40 Water / Wastewater
Cooling tower ozone disinfection systems rely on reagent-less analyser for monitoring O3
Plant engineers who’ve switched or who are thinking about the switch to Ozone (O3) disinfection of water for high-temperature evaporative cooling towers will find the reagent-less OZ80 Ozone Analyser from Electro-Chemical Devices provides a green-friendly design that helps them optimize treatment while at the same time reducing cost, simplifying maintenance and avoiding complex environmental issues.
ECD’s advanced OZ80 Analyser helps ensure effective ozone treatment of cooling tower water to prevent bacterial growth, scaling and corrosion. Ozone as a disinfectant replaces the need for chlorine and other harsh biocides and inhibitor chemicals that are considered toxic hazards, require special wastewater treatment and effluent monitoring.
In comparison to reagent-type analysers that come with multiple components which first must be installed and then require field calibration, the OZ80 Analyser is factory assembled and factory calibrated prior to arrival. All the technician needs to do is mount the panel and connect the drain lines, plug in the power cord and select the outputs on the display as 0 to 2.0 ppm for water disinfection or 0-20.00 pm for oxidation and bleaching operations.
Dual range measurement of both Ozone (O3) parameters also is available with the OZ80 Analyser. O3 is a colourless to pale blue gas that in low concentrations gives off an irritating acidic odour. It is a strong oxidiser, stronger than either chlorine (Cl) or chlorine dioxide (ClO2). O3 reacts quickly and disintegrates into oxygen gas without the formation of harmful disinfection byproducts (DPB’s) common to chlorine disinfectants that require additional costly treatment. It also increases the amount of oxygen in the water.
O3 is gaining ground as a disinfectant and bleaching agent in multiple industrial processes. It has been used for years in municipal drinking water and wastewater treatment plants. It is useful at several points in the drinking water treatment process as an oxidiser for removing metals from well water as well as organics, odours and colour from surface water too.
ECD’s OZ80 Analyser features powerful amperometric sensors to detect and monitor O3 levels. These amperometric sensors are manufactured with a gold cathode, a silver anode and a rugged microporous membrane. Unlike many other instruments, there are no reagents required with the OZ80 Analyser. Its O3 sensor technology and pH measurement are reagent-less designs. These sensors keep the cost of ownership low by not requiring expensive reagents.
The O3 sensors are smart sensors with their identity and calibration information stored internally. Communication between the OZ80 Analyser’s T80 Transmitter and the O3 sensor is via MODBUS. The sensors are flow sensitive requiring a minimum flow rate of 0.5 ft/sec, above this flow rate, the reading is virtually independent of the flow rate.
The OZ80 Analyser’s constant head flow control device (CFD) maintains the optimum flow rate moving past the sensor for sampling purposes. The CFD’s automatic flow control capability eliminates the need for pressure regulators and rotameters, which are required by many other H2O2 analysers, to reduce system maintenance and lifecycle operating costs. The minimum flow rate required by the CFD is 10 gal/hr, and the maximum flow rate is 80 gal/hr with the sample draining at atmospheric pressure.
The OZ80 Analyser is available with an optional sensor auto clean configuration. The sensor auto clean features a solenoid actuated spray cleaner that provides either a 30 psi process water or air. The spray cleaner removes films from the sensor head, which over time can affect measurement accuracy. There is rarely a need for manual wiping of the sensor head by maintenance technicians with the spray clean configuration.
Designed with ECD’s T80 Universal Transmitter, the OZ80 Analyser includes a 128-x-64 pixel (2.75-x-1.5-inch) display. The display is black on grey with no backlight or blue on a white background with the LED backlight. The standard configuration features two 4-20 mA outputs, three alarm relays and MODBUS RTU. The enclosure is rated to IP65 and weatherproof.
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Scottish Government awards contract to research sustainable improvements to private sewage discharges impacting
on bathing waters The Scottish Government has awarded Aqua Enviro a research contract to inform future policy to reduce the impact from private sewage discharges on bathing water quality. The project “Identifying the Most Cost-effective and Sustainable Method of Mitigating the Impact from Private Sewage Discharges on Bathing Waters” will focus on a rural case study catchment.
It is estimated around 250,000 properties in rural areas of Scotland are not connected to the mains sewerage network, so discharge their treated wastewater into the local water environment instead. Existing domestic treatment systems, whilst reducing the number of suspended solids and the associated nutrient load, don’t always reduce bacterial pollution to an acceptable level when being discharged into a bathing water area. The standards laid out in the regulations for Intestinal enterococci and Escherichia coli are used by SEPA to classify bathing waters as “excellent”, “good”, “sufficient”, or “poor”. These classifications are displayed on signage at bathing locations where a Bathing Water has been designated during the bathing season, which is defined as 1st June to 15th September. Prior to the bathing season in 2019 SEPA announced that out of the 86 officially designated bathing waters in Scotland, 10 of them have been rated as having a ‘poor’ EU water quality classification.
Both bacterial species originate from the intestinal tract of warm-blooded animals but are known to survive in the wider environment after being released in faeces. Survival rates are dependent on several factors including availability of nutrients, temperature, pH, oxic versus anoxic conditions, and exposure to UV light (sunlight). Whilst both species can themselves cause adverse health effects in humans, they are also used as an indicator of the presence of faecal matter and therefore the presence of other water-borne pathogens.
The aim of the project is to identify potential solutions for upgrading private wastewater discharges in a cost-effective and sustainable way. Each of the potential options will be assessed and their relative advantages and disadvantages compared in terms of the space required, cost of installation, cost of operation, energy usage, maintenance requirements, aesthetic impact etc. The favoured solution will ideally be an environmentally friendly, low cost, low maintenance, passive system. The outcome of this project will inform future policy and set out guidelines for applying the approach to other impacted areas.
Paul Pickard, Technical Sales Manager for Aqua Enviro says ‘we are extremely pleased to be involved in such a high-profile project with potential benefits to the public and the environment in the areas affected. Aqua Enviro has been involved with several Scottish Water projects concerned with controlling point source pollution from municipal treatment works, but this project affords the chance to work with the government to improve water conditions across all parts of Scotland’.
Aqua Enviro will work in conjunction with French firm Nobatek/Inef4 who have experience of installing eco-friendly treatment systems in developing countries. The two firms have collaborated in the past when working on the EU Horizon 2020 funded INNOQUA project which was a multilateral, multinational programme aimed at developing sustainable water sanitation technologies in the developing world.
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IET September / October 2019
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