Industrial effluent in the 21st Century
As legislative pressure mounts on industry to reduce its effluent discharges, Emma Cowley of Aqua Enviro considers the drivers and reviews treatment options
The UWWTD is the latest in a series of directives affecting industry today with the others including the nitrate directive, which mainly covers agricultural issues and Integrated Pollution Prevention & Control (IPPC). IPPC has applied to new installations since 31 October 1999 and is being gradually phased into existing installations, sector by sector until the final quarter of 2007.
The main function of the UWWTD is to offer some protection to the environment from the undesirable effects of urban wastewater discharges and the emissions from some industrial sectors. It covers sewage treatment works and industrial discharges with population equivalents (p.e.) of 2,000 and greater. Under UWWTD, treatment options vary and although most emissions will require secondary treatment, in areas of high natural dispersion, such as estuaries and coastal areas, primary treatment alone may be acceptable. Likewise in more sensitive areas the removal of nutrients may also be an additional requirement. As this applies to all sectors the water companies themselves are taking action to upgrade and retrofit their treatment sites to meet the new regulations. On the other hand IPPC seeks to ensure that industrial installations:
As the points above relate to any process that occurs within a specific site it is important to monitor the efficiency of any effluent treatment process that is carried out. This will help to ensure the plant operates in compliance with any consent limits.New regulations
New regulations are continually causing industry to reassess its effluent treatment options and the latest additions are no exception. The two pieces of legislation will together cover most industry whether it partially/completely treats its wastewater and discharges to a watercourse or if it disposes straight to sewer for the local water company to treat. For obvious reasons it is important to keep an eye on the trade effluent charges and consider whether the self-treatment option is best for the individual site in question. For example, Mr ICR Byatt, former director of water industry regulator OFWAT, warned water companies in 1999 about increasing charges to cover plant upgrades without prior warning to trade effluent customers. He quoted that in some instances water companies had been increasing the trade effluent bills up to five fold, to incorporate secondary and tertiary treatment, without giving prior warning to their trade effluent dischargers.
In certain cases this created the situation whereby it would have been far cheaper for trade effluent customers to initiate a partial treatment process before discharging to sewer. It may also be beneficial, especially after process changes, to review the volumes and the values of COD and solids used by the water company to calculate the bill in the Mogden formula as these may change over time resulting in incorrect billing. All the water companies use slightly modified versions of the Mogden formula.
The formula generally takes into account the average strength and solids concentration of the influent to the treatment works that the trade effluent will be discharged to, in theory this ensures that industry only pays for the extra treatment that their wastewater requires in addition to that which the treatment works has to provide already. However, there are issues with industries that produce wastewater that is 'cleaner' than domestic sewage, these discharges often end up paying large reception costs especially if the receiving sewage treatment works is fairly small and the works has to be made larger to accommodate the trade effluent. The volumes of water consumed can be reduced through the application of waste minimisation, and it is also beneficial to monitor levels of the COD and suspended solids. In some cases this can reduce the trade effluent bills by up to 20 per cent.Treatment options
IPPC can encourage industry to update or install new treatment options. One of the projects in the area of industrial effluent that Aqua Enviro has been involved with is in association with a food processor who, by looking to expand production in the near future, wanted to reduce effluent discharge and implement water re-use within the plant as a precursor to eventual increase in the discharge. An initial survey of the site discovered that the effluent treatment plant was undersized and hard water was leading to the boiler plant spending around 20 per cent of the time blowing down to remove accumulated solids. The normal acceptable range is 3-6 per cent of the time.
A pilot scale project was undertaken in which feed was taken from the aerobic digester into a membrane plant and then through reverse osmosis (RO) and UV disinfection. The eventual aim is to reuse throughout the plant. The RO proved to be so successful in removing the hardness from the water that it is being commissioned at present, at a cost of around £240,000. The building that houses the RO plant is large enough to house the rest of the equipment once capital expenditure has been approved. Once the equipment and pipe work is installed the feed water for the boiler system will be fed directly to the RO plant and the levels of dissolved solids should be lowered from around 680mg/l to 10mg/l before the water enters the boiler as feed water. The aim of this is to reduce the blow down costs within the boiler system by around £300,000 per year, which results in a payback time of less than 10 months for the reverse osmosis part of the upgrade.
Once the upgrade is completed the project will reduce the quantity of water that is discharged through reuse in other parts of plant. It will also allow the quantity of clean water used to be reduced. It is a good example of meeting the IPPC regulations in terms of using energy and raw materials efficiently and it shows that latest technology can be installed and the capital expenditure quickly recouped.