overcomes the previous limitations of oxidation ditch technology and can be used to revitalise existing oxidation ditches and technology.
Oxidation ditch technology is one of the oldest ways of treating wastewater. Whilst it enables wastewater to be treated to a high standard, including nitrification and de-nitrification, it does have significant limitations.
The process requires aerated and mixed liquor to continuously move through the aeration ditch. Brush rotors and disc rotors aerate and mix the liquor but, because they can only maintain the necessary fluid velocity of 0.3 – 0.4m/s in a shallow depth of no more than 2m, the footprint area of the oxidation ditch is extremely large.
The Triton Aerator and Mixer Aerator is an energy efficient, dual mode (aeration and mixing) process aerator that is capable of nitrification and de-nitrification all in one unit. With two propellers and a regenerative blower, it is able to operate either as an anoxic mixer with the blower turned off, or a very efficient aerator/mixer with the blower turned on.
With its two mixing propellers, the Triton is able to achieve significant velocities in depths of up to 10m. This means the oxidation ditch basin can now be built up to 10m deep, therefore significantly reducing the footprint area.
The Triton Aerator/Mixer’s primary and secondary propellers inject air bubbles (defined by the Environmental Protection Agency as “fine bubble”) into a high velocity stream (plume) below the surface of the water and provide flow linkage mixing in multiple unit arrangements.
The Triton can also be used to revitalise existing oxidation ditch systems with failing brushes or disc rotors. If the rotors have totally failed, the Triton can replace them.
Franklin’s plant has two oxidation ditch systems operating in parallel, each of which treats 4536m3/day, with influent BOD of 185mg/l and TSS of 90mg/l. The Oxidation Ditch Wastewater Treatment Plant at Franklin was failing to meet the consent of 15mg/l BOD and 23mg/l TSS. Because the rotors required daily lubrication, maintaining them was a time consuming and costly exercise. So when the rotors fractured and failed four years ago, the decision was made to upgrade the plant by replacing the brush rotors with the Triton Aerator/Mixer.
During the upgrade each ditch was fitted with four Triton each rated 18.6 kW. This represents a maximum of just over 2kWh of electrical energy per kg of BOD or 0.4 kWh/m3 flow.
The final effluent quality from the refurbished oxidation ditch is testimony to the excellence of the Triton. The result of the upgrade was final effluent with BOD of between 2 and 3mg/l and TSS well below 15mg/l. Independent velocity measurements at extremities are well above the minimum 0.3m/sec, therefore guaranteeing that no solids deposit would develop in the basin. At the same time, maintenance requirements have been substantially reduced to a simple lubrication task once every six months.