Case Study:

Dealing with Oil and Grease in Sewerage Systems

 

In the UK the true impact of fats, oils and greases, (FOG) in sewer systems has never been assessed, but it is known that FOG does create problems and increased operational costs in sewers, pumping stations and treatment works, that it can lead to sewer flooding and hence pollution and the risk of prosecution, and that many premises that discharge FOG to the public sewer do so without the requirement of a trade effluent consent.

Industrial premises that make discharges to sewer as a consequence of their processes have to have a Trade Effluent consent; and typically this will include a limit on FOG such as "no visible oil and grease" or "10 mg/l". These premises have to install complex grease trap systems to meet the discharge requirements, and these require a maintenance procedure involving the emptying of the grease traps regularly, and disposal of the contents at licensed waste disposal sites. This disposal cost is continuing to escalate.

Many commercial premises such as shopping malls with food halls, supermarkets providing "ready cooked" meals, and restaurants produce FOG way in excess of the limits that trade effluent control would require. But sewerage undertakers consider them exempt from trade effluent control because "domestic sewage" is exempted from trade effluent regulation and the contention, made many years ago, that the result of cooking a meal for consumption must be a "domestic" activity. This differentiation has to be questioned in the context of FOG.

FOG is not in solution; it's emulsified, in suspension, or floating; differences in temperature and flow rate (quiescence) affect the impact of FOG which can create localised effects, the location of which can be far removed from the point of discharge.

There is legislative power in sectn.111 of the Water Industry Act 1991 to take action against anyone that discharges any matter liable to cause damage to the sewerage system or to interfere with the free flow of its contents. But this permissive power has not been used to any extent by sewerage undertakers to try to mitigate the effect of FOG.

The reality is that even if Sewerage Undertakers feel they cannot use legislative procedures on dischargers of FOG they still have to suffer the consequences of it, which include increased operational costs at pumping stations and inlet works, fines for sewage overflows and the clean-up of them, and detrimental publicity.

Inevitably all of this is passed on to the domestic water charge payer; the real causes of the costs, mainly restaurants and supermarkets, get off scott free.

A number of products have been touted around the UK Water Companies and their trade customers that purport to deal with FOG. They claim to work through their biological, enzymatic or chemical attributes, or a combination of these. However the effectiveness of the products has been patchy and has led to a great deal of scepticism among professionals in the sewerage business.

BioClear Solutions is an American Company that has developed a system for the control of build-up of organic matter in waste lines from commercial premises and public sewers. This company has been extremely successful in providing service to multinational corporations and to sewerage Authorities over many areas of the USA.

The system has been used in many other countries including Australia, where Sydney Water, after extensive testing, has specified the system as the only acceptable system for use within the Sydney Water environ. Sydney has also waived the requirement for mandated pump-out schedules for commercial users, which can pump on as needed basis if they have contracted with BioClear Solutions.

In the UK the sewerage undertaker with the most sewage pumping stations is Anglian Water Services. Not surprisingly they experience problems with FOG and they have tried a number of potential remedies for the problems they experience, but so far have no unified strategy to combat the problem of FOG.

Anglian Water Services (AWS) management agreed to a trial being set up to test the efficacy of the Environmental Biotech system at a sewerage pumping station they identified as being particularly troublesome and expensive to operate because of the accumulation of FOG.

This station is at Shenfield in Essex, situated on the same site as a garage and a fast-food restaurant. Some 10 domestic properties also drain to the pumping station and the discharge from the pumping station is to the head of a gravity sewer some 500m away. This gravity sewer then drains to Shenfield STW via further in-line pumping stations.

The trial site is just off of the A12 trunk road at the junction immediately prior to the M25 motorway and is an extremely busy location for food sales. The records show AWS has had frequent problems with the pumping station and its rising main; when the pumps fail sewage back-up in the restaurant's toilets occurs.
AWS have had to adopt a management regime of regular pump-down by tankers and inspection visits to ensure satisfactory service for their customers and to safeguard the environment.

Measurement of the level of FOG is notoriously difficult. Whilst solvent extraction techniques can be used on continuous discharges, with limited success, actual measurement in a pumping station wet well is impractical. Description and photographic records were used to assess the situation in this trial.

Prior to the trial, Anglian Water was having to pump out the station every 12 weeks to clear accumulated FOG from the surface of the wet well. If this were not done then pumping station failures occurred regularly with consequential sewer overflows and backing up of toilet facilities in the fast-food restaurant. Whilst some may think this is just retribution for the difficulties caused by the restaurant company, the reality is that it's their customers who suffer rather than the Company!

The station was assessed for the trial on 6th June 2003. The regular pump-down had last been carried out on April 30th. It was decided, in the interests of really testing the system, not to tanker out the wet well, pump it down or even wash down the station walls. Photos taken at this initial inspection demonstrated the extent of FOG in the station and downstream at the point of discharge into the gravity sewer.

Following this initial inspection, personnel devised a dosing system which was installed on 12th June 2003. A 20 litre reservoir for BioClear Solutions' vegetative bacteria was placed in the electrical control kiosk together with a peristaltic pump and a air small compressor. These were controlled by a simple timer mechanism.

Air and bacterial solution were introduced via a simple plastic stilling chamber near the surface of the sewage. The bacteria, which is imported freeze-dried from the USA, remains active for up to 21 days, but for this station it was decided to replenish on a weekly basis.

At each visit the technician examined the dosing arrangements, replenished the bacterial solution and inspected the wet well, spraying a more concentrated solution of bacteria onto the fat layer accumulating on the wet-well walls, the pumps and the floats. The visit time is about 30 minutes.

Clear evidence of removal of FOG is demonstrated by the photograph taken 5 weeks after the start of the trial - one would have expected a significant increase in fat build-up rather than the decrease demonstrated in the photograph.

The hot dry summer of 2003 proved a severe test for the BioClear Solutions system but the bacteria and dosing regime was able to keep FOG under control with fewer call-outs than had been previously required. Unfortunately, presumably to reduce the odour potential of the pumping station during the hot weather, AW altered the pump stop start settings during the trial period which resulted in lowered liquid levels and gave greatly reduced retention period in the wet well. This meant that for a period the bacteria, whilst still softening the grease, was not able to remediate long enough to continue reducing FOG levels.

The dosing regime was changed to accommodate this, dosing mainly in the small hours after the midnight rush, with some improvement but the system rapidly returned to clearing the grease when the pump operating levels were reset to a longer time period in week 15. of the trial, raising liquid levels. Because this was only a trial, a more sophisticated dosing system linking the dosing pump operation to the sewage pumps operation, was not carried out.

One method used to demonstrate the cost-effectiveness of the BioClear Solutions System is to compare time allocated to the station from emergency call outs. This station has telemetry alarms for pump failure and for high wet-well levels and sustained high wet-well levels. Analysis of AW's record of cost allocation due to alarms shows that the period of 17 months prior to the trial 70 alarm visits involved expending 219 hrs on site (2 operators/craftsmen attend each alarm call-out), but during the 5 months of trial there was only 11 alarm call-outs involving 38 hrs on-site, ie on average 12.8 hrs per month without treatment, versus 7.6 hrs a month with dosing. This provides considerable saving of both direct and indirect costs of pumping station failures.

In addition, no tankering charges were incurred over the trial period, which was a 12 week cycle previously.

On 10th. December 2003 the pumps were overhauled and new impellers and wear rings fitted. A month later there had been no call- outs or visits recorded at the station. The extent of FOG was slight and was of a very soft and "fluffy" nature both on the wet well surface and on the walls between pump start and stop levels.

Conclusion

BioClear Solutions' system of FOG control involving a freeze dried bacterial product that is regularly activated and routinely installed at the site by trained technicians who identify any other problems with the station has proved its effectiveness during this trial. It has prevented the accumulation of FOG and kept any residual material in a soft form satisfactory for pumping station operation. There were no odor complaints about the station during the trial and no problems with the rising main. It shows clear benefit for FOG removal and consequentially, less interrupted pumping operations. It also demonstrated the importance of the BioClear Solutions "system" that involves not only addition of a substance but also the use of trained technicians to recognise and compensate for pumping station irregularities.

Contact Us