Existing monitors for organics, nitrogen,
phosphorus and other contaminants in industrial wastewater and municipal
sewage are bulky and expensive. With an eye on tightening European
water quality laws, the partners in this project set out to build
a simpler, cheaper analyser suitable for small treatment plants.
A French university led the project with support from a French spectrometer
manufacturer and universities in the Balearic Islands and Greece.
The instrument they developed uses a newly-designed ultraviolet spectrometer
and some innovative techniques for wet chemical analysis. The first
simplified commercial version of the instrument has attracted considerable
interest, and a fully-featured version will follow soon.
The EC's 1991 directive on wastewater quality
has far-reaching implications. By the end of the year 2000 every
town with a sewerage load equivalent to 15,000 or more people must
be equipped with a wastewater treatment plant. By 2005 this requirement
will extend to villages with more than 2,000 inhabitants.
The resulting growth in the number of small wastewater treatment
plants raises challenges for the instruments used to monitor the
quality of the water entering and leaving the plants. Quantities
to be monitored include nitrogen compounds, phosphorus, suspended
solids and the loading of organic substances - measured as total
organic carbon (TOC), biological oxygen demand (BOD) and chemical
oxygen demand (COD). The instruments to do this are currently bulky
and expensive both to buy and to maintain.
Researchers at the University of Provence in France decided that
it should be possible to develop a compact, cheap and versatile
instrument to measure contaminants in water. While not replacing
existing instruments in large municipal sewage treatment plants,
the new monitor would be ideal for the next generation of small
plants and industrial wastewater treatment facilities. Project SMT-2
has successfully developed such a device and its commercial prospects
The versatile spectrometer
Team leader Dr Olivier Thomas at the University of Provence already
had a good working relationship with Secomam, a French spectrometer
manufacturer specialising in environmental applications. By autumn
1993 he had found two other partners, the University of the Balearic
Islands (Spain) and the University of Ioannina (Greece), and the
two-year project was born.
The new instrument is based on a spectrometer that works in the
ultra-violet and visible ranges of the spectrum. Spectroscopy is
a powerful technique that can measure many variables important in
the analysis of wastewater: total organics and suspended solids,
specific components including nitrogen, phosphorus and phenolics,
and whole groups of contaminants such as anionic detergents.
However, adapting spectroscopy to the specific demands of wastewater
analysis brought some new challenges. The project partners were
unable to find a suitable low-cost spectrometer, so Secomam designed
a new one with a detector based on a simple array of 16 photodiodes.
A patented self-cleaning quartz sample cell ensures reliability
when the instrument is used with dirty water samples.
For the light source the company faced a dilemma: the deuterium
lamps found in laboratory spectrometers consume a lot of power and
have short working lives, while a possible alternative, xenon flash
tubes, give a poor spectral distribution in their light output.
Secomam solved this problem by developing a pulsed deuterium lamp
that combines excellent optical performance with long life and low
The basis of spectroscopy lies in matching the peaks in the sample
spectrum to the contaminants that absorb UV light at these frequencies.
To do this the researchers developed a new method of 'deconvolution'
- the process of analysing the sample spectrum and comparing it
with a series of reference spectra. An important advantage to the
team when building up the reference spectra was that Dr Thomas was
able to call on a library of around 100,000 spectra, and their corresponding
chemical analyses, collected during his 20 years' work in this area.
Careful choice of the reference spectra has allowed the researchers
to develop an instrument that can be used off-the-shelf in a sewage
treatment plant without the need for calibration. For increased
accuracy, especially in industrial applications, the instrument
can also be calibrated. Because the detector is small and the deconvolution
algorithms are relatively simple, the spectrometer needs only a
standard microprocessor to run it. Because the operating sequences
are programmed into the computer, changes to the way the analyses
are done can be made simply by updating the software, with no need
to alter the physical layout of the system.
Reagents extend scope
Some contaminants such as nitrate, total organics carbon, suspended
solids and detergents can be measured by direct spectroscopy. Others,
notably nitrogen compounds, and phosphorus, are detected by adding
chemicals with which they react, causing a colour change that can
be measured by the spectrometer.
For this 'wet chemistry' the project partners used sequential injection
analysis (SIA), a relatively new variant of an established technique
called flow injection analysis (FIA). In both SIA and FIA, reagents
are added to the sample as it flows through a narrow tube at a known
rate. The time taken for the sample to pass through the tube and
into the measuring cell allows the colour-producing reaction to
In FIA this injection is a continuous process; in SIA it takes place
batchwise, as doses of sample and reagent are fed sequentially into
a 'delay loop' of tubing. SIA can use a simple piston or syringe,
so it is cheaper than conventional FIA, which needs a more complex
pump to give accurate control of flowrates.
Researchers at the University of the Balearic Islands applied their
experience in SIA to the design of the new instrument. Careful control
of residence times and reaction kinetics has allowed them to get
reproducible results without waiting for the colour-change reactions
to go to completion, so analyses can be made accurately in a few
seconds or minutes.
Testing and commercialisation
Researchers from the University of Ioannina tested the instrument
on two municipal sewage treatment works: one at Ioannina itself
and a smaller plant near the university.
Following the successful field trials, Secomam is now commercialising
a field portable version of the spectrometer, without the SIA system.
It measures a compact 30 cm x 15 cm x 15 cm and is inexpensive enough,
the company hopes, to find wide use even in small treatment plants.
Among other potential buyers the major water companies are reported
to be interested.
Spectrometers incorporating the SIA system for measuring nitrogen
and other contaminants should be on the market by the end of 1997.