Traditional sludge systems - heading for the scrapheap?
Next-generation Sequencing Bath Reactors are rapidly making inroads into WwTWs. Ian Sully takes an in-depth look at the technology, and reveals how it is being used at Wessex Water's Charmouth site.Sequencing Batch Reactors (SBRs) have made their mark as an effective option to conventional activated sludge systems at WwTWs. As a result, the new-generation ill-and-draw method of treating and removing undesirable components from wastewater has become widely adopted.
Incorporating Auma's modular electric actuator technology, ITT Sanitaire has pioneered the Intermittent Cycle Extended Aeration System (ICEAS) sequencing batch reactor solution where influent wastewater continually flows into the reactor. More than 500 facilities are now in operation around the globe with processing flows ranging from 40m3/d to 520,000m3/d.
ITT Sanitaire's ICEAS SBRs work on a time principle to treat the effluent that they contain. The effluent is treated by air blown into the bottom of the SBR and distributed
by Sanitaire fine-bubble diffusers, which efficiently transfer the oxygen required to activate the sludge. The ICEAS SBR then has a settle phase to allow solids to fall to the bottom before the clean, treated liquid is decanted from the top of the SBR.
The ITT ICEAS SBR solution was initially produced in response to challenges in the wastewater treatment industry in Australia in the mid-1970s. Developed to meet the demanding criteria of the country's small towns and remote industrial centres,
the system had to be as economical as possible.
It had to function reliably on its own and operate under a range of changing influent conditions as plants were unattended for extended periods. The solution also had to be designed to expand easily to meet future population needs.
The innovative ITT ICEAS solution was produced including a non-hydraulic baffle wall separating the basin into two zones - react and pre-react.
Wastewater flows continuously into the pre-react zone, which acts as a biological selector. Wastewater also flows through openings at the bottom of the baffle wall and into the main react zone where Biological Oxygen Demand (BOD) removal and nitrification occur.
After aeration, liquid/solids separation takes place with the sludge then settling to the bottom of the basin leaving a layer of clear water on the top.
After settling, the clear water is removed by an automated, time-controlled decant mechanism. Sludge wasting is accomplished during this phase.
A recent enhancement to the decant mechanism made to ITT's ICEAS SBR solution incorporates Auma Sipos actuators. The SBR decanter upgrade moves away from external components to integrate intelligent functions within the actuator.
Benefits include advanced data feedback with increased detail of decanter functionality. Reliability and safety benefits are also cited as advance warning is given regarding potential problems.
Additionally, variable decanter movement is provided, which gives superior flow control for the SBR's fill-and-draw wastewater treatment activated sludge system.
Prior to introducing Auma's actuator technology, ITT Sanitaire's SBR decanters used a metric screw-jack mechanism driven by a separate variable-speed drive located in the motor control centre.
However, with the introduction of an integral actuator inverter, variable frequency drive starters are no longer required and cabling costs are reduced.
Over a period of 70 minutes, the decant arm is required to lower slowly from its park position to the top of the water and then on to the bottom water level.
From the bottom of the decant, having completed the decanting process, the decant arm is required to raise to its top (parked) position in about 20 minutes. This is a constant process performed 24 hours a day, seven days a week.
Due to fixed speed constraints, it was clear that a standard actuator could not be used. And this was the primary reason that the Auma Sipos actuator was chosen as, operating via an internal frequency converter, the actuator offers total and continual variation in speed.
Other benefits of the Auma Sipos solution include integral controls and self-monitoring functionality. The actuator also contains torque and position sensing to accurately feedback the position of the decant arm at any given time.
Additionally, motor temperature is monitored throughout the decant arm travel and
a warning is sent to the control system if temperature becomes excessive.
Ian Sully is managing director of Auma UK.
T: 01275 871141.
The Charmouth project
ITT's SBR development has been installed at a number of the UK's WwTWs, with Charmouth in West Dorset being one of the first sites to incorporate the technology.
Forming part of a £4.5M programme by Wessex Water to upgrade the WwTW, various treatment options were considered to determine how best to redevelop the site.
Michael Mackintosh, project manager for Wessex Water, outlines the application of ITT's SBR solution: "Charmouth is popular with holidaymakers and, as a result, the town's normal population of around 2,500 people swells to over 7,000
during the summer months, with many visitors staying in caravan sites in the surrounding area.
"When developing the secondary treatment works at the site, a conventional solution using filters with flow trickling through stone was discarded for a number of reasons, including potentially unacceptable odour and fly nuisance.
ITT's ICEAS SBR solution was selected as the optimum solution for a number of reasons, including lowest cost, space efficiency and the company's track record.
Flexibility was particularly important. With seasonal load fluctuations of up to a three fold increase being a major consideration, ITT's ICEAS SBR technology enables us to put one of our four basins out of service during the winter months.
"This is a compact, efficient solution offering the functionality, robust features and advanced technology we require. ITT's SBR solution at Charmouth will ensure we can meet the peaks and troughs that are experienced at a tourist town."