Performance correction of Activated sludge plant: Reviving the Biomass

Further to our blog on steel industry activated sludge performance correction, we would like to cover some of the aspects related to process correction with this article.

Inlet Wastewater Parameter Quality Control

One of the daunting task for this project was to make sure that inlet wastewater parameters are maintained within certain range and limit. Most of the industries think that ETP is a dumping yard and thus they dont care for what is going to the ETP. Based on our initial assessment of the project, We had explained management that the plant has X kg/day load bearing capacity in terms of COD, Phenols, Ammonia (total) , CN and other parameters. Within this limit, we can do anything with this ETP provided inlet wastewater quality parameters are maintained. Again the proposal had created a lot of ripples within all associated parties!

But finally, they agreed to our proposal of maintaining the parameters within the given range. We explained them very clearly that if we want to revive this plant and achieve parameters, we must make sure that the inlet wastewater quality is maintained within the range given by us. And we must thank both the units and their associated team for making sincere efforts in maintaining the parameters. We have internal groups formed where daily we are exchanging shift wise parameters of water quality that is being sent to the ETP. There is serious interest even from the Top Most management about this and they were monitoring the situation almost on daily basis personally.

The continuity in the parameters within specific range had helped us a lot to minimize any shock load events and preventing disturbance in the biological system.

On a philosophical note, we would advise fellow professionals in the field of biological wastewater treatment that, as professionals our job is to produce right environment for the optimum growth of bacterial communities in the biological reactors using available electro mechanical equipment, civil structures and chemical programs available to us. These optimum environmental conditions would be effluent specific. At design stage, we must have clear and concise picture of these optimum conditions for the target effluent and treatment goals and thus all necessary unit processes, operations and equipment must be designed in such a way that during operation and management of the process, the required conditions for optimum biological growth can be achieved with ease and economically.

Sadly most of the designers are overlooking this aspect of the design. The principle work force of a biological process are microorganisms and they are purely subconscious mind, they don’t have brains. 🙂 They just do as directed and thus we have to use our brains to develop required conditions for their beneficial use.

Reviving the Biomass: The most crucial aspect of the project

The most crucial step was to revive the nearly dead and poor biomass. One of the crucial aspect of any good large biological process is modularization of the plant. The plant must be designed in modules so that each module can be used as individual biological unit. Sadly in this project, this modularization was solely missing. Indeed there are two trains of Anoxic and Aerobic reactors available to us but finally due to single clarifier and also due to combining of both streams in a central launder where all RAS, nitrate recycle flows are mixed together with the inlet flow, there is actually no benefit to us for the modularization. It was very much challenging to maintain crucial parameters.

There were operational issues with the Anoxic Tanks where denitrification takes place in the absence of the Oxygen. The mixing was so poor that virtually we were losing all biomass in the Anoxic Tanks. So one of our first suggestion was to improve the mixing in the Anoxic Tanks!

Lot of work was done on this part and finally we had to come up with some homemade remedies which finally worked well and we had stopped settling of biomass in the anoxic tank which then helped us a lot to build up the biomass quickly.

Now again in the main aeration tank compartments, there was lack of proper mixing due to less number of running blowers. So we increased the number of working blowers and made sure that the content in the aeration tank was thoroughly mixed.

Then came the most important aspect of nitrifying bacteria. Nitrifiers are autotrophs, and thus, they require inorganic carbon as their food source. Any effluent like steel industry requires a lot of amount of inorganic carbon supplement through addition of certain chemicals. In fact microorganisms utilize the alkalinity available in the inlet wastewater for obtaining this inorganic carbon as food source but when the amount of alkalinity required exceeds the availability in the inlet, we require to top up it with addition of chemicals which provides additional alkalinity as carbonate or bicarbonate ions.

So when we suggested addition of such chemicals, again there was an uproar! No body advised them to add such chemicals! Even the EPC Company who is a leading player had not suggested it and made provision for Lime instead! My goodness! What an ignorance on their part. Reminded me the proverb of blind leading the blind!

But finally, we won over the debacle and management had opened up their purse to provide me ample quantity of chemicals for alkalinity addition. We must thank them whole heartedly for trusting us on this matter because it has a huge cost consideration. But finally the results were showing up and outlet ammonia was on reducing trend, so management was also happy and was agreeing to the suggestions we had been making to them.

So with the addition of correct chemicals for alkalinity addition, major mistake of the earlier plant operation in terms of alkalinity supplement for nitrification was corrected.

As a final step and to boost up the biomass in the ETP, we had engaged our trusted partners from Ireland who had developed a specialized steel industry specific culture for the project. We must say the culture is highly specific for the project and steel industry. We had devised a systematic dosing program for the culture dosing and implemented it on site very carefully. The results are fantastic. We have now developed fully acclimatized biomass for the Activated Sludge process which is even now tolerating the shock loads well enough and beyond our understanding!

Continuous Monitoring and testing:

One of the most important part of any biological process management is continuous monitoring and testing for vital parameters. It is like keeping a patient in ICU and thus needs all vital information for its effective operation if we want to achieve desired outcome all the time.

We must say, management had realised this important aspect and thus offered us to take up the operation and maintenance of the plant for next one year. We also had an impression that if the plant is not operated under our supervision then there would be less chances of success and thus all the changes we had made in the plant might go in vain!

So next challenge was to train and make the local operators to run the plant as per our guidance and instruction. Many of them were working in the plant since the inception of the project and thus changing their mind-set needed a lot of effort.

But we have made it with the ever helping support of the Plant management. Presently we are running the plant as O&M contractor too and maintaining the process very well. The operators are now well trained and informed about what to do for the efficient management of the plant. In fact after seeing the current plant, they are also much encouraged as they have seen the worst conditions in the plant in the past!

We have made them to measure certain crucial parameters like DO,pH, alkalinity , PO4 at various levels shift wise with the help of onsite measurement kits. A low cost but very effective solution. Our entire alkalinity dosing is now based on maintaining certain minimum level of alkalinity in the clarifier outlet. This has resulted in much economical operation of the alkalinity addition.

Way forward for optimization: ETP A Centre of Focus and not a NPA

So finally management is happy with the work we have carried out for this plant. In fact, it has resulted in a kind of paradigm shift for them too. For them ETP has become a centre of focus rather than a neglected area. Even the individual cluster heads and CEO Sir are directly taking interest in the ETP operations and checking that all requirements for the ETP are met with an urgency tag which is really encouraging that an industry is taking their ETP operations so seriously.            

A lot has been done and yet the work is going on continuously to make this particular ETP perhaps the best ETP in the steel industry within Indian subcontinent.

We must thank the management for their trust and extensive support on the project.

For various design and engineering related issues, we will put up separate article so that they can be discussed in much detail. Stay tuned.