A fascinating story: Trash to gas project to help life on Mars!

30/11/2014
If you are travelling to Mars on a journey that will last for several months, you need to maintain good breathing air quality and you need to manage your resources very carefully. This article describes research on the off-gases from astronaut waste; checking that they are not harmful and figuring out if they can be converted into water, oxygen and rocket propellant.

As part of a project to measure the effects of long-term isolation on astronauts, small groups of individuals have been selected to live in a tiny ‘Habitat’ perched on the upper slope of a volcano in Hawaii. In doing so, the project team has contributed to the understanding of issues that would confront a manned mission to Mars.

NASA’s Anne Caraccio analyzing waste gases during simulated Mars mission

NASA’s Anne Caraccio analyzing waste gases during simulated Mars mission

For example NASA’s Anne Caraccio studied off-gases from the crew’s trash with a portable Gasmet FTIR gas analyzer. “Waste from the crew’s everyday activities are routinely sorted and stored, but we need to know the composition of the off-gases from these materials for health and safety reasons, and also to determine whether these gases could be utilised beneficially,” Anne reports.

The work was undertaken during the second of four HI-SEAS (Hawaiʻi Space Exploration Analog and Simulation) missions which involved living with 5 other crew members for a period of 120 days in a two-story solar powered dome just 11 metres in diameter with a small attached workshop the size of a shipping container. In addition to the completion of a range of tasks that were set by the project, each crew member conducted their own research, which in Anne’s case was known as ‘Trash to Gas’, a programme working on the development of a reactor to convert waste from long-duration missions into useful commodities such as water, life-support oxygen and rocket propellant.

The main objective of the second HI-SEAS mission was to evaluate the performance and the social and psychological status of the crew members whilst they lived in cramped isolated conditions in a lava rock environment that resembled Mars.

Crew members were allowed outside of the Habitat, but in order to do so they had to wear simulated spacesuits and undergo a 5 minute mock compression/decompression. Since the FTIR gas analyser is portable (14Kg), Anne was able to conduct additional monitoring both inside and outside the Habitat in order to compare data with the waste off-gas measurements. “Size, weight and portability are obviously of major importance on a project such as this, but the main advantage of this technology was its ability to measure a large number of compounds simultaneously; I measured 24 VOCs such as acetaldehyde, methane and ethylene, but the instrument also stores spectra for the measurements so it is possible to retrospectively analyze data if it becomes necessary to look for a particular compound at a later stage.”

Anne’s monitoring provided a clear view of the most important gases within the Habitat. For example, stored waste had the highest relative levels of ethanol (due to crew members’ hygiene wipes and cleaning products) and water vapor (due to residual water from food and plant waste). The laboratory where plants were growing had the lowest relative level of methane. The waste bins had higher relative levels of nitrous oxide and pentane, and the bathroom had the highest levels of acetaldehyde.

The FTIR gas analyser, a DX4040, was supplied by the company Gasmet Technologies. “We were very pleased to be able to help with this project,” says Gasmet’s Jim Cornish. “The simultaneous monitoring of multiple compounds is a common application for our FTIR analyzers, however, they are usually employed measuring gases in stack emissions, industrial processes, greenhouse gas research and in hazmat scenarios. We usually tell prospective customers that advanced FTIR technology is simple to use; ‘it’s not rocket science’ we tell them, so I guess we will have to rephrase that now.”

The waste produced during the HI-SEAS mission was measured during the entire mission, although this was for a shorter period than would be expected of an actual long duration mission. The Trash-to-Gas reactor processed HI-SEAS waste simulant at the Kennedy Space Center with results demonstrating that a future reactor would be most efficient with specific material processing cycles to maximize the desired output. Automation will also be needed in the future Trash-to-Gas reactor because the current technology would require too much of a crew member’s logistical time. The Trash-to-Gas reactor first converts waste into carbon dioxide, which is then mixed with hydrogen in a Sabatier reaction to produce methane and water.

The Kennedy Space Center Trash-to-Gas reactor processed three waste types and produced 9% of the power that would have been needed during the HI-SEAS mission. As part of the psychological assessment, each member of the crew completed regular surveys and kept diaries. They also wore ‘sociometric’ badges that recorded conversation patterns and voice tone.

Commenting on the psychological results of the project, Anne says “The crew were essentially strangers when they entered the Habitat, which is unlike a typical space mission in which the crew would have worked and trained together for a number of months or even years. Nevertheless, the crew coped extremely well with living and working in such close proximity, and there were no significant periods of stress in my opinion.”

The third Hi-SEAS mission began on October 15, 2014. Again, a 6 member crew will conduct a similar mission, with the exception that it will last for 8 months. Anne says: “Participation in these missions requires a real passion for science, technology and space travel. The application process includes a class 2 flight medical, a personal research project proposal, essays, interviews and educational requirements, all of which is similar to the NASA astronaut application procedure.” Looking forward, she says: “The technology to travel to Mars has not yet been fully developed, but it is anticipated that a human mission could be possible in the future. The journey to Mars would take around one year, so I hope that our Trash-to-Gas research will contribute to the science that could make such a mission possible.”


Safer containers with FTIR

04/03/2013

antti HeikkilaThis paper, by Gasmet’s Antti Heikkilä, describes how sophisticated gas analysis is being used to check these cargo containers, but this is just one example of the advantages that are available from an analytical technology that can measure almost any gas.
Antti Heikkilä (right) is a senior manager at Gasmet Europe Oy, specialising in developing new applications for the Gasmet FTIR gas analyzers. He holds a MSc degree in Physical Chemistry and has 14 years’ expertise in FTIR spectrometry and quantitative gas analysis, working for the University of Helsinki and Gasmet Technologies group.

Introduction
Entry to freight containers represents a significant hazard to staff responsible for inspection, stuffing or destuffing because of the large number of airborne chemicals that can be present. Research in Germany and the Netherlands found hazardous levels of gases and vapours in around 20% of all containers and this level of contamination is now accepted as commonplace.

Container testing!

Container testing!

It is therefore necessary to examine containers before entry and this work is usually conducted with a wide variety of gas detection techniques in order to be able to assess, individually, all of the substances of greatest concern. However, a Dutch firm of health and safety consultants, Reaktie, has employed FTIR (Fourier Transform Infra Red) gas analysis to dramatically improve the speed and effectiveness with which containers are assessed, because this technology enables the simultaneous measurement of the 50 gases of most concern.

Chemical Hazards
There are two potential sources of hazardous chemicals inside cargo containers; fumigants and chemicals that arise from the goods or packing materials.

Fumigants are applied to goods to control pests and micro-organisms. Cargoes most likely to have been fumigated include foodstuffs, leather goods, handicrafts, textiles, timber or cane furniture, luxury vehicles and cargo in timber cases or on timber pallets from Asia.

According to the IMO’s international regulations, ‘Recommendations on the safe use of pesticides in ships’, fumigated containers and ship cargoes must be labelled giving specifications about dates of fumigation and the fumigation gas used. Furthermore, appropriate certificates are necessary and these records have to be forwarded to the Port Health Authorities without their explicitly asking for them. However, absence of marking cannot be taken to mean fumigants are not present. Containers marked as having been ventilated after fumigation may also contain fumigant that was absorbed by the cargo and released during transit. There is also concern that fumigants may be retained in the goods and subsequently present a hazard to logistics providers, retail staff and consumers.

Common fumigants include Chloropicrine, Methyl bromide, Ethylene dibromide, Sulfuryl fluoride and Phospine. However, with over 20 years of experience testing gases in containers, Peter Broersma from Reakti says “While the fumigants are highly toxic, the number of containers exceeding occupational exposure limits (OEL) due to other chemicals is much greater and the number of ‘failed’ containers is likely to rise as more containers are tested, detection methods improve and new gases are identified.”

Containers often travel for extended periods and experience a wide range of temperatures. It is therefore not surprising that unsafe levels of gases should accumulate in the confined space of a container. Peter identifies the typical sources of gases over their OELs as follows:

  • Solvents from glues used to produce clothing, accessories and shoes
  • 1,2, dichloroethane from plastic products, PVC, blister packaging etc.
  • Formaldehyde found in cheap furniture (Plywood,MDF etc.) but also in used pallets and lashing materials
  • Solvents and formaldehyde from poly-resin products
  • Carbon monoxide from charcoal and natural products
  • Carbon dioxide from natural products
  • Ethylene oxide from medical equipment sterilised with ethylene oxide
  • Solvents including Benzene, Toluene, Ethylbenzene and Xylene (BTEX) in Christmas and decoration products
  • Flammable gases from disposable lighters
  • Ammonia in household equipment with Bakelite parts
  • Volatile Organic Compounds (VOCs) from fire blocks
  • Pentanes and hexanes from consumer electronics
  • Phosphine/arsine from natural minerals such as ferrosilicon

Inspection procedures
Major ports have strict regulations in place to protect against potential hazards in cargo containers. In general terms, every incoming stream of products has to be checked for dangerous gases and if one of more gases are detected during the preliminary investigation, all of the containers from this specific producer must be checked. If no gases are detected, it may be possible to only conduct random tests a few times per year. If it is necessary for Customs staff to enter a container, all containers must first be tested and if necessary de-gassed.

Gas detection
Since there are a large number of gases that might be present inside a container, the traditional approach to monitoring has been either to employ a wide range of instruments or to use chemical stain tubes for the most common gases, or a combination of both.

Chemical stain tubes provide a colorimetric assessment of an individual gas, typically with an accuracy of +/- 15%. Different tubes are available for many gases and results can be obtained between 5 seconds and 15 minutes depending on the test. Once a result has been obtained, the tube itself is hazardous waste and must be disposed of. Historically stain tubes have been popular because the cost per test is low. However, the number of tubes that have to be employed in order to demonstrate that a container is safe can be prohibitively expensive and time-consuming to employ.

Instrumental gas analyzers such as electrochemical sensors, that measure either a single gas or a small number of gases impart a similar level of risk to stain tubes because of the possibility of missing or failing to measure a harmful gas. Deploying multiple instruments also presents practical problems because each will require maintenance and re-calibration in addition to a power source or re-charging. Nevertheless, Reaktie for example, would normally conduct a preliminary assessment with a PID gas detector for total VOCs; an LEL combustible gas sensor and handheld electrochemical sensors might be employed for toxic gases such as carbon monoxide, phosphine, ammonia and ethylene oxide. An FTIR analyser would then be employed to measure 50 target gases simultaneously in a test that would take approximately 3 minutes. This ability to measure compounds individually is important because, for example, whilst a PID gas detector measures total VOCs, it does not provide an individual value for, say, benzene, which is a known carcinogen.

One of the potential problems with electrochemical sensors is their inability to cope with high concentrations in a sample gas. This can result in poisoning of the cell, which would normally result in instrument failure. In contrast, similar high concentrations do not harm FTIR, and the instrument can recommence analysis after a few minutes of backflushing.

DX4040

Gasmet DX4040

Peter Broersma has been one of the first to utilise FTIR in the assessment of containers since it first became possible to acquire the technology in a portable battery powered unit. He says “The problems with hazardous gases in cargo containers is now widely publicised and the requirement for testing is growing as employers fulfil their responsibility to protect the health and welfare of staff. However, the traditional testing methods are laborious, time-consuming and risk failing to find a potentially harmful gas.
“FTIR has long been established as an accurate technology for the simultaneous measurement of gaseous emissions from industrial processes, so when the Finnish company Gasmet developed a portable version we were very eager to investigate its feasibility in container testing.
“Following our initial tests, we worked with Gasmet to develop a configuration for the portable FTIR (a Gasmet DX4030) that would measure the 50 compounds of greatest concern. As a result, we are now able to test for all of these gases in around 3 minutes, which dramatically lowers the time taken for container inspection and greatly increases the number of containers that can be examined every day.
“A further major advantage of this technology is the minimal amount of calibration and maintenance that is necessary. A new instrument can be delivered pre-configured and factory calibrated and from then on the only calibration required is a quick zero check with nitrogen once or twice per day. As a result, it is not necessary to transport a large number of expensive, bulky calibration bottles.
“We now use a portable FTIR for all of our container examination work and we have also supplied a number of these units to freight companies that wish to conduct their own testing. This technology is now in use at Rotterdam, Amsterdam, Vlissingen, Antwerp and Hamburg, and a company providing ship fumigation and degassing is using portable FTIR all over the world.”

Fourier Transform Infra Red (FTIR)
An FTIR spectrometer obtains infrared spectra by first collecting an ‘interferogram’ of a sample signal with an interferometer, which measures all infrared frequencies simultaneously to produce a spectrum.

Over a number of years, Gasmet has established a library of reference spectra that now extends to simultaneous quantification of 50 gases or identification of unknowns from a collection of 5000+ gases. This means that it is possible to
reanalyze produced spectra with the instrument’s PC based software (Calcmet) and thereby to identify unknown gases – a major advantage of FTIR.

Whilst FTIR is able to analyse an enormous number of gases, the technique is not suitable for inert gases, homonuclear diatomic gases (e.g., N2, Cl2, H2, F2, etc) or H2S (detection limit too high).

High levels of accuracy and low levels of maintenance are achieved as a result of continuous calibration with a He-Ne laser, which provides a stable wavenumber scale. In addition, high spectral signal to noise ratio and high wavenumber precision are characteristic of the FTIR method. This yields high analytical sensitivity, accuracy and precision.

Summary
Millions of containers arrive in international ports every year and it is clear that a large proportion of them represent a significant hazard. Employers have a duty of care to protect their staff and court cases have found in favour of workers that have suffered ill-health from container gases. It is inevitable therefore that the amount of testing required will continue to increase so there will be a greater emphasis on speed, risk reduction and cost.

Portable FTIR gas analysers substantially reduce the amount of equipment required to test a container, but more importantly, the technology enables the simultaneous analysis of a large number of target compounds, which improves the effectiveness of the assessment and reduces risk to staff. The technique is also much faster and avoids the use of disposable equipment.


FTIR analyser reveals surprising solution

09/10/2012

Emissions analysers have to be checked annually by certified testers and during recent functionality tests for a Gasmet FTIR continuous emissions monitor (CEM) at a British Energy from Waste plant, the Nitrogen Dioxide span check results were found to be incorrect. A subsequent investigation revealed surprising results that would not have been apparent had the plant been using traditional CEMs.

NO2 values should have been 76mg/m3 but the FTIR was reading 31mg/m3, so Dominic Duggan from Quantitech, the company which installed the monitor, was contacted to investigate.

As a multigas monitoring technology, FTIR provides a complete analysis spectrum from the sample gas and as a result it was possible to investigate the response peaks for NO2 in addition to any other gases present. Duggan’s investigation showed peaks for NO2 and also found peaks for NO and HCl. In addition he found an unknown peak at 1750-1850 cm-1 in the sample spectrum.

The investigators speculated that there may be a problem with the regulator, which had previously been used to deliver HCl test gas and a quick piece of internet research revealed that Nitrosyl Chloride (NOCl) can be formed if NO2 and HCl are mixed. This gas is a decomposition product of Aqua Regia and was found to be responsible for the ‘unknown’ peak.

Aqua Regia (a mixture of Nitric and Hydrochloric acids) is so-called because it is able to dissolve royal or noble metals such as gold. As an interesting aside, when Germany invaded Denmark in World War II, a cunning chemist dissolved the gold Nobel Prizes of two German physicists in aqua regia to prevent the Nazis from confiscating them because Nobel Prizes had been banned in Germany. He placed the resulting solution on a shelf in his laboratory and it avoided the attention of the Nazis who thought the jar contained common chemicals. After the war, the chemist returned to find the jar still on the shelf, so he precipitated the gold from the acid and returned it to the Nobel Foundation which re-cast the medals.

This shows the sample spectrum with NOCl and NO2 peaks (in black) plus NOCl reference spectrum (in red) for comparison.

Clearly, aqua regia is a highly corrosive chemical, so it is important to avoid its generation. A clean regulator was therefore fitted to the CEM and subsequent analysis showed the correct result for NO2.

Dominic Duggan says “The main advantage of FTIR is that it provides continuous analytical data for an almost endless list of chemicals. Most CEMs are configured to monitor up to 50 parameters, the most common configurations include H2O, CO2, CO, SO2, NO, NO2, N2O, HCl, HF and NH3, however, it is also a simple and low cost process to add further parameters at a later date, which means that the monitoring regime is ‘future proof’.

“This investigation highlights a further advantage of FTIR; if traditional single parameter analysers, such as chemiluminescence or NDIR, had been in place, the logical conclusion would have been to blame the analyser for reading incorrectly, resulting in a costly exercise to have it replaced. But the FTIR enabled us to study the complete spectrum and quickly identify and resolve the problem.”


Interacting with pH probes….The White paper!

01/03/2012

pH Sensors: Know whether to calibrate the sensor, clean the sensor, perform a calibration check or …?

by Fred Kohlmann – Analytical Product Business Manager, Endress + Hauser.

This is a white paper that outlines the proper procedures for maintaining and calibrating pH sensors. All pH sensors in a process need to be inspected, cleaned and calibrated on a regular maintenance schedule to ensure accurate readings. In some companies, however, maintenance and quality control directives may not be specific enough when dealing with pH sensors.

The Author

Fred Kohlmann is a Product Business Manager for Analytical Products with Endress+Hauser. Since 1976, he has been involved in engineering, design service, marketing, and sales of online
analytical water quality and process control instrumentation. He has taught accredited course work and authored numerous articles relating to pH, ORP and conductivity measurements.
Past publications include “What Is pH and How Is It Measured?”, a primer on the use of pH instrumentation, and “Electrical Conductivity Measurements” in the “Process/Industrial Instruments and Controls Handbook”, Fourth Edition, by McGraw Hill, Douglas M. Considine Editor.

The phrase in the above title is actually incorrect in its sequence of wording. All pH readings are supposed to be taken and accepted only when the pH sensor is clean. After all, a contaminated pH sensor may yield an incorrect reading. So one must make sure the sensor is clean before doing a calibration. Once a pH sensor is installed in the process and operating, how do you determine when it is time to take the sensor out of the process and do a cleaning, or a calibration? Does one perform both a cleaning and a calibration or just a cleaning, or just a calibration, or does one just perform a calibration check in buffers or…?

This is something that can be quite confusing, especially when the operational practices and procedures documented by your company’s Quality Control or Environmental Practices department may not be specific enough when they describe the procedure or the timing on when to conduct the pH calibration and maintenance. Inversely, the procedures may be too specific, detailing many more procedures and operations than are actually required.

Due to manufacturing criteria, pH measurements are sometimes made in areas of the process plant where accessibility to the pH sensor is less than ideal.

In practical terms, users must develop their own maintenance and calibration schedule. This schedule is accomplished by taking the pH sensor out of the process after a set amount of time, perhaps after a day or two to perform a visual inspection of the sensor. If after inspection you find no debris or fouling on the electrode and reference surfaces with the naked eye, rinse the sensor off in distilled water and perform a buffer check.

To perform a buffer check, place the sensor into the calibration buffers you typically use and note the readings. If the readings are within the tolerances defined by your operational procedures, it is not necessary to perform a calibration. For example, let us use ±0.2 pH as your tolerances for pass/fail of a pH sensor reading in a calibration buffer. If the sensor reads within this value, in the offset (7 pH) and span buffers, (4 pH), the sensor needs no further action and can be reinstalled into the process. A calibration is not necessary. Repeat this exercise every few days until you see a change in either the level of debris/foulant on the electrode and reference surfaces, or more than the ±0.2 pH deviation as shown in the example above.

To a certain extent, the above procedure sets the benchmark for time between cleaning and calibration. Now, one needs to determine whether the sensor needs just a cleaning or a cleaning and re-calibration. This is done easily by first making sure the sensor is clean. (Refer to the section on Cleaning pH sensors). It may be as easy as rinsing the sensor in water or as complicated as using acid or caustic solutions to remove the particular
contaminate buildup that has occurred.

pH CALIBRATION – CALIBRATION CHECK – CLEANING
Should the above steps not yield results that are within your pass/ fail criteria, it is time for a sensor cleaning.

About Cleaning the pH sensors:
For the pH sensor to maintain an accurate reading of the process pH, the pH sensor must remain clean. Specifically, the glass measuring electrode can not become coated and the reference electrode assembly must similarly not become coated, plugged or otherwise contaminated by the process solution.

If the pH sensor has a slight coating or scaling, this might be removed using a water jet from a faucet or spray bottle. More entrenched coatings may require the use of a gentle acid brush or tooth brush to carefully remove the coating. Depending on the nature of the scale or coating, you may find it necessary to dip the sensor in a hot water solution containing Dawn® dishwashing detergent and then lightly scrub the electrode for a few seconds or so to facilitate cleaning.

For a more aggressive coating of the sensor and one in which the detergent cleaning does not suffice, you may have to dip the brush
in a 2% HCI acid solution and then lightly scrub the electrode for a few seconds or so to facilitate cleaning. Alternatively, you may have to allow the sensor (electrodes) to soak in a similar solution for a few minutes to really work at attacking the contaminant. Immediately after cleaning, rinse the sensor in water and allow the pH sensor to soak in tap water or a 7 pH buffer solution for a few
minutes to allow the pH sensor to stabilise.


General Cleaning Procedure:
1. Keep sensor as reasonably clean as possible.

2. Remove the bulk of contaminant by carefully blotting/wiping away debris. Be careful not to rub too vigorously as this may cause static charge.

3. Rinse the sensor in warm tap water or distilled water.

4. Prepare a cleaning solution containing a soap and water mixture. Use dishwashing detergent and warm water. Use only soaps that do not contain abrasives or lanolin.

5. Soak the sensor in this solution for up to five minutes and then gently or while soaking, use a soft bristle brush to gently scrub the bulb and reference area of the sensor.

6. Rinse the pH sensor in warm tap water and check/standardize the sensor in buffer solutions.

If the readings in buffers are still out of tolerance:
7. Soak the sensor in 5% to 10% HCI acid solution for a few – less than five – minutes.

CAUTION! 

Do not use this procedure if the sensor has been used in a solution containing cyanide as this may produce poisonous cyanide gas.

8. Rinse the sensor in warm tap water and then place the sensor into a mild soap solution for a minute or two to neutralize any remaining acid and let the sensor come to equilibrium.

9. Rinse in warm tap water and check/standardize the sensor in buffer solutions.

Should the above procedures yield results that are within your operational tolerances, the pH sensor is once again suitable for use. However if the above results do not bring the readings of the pH sensor within tolerance, it is time to replace the sensor.

Quality buffers are traceable, can cover the full pH measurement range and are usually available in package sizes of 18 ml up to 5000 ml.

DECISION TREE
The decision tree is a quick graphic interpretation of the procedures outlined in the previous text.

Download the paper from the Endress+Hauser website here!


Wastewater treatment optimisation provides cost savings

25/08/2010

Dr Michael Haeck, Hach Lange

Background
The operators of wastewater treatment plants constantly seek new opportunities to improve plant efficiency and environmental performance. In order to achieve this they need to be able to maintain the effectiveness of the treatment process, producing a consistent discharge within consent limits, whilst minimising inputs such as energy, labour and raw materials.

Real-time control (RTC) has become very reliable.

As technology advances new opportunities materialise and this article will outline the considerable benefits that can be obtained from the latest sensors coupled with a new breed of real-time controllers. Improvements in the accuracy and reliability of sensors, coupled with a new facility providing  information about the sensors’ performance, in addition to the measurement itself, means that real-time control (RTC) has become very reliable which means that it has become an attractive option in a large number of applications.

Hach Lange has developed a set of standardised control modules, enabling the application of processes improvements and optimisation strategies without the need for complex programming and expensive customisation.

In combination with Hach Lange sensors, Nutrient Removal and Sludge Treatment Processes can now be easily optimised in order to achieve savings in aeration energy and chemical consumption, even on small waste water treatment facilities.

RTC opportunities
Stand-alone wastewater treatment optimisation solutions (WTOS) control modules are now available to optimise individual treatment processes at treatment plants. These can be easily integrated into an existing plant structure and currently include (1) the chemical elimination of phosphorus and (2) dissolved oxygen adjustment according to the actual NH4-N load in an aeration tank.  Control modules for sludge management as sludge retention time controller or desludging controller will be added in the near future.

In addition to the stand-alone modules mentioned above, it is also possible to combine different RTC modules to optimise an entire plant, as outlined in the trial below. Termed an ‘enterprise solution’ this activity involves a review of the plant as a whole and the creation of customised specifications for the application of different control modules for nitrification, sludge retention time, methanol dosing, and/or chemical phosphate removal to achieve the best overall performance.

Sensor technology
In recent years, improvements in sensor technology have focused on greater resolution and accuracy in combination with longer intervals between calibration or service. However, in order for an RTC system to operate effectively it is also necessary for sensors and analysers to be able to provide information on the quality of the signal and the service status.

Hach Lange has filed a patent application for this facility under the brand name ‘PROGNOSYS’. This provides the RTC control modules with a continuous indication of a sensor’s status so that if pre-determined conditions occur (sensor failure, outside calibration, service overdue, drift etc) the RTC automatically adopts an alternative control strategy, which might be a typical weekly and diurnal flow profile that has been stored in the system’s memory.

Stand-alone RTC example: chemical Phosphate removal
As outlined above, the measurement technology for phosphate has advanced considerably in recent years in tandem with a reduction in capital and operational costs. As a result, an easy to integrate RTC module in the phosphate removal process can deliver pay back periods of less than one year.

The measurement of phosphate levels in combination with an RTC system can be utilised to manage the dosing of precipitant salts. This precipitates the phosphate and facilitates sedimentation and removal. Accurate continuous monitoring is necessary to ensure that (a) sufficient dosing is applied to remove the phosphate and (b) excessive dosing does not take place. Over-dosing would be undesirable on three counts; firstly, from an environmental perspective the objective is to minimise the amount of iron being added that could remain in the effluent; secondly, ferric sulphate is expensive and excessive dosing would be costly; thirdly the amount of precipitation sludge should be kept to a minimum because sludge disposal can represent a significant cost.

A unique feature of the RTC system is the continuous automatic calculation of the ‘ß’ value (overdosing rate), which is required to calculate the right amount of precipitant dosing for open loop control. The calculated ß-value takes into account the percentage of phosphate which has to be removed. The less phosphate there is; the more difficult removal becomes and the more precipitant is required to eliminate the same amount. For example, more precipitant is required to lower phosphate concentrations from 4 to 2 mg/l than from 6 to 4 mg/l.

Wastewater treatment plants operating an open loop real time control system for phosphate removal have demonstrated considerable savings – a UK works has saved approximately 37% of the ferric sulphate cost and 57% of caustic chemical costs and a plant in Italy has shown 50% cost savings in comparison with a constant dosing system, which represents a 7 month payback.

If closed loop control is applied, the RTC system requires a measurement of phosphate levels immediately after dosing. As a result, the Phosphate concentration can be held at a fixed desired level and the control performance is monitored as indicated in figure 1.

Figure 1: Example for Stand Alone P-RTC performance

UK RTC Trial – activated sludge process control
The results of a trial investigating the benefits of an RTC system on the management of the activated sludge process (ASP) have been published by Thornton, Sunner and Haeck[i].

Managed by MWH UK Ltd and employing monitoring instruments from Hach Lange, the trial employed online sensors and control algorithms to optimise the operation of the ASP, leading to greater efficiency and sustainability. Undertaken at full scale, the trial assessed the benefits of RTC at a 250,000 population equivalent (PE) works in the UK and consisted of two identical ASPs (each with four lanes) configured as a 4-stage Bardenpho plant with methanol addition in the secondary anoxic zone.

Standard aeration lanes (fixed DO set-points with fluctuating NH4 effluent concentration) were compared with lanes running an RTC system operating variable DO set-points based on actual load. The RTC lanes deployed extra sensors for dissolved oxygen, ammonium and nitrate.

The trial demonstrated that the RTC system was able to respond quickly to ammonium influent spikes and to maintain a stable effluent ammonium level. The trial also demonstrated that the RTC system was able to reduce methanol consumption by 50% and energy (measured as air flow) by 20% (figure 2). The system has now operated successfully for more than one year

Figure 2: RTC savings

Summary
The Hach Lange optimisation system combines process measurement technology with advanced RTC control modules to provide substantial savings in operational costs at wastewater treatment plants, whilst maintaining compliance with consent values.

Recent advances in sensors, analysers and controllers mean that wastewater treatment no longer has to be managed on a ‘worst case scenario’ basis. Processes can now be monitored and adjusted instantaneously to maximise efficiency and improve process stability. Cost reduction is obviously a key benefit, but the ability to reduce energy consumption is becoming an important objective in many countries.


[i] Thornton, Sunner and Haeck, 2010. Real time control for reduced aeration and chemical consumption: a full scale study. Water Sci. Technol.61, 2169–2175