AERATION
The greenest of upgrades
New aeration and mixing units at the Mountmellick wastewater treatment plant are having a positive impact.
They are helping to reduce the carbon footprint – and improving plant performance, too
T
he existing wastewater treatment plant reduced from 42kW to 30kW and the treatment
serving the village of Mountmellick in objectives were completely achieved.
County Laoise, Ireland, was designed and Furthermore, the energy efficiency gains and
installed in the mid 1970s. The works consisted optimisation objectives were achieved by
of a wham mechanical screen followed by an controlling the aeration mode to provide oxygen
oxidation ditch for biological treatment, two final as and when required but the mixing mode was
settlement tanks and sludge dewatering works. always maintained to ensure the process
The biological treatment of the wastewater was performance. Thus, an energy saving in
provided by use of an activated sludge process excess of 28.5% was achieved and at the same
through a ‘race track’ shaped oxidation ditch of time the environmental objective for effluent
60m long straight lanes and semi-circular ends quality was met.
of 7m radius: each lane was 7m wide. The The phase two upgrade is still to be
average depth throughout the ditch was 1.57m. implemented but it is expected that the energy
The main aeration equipment in use was a efficiency gains and carbon footprint objectives
horizontal brush aeration system. Kee Triton®s can be bridge or side-wall mounted will be met.
At Mountmellick WwTP, this consisted of four
horizontal rotors, each 2m in length. The brush two phases using KEE Process Triton® dual Aero 02 Triton® Units
rotor aeration capacity was inadequate and was mode fine bubble aerator/mixer. Triton® units offer a cost-effective and efficient
supplemented by Venturi Aerators. The design aeration and mixing of the effluent. As the
capacity of the works was 5,000PE and the Phase one aeration/mixing function is combined in
discharge consent was 20mg/l BOD and 30mg/l Based on the current load and process dissolved a single processor and operate independently of
SS. Consequently the plant was failing consent. oxygen (DO) demand for phase one, it was each other, there is no longer the need for
necessary to install four 3.7kW Tritons® to additional mixing equipment for process
Design and supply provide the supplemental DO and all the mixing optimisation. Triton® is a ‘fine bubble’ aerator as
During mid 2007 KEE Process was contacted by for the oxidation ditch. These four Tritons® would per EPA guidelines and as it is capable of
Larry Gittens of Laois County Council, about its provide complete mixing of the ditch and aerating and mixing contents of reactors up to
Triton® aerators and mixers. He was interested generate the optimum horizontal velocity of 10m deep, it is possible to improve on the
in their potential capability to overcome the 0.3m/s to ensure that the suspended solids in oxygen transfer efficiencies by the strategic
process issue facing the plant for the current load the mixed liquor remained in suspension. arrangement of Tritons® in deep basins.
and explore the option to save power and KEE has installed Triton® units on a number
increase the plant capacity. Supply and installation of sites throughout the UK and Ireland such as
After discussions with Laois County Council, Of all the aeration equipment on the market, Keith WwTP, Aberfeldy WwTP, Taw Valley
together with their consultants Michael Madden Triton® aeration units are the easiest to install, Creamery and Ulster Farm By-products Ltd with
and Alice O’Sullivan of Nicholas O’Dwyers, KEE with no need to decommission existing works. all sites now showing a marked improvement in
visited the site to obtain the relevant information Four out of the eight Tritons® for phase two will treatment and carbon footprint.
and gain an overall knowledge of the works. be operated in aeration and mixing mode at all The maintenance requirements for
After further liaison and evaluation of the actual times and the other four Tritons® would be Tritons® are minimal with simple water-
dissolved oxygen requirements, it was agreed operated in mixing and/or aeration mode. lubricated bearings requiring change every
that the plant upgrade should be carried out in For phase one the installed power was five years. ■■■
The design criteria for phase two upgrade
Type of wastewater Municipal Although the stated environmental For carbonaceous BOD removal only,
Dry weather flow (DWF) 1,575m3/day objectives do not require nitrification, the the AOR would be 773kg/day.
Full flow to treatment NH4-N in the influent would exert an (AOR is the oxygen required under field
(FFT) 3.3 x DWF = 5,184m3/day oxygen demand due to high retention conditions of temperature, elevation,
Total influent BOD5 load 420kg/day time of 20 hours at DWF in the desired dissolved oxygen operating
Total influent nitrogen load 77kg/day oxidation ditch, the projected AOR concentration).
Oxidation ditch approximate volume 1,340m3 (actual oxygen requirement) of To provide the projected AOR
Treatment objectives BOD5<20mg/l; 959kg/day accounts for both (as stated), eight 3.7kW Tritons® were
SS<30mg/l carbonaceous BOD reduction required, in addition to the existing
(no nitrification) and Nitrification. horizontal brush rotors.
September 2009 Water & Wastewater Treatment 25