Welcome to issue 31; this month we continue with part 6 of our serialisation of the UK's primary Legionella control document "Legionnaires' disease: The control of legionella bacteria in water systems", with extracts dealing with preventing or controlling the risk from exposure to Legionella bacteria. We also feature guides that look at the application of separation technologies for minimising waste and effluent, and the use of electrochlorination plant for the treatment of swimming pool water.

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In this issue:

• Cost effective separation technologies for minimising wastes and effluents.
• Part 6 - "Legionnaires' disease: The control of legionella bacteria in water systems".
• Electrochlorination plant for use in the treatment of swimming pool water.
  

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Cost Effective Separation Technologies

for Minimising Wastes and Effluents

Many industrial processes generate effluent streams that contain a mixture of substances. To reduce the cost of processing these streams, operators can remove the substances that they contain using a range of separation technologies.

Using separation technologies as part of the production process - for instance as a method of cleaning continuously re-circulating process water - can prove more cost-effective than using a larger effluent treatment plant. It is an approach that usually requires less energy and: is less capital-intensive in terms of plant; allows the recovery and re-use of individual substances, many of which may be valuable; retains water of an appropriate purity within the process so that it can be recycled.

This guide describes proven technologies and techniques for the cost-effective separation of four types of dissolved substance from liquid streams:

• heavy metals;
• anions (metals and non-metals);
• organics;
• water in organics.

It also considers the separation of gases and liquids.

This guide is intended to help companies decide whether separation technology can be used to minimise their waste streams and, if so, to indicate the most appropriate technologies available.

For each of the technologies examined, this guide first discusses the general principles of the technology, its typical applications, main advantages and disadvantages and approximate costs.

It then considers issues such as the technology’s efficiency and limitations, scale of operation, the main outputs and any ancillary plant required.

The choice of technology in any situation will depend on the specific nature of the streams involved. However, this g Legionella bacteriauide offers guidelines as to the likely suitability of each technology for certain tasks, basing its conclusions on that technology’s general characteristics.

In some cases, a technology is applicable to the removal of a whole range of substances. Reverse osmosis and nanofiltration, two membrane separation technologies, can, for instance, be used to remove dissolved heavy metals, anions, organics and water in organics. The same is true for evaporation. In other instances, a technology has a much narrower application. Adsorption and air stripping are only used in the separation of dissolved organics, for example. Some technologies fall between these two extremes. The main application of the various electrical technologies, for instance, is in the removal of dissolved heavy metals and anions, and the same is true for ion exchange and precipitation techniques.

In the separation of gases from liquids, demisters and electrostatic precipitation techniques are used to remove mists in gas streams, while defoaming technologies and separation vessels are used where bubbles of gas occur in a liquid and also for treating two-phase mixtures.

Contents of the guide include:

Selecting the appropriate technology

Separation of dissolved substances from liquids using:

• Adsorption
• Ion exchange
• Precipitation
• Membrane technologies
• Electrical technologies
• Evaporation
• Distillation
• Dissolved air flotation
• Air/steam stripping

Separation of gases from liquids using:

• Separation vessels
• Defoaming technologies
• Demisting technologies
• Electrostatic precipitation

Extracted from a guide originally published by the Environmental Technology Best Practice Programme - © Crown copyright

For your complimentary copy of this excellent guide please e-mail info@accepta.com quoting the full title of the document.

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Approved Code of Practice Part 6

"Legionnaires' disease: The control of legionella bacteria in water systems" (L8)

Preventing or controlling the risk from exposure to legionella bacteria

Regulations

Control of Substances Hazardous to Health Regulations 1999, Regulation 7 and 9

Health and Safety at Work etc. Act 1974, Sections 2, 3 and 4

ACOP

52 - Where the assessment shows that there is a reasonably foreseeable risk, the use of water systems, parts of water systems or systems of work that lead to exposure has to be avoided so far as is reasonably practicable.

53 - Where this is not reasonably practicable, there should be a written scheme for controlling the risk from exposure which should be implemented and properly managed. The scheme should specify measures to be taken to ensure that it remains effective.

The scheme should include:

(a) an up-to-date plan showing layout of the plant or system, including parts temporarily out of use (a schematic plan would suffice);

(b) a description of the correct and safe operation of the system;

(c) the precautions to be taken;

(d) checks to be carried out to ensure efficacy of scheme and the frequency of such checks; and

(e) remedial action to be taken in the event that the scheme is shown not to be effective.

54 - The risk from exposure will normally be controlled by measures which do not allow the proliferation of legionella bacteria in the system and reduce exposure to water droplets and aerosol. Precautions should, where appropriate, include the following:

(a) controlling the release of water spray;

(b) avoidance of water temperatures and conditions that favour the proliferation of legionella bacteria and other micro-organisms;

(c) avoidance of water stagnation;

(d) avoidance of the use of materials that harbour bacteria and other micro-organisms, or provide nutrients for microbial growth;

(e) maintenance of the cleanliness of the system and the water in it;

(f) use of water treatment techniques; and

(g) action to ensure the correct and safe operation and maintenance of the water system.

Extracted with permission from "Approved Code of Practice (ACoP) and Guidance "Legionnaires' disease: The control of Legionella bacteria in water systems" (L8)" © Crown copyright

more next time.....>>

About Legionella Training

For information about Accepta's specialist Legionella training courses please call us on +44 (0) 161 240 2100 or email info@accepta.com.

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Electrochlorination Plant

for use in the Treatment of Swimming Pool Water

The use of chlorine gas as a disinfectant for swimming pool water caused several problems and the UK's Department of the Environment recommended that this use should cease by January 1985. In its place a variety of water treatment methods were introduced. One of these utilises an electrochlorination plant which is an on-site process for the production of sodium hypochlorite.

This document provides background information and guidance on the safe installation and use of one type of equipment which disinfects swimming pool water.

The use of chlorine gas as a disinfectant for swimming pool water has caused several serious incidents and is not recommended. There is a variety of safer water treatment methods. One of these utilises an electrochlorination plant which is an on-site process for the production of sodium hypochlorite. These units are basically small scale versions of the type of electrochlorination plant which is already widely used for water treatment at, for example, power stations and offshore drilling installations.

The plant normally consists of a water softener and sodium chloride brine make-up system; an electrolytic cell, rectifier and associated electrical equipment; an intermediate bulk storage tank for sodium hypochlorite (day tank), although some installations use direct injection of sodium hypochlorite into the pool water recirculation system and, therefore, do not utilise a day tank; and water monitoring instruments, associated pumps, sampling lines and inter-connecting piping .... more >>

© Crown copyright

For your complimentary copy of this excellent guide please e-mail info@accepta.com quoting the full title of the document.