Water and Effluent Treatment Magazine
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16 WET NEWS APRIL 2016 Treatment facilities are noisy places, particularly at night, putting staff at risk and upsetting residents. Wakefield Acoustics' Lee Nicholson explains. The challenge: Turning down the noise INSIGHT Noise management The blowers were used to supply pressurised air for the aeration systems I t is estimated that more than one million employees in Great Britain are exposed to levels of noise which put their hearing at risk. What is also apparent is that public attitudes towards environmental noise appear to be changing as people become less tolerant of excessive noise. Throughout Europe important changes are taking place with regards to environmental noise policy, legislation and management Faced with these challenges most water authorities have, over the course of recent years, been taking a proactive approach to implementing noise management and mitigation measures within water and wastewater treatment plants. The processes used to treat wastewater and sewage necessarily comprise large areas of mechanical equipment, most of which have a high potential for creating excessive noise. Equipment such as hydraulic pumps, high-speed decanter centrifuges, exhaust fans, generators and blowers and associated pipework can all combine to cause noise levels that are potentially harmful to both staff working within the facilities, as well as to residents who live close by. Add to the mix, the fact that plants o en operate on a 24/7 continuous basis, and are o en A solution: Identiing the noise-makers A night-time survey identified the blower plant room as a culprit for excessive noise. T o combat the detrimental effects of environmental noise, and in turn signifi- cantly reduce noise in the sur- rounding residential areas, Wakefield Acoustics conducted an accurate diagnosis of noise sources within the plant. As dis- turbances had been frequently reported during non-traditional working hours, a night-time survey was conducted and a report was generated in accord- ance with BS4142 procedures. By taking a range of sound readings at various frequencies and turning off machinery, the company was able to identify and report dominant noise sources within the facility, which meant specific noise con- trol solutions could be suggested. Following an accurate diag- nosis of noise sources, the noise control specialist identified the blower plant room as a central area to address, to reduce exces- sive noise at the plant. The blowers were used for the sup- ply of pressurised air for the aeration systems, where they were utilised to treat water entering the plant – a key ele- ment in the water treatment process. The solution was to supply bespoke designed and purpose- built intake attenuators on to the blowers. The attenuators comprised a pre-galvanised mild steel casting which could be riveted, screwed or welded dependent on the application. Taking into account the spe- cific site requirements, Wake- field Acoustics designed the attenuators to be installed into the existing ductwork, elimi- nating the exceptionally costly nature of retrofitting. The designs not only took into con- sideration the inherent noise of equipment, but also the logisti- cal and spatial limitations in terms of access to, from and around the wastewater treat- ment facility. Following installation of the intake attenuators, a post instal- lation noise assessment was completed which recorded sig- nificant reductions in noise lev- els. This decrease in noise out- put not only resulted in noise complaints being resolved, but also further ensured the safety of workers operating within the facility. Wakefield Acoustics supplied a large number of noise control solutions includ- ing enclosures, attenuators, acoustic screens and louvres for a wide variety of plant applica- tions to most of the water authorities in the UK and worldwide. Most recent installations include completing a number of UK and international projects including a wastewater treat- ment plant in Turkey where being expanded and upgraded, and the risk to workers and the environment becomes even more apparent. This is a particularly major issue for wastewater treatment plants as noise outputs from machinery, which le untreated, can easily exceed 90dB(A). This means plants are potentially not only placing workers at risk but, without noise mitigation measures, are also in breach of noise legislation which has placed an added emphasis on reducing noise levels at source. Against a backdrop of increasingly stringent noise at work and environmental noise legislation, along with a public which is less tolerant of noise, it is clear that water authorities are now regarding noise control and management as a key area in the planning and ongoing management of wastewater treatment facilities. Given the capacity to create excessive noise, most wastewater treatment plants fall within the two key pieces of European noise legislation. Firstly, the Noise At Work Regulations 2005 which lowered the upper and lower action levels by 5dB(A) from 90dB(A) to 85dB(A) and from 85dB(A) to 80dB(A) respectively, and secondly, key legislation in the form of the Environmental Noise Directive, along with BS4142. A good example of the implementation of such noise control solutions in practice is one of Wakefield Acoustics recent projects at the water treatment plant of a leading water authority. Water treatment processes, particularly at night, whilst necessary for the efficient operation of the plant, had led to a history of noise complaints from local residents living in close proximity of the facility. This resulted in the water authority bringing in Wakefield Acoustics, to provide a solution. The critical problems to address from the plant's point of view were the blowers, which emitted substantial noise levels in excess of the upper action limit of 85dB(A) daily exposure levels. It was such noise emissions that had led to local residents suffering sleep deprivation and lengthy disturbances, meaning immediate action was required. Given the rigorous requirements placed on the plant under the Environmental Noise Directive – which has been adopted in the UK under the Environmental Noise Regulations 2006 – the water authority was keen to address the noise issues quickly and find a cost-effective and practical resolution that would not have a detrimental impact on operations. THE CONCEPT • Bespoke designed and purpose-built intake attenuators for the blower were supplied • The attenuators comprised a pre-galvanised mild steel casting • Could be riveted, screwed or welded dependent on the application NEED TO KNOW 1 The blowers emitted noise levels in excess of the upper action limit of daily exposure levels 2 Most WwTWs fall within the two key pieces of European noise legislation 3 Equipment such as hydraulic pumps, high-speed decanter centrifuges can combine to cause harmful noise levels THE VERDICT "Following installation of the intake attenuators, a post installation noise assessment was completed which recorded significant reductions in noise levels" Lee Nicholson sound power levels emitting from six turbo compressors were reduced from 140dB(A) to 85dB(A) at 1m following the design, manufacture and sup- ply of six high specification acoustic enclosures. Within the UK, Wakefield Acoustics has most recently completed work at one of United Utilities' North-west sites. This included Wakefield Acoustics' experienced engineers design- ing and providing four drop over enclosures for root blow- ers, reducing noise levels to the 80dB(A) noise specification. A substantial reduction, given that typical untreated noise lev- els from the blowers were approximately 105dB(A). Renewed legislation, paired with a public less willing to accept environmental noise indicates the harmful effect noise can have at workplaces, like wastewater treatment plants. Noise therefore will need to be addressed increas- ingly through the design and development of noise control solutions. n Lee Nicholson is managing director of Wakefield Acoustics.