Treatment plant the source of Shannon odours

SHANNON has been plagued by foul odours for months and an audit report carried out by the Environmental Protection Authority (EPA) into the town’s wastewater treatment plant says much of the blame lies with inadequacies at the plant.

The audit was carried out in mid-October by John Feehan and Joseph Hunter of the EPA, with consultant John Kilgallon.

Their report had seven main findings, one of which was that the plant was “generating significant hydrogen sulphide odours”. Hydrogen sulphide generates a strong smell similar to that of rotten eggs.

Other findings were that the plant was designed and built without preliminary treatment facilities and that the plant is “currently achieving very little in terms of wastewater treatment’.

The report’s sixth finding is that “The problems identified at the Waste Water Treatment Plant (WWTP) must be addressed and if any residual odour sources remain, they can then be more easily identified and remedied”.

The final one stated, “Urgent priority measures need to be taken ahead of the longer-term planned upgrade of the Shannon Town WWTP in the context of the nuisance now being caused by the WWTP”.

Outlining the background of why the audit was taking place, the report stated, “Since late September 2013, both the EPA and Clare County Council have received complaints about foul odours from residents of Shannon Town. Between September 24 and October 7, the EPA received 30 complaints, while Clare County Council received 41 complaints in the same period.

“The complaints have come from various areas of Shannon town and its environs but were concentrated in the Ballycasey, Bóthar Mór and Tullyvarraga areas. Offensive odours have also been reported in the Bunratty and Cloverhill areas to the east of Shannon Town.

“A number of the complainants described the odours as having a characteristic rotten-egg smell (ie a hydrogen sulphide type odour).”

It provides data on the plant and states, “It appears that the Shannon WWTP is currently providing little or no biological treatment and is essentially functioning mainly as a solids removal facility”.

The report says influent streams to both the domestic and industrial sides of the plant were black in colour. It noted there was just one dissolved oxygen meter at the plant, while the calibration meter on it indicated it was due to be recalibrated last year.

It states there are no preliminary treatment facilities for raw wastewater, while it described some of the inadequacies in terms of aeration.

“Due to the inadequacy of the surface aerators in the aeration basins and the absence of any mixing equipment in the flow balancing tanks, there is the potential for the accumulation of solids in these tanks.

“The absence of screening is allowing objectionable materials to enter the WWTP. The installation of screening is needed in order to protect existing equipment and any new mechanical equipment that will be installed at this WWTP.”

There are issues with the industrial side of the plant, it found. “The industrial side of the Shannon WWTP is not capable of satisfactory removing specific individual metals and chemicals. Such substances require specific individual treatments and a ‘one size fits all’ option is not appropriate.

“As there is no biological process on the industrial side of the WWTP, it essentially just removes some solids and some chemically flocculated material.”

Consideration should be given to changing its use. “The industrial side of this WWTP may be regarded as redundant with respect to its original concept and is therefore available for a more productive use, namely conversion into a biological treatment plant.”

A number of issues with the domestic side of the plant were also identified. Summing it up, the report stated, “In conclusion, the domestic side of this WWTP is not effectively treating the wastewater discharging to the Shannon Waste Water Treatment Plant and appears not to have been for some time.”

In the recommendations section, it states that both industrial and domestic influent streams should be combined for joint treatment at the plant. It states there are practical steps that can be taken to offset the odour problem.

“To achieve consistent aerobic operation, thereby eliminating the odour problem, the following options need to be implemented immediately: the ‘domestic’ side will need to be refitted with adequate mixing/aeration equipment. A diffused air system would be preferable; the ‘industrial’ side of the WWTP will need to be converted into an activated sludge plant by fitting appropriate mixing/aeration equipment into the existing twin (1269m3) flow balance tanks. A diffused air system would be preferable. A sludge return line from the clarifiers (chemical precipitation tanks) to these tanks should be installed.”

It adds, “The implementation of both of the above should efficiently utilise the potential of the existing civil works and increase the BOD removal capability of the WWTP to approximately 38,000 population equivalent, which is the same order of capacity as originally envisaged in the proposals for the future upgrading of the facility and should meet the requirements of the Waste Water Discharge Licence for the Shannon Town agglomeration to ‘refurbish the existing WWTP and upgrade it, resulting in a population equivalent of 35,000 by December 31, 2015.”

Another recommendation is for “suitable screening equipment” to be installed.

It also states, “An evaluation should be conducted of all industrial point sources discharging into the WWTP that contain substances with the potential to cause inhibition of activated sludge and/or have the potential to generate odours at the Shannon WWTP or in the sewerage system.

“A strategy should be put in place to examine the feasibility of requiring such streams to be treated at source prior to the discharge of that effluent to the Shannon town sewerage system.”
Works needed to preserve or restore the “structural integrity” of the local sewerage system should go ahead, while it also says that should “any acute health and safety problems be identified during ongoing investigation of the town sewerage system (especially from gas monitoring carried out on the sewerage network), these should be given priority attention and should be done so in consultation with the Health and Safety Authority and the Health Service Executive.”

Clare County Council is required to submit a statement on how the main recommendations of the audit will be progressed.