On-line effluent monitoring savings
Mike Pearce of Envitech explores the financial importance of on-line effluent monitoring techniques in food and drink processing applications.
Historically anything associated with effluent disposal has been regarded as low priority within manufacturing organisations.
This has been brought about by the perception that disposal of waste products can be achieved at no cost by dumping in sea, river or land. Obviously this view had to change when the regulators got to work and imposed consents. It is now well accepted that there is a real and significant cost for treatment or disposal to sewer. However, old attitudes die hard and effluent monitoring is regarded just as a cost and not an opportunity to increase profit.
In some ways this is surprising since, almost without exception, organisations have embraced the need to monitor and control energy consumption and water usage. It’s now only a comparatively small step to take on board the monitoring and control of effluent generation, treatment and disposal.
One of the stumbling blocks for the implementation of effluent monitoring has been the capital cost of equipment required and the associated maintenance requirements. Obviously the level of expenditure that may be justified will be determined to a large extent by the size of the operation in question. A handful of people making pies in a small unit are not going to spend many thousands of pounds on a continuous effluent monitor. However knowledge is strength, and a modest investment in suitable sampling and flow measurement technology may prove cost-effective in reducing effluent charges.
The following case studies will illustrate the ability of food and drink processors to save money and improve profitability by the application of on-line monitoring techniques.
Dairy industry case study
All food and chemical processing plants generate wastewater containing valuable product, some of which is an inevitable part of product processing. The question is how much is inevitable and how much is preventable?
Data obtained from a number of dairy sites in Europe and elsewhere was analysed, and results revealed that the net profit of many dairy processing facilities may be increased by approximately 33 per cent with effective loss minimisation. This does not include the savings made on either effluent discharge or treatment costs.
Sustained long-term reduction of losses relies on some basic requirements being fulfilled. These are:
- accurate, continuous quantified data on losses from each production area. This may be achieved using on-line carbon measuring instruments (BOD/COD/TOC),
- continuous availability of the data to all staff. This may be by means of a SCADA system or something as simple as flashing lights and alarms when certain limits are exceeded,
- acknowledgement of gains made to staff involved. Continuous feedback of quantified saving successes will create an incentive for management to encourage and reward operators.
Instruments for measuring BOD/COD/TOC on-line are all available and well proven. In this instance, the control system was as simple as it could come. The BOD strength was monitored using the Stip on-line machine (pictured). Alarm limits were set up and if these were exceeded alarm lights and audible alarms were sounded in each section of the production facility. It was then up to the responsible supervisors to check that their particular operation wasn’t responsible for the discharge, if it was then preventative action was taken immediately.
This example yielded the following results:
- product losses were substantially reduced giving an estimated increase in profit of 30 per cent.
- in addition the energy consumption of the waste treatment plant decreased. After start up of the system in August, energy consumption reduced by approximately 28 per cent by the following January,
- unlike earlier loss prevention attempts, savings steadily improved as more loss sources were identified. Operators directly measured their performance by comparing results to previous data and to other shifts. This invoked friendly competition between shifts, with bonuses targeted at across the board gains, and provided an incentive for shifts to assist each other in loss prevention.
The second case study took place in a pre-cooked meal production facility in the UK.
The wastewater generated from this manufacturing process is discharged to sewer for subsequent treatment by the local water company. Trade effluent charges based on the Mogden formula amount to some £450-£800K per annum. Currently flows are estimated and COD/SS are obtained from spot samples. Subsequent error in these measurements could easily result in significant overcharge.
A scheme is underway to install flow measurement on the waste stream and to install a composite automatic sampling machine. This should improve the accuracy of charging considerably, but will not help management control of unauthorised waste discharge, the potential cost of which could amount to some £50K pa for one unauthorised discharge per week.
In order to reduce product loss to sewer it is necessary to implement a continuous monitoring program using one or more relevant parameters.
Since COD is one of the charging parameters it was decided to approach Envitech to determine which on-line machines were available and whether they would function suitably when exposed to typical wastes from this facility.
The machine which related best to the parameter required and to the speed of response needed for this particular application was the Phoenix 1010. It was decided therefore to test the machine using typical effluent from the factory.
Samples were taken manually from the discharge sewer, by factory personnel, at intervals throughout the working day. Six samples were taken in total and stored until the following morning. These were then transported to Envitech’s premises where tests were performed.
Sub-samples from each bottle were taken after vigorous shaking and then analysed using a heated block dichromate COD method.
A further sub sample was put into a stirred container and gravity fed into the Phoenix 1010 analyser. The indicated reading was allowed to equilibrate and was then noted down. This procedure was repeated for all six samples.
On-line oxidation, using ozone, of the waste stream tested, gives a most acceptable correlation with acid dichromate oxidation as per the blue book method.
It must be concluded therefore that the instrument offers a viable on-line method of COD determination, for use in product loss control strategies and effluent charging scenarios.
The likely savings if even one unauthorised discharge per week were stopped would be approximately £50K. With a cost of the instrument at about £25K this would represent about a six-month payback.
Case studies for the application of on-line organic strength monitoring in the food and drink industry are many and varied. It is hoped that the two presented here will just give a taste of what might be achieved by illustrating the viability of the machines and indicating the financial implications of their deployment. We are no longer in the ‘on cost’ scenario, we are in the game of increased profit through effluent monitoring.
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