Wastewater Treatment Plant Optimisation PLANT C - Case Study

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Site Details:: PLANT C Wastewater Treatment Works, Co. Cavan, Ireland.

Operator details: Undisclosed

Description of Wastewater Treatment Facility: PLANT C is a Municipal Wastewater Treatment Facility which uses a trickling filter and RBC for treatment of the wastewater and has tertiary treatment using a reed bed before final discharge. Plant consists of an inlet screen followed by an Imhoff tank which removes grease and solids. The wastewater is then split between a trickling filter with plastic media and a Rotating Biological Contactor (RBC). Both the trickling filter and RBC have secondary clarifiers and the combined flow then passes through a reed bed before final discharge to river.

Difficulties encountered on the WWTP

The facility had little flow to the trickling filter when first visited. The flow was insufficient to turn the rotating arms. This was leading to very poor treatment and the plastic media was drying out. This had been a problem for some time as there was no evidence of biofilm growth on the medium. The RBC was operating quite well with consistent flow. The lack of performance of the trickling filter was having a detrimental effect on the overall performance of the plant.

Solution from: Combined Environmental Technologies

Combined Environmental Technologies was approached for help to restore the performance of the trickling filter and thus improve the overall performance of the plant. Combined Environmental Technologies engineers are specialists in plant optimization and providing affordable technological solutions to wastewater treatment operators who have ongoing issues with their plants, whether the plant be overloaded, over capacity or simply not regularly meeting discharge standards.

The first priority was to ensure a consistent feed to the trickling filter to make sure the whole bed was kept wet and the distribution arms were turning. Then a program of dosing carbonaceous bacteria to re-seed the trickling filter and re-establish a biofilm was undertaken. Having established a good biofilm on the medium the second part of the program was to dose nitrifiers to the trickling filter to restore its ability to oxidise ammonia. Dosing was conducted on a sequential basis with the biofilm established first and then the nitrifiers dosed to attach to the biofilm. Dosing was also conducted to the feed to the RBC to improve and strengthen the biofilm on the disks and boost the ability to nitrify.

Detail of Operations to remedy the problem

1.       The first action was to better balance the flow to the trickling filter to make sure of consistent loading on the bed and to keep the medium wet.

2.       Dosing of carbonaceous bacteria was conducted with initial dosing on a daily basis. The objective was to build up a strong and efficient biofilm on the medium in the trickling filter.

3.       The boosting of the biofilm was also designed to improve BOD removal and to reduce any inhibition to nitrifiers before these were added to the system.

4.       Dosing was also conducted on the RBC since that is also an attached growth system.

5.       Once the biofilm had been established the second objective was to dose nitrifiers to the medium as these can then stick to the existing biofilm.

6.       Once the system has been inoculated all that is required is to have regular weekly maintenance dosing to help maintain the biofilm population of efficient carbonaceous bacteria and maintain the nitrifier population in the plant.

List of products used to remedy the problem:

a)       BFL 4000SU - This is a natural microbial product which has been specially formulated to deal with municipal wastewater. It contains a wide range of strains which have the ability to degrade the organic materials found in municipal wastewater. It also has the ability to form biofilm on plastic media in a quick and efficient way. It also acts to remove any inhibition to the nitrifier population.

b)      BFL 5800NT -This product contains a blend of nitrifying organisms which can quickly establish and attach themselves to an existing biofilm. In this way a strong nitrifier population can be quickly established so that ammonia oxidation can be restored. Regular maintenance dosing will help to maintain a suitable nitrifier population in the system.

Long Term solution to keep the plant working well

A weekly dosing program was established for the facility and is now administered by Combined Environmental Technologies at regular weekly intervals to maintain the biomass population of efficient carbonaceous bacteria and maintain the Nitrifier population in system to help strengthen the systems performance and to help the facility to recover quicker from occasional overloading. It has been observed that following initial dosing and regular biological maintenance that the plant biomass is more robust and recovers faster from upsets. Good biological growth is now evident on the Trickling Filter due to the program and is delivering more consistent results.

Weekly Lab Testing is essential to monitor the results from the plant to ensure performance is maintained. If performance starts to decline action can be taken to correct things before they get out of control. Ongoing monitoring of the results from the plant will ensure performance is maintained. If performance starts to decline action can be taken to correct things before they get out of control.

See also:

Wastewater Treatment Plant Optimisation PLANT A - Case Study

Wastewater Treatment Plant  Optimisation PLANT B - Case Study

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