You should consider to convert the plant sludge tanks to an integrated system. It is possible to have MBBR carriers in the sludge tanks together with the sludge which increases the capacity.

The system configuration is known as IFAS. The Veolia subsidary AnoxKaldnes have a system that they name HYBAS whoch is well known in Scandinavia.

http://www.anoxkaldnes.com/news-resources/technology-information/hybas.htm

I feel the option of converting existing aeration tank (bio reactor) as moving bed bio reactor(MBBR) is worth trying. You need to add suitable media. This way the cost of additional civil works will not be required.

You can put the media (e.g., commercialized plastic media) directly to the AS tank to increase the biomass to decrease the retention time. The steel nets are needed to keep the media from washing away. Also, the volume percentage of the media should be calculated according to how much retention time you want to decrease, My experience indicate the volume percentage of the added media should be no more than 40%.

If you are storing treated wastewater, then my suggestion is to upgrade chemical dosing system, rather than installing UV disinfection

For your need, i.e. reduction in retention time, you should utilize the existing ASP as an MBBR, by simply adding the required quantity of the media (approx. 50 to 75 vol % of the reactor) with screens in the aeration tank outlet.

Dear Ali,

Of course hydraulic residence time (HRT) can be decreased if the microbial capacity = activity + mass is increased as to maintain a suficiently low F/M. Hence I would recommend to first analyze the performance (load and removal of COD, BOD, TSS, TN, ...) and the operating parameters of your AS system : MLSS, MVLSS, SVI, SRT, F/M, DO, SOUR, ... According to my 37 years experience, most conventional AS systems operate at fairly low MLSS (3 - 5 gDS/l) which is limited by poor settle-ability (SVI  > 100 ml/gDS). Adding inert (plastic, ...) biofilm carriers may  increase the mass of biosludge in the AS basins. However our assessment of such MBBR / IFAS = hybrid AS-MBBR) showed only a marginal increase in mass (biofilm) and even less in activity (SOUR, ...). Hence the addition of inert biofilm carriers would probably not meet your objectives.

Fortunately there is a far better approach to boost the capacity and performance of AS systems with low-medium biosludge activity (SOUR, ...) + mass (MLVSS, ...). Since 25 years we develop and apply a more advanced AS (AAS) which results in high biosludge activity + mass (up to 12 gDS/l) by kinetic + metabolic selection of the bio-sludge and by biosorption + hydrolysis(by exo-enzymes) of the substrate without membranes or addition of any (bio)chemicals. In this way the treatment capacity of existing AS systems can be doubled (+100%) at higher performance (typically 50% lower residual COD, BOD, ...) by retrofit upgrading to AAS.

If interested I can send you more info via email.

To give a clear answer to your question we will need to know what the effluent quality that you are searching are, and what kind of treatment the plant originally was designed for.

If the goal is increasing Organic removal capacity i.e the answer is not the same as if your goal is to add nitrification to your plant ?

Dear Ali

I recommend to you the Hybas process which was developed by Anox Kaldness- the leading in membrane technology- 

Hybas™ hybrid process combines the AnoxKaldnes™ biofilm technology and activated sludge in the same tank. The Hybas™ hybrid process is especially suitable for nitrogen removal with municipal wastewater but can also be used for some industrial applications.

The Hybas™ combination process is a compact solution requiring little process volume to achieve both reduction of organic material and nitrogen.This process solution is often a cost effective way of upgrading an existing activated sludge system to also comprise nitrogen removal or improve the capacity of the nitrogen removal process. By adding carriers to the whole or a part of the aerated activated sludge volume, the nitrification capacity can be increased within the existing volume because high amounts of nitrifying bacteria are enriched on the carriers. BOD removal and denitrification will typically occur in the suspended phase. Thanks to the biofilm solution, the long suspended sludge age normally needed in the AS to achieve nitrification can be reduced. A reduction of the sludge concentration in the AS will also lead to less sludge load on the secondary clarifiers. Another benefit is that a short sludge age will often reduce the risk of growth of filamentous bacteria and generally, the biological activity is higher in an AS process with low sludge age than in one with a high sludge age. One can therefore achieve high denitrification activity in a Hybas™ combination process.

Good Luck,

Ata

It depends strongly to the type of your aeration system . If your using Air bubble diff-users you you can add media in aeration tank and you must use some screens to avoid escaping of media.you can use 50% of media's volume with media.