Water and Effluent Treatment Magazine
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20 WET NEWS APRIL 2015 Odour control is much higher on water companies' agendas as residents become less tolerant of nuisance odours. The challenge: Controlling odour OdOuR cOntROL W ith ever tightening envi- ronmental pollution legislation, the impact on odour control in wastewater treatment facilities can be huge. And in the modern world of wastewater treatment, control of odours has moved from an aer- thought to a primary design con- sideration. THE CONCEPT • the Q45S monitor is that it utilises a Wet H2S sensor that eliminates water vapour bleeding • the technology is directly installed in the stack with no need for sample conditioning • the detection limit is around 20ppb • An outlet monitor will read 0.05ppm to 0.200ppm NEED TO KNOW 1 Regulators have a duty to investigate cases where odour may be causing statutory nuisance 2 Some H2S monitors can cost up to £20,000 3 A local authority can issue an Abatement notice to bring about compliance within a given timeframe THE VERDICT • At £2,000 installed, this represents around 6% of the value of even the smallest plants, it is a cost effective solution to avoiding expensive breaches of regulations and resident complaints. With the attention paid to odour control increasing, the number of technologies available in the marketplace has expanded too. A solution: Monitoring eliminates odours E ach wastewater treatment site faces real challenges when it comes to balancing the expense of running the plant with the cost of installing appropriate sensors to tackle the issue of odour control. Smaller air cleaning plants may only be worth £30,000, yet some H2S monitors can cost up to £20,000, which is just not viable. However, there are a number of technologies available at varying costs, meaning there are sensors available for all budgets and applications. Chemical scrubbing is normally used for cleaning large air volumes on sewage treatment plants with an airflow rate of between 5,000-10,000m3/hour. These scrubbers can achieve high efficiencies of up to 99.95%. A typical system treating air with an average of 25ppm H2S at the inlet at 25,000m3 hour would cost around £175,000. This monitor is efficient, has good turn down flow rate and inlet odour loading, the dosing chemical use is optimised and it's suitable for carbon polishing. Used for treating small airflows from wet wells and pumping stations, dry media carbon filters are used for smaller volumes of between 200-10,000m3/hour and sometimes as a polisher aer chemical treatment. Carbon filters also achieve high efficiencies up to 99.5%. These systems treat smaller volumes and can be installed for around £30,000. Carbon dry media sensors effectively monitor odour control at low outlets, are upgradeable for low outlet odour and have regenerable carbon. Bio scrubbers sit somewhere in the middle. Generally used for treating media airflow rate volumes of up to 10,000m3/hour and high loadings from inlet works and sludge processing, they achieve efficiencies of up to 99.5% with systems costing around £50,000. On the other hand, specialist electrochemical sensor makers offer cost-effective breakthrough As development encroaches on facilities and residents become less tolerant of nuisance odours, wastewater professionals have become more motivated to look for new reliable and effective methods to address odour as a priority. Odours emitted by sewage treatment are typically an indication of an anaerobic condition that occurs when there is limited surface area for oxygen to penetrate. In this anaerobic state, microbes present in the wastewater have no dissolved oxygen available for respiration and this allows anaerobic microbes to thrive and grow. Regulators have a duty under the Environmental Protection Act 1990 (EPA 90) and Environmental Permitting Regulations 2010 (EPR 2010) to investigate cases where odour may be causing statutory nuisance or breaching the conditions of an EPR Permit. Offenders are taken to court and fined a substantial amount of money and failure to comply with a permit could ultimately lead to the closure of site operations. Whilst the closure of a sewage treatment works would be impracticable, a local authority can issue an Abatement Notice to bring about compliance within a given timeframe. the Q45S monitor utilises a Wet H2S sensor that eliminates water vapour bleeding monitoring at a cost of under £2,000 installed. Systems like the ATi Q45S Wet Sensor for Scrubbers provide a lower priced alternative to expensive tape and film based H2S monitors and utilise a sensor designed to operate in condensing gas streams without the water vapour blinding, which can be typical of standard sulphide sensors. This low cost, affordable technology now makes it possible to monitor even small scrubbers. The key advantage of the Q45S monitor is that it utilises a Wet H2S sensor that eliminates water vapour bleeding for accurate and cost-effective H2S monitoring, where condensing humidity conditions are normal. This technology is directly installed in the stack with no need for sample conditioning and the detection limit is around 20ppb. In normal use an outlet monitor will read 0.05ppm to 0.200ppm. At these levels the scrubber is working effectively but in the event of a breakthrough, the reading will rise rapidly and the in-built alarms are activated before the legislative limit is reached. Historically, sewage treatment plants have oen struggled to justify the expense of installing H2S monitors that can cost up to 80% of the value of smaller plants. However, there is now a monitor available to suit all budgets and applications. At £2,000 installed, this represents around 6% of the value of even the smallest plants, it is a cost effective solution to avoiding expensive breaches of regulations and resident complaints. n