There is not one best method! It depends on many different factors, like what pollutants are in the water, the ambient temperature, required purity after treatment, the volume to be treated, if the water flow is constant or not. There is no way around this, each plant must be optimised based on the specific conditions and requirements at the site. 

I completely agree with Jonas. Another very important factor is the available land for the treatment plant or the cost of land at the site. Lagoons tend to take more surface area then activated sludge plants which again take more space than MBR and biofilm systems. 

 Overall Aerobic treatment  treatment of wastewater is a better option.

Anaerobic degradation followed by aerobic is best suited biological wastewater treatment strategy. During anaerobic degradation, most of the recalcitrant molecules are broken down into smaller ones. This, when followed by aerobic degradation mostly, results in less BOD in the treated water.

I do agree with Jonas Nyman and Prof.Henrik R Anderson - there is not one best method for biological treatment. It depends on so many things.

Microalage based wastewater treatment is also an feasible and attractive option.Proper selection of the algal species and particular reactor operation are the key to the application.

Dear Hossein,

Out of the 3 methods for biological treatment of municipal sewage and most industrial organic wastewaters, the activated sludge (AS) method is definitely the best because it can be well controlled ant takes far less space as opposed to lagoons and it removes both soluble and solid organics as opposed to filtration which removes only solids.

However the best biological treatment for most medium-low strength organic wastewaters is advanced activated sludge (AAS) which also captures and biodegrades "hard" organics resulting in superior water quality for reuse.

I do agree with Jonas Nyman and Prof.Henrik R Anderson - there is not one best method for biological treatment. It depends on so many factors

I am thank ful to my friends specially jonas and henrick.

Best wishes for all

Micro algae such as Chlamydomonas, Chlorella, Scenedesmus and some other micro algal forms  are able to assimilate and accumulate the toxic and waste material from the sewage and other waste waters. Next step in this treatment is treat with macro algal forms such as foliaceous forms.

Algae based treatment is not yet used in full scale wastewater treatment. Pilot studies show it requires unrealistic much land for a city sized treatment plant.

Perhaps algae based treatment floating in the sea can solve this in the future.

https://www.researchgate.net/project/OMEGA-Global-Initiative-OGI

Hossein: as other have stated there is no better treatment, it depends o factors such as wastewater income (volume and type), land available, you can use Adigestion if your COD or BOD is high, or try SBR or MSBR for municipal wastewaters, the only problem i see regarding activaded sludge is the amount of energy required for the blowers and the need for sludge treatment and/or disposition.

Lagoons may be effective but need more area to operate.

regards

Using photobioreactors employing microalgae can also be employed

I think the new method give valuable results of curing is biopipe systems ..the discover this technique called anas live in turkia -astanbol .. it is claim that results BOD,odor,suspended , sound ,,very excellent >> you can search about this topic