StrathKelvin Instruments Ltd.

Strathkelvin Instruments was founded in 1981, to develop instruments based upon precision dissolved oxygen measurement, for use in the biomedical research field. In 1998, the opportunity arose to exploit the technology of a respirometer designed for biomedical research, for use in activated sludge respirometry.

Initially the respirometry software was directed towards toxicity testing, since there was no method anywhere in the world that would measure and calculate toxicity of wastewater to the actual activated sludge of the receiving works, in as little as 5-10 mins. Subsequently it became clear that, since respirometry is one of the 3 major processes in biological treatment (biodegradation, growth and respiration), by adding additional software, the respirometer could be used as a major tool in process control in treatment works.

The company, based in Scotland sells its instruments wordwide. It has a policy of continuing development and innovation, and of ensuring quality in all aspects of its products. It also has an excellent record in after-sales service and customer satisfaction. Support for all instruments is provided by highly qualified technical staff, who are also available for pre-purchase advice.

Our instrumentation can quickly and directly measure Activated Sludge bacterial performance saving our clients time and money by determining the toxic effects of influents on your activated sludge and also the effects of optimising feeding and aeration programmes. The company has been making high quality instrumentation in the field of Respirometry since 1981 and has established an enviable reputation for quality, robustness and ease of use.

Strathtox is a fully integrated Respirometer where all testing is quick and simple, and tests are routinely completed within 10 minutes. Easy-to-use software provides automated results and graphs allowing a wide range of personnel to make effective use of Strathtox.

Bio-scope is our latest development providing a portable instrument that measures the respiration rate of bacteria in the plant under the prevailing load and environmental conditions. This provides operators with a real insight into the operation of their wastewater treatment plant.

For more information on AS Bio-Scope please visit

Clients such as Water Companies, Consulting Engineers, Industrial Waste Generators, Utility Operators and Academic Establishments have purchased the instrument for a wide range of applications including:

• Toxicity management
• Plant profiling
• Aeration optimisation
• Plant efficiency
• Pilot plant monitoring
• Tankered waste testing
• Feed programme optimisation
• Nitrification management
• Audit and conformance management

Strathtox (™) is a highly flexible and robust Respirometer used for the measurement of:

• Respiration inhibition (toxicity of influents to activated sludge)
• Nitrification inhibition
• Aeration efficiency
• Sludge health monitoring
• Critical Oxygen Point Analysis
• Short-term BOD
• Process optimisation testing including Nutrient optimisation and Aeration set point optimisation
• BOD and Nitrification capacity testing

Bioscope is a robust multiple parameter respirometer for in-plant basin bacterial analysis and is used for:

• Comparative analysis of bacterial respiration at single or multiple points over a number of plants
• DO and temperature measurements
• SVI or SSVI settlement characterisation

Working in combination these two instruments allow Plant operatrors to gain the operational and financial benefits of achieveing full control over their wastewater treatment operation. Many of our customers have been able to recover their investment in well under 12 months.

• Process optimisation
• Wastewater toxicity testing
• Wastewater toxicity tracking
• Toxicity-based consents
• Toxicity reduction tests
• Monitoring sludge 'health' 

Process Optimisation

Respiration rate of activated sludge has been recognised as a key controlling element in the modelling of process control, by the International Water Association Task Group. Actual respiration rate of the sludge in the aeration tanks, as well as the endogenous and maximum respiration rates are variables that indicate the rate of BOD removal and aeration requirements. The maximum respiration rate is also closely linked to the Critical Oxygen Concentration point, that is, the point at which diffusion over the bacterial cell walls ceases and therefore biodegradation is significantly compromised.

Strathtox™ simply and quickly provides the endogenous and maximal respiration rate of the bacteria, as well as providing the platform for in-depth analysis of the critical oxygen concentration point. AS Bioscope provides the data concerning the activity of the bacteria in the aeration basins, clarifiers and return lines under the prevailing load conditions. Further tests allow the settlement characteristics to be ascertained. Therefore these two instruments in combination allow a treatment works to be optimised for both performance and aeration efficiency.

Wastewater Toxicity Tracking

If industrial wastewater entering a treatment works contains toxic components the rate of biodegradation will be inhibited or stop completely. This can result in failed consents and will certainly give rise to operational problems. Visible indications include deflocculation, bulking and the appearance of filamentous bacteria. Sometimes, there are no visible effects. When the sludge bacteria are inhibited, there is the possibility of toxicity carryover in the effluent that is discharged to receiving waters. With new environmental legislation being introduced, worldwide, to protect the natural environment, toxin discharge is now a serious concern for treatment plant managers. Toxicity, therefore, results in:

• Increased costs of treatment
• Failure to comply with discharge consents
• Financial penalties for discharging toxic effluent

In order to protect a treatment works, from unknown toxic influents entering by sewer, a toxicity management regime is required. Tests with a laboratory respirometer are then required to measure the toxicity of the effluent, in order to determine the safe rate of discharge into the aeration tanks. For tankered waste, laboratory tests on samples of the wastewater are carried out prior to its acceptance for treatment. Manufacturing companies who treat their own waste and are concerned to minimise treatment costs, use the respirometer to monitor the toxicity of effluent streams. In this way, discharge rates can be controlled in order to ensure that toxicity does not inhibit the activated sludge bacteria of the aeration tanks.

Wastewater Toxicity Tracking

If toxicity is identified in a mixed sewage entering a treatment works, the problem for the plant manager is to track and identify the source of the toxicity. This can be done by sampling the effluent stream at various points in its length. . By working in a logical sequence back up the sewer network the number of samples can be minimised. This type of testing should be rigorously enforced for new product introduction by a waste producer, as well as sampling the effluents directly at source. The samples would be tested against the activated sludge of the receiving works, using the Respiration Inhibition Test or the Nitrification Inhibition Test.

Toxicity Based Consents

Water companies, water authorities or publicly-owned treatment works (POTW) need to have some knowledge of the composition of the wastes they it receive. In addition to testing for ammonia and BOD or COD levels, treatment works can license industrial discharges on the basis of concentrations of some of the known toxic compounds. However, it is recognised that very many non-regulated toxic materials still enter the treatment works and reduce the efficiency of biodegradation, and may cause toxic shock. The way is now open for more widespread use of direct toxicity tests as a basis for toxicity-based consents. Samples of the industrial effluent are collected at source, for testing on the actual bacteria of the receiving activated sludge. The tests used are the Respiration Inhibition Test and the Nitrification Inhibition Test. Note that this approach mirrors that of the regulators of discharges to receiving waters, who are now using direct toxicity tests (DTA) or w

The software supplied with each Activated Sludge Respirometer includes 6 separate tests:
 
1. Respiration Inhibition Test
This test measures the inhibition of the respiration rate of the activated sludge bacteria when exposed to toxic wastewater. The inhibition may be measured immediately after mixing the wastewater with the sludge or after a 3 hour exposure. The latter is more useful if toxicity to heavy metals is suspected. Two different forms of the test are included:
 
EC50 Respiration Inhibition Test. This gives valuable information on how toxic the wastewater is. It does this by calculating EC50, EC20 and EC10 values i.e. the concentrations of wastewater that will cause 50%, 20% or 10% respiration inhibition respectively. Five different dilutions of the wastewater are prepared and to each the same volume of fed activated sludge is added. The sixth (control) receives distilled water in place of wastewater. Respiration rates are measured for 5-10 mins. If toxic substances are present, the respiration rates will be inhibited, enabling the software to calculate the EC values.

% Respiration Inhibition Test. This is a quick test that is used to measure whether toxicity is present in the wastewater. Two samples only are used. In the control, an equal volume of distilled water is added. In the test sample, an equal volume of wastewater is added to the sludge. The respiration rates of both samples are measured, and the % inhibition due to the wastewater is calculated. Up to 5 different samples may be compared to the control.

2. Nitrification Inhibition Test
This test is carried out when inhibition of nitrification and the possibility of failed ammonia consents in the final effluent is the main concern. The test calculates and reports separately on nitrification inhibition of the nitrifying bacteria and respiration inhibition of the carbonaceous bacteria.
As with the Respiration Inhibition tests above, the test may be carried out immediately after mixing the sludge and wastewater or after a 3-hour exposure. Similarly both, % inhibition tests and EC50 versions of the test are provided. Two separate respirations runs, each of 5-10 minutes are made on the sample of fed sludge. The first run follows the procedure of the Respiration Inhibition Test. The second run measures the respiration rate of the carbonaceous bacteria alone, following inhibition of nitrification rate of the allyl thiourea. The software automatically subtracts the carbonaceous respiration rate from the total respiration rate of the first run, to calculate the oxygen uptake of nitrification. The report shows inhibition values for nitrification inhibition together with carbonaceous respiration inhibition.
 
3. Short-Term BOD
Whilst regulators still require the use of standard 5-day BOD tests, it is increasingly recognised that this test, is both time consuming and not relevant to the BOD removal during wastewater normal residence time in the secondary tanks. Short-term BOD tests are carried out to measure the readily biodegradable BOD and are in many cases of much greater value to the treatment plant operator, than the BOD5 test. Furthermore the data produced refers to the BOD breakdown by the actual receiving sludge of the treatment plant. In this test which the user can vary between 30 minutes and 6 hours, the increase in respiration rate of the activated sludge from the endogenous state is recorded, following the addition of a sample of the effluent.
 
4. Health Monitoring.
In order to monitor the 'health' of the activated sludge bacteria, as an indication of the efficiency of biodegradation, daily measurements are made of the respiration rates of samples from the aeration tanks. The rates are normalised to the quantity of MLSS present to give a measure known as sour or specific oxygen uptake rate. The program provides a log of the past 30 days respiration rates, in tabular and graphical format, in order to spot any deviations from the norm, which may be due to toxicity, but could have other causes.
 
5. Respirometry.
This is a general purpose procedure which can be used in a number of different applications, including process control, and toxicity reduction tests. Samples of activated sludge, in endogenous state or at maximum respiration rate, with or without allyl thiourea addition (according to the objectives of the test), are placed in the respiration tubes. Respiration rate is measured over 5-10 minutes and reported as uncorrected respiration rates or as MLSS-normalised respiration rates (SOUR).

• Respiration rate measures the rate of biodegradation by sludge bacteria
• Toxic wastes inhibit both respiration and biodegradation
• Respiration rate measurements are used for both toxicity management and process optimization

Respiration basics

In the aerobic tanks of a biological treatment plant, the complex molecules of the wastewater are broken down by the combined activities of heterotrophic bacteria (that break down organic carbon compounds), nitrifying bacteria (that break down ammonia) and other micro organisms. In terms of process control, there are three major processes at work:Biodegradation (the breakdown and removal of organic carbon and ammonia), Growth (growth and multiplication of the bacteria, which results in new biomass) and Respiration (oxygen consumption that provides the energy that the bacteria require for growth).

The three processes are interdependent. As a result, by measuring the rate of respiration, a measure of the rate of biodegradation can be obtained. For this reason, a respirometer maybe used as the control variable in process optimisation. If toxicity in the influent wastewater inhibits the respiration rate of the activated sludge, it follows that there will be an associated reduction in the rate of biodegradation.

A simple explanation of the relationship between biodegradation, growth of biomass and respiration is provided in a paper by Davies and Murdoch (2002).

On-line v laboratory respirometers
On-line and laboratory respirometers have complementary roles in toxicity management. Laboratory respirometers have an additional role to play in process control and management.

On-line respirometers and other early warning devices. A review of available early warning devices and their efficiency has been published recently in the USA by a WERF working party, together with recommendation for further developments. At the time of installation of on-line monitors, storage facilities need to be built, in order to contain the diverted toxic waste. Such waste is normally treatable. However, the extent of the toxicity has to be determined, using a laboratory respirometer, in order to calculate the rate at which it should be fed into the treatment tanks, to achieve a dilution at which it will no longer cause a toxic effect. Currently, as shown by the WERF report, on-line systems are prone to generating false results, and they require some care in their operation.

Laboratory respirometers. The Strathkelvin respirometer was developed by technology transfer from the biomedical division of the company. It is a closed chamber respirometer requiring only small (20ml) samples of activated sludge. By using multiple electrodes and dedicated software, respiration rates can be measured in only 5-10 mins. All of the time-consuming aspects of respirometry have been removed. Wastewater treatment plant staff can be readily trained to operate the instrument, for a wide range of applications in both process control and toxicity management.