Monitoring turbidity and suspended solids content in final effluent discharges is a growing issue for manufacturers. Angus Fosten, of Partech Instruments, explains how new monitoring equipment is being used, assessed and endorsed
One area of importance to companies and industries that use water in their processes is the monitoring of turbidity and the suspended solids content in final effluent discharges. The constant tightening of consent levels from environmental organisations such as the UK's Environment Agency means that greater attention has to be given to monitoring emissions and this is leading to a situation where extracting samples for laboratory analysis and data recording may be insufficient to ensure consent level compliance.
For companies with installations falling under the Integrated Pollution Prevention and Control (IPPC) regulations and those that want or need to self-monitor effluent flows, the introduction and implications of the Environment Agency's Monitoring Certification Scheme (MCERTS) needs to be studied carefully.
MCERTS has now become an established scheme for any organisation involved in the operation of a wastewater or industrial effluent treatment plant as well as for manufacturers of instrumentation used in this industry. It has been set up to provide a framework for the certification of instrumentation and samplers and for the accreditation of flow inspectors in the water environment in addition to the previous schemes for air monitoring. It has become a standard requirement in effluent quality monitoring under IPPC schemes and is any integral part of Operator Pollution Risk Assessment (OPRA) and Operator Monitoring Audit (OMA) scoring.
In addition, it gives confidence to potential users that the instrument selected is robust and performs to the standards accepted by the Environment Agency. Where an application requires the employment of continuous water monitors, MCERTS provides instrument manufacturers with an independent authoritative endorsement of their products.
Under the IPPC the activities in processing plants are assessed according to the OPRA guidelines combined with the OMA. Scores in these assessments will dictate the monitoring requirements for the site. Continuous monitoring determinants covered by MCERTS are: Turbidity, pH, ammonia, chemical oxygen demand, total organic carbon, dissolved oxygen, total phosphorous, nitrate and total oxidised nitrogen. These are some of the most important parameters when monitoring discharges from wastewater treatment works and other industrial processes. The use of MCERTS certificated measurement equipment will help boost OPRA and OMA scores, which in turn can reduce EA monitoring charges.
Partech Instruments has embraced MCERTS for its instruments, and its 7200 Monitor and Turbi-Tech 2000LS Sensor combination was the first Turbidity Monitor to be awarded MCERTS certification. The system is suitable for monitoring turbidity in effluent discharges and can also be configured to monitor suspended solids in the final effluent flow.
The Turbi-Tech sensor's fully integrated self-cleaning system provides low cost ownership and gives users confidence in the information being gathered.
Partech's MCERTS system is suitable for monitoring turbidity in effluent discharges, river water and inlet protection applications in ranges from 0-50 to 0-500 FTU (formazin turbidity units). It can also be configured to monitor suspended solids in the final effluent flow. This gives an indication of process problems that are causing solids to leave the site and enter the watercourse.
Armed with this information, the plant operator can make adjustments to the control system to prevent pollution and make efficiency improvements. Where discharge consent levels are particularly tight, turbidity monitoring at the final outflow should be considered as essential.
The sewerage company Southern Water in the UK has been using Partech's Turbi-Tech 2000LA for several years and has taken a decision to replace monitors that have proved to be problematical with the Turbi-Tech 2000LA as part of its Process Compliance Programme.
"With the Partech Turbi-Tech 2000LA system, setting up is intuitive and once set up the instruments hold their calibration," says David Manley of the Instrumentation Control and Automation (ICA) department. "Once calibrated, we know that there will be little drift between calibrations."
In order to monitor suspended solids and turbidity, it is essential to employ instrumentation that is calibrated in accordance with Reference Method 2540 Total Suspended Solids (dried). The Partech Turbi-Tech 2000 operated in conjunction with the Partech 7200 Monitor uses infrared light that is either scattered or absorbed by the particles in suspension, the amount of received light being proportional to the level of suspended solids. The geometry of the sensor, either light scatter or light attenuation, is chosen to suit the suspended solids or turbidity range.
The amount of received light is converted by the 7200 Monitor into suspended solids using specifically developed algorithms. The sensor has been designed to cope with problems of fouling and also features an integral cleaning mechanism that ensures accurate measurement with little routine operator involvement.
According to the EA, enforcing MCERTS will take more of a persuasive than a draconian approach. There can be no single or blanket set of rules as compliance is very much site-specific. EA inspectors advise and make recommendations where an OMA (Operator Monitoring Assessment) audit has identified problems and where it is clear that a site needs bringing up to scratch. The timescales for these improvements will depend on the significance of the problem and site-specific circumstances.
Throughout the EU and many other parts of the world there is a growing demand for continuous water monitors that conform to a single international certification scheme and it is inevitable that this will come about in the not too distant future. MCERTS will be a contract tendering requirement and, most importantly, it will create a level playing field in what is becoming a very competitive market and eventually eliminate those products that are not fit for purpose.
MCERTS certified analysers will give operators the confidence that the equipment they are using is of the highest standard and that by doing so they can be safe in the knowledge that they are meeting the criteria for safe discharge consents. Should plant operators have any doubts about conformity and whether they fall under the IPPC scheme, they can go to the MCERTS website (www.mcerts.net).
Attaining MCERTS approval will prove to be necessary for all manufacturers of continuous water monitors seeking to maintain their presence in the industry. There are no short cuts to gaining certification as conformity testing should be carried out by laboratories that are accredited to EN ISO/IEC 17025:2000. Conformity testing is available from several test houses including WRc, the Environment Agency's national testing laboratory service and Sira Environmental, which manages the scheme.
Product certification also requires the manufacturer to be able to demonstrate that the manufacturing process is controlled under a quality management system and producing equipment that delivers consistent performance. However, it is accepted that design and manufacturing changes will take place, so the manufacturer is required to keep Sira informed of any changes.
For potential customers and regulators, MCERTS product certification provides valuable assurance that equipment performance is being maintained as all changes are tracked and periodic audits are carried out.