Not my field, but here is some general advice: It is not entirely clear what is being produced, but I assume the problem would be nitrogen and or phosphorus? It should be possible to find suitable analysis methods, for example here: https://www.standardmethods.org/ Nitrogen is usually converted to ammonia or nitrite NO2- before colorimetric analysis. Nitrate NO3- can also be analyzed with an ion-selective electrode. (Perhaps there is a simpler method for NO3- and total nitrogen?) To remove nitrogen, denitrification is the easiest. Any phosphorus must be removed with suitable means. The methods used in normal sewage treatment plants should be relevant here?

Arne Andersen Thanks for your answer, effluent for desired treatment is nitrogen based contaminants.

Arne Andersen I concur with you. Being a fertilizer producing company we expect more pollutants to be nutrients, and these can be analyzed by spectrophotometer and other methods. As for sampling I suggest passive sampling and composite sampling might help you characterize and quantify the pollutants for treatment. Wastewater treatment maybe a carbon-based biochar can be effective, research should be done on the same.