Site Details: PLANT A, Co. Cavan, Ireland.
Operator details: Undisclosed
Description of Wastewater Treatment Facility: PLANT A is an activated sludge Municipal Wastewater Treatment Facility which has inlet works followed by an oxidation ditch, secondary clarifier and a tertiary clarifier.
Difficulties encountered on the WWTP
The facility was operating very well according to the records kept and discharge lab results before a toxic spike occurred due to a load of sludge which was high in toxic chemicals. The spike in toxicity lead to the complete killing off of all the good biomass in the activated sludge oxidation ditch.
A few loads of sludge were brought in from another activated sludge WWTP to boost the biomass but was unsuccessful in bringing any meaningful buildup of good biomass in the system.
As a result the ammonia was discharging at 27mg/L to the river and had become an environmental risk and needed to be sorted out as soon as possible to bring the ammonia levels down to safe discharge.
Solution from: Combined Environmental Technologies
Combined Environmental Technologies was approached for help to boost the biomass growth through the supply of carbonatious bacteria as well as nitrifiers to restore the biomass growth to support the ammonia removal.
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.
Detail of Operations to remedy the problem
1. The first action was to survey the DO profile throughout the oxidation ditch.
2. The MLSS and SV30 were also checked and the SVI then calculated.
3. The target MLSS was identified as being in the range 5,500 – 6,000mg/L.
4. As a result of the survey the position of the DO probe was moved to give a better reflection of the DO in the system.
5. Dosing of carbonaceous bacteria was conducted with initial dosing on a daily basis. The objective was to build up a strong and efficient biomass with good settling and BOD removal capabilities.
6. The boosting of the biomass was also designed to reduce any inhibition to nitrifiers before these were added to the system.
7. Once the carbonaceous biomass had been established and floc formation was good with improved settlement the second objective was to dose nitrifiers to the system to restore full nitrification.
8. Once the system has been inoculated all that is required is to have regular weekly maintenance dosing to help maintain the biomass population of efficient carbonaceous bacteria and maintain the Nitrifier population in system.
9. The WAS and RAS to be adjusted to maintain the MLSS in the specified range.
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 floc in activated sludge plants so that settlement is quickly restored. The use of BFL 4000SU acts to stabilize the biomass and allow better performance of the nitrifiers.
b) BFL 5800NT - This product contains a blend of nitrifying organisms which can quickly establish and attach themselves to existing floc and form an integral part of the biomass. In this way a strong Nitrifier population can be quickly established so that ammonia oxidation can be restored. Since nitrifiers are very slow growing it is necessary to dose to ensure good Nitrifier performance is quickly restored and ammonia levels in the final discharge are kept within limits.
Long-Term solution to keep the AS strong
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.
Weekly consulting with the caretaker should be conducted on the facility. The objective is to get updates on the regular maintenance on the plant such as sludge wasting and to review any unusual happenings during the week such as mechanical breakdowns, storm flows, spills or other observations.