Simon Kimber, discusses why industrial wastewater is as challenging as it is varied, which is why careful assessment and customised solutions are required.
Industrial processes can produce effluents that are challenging in terms of their strength, variability and composition. Careful assessment of the physical, chemical and biological characteristics of the load can deliver a cost-effective and efficient treatment process.
Why is some effluent hard to treat?
Difficult-to-treat effluent is often the result of challenging industrial processes which create complex wastewater streams which may have high levels of oil and grease, heavy metals and high bacterial and viral loads that require specialist treatment. Additional challenges may come from a huge range of micropollutants that could also be present.
Hard-to-treat effluent may have high biological oxygen demand (BOD) or chemical oxygen demand (COD) as well as high levels of suspended solids.
Treating industrial effluent is complex and depends very much on the kind of load and the nature of the process generating the wastewater stream. As specialists in custom-designed wastewater treatment plants, WPL has had to tackle many challenging effluent streams over the last 25 years.
How much does the treatment vary from job to job?
It is rare to find two industrial wastewater streams that are the same, so treatment will vary from site to site. Because our custom-made plants are designed for each job, the company has found a range of ways of dealing with difficult effluents.
A fish farm in Scotland, where the effluent contained a high level of biological material, was assessed as requiring a combination of submerged aeration filter (SAF) plants and dissolved aeration filter (DAF) plants, as well as a series of settlement tanks.
At a blood-processing laboratory in England, engineers were able to customise the existing treatment works by fitting fine screens which could filter out troublesome lumps of biological matter. For a municipal waste disposal site in England, WPL created customised chemical treatment which could remove the variety of pollutants seeping from black bin-bags.
Which treatment options are available to industrial users?
Each case is different when it comes to the kind of treatment an industrial user requires. SAF technology is most suited to biodegradable waste where there may also be high ammonia levels. SAF treatment plants have a small footprint and are economical.
If separating suspended solids is the main issue, then a DAF plant may be more effective. DAF plants are often used in abattoirs, fish processing or other cases where there is a high level of particulate, biological solids.
In some cases, for instance where there is a high concentration of hair, it may be important to fit screens. Additional chemical processes may be necessary to clear micropollutants, including heavy metals, bacteria and viruses.
How is hard-to-treat effluent assessed and tested?
Each case begins with a site visit in order for WPL engineers to understand the nature of the site and the nature of process taking place. Initially it is important to assess the quantities of effluent being produced. If the effluent strength is variable, this also has to be taken into account.
Effluent samples are taken to our in-house laboratory and assessed for levels of COD and BOD and a range of micropollutants. The samples are then subjected to a range of different processes to assess their treatability with biological, physical and chemical processes.
Once it has been established that the effluent can be successfully treated in the lab, it is important to carry out a pilot study onsite.
Why is a pilot study important?
During the pilot study, engineers will establish the parameters for treatment as well as calculating the whole-life running costs. Treatment options can be adjusted during the pilot to ensure the effluent is treated to optimal standards for a given site.
At a large site, the pilot can be carried out by intercepting a sidestream of effluent, taking as little as five per cent of the total produced onsite. In other cases the pilot study will treat the entire effluent stream.
A pilot study is carried out for one week on a chemical process and eight to twelve weeks for a biological process. Both capital and operational costs can be calculated, taking into account energy use, chemical costs and maintenance.
Sewerage charges for industrial users are calculated by utilities using the Mogden formula. This means costs vary from month to month depending on the strength of the treated effluent released into the public sewers.
In some cases sewerage charges for industrial and agricultural customers can increase tenfold if an unusually high level of contaminants is detected in effluent streams. Industrial users can even face fines if they exceed consents set by the water utility. For these reasons an increasing number of industrial clients are looking for stable, reliable onsite treatment which treats effluent to a consistently high standard.
It is important to find the right combination of treatment for the effluent being treated, which is why WPL takes such a systematic approach to the issue. Hundreds of thousands of pounds are wasted every year on industrial treatment plants which are inadequate or unsuited to the job in hand.
Investing in a custom-made plant, designed according to the nature of the effluent to be treated, is the answer to tackling hard-to-treat effluent. It is more efficient, better for the environment – and will deliver long-term cost savings.